2008 AES Abstracts

Montreal

TALKS

Shaara M. Ainsley, David A. Ebert, Gregor M. Cailliet

Age, Growth and Reproduction of the Bering Skate, Bathyraja interrupta (Gill & Townsend, 1897), from Alaskan Waters

Pacific Shark Research Center, Moss Landing Marine Laboratories, Moss Landing, CA 95062, United States

Life history traits of a common commercial bycatch species from the Gulf of Alaska were examined. Collections of Bathyraja interrupta were obtained from annual surveys, port sampling of commercial catch and observer collections from 2005 to 2007 in the Gulf of Alaska. Observed total lengths for males ranged from 19-82 cm and females from 20-87 cm. There was no difference in mean MIRs amongst months (n = 131, F = 0.903, p = 0.481) using samples from 6 consecutive months. No significant difference was found in B. interrupta growth parameters between sexes (F = 0.8259, p = 0.4804). B. interrupta has a relatively short life span with growth parameters comparable to other skates of a similar size (Linf = 126.40, k = 0.07, t0 = - 2.32). Age estimates show a minimum longevity of 12 years for males and 13 for females. Total lengths at 50% maturity were approximately 68 cm for males and 70 cm for females (Males: r2 = 0.8836, p < 0.0001, n = 40; Females: r2 = 0.9947, p < 0.0001, n = 43), which corresponds to 7 years and 7.5 years respectively (Males: r2 = 0.9937, p < 0.0001, n = 12; Females: r2 = 0.9969, p < 0.0001, n = 14). Gravid females were found in all months between April and September.

 

Charles R. Anderson, Shiham M. Adam, Joaquim I. Goes, Anne-Marie Kitchen-Wheeler, Guy M.W. Stevens

Manta Rays, Manta birostris, in the Maldives: Seasonal Distribution and Economic Value

1Marine Research Centre, Malé, Maldives, 2Bigelow Laboratory for Ocean Sciences, West Boothbay Harbor, ME, 04575, United States, 3School of Biology, University of Newcastle, Newcastle, United Kingdom, 4Four Seasons Resorts, Baa Atoll, Maldives

The Republic of Maldives in the central Indian Ocean is home to large numbers (many ‘000s) of Manta Rays, Manta birostris. They are an important component of the nearshore pelagic ecosystem, and a significant attraction for tourist divers and snorkellers. The aims of this study were to map the seasonal distribution of manta rays within the Maldives, and to assess their economic value for tourism. Seasonal distribution and economic value were determined from personal observations, interviews with experienced divers and a national survey of fishermen. The distribution of Mantas is strongly influenced by the seasonally alternating monsoon currents. Mantas occur on the (seasonally alternating) downstream sides of the atolls, and are rare on the upstream sides, switching sides biannually with changing currents. Manta presence is correlated with turbidity and ocean colour, both proxies for zooplankton abundance. Diving and snorkelling with Mantas is estimated to be worth about US$ XX million per year. Tourism is the largest sector of the Maldivian economy; appreciation of the value of marine-life, and particularly of the charismatic mega fauna, can play a major role in its conservation.

 

Neil Aschliman, Gavin Naylor

Phylogeny of Skates, Rays, and Allies (Chondrichthyes: Batoidea) Using RAG-1 and Complete Mitochondrial Genomes: Preliminary Results

Florida State University, Tallahassee, FL, United States

Skates, rays and their allies (Batoidea) are a prominent but under-studied clade of stem vertebrates that exhibit broad morphological diversity. Batoids include forms as varied as ragged-snouted sawfishes, circular torpedo rays and seven-meter-wide mantas. How did this diversity in form arise from a shark-like ancestor? The lack of a reliable phylogenetic hypothesis has impeded an understanding of the changes in body form affecting the diversification of this group. The most taxon-rich batoid phylogenies are morphological and have been important in identifying suites of characters that appear constrained and/or convergent. Even so, the lack of confidence in any one topology has led to ambiguity about the way in which putatively convergent changes were brought about. Previous molecular phylogenies have included very few taxa and limited sequence data. We generated both nuclear DNA sequence data (RAG-1, ~60 taxa) and the complete protein-coding component of the mitochondrial genome (~25 taxa), sampling broadly across Batoidea. Data were analyzed under Maximum Likelihood and Bayesian approaches, and a number of well-supported clades were recovered. Some are novel, while others are anticipated by morphology.

 

Robert Aston

Framework for the Establishment of a Global Conservation Program for Manta and Modula Rays

The Manta Network, Santa Cruz, CA, United States

Since the year 2002, the 501(c)(3) non-profit organization, The Manta Network (TMN), has been establishing a global framework for the conservation, protection and management of manta and modula rays. Aspects of this framework include a Manta Science Advisory Board, Manta Research Affiliates Program, Global Manta Database and resources library, sponsored field research, educational programs and a manta awareness program that includes the scientific community, conservation groups, the dive industry, underwater photographers, the media and the general public. Results of these programs will be discussed including the development of an online global database, automated spot identification software, manta research and expeditions and the use of a uniquely designed, underwater, live IP video camera system for research and education.

 

Ivy Baremore, Loraine Hale, Kate Andrews

Determination of Age in Atlantic Angel Sharks: What Does it All Mean?

NOAA Fisheries Service, Panama City, FL, United States

Species-specific age and growth estimates, while necessary for age-structured population dynamic models, are often difficult to obtain for elasmobranch species. Although angel sharks (Squatinidae) are highly exploited and considered ‘endangered’ in many parts of their range, very few studies have examined the age and growth of species in this family, likely due to difficulties associated with traditional ageing techniques. Investigation of Pacific angel shark Squatina californica vertebrae found band deposition to be related to somatic growth, but temporally unpredictable. Atlantic angel sharks Squatina dumeril were collected for age and growth analysis (n=343) from fishery-independent and dependent sources from January 2001 through June 2007. Vertebral samples were collected from the area of the spinal column located dorsally to the abdominal cavity, and band counts were obtained from whole, halved, and sectioned (0.6 mm) vertebral centra. Several methods were employed in order to investigate the age and growth of the Atlantic angel shark, including tradition growth models using band counts (e.g. von Bertalanffy Growth Model and Gompertz Growth Model), and newer Bayesian methods that estimate L (asymptotic size) using only length data.

 

Lewis Barnett1, David Ebert1, Gregor Cailliet1, Ryan Earley2

Maturity, Fecundity, and Reproductive Cycle of the Spotted Ratfish, Hydrolagus colliei (Lay and Bennett, 1839)

1Moss Landing Marine Laboratories, Moss Landing, CA, United States, 2California State University, Fresno, Fresno, CA, United States

Size at maturity, fecundity, and reproductive periodicity of the spotted ratfish, Hydrolagus colliei, were estimated from off the coast of California, Oregon, and Washington. Maximum body size and size at median maturity were greater for females than males. Skeletal muscle concentrations of the steroid hormones testosterone (T) and estradiol (E2) predicted similar, but slightly smaller sizes at maturity than morphological criteria. Stage of maturity for males was estimated identically using either internal organs or external secondary sexual characters, facilitating non-lethal maturity assessments. Latitudinal differences in sizes at median maturity were observed, with greater values north of Point Conception for females, and north of Cape Mendocino for males. Peak parturition occurred from May through October, with elevated skeletal muscle concentrations of E2 in females correlating with ovarian recrudescence during November through February. No significant seasonal trends in female T were apparent, but mean female 11- ketotestosterone (11KT) was 300% greater in April than any other month during the parturition season. There was marginal evidence for increased number and size of ova with maternal size. Extrapolation of the hypothesized 6-8 month egg-laying season to observed mean parturition rates of captive specimens yielded an estimated annual fecundity of 19.5-28.9 egg cases. Differences in fecundity among higher taxonomic classifications of chondrichthyans were detected, with chimaeriform fishes being more fecund than myliobatiform, squaliform, and rhinobatiform fishes.

 

Ransom A. Myers (Deceased)1, Julia K. Baum2, Travis D. Shepherd1, Sean P. Powers3, Charles H. Peterson4

Are there Cascading Ecosystem Effects of Depleting the Oceans’ Great Sharks?

1Dalhousie University, Halifax, NS, Canada, 2Scripps Institution of Oceanography, La Jolla, CA, United States, 3Golder Associates, Calgary, AB, Canada, 4University of South Alabama, and Dauphin Island Sea Lab, Dauphin Island, AL, United States, 5University of North Carolina at Chapel Hill, Morehead City, NC, United States

Top-down control can be an important determinant of ecosystem structure and function, yet has rarely been demonstrated in oceanic ecosystems, where the cascading effects of predator removals by fishing could be significant. Here, we present evidence from a case study on the U.S. east coast, which draws upon multiple research surveys, meta-analysis, long-term field observations, and controlled experiments. We show that as abundances of all 11 great sharks, which consume other elasmobranchs, fell over the past 35 years, 12 of 14 of these prey species increased in abundance. Effects of this community restructuring appear to have cascaded downward from one elasmobranch mesopredator, the cownose ray, whose enhanced predation on its bay scallop prey was sufficient to terminate North Carolina’s century-long scallop fishery. Analogous cascading effects may be a predictable consequence of depleting populations of large sharks, and we conclude by exploring the evidence to date for them in other regions.

 

Andrea Bernard1, Kevin Feldheim2, Lucy Howey1, Bradley Wetherbee3, Michael Heithaus4, Mahmood Shivji1

Defining Management Units of a Migratory Species: the Global Genetic Population Structure of the Tiger Shark (Galeocerdo cuvier)

1Guy Harvey Research Institute, Nova Southeastern University, Dania Beach, Florida, United States, 2Field Museum, Pritzker Laboratory for Molecular Systematics and Evolution, Chicago, Illinois, United States, 3Department of Biological Sciences, University of Rhode Island, Kingston, Rhode Island, United States, 4Marine Biology Program, Florida International University, North Miami, Florida, United States

The tiger shark (Galeocerdo cuvier) is a migratory and globally distributed species, inhabiting warm-temperate and tropical waters. This species likely plays a key role in marine ecosystems and recent evidence of its over-exploitation and population decline in some regions underscores the need for accurate delineation of its population structure worldwide to inform management efforts. We analyzed the global population structure of tiger sharks (n = 289) using 11 nuclear microsatellite loci and sequences of the entire mitochondrial control region (n = 201). Population- level microsatellite analyses revealed strong genetic differentiation among tiger sharks from Atlantic and Indo-Pacific waters (FST > 0.102), and between samples from South Africa and the Southwestern Atlantic (FST = 0.185). There was relatively weak differentiation among sample sites within basins (FST < 0.026). Although individual- level analyses using the software STRUCTURE and BAPS found significant within- basin differentiation, these groupings did not correspond to geographic capture locations, suggesting extensive mixing of adult populations within basins. Preliminary mitochondrial sequence analysis revealed high congruence with nuclear markers, showing strong division of the Atlantic and Indo-Pacific groups. Collectively, these findings imply a strong barrier to dispersal across the South Atlantic, and between ocean basins. In contrast, open ocean expanses appear not to inhibit dispersal across the Indo-Pacific, suggesting an absence of barriers to gene flow across this basin. The detection of mainly basin-wide management units emphasizes that managing and conserving large, migratory species will require collaborative, multi-national and global-scale approaches.

 

Dana M. Bethea, Loraine Hale, Lisa Hollensead

Diet of the Roundel Skate, Raja texana,from the Northern Gulf of Mexico

NOAA Fisheries Panama City Laboratory, Panama City, FL, United States

To evaluate the trophic role of skates in benthic marine ecosystems, diet and feeding habits of the roundel skate, Raja texana, have been examined from offshore waters in the northern Gulf of Mexico. Diet was assessed by life-stage (immature and mature) and quantified using several relative measures of prey quantity: percent by number (%N), percent by weight (%W), frequency of occurrence (%O), the index of relative importance (IRI), IRI expressed on a percent basis (%IRI), %IRI based on prey category (%IRIPC), and the geometric index of important based on prey category (%GIIPC). Analysis of stomachs from 222 immature individuals (195 non-empty; mean) and 191 mature individuals (167 non-empty) indicate shrimp make up 90.7 %IRIPC (69.6 %GIIPC) of immature skate diet, with decapod shrimp and euphausiids the most important identifiable type present. Although in smaller amounts, fishes were found in the diet of immature skates (7.9 %IRIPC,18.8 %GIIPC), with Bregmaceros spp. the most important identifiable species present. Mature skate diet was also predominantly shrimp (64.8 %IRIPC, 46.6 %GIIPC); however, fishes made up a much larger percentage by prey category (24.8 %IRIPC, 26.9 %GIIPC). Crabs and other crustaceans were also relatively important in the diet of mature animals (4.4 %IRIPC, 12.1 %GIIPC and 2.7 %IRIPC, 9.5 %GIIPC, respectively).

 

Maria-del-Pilar Blanco-Parra1, Fernando Márquez-Farías2, Felipe Galván- Magaña3

Reproductive Biology of the Banded Guitarfish, Zapteryx exasperata, from the Gulf of California México

1Posgrado en Ciencias del Mar y Limnología, UNAM, Mexico City, Mexico, Mexico, 2Instituto Nacional de la Pesca, SAGARPA, Mazatlán, Sinaloa, Mexico, 3Centro Interdisciplinario de Ciencias Marinas (CICIMAR-IPN), La Paz, Baja California Sur, Mexico

The banded guitarfish, Zapteryx exasperata, is an important target specie in the artisanal elasmobrach fishery into the Gulf of California during spring and early summer. Males and females banded guitarfish have two functional testes and ovaries, respectively. Using the logistic model median size at maturity (L50%) was estimated 64 cm total length (TL) for males and 69 cm TL for females. Average length of pregnant females was 78.8 ± 3.8 cm TL. Histological analysis showed sperm clumps in the epididymis and no evidence of sperm storage in the oviducal gland was observed. Embryos development starts in February and ends in June or early July when embryos average size (149.1 ± 17.8 cm TL) reach the reported birth size (15-22cmTL). Oocyte development is concurrent with the embryonic growth with largest oocyte diameter of 25 mm in July. Mean fecundity was estimated at 7 pups (range 1-13, s.d. = 2.92) with a 1:1 embryos sex ratio. Reproductive cycle in banded guitarfish from the Gulf of California seems to be 1 year long. Differences of the reproductive pattern with the population of the Mexican Pacific are discussed.

 

Erin Blevins, George Lauder

Stingray Swimming: Three-dimensional Kinematics of Pectoral Fin Locomotion

Harvard University, Cambridge, MA, United States

Batoids swim using distinctive undulations and oscillations of expanded, flexible pectoral fins. Previous work has described fin motion in two dimensions, placing species along a continuum from undulatory to oscillatory locomotion. However, the flexible fins of stingrays allow complex deformations, in addition to the traditionally described anterior-posterior propulsive wave. A three-dimensional analysis of pectoral fin motion is needed to fully describe batoid locomotion, including changes in kinematics with swimming speed, and to generate hypotheses about fluid flow around the flexing fin. In this study we characterize the pectoral fin motion of freshwater stingray Potamotrygon hystrix in three dimensions. Three synchronized, one megapixel high speed video cameras (250 frames/s) were calibrated using direct linear transformation and used to film three individuals (mean disc length=13 cm) swimming at two speeds (1.5 and 2.5 disc lengths/s). Multiple finbeats per individual, per speed, were analyzed to create a three-dimensional model of the moving fin, with approximately thirty points describing surface deformations. Kinematic variables including wave speed, frequency and amplitude were determined for the propulsive wave, and combined with angular variables to quantify fin motion in other planes, based on x, y and z excursions of points across the fin surface. This three-dimensional analysis of batoid locomotion reveals fin postures with significant hydrodynamic implications, including a “cupping” of the distal margin. Future experiments using particle image velocimetry will explore these implications and characterize flow patterns around the fin.

 

Karyl Brewster-Geisz, Michael Clark, Jacqueline Wilson, LeAnn Hogan, Chris Rilling, Heather Halter, George Silva, Joseph Desfosse, Margo Schulze- Haugen, Heather Balchowsky, Robert Smith, Jessica Beck

Status of Atlantic Shark Management in the United States

NMFS/HMS, Silver Spring, MD, United States

The Highly Migratory Species (HMS) Management Division of the National Marine Fisheries Service (NMFS) is responsible for the management of the Federal Atlantic shark fisheries including the Gulf of Mexico and Caribbean Sea. In late 2006, NMFS revised the stock status of several large coastal sharks (LCS), including sandbar, dusky, blacktip, and porbeagle sharks, based on the findings of recent stock assessments. Since then, the HMS Management Division has been developing management measures that will change the regulations for all commercial and recreational fishermen, as well as scientists and aquarium collectors. Implementation of this rule is expected in early Summer 2008. In addition to these measures, the HMS Management Division will be beginning the rulemaking process to change regulations on small coastal sharks (SCS) based on the 2007 stock assessment. This process is anticipated to begin in early Summer 2008. The alternatives initially considered in this rulemaking will be based on the findings of the 2007 stock assessment, as well as comments received during upcoming public scoping meetings.

 

Walter Bubley1, James Sulikowski2, Paul Tsang1

Utilizing DNA Microsatellites to Study Population Structure of Spiny Dogfish, Squalus acanthias, in the Western North Atlantic

1University of New Hampshire, Durham, NH, United States, 2University of New England, Biddeford, ME, United States

In the year 2000, as a result of the declining spiny dogfish stock, the Atlantic States Marine Fisheries Commission implemented an Interstate Fisheries Management Plan that places an annual quota limit on US landings. Thus, this is a timely opportunity to conduct studies that provide updated life history information on this species. Since population structure is an important component of any successful management plan, the objective of the present study is to employ DNA microsatellite markers to determine the population structure of spiny dogfish in the Northwest Atlantic. To assess molecular markers, fin clips were taken from sharks at six locations along the eastern coast of the United States and Canada. Due to evidence suggesting a possible north/south division between spiny dogfish populations in the Western North Atlantic, the six sampling locations were selected with three being north and three being south of Cape Cod, MA. DNA was then extracted from the fin clips and four microsatellite loci were amplified using polymerase chain reaction with fluorescently labeled primer sets specifically developed for spiny dogfish. The products were genotyped and alleles for each locus were scored based on size. Hardy Weinberg Equilibrium was examined as well as statistical analyses using F statistics and pair- wise comparisons to determine the presence or absence of any population structure present within spiny dogfish in the Northwest Atlantic. Preliminary results suggest little to no division between northern and southern sampling locations, but more samples are being analyzed as well as comparisons between individual locations By utilizing this approach to acquire updated knowledge of population structure, it allows for improved accuracy and reliability of the underlying biological information obtained for and incorporated into fisheries models for spiny dogfish in the Atlantic waters off the coasts of Canada and the United States.

Marta Calosso, Kristene Parsons, Steve Newman

Juvenile Lemon Sharks (Negaprion brevirostris) Around South Caicos, Turks & Caicos Islands: A Nursery Without Neonates?

The School for Field Studies, Center for Marine Resource Studies, South Caicos, Turks and Caicos Islands

Juvenile lemon sharks (Negaprion brevirostris) depend on shallow near shore areas as nurseries. These critical habitats may be vulnerable due to their proximity to land and exposure to anthropogenic impacts. This study aimed to assess the use of shallow habitats by immature lemon sharks around South Caicos, Turks & Caicos Islands, an island facing burgeoning coastal development and tourism. Specific objectives were to investigate the abundance of sharks using the area, their size frequency distribution, growth rates, and residency. Sharks were caught with monofilament gillnets at selected sites around South Caicos between August 2006 and present. A total of 100 individuals were captured and tagged with T-bar tags (August to December 2006) and passive integrated transponder tags (January 2007 to present). The area sampled appears to be used predominantly by juveniles of an intermediate size class (mean PCL 63.8 ± 1.02 cm S.E.; range 50.5 - 91.0 cm). No individuals had open umbilical scars and no adults were observed during the study period, suggesting that pupping may occur elsewhere and neonates may use alternative areas until they attain a larger size. Preliminary results indicate a fast growth rate (26 cm yr-1 PCL) compared to other well-studied lemon shark populations. A relatively low recapture rate (15.2%) was recorded which may be attributed to high mortality, size-related emigration, or sampling effort spread across a large open study area. The use of nurseries throughout this species’ range could be more complex than originally thought and the details of ontogenetic shifts in habitat use may be location specific. For a more comprehensive understanding of lemon shark life history, further research in alternative locations is required. This would enhance our ability to conserve this species, especially in the face of rapid coastal development occurring worldwide.

 

Steven Campana1, Warren Joyce1, Michael Manning2

Estimation of Discard Mortality in Blue Sharks Using Popup Archival Tags, with Implications for the Status of the North Atlantic Population

1Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada, 2National Institute of Water and Atmospheric Research Ltd (NIWA), Wellington, New Zealand

A confounding issue in the interpretation of shark population status is the survival rate of sharks discarded at sea. In the Northwest Atlantic, virtually all blue sharks (Prionace glauca) caught by the Canadian and U.S. large pelagic longline fleets are discarded after capture, for a total of more than 30,000 mt annually. Observer records of >10,000 blue sharks indicated that ~20% appeared to be dead at the time of discarding, with most of the remainder being injured to varying degrees. To estimate the medium-term survival rate of the discarded blue sharks, we applied popup archival transmitting (PAT) tags to more than 45 blue sharks discarded as part of ongoing commercial fishing operations. Tags were programmed to release from the sharks after 3-6 months. Survival rates greatly exceeded expectations, with most of the mortality occurring within 3 days of release. Injured blue sharks appeared to return to what was interpreted as normal behaviour about 3 weeks after release. The implications of delayed discard mortality to population status calculations are substantial.

 

Simonepietro Canese, Andrea Cardinali, Teresa Romeo, Michela Giusti, Eva Salvati, Michela Angiolillo, Silvestro Greco

Giant Devil Ray Satellite Tagging in the Mediterranean Sea

ICRAM (Central Institute for Marine Research), ROME, Italy

The giant devil ray (Mobula mobular) (Bonnaterre 1788) is the only mobulid species regularly present in the Mediterranean Sea. The distribution, biology and ecology of this species are poorly known and, given its high bycatch mortality, low reproductive capacity and limited range, it is enlisted in the IUCN endangered species list (A4d). The present study describes the diving behavior and movements of three individuals tagged with Popup archival satellite tags in the Messina Strait (Central Mediterranean Sea) during summer 2007. Two tags were programmed to detach from the individuals after 120 days and one after 60 days. All tags detached at the pre-established time and far from the tagging positions (156 – 421 km). The data collected show the ability of these individuals to dive extremely deep (up to 700 meters). Despite this, they spend most of their time (81.5 %) between the surface and 50 meters, in waters having temperature between 20° C and 29° C. The preference for warm surface waters exposes this species to threats such as accidental captures in driftnets and surface long lines.

 

Daniel Cartamil1, Nick Wegner1, Dovi Kacev2, Noah Ben-aderet3, Jeffrey Graham1

Movements and Nursery Habitat of Juvenile Thresher Shark (Alopias vulpinus) in the Southern California Bight

1Scripps Institution of Oceanography, La Jolla, CA, United States, 2San Diego State University, San Diego, CA, United States, 3Inter-University Institute for Marine Science, Eilat, Israel

The common thresher shark, Alopias vulpinus, comprises the largest commercial shark fishery in California waters. However, very little is known about the early life history of this species. We used acoustic telemetry to study the movement patterns and habitat preferences of juvenile common thresher sharks in their nursery habitat along the coast of southern California, between March 2006 and September 2007. Seven juvenile threshers (fork length: 66 to 108 cm) were tagged with temperature and depth sensing acoustic transmitters and tracked for up to 75 h. In contrast to behavior recorded for adults and subadults in an earlier study, juveniles almost exclusively utilized shallow waters of the continental shelf. Juvenile threshers exhibited diel patterns in depth preference, remaining closer to the surface at night and deeper by day, often near bottom depth. The depth and habitat preferences of thresher sharks make them vulnerable to artisanal gillnet fisheries in California and Baja California waters.

 

Felipe Carvalho1, Jose Pacheco2, Fabio Hazin2, Debra Murie2, David Kerstetter2, George Burgess1, Humberto Hazin3, Andre Afonso1

Fishing Gear Modifications to Reduce Elasmobranch Mortality in Pelagic and Bottom Longline Fisheries off Northeast Brazil

1University of Florida, Gainesville, FL/Southeast, United States, 2Universidade Federal Rural de Pernambuco, Recife, PE/Northeast, Brazil, 3Nova Southeastern University, Dania Beach, FL/Southeast, United States

Terminal gear modifications, particularly the use of circle hooks, are showing promising results in reducing bycatch mortality for teleost fishes, but similar data on elasmobranchs are rare. We conducted two experiments to test the influence of hook type and physical position of the hook in catch composition, catch rates, and mortality of elasmobranchs with longline fishing gear. In the first experiment, a commercial vessel conducted 12 pelagic longline research sets off the coast of Natal, Northeast Brazil. In the second, 1,128 bottom longline research sets were monitored off the coast of Pernambuco, Northeast Brazil. The vertical hook position comparisons in the bottom longline fishery were analyzed by deploying half of the hooks demersally and the other half suspended in midwater using only “J” (size 9/0, 10° offset) hooks. For hook type comparisons, circle (size 18/0, 0° offset) and “J” (size 9/0, 10° offset) hooks were alternated along the mainline for each pelagic or midwater set. Catch rates for blue, night, silky, tiger, shortfin mako, dusky, nurse, and oceanic whitetip sharks were significantly higher for circle hooks in the pelagic longline experiment. However, all shark species caught by circle hooks were hooked significantly more often in the mouth in contrast with “J” hooks, which hooked more often in the throat or gut. Suspending the hooks midwater versus demersally reduced the catches of blacknose sharks (-85%), nurse sharks (-97%), and southern stingrays (-68%), while increasing the catch rates of bull (+20%) and tiger sharks  (+20%). For the midwater sets, the number of tiger, bull, and blacknose sharks and southern stingrays alive at haulback was significantly higher for circle hooks. However, no significant mortality differences between hooks were found for nurse, hammerhead, and blacktip sharks. No significant differences in catch rates between hook types were found for any species in the midwater sets.

 

Jose I Castro

The Reproductive Cycles of North American Sharks


NOAA/Mote Marine Laboratory, Sarasota, Florida, United States

The reproductive cycle of sharks is how often a species breeds and consists of two parts or periods. The first is the vitellogenesis period, when nutrients stored in the liver are transferred to the developing oocytes, and when oocytes accumulate yolk and grow rapidly. The second part consists of the gestation period, or the time of embryonic development from fertilization to birth. These two periods, vitellogenesis and gestation, can run concurrently or consecutively, and the duration of each period is variable. In a given population, the females can be reproductively synchronous or asynchronous. Synchronous females are in the same stage of the reproductive cycle, while in a population of asynchronous females, all are at different stages of the cycle. Different types of reproductive cycles can be discerned: 1. Biennial cycle with concurrent vitellogenesis and gestation, as in the spiny dogfish and other squaloid sharks. 2.Biennial cycle with consecutive vitellogenesis and gestation, the type of reproduction found in many of the sharks of the genus Carcharhinus and Sphyrna mokarran. The nurse shark (Ginglymostoma cirratum) exhibits a similar biennial cycle but with a much shorter gestation period. 3. Annual cycle with concurrent vitellogenesis and gestation, a type cycle found in the more advanced sharks of the genera Rhizoprionodon and some Sphyrna (e.g., S. lewini and tudes). 4. Lamnoid annual cycle with discontinuous ovulation, as in the sand tiger shark (Carcharias taurus) and probably the mako (Isurus oxyrinchus). 5. Lamnoid annual cycle with continuous vitellogenesis, as in thresher sharks (Alopias). 6. Triennial cycle with consecutive vitellogenesis and gestation. A triennial cycle with an 18 month gestation period has been postulated for the dusky shark (Carcharhinus obscurus) and for the tiger shark (Galeocerdo cuvier). Caribbean data shows the tiger shark to have a 12 month gestation period. It is likely that there are many other patterns of reproductive cycles but it may take a long while to elucidate these, given the difficulties of obtaining specimens.

 

Jui-Han Chang, Kwang-Ming Liu

Stock Assessment of the Shortfin Mako Shark in the Northwest Pacific - a Demographic Approach

University of Maine, Orono, ME, United States

The shortfin mako shark (Isurus oxyrinchus) owns the life history characteristics of large sharks such as slows slowly, matures late, and produces few offsprings. It is vulnerable to overexploitation and has been put on the “Near threatened” category of IUCN Red List. The abundance of shortfin mako reduced 40% during 1986-2000 in the Atlantic. However, the stock status in the Pacific is still unknown.The objective of this study is to assess the stock status of the shortfin mako shark in the Northwest Pacific from 1990 to 2004 based on stochastic stage-based model. The virtual population analysis (VPA) results showed that the age-specific fishing mortality of 3+~6+ for females and 2+~7+ for males appear to be increased since 1996. The 20-year projection from stochastic stage-based model indicated that the abundance will decrease seriously under current fishing effort. The above results indicate the population will be collapse under current fishing pressure. The population will maintain equilibrium for the next 20 years if the total allowable catch (TAC) is set at 265 mt, which is equivalent to 57% reduction of current fishing pressure. However, close monitoring and modification of the TAC year by year is a necessary measure to ensure the long-term sustainability of the stock.

 

Demian Chapman1, Kevin Feldheim2, Colin Simpfendorfer3, Tonya Wiley4,

Gregg Poulakis5, Beau Yeiser4, Mike Tringali6, John Carlson7, Ellen Pikitch1

Conservation Genetics of the Endangered Smalltooth Sawfish (Pristis

pectinata)


1Pew Institute for Ocean Science, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, United States, 2Pritzker Laboratory of Molecular Systematics and Evolution, The Field Museum, Chicago, IL, United States, 3James Cook University, Townsville, Qld, Australia, 4Mote Marine Laboratory, Sarasota, FL, United States, 5Florida Fish and Wildlife Conservation Commission, St Petersburg, FL, United States, 6Florida Marine Research Institute, St Petersburg, FL, United States, 7National Marine Fisheries Service, Panama City, FL, United States

Smalltooth sawfish (Pristis pectinata) were once common in the southern U.S. Atlantic and Gulf of Mexico but declined by an estimated 95% last century, primarily due to incidental mortality in fisheries. Today, the U.S. range of the species is severely contracted and remnant breeding areas are now primarily located in a handful of sites in Southwest Florida. Now listed under the U.S. Endangered Species Act, it is critical that we develop a comprehensive understanding of the biology and status of smalltooth sawfish so that we will be fully prepared to meet the challenge of facilitating their long-term recovery. Given the magnitude of decline that has taken place and the well established link between genetic diversity and population viability, there is some concern about the genetic health of smalltooth sawfish in Florida. It is also important to understand the level of connectivity between different sawfish breeding grounds in Florida to effectively scale management actions. We have developed a suite of eleven microsatellite DNA markers (10-46 alleles per locus, average heterozygosity 0.84) that have proven useful for addressing these issues. By genotyping 117 sawfish sampled from Panama City to the Lower Florida Keys, we discovered that robust genetic variation persists in the Florida smalltooth sawfish population and there is only a modest signature of a genetic bottleneck arising from the recent large decline in their numbers. We also show a high degree of genetic connectivity between different Southwest Florida breeding grounds, indicating that they should be managed as a single interbreeding unit. As an interesting side observation on the natural history of smalltooth sawfish we also present evidence that pairs or groups of juvenile sawfish captured together are often composed of siblings, to our knowledge the first evidence of an extended postnatal association of littermates in a batoid elasmobranch.

 

Demian Chapman1, Samuel Gruber2, Joseph DiBatista3, Elizabeth Babcock1, Ellen Pikitch1, Kevin Feldheim4

“Homebodies”: Extended Natal Philopatry in Immature Lemon Sharks

1Pew Institute for Ocean Science, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, United States, 2Bimini Biological Field Station, Miami, FL, United States, 3Redpath Museum and Department of Biology, McGill University, Montreal, Quebec, Canada, 4Pritzker Laboratory of Molecular Systematics and Evolution, The Field Museum, Chicago, IL, United States

Understanding the balance between philopatric (“home-loving”) behavior and dispersal from the natal area is a central issue in marine ecology, yet it has never been robustly examined for any cartilaginous fish. Near-exhaustive sampling and DNA profiling of 0-3 year old lemon sharks (Negaprion brevirostris; nearly 1000 individuals) within a tropical nursery (Bimini, Bahamas) over eight years (1995-2002) was followed by another five years (2003-2007) of sampling in adjacent, deeper habitats for immature sharks that originated from the 1995-2002 year classes (90-230 cm total length, N=150). This level of physical and genetic tagging allowed us to confidently identify locally-born individuals among all immature sharks captured adjacent to the nursery and to make an unprecedented estimation of the proportion of philopatric individuals relative to migrants in the juvenile population. We estimate that over 50% of juvenile sharks up to lengths of 150 cm (around six years old) sampled off Bimini were born locally, illustrating the importance of natal philopatry and local recruitment by immature individuals. The proportion of philopatric individuals was significantly higher in females than in males, indicative of possible male-biased dispersal. The proportion of local recruits significantly diminished after age six as sharks began to approach adult sizes, indicating that dispersal predominates during this “subadult” phase. Extended philopatric behavior by immature sharks-especially females-may be a precursor to natal homing later in life for purposes of reproduction, which is suspected to occur in sharks but has never been directly demonstrated. Given their antiquity, growing evidence for natal philopatry in sharks suggests an early origin of this behavior in vertebrates. The strong association of immature lemon sharks with their natal area also indicates that spatial management strategies focused around coastal nursery areas and adjacent juvenile habitat could significantly contribute to much-needed conservation for this and perhaps many other tropical shark species.

 

Patricia Charvet-Almeida1, Otto Gadig2

Diversity and Conservation of Manta and Mobulid Rays from Brazilian Waters, Southwestern Atlantic

1Museu Paraense Emilio Goeldi, Belem, Para, Brazil, 2Universidade Estadual Paulista Julio de Mesquita Filho, Sao Vicente, Sao Paulo, Brazil

Mobulidae comprises medium to large size rays that feed on plankton and are found worldwide in tropical and subtropical regions. There are 10 known species and these are among the most vulnerable elasmobranchs to fisheries. Most of these species have a very low fecundity producing a single offspring. Lately there were only three species known to occur in Brazilian waters (Manta birostris, Mobula hypostoma and M. rochebrunei). As sampling carried out with the fishing fleets increased and with examining of scientific collection specimens, three additional species were confirmed in this region (Mobula japanica, M. tarapacana and M. thurstoni), totalizing six species. The Mobulidae world distribution pattern reveals regional faunas characterized by the presence of large widely distributed oceanic-coastal species (Manta birostris, Mobula japanica, M. tarapacana and M. thurstoni) plus an accessory small coastal restricted range species, such as M. munkiana (eastern Central Pacific), M. kuhlii (western Indian Ocean), M. eregoodootenkee (Central Indo-Pacific), M. rochebrunei (eastern Central and western South Atlantic) and M. hypostoma (western Atlantic). The Brazilian coast is the only region in the world presenting two of these accessory species, which makes it the richest coast in terms of mobulid diversity (60% of all mobulids). In Brazil these elasmobranchs are captured mainly by drift nets and surface longlines. Mobulids are not a target species but most of the specimens caught are landed in fish markets. Occasionally very large individual are released from nets due to their size. The giant mantas (Manta birostris) are a highlight for contemplative diving around the world and may contribute to the eco-touristic industry as an important resource in some regions, such as in the Laje de Santos Marine State Park (São Paulo). Public and governmental awareness are needed to provide adequate management and protection for mantas and mobulids in Brazil.

 

Jennifer Ciaccio

Older and Wiser: The Effects of Maturation and Experience on the Predatory Efficiency of Whitespotted Bamboosharks

University of Miami, Coral Gables, FL, United States

Foraging presents a significant challenge for neonatal predators. Adequate predatory skills must initially be present or must quickly develop. Additionally, predatory abilities may change over time. Physical maturation may increase predatory abilities due to improved neuromuscular coordination, increased sensory abilities, or morphological changes. Experience may allow predators to hone existing skills and develop new ones. To tease apart which improvements in predatory abilities were due to increased maturation and which were due to increased experience, three sets of comparisons were made on the predatory efficiencies of hatchling whitespotted bamboosharks: comparisons of sharks before and after 20 days of foraging experience to determine whether predatory efficiency does improve, comparisons of naïve sharks of different ages to determine whether predatory efficiency improves with increases in maturation, and comparisons of naïve and experienced sharks of the same age to determine whether predatory efficiency improves with increases in experience. Sharks of different ages (2 days old or 21 days old) were given 20 days of foraging trials with live prey (either worms only or shrimp only). Predatory efficiency, defined as duration of predatory event, was measured for sharks’ initial foraging trials and final foraging trials. Individual sharks improve predatory efficiency after 20 days of foraging experience. Predatory efficiency improves with maturation alone for sharks foraging on shrimp, a highly elusive prey. Predatory efficiency improves with experience alone for sharks foraging on worms, a non-elusive prey. Maturation likely improves sharks’ ability to create suction while feeding, a necessary ability when foraging on elusive prey. Experience likely improves predatory abilities through associative learning and search image formation. Both experience and maturation are necessary for sharks to exploit all possible prey.

 

Angela Cicia1, William Driggers2, Walter Ingram2, Jeff Kneebone3, Paul Tsang3, James Sulikowski1, David Koester1

Age, Growth, and Maturity of the Little Skate, Leucoraja erinacea, from the Western Gulf of Maine, USA

1University of New England, Biddeford, ME, United States, 2National Marine Fisheries Service, Pascagoula, MS, United States, 3University of New Hampshire, Durham, NH, United States

The little skate, Leucoraja erinacea, is the most common skate found in near-shore waters of the Gulf of Maine. Despite their high relative abundance, there is limited data describing their biology within this region. Moreover, recent stock assessment in the northeast United States indicated that the little skate’s population is declining. In order to gain insight into the life history of little skates, growth rates and sexual maturity were evaluated from 435 specimens, collected within the coastal waters of New Hampshire and Massachusetts. Ages were estimated using vertebral band counts from skates ranging in size from 9.3 to 57 cm total length (TL). The index of average percent error (IAPE) and age-bias plots indicated our aging methods were precise and nonbiased. Growth rates did not differ between male and females and the combined age-at-length data resulted in Von Bertalanffy growth parameters of L= 59.5 cm (TL) and k= 0.16. In order to validate the annual periodicity of band formation, oxytetracycline was injected into 20 individuals (10 male and 10 female) that were held in captivity for 12 months. Maturity ogives, based on data from shell gland mass, follicle size and circulating estradiol concentrations, suggest that 50% maturity in females occurs at age 9.5 years and 48 cm TL. Maturity ogives for males, based on clasper length, testes mass, circulating testosterone concentrations, and the proportion of mature spermatocysts in the testes, suggest 50% maturity occurs at 7.7 years and 46 cm TL.

 

Eugenie Clark1, John Randall2

A New Species of Swell Shark (Carcharhiniformes: Scyliorhinidae) from Papua New Guinea with Coments on Clasper Grove/tube Function in Sharks

1Mote Marine Laboratory, Sarasota, FL, United States, 2Bishop Museum, Honolulu, HI, United States

A new species of Cephaloscyllium is described from five adult specimens (445-660 mm TL) taken in a “nautilus trap” in 240-274 m off the east coast of mainland Papua New Guinea. These are compared to two immature specimens from Rowley Shoals off NW Australia collected in 390-700 m, referred to as Cephaloscyllium sp. E by Last and Stevens (1994), that may be the same as, or closely related to, our PNG specimens. Our new species is distinguishable from other congeners by a unique pattern of small white spots, larger in males than females, that shows up especially in the dark large patches on the dorsum. These dark patches form nine irregular saddle-like marks across the head, body, and fins and extend paler onto the ventral surface. A mature female (660 mm TL) had 16 large yellow eggs (8-21 mm diameter). Claspers of the two adult male paratypes have their grooves fused into a closed tube for half their length. The adaptive function of this fusion into a closed tube on the proximal part of the claspers is discussed. In this and other sharks.

 

Tim Clark

Movement Patterns and Foraging Ecology of the Manta Ray (Manta birostris) University of Hawaii, Honolulu, Hawaii, United States

Manta rays (Manta birostris) were acoustically tracked in order to determine their daily movement patterns and foraging ecology in Hawaii. A combination of active and passive tracking was used to provide information on both the fine scale, short term and the course scale, long term movement patterns of the manta rays. Manta rays are shown to have site fidelity to specific foraging areas and cleaning stations. Manta rays optimize their foraging through the use of area restricted search patterns, allowing them to remain in dense plankton patches. Preliminary studies in the Gulf of Mexico and the Maldives suggest that foraging strategies may differ between oceanic and coastal areas.

 

Rui Coelho1, Javier Rey2, Luís Gil-de-Sola2, Karim Erzini1

Comparing Biological Parameters of the NE Atlantic and Mediterranean Populations of the Deep Water Lantern Shark, Etmopterus spinax

1University of the Algarve - Centre of Marine Sciences, Faro, Portugal, 2Spanish Oceanographic Institute, Malaga, Spain

Etmopterus spinax is a small sized deep water lantern shark that occurs in the Eastern Atlantic and the Mediterranean. Differences in depth distribution, catch per unit effort (CPUE), size at maturity and fecundity were compared between a population that has suffered high levels of fishing mortality during the last decades (southern Portugal in the NE Atlantic) and a population where low fishing pressure below 500 m occurs at present or has occurred in the last decades (Alboran Sea in the W Mediterranean). The research survey CPUE in the NE Atlantic is substantially lower than in the Mediterranean throughout the entire depth range. The NE Atlantic population is maturing at smaller sizes than the Mediterranean population and has a lower mean fecundity. Specifically, sizes at maturity for the NE Atlantic and the Mediterranean were respectively 25.39 and 28.31cm TL for males and 30.86 and 34.18cm TL for females, while mean fecundities for the NE Atlantic and the Mediterranean were respectively 9.94 and 11.06 oocytes per mature female. This work evidenced the possible presence of density dependant mechanisms in the NE Atlantic population of E. spinax that has lowered the size at maturity as a result of excessive fishing mortality. However, given that this is an aplacentary viviparous shark, where fecundity is dependant on female size, this compensatory mechanism seems to be less efficient than what would be expected.

 

Jorge Horacio Colonello1, Mirta Lidia García2, Carlos Angel Lasta3, Roberto Carlos Menni2

Reproductive Biology and Gonadal Cycle of the Lesser Guitarfish, Zapteryx brevirostris, from the Coastal Southwest Atlantic

1Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP); Consejo Nacional de Investigaciones Cinetíficas y Técnicas (CONICET), Mar del Plata, Buenos Aires, Argentina, 2Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); Departamento de Zoología de Vertebrados, FCNyM., La Plata, Buenos Aires, Argentina, 3Consejo de Investigaciones Científicas (CIC), La Plata, Buenos Aires, Argentina

The Lesser guitarfish Zapteryx brevirostris (Chondrichtyes: Rhinobatoidea) is a common lecithotrophic viviparous batoid from coastal Southwest Atlantic waters. In order to study the reproductive ecology a total of 656 (334 males and 656 females) individuals of Z. brevirostris were captured by bottom trawl in the Southwest Atlantic coastal ecosystem between 34° and 42°S. The size of the smallest mature male was 462 mm and the largest immature female was 572 mm. Male size at maturity was 106 estimated in 502 mm total length (77% of the maximum TL). The range between smallest mature and largest immature female was 460-600 mm and size at maturity was estimated in 505 mm (65% of the maximum TL). An opposite trend was observed between spermatogenesis and gonadosomatic index (GSI) in males. The smallest GSI (Jul-Aug) was related to mature spermatocysts and deferent ducts filled with sperm, while the highest GSI (Feb) was associated with immature spermatocysts and empty deferent ducts. Female reproductive cycle is most likely to be triennial. This conclusion was based on the monthly variation of the GSI and largest ovarian follicles diameter. Ovulation occurs in Oct-Nov and embryos born with 150 mm TL after a gestation period of approximately 10 months. This reproductive information is important for fisheries assessments in order to determine the resilience of each species to fishing pressure.

 

Leonard J. V. Compagno1, Andrea D. Marshall2, Tom Kashiwagi2, Michael B. Bennett2

Manta Systematics and Nomenclature

1Shark Research Center, Iziko - Museums of Cape Town, Cape Town, Western Cape, South Africa, 2The University of Queensland, St. Lucia, Brisbane, Queensland, Australia

The devilrays (Family Mobulidae, Suborder Myliobatoidei, Order Rajiformes), are currently divided into two distinctive confamilial genera, Mobula Rafinesque, 1810 and Manta Bancroft, 1828 which rarely have been split into two families. Manta, the giant devil rays or mantas (blanket in Spanish) includes one of the largest living cartilaginous fishes reaching a width of 6-7 m. Authors of the late 20th Century and early 21th Century generally consider Manta to be monotypic and to include a single species, M. birostris (Walbaum, 1792). Manta has one of the more extensive generic and species synonymies of any living genus of cartilaginous fish. The genus Manta has 10 generic and 25 species synonyms, mostly without type specimens. Recent research on Manta off Mozambique, Mexico and Indonesia, conducted by A. Marshall and involving photographing individuals and groups of animals, has revealed two obvious species of Manta that are separable by morphology, size and behaviour. Genetic analyses by T. Kashiwagi provide support for the presence of more than one species of Manta. We discuss the systematics and nomenclature of Manta including problems with the identity of the original M. birostris from ‘Carolina’, United States of America, and its possible synonyms, the status of regional species of Manta with notes on Whitley’s 1936 attempt to split Manta into three poorly characterized genera and 10 poorly defined geographic species (including three new species), and the applicability of nominal species of Manta to the two species from Mozambique. We suggest that a neotype should be designated for M. birostris based on an extant specimen cited by Bigelow & Schroeder’s 1953 monograph on Western North Atlantic batoids.

 

Mark Corcoran2, Brad Wetherbee1, Mahmood Shivji2, Matt Potenski2, Demian Chapman2, Guy Harvey2

Supplemental Feeding for Tourism Radically Alters Movement Patterns and Spatial Distribution of the Southern Stingray, Dasyatis americana

1University of Rhode Island, Kingston, RI, United States, 2Guy Harvey Research Institute, Oceanographic Center, Nova Southeastern University, Dania Beach, FL, United States

Supplemental feeding of southern stingrays, Dasyatis americana, has occurred at Stingray City Sandbar (SCS) at Grand Cayman as a tourist attraction since 1986. We investigated the influence of supplemental feeding on the movement patterns of stingrays by actively tracking both fed and non-fed stingrays using acoustic telemetry. Seven wild and seven provisioned stingrays were tracked manually for between 5-72 h, and site fidelity of five mature females at SCS was investigated over the course of one year using automated acoustic receivers anchored to the seafloor. Female stingrays at SCS utilized significantly smaller 24 h activity spaces (0.13 ± 0.08 km2) than wild female stingrays (0.88 ± 0.17 km2). Fed stingrays were highly active over a small area during daytime at the feeding site, but had limited nocturnal activity, whereas wild stingrays were more active during the night with limited activity during the day. Core areas of activity overlapped little among wild stingrays (3%), whereas core activity areas of provisioned stingrays at SCS overlapped much more (72%). Provisioned female stingrays consistently frequented SCS during periods of supplemental feeding and exhibited long term (up to six years) site fidelity to this site. Supplemental feeding has altered diel activity patterns and spatial distribution of stingrays at SCS and has enabled the local density of D. americana to increase to atypical levels. Our study suggests that food availability directly influences size and location of core areas of activity as well as population density of southern stingrays. The dramatic shifts in behavior and the altered population structure of stingrays also suggest that the aggregation of stingrays at SCS may alter predator-prey relationships and nutrient cycling, and possibly mating systems within the entire community at this location over long time periods. Supplemental feeding of wild marine animals may potentially alter movement patterns of individuals being fed, modify population structure and may ultimately affect the entire marine ecosystem. Managers charged with regulating existing sites where marine animals are fed by humans and policy makers responsible for management of similar sites established in the future should recognize potential far- reaching impacts of such activities on the local marine environment and take appropriate measures to monitor and if necessary enact mitigation measures.

 

Joao Correia

Elasmobranch Commercial Landings in Portugal from 1986 to 2006, with Virtual Population Analysis and a Method for Evaluating “Supply and Demand”

Flying Sharks, Lisboa, Portugal

Portuguese commercial elasmobranch landings were analyzed for the period 1986 - 2006 and totaled 108.671 ton. An average of 5.175 ton were landed yearly, representing 8 orders, 14 families and 44 species. Annual landings for the fishery generally decreased over time, with a corresponding increase in price per kilogram. The most landed group, Skates (Raja sp.), accounted for 33% of the landings, or 35.614 ton. They were followed by Catsharks (Scyliorhinus sp.), Portuguese dogfish (Centroscymnus coelolepis), Leafscale gulper shark (Centrophorus squamosus) and Gulper shark (Centrophorus granulosus) (accounting for 12%, 12%, 10%, and 9% of the landings, respectively). In the absence of CPUE data, the comparative trends of landings and price were employed as an indicator of the “status” of specific elasmobranch species. Raja sp., Centrophorus granulosus, Smoothounds (Mustelus sp.), Torpedo rays (Torpedo sp.), Kitefin shark (Dalatias licha) and Angel sharks (Squatina sp.) displayed indications of possible overexploitation, and merit the focus of future research. The pattern shown by fishing effort over time (i.e. number of fishing vessels over time) displayed a marked decrease, although this was substantially lesser than the decrease shown by landings of the species mentioned earlier. It is unlikely, therefore, that such decrease in landings is justified solely by a decrease in number of fishing vessels. Similarly, the increase in price shown by all species was largely superior to the increase in inflation, which would suggest that the increase in inflation alone would not account for the increase in price. All the results and data seem to corroborate the notion that some species are, in fact, under over-exploitation and in need of immediate management. These findings were all substantiated by virtual population analysis, which yielded higher fishing mortalities to those species where previous methods suggested overfishing.

 

Shannon Corrigan, Luciano Beheregaray

Molecular Phylogenetics and Biogeography of Wobbegong Sharks (Orectolobiformes: Orectolobidae)

Molecular Ecology Lab, Macquarie University, Sydney, NSW, Australia

Wobbegong sharks (Orectolobiformes: Orectolobidae) are dorso-ventrally flattened, demersal sharks that are endemic to the western Indian and eastern Pacific Oceans. They are medium to large in size and are harvested as a food source at several locations throughout their distribution including Australia, China, Japan and Malaysia. In Australia, where they are the most speciose, they are commercially targeted in New South Wales and Western Australia and there is evidence to suggest that populations are declining. This, together with considerable taxonomic uncertainty, has stimulated conservation concern for these sharks. Irrespective of this, there are very few management strategies in place for wobbegongs and available biological information is limited. Morphometric and meristic investigations aimed at answering questions of taxonomy constitute a large proportion of wobbegong research effort. Despite such investment, there has been little focus on the study of species interrelationships or Orectolobid evolution. Furthermore, no prior investigations have adopted a molecular approach to studying these sharks. One component of our work, a molecular phylogenetic analysis of the family Orectolobidae functions to fill this void. Samples of all Orectolobid species (and some undescribed taxa) were collected from Australia and the Indo-Pacific. We obtained genetic information from both mitochondrial and nuclear DNA markers and used the data to reconstruct the evolutionary relationships among wobbegong species. Here, we will demonstrate how our molecular data is inconsistent with the current taxonomic arrangement of the family and go on to describe how these results can contribute to resolving taxonomic uncertainties. We will also propose a biogeographic scenario for the wobbegong sharks that begins with a tropical origin, subsequent colonisation of Australian waters followed by re-colonisation of the tropics.

 

Enric Cortes1, Michelle Heupel2, Colin Simpfendorfer2, Marta Ribera1

Productivity and Susceptibility Analysis of Coastal Sharks in U.S. Atlantic and Gulf of Mexico Waters

1NOAA Fisheries, Panama City, Florida, United States, 2James Cook University, Townsville, Queenland, Australia

Productivity and Susceptibility Analysis, or PSA, is a risk assessment approach useful for evaluating the vulnerability of stocks of different species to fisheries. Depending on data availability, PSA can range from simple qualitative assessments to more detailed quantitative evaluations. We applied a quantitative approach to evaluate the biological productivity and susceptibility to different gears of large and small coastal sharks off the U.S. East Coast and Gulf of Mexico. For the productivity component, we used published biological information to develop Leslie matrices, and incorporated uncertainty in age at maturity, lifespan, and annual age-specific fecundity and survival rates though Monte Carlo simulation. The susceptibility of each species or population to different gear types was evaluated as the product of four sub-components or probabilities: availability, encounterability, selectivity, and post-capture mortality. Availability of the population to the fishery of interest was calculated as the percentage overlap of the range area of the fishery with the range area of the population; encounterability of the population by the gear in question was calculated as the degree of overlap between the population and gear depth ranges; selectivity of the gear was estimated using the mean size at capture and known selectivity curve or the selectivity of a similar species in a similar gear; and post-capture mortality was derived from multiple scientific observer programs that collect information on the status and/or disposition of the shark catch. We plotted productivity and susceptibility paired values to facilitate interpretation, and calculated a risk index based on the Euclidean distance to rank each population or species and help identify those that should receive preferential research and management efforts.

 

Donald Croll1, Kelly Newton1, Kevin Weng2, Felipe Galvan3, John O'Sullivan4, Heidi Dewar5

Movement Patterns and Habitat Preferences of Ten Mobula japanica Tagged in the Gulf of California, Baja California Sur, Mexico

1University of California, Santa Cruz, CA, United States, 2University of Hawaii at Manoa, Honolulu, HI, United States, 3Centro Interdisciplinario de Ciencias Marinas, La Paz, BCS, Mexico, 4Monterey Bay Aquarium, Monterey, CA, United States, 5NOAA Fisheries, La Jolla, CA, United States

Mobulid rays are the subject of an intensive and expanding artesanal fishery in the Gulf of California. Anecdotal reports suggest that populations in the Gulf of California have declined dramatically over the last 20 years. Mobula japanica is a pan- tropical species that appears in the Gulf of California seasonally and is listed as near threatened in the 2007 IUCN Red List of Threatened Species. Our research is focused in this region and on this species because they are relatively abundant, can be reliably sampled, and are the subject of directed and bycatch fisheries mortality in artisanal and purse-seine fisheries in the region. M. japanica occurrence seems to coincide with the large influx of warm water apparent each spring. However, it is unlikely that this summer increase is caused by migration, as their increase in abundance is simultaneous both in tropical and warm temperate waters. It is more likely that mobulid rays disperse offshore or move to deep waters during the winter in tropical and warm temperate areas but seasonally aggregate in certain locations of high prey density, such as the waters offshore of the Baja California Peninsula, making them highly vulnerable to intensive fisheries in the area. Ten M. japanica were tagged with Pop-Up Archival tags near La Paz in the Gulf of California during 2004 – 2006. Preliminary results indicate that M. japanica move out of the Gulf and into the Pacific during late summer/early fall. Resolving these seasonal movement patterns and aggregating areas are key to the conservation of this species.

 

Mark Deakos, Jason Baker, Allan Ligon, Jonathan Whitney, Tim Clark

Demographics of an Island-Associated Manta Ray (Manta birostris) Population in Maui, Hawaii, and Implications for Management

1The Hawaii Association for Marine Education and Research, Inc., Lahaina, Hawaii, United States, 2University of Hawaii, Manoa, Hawaii, United States, 3Pacific Islands Fisheries Science Center, National Marine Fisheries Service, NOAA, Honolulu, Hawaii, United States, 4Manta Pacific Research Foundation, Kona, Hawaii, United States

During 2005 - 2007, 187 individual manta rays were photo-identified from a single cleaning station site in Maui, Hawaii. A discovery curve showed no asymptotic trend, indicating the number of individuals using the site is considerably larger than the total identified. Of these individuals, 58% were observed on more than one occasion within and across years, suggesting philopatry to this area. Males accounted for 47% of the individuals in the population, of which 69% were considered sexually mature based on the claspers extending beyond the pelvic fins. The average encounter rate per dive was 5.50 manta rays per hour. They were habitually absent at first light, with encounter rates increasing throughout the day. No matches were found when compared against 133 individuals photo-identified from a well-studied population off the Big Island (www.mantapacific.org), a distance of only 60 miles. Evidence of shark predation was seen in 12% of the population, and 6% had a missing or non-functional cephalic fin, likely caused by entanglement in monofilament fishing line. During an intensive survey period from September to December 2007, a mean of 140 individuals (95% CI = 119-175) was estimated to be using the area at this time. Estimated annual apparent survival (survival minus emigration) was 0.77 (95% CI = 0.65 – 0.86). These findings are consistent with a population of manta rays moving into and out of the cleaning station vicinity, with a varying portion of the total population temporarily resident at the study site at any given time. These findings add further support to the existence of demographically independent, island-associated populations in Hawaii. The lack of protection for these populations makes them vulnerable to impacts from target and non-target fisheries, and from exploitation of manta ray aggregation sites by commercial scuba diving operations. Management on an island-area basis is recommended.

 

Heidi Dewar1, Peter Mous3, Michael Domeier2, Jos Pet3, Jeff Whitty4

Movements and Site Fidelity of Manta birostris in the Komodo Marine Park, Indonesia

1NOAA, La Jolla, CA, United States, 2Pfleger Institute of Environmental Research, Oceanside, CA, United States, 3The Nature Conservancy, Denpasar, Bali, Indonesia, 4Murdoch University, Murdoch, Australia

To examine the movements of manta rays in the Komodo Marine Park, Indonesia an acoustic array was installed at up to seven sites in the park between 2000 and 2003. A total of 41 acoustic tags were deployed in three separate deployments. Mantas were recorded in the park for up to 526 days with an average duration of 183 days (±136 days) when mantas made from 3 to 303 individual visits to different sites (median 58 visits). There was a clear preference for three sites that comprised over 90% of manta activity. The most popular site (German Flag) was off the southern tip of Komodo Island in an area with a high degree of bathymetric structure. Examination of the longest records suggests some site preference with 5 of 7 individuals spending greater than 90% of their time at the location where they were tagged. Using a general linear model it was possible to examine the effects of daytime, lunar phase, aggregation site, season and tidal phase on visitation patterns. The vast majority of visits were recorded during daylight hours at all sites. The strongest effects of both the lunar and tidal phase were apparent in the northern sites with the most visits occurring when tidal intensity was the greatest during full and new moons. The strongest seasonal pattern was observed in the south were no mantas were recorded during the first quarter in any year. This coincides with a regional increase in temperature and reduction of productivity associated with monsoonal shifts. This study improved the predictability of manta visitation patterns, which will increase the success of manta-based ecotourism. The long-term fidelity indicates that marine protected areas centered around aggregation sites is one tool that could help protect this species from overexploitation.

 

Joseph DiBattista1, Kevin Feldheim2, Dany Garant3, Samuel Gruber4, Andrew Hendry1

Estimating Heritability of Life-history Traits in a Natural Population of Lemon Sharks (Negaprion brevirostris) Using Long-term Pedigree Data

1McGill University, Montreal, Quebec, Canada, 2Field Museum, Chicago, Illinois, United States, 3University of Sherbrooke, Sherbrooke, Quebec, Canada, 4University of Miami, Miami, Florida, United States

Determining the genetic basis of phenotypic traits is central to our understanding of evolution and conservation of natural populations. This requires accurate knowledge of the relatedness among sampled individuals, which is a rarity for most marine systems. We address this issue by performing quantitative genetic analyses on a natural population of lemon sharks (Negaprion brevirostris) from a nursery site at Bimini, Bahamas. We specifically test whether genetic differences can explain the observed divergence in early life history traits between juvenile sharks from Bimini, and those at other surveyed nursery sites in the western Atlantic (i.e., Marquesas Key, Florida; Atol das Rocas, Brazil). Indeed, Bimini sharks are selected to be smaller at age and slower growing than other populations of lemon sharks, but it remains to be seen whether these trait differences are genetically or environmentally determined. Here, we use newly developed litter reconstruction methods based on microsatellite data to generate a long-term pedigree (1991-2007) for Bimini sharks containing 112 dams, 358 sires, and nearly 1400 offspring. The heritability of size (i.e., body length and mass), condition, and growth was estimated using a restricted maximum-likelihood “animal model”, which accounts for potential confounding factors (maternal and environmental effects). Power and sensitivity analysis were also performed to help define the apparent bias and precision of our methods. That is, we estimated the power of our pedigree to detect significant heritability, when present, as well as simulated the effects of parental genetic misassignment on our ability to recover quantitative genetic parameters. This study advances knowledge in this area as the genetic and environmental influence on morphological traits has rarely been studied under natural conditions, and never before in a large marine vertebrate.

 

Wes Dowd, Gillian Renshaw, Dietmar Kültz

Proteomic Analysis of Mechanisms of Anoxia Tolerance and Hypoxic Preconditioning in the Epaulette Shark

University of California, Davis, Davis, CA, United States

Epaulette sharks (Hemiscyllium ocellatum) withstand severe, episodic hypoxia and even anoxia at tropical temperatures. The reef platform around Heron Island, Australia, serves as a natural hypoxic preconditioning environment. We adopted a discovery-based approach to identify proteins/mechanisms involved in low oxygen tolerance. Using two-dimensional gel electrophoresis, we examined proteome changes in response to hypoxic preconditioning (1 or 2 sessions of ~5% oxygen saturation, 24 hours apart) and anoxia (1 or 2 sessions of <0.3% oxygen saturation, 24 hours apart) in epaulette shark tissues. Proteins that were regulated by anoxia exposure and/or hypoxic preconditioning were identified by MALDI-TOF/TOF mass spectrometry and mapped to molecular pathways using bioinformatics tools. Using these data, we tested the hypotheses that 1. the severity of low oxygen exposure influences patterns of protein abundance in relevant cellular pathways (e.g., cellular stress response, redox balance, metabolism), and 2. preconditioning leads to upregulation of compensatory mechanisms of low oxygen tolerance.

 

Marcus Drymon1, Sean Powers2

Quantifying Regional Differences in Shark Abundance and Distribution: A Step Towards Ecosystem Management

1NMFS Mississippi Labs, Pascagoula, MS, United States, 2University of South Alabama, DISL, Dauphin Island, AL, United States

A directive of the United States Magnuson-Stevens Fishery Conservation and Management Act (MSFCMA) is incorporation of ecosystem principles into future stock assessment. Ecopath/Ecosim routines are a common way to model such ecosystem effects, but rely on detailed biological data for model inputs. Modelers often lump sharks and other predatory fishes into a single group of apex predators, when in reality this apex predatory role is likely species and region specific. To investigate the trophic role of sharks in our region, monthly longline surveys were conducted to assess fine scale patterns of shark abundance and distribution in the northern Gulf of Mexico. This survey straddles an area where disjunctive shark abundances have historically been shown. Multivariate analysis of 2007 data indicate adjacent areas within the Gulf of Mexico Large Marine Ecosystem (LME) show differences in shark community structure as revealed by non-metric multi- dimensional scaling and ANOSIM routines. Consequences for region specific differences in trophic transfer and management issues are discussed.

 

Nicholas Dulvy, Arne Mooers

Using Trees to Save Sharks and Rays


Simon Fraser University, Burnaby, BC, Canada

The typical approach to conservation is to save the species most at risk of extinction and these are typically the most charismatic or distinctive species. For example, the only elasmobranchs on the CITES annexes are Whale, White and basking sharks - arguably the world’s most charismatic animals. While protecting charismatic species is a valid and important approach to saving the biodiversity we care about – how do we ensure that the less-charismatic underworld of elasmobranchs is prioritised for conservation action in an appropriate objective manner? Recent advances in our understanding of the evolutionary phylogenies of sharks and rays can be used to identify the most evolutionary distinct globally endangered species. Evolutionarily distinct species have few close relatives and harbour proportionally more genetic diversity and are often extremely distinct in the way they look, live and behave. We outline our approach to updating a global phylogeny of sharks, ray and chimaeras and combining this with the IUCN SSG Global Shark Assessment to generate a list of Shark EDGE species deserving further conservation or management attention.

 

Vicente Faria1, Matthew McDavitt2

The Status of Pristis pristis (Chondichthyes, Pristiformes) Reconsidered

1Instituto de Ciências do Mar, Universidade Federal do Ceará, Fortaleza, CE, Brazil, 2National Legal Research Group, Inc., Charlottesville, VA, United States

Sawfishes (Chondrichthyes, Pristidae) are considered endangered species worldwide, but their conservation and management have been undermined due to poor understanding of the group’s taxonomy. A central issue to be resolved regarding sawfish taxonomy and conservation is the status of Pristis pristis (Linnaeus 1758), a species commonly presumed to have been extirpated from European and north African waters. The purpose of this work was to review this particular aspect of sawfish taxonomy and properly propose an assignment for this nominal species. This goal was accomplished through a thorough review of the historical taxonomic literature and specimens, supplemented with empirical observations on specimens examined at collections for external morphology and DNA sequence comparisons. The nominal species P. pristis is a composite and it has historically been associated with features from several different species, and as such, is a chimaeric taxon that does not exist in nature. The more recent asserted association between P. pristis and the largetooth sawfishes is the product of taxonomic misinterpretation. The suppression of the name P. pristis is proposed.

 

Lara A. Ferry-Graham1, Eileen D. Grogan2, Ashley Neway1

Under Pressure: Ventilation and Feeding in the White-spotted Ratfish,

Hydrolagus collei (Chimaeroidea)


1Moss Landing Marine Laboratories, Moss Landing, CA, United States, 2St. Joseph's University, Philadelphia, PA, United States

Holocephalans possess a fused upper jaw and a non-suspensory hyoid. They are commonly considered to be durophagous fishes, but there is evidence that they may also be capable of suction feeding. This implies that suction is being generated in a mechanical system where the upper jaw cannot protrude and the hyoid cannot depress the jaws, posing serious potential limitations on suction generation as we have come to understand it based upon elasmobranchs and actinopterygians. As a first attempt at understanding if, and how, suction is generated within the extant Holocephali, we measured intra-oral pressures in nine individuals of Hydrolagus collei during ventilation and prey capture. Pressure transducers were implanted in the orobranchial and parabranchial cavities, and pressure was recorded during several modes of respiration; ventilation during paired sculling of the fins, ventilation during alternating sculling of the fins, ventilation with fins at rest and head elevated, ventilation with the fins at rest and head resting on the substrate, ventilation during quiescent swimming along the bottom, and during prey capture. In each of the modes there appeared to be a trend whereby a single pump dominated; that is to say, the two-pump (i.e, suction-pressure) models prevalent in elasmobranchs and actinopterygians does not appear to fully function in Hydrolagus. We postulate that during ventilation, water is drawn into the orobranchial cavity using primarily the hypobranchial musculature. The activity of these muscles greatly increases the volume of the branchial region as the nested branchial arches are expanded ventroposteriorly and the orobranchial chamber is extended posteriorly. The net effect is for water to be pulled through the retracted gill curtain, as opposed to being pushed through by forces generated anterior to the gill region. Subambient pressure drops of up to 1000 Pa were recorded during feeding strikes on small crabs or pieces of mussel body. A subset of these strikes were recorded using high-speed video which revealed that the labial folds on either side of the mouth descend to create a small, tubular mouth opening. A small, laterally enclosed mouth opening is ascribed to enhanced suction producing abilities in other aquatic lineages, and the labial folds in chimaeroids may be convergent in this sense.

 

Lyndsay Field, Diego Bernal

Using Blood Physiochemistry To Compare Capture-related Stress Responses in Pelagic Sharks

UMass Dartmouth, Dartmouth, MA, United States

Pelagic sharks with a high degree of swimming activity, such as those in the family Lamnidae (e.g., shortfin mako, Isurus oxyrinchus, and porbeagle, Lamna nasus), are well known for long distance migrations, high endurance, and aggressive fights when caught on recreational and commercial fishing gear. By contrast, non-lamnid species, such as the blue shark (Prionace glauca, Family Carcharhinidae), that inhabit the same pelagic environment appear to be more sluggish swimmers. This study examined blood chemistry of pelagic sharks in order to compare the degree of capture-stress between lamnid (active) and non-lamnid (sluggish) species. Blood samples were taken from all sharks caught using commercial long-line gear and hematocrit (a potential indicator of aerobic capacity) was measured at capture and was used to determine whether erythrocyte swelling and/or lysing had occurred during capture. The concentrations of plasma ions and metabolites (i.e., Na++, K+, Cl-, Ca++, Mg++, glucose and lactate) were used as additional potential indicators of cellular stress. Additionally, blood samples were analyzed for levels of heat shock protein, Hsp70, an indicator of the cellular stress response. Hematocrit values for lamnids (mean=28.8±9.4%, n=51) were significantly higher (p<0.05) than those of non-lamnid species (mean=17.4±6.3%, n=77). Initial results from plasma chemistry analysis indicate significant differences in glucose and lactate levels between lamnids (mean glucose=122.0±22.1mg/dL, mean lactate=23.0±8.0mmol/L, n=19) and non- lamnids (mean glucose=91.6±20.7mg/dL, mean lactate=8.5±7.0mmol/L, n=25). Initial stress protein results show Hsp70 levels for both groups after 15-240 minutes of long-line gear fight time were approximately four times as elevated when compared to results obtained for unstressed sharks in a previous study. Overall, preliminary findings indicate that active and sluggish sharks species display differences in physiochemical blood parameters resulting from capture on longline gear. Further investigation will reveal whether swimming activity can be used as a means of estimating stress at capture and potentially post-release survival.

 

Brooke Flammang-Lockyer

Morphological and Functional Investigation of the Radialis Muscle in Shark Tails

Harvard University, Cambridge, MA, United States

The swimming kinematics and hydrodynamics of heterocercal tails in elasmobranchs have been the focus of a number of recent studies. However, the locomotor functions of the internal morphological structures of the heterocercal tail remain unexplored. In this study we examine the morphology and function of the radial muscle, or radialis, during swimming in the spiny dogfish Squalus acanthias. The radialis consists entirely of red muscle fibers and is located ventral to the segmented axial myomeres in the most distal region of the caudal fin, originating on the ventral processes of the vertebral column and inserting along the horizontal septum. The muscle fibers of the radialis share a similar fiber orientation and lie in close association with the deepest layer of the subdermal connective tissue sheets. We combined bilateral electromyography of the radialis with simultaneous video to determine the point of activation of the radialis within the tailbeat cycle. Our results indicate that the radialis is active immediately after maximum lateral excursion of the caudal fin to the ipsilateral side. We also find that the activity patterns of the radialis on the right and left side of the body are approximately 180 degrees out of phase. Morphology and motor patterns of the radialis suggest that this muscle is acting as postural reinforcement, and controlling the orientation of the dorsal lobe of the caudal fin during steady swimming.

 

Malcolm Francis

Distribution and Assemblages of New Zealand Demersal Chondrichthyans

National Institute of Water and Atmospheric Research, Wellington, New Zealand

Data from more than 19,000 research trawl tows were used to determine the depth and latitudinal distributions of New Zealand’s demersal chondrichthyans. Thirty- seven species or species groups of sharks, rays, and chimaeras were included, of which 28 were deepwater forms, preferring depths greater than 200 m on the continental slope. Skates and rays generally occurred shallower than 600 m, except for Brochiraja spp. and Bathyraja shuntovi, which extended to 1200 m and 1400 m respectively. Chimaeras were typically found deeper than 400 m, except for Callorhinchus milii (shallower than 100 m) and Hydrolagus novaezealandiae (200–500 m). Shark species occurred from the surface to depths exceeding 1450 m (the effective maximum depth of the trawl samples). Most species had wide latitudinal ranges (10– 15o), but some were restricted to northern waters (Dasyatis brevicaudata, D. thetidis, Myliobatis tenuicaudatus, Sphyrna zygaena, Centroscymnus coelolepis), some to central New Zealand (Callorhinchus milii, Typhlonarke spp.), and one to southern waters (Bythalaelurus dawsoni). Depth range was positively correlated with preferred depth and latitudinal range was positively correlated with preferred latitude. Assemblages of species were determined using correspondence analysis and Ward’s cluster analysis. Species split into two main groups: those preferring depths shallower and deeper than 400 m, respectively. The shallow group was further subdivided by latitude into northern and central New Zealand assemblages. The large deepwater assemblage was relatively stable because of strongly overlapping depth and latitudinal ranges for many of the species.

 

Lorenz Frick1, Richard Reina1, Terry Walker2

What Happens after We Throw Them Back? The Physiological Response of Sharks to Capture Stress

1Monash University, Clayton, VIC, Australia, 2MAFFRI, Department of Primary Idustries Queenscliff Centre, Queenscliff, VIC, Australia

Quantifying post-release mortality of chondrichthyans poses a considerable challenge to researchers. Understanding the physiological mechanisms that can carry an organism beyond its homeostatic limits under very stressful circumstances is of paramount importance to developing a method that allows predicting the post- release fate of an animal. However, studying the capture-related stress physiology of chondrichthyans in the field is very difficult because many factors such as duration of stress exposure or water temperature, may have profound effects on physiological processes, and obtaining further blood samples without recapture is virtually impossible once an animal is released. To avoid the difficulties associated with monitoring the condition of sharks following capture and release in the wild, we captured Port Jackson sharks, Heterodontus portusjacksoni, and gummy sharks, Mustelus antarcticus, by gill-net, hook-and-line, and trawl-net in a controlled laboratory setting, and measured struggling effort and obtained repeated blood samples during a recovery period of 72 hours post-stress. We found dramatic species-specific differences in stress tolerance. Increasing plasma lactate concentration appears to be a good indicator of stress in sharks. Lactate accumulates in white muscle cells as a metabolic by-product of anaerobic muscle activity, and is slowly released into the bloodstream, but a lack of concordance between struggling effort and plasma lactate concentration suggests that elevated circulating lactate levels do not merely reflect increased physical activity of an animal. Different types of fishing gear affected sharks to a varying degree, but the duration of stress exposure had a minor effect on the magnitude of the lactate response. In some cases, severe disturbance of the electrolyte balance presumably led to delayed mortality. Plasma lactate and potassium levels were extraordinarily high in moribund sharks. The data collected will be very useful in understanding and managing the consequences of capture stress.

 

Jim Gelsleichter1, Nancy Szabo2

Shark Pharming: Human Pharmaceutical Exposure and Uptake in Juvenile Bull Sharks (Carcharhinus leucas) Residing in Wastewater-impacted Freshwater Habitats

1Center for Shark Research, Mote Marine Laboratory, Sarasota, FL, United States, 2Analytical Toxicology Core Laboratory, University of Florida, Gainesville, FL, United States

Recently, there has been growing concern about the ecological and human health risks posed by pharmaceutical-related pollutants originating from human excretion. These compounds can have unexpected and often profound effects on non-target species because many drugs function by altering biological processes that are common in most organisms. Since these contaminants enter the natural environment primarily through domestic and industrial wastewater discharge, they pose their greatest threats to wildlife residing in aquatic habitats bordering highly populated regions. However, there has been very little research conducted on the exposure to and uptake of these pollutants in aquatic species. In this presentation, we discuss data on the presence and concentrations of nine widely prescribed human pharmaceuticals in juvenile bull sharks (Carcharhinus leucas) residing in wastewater- impacted Florida rivers. The compounds that were examined include the synthetic estrogen commonly used in human contraceptives, 17α-ethynylestradiol (EE2); the antidepressants (Brand names listed in parentheses) citalopram (Celexa), fluvoxamine (Luvox), paroxetine (Paxil), sertraline (Zoloff), venlafaxine (Effexor), and fluoxetine (Prozac); the lipid-lowering compound, atorvastatin (Lipitor); and the impotence drug, sildenafil citrate (Viagra). Several of these compounds have been detected in surface waters of aquatic ecosystems and the tissues of aquatic organisms in previous studies. Two of these compounds, EE2 and fluoxetine, have also been shown to be capable of altering reproduction and/or embryonic development in aquatic vertebrates. Juvenile bull sharks depend on freshwater and brackish rivers as “nursery grounds,” areas that are believed to provide young fish with protection from predators and abundant food to sustain high survival and rapid growth to maturity. Since these habitats are increasingly contaminated by wastewater-related pollutants including human pharmaceuticals, it is important to assess the risks that these contaminants pose to this unique species By doing so, our larger study will contribute valuable data on a non-fishing related human activity that may adversely affect Essential Fish Habitat for C. leucas.

 

Shannon Gerry

A Comparison of Feeding Mechanics in a Generalist and a Specialist Shark Species

University of Rhode Island, Kingston, RI, United States

Partitioning of resources within a community can be determined by the degree of plasticity or degree of specialization used in resource acquisition by the members. This research studies the feeding ecology, behavior and function of a trophic generalist, spiny dogfish, and a specialist, smooth-hounds, from Narragansett Bay, Rhode Island in order to investigate the interaction of these predators within the environment. A dietary specialist is expected to feed on a subset of available prey items while a generalist will feed on a wide range of available prey. A specialist will use a stereotyped behavior and jaw muscle function for prey capture and processing, however a generalist will modulate function and behavior dependent on prey type. These hypotheses were tested in performance tests of prey selection, temporal variation of feeding behaviors and asynchronous pairwise activation of the jaw muscles. In the absence of conspecifics, dogfish and smooth-hounds foraged optimally by selecting the prey item with the highest energetic return. However, smooth-hounds did not select crabs, the preferred natural prey. Dogfish modulated specific prey capture and processing behaviors by choosing the behavior that best corresponded to prey type. Smooth-hounds used a stereotyped ram capture behavior as well as a stereotyped crush processing behavior. Dogfish varied jaw muscle function between synchronous pairwise activation during capture to asynchronous pairwise activation during prey processing. In contrast, smooth- hounds used a stereotyped relatively synchronous activation pattern during prey capture and processing. Based on these comprehensive analyses, spiny dogfish are generalist predators that exhibit flexibility to feed on a variety of prey items. Although smooth-hounds did not show the same dietary specialization they do in the wild, the stereotyped behavior and function indicates these sharks are specialist predators. In a natural environment, smooth-hounds are constrained to feed on a specialized resource using morphological, behavioral and functional specializations.

 

Kate Gledhill1, Joesph DiBattista2, Kevin Feldheim3, Samuel Gruber1

Highly Site Specific Philopatry Displayed by Female Lemon Sharks

(Negaprion brevirostris)


1Bimini Biological Field Station, Bimini, Bahamas, 2McGill University, Montreal, Canada, 3Field Musuem, Chicago, United States

Reproductively active female lemon sharks (Negaprion brevirostris) show strong philopatry to the nursery areas of Bimini, Bahamas, with females returning biennially for parturition. The present study assessed whether returning females give birth over successive years at specific sites, or at random locations around the island. To this end, 1558 genetic samples were obtained during the years 1995 to 2007. Genetic materials were collected during exhaustive sampling held annually at Bimini from juvenile lemon sharks caught in gillnets. Additional samples were collected opportunistically throughout the year with gillnets, rod and reel, or longlines. Recently developed genetic methods were used to: 1) identify full and half-sibling groups within and between years (i.e., litters) using the program COLONY v 1.2; 2) assign sampled adults as parents to offspring (using CERVUS v 3.0); 3) reconstruct parentage from the juvenile DNA samples for all other unsampled adults; and 4) create a complete population pedigree. One-hundred-twenty dams and 480 sires were thus identified for all sampled offspring, representing 181 litters over 16 years. Using this pedigree we then compared the birth location of offspring from each sampled or reconstructed adult female, over all years. The information gathered from these results can then be used to determine whether specific sites within a small island system, may be separate primary nursery grounds and whether females select a specific site for their offspring over time. This is important from a conservation perspective, as a lack of nursery connectivity might limit the recovery of particular nursery site from degradation. Funded by the NSF, BBFS and PIOS.

 

Rachel Graham1, Emma Hickerson2, Dan Castellanos3, Marissa Nuttall2

Site Fidelity and Movements of Juvenile Manta Rays in the Gulf of Mexico

1Wildlife Conservation Society, Punta Gorda, Belize, 2Flower Garden BAnks National Marine Sanctuary/NOAA, Galveston, Texas, United States, 3BlueBelize, Punta Gorda, Belize, 4Flower Garden BAnks National Marine Sanctuary/NOAA, Galveston, Texas, United States

Manta rays (Manta birostris) are the world’s largest batoid and little is known about its population or behaviour throughout its broad distributional range. We present the first information on manta ray populations and behaviour in the Gulf of Mexico. Using the photo identification catalogue compiled by the Flower Garden Banks National Marine Sanctuary staff, we used distinct ventral spot patterns to identify a minimum of 32 individual manta rays that have visited the banks over three decades. Mantas have been resighted between years indicating site fidelity to the sanctuary banks. Additionally, we conducted an 18 month study of the site fidelity and inter bank movements of mantas at the Flower Garden Banks National Marine Sanctuary. We tagged eight mantas with coded acoustic tags and placed receivers on the three banks encompassed by the marine sanctuary. Mean disc width of tagged mantas was 1.8 m, suggesting that all animals tagged were juveniles. Based on time recorded at the receiver, manta site fidelity was highest on the East Flower Garden Bank. Three 187 mantas undertook inter-bank movements ranging from 18 km to 67 km distance and provide proof of connectivity between the distant banks that comprise the sanctuary.

 

Dean Grubbs1, Charles Cotton2, Toby Daly-Engel3

A Comparison of Diel Vertical Movements of Bluntnose Sixgill Sharks

(Hexanchus griseus) in the Atlantic and Pacific Oceans

1Florida State University Coastal and Marine Lab, St. Teresa, FL, United States, 2Virginia Institute of Marine Science, Gloucester Point, VA, United States, 3University of Hawaii at Manoa, Honolulu, HI, United States

The bluntnose sixgill shark (Hexanchus griseus) occurs worldwide in tropical and temperate seas. H. griseus often associate with geomorphological features (e.g. submarine canyons) between continental and insular shelf edges and slopes where they are top predators and scavengers. While H. griseus have been captured from the surface to depths of 1,875 meters, very little is known about their movements and behavior. These sharks typically occur deeper than 200 m, though they are common much shallower in some areas where waters remain cool year-round (e.g. Puget Sound). Much of what is known about the movements and behavior of H. griseus has been gleaned from submersible and baited camera sightings and from a single, short- term telemetry study. We used modified longlines from small vessels to capture adult H. griseus (267 to 451 cm total length) at depths of 250-500 m near submarine canyons off Hawaii (Central North Pacific Ocean) and Virginia (Northwest Atlantic Ocean). A subset of the sharks were fitted with high-rate, archiving, pop-off satellite transmitters to 1) assess survivorship and recovery time following capture, 2) examine patterns of vertical movements, and 3) compare patterns of vertical movements between locations. Results to date indicate H. griseus have high post- release survivorship, but require 48 to 72 hours recovery time until resuming what we interpret as normal behavior. Swimming depth and water temperature ranges were 196-839 m and 4.9-17.3°C for H. griseus tagged offshore of Hawaii and 171-623 m and 5.2-14.3°C for H. griseus tagged offshore of Virginia. Following recovery, all H. griseus displayed obvious diel patterns in vertical movements. Offshore of Hawaii, swimming depths were 500-700 m (6-7°C) during day and 225-325 m (13-16°C) during night. Offshore of Virginia, the diel pattern was shallower, with swimming depths of 250-300 m (10-12°C) during day and 175-225 m (12.5-13.5°C) during night.

 

Simon Gulak1, Chryssoula Gubili1, Lara Meischke2, Sabine Wintner3, Dennis Reid4, Catherine Jones1, Leslie Noble1

Mitochondrial Haplotype Analysis of the Bull Shark, Carcharhinus leucas, (Valenciennes, 1839) Control Region

1University of Aberdeen, Aberdeen, Scotland, United Kingdom, 2University of St Andrews, St Andrews, Scotland, United Kingdom, 3Natal Sharks Board, Umhlanga, KwaZulu-Natal, South Africa, 4NSW Fisheries, New South Wales, Australia

The bull shark, Carcharhinus leucas, is known for its wide distribution, along the coastal areas of tropical and subtropical seas, and its ability to penetrate freshwater systems. This species is usually found close inshore in marine habitats, in water less than 30m deep and occasionally less than a metre. These characteristics combined with its distribution bring this elasmobranch into contact with humans on a regular basis and make it especially susceptible to anthropogenic effects. The bull shark is considered an important fisheries species and although mainly sought for its fins for shark-fin soup, it is also utilised fresh, fresh-frozen or smoked for human consumption. Knowledge of the genetic structure is essential for effective fisheries management and comparative phylogeography, using mitochondrial DNA (mtDNA), has become a powerful tool in the study of populations. An 820 base pair fragment was sequenced from the control region of 102 samples from Eastern Australia (n=51), South Africa (n=19) and the United States (n=32). Seven samples included in the analysis were previously sequenced (Nova Southeastern University, Florida). The sequences were aligned and analysed, yielding 18 haplotypes (diversity 0.831, standard deviation ± 0.024). A preliminary analysis of molecular variance (AMOVA) indicates significant differences among sample sites across ocean basins (77.3% variation, ΦST 0.773, p <0.00001). These early results indicate the presence of at least three separate stocks, with the likelihood that U.S. East Atlantic coast and Gulf of Mexico form a single population. More samples are required to explain the low genetic diversity in Eastern Australia and make firm conclusions on the structure of these stocks, and their potential vulnerability.

 

Tristan Guttridge1, Darren Croft3, Kate Gledhill2, Samuel Gruber2, David Sims4, Jens Krause1

Social, Size and Species Group Living Preferences in Juvenile Lemon Sharks, Negaprion brevirostris

1University of Leeds, Leeds, United Kingdom, 2Bimini Biological Field Station, South Bimini, Bahamas, 3University of Bangor, Bangor, United Kingdom, 4Marine Biological Association, Plymouth, United Kingdom

Group living in sharks is a widespread phenomenon but relatively little is known about the composition and organization of these groups. Using 40 juvenile lemon sharks, Negaprion brevirostris caught in the South Bimini, Bahamas nursery area a range of choice tests were conducted to determine whether individual lemon sharks make non-random grouping decisions. Results of the trials revealed that juvenile lemon sharks exhibit a strong preference to behave socially even when the conspecific stimulus group was reduced to a single lemon shark (Wilcoxen matched pairs, n = 8, p-value = 0.015). Additional size-preference trials indicated that during the juvenile phase of the lemon shark’s life cycle there was evidence for association (t test, t = -2.37, n = 10, p-value = 0.038) with size-matched groups of lemon sharks. Further species-preference testing using juvenile nurse sharks, Ginglymystoma cirratum also demonstrated that lemon sharks have a strong preference to group with conspecifics (Wilcoxen, n = 10, p-value = 0.00013). Implications of these social preferences for group living of wild sharks are discussed, along with the potential factors that may contribute to the development of non-random grouping behaviours. Supported by the Leverhulme Trust, University of Leeds, Hoover Foundation and Bimini Biological Field Station.

 

Diane L. Haas, David A. Ebert, Gregor M. Cailliet

Comparative Life History Characteristics of the Aleutian skate, Bathyraja aleutica, in Two Alaskan Ecosystems

Pacific Shark Research Center, Moss Landing Marine Labopra, Moss Landing, CA, United States

The Aleutian skate (Bathyraja aleutica) is a large deep-water species that commonly occurs in bycatch of Alaskan trawl and longline fisheries. Although prominent in the skate biomass of both the eastern Bering Sea (EBS) and Gulf of Alaska (GOA) ecosystems, minimal biological information exists for this species. This is of concern, because skates often exhibit k-selected life history characteristics that make them susceptible to fishery exploitation. To increase our understanding of this potentially vulnerable species, and address the possibility for two separate populations in Alaskan waters, the age, growth, and reproductive biology of B. aleutica was studied. In total, 1,281 skates were collected since 2004 in the EBS and GOA during exploratory trawl surveys, by fisheries observers, and from fishery landings. Gonads were examined using visual and histological analysis, and compared with external morphology to determine maturity stage and reproductive seasonality. Vertebral thin sections were examined for age determination, and multiple growth models were used to evaluate growth characteristics. Median sizes at maturity were similar between sexes, but significantly different between areas. TL50 was 124.4 cm TL for females and 122.8 cm TL for males in the EBS, and 120.7 cm TL for females and 117.7 cm TL for males in the GOA. The presence of males with mature spermatozoa and gravid females indicated reproductive capability during all months sampled (April – September). For skates from the EBS, maximum age estimates were 16 and 17 years for males and females, and the three-parameter von Bertalanffy growth functions generated estimates of k = 0.11 yr-1 and L= 172.6 cm TL. Age determination is nearing completion, but estimates thus far indicate skates from the GOA attain greater ages. Final age estimates and growth parameters will be presented. These data suggest B. aleutica is a moderately slow-growing and late-maturing species.

 

Laura Habegger1, Daniel Huber2, Philip Motta1

 

Theoretical Calculations of Feeding Biomechanics in Bull Sharks over Ontogeny 1University of South Florida, Tampa, Florida, United States, 2University of Tampa, Tampa, Florida, United States

Bull sharks (Carcharhinus leucas) are one of the most aggressive coastal shark species inhabiting subtropical and tropical seas worldwide. Although a very broad head, robust jaws, and large serrated teeth are obvious and notorious features of C. leucas, the feeding biomechanics of this species have scarcely been investigated. The goal of this study is to describe the functional morphology of the jaw apparatus and investigate ontogenetic changes in bite performance in this top level predator. Theoretical calculations of jaw leverage and bite force were performed for an ontogenetic series of ten individuals using a three dimensional static equilibrium model. Values of theoretical bite forces ranged from 68 to 1023 N at the most anterior tooth of jaw and from 194 to 3721 N at the corner of the jaw in a range of sizes of 73- 258 cm, TL. Although little is know about the feeding ecology for this species, dietary literature suggests that bull sharks exhibit an ontogenetic dietary shift where type of prey ranged from bony fishes to elasmobranchs and mammals at approximately 140 cm TL. Bite force as measurement of performance could provide a better understanding of the feeding ecology and foraging capabilities of this apex predator over ontogeny.

 

Blake Harahush, Nathan Hart, Kerstin Fritsches, Shaun Collin

The Development of Visual Function in the Embryonic Brown Banded Bamboo Shark, Chiloscyllium punctatum (Elasmobranchii)

University of Queensland, Brisbane, Queensland, Australia

Anatomical studies have shown that the retina of the oviparous brown banded bamboo shark, Chiloscyllium punctatum, is fully differentiated about 30 days prior to hatching (158 days post deposition, dpd). However, it is not known whether the retina is physiologically capable of vision at this early stage and, if so, why. To assess the onset of retinal function, we used microspectrophotometry (MSP) to measure the presence of visual pigment in photoreceptor outer segments and electroretinography to assess light sensitivity. MSP revealed the presence of a vitamin A1-based (rhodopsin) visual pigment (wavelength of peak absorbance, λmax 500 nm) in the rods as early as 115 dpd, providing the fundamental basis for light detection. Retinal sensitivity to light and temporal resolution (indicated by flicker fusion frequency, FFF) were recorded electroretinographically from whole animals and isolated eye-cup preparations using a graduated series of light intensities and flicker frequencies in embryonic sharks from 110 dpd (50 days pre-hatch) to hatched sharks up to one year old. The youngest shark that produced a measurable response to light was 127 dpd, which correlates well with the timing of the appearance of retinal synaptic connections. Peak voltage responses to light were observed in animals at the time of hatching (just prior to, or within 24 hours post-hatch). Temporal resolution (FFF) ranged from 6 Hz to 22 Hz, which is relatively slow compared to other aquatic predators. This study shows that the retina of C. punctatum is both anatomically mature and physiologically functional prior to hatching. The behavioural advantage of a functional visual system early in embryonic life is unclear, especially for an animal that develops in an opaque egg case, but we suggest it may allow time for fine-tuning of the system prior to birth, providing the animal with optimised vision upon hatching.

 

Paulo Oliveira1, Fabio Hazin1, Felipe Carvalho2, Monica Souza1, George Burgess2

Reproductive Biology of the Crocodile Shark, Pseudocarcharias kamoharai (Matsubara, 1936), from the Southwestern Atlantic Ocean

1Universidade Federal Rural de Pernambuco, Recife, Pernambuco/Northeast, Brazil, 2University of Florida, Gainesville, Florida/Southeast, United States

The monotypic crocodile shark, Pseudocarcharias kamoharai, is commonly caught, as by-catch, in the tuna longline fishery worldwide. Despite its common occurrence, many details of its reproductive biology are still poorly known. We studied the reproductive biology of crocodile sharks using 490 specimens (313 females and 177 males) captured in 2005-2007 by the commercial tuna longline fleet operating in the southwestern Atlantic Ocean. Maximum observed total lengths (TL) were 122 and 109 cm for females and males, respectively, with a mode in both sexes at 90-100 cm. Sexual maturity was attained at about 84- 94 cm TL in males and at about 90 cm TL in females. Results suggested that the crocodile shark gives birth throughout most of the year, peaks in July when the frequency of females bearing near-term pregnant specimens was highest.

 

Ed Heist1, Harold Pratt2, Jeffrey Carrier3

Why is there Multiple Paternity of Nurse Shark?


1Southern Illinois University, Carbondale, IL, United States, 2Mote Marine Lab, Summerland Key, FL, United States, 3Albion College, Albion, MI, United States

Multiple paternity has been demonstrated in several shark species including placentally viviparous hammerhead and requiem sharks and the lecithotrophic nurse shark (Ginglymostoma cirratum). Cited reasons for multiple paternity in sharks include indirect genetic benefits or convenience polyandry. Most studies either dismiss or do not mention fertility assurance as potentially important. Nurse sharks produce very large energy-rich eggs that slowly pass through the reproductive tract one at a time, precluding rapid fertilization of multiple eggs. Because nurse sharks do not store sperm, they likely require multiple matings to fertilize all egg clutches in a litter. Based on nurse shark mating behaviors, reproductive anatomy, and genetic analysis of clutches, we believe that fertility assurance is the most parsimonious explanation for multiple paternity in nurse sharks. We examined three complete nurse shark litters and found that each had six to seven sires with the number of pups per sire ranging from one to 17. The mean number of pups per sire was five. We have observed hundreds of copulations and failed copulations in nurse shark as well as cooperative breeding behavior among males. Female nurse sharks can usually control copulation by refuging and successfully avoid mating with pursuing males and even groups of males. Because clutch sizes are small, we cannot invoke kin selection to explain the more successful group mating behavior among males and instead hypothesize that male cooperation is a strategy of less dominant males to overcome a female’s ability to avoid mating. Fertility assurance may be less important for viviparous species with many pups because there is less energy invested in an unfertilized egg. Because most sharks are either oviparous or ovoviviparous, fertility assurance has important consequences for elasmobranch conservation.

 

Fiona Hogan1, Steve Cadrin2, Alyssa MacDonald1, Katherine A. Sosebee3

Seasonal Temperature Habitats of Skate Species off the Northeast Coast of the U.S.

1University of Massachusetts School for Marine Science, Dartmouth, Massachusetts, United States, 2NOAA/UMass Cooperative Marine Education and Research Program, Dartmouth, Massachusetts, United States, 3Northeast Fisheries Science Center, Woods Hole, Massachusetts, United States

The role of temperature in affecting seasonal distribution patterns of skate species off the Northeast coast was investigated using Northeast Fisheries Science Center spring and autumn trawl survey data. Survey data on (a) skate catches and catch locations and (b) bottom water temperatures were analyzed to identify seasonal habitats and temperature preferences of juveniles and adults of each species, and to determine habitat overlaps. Temperature habitats differed among species, and some species exhibited partially overlapping habitats. Autumn and spring temporal habitats differ more for juveniles than for adults of the same species. Seasonal differences in catch-weighted temperature are species-specific, but most of the species are distributed in cooler waters during spring and in warmer waters during autumn.

 

Rebekah Horn1, William Robbins2, Douglas McCauley3, Mahmood Shivji1

Genetic Structure of the Gray Reef Shark (Carcharhinus amblyrhynchos), Based on Microsatellite and Mitochondrial DNA Analyses With Implications For Management

1Guy Harvey Research Institute, Nova Southeastern University, Dania Beach, FL, United States, 2Cronulla Fisheries Research Centre, NSW Department of Primary Industries, NSW, Australia, 3Hopkins Marine Station, Stanford University, Pacific Grove, CA, United States

The gray reef shark (Carcharhinus amblyrhynchos) is an Indo-Pacific, coral reef associated species that presumably plays an important role as apex predator in maintaining the integrity of coral reef ecosystems. Populations of this shark have declined substantially in some regions due to over-fishing, with recent estimates suggesting a 17% decline per year on the Great Barrier Reef (GBR) and projections of only 0.1% of current populations remaining after 20 years at current exploitation rates. There is no information on population structure of gray reef sharks to aid in their management and conservation. We are assessing genetic structure in this species by using entire mitochondrial control region sequences and 15 nuclear microsatellite loci as markers. 275 gray reef shark samples were obtained from across the species’ Indo-Pacific distribution: Western Indian Ocean (Madagascar/Seychelles), Eastern Indian Ocean (Cocos (Keeling) Islands, Western Australia), Central Pacific (Hawaii, Palmyra Atoll, Fanning Atoll), and Southwestern Pacific (Eastern Australia - GBR). Mitochondrial and microsatellite data concordantly identify Hawaii, the western Indian Ocean and Cocos (Keeling) Islands populations as genetically distinct relative to other sampling locations. Interestingly, the Palmyra and Fanning Atoll sharks, although showing significant genetic differentiation from the geographically closer Hawaii population, are not genetically differentiated from the geographically farther GBR population. Overall, at least four genetically identified management units appear to exist despite the modest geographic sampling depth: 1. Western Indian Ocean, 2. Cocos (Keeling) Islands, 3. the Southwestern Pacific/Palmyra-Fanning Atolls, and 4. Hawaii. These results show strong genetic differentiation exists in gray reef shark populations separated by expanses of open ocean, and suggest proper management of this declining species will have to occur at the very least on a regional geographic scale.

 

Lucy Howey1, Bradley Wetherbee2, Mahmood Shivji1

Movement Patterns and Environmental Preferences of Blue Sharks (Prionace glauca) Determined by Satellite Archival Tagging

1Guy Harvey Research Institute, Oceanographic Center, Nova Southeastern University, Dania Beach, FL, United States, 2Department of Biological Sciences, University of Rhode Island, Kingston, RI, United States

Blue sharks (Prionace glauca) are common, highly migratory, pelagic sharks with hundreds of thousands captured annually in pelagic longline fisheries. They also form the largest component of the international fin trade. Despite their prevalence in global fisheries, management relevant information on their habitat utilization and movement patterns is fragmentary. During the summer of 2007, twenty-three blue sharks (male, n=21; female, n=2) were tagged with Microwave Telemetry Inc., satellite pop-up transmitters near Cape Cod, MA. Programmed pop-off dates ranged from 30 days to 12 months. To date, tags have collected information ranging between 4-186 days with seven tags still at liberty. Blue sharks preferred surface waters and spent 43% of their time at less than 2.4 m depth, 66% of their time at depths less than 5 m (±2.4 m) and 77% of their time at less than 11 m (±2.4 m). Sharks spent 70% of their time in waters between 14-20°C. When sharks traveled off the continental shelf into deeper waters they dove more frequently. Geoposition was determined based on light level data and analyzed using the Kalman-SST filter. Sharks remained on the continental shelf during summer months, but moved to distant, off-shelf locations as the seasons progressed. One male shark moved at least 2,485 km over 6 months from its September tagging location to coastal Puerto Rican waters; another male shark moved at least 1,447 km from Cape Cod to the east of Bermuda between August and February. We will report a more detailed perspective on movement patterns from these and additional tags scheduled to release within the next few months.

 

Daniel Huber1, Matthew Kolmann1, Anthony Herrel2, Julien Claes3

Chondrichthyan Feeding Biomechanics: Intra- and Inter-specific Scaling Patterns

1University of Tampa, Tampa, FL, United States, 2Harvard University, Cambridge, MA, United States, 3Catholic University of Louvain, Louvain-la-Neuve, Belgium

The feeding performance of chondrichthyans is paramount in their ecological and evolutionary success. As performance is determined in part by morphology, it can be expected to change as an organism grows, thereby resulting in changes in resource acquisition. Changes in bite force were therefore investigated over ontogeny in the horn shark (n = 12, 19-59 cm SL), blacktip shark (n = 14, 48-121 cm SL), and spotted ratfish (n = 8, 21-44 cm SL) (intraspecific scaling) via biomechanical modeling. As aquatic poikilotherms, chondrichthyans can grow very large, making them ideal subjects with which to investigate the effects of body size on bite force among species as well. Therefore, an interspecific scaling analysis of bite force among ten species varying in size by nearly three orders of magnitude (16-300 cm SL) was used to determine if the high bite forces of large chondrichthyans are simply a consequence of their large body size, or rather the result of diet-related adaptation, and if changes in bite force are correlated with changes in head and tooth shape among species. Positive allometry of bite force over ontogeny was observed in all three species via positive allometry of jaw adductor muscle force (horn shark), jaw leverage (spotted ratfish), or both (blacktip shark). However, bite force scaled isometrically among chondrichthyan species, perhaps indicating that at large sizes, high absolute magnitudes of bite force overcome any mechanical constraints set by prey, precluding the need for relatively high feeding performance. Additionally, head width was found to be the best predictor of bite force among these ten species. These contrasting scaling patterns are indicative of the unique selective pressures acting on chondrichthyans varying widely in size.

 

Robert Hueter1, John Tyminski1, Rafael de la Parra2

Deep Diving and Distant Travels: Vertical and Horizontal Movements of Whale Sharks (Rhincodon typus) Tagged off Quintana Roo, Mexico

1Mote Marine Laboratory, Sarasota, Florida, United States, 2Proyecto Domino, Cancun, Quintana Roo, Mexico

Satellite-linked pop-up archival transmitting (PSAT, Wildlife Computers) tags affixed to eleven whale sharks (six male, five female) ranging 5.5-8 m TL off Isla Holbox, Mexico have successfully transmitted data on depth, temperature and geolocation of animal movements. Once off the continental shelf, the sharks display dives to as much as 1,720 m (over one mile deep). Four of the 11 tags have been recovered and two provided significant minute-by-minute data. In some cases dives show a distinct crepuscular pattern of deepest diving at sunrise and sunset. Dive profiles are steep with descents of more than 30 m/min and even faster ascents, with no leveling off between surface and deepest point of the dive, indicating that feeding may not be the primary purpose of the diving behavior. Most geographic movements observed to date have been confined to the Gulf of Mexico basin, the northwest corner of the Caribbean Sea, or the Straits of Florida. However, one female shark demonstrated a migration of at least 7,213 km in 150 days, during which the shark moved from the southeastern Gulf of Mexico, through the northern Caribbean Sea, into the North Atlantic Ocean and across the equator to the South Atlantic Ocean, where the tag popped up near the Mid-Atlantic Ridge between Brazil and western Africa. This long-distance movement is consistent with genetic evidence that the Atlantic probably contains a single population of whale sharks.

 

Katherine Jirik, Christopher Lowe

Influence of Temperature on the Habitat Use and Movement Patterns of Round Stingrays in a Southern California Estuary

California State University Long Beach, Long Beach, CA, United States

Sexual segregation among elasmobranchs often results in differential habitat use, with females of some species moving into shallow, inshore environments during summer. Although behavioral thermoregulation has been purported to explain this pattern, difficulties remain in linking a thermal preference to reproductive behavior or pregnancy. Generalizing habitat preferences can be complicated further if thermal regimes differ between habitat types within an inshore environment (e.g. restored vs. natural estuarine areas). This study compared the abundance and movement patterns of round stingrays (Urobatis halleri) in restored and natural habitats of the Anaheim Bay Estuary (California, USA) to determine whether rays prefer warmer water habitats and if females utilize these areas during pregnancy. Rays were seasonally abundant with the highest densities occurring from May-August and few rays present from October-April (2006-07). Higher ray densities correlated with warmer seafloor water temperatures. Ray densities were also higher in the restored habitat than the natural habitat, except during September. Sex ratios were highly skewed toward female rays in restored habitats but only slightly skewed toward females in natural habitats. Ultrasonography, performed on a subset of female rays in restored areas, confirmed that 80% of rays were pregnant. In addition, passive acoustic telemetry revealed that rays showed site fidelity to restored areas during spring and summer, but moved into natural areas during early fall or emigrated from the estuary altogether by winter. This was supported on a shorter temporal scale by quantifying the daily activity spaces of rays during summer and fall. These results, combined, suggest that water temperature influences ray habitat preference and pregnant females that aggregate in restored areas may attain a thermally- derived reproductive benefit by selecting warmer habitats during gestation.

 

Laura Jordan

Functional Consequences of Structural Differences in Stingray Sensory Systems (Elamobranchii: Batoidea)

UCLA, Los Angeles, CA, United States

This comparative study of stingray species addresses the relationship of form and function in two sensory systems. Elasmobranchs demonstrate remarkable sensory capabilities. Particularly high interspecific diversity exists in batoid mechanosensory lateral line and electrosensory systems, which allow elasmobranches to detect water movements and electrical fields respectively. This study compares sensory anatomy and detection capabilities of the lateral line and electrosensory systems in the benthic round stingray, Urobatis halleri, benthopelagic bat ray, Myliobatis californica, and the pelagic stingray, Pteroplatytrygon violacea. Predictions based on detailed sensory system maps were tested in behavioural detection experiments. U. halleri feeds primarily on small epifaunal benthic invertebrate prey and the lateral line shows a high proportion of ventral non-pored canals while the electrosensory pores are highly concentrated around the mouth. M. californica, which feeds primarily on infaunal benthic invertebrates, has extensive and highly branched pored lateral line canals and a high electrosensory pore number and density concentrated anteriorly. Both systems in M. californica have dramatic lateral extension toward the wing tips on anterior edges of the ventral surface of the pectoral fins. P. violacea feeds primarily on squid and teleost fish, and has an intermediate proportion of pored and non-pored canals with little branching of pored canals and a significantly reduced electrosensory pore number and density. Responses of each species to weak water jets and electrodes are compared. M. californica responds to water jets at a higher rate over a significantly greater proportion of its disc width. Responses to weak electrical fields were comparable to those observed for sharks with minimum responses below 1 nanovolt per cm for benthic feeding species. Ecological and evolutionary implications of these results are discussed.

 

Salvador Jorgensen1, Scot Anderson3, Adam Brown3, Taylor Chaple2, Chris Perle1, callaghan Fitz-cope4, A. Peter Klimley2, Carol Reeb1, Sean Van Sommeran4, Kevin Weng5, Barbara Block1

White Shark (Charcharodon charcharias) Homing and Fidelity in the Eastern Pacific

1Hopkins Marine Station of Stanford University, Pacific Grove, United States, 2UC Davis, Davis, United States, 3Point Reyes Bird Observatory, Inverness, United States, 4Pelagic Shark Research Institute, Santa Cruz, United States, 5University of Hawaii, Honalulu, United States

White sharks (Charcharodon charcharias) have been assessed as ‘threatened’ by the IUCN and are listed for protection under appendix II of CITIES yet basic aspects of their biology such as habitat preference, distribution and population structure are still poorly understood. Through collaborative efforts under the Tagging of Pacific Pelagics (TOPP) research program, we have deployed over 100 satellite and 50 acoustic telemetry tags on white sharks at seal rookeries off central California, and are revealing a predictable migratory pattern highly structured in space and time. The consistent use of discrete offshore habitats, followed by a return to the same coastal pinniped rookeries, was determined from long-term tagging and photo identification studies. During the coastal phase, the fine-scale movement of individuals was elucidated using passive acoustic telemetry. Individuals transited between Ano Nuevo, South East Farallon Island and other coastal white shark hotspots but resided at each site for periods of days to months. Satellite tracking revealed highly consistent use of two offshore habitats, one near Hawaiian waters, and another between Hawaii and Mexico known as the ‘white shark café’. Despite a long migratory route and the potential for trans-oceanic passage, there was no evidence of straying from the eastern Pacific. Mitochondrial genetic data indicate that white shark females in the North eastern Pacific have maintained long term isolation from the other known white shark populations near South Africa and Australia. Despite a cosmopolitan distribution, site fidelity is a mechanism which may explain reproductively isolated populations.

 

Michelle McComb, Stephen Kajiura

Visual Fields in Carcharhinid and Sphyrnid Sharks


Florida Atlantic University, Boca Raton, FL, United States

The bizarre “T” shaped head morphology of hammerhead sharks (Carcharhiniformes, Sphyrnidae) has captivated biologists for centuries and the selective forces behind its evolution remain the source of many untested hypotheses. The lateral expansion of the head shifted the spatial location of various sensory structures with the eyes being displaced to the distal tips of the cephalofoil. It has been suggested that the widely separated eyes confer upon hammerheads a broader visual field compared to their carcharhinid relatives. This concept pervades the popular media, despite the lack of supporting evidence. We tested the “expanded visual field” hypothesis by measuring the horizontal and vertical visual fields, convergence distance, and blind area for the scalloped hammerhead, Sphyrna lewini, the bonnethead, Sphyrna tiburo, and a representative carcharhinid, the blacknose shark, Carcharhinus acronotus. All three species shared similar monocular visual fields (171o - 181o) but S. lewini had a significantly greater horizontal binocular overlap (31.0o) than both S. tiburo (13.4o) and C. acronotus (10.6o). In addition, S. lewini achieved anterior binocular convergence at a closer distance (38 cm) than either S. tiburo (51 cm) or C. acronotus (47 cm). However, despite possessing the closest convergence distance, S. lewini demonstrated the largest anterior blind area (384 cm2) which is principally a result of head width. To determine if the hammerheads behaviorally compensate for this enlarged anterior blind area, we also analyzed the swimming kinematics of all species to measure the maximum head yaw angle. In addition to the horizontal visual fields, we also assessed the vertical visual fields for all three species. All three species demonstrated a full 360o visual field in the vertical plane. The comparable visual field dimensions, close binocular convergence distance and large binocular overlap demonstrated by S. lewini lend support to the expanded visual field hypothesis.

 

Tom Kashiwagi1, Andrea Marshall1, Michael Bennett1, Jennifer Ovenden2

DNA evidence for cryptic species boundaries within Manta birostris?

1University of Queensland, St. Lucia, QLD, Australia, 2Queensland Department of Primary Industries and Fisheries, St. Lucia, QLD, Australia

Molecular evidence to support/refute hypothesised cryptic species boundaries within Manta birostris were investigated. Genetic profiles of Indo-Pacific manta rays showed two distinctive clusters, with a pattern supporting speciation rather than geographic differentiation.

 

Steven Kessel2, Samuel Gruber1, Rupert Perkins2, Todd Gedamke3

Seasonal Residency And Migration Of Mature Lemon Sharks (Negaprion brevirostris) Off The Southeast Florida Coast

1Bimini Biological Field Station, South Bimini, Bahamas, 2Cardiff University, Cardiff, United Kingdom, 3National Marine Fisheries Service, Miami, Florida, United States

In 2001 aggregations, of ~75, mature lemon sharks (Negaprion brevirostris) were discovered just off the Jupiter coast, FL, by a local SCUBA diver. The presence of concentrated groups presented us with the first opportunity to study wild lemon sharks of mature life stage. To assess the potential of utilising this aggregation for research, feasibility studies were conducted from 2003 - 2005 revealing that these sharks could be caught for further study. During the subsequent winter seasons of January to March 2006 - 2008, sharks were caught on hooks using rod and reel and polyball drop-lines. Captured individuals were secured to the boat measured, sampled for DNA and tagged (NOAA M-type dart tag and PIT tag). All mature lemon sharks received a Vemco V16H transmitter implanted in their coelom. These three-year transmitters in concert with an array of 18 VR2 monitors along the putative aggregation migration route were used to describe local movements. Our monitors form part of the Florida Atlantic Coast Telemetry (FACT) VR2 array consisting of approximately 123 monitoring stations, with 26 to date receiving hits from our study population (total of 31 mature lemon sharks, 11 females and 20 males). A male previously caught off Long Key, FL, and another previously caught in Winyah Bay, NC, were originally tagged under the NMFS co-operative shark tagging program. This demonstrated that mature lemons will undertake long migrations to join this aggregation. Results from the monitors showed that males left the array area around March/April 2007 then returned between December 2007 and January 2008. In contrast, the females produced hits on the array year round. Contact at the most commonly visited station predominately occurred during daylight hours. The further deployment of two wildlife computer MK10 PAT tags (three and six months release) should further reveal the longer-term movements of the mature males.

 

Anne-Marie Kitchen-Wheeler

Migration Behaviour of the Giant Manta (Manta birostris) in the Central Maldives Atolls

School of Biology, Newcastle University, Newcastle, United Kingdom

Worldwide, populations of Giant mantas (Manta birostris) exhibit three types of migratory behaviour which can be categorised according individual home ranges. These are: 1) resident, inhabiting a specific home range at one location year round; 2) migratory, moving from one location to another with changes in season; and 3) oceanic, travelling between different locations across open oceans. Although articles in SCUBA-diving related literature have suggested that mantas in the Maldives migrate between the western and eastern sides of atolls with the monsoons, perhaps in order to benefit from upwelling stimulated plankton growth occurring on the lee sides of the atolls, there has been no scientific research into this phenomenon prior to this study. Having developed a robust method for the visual identification of individual mantas, surveys were carried out throughout the central Maldives atolls recording manta visits to “cleaning stations” on reefs located along the peripheries of the atolls. Over 99% of 2680 manta encounters during the study occurred at leeward side cleaning stations. In North Male’ atoll where the data set included sightings for all months in the year, 48.3% of mantas (n=153) that were re-sighted, were sighted on both sides of the atoll during the relevant monsoon. All those re-sighted in both North-east and South-west monsoon seasons had migrated between the west and east sides, suggesting that a single population migrates between the cleaning stations on opposite sides of the atolls with the alternating seasons, rather than there being two distinct, east and west populations. Pursuit of food was not the only factor involved in migration with some animals making journeys between different atolls, or between different sites along the side of an atoll during a single season, having travelled a distance of 20-160km between survey sites. In summary the Maldives population would be considered migratory.

 

Jeff Kneebone1, Lisa Natanson2, Allen Andrews3, Hunt Howell1

Using Bomb Radiocarbon Analyses to Validate Age and Growth Estimates for the Tiger Shark, Galeocerdo cuvier, in the Western North Atlantic

1University of New Hampshire, Durham, NH, United States, 2National Marine Fisheries Service, Narragansett, RI, United States, 3Moss Landing Marine Laboratories, Moss Landing, CA, United States

Refined and validated age and growth determinations are necessary for a proper understanding of tiger shark (Galeocerdo cuvier) life history characteristics in the western North Atlantic. Age and growth estimates were derived from band counts of 238 sectioned vertebral centra. Bomb radiocarbon analysis of ten band pairs extracted from four vertebral sections suggested band pairs are deposited annually up to age 20. Males and females were aged to 20 and 22 years, respectively, although longevity estimates predict maximum ages of 27 and 29 years, respectively. Two and three-parameter von Bertalanffy and Gompertz growth functions fit to length at age data demonstrated that growth rates were similar for males and females up to around 200 cm FL after which male growth slowed. Both sexes appear to reach maturity at age 10. The two-parameter von Bertalanffy growth function provided the best biological fit to length at age data generating parameter estimates of: L= 330 cm FL, k=0.131 for males and L=347 cm FL, k=0.124 for females, with L0set at 62cm FL. This study provides a rigorous description of tiger shark age and growth in the western North Atlantic and further demonstrates the utility of bomb radiocarbon as an age validation tool for elasmobranch fish.

 

Peter M. Kyne1, Rachel D. Cavanagh2, Andrés Domingo3, Enzo Acuña4, Ricardo S. Rosa5, Sarah V. Valenti6, Claudine Gibson6, Sarah L. Fowler6

The Conservation Status of South American Marine Chondrichthyans: Assessing Species for the IUCN Red List of Threatened SpeciesTM

1The University of Queensland, Brisbane, Queensland, Australia, 2British Antarctic Survey, Cambridge, United Kingdom, 3Dirección Nacional de Recursos Acuáticos, Montevideo, Uruguay, 4Universidad Católica del Norte, Coquimbo, Chile, 5Universidade Federal da Paraiba, Joao Pessoa, Paraiba, Brazil, 6IUCN SSC Shark Specialist Group, Newbury, United Kingdom

The IUCN-World Conservation Union’s Shark Specialist Group has a global programme underway to assess the conservation status of the world’s chondrichthyans for the IUCN Red List of Threatened SpeciesTM. Assessments of South America’s chondrichthyan fauna (~270 species) have been drawn together into the report The Conservation Status of South American Marine Chondrichthyans. Species were evaluated against the IUCN Red List Categories and Criteria to assess their global conservation status, and assigned to one of the following categories: Critically Endangered (CR; extremely high risk of extinction), Endangered (EN; very high risk of extinction), Vulnerable (VU; high risk of extinction), Near Threatened (NT; close to qualifying for, or is likely to qualify for a threatened category in the future), Least Concern (LC; does not qualify for a threatened category or Near Threatened) or Data Deficient (DD; presently inadequate information for an assessment of threatened status). At the global level, 25.1% of species occurring in South American marine waters are considered threatened (3.1% CR, 5.3% EN, 16.7% VU), 15.9% NT, 14.5% LC and 44.5% DD. Of the South American endemics, nearly one third (30.1%) are listed as threatened (2.8% CR, 7.5% EN, 19.8% VU) while 6.6% are NT, 9.4% LC and over half (53.8%) are considered DD. The vast majority of those species assessed as CR are coastal species that face strong fishing pressure as a result of being targeted or incidentally captured in often unregulated artisanal and/or industrial fisheries. While those species considered to be threatened require urgent actions to arrest population declines and ensure their long-term viability, the large proportion of DD species highlights the overall lack of knowledge of many species in the region. This is of concern, as some of these species are currently fished directly or taken as bycatch while little information is available on their population status.

 

Agnes Le Port, Shane Lavery, John C. Montgomery


Population Genetics of the Short-tailed Stingray, Dasyatis brevicaudata

University of Auckland, Auckland, New Zealand

Many stingray species have very broad distributions, but there have been few phylogeographic investigations into the genetic relatedness of stingray populations. The short-tailed stingray (Dasyatis brevicaudata) is a large temperate stingray solely distributed in the southern hemisphere and has been recorded in New Zealand, southern Australia and South Africa. We examined the genetic relationships of short- tailed stingrays (n = 156) throughout this species’ known range using the entire mitochondrial DNA control region (1934 nucleotides). Of 18 haplotypes found, 4 were shared by Australia and New Zealand, whereas Australia/New Zealand and South Africa shared none. New Zealand and Australia had 4 and 7 unique haplotypes respectively. The degree of differentiation and genetic isolation between populations assessed with AMOVA revealed significant levels of population structure at both large and small scales. Gene flow between Australia/New Zealand and South Africa separated by ca. 11,000km was highly restricted. However, restricted gene flow was also apparent between Australian and New Zealand populations separated by shorter geographic distances (ca. 2,500km, FST = 0.084). These results give an insight into the evolutionary history of short-tailed stingrays in the southern hemisphere.

 

Kwang-Ming Liu, Chun-Hui Chen, Jui-Han Chang

Shark Management Based on Vital Parameters Analysis

National Taiwan Ocean University, Keelung, Taiwan

As sharks own various life history characteristics shark management based on vital parameters is more reasonable and realistic. In this study, the vital parameters of 63 populations from 39 species were collected from literatures. The vital parameters including the ratio between size at birth and asymptotic length (Lb/L), the ratio between size at maturity and asymptotic length (Lm/ L), maximum age (Tmax), age at maturity (Tm), growth rate (k), and annual fecundity (f/Rc) were analyzed with principal components analysis (PCA) and cluster analysis. Four groups were categorized and the empirical equations describing the relationships between finite population increase rates (λ’) and vital parameters were developed as followings: (1) for species with slow growth rate (0.034 yr-1 < k < 0.103 yr-1) and high longevity (26 yr < Tmax < 81 yr), e.g. Isurus oxyrinchus, Carcharhinus obscurus etc.; (2) for species with fast growth rate (0.103 yr-1 < k < 0.358 yr-1) and low longevity (9 yr < Tmax < 26 yr), e.g. Mustelus manazo, M. californicus etc.; (3) for late mature (Lm/ L ≧0.75) and low longevity (Tmax < 29 yr) species, e.g. Alopias pelagicus, Notorynchus cepedianus, (4) whale shark, Rhincodon typus, with the most fecundity, highest longevity and slowest growth rates than other species. The finite population increase rates predicted by empirical equations developed in this study have good agreement with those calculated from conventional demographic analysis. Our empirical equations which need fewer parameters not only can reduce the uncertainties from vital parameter estimations to increase the accuracy of estimation but also account for the difference in life history among groups. This approach provides an economic and effective way for shark management.

 

Christopher Lowe1, Bradley Wetherbee2, Yannis Papastamatiou3, Gwen Goodmanlowe1, Gerald Crow3, John O' Sullivan4

Occurrence of Cookie Cutter Shark Bites on Pelagic Fishes Landed in the Hawaii Long-line Fishery

1Calif. State Univ. Long Beach, Long Beach, CA, United States, 2Univ. of Rhode Island, Kingston, RI, United States, 3Univ. of Hawaii, Honolulu, HI, United States, 4Monterey Bay Aquarium, Monterey, CA, United States

Based on its unique dentition and bite mark, the cookie cutter shark (Isistius brasiliensis) is known to prey on a wide variety of pelagic organisms. Its bite mark is characterized as a slightly oval semi-circular gouge ranging in diameter from 3-8 cm. To examine feeding and distribution of cookie cutter sharks around the Hawaiian Islands, long-line, hand-line, and troll caught pelagic fish landed at the Honolulu Fish Auction were sampled every week for 1-year. Ten pelagic fish species comprising a total of 15,107 fish were sampled for cookie cutter shark bites over the year. Seventy three percent (± 23.6 %) of the swordfish (Xiphias gladius) surveyed each week had cookie cutter shark bites and 43 ± 16.7 % of the opah (Lampris regius) surveyed had bite marks. None of the 430 blue marlin (Makaira nigricans) sampled were found to have bite marks. The percentage of all fish with bites was consistent from Feb – Dec (~15.3 %), but was the lowest during the month of Jan (6.7 %), even though this was when the second highest number of fish were sampled (n = 1029). Swordfish (range: 1-8) and opah (range: 1-7) had the greatest numbers of bites per fish; however, swordfish, yellowfin (Thunnus albacares), bigeye tuna, and opah had a higher occurrence of healed bites to fresh bites. Skipjack tuna (Katsuwonus pelamis) and sickle pomfret (Taratichthys steinachneri) had a higher occurrence of fresh bites than healed bites. This suggests that cookie cutter sharks take advantage of pelagic fish caught via hook & line, but may more regularly prey on swordfish and opah than blue marlin, skipjack, or sickle pomfret. Because cookie cutter sharks are rarely observed, the high percentage of fish landed with bites throughout the year may indicate that they more common around the Hawaiian Islands than previously expected.

 

Luis Lucifora1, Verónica García1, Alicia Escalante2

How Can the Feeding Habits of Sand Tiger Sharks, Carcharias taurus, Affect the Success of Conservation Programs?

1Dalhousie University, Halifax, Nova Scotia, Canada, 2Universidad Nacional de Mar del Plata, Mar del Plata, Buenos Aires, Argentina

The sand tiger shark, Carcharias taurus, is one of the most threatened species of shark worldwide. Recovery programs are now in effect, but it is unknown how them can be furthered or hampered by the ecology of sand tigers. Using data collected from a north Patagonian recreational fishery (n = 164), we analyze the relationships between prey consumption and life history traits (size, sex, maturity stage) and season; assess how prey capture behaviour may affect the success of mandatory catch-and-release measures to alleviate fishing mortality; and measure prey selection and overlap with fisheries to evaluate how they affect sand tiger populations. Body size was the main determinant of benthic elasmobranch consumption, indicating that the largest individuals – the target of fisheries – have the greatest effects on keystone mesoconsumers and hence on the community as a whole. Sand tigers did little prey handling, resulting in rapid hook swallowing and consequently severe damage to the internal organs from the hook in most individuals (87.4%), indicating that the release of hooked individuals would not minimize fishing mortality substantially. Sand tigers fed selectively on skates (Rajidae), Sciaenid fishes, smooth-hound (Mustelus schmitti) and angel (Squatina guggenheim) sharks, and flatfishes (Paralichthyidae), all of which are preponderant in fishery landings. This results in an almost complete (>90%) overlap with fisheries. We conclude that ignoring the feeding habits of sand tigers – characterized by low plasticity, high selectivity, high overlap with fisheries, and little prey handling – could substantially affect the success of recovery programs.

 

Carl Luer1, Stephen Kajiura2

Developmental Anomalies in Batoid Fishes


1Mote Marine Laboratory, Sarasota, FL, United States, 2Florida Atlantic University, Boca Raton, FL, United States

Developmental anomalies in skates and rays have been documented since the 16th century, although not accurately recognized as such until the 1830’s by Müller and Henle. For several centuries, deformed specimens were given new genus and species names, with drawings often grotesque or depicting the creatures as monsters. The most commonly documented anomaly is the incomplete fusion of the pectoral fin with the head, resulting in large gaps or clefts between the pectoral fins and rostrum. Since the batoid “disc” is formed during embryogenesis by the rostral migration of the anterior margins of the pectoral fins, it is logical that this process might occasionally terminate prematurely before the fusion is complete. In fact, a permanent condition of incomplete closure between head and pectoral fins has evolved in the angel sharks, Squatinidae. In skates and rays, if the incomplete closure does not impair locomotion or sensory function, the anomaly is not usually fatal. If the deformity is so severe that structures such as mouth or nares do not fully develop, mortality is generally assured. Radiography and/or clearing and staining of specimens help to visualize skeletal deformities resulting from incomplete pectoral closure. One skeletal defect common to several specimens examined appears to be the abnormal formation or disarticulation of the antorbital cartilage, although the functional significance of this structural deformity is not clear. Other developmental anomalies that occur very rarely in batoids are hermaphroditism, dicephalus and multiply fertilized ova.

 

Laura Macesic, Stephen Kajiura


Pelvic Fin Locomotion In Benthic Batoids


Florida Atlantic University, Boca Raton, FL, United States

Studies of locomotion in batoids have largely focused on pectoral fin movements. However, pelvic fin ‘punting,’ has been described as an important locomotive mechanism in skates. Other benthic batoids have been observed performing similar punting movements despite lacking the skate’s specialized pelvic fin structure. In this study, we compared the use of pelvic fins in locomotion among four benthic batoid species: the lesser electric ray, Narcine brasiliensis, the yellow stingray, Urobatis jamaicensis, and the Atlantic stingray, Dasyatis sabina, and the little skate, Raja erinacea. These species allow for comparative analyses across the three benthic batoid swimming styles: axial undulation, pectoral undulation and an intermediate between pectoral undulation and oscillation. To determine structural and locomotory differences between the pelvic fins of these species, we compared the pelvic fin to pectoral fin surface area ratios, pelvic fin skeletal elements and musculature, and swimming kinematics, including punting distance (body length (BL)), speed (BLsec- 1), glide duration (sec), and thrust duration (sec). The relative size of the pelvic fins may indicate their importance in locomotion, as the fins of N. brasiliensis (n=10) were significantly larger than those of U. jamaicensis (n=6) and D. sabina (n=10). In fact, whereas speed is highly variable, N. brasiliensis punted a significantly greater distance (0.80±0.26 BL; n=4) than U. jamaicensis (0.69±0.39 BL; n=4) and D. sabina (0.32±0.17 BL; n=4), without any difference in effort. Moreover, punts by U. jamaicensis and D. sabina were always accompanied with pectoral fin movement. By coupling the kinematic and morphological results of this research with those from past studies on batoid pectoral locomotion and feeding, we can begin to construct a comprehensive view of batoid ecomorphology.

 

M. Aaron MacNeil2, John K. Carlson1

Nibbles from the Sea: Sourcing Shark Damage on Pelagic Longlines


1NOAA Panama City Laboratory, Panama City Beach, FL, United States, 2National Research Council, NOAA Panama City Laboratory, Panama City Beach, FL, United States

Considerable ecological and economic problems can occur from shark interactions in pelagic longline fisheries. Depending on where fisheries are located, shark catches can be good or bad, but when sharks damage (depredate) catches the economic results are certainly negative. Incentive for fishermen to avoid depredation events is high, motivating this study into the factors contributing to depredation events in the US Atlantic pelagic longline fishery. Many factors can contribute to depredation rates including effort, gear type, target species, catch location, time, and the diversity of the catch. But because depredation events are relatively rare, a large number of zeros appear in the data, and conventional modelling approaches become ineffective means for understanding these processes. To accommodate this issue, this study utilizes zero-inflated Poisson and negative binomial models (mixture models) to understand how depredation events occurred in a large scale fishery and what factors contribute most to their occurrence.

 

Anabela Maia, Cheryl Wilga

3D Dorsal Fin Function in Spiny Dogfish during Steady Swimming

University of Rhode Island, Kingston, Rhode Island, United States

Sharks exhibit a great diversity of locomotor modes with different body shapes across phylogeny and habitat. Dorsal fin size and anteroposterior placement also vary considerably across shark taxa. This diversity could be related to both evolutionary history and habitat requirements. Little is known about the function of dorsal fins in sharks, although in teleosts the dorsal fins function as stabilizers and thrust enhancers. In order to investigate the function of the dorsal fins in sharks, high speed video was used to record movements of the dorsal and caudal fins of four spiny dogfish, Squalus acanthias, swimming at 0.5 BL s-1 and 0.75 BL s-1 in a flow tank. Two cameras, capturing dorsal and lateral views, recorded images at 125 f s-1, enabling 3D visualization. Points on the dorsal and caudal fins were tracked during five tail beats for each individual. The data was plotted and analyzed for 3D displacement and temporal variables. Average tail beat frequency increased from 0.88 s-1 at 0.5 BL s-1 to 1.20 s-1 at 0.75 BL s-1, although amplitude remained constant. The first dorsal fin moves independently of the body with a higher amplitude at lower speeds, indicating a stabilizing function to counter increased instability at lower speeds. The first dorsal fin has a three dimensional conformation at maximum displacement. The second dorsal fin appears to be moving passively with the caudal portion of the shark, although the dorsal fin could be augmenting thrust by increasing total area of the caudal region. Further investigation using electromyography and fluid dynamics will reveal whether sharks are actively controlling dorsal fin movements. The function of the first dorsal fin as a stabilizer may partially explain differences in size and placement of this structure in relation to habitat and locomotor mode.

 

John Mandelman2, Michael Stratton1, Michael Tlusty2, Shelly Tallack3, Tom Fisher2, Cheryl Harary2, Nils Wernerfelt4

The Shifting Baseline of Threshold Feeding Responses to Electropositive Metal Deterrents in Two Species of Dogfish

1St. Sebastian's School, Needham, MA, United States, 2New England Aquarium, Boston, MA, United States, 3Gulf of Maine Research Institute, Portland, ME, United States, 4Harvard University, Cambridge, MA, United States

Due to the potential repercussions for fisheries, the use of electropositive rare earth metals to deter sharks from interacting with baited fishing gears is undergoing extensive investigation across multiple species. This lab-based study aimed to assess the behavioural responses to rare-earth metal variants in a squaloid, the spiny dogfish (Squalus acanthias), and a triakid, the smooth dogfish (Mustelus canis), two species commonly captured as bycatch in western North Atlantic commercial and recreational fishing operations. In species-specific trials, tank-acclimated animals were exposed to squid-baited hook-gear setups. Either a lanthanide/cerium alloy (“mischmetal”) or rare-earth magnet (neodymium-iron-boride), and corresponding chemically inert stainless steel decoys were deployed just above (mock) hooks to “protect” associated baits. In total, 89 videotaped trials were conducted, in which the response behaviour (e.g. approaches, flinches, general avoidances, complete disregard, bites) of dogfish around the baits/metals was carefully monitored. A nested repeated measures design was utilized where animals were changed out weekly to reduce the potential for learned behaviour, and to enhance the overall sample of experimental animals. Relative to decoys, spiny dogfish were significantly more averse (e.g. > rate of avoidances and flinches; lower bite rate) to alloys, and smooth dogfish to magnets, when trials followed same-day routine feedings. However, bait selectivity in both species progressively declined in trials following 2- and 4-day periods of food deprivation, whereby the repellents no longer had any effect. Animal density (either three or 15 animals per tank trial) had no effect on selectivity regardless of hunger level. Results suggest that once a threshold hunger level is surpassed, neither metal variant appears to effectively repel these two dogfish species. The significant interspecific variation in response to the two metals when satiated indicates possible divergences in sensory processing of the metallic repellents and associated behaviours between the two species.

 

Andrea Marshall1, Michael Bennett1, Leonard Compagno2

Redescription of Two Species of Manta Rays with Resurrection of Manta hamiltoni to species level

1University of Queensland, St Lucia, QLD, Australia, 2Iziko - South African Museum, Cape Town, South Africa

The taxonomic status of the genus manta has historically been questionable and convoluted. Currently it stands as a monospecfic genus, with a single recognized species, Manta birostris. This species has been documented to occur as far north as southern California and Rhode Island on the United States east and west coasts, Japan, and the Azores Islands in the northern hemisphere and as far south as Uruguay, South Africa and New Zealand in the southern hemisphere. A worldwide survey and a five-year study in Mozambique has unveiled enough empirical evidence to suggest that there are at least two extant species of the genus Manta. The two species are often separated geographically, but ‘sympatric’ populations do occur, although interaction between the species appears to be uncommon. The two species have fundamentally different distributions throughout the world’s oceans, appearing to prefer different conditions. Based on morphometrics and several different external characteristics, the genus Manta should consist of at least two species, both of which are comprehensively described and contrasted for the first time. Manta birostris maintains its authenticity, with a second species, Manta hamiltoni, resurrected from a previous description by Newman in 1849. Distinct differences in the biology and behaviour of the two species are also noted. The inherent differences of these two species have significant implications for conservation and management strategies throughout their various distributions.

 

Heather Marshall, Diego Bernal

Comparative Metabolic Biochemistry Of Shark Myocardial Tissue

University of Massachusetts Dartmouth, North Dartmouth, MA, United States

Recent work on lamnid sharks (Family Lamnidae) has revealed their ability to undergo broad high-latitude migrations and rapid sojourns into depths repeatedly well below the thermocline. Both scenarios significantly expose these fishes to cold temperatures. Lamnids also have the ability to maintain their swimming muscles at temperature levels above ambient (regional endothermy), and this unusual quality may allow these sharks to sustain muscle metabolic biochemical capacities when exposed to colder water temperatures. However, the lamnid heart does not benefit from regional endothermy, and the pericardial cavity and all myocardial tissues are at thermal equilibrium with ambient temperatures. Because proper cardiac function is essential for providing lamnids with adequate supplies of oxygenated blood that are suitable for preserving swimming muscle function, a heart that is exposed to either prolonged cold or to rapidly fluctuating ambient temperatures should be capable of maintaining elevated metabolic biochemical capabilities. Therefore, the objective of this study was to compare the activities of citrate synthase (CS), lactate dehydrogenase (LDH), and myofibrillar ATPase (ATPase) in the myocardial tissue of lamnids and non-lamnid at various temperatures in order to determine how activities are affected by temperature. Initial analysis shows that the CS activity for lamnid sharks relative to non-lamnids is ~2.35x higher at 10oC, ~2.08x at 20oC, and ~1.89x at 30oC. LDH activities were also higher in lamnids relative to non-lamnids (~1.37 at 20oC). The thermal rate coefficients (Q10) were lower in lamnids relative to non-lamnids for CS (1.39±0.15 for lamnids at 10-30oC, 1.55±0.19 for non-lamnids at10- 30oC). The Q10 value for LDH is ~1.03±0.01 for lamnids at 10-30oC. Overall, it appears that lamnids have higher cardiac enzyme activities than non-lamnids, but respond to temperature changes in a similar manner.

 

M. Kathleen Maxwell1, Daniel Abel1, Dennis Allen2, Keshav Jagannathan1

Distribution and Movements of Neonate Atlantic Sharpnose Sharks, Rhizoprionodon terraenovae, in a South Carolina Estuary and Nearby Coastal Ocean Waters

1Coastal Carolina University, Conway, SC, United States, 2University of South Carolina, Columbia, SC, United States

Distribution and movements of neonate Atlantic sharpnose sharks (Rhizoprionodon terraenovae) were investigated using tag-recapture methods in North Inlet, SC. One hundred fifty four sharks were captured on standardized hook-and-line gear from May to September 2007. Atlantic sharpnose sharks were measured, tagged, sexed, and released. Hierarchical loglinear analysis showed no dependence of neonate shark abundance on creek size and tide. A Kruskal-Wallis test showed no significant differences between CPUE for any of the creeks sampled (χ2 = 8.176, df = 5, p = 0.147). A t-test showed no significant difference in CPUE for small or large creeks (p = 0.89). Concurrently, the average pre-caudal length (PCL) of these estuarine sharks was compared to that of sharks caught at a nearshore ocean location (Springmaid Pier in Myrtle Beach, SC, n = 214) to investigate the importance of the estuary habitat as a nursery area for this species. An ANCOVA showed that location (estuary or nearshore) was not a predictor of average PCL (p = 0.30), indicating that neonates were about the same size at the two locations throughout the period. However, regression analyses showed a significant increase in neonate length in the estuary but not at the nearshore site over about a 30 day period. Ten of the 410 R. terraenovae tagged during this study were recaptured over the summer (2.4% recapture rate). Five of the 154 sharks tagged in the estuary were recovered there while one was recaptured about 20 miles north. Four of the 214 sharks tagged at Springmaid Pier were recaptured at that location or at other nearshore locations further north. Mixed results regarding site fidelity and growth of neonates at the estuarine and nearshore ocean indicates that both areas are extensively used by young Atlantic sharpnose sharks. Additional mark-recapture studies and estimates of mortality will be necessary to determine whether either or both habitats serve as nurseries for the species in South Carolina.

 

Mollie McDonough, Daniel Abel, Keshav Jagannathan

Comparison of the Elasmobranch Fauna in Two South Carolina Estuaries, Differing in the Degree of Human Impact

Coastal Carolina University, Conway, SC, United States

A pilot study of urbanized Murrells Inlet and relatively pristine North Inlet, similar- sized northeastern South Carolina estuaries suggested decreased abundance and diversity of elasmobranchs in the former. We set 58 longlines from May-November, 2007 in each estuary and also conducted a hook-and-line survey. Forty-five elasmobranchs (36 sharks, 9 skates and rays) were captured in North Inlet, including 19 adult and neonate Atlantic sharpnose sharks (Rhizoprionodon terraenovae), 8 female blacktip (Carcharhinus limbatus), 5 adult bonnetheads (Sphyrna tiburo), 4 juvenile blacknose (C. acronotus), 4 southern stingrays (Dasyatis americana), 3 bluntnose stingrays (D. say), 1 Atlantic stingrays (D. Sabina) and 1 clearnose skate (Raja eglanteria). In Murrells Inlet, we caught one shark (young-of-year bonnethead) and 5 female southern stingrays. Elasmobranchs and sharks, but not ray abundance differed significantly (Wilcoxon rank sum test, p<0.05) between the systems. Environmental factors were similar between the two inlets throughout the sampling season. Boat traffic was higher in Murrells Inlet than North Inlet over the sampling period (257 observations vs. 30). Shark diversity and abundance in Murrells Inlet is reduced compared to North Inlet, suggesting that some aspect of the system, human or otherwise, is causative.

 

W. David McElroy1, Camilla T. McCandless2, Nancy E.2

Monthly Changes in Diet and Foraging Patterns for Two Shark Species in a Temperate Estuary: Evidence for Improved Hunting Capacity?

1University of Rhode Island, Kingston, RI, United States, 2NOAA Fisheries, Narragansett, RI, United States

Short term changes in feeding are difficult to study in large highly mobile predators that typically occur at low densities. The Delaware Bay estuary supports substantial populations of several shark species including Carcharhinus plumbeus and Mustelus canis. Non-lethal diet sampling of both these species was conducted during the middle week of June, July, and August for three years. M. canis adult females and young of the year (YOY) exhibited no significant monthly changes in mass of stomach contents, diet diversity, or meal size. Some prey changed in importance for both sizes during the summer, particularly in August. Several prey exhibited concurrent shifts for both M. canis size classes and coincided with published information on their seasonal movements. Some changes in YOY diet may have been related to ontogeny, but the continuous feeding pattern of M. canis and small size of YOY limited elucidating these relationships. C. plumbeus exhibited some changes in feeding during the summer. YOY had significant shifts in feeding pattern and diet composition by August. Early in the summer YOY had less stomach contents, smaller meal sizes, and consumed predominately less mobile prey types. Both juvenile size classes had limited changes in feeding patterns and diet composition between months. C. plumbeus YOY in August were similar in diet to small juveniles in June and July, and small juveniles by August had a diet more consistent with large juveniles. Dramatic changes in feeding by YOY C. plumbeus suggested improvement in hunting capability by late summer, and some shifts to larger or more mobile prey continued for juveniles. Shifts in consumption of some prey were consistent with reported times of peak abundance for those species, and suggest a generally opportunistic feeding strategy on abundant fish species.

 

Frazer McGregor1, Mike Van Keulen1, Anya Waite2, Mark Meekan3

Foraging Ecology and Population Dynamics of the Manta Ray, Manta birostris in Lagoonal Waters of Ningaloo Reef, Western Australia

1Murdoch University, Perth, Western Australia, Australia, 2University of WA, Perth, Western Australia, Australia, 3Australian Institute of Marine Science, Darwin, Northern Territory, Australia

In response to increasing tourism pressure on Manta Rays (Manta birostris) within Bateman Bay, Ningaloo Reef, Western Australia, a number of baseline studies are being undertaken. Included in these are a) photographic identification to determine population demographics including residence, b) an investigation of prey availability and foraging behaviours, and c) acoustic tagging to determine habitat use. So far using photographic records over 300 individuals have been identified engaged in a number of behaviours. Of over 700 photographic observations the dominant behaviours within Bateman Bay were foraging (44%), presence at ‘cleaning stations’ (25%), and simply traversing the area (23%). Mature females, some of which have been recorded on over 25 occasions in 2 years make up the bulk of the population year round, whilst mature males and juveniles of both sexes appear to be highly seasonal. Results of plankton net tows adjacent to both foraging and non-foraging manta rays have shown that they utilise different foraging strategies depending on season, prey type and prey density. Swarming prey, predominantly small (<500um) calanoid copepod species are targeted within Bateman Bay throughout the year and appear to be the main prey type for ‘resident’ manta rays, whilst no active feeding was observed on mixed assemblages, the majority of gelatinous planktonic species, organic debris or phytoplankton blooms. This tendency to prey specificity may add to the difficulties of obtaining sufficient nutrient intake and place additional importance on lagoonal areas known to be rich in targeted species abundance. Use of an extensive acoustic array is hoped to further elucidate movements of both resident and transient individuals and confirm Bateman Bay as critical habitat for Manta Rays along Ningaloo Reef.

 

Tricia Meredith, Stephen Kajiura

Olfactory Morphology and Physiology of Batoids

Florida Atlantic University, Boca Raton, FL, United States

The olfactory capabilities of elasmobranchs are legendary, but their reputation is based on surprisingly little empirical evidence. Olfaction plays an important role in the localization of prey, with amino acids acting as particularly effective odorants for elasmobranchs. Despite the importance of this sensory modality, olfactory thresholds have been assessed for only four elasmobranch species using a handful of amino acids. Literature values for these species indicate sensitivities at approximately 10-7 to 10-8 M. This study integrates the comparative olfactory morphology and physiology for batoid species from three families in two orders: the Atlantic stingray, Dasyatis sabina; the yellow stingray, Urobatis jamaicensis; and the clearnose skate, Raja eglanteria. The olfactory organs (rosettes) were dissected from representatives of each species (n ≥ 6) and the total surface area of the olfactory lamellae was quantified. The surface areas were compared using an ANCOVA with disc width as a covariate. To supplement the morphological data, an electro- olfactogram (EOG) technique was employed to assay the sensitivities of these species (n ≥ 6) to a suite of twenty proteinogenic amino acids. The results indicate that the olfactory rosettes of the skate R. eglanteria are significantly smaller than those of the stingrays D. sabina and U. jamaicensis. Despite the morphological differences, the olfactory thresholds were similar for all three species, with each detecting amino acids down to a concentration of approximately 10-8 to 10-9 M. The most stimulatory amino acids differed somewhat for each species; which may reflect prey preferences. The results obtained corroborate the sensitivities reported in the literature, and illustrate that physiological sensitivities can converge independent of morphology. This study provides the first comparative analysis of the olfactory morphology and physiology of elasmobranchs.

 

Johnny Moore1, Dewayne Fox1, Bradley Wetherbee2, Camilla McCandless3

Patterns of Habitat Use and Residency for Sand Tiger Sharks (Carcharias

taurus) in Delaware Bay

1Delaware State University, Department of Agriculture and Natural Resources, Dover, DE, United States, 2University of Rhode Island, Department of Biological Sciences, Kingston, RI, United States, 3Apex Predators Investigation, NOAA/National Marine Fisheries Service, Narragansett, RI, United States

The sand tiger shark (Carcharias taurus) typically inhabits coastal waters and bays including Delaware Bay, which is thought to serve as important secondary nursery habitat as well as a foraging area for adults. Due to low reproductive potential and overharvest, sand tigers have experienced marked population declines. With this decline in mind, our objectives included collecting information on habitat utilization, depth selection, and residency patterns for sand tigers in Delaware Bay. We utilized both manual and passive tracking (VEMCO Ltd. VR-2) to monitor sand tiger habitat utilization patterns during their Delaware Bay residency. Sand tigers were implanted with standard acoustic (n=19) and depth sensing transmitters (n=10) during the summers of 2006 and 2007. Two sand tigers tagged in June of 2006 returned to Delaware Bay during the third week of June 2007, which closely corresponded to the time of our first successful captures that year. A total of 72,241 detections of telemetered sand tigers were collected on receivers during the 2006 and 2007 field seasons. Although their distribution overlapped, when the sand tiger data was segregated by sex, the males were more commonly found in the lower salinity middle portion of Delaware Bay whereas females were more common in the higher salinity waters at the mouth of the bay. We documented a significant difference in depth utilized by male and female sand tigers, with females typically occupying deeper waters than males. Through this study we hope to improve our knowledge of habitat requirements and residency of sand tigers in Delaware Bay thus providing a greater understanding of essential habitat for this species as well as enhance recovery of sand tiger stocks.

 

Christopher Mull, Kelly Young, Christopher Lowe

Using Ultrasound and Steroid Hormones to Determine Pregnancy in Seasonal Aggregations of Female Round Stingrays (Urobatis halleri) in a Coastal Estuary

California State University Long Beach, Long Beach, CA, United States

The round stingray (Urobatis halleri) is a common nearshore elasmobranch in southern California, known to breed in late spring. Despite a large seasonal aggregation of round stingrays in Seal Beach, CA, no behavioral or physical evidence of mating has ever been observed in this population. Mating in this population is thought to occur in nearby Anaheim Bay estuary, which is part of the Seal Beach National Wildlife Refuge (SBNWR). SBNWR is composed of 1.1 km2 of estuary and four mitigation ponds. Round stingrays were sampled in mitigation ponds every month from June 2005 to September 2007. All captured rays were weighed, sexed, and examined for mating scars as evidence of recent breeding behavior. From June 2006 to September 2007 blood was sampled via the caudal vein from a subset of female rays and analyzed for progesterone and estradiol using radioimmunoassay. In addition to blood sampling, a subset of female rays were also examined using ultrasound to determine pregnancy state from July to September 2007. All females sampled during July and August exhibited developing embryos based on ultrasonography. In September 20% of the females sampled appeared to have pupped based on ultrasonography and physical appearance. Progesterone concentrations were elevated in females sampled through July and August (0.75 ng/ml), and decreased significantly to 0.16 ng/ml by September. September progesterone concentrations varied; one female who appeared to have pupped in September had non-detectable progesterone levels, while other pregnant females had progesterone levels ~0.24ng/ml. Our data suggest that ultrasound and steroid hormones can be sensitive indicators of reproductive status, and support the theory that this coastal estuary serves an important function in round stingray reproduction. Female round stingrays may be entering these warm shallow ponds to increase the gestation rate, purported to be three months, which is relatively short for a live bearing elasmobranch.

 

Marc Nadon, Benjamin Richards, Brian Zgliczynski, Robert Schroeder, Russell Brainard

Central Pacific Survey Reveals Lower Reef Shark Density near Human Population Centers

1Joint Institute for Marine and Atmospheric Research, Honolulu, Hi, United States, 2NOAA - National Marine Fisheries Service, Honolulu, Hi, United States

Biennial surveys (2000-2007) of coral-reef shark populations were conducted around 50 U.S. Pacific Islands in several regions: the Hawaiian Archipelago, the Marianas Archipelago, the Line Islands, the Phoenix Islands, and the American Samoa Archipelago. Two fisheries-independent census methods were implemented by divers: stationary point counts and towed-diver surveys. Five species of sharks were recorded in sufficient frequency to allow meaningful statistical analyses: grey reef shark (Carcharhinus amblyrhynchos), galapagos shark (Carcharhinus galapagensis), whitetip reef shark (Triaenodon obesus), blacktip reef shark (Carcharhinus melanopterus), and tawny nurse shark (Nebrius ferrugineus). Preliminary analyses showed a highly significant negative relationship between grey reef and galapagos shark densities and proximity to human population centers (e.g., proxy for potential fishing pressure and other human impacts). Average combined numerical density for these two species near population centers was less than 1% of densities recorded at the most isolated islands (e.g., no human population, very low present or historical fishing pressure or other human activity). Even around islands with no human habitation but within reach of populated areas, gray reef and galapagos shark densities were only between 15 and 40% of the population densities around the most isolated near-pristine reefs. Trends in whitetip and blacktip reef shark numbers were similar, but less dramatic. Tawny nurse shark densities were low around most islands. This study is the first fisheries-independent large-scale survey of reef shark populations in the central Pacific. From our preliminary results we infer that some shark populations near human population centers are severely depressed.

 

Kazuhiro Nakaya, Rui Matsumoto, Kenta Suda

Feeding Behavior of the Megamouth Shark, Megachasma pelagios (Lamniformes, Megachasmidae)

Hokkaido University, Hakodate/Hokkaido, Japan

Since the discovery of the first megamouth shark in 1976 to date (March 31, 2008), 40 individuals have been captured, landed or witnessed in the world. However, very few is known about its biology, except some spotty information. The megamouth

shark is known to feed on planktonic animals, same as the basking shark and whale shark. A female megamouth of 5440 mm in total length, which is the 10th individual and was captured in Mie Prefecture, Japan, was dissected to resolve the feeding behavior of the megamouth shark. The morphological examination of the specimen disclosed that the megamouth shark has a suite of unique characteristics among sharks, such as a large mouth, a long bucco-pharyngeal cavity, a large tongue, a flat and wide chondrocranium with a deep rostral groove below rostral cartilages, extremely elongate jaw cartilages, long hyomandibular and ceratohyal cartilages, long palatoquadrate levator and preorbital muscles, a wide “palatorostral” ligament, long ethmopalatine ligaments, and elastic skin around the pharynx underlain by two layers of very loose elastic connective tissue. The basking shark is known to perform continuous ram-filter feeding, and the whale shark performs suction and ram-filter feeding. The megamouth shark was considered to be a suction feeder before, but such unique characters in the megamouth shark mentioned above suggest that the megamouth shark developed an engulfment feeding that is typically seen in the rorqual and humpback whales.

 

Kiyonori Nishida, Hiroshi Obata, Minoru Shimomura, Hideto Nakagawa, Takahiro Inoda

Rearing of Mantas and Mobulids

Osaka Aquarium KAIYUKAN, Osaka, Japan

Osaka Aquarium KAIYUKAN has been engaged in exhibiting elasmobranch fishes since its opening in 1990. Especially, a manta ray (Manta birostris) is one of popular species as well as a whale shark (Rhincodon typus) due to its unique shape and its size. Subfamily Mobulinae including two genera (Manta and Mobula) and 10 species (Nelson, 2006) inhabit the waters from the tropical to the temperate zone. Four species such as Manta birostris, Mobula eregoodootenkee, M. japanica and M. tarapacana are well known to inhabit the sea region around the Japanese archipelago. KAIYUKAN built the Osaka Aquarium Biological Research Institute of Iburi Center in Iburi, Tosashimizu City, Kochi Prefecture on the coast of the Pacific Ocean, and has been engaged in collection and research of exhibiting sea life. The research has been continued for our exhibition, since in the fisherman’s set-net around the research center, three species such as Manta birostris, Mobula eregoodootenkee, and M. japanica are sometimes captured with other fishes. KAIYUKAN transported Manta birostris which was captured in the set-net off Tosashimizu to the Osaka Aquarium taking about 14-16 hours. KAIYUKAN has tried to keep and exhibit it five times in the Pacific Ocean tank which water capacity is 5,400 tons until now. The shortest exhibiting period was two days and the longest one is updating its period since its carrying in on December 14, 1999 (DW: 1800 mm) in good condition. Its disc width reached 3000 mm on November 1, 2007. KAIYUKAN transported Mobula eregoodootenkee to the Osaka Aquarium and has observed the behavior of it (DW: about 600-700 mm) in the fish pen installed in the port in front of our research center and in the large tank which containing 1600 tons of water. KAIYUKAN has not done long-distance carriage of Mobula japonica to the Osaka Aquarium yet, but has kept it in the large tank of Iburi Center since January 23, 2008 (DW: 2200 mm). This article introduces the appearance in the water around our research center, the information gained in the fish pen and the large tank of our research center, skills of long- distance carriage to Osaka and information acquired from rearing in the large sized exhibition tank.

 

Yannis Papastamatiou1, Jenn Caselle2, Alan Friedlander3, Christopher Lowe4

Movements and Foraging Success of Blacktip Reef Sharks, Carcharhinus melanopterus, at Palmyra Atoll: A Predator Dominated Ecosystem

1University of Hawaii at Manoa, Kaneohe, HI, United States, 2University of California Santa Barbara, Santa Barbara, CA, United States, 3Center for Coastal Monitoring and Assesment, Oceanic Institute, Waimanalo, HI, United States, 4California State University Long Beach, Long Beach, CA, United States

Understanding the ecological impacts of apex predators in pristine habitats can provide baseline information for more effective conservation and fisheries management. We utilized acoustic telemetry and stable isotopes to correlate movements with foraging ecology of blacktip reef sharks, Carcharhinus melanopterus, at Palmyra Atoll, a US Federal Wildlife Refuge. Palmyra consists of two large lagoons and sharks rarely showed movements between lagoons. Sharks in the west lagoon had small home ranges, showed selection for ledge habitats, and utilized patches that were 3 – 17 % of the scale of their home range. Sharks in the west lagoon had larger body condition indices, and longer residence times than those in the east lagoon. Stable isotopes show that shark length has no influence on trophic level for sharks in the west lagoon, as opposed to those in the east lagoon which show a linear increase in trophic position with shark length. Together these findings suggest that foraging success of sharks is greater in the west lagoon, and also highlights the importance of habitat on the ecology of apex predators, even over small spatial scales.

 

Susanne Plank, Chris Lowe, Judy Brusslan

The Population Genetic Structure of the Round Stingray in Southern California

California State Univeristy Long Beach, Long, Beach, CA, United States

Round stingrays (Urobatis halleri) are very common along the coast of Southern California, but little is known about the genetic structure of this species. Stingrays were collected from various locations in Southern California including the San Gabriel River outfall site in Seal Beach as well as the Seal Beach National Wildlife Refuge (SBNWR), San Diego Bay, and Santa Catalina Island. Santa Catalina Island is separated from the mainland by a deep channel and that may pose as a geographic barrier to the stingrays. Results from microsatellite loci indicate that there is no variation in the genetic structure between the San Gabriel River outfall site, SBNWR or Sand Diego Bay. This is representative of a large, homogeneous population in coastal Southern California. However, the stingrays from Santa Catalina Island exhibited a different genetic structure than the other locations sampled suggesting that the deep water separating the island from the mainland represents a barrier to gene flow.

 

Marianne Porter

Spines of Swimming Sharks: Kinematics and Morphology from Five Species

Vassar College, Poughkeepsie, NY, United States

Maneuverability is a characteristic of animal locomotion that can be quantified in a number of ways, for example, as turning radius, turning speed, or translational and rotational acceleration. Flexibility is a morphological measure that correlates with maneuverability and is defined as the maximum lateral displacement in a swimming animal. The flexibility of a shark is influenced by the vertebral column and the musculotendinous system pulling on the vertebral column. In bony fishes, increasing vertebral column flexibility has been modelled in two ways either by increasing vertebral number or angle at the intervertebral joint while holding the other variable constant. Despite that relatively simple model of vertebral column flexibility, previous research on three species of Carcharhinid sharks has shown total vertebral number does not correlate with flexibility suggesting that other aspects of vertebral column morphology might affect flexibility. The goals of this study were to quantify flexibility in five shark species with varying swimming modes and describe the morphology (number of vertebrae, angle between vertebrae, shape of vertebrae, intervertebral joint length) of the vertebral column. I quantified maneuverability by filming sharks housed in southern California aquaria. Vertebral column morphology was obtained from live sharks when possible or from museum and lab specimens. I found that total vertebral number does not correlate with flexibility. However, vertebral centrum shape and overall shape of the shark may make significant contributions to increasing flexibility in swimming sharks. Additionally, I obtained kinematic data from a range of sizes for three species to further examine the effects of shark shape on maneuverability. The overall shape of species changed with increasing total length, but flexibility changed with increasing total length only in one species. These data are a detailed description of axial skeleton morphology and maneuvering kinematics during swimming in sharks.

 

Matthew Potenski

Investigation of an Aggregation of Whale Sharks (Rhincodon typus) at Mafia Island, Tanzania, Utilizing Placard Identification and Pop-Up Archival Satellite Tags and Photo-Identification

The Shark Research Institute, Princeton, NJ, United States

Whale sharks (Rhincodon typus) feed primarily on plankton. In areas where plankton can become concentrated, whale shark may be observed aggregating to feed. A whale shark aggregation site has recently been identified in the waters of Mafia Island, off the coast of Tanzania in the Indian Ocean. This island sits just off the Rufiji River delta, and the nutrient runoff may cause high concentrations of plankton in the water. The population of whale sharks using this area was looked at in two field seasons. Individuals were identified by the attachment of numbered placard- style tags attached in-situ via speargun and photo-identification via spot pattern using two different software programs. In addition, eight P A T-style tags were deployed in early 2007 with durations ranging between 2 and 12 months. Analysis of tagging data indicates a population estimate of between 50-60 whale sharks using this area. The population includes juvenile sharks in the 2-8m range and is highly dominated by males in a ratio of about 3.5:1. Satellite tag telemetry shows use of a relatively small area off east Africa, dominated by time around Mafia Island, but using waters in other areas of Tanzania and possibly southern Kenya. This area may be used by the juvenile sharks as they grow and approach maturity, at which time they may transition to a more pelagic lifestyle.

 

Theo C. Pratt1, Harold L. Pratt Jr.1, Jeffrey C. Carrier2

Evidence for Behavioral Thermoregulation after Mating by Wild-living Adult Female Nurse Sharks, Ginglymostoma cirratum

1Mote Marine Laboratory, Summerland Key, FL, United States, 2Albion College, Albion MI, United States

The annual fall gathering of recently mated female sharks in a shallow lagoon in the Dry Tortugas, FL, provided the opportunity to study the thermal preferences of a wild population of adult sharks. Nine adult female nurse sharks, Ginglymostoma cirratum, were captured during or subsequent to observed mating events in June of 2005 and fitted with acoustic transmitters. Six of these females were also fitted with external temperature loggers. In 2007, after over two years at liberty, one of the females carrying a temperature logger was recaptured. By comparing the temperature record on the shark-borne logger to data from stationary temperature loggers and examining the record of her movements from acoustic receivers, it was possible to determine that the female shark exhibited temperature preferences for several months within the period during which we presume she was gravid if she had been successfully impregnated. In the fall of 2005 she moved into shallow waters during periods when the water temperature exceeded that available in deeper water, but as the surface waters cooled, she spent more time in deeper locations which provided higher temperature. In the summer and fall of 2006, when the female was not observed to mate or visit the lagoon, her on-board temperature logger showed that she did not seek warmer water as she had the previous year. A summary of eleven mature females transmittered between 2002 and 2006 also exhibited heat-seeking behaviors in October. This is the first study to present temperature data showing that this behavior is not seen in the non-mating year. We believe that these results indicate that the female sharks were behaviorally thermoregulating after mating and that the probable cause of this behavior is to enhance development of embryos.

 

Getulio Rincon, Miguel Petrere

Reproduction of the Smooth Back River Stingray Potamotrygon orbignyi in the Araguaia/Tocantins Basin, Brazil

Universidade Estadual Paulista-UNESP, Rio Claro/São Paulo, Brazil

The smooth back river stingray, Potamotrygon orbignyi, is a small to medium size Neotropical freshwater stingray with a wide distribution along the Amazon and Araguaia/Tocantins basins. Although not frequently consumed as fish meat, this species has an ornamental economic value and is periodically exported from Brazil when legislation permits. In order to evaluate the ornamental fishery impact on regional populations of the smooth back river stingray, several specimens (162 specimens; 97 females and 65 males) were collected at the Paranã River, a tributary of the Araguaia/Tocantins basin, and their reproductive aspects were studied. All collects were performed from January 2002 to September 2003 by longline and spear and specimens were conditioned in formalin (4%) for posterior laboratory analysis. The female reproductive system consists of two ovaries (the left one is usually larger), two anterior oviducts, two nidamental glands and two uterus. The male reproductive system consists of two testis, two epididymis (head, body and tail), two ductus deferens and two seminal vesicle. The sexual maturity (DW50) was estimated to occur in 251 mm disc width-DW for males and 260 mm DW for females. The uterine fecundity per gestation was just one embryo and the parturition occurred along the rainy season for most of the reproductive population (September to February). The neonates are estimated to have 115 mm DW and 60 grams of total weight, which corresponds to a weight increase of 1605% in relation to the initial ova weight (3,8 g). The hepatosomatic index variation along the year indicates a lower hepatic reserve condition in the dry season and higher reserve hepatic condition in the rainy season. Based on preliminary readings of vertebral rings, the sexual maturity was estimated to occur at the age of 5 with a maximum longevity of 10 years.

 

Robert D. Rubin, Katherine R. Kumli, Gavin Chilcott

Dive Characteristics and Movement Patterns of Acoustic and Satellite- Tagged Manta Rays (Manta birostris) in the Revillagigedos Islands of Mexico

Santa Rosa Jr. College, Santa Rosa, California, United States

Individual manta rays (Manta birostris) were tagged with either PAT or coded acoustic tags for a period of 12 days at two separate Islands (San Benedicto and Roca Partida). Three subsurface recorders were placed around San Benedicto and continuous movements of animals were monitored around the island and between the islands and the Baja California peninsula. Analysis of recorded data indicated that the animals are within range of the fixed recorders less than two percent of the total time and that attendance appears to be primarily between 0100 hrs and 1300 hrs. Animals fitted with PAT tags travelled between the attachment sites and areas adjacent to the Baja California peninsula. Travel routes to and from the peninsula were similar in both animals. Total travel distances were 2249 and 1063 km., at calculated average speeds of 8.8 and 2.5 km/hr. respectively. Initial analysis show that both mantas move in sinusoidal cycles from the surface and between 72 and 80 meters during the period of travel. Hours of sunlight were spent at shallower depth than those during the night, where animals appear to be following the lower boundary of the thermocline. Several descents exceeded 200 meters, with a maximum of 450 meters, ranging between surface temperatures of 28 C to 10 C at depth.

 

Keisha Russell

Acquisition, Husbandry and Release Techniques for the Giant Manta Ray (Manta birostris) At Atlantis Resort, Bahamas

Atlantis Resort, Nassau, Bahamas

Over the past 7 years the Atlantis Resort has successfully displayed 8 Giant Manta Rays (Manta birostris) with 3 of them currently on exhibit in a 2.3 million gallon lagoon that also features other tropical marine species. As the only aquarium facility in the Western Hemisphere displaying Giant Manta Rays, we have been afforded the unique opportunity to observe how mantas behave, feed and interact with each other, each displaying distinguishing characteristics and different personalities. Recent tracking programs using satellite tags has provided further insight to some of the natural habits of this species.

 

Laura Sampson1, Felipe Galván-Magaña1, Roxana De Silva-Dávila1, Sergio Aguíñiga-García1, John B. O ́Sullivan2

Diet and Trophic Position of Mobula thurstoni and Mobula japanica as Inferred from Stable Isotopes of Nitrogen and Carbon

1Centro Interdisciplinario de Ciencias Marinas, La Paz, Baja California Sur, Mexico, 2Monterey Bay Aquarium, Monterey, California, United States

Mobula thurstoni and Mobula japanica are two of the five mobulid species present in the Gulf of California. They have been an important component of the artisanal elamosbranch fishery of Mexico, but are presently protected as their populations are vulnerable to over-exploitation. Stable isotopes of nitrogen and carbon were used to infer the diet and trophic position of M. thurstoni and M. japanica in the SW Gulf of California. A total of 32 M. thurstoni and 6 M. japanica muscle samples were obtained from May 2006 to January 2007. Eleven monthly diurnal and nocturnal plankton tows were carried out from March to November 2006. We analyzed stable isotopes of Nyctiphanes simplex (a euphausiid, and the mobulid’s most probable prey) as well as of herbivorous, carnivorous and omnivorous zooplankton. Based on isotopic fractionation between mobulids and their potential prey, we conclude that both mobulid species fed on N. simplex and not on other zooplankton groups analyzed. We calculated a trophic level of 3.43 for M. thurstoni and 3.48 for M. japanica. The isotopic signal of zooplankton varied with oceanographic conditions, with lower δ15N values in times of higher productivity.

 

Javier Serrano-Lopez, Felipe Galvan-Magaña, Rosa Ochoa-Baez, John O ́Sullivan

Reproduction of Three Species from the Mobulidae Family in the SW Gulf of California, Mexico

Centro Interdisciplinario de Ciencias del Mar, La Paz, Baja California Sur, Mexico, Mexico

The highest mobulid catches in Mexico occur in the southwest Gulf of California. There is, however, a lack of information about the general biology and reproduction of the dominant species in the catch. During two years (2002 and 2004) we collected 358 mobulid samples in the fishing camp of Punta Arena de la Ventana. The most abundant species was Mobula japanica (37%), which we established that sexual maturity was reached at 200cm DW using the length and calcification of claspers in males from different sizes, and oocites development and oviduct condition in females. We suggest that M. japanica gives birth during May and June, and mating occurred during July to August. The second most abundant species was Mobula munkiana (36%). There was size segregation and sex segregation depending on the time of year. Mobula munkiana individuals attained sexual maturity at 100 cm DW; we suggest that they give birth in May and June and mate in July and August. The least abundant species was Mobula thurstoni (27%). For this species the sexual maturity was attained at 150 cm DW. This species gave birth in July and August and mating occurred in September and October. We found that mobulid species analyzed, had functional only the left ovary and oviduct, and only one pup by reproductive cycle. The mating season happen during summer and fall; however the mating months were different in each mobulid species.

 

Kate Siegfried1, Aaron MacNeil2, John Carlson1

Application of a Bayesian Hierarchal Meta-analysis in the Assessment of Pelagic Sharks: A Case Study Using the Night Shark, Carcharhinus signatus

1NOAA Fisheries Service, Panama City, FL, United States, 2National Research Council and the NOAA Fisheries Service, Panama City, FL, United States

Night sharks, Carcharhinus signatus, are an oceanic species generally occurring in outer continental shelf waters in the western North Atlantic Ocean including the Caribbean Sea and Gulf of Mexico. Although information from some fisheries has shown a decline in catches of night sharks, it is unclear whether this decline is due to changes in fishing tactics, market conditions, or species identification. Despite the uncertainty in the decline, the night shark is currently listed as a species of concern due to alleged declines in abundance resulting from fishing effort, i.e. overutilization. A previous study concluded that the night shark did not qualify as a species of concern but the uncertainty in the trends in relative abundance precluded any determination of changes in stock status. Further, the “data-poor” situation precluded the application any typical stock assessment models. While some modeling-based frameworks (e.g. catch-free model) for estimating stock status in situations where catch data are poor have been utilized, the highly uncertain nature of the data for night shark also prevented application of these models. Previous standardized catch rates using a two-part generalized linear model gave conflicting results, with one series showing a decline, two series showing an increase and one series showing constant abundance. To address this uncertainty, we used a hierarchical meta-analysis in a Bayesian framework to estimate changes in relative abundance from fishery dependent and independent catch rate series. Prior probability distributions of the estimated parameters were developed using knowledge of data source and collection method. The final model was fit using R and estimates of trends were based on Markov chain Monte Carlo posteriors. The meta-analytic estimate indicated little decline overall suggesting night sharks have not suffered significant declines in abundance.

 

Colin Simpfendorfer1, Rory McAuley2, John Stevens3, Richard Pillans4, Tonya Wiley5

Life in a Macrotidal World: Movements of the Dwarf Sawfish (Pristis clavata) in Northern Western Australia

1James Cook University, Townsville, QLD, Australia, 2Fisheries Department of Western Australia, Perth, WA, Australia, 3CSIRO, Hobart, TAS, Australia, 4CSIRO, Brisbane, QLD, Australia, 5Mote Marine Laboratory, Sarasota, FL, United States

The short-term movements of adult dwarf sawfish (Pristis clavata) were studied using active acoustic telemetry in northern Western Australia. The semi-diurnal tidal variation in this region is extremely large, with a range over 10 m during spring tides. Individual sawfish were tracked for up to four days in shallow coastal waters using small boats. The tracks of five individuals showed very similar movement patterns. For approximately 100 minutes either side of high tide individuals rested in inundated mangrove forests. As the tide fell sawfish moved out of the mangroves and moved to remain in depths from 0-2 m. Individuals moved distances of 3-10 km during each tidal cycle before returning to the mangrove forest on the next high tide. High tide resting locations for individuals were often within 50 m from the previous tide. The macrotidal environment was concluded to be the dominant factor controlling the movement of dwarf sawfish in this region.

 

Gregory Skomal1, Diego Bernal2, Heather Marshall2, John Chisholm1, Lisa Natanson3

Habitat Utilization and Movement Patterns of Juvenile Porbeagle Sharks (Lamna nasus) in the Western North Atlantic

1MA Marine Fisheries, Vineyard Haven, MA, United States, 2University of Massachusetts, Dartmouth, MA, United States, 3NOAA/NMFS, Narragansett, RI, United States

The porbeagle (Lamna nasus) is a large, highly migratory endothermic shark broadly distributed in the higher latitudes of the Atlantic, South Pacific, and Indian Oceans. In the North Atlantic, the porbeagle has a long history of fisheries exploitation and recent assessments indicate that this stock is severely overfished. Although much is known of the life history of this species, there is little fisheries-independent information about habitat preferences and ecology. To examine migratory routes, potential nursery areas, swimming behavior, and environmental associations in the western North Atlantic, we deployed pop-up satellite archival tags on 20 juvenile porbeagles in late November, 2006. The sharks, ten males and ten females ranging from 128-154 cm fork length, were tagged and released from a commercial longliner on the northwestern edge of Georges Bank, about 150 km east of Cape Cod, MA. The tags were programmed to release in March (n=7), July (n=7), and November (n=6) of 2007 and 17 (85%) successfully reported. Based on known and derived geopositions, the porbeagles exhibited broad seasonally-dependent horizontal and vertical movements ranging from 77-870 km and from the surface to 1300m, respectively. All of the sharks remained in the western North Atlantic from the Gulf of St. Lawrence and the coast of Nova Scotia to Georges Bank and oceanic and shelf waters south to North Carolina. In general, the population appears to contract during the summer and fall with more expansive radiation in the winter and spring. Although sharks moved through temperatures ranging from 2-26°C, the bulk of their time (77%) was spent in water ranging from 8-16°C. In the spring and summer months, the sharks remained epipelagic in the upper 200m of the water column. In the late fall and winter months, some of the porbeagles (n=10) moved to mesopelagic depths (200- 1000m). Temperature records indicate that these fish were likely associated with the Gulf Stream.

 

Joanna Stead, Michael Bennett

The Diet and Feeding Ecology of Sympatric Orectolobiform Sharks: An Example of Resource Partitioning

University of Queensland, Brisbane, Queensland, Australia

Dietary studies are vital for determining a species’ role within an ecosystem. It is recognised that elasmobranches play an integral role in the transfer of energy within marine ecosystems. However, studies of elasmobranch feeding ecology lag behind those on other vertebrates and knowledge remains limited, despite the global trend in declining elasmobranch numbers. Resource partitioning is an important mechanism that allows species to co-exist within an assemblage but there have been few investigations comparing the diets of sympatric elasmobranch species. The diet and feeding biology of three sympatric benthic shark species (Chiloscyllium punctatum, Orectolobus maculatus, and Orectolobus ornatus) were examined. Specimens were collected by commercial fishermen from the sub-tropical waters of Moreton Bay, off south eastern Queensland, Australia. The Index of Relative Importance (IRI) indicated that C. punctatum are generalist feeders, which prey on benthic invertebrates (polycheates, 33.58%IRI; crustaceans, 33.80%IRI, predominantly carid shrimps and brachyuran crabs; cepaholopod molluscs, 4.18%IRI) and demersal vertebrates (teleost fishes, 28.33%IRI). An ontogenetic shift was evident with teleosts more prominent in the diets of larger individuals. The wobbegong sharks (O. ornatus and O. maculatus) were predominantly piscivorous, with 96.98%IRI and 99.85%IRI for teleosts respectively. The diets of the wobbegongs were not significantly different at the prey taxonomic level of Order, but were significantly different (P<2.9%) at the Family level, with O. maculatus ingesting predominantly pelagic and soft substrate associated species and O. ornatus reef associated species. Teleosts ingested by C. punctatum and both wobbegong species were significantly different (P<0.1%), revealing that all three are targeting different teleost species. The dietary composition of the bamboo shark, C. punctatum complemented findings from acoustic tracking, which indicated that this species commonly feeds over inter-tidal mudflats adjacent to mangroves. It is proposed that spatial resource partitioning allows these benthic shark species to co-exist within Moreton Bay without inter- species competition.

 

Guy Stevens1, Robert D. Rubin2

Reproductive Behaviour, Mating and Male Competition in Manta Rays (Manta birostris) in the Indian Ocean

1Four Seasons Resort, Landaa Giraavaru, Baa Atoll, Maldives, 2Santa Rosa Jr. College, Santa Rosa, CA, United States

Underwater observations and photographic capture of reproductive behaviours, including copulation and male/male competition for mates were obtained for continuous mating seasons (2005-2008) at North Male Atoll, in the Republic of the Maldives. Two types of male/female interactions have been documented. Males swimming in a linear pattern (mating “trains”) consisting of 1 to 21 males following and chasing single, fast swimming females were well defined during October and November. A second association consists of males in smaller numbers (1 to 4), “shadowing” rather than chasing, slower swimming individual females. The former pattern appears to temporally follow the latter. Male group size appears to increase through time, reach a peak number and decline until only a few males remain and compete for access to a given female. During copulation the few remaining males attempt to dislodge the successful male from his attachment to the female by head ramming. Of the known resident females, 41 of 65 (63%) were pregnant in 2008 while only one was visibly pregnant in 2007. Some females involved in mating trains one season were pregnant the following year and shortly after giving birth, were observed bearing fresh pectoral fin mating scars. These data seem to suggest a biennial mating cycle as the norm and an annual reproductive cycle for some individuals.

 

Eric Stroud1, Patrick Rice1, Craig O'Connell1, Samuel Gruber2

Advances in Shark Repellent Research Using Highly Electropositive Metals

1SharkDefense Technologies LLC, Oak Ridge, NJ, United States, 2Bimini Biological Field Station, Miami, FL, United States

Recent studies conducted by the National Oceanic and Atmospheric Administration - National Marine Fisheries Service (NOAA – Fisheries) suggest that electropositive metals hold promise as shark bycatch reduction devices. To understand the underlying electrochemical processes, voltammetry was performed with flowing seawater electrolyte and moveable fritted glass half-cells. Voltage and current were monitored as the distance was increased between half-cells. Voltammetric measurements indicate that shark skin is more electronegative than the electropositive lanthanide metals and mischmetals. We hypothesize that a galvanic cell, created by an electropositive metal in seawater, spontaneously produces trivalent cations in solution. These cations are attracted to the electronegative shark skin, resulting in a net positive charge on the shark skin, which is measured by the electrode. Further research is required to understand the mechanism by which the accumulation of a positive charge is detected by the ampullae of Lorenzini. In practical fishery terms, because of the limited detection range of the ampullary organs, it is desirable to place electropositive metals as close to the hook as possible without interfering with capture. A simple hook modification has been developed which can be applied to multiple hook types. The modification utilizes thin ribbons of electropositive metal wrapped around a steel circle hook. Galvanometric analysis was utilized to confirm that the hook corrosion rate is not increased by the presence of the electropositive metal ribbon, thus ensuring that the structural integrity of the circle hook is not compromised during fishing.

 

James Sulikowski1, Walter Bubley2, Paul Tsang2, G. Walter Ingram Jr3, William Driggers III3

The Potential Use of Pop-up Archival Transmitting (PAT) Tags to Examine Habitat Use and Migration Patterns of Spiny Dogfish (Squalus acanthias) in the Western Gulf of Maine

1University of New England, Biddeford, ME, United States, 2University of New Hampshire, Durham, NH, United States, 3National Marine Fisheries Service, Pascagoula, MS, United States

Central to any successful fishery management plan is the availability of accurate, detailed and updated life history information on the species. Pop-up satellite archival tags (P A T) offer an innovative tool for examining the movement patterns, temperature, and depth preferences of many marine species. In the past, this technology has been too large or cumbersome for use in sharks less than 100cm in fork length. However, with the advent of the relatively small X-Tag by Microwave Telemetry, the value of using satellite technology on smaller shark species was tested on the spiny dogfish, Squalus acanthias, within the Gulf of Maine. Between October 31st and November 7th, 2007, a total of three X-Tags were attached to dogfish captured 6 miles off the coast of Southern Maine. Although two of the three tags prematurely released from the animal (expected “pop off” date was set at May 31st 2008), the data that was recovered (approximately 3 months worth) offered information that goes against many current paradigms for this species in the western Atlantic. This includes north-south movement ranges that are much wider and more active in scope than previously described for this shark. Moreover, deeper more constant depth profiles were also observed for this species. We anticipate the third tag will reveal similarly unique findings.

 

Shelly Tallack1, John Mandelman2

Do Rare Earth Metals Deter Spiny Dogfish? A Feasibility Study on the Use of Mischmetal to Reduce Dogfish Catches in Hook and Lobster Gear in Gulf Of Maine

1Gulf of Maine Research Institute, Portland, ME, United States, 2New England Aquarium, Boston, MA, United States

Spiny dogfish, squalus acanthias, are considered to be unacceptably abundant by many inshore fishermen (commercial and recreational) during the summer and fall in the Gulf of Maine. Finding a practical and economic dogfish deterrent for application in various fishing gears is of strong interest. An industry-science collaboration afforded six research trips during September 2007. Triangular slices of a cerium/lanthanide alloy (‘Mischmetal’) were incorporated into three baited gears (longlines, rod and reel gear and lobster traps) and the catches were compared for ‘treatment’ (Mischmetal present) versus ‘control’ (mischmetal absent). Field observations were inconclusive for the lobster gear since the traps caught no dogfish, regardless of treatment. Some reduction in dogfish catch was recorded for rod and reel (~2%) and longline (~9-25%), but these results were not statistically significant. One complicating factor was the high rate of Mischmetal dissolution, which led to the rapid disintegration of the Mischmetal slices in all gears. In situ video footage verified that dogfish feeding behaviour is persistent on bait, regardless of Mischmetal presence. A parallel laboratory study provided video-taped, behavioural observations on the effects of alloys versus a chemically inert stainless steel ‘decoy’, under varying levels of food satiation and dogfish density. The laboratory assessments found some evidence of aversive behaviour in dogfish approaching baits protected by Mischmetal, but only when the dogfish had been fed to satiation before undertaking the study; after any period of starvation, no aversion to Mischmetal was observed. Dogfish density had no effect on feeding in the laboratory and the in situ footage showed that bait pursuit by one dogfish would escalate to frenzied feeding by multiple dogfish, with or without Mischmetal. Overall, there is little evidence to suggest that Mischmetal has the potential to reduce dogfish catches in either commercial or recreational gear types in the Gulf of Maine.

 

Christine Testerman1, Paulo Prodohl2, Mahmood Shivji1

Global Phylogeography of the Great (Sphyrna mokarran) and Smooth

(Sphyrna zygaena) Hammerhead Sharks

1Guy Harvey Research Institute, Nova Southeastern University, Dania, Florida, United States, 2School of Biological Sciences, Queen’s University, Belfast, United Kingdom

The great (Sphyrna mokarran) and smooth hammerhead (S. zygaena) sharks are globally distributed species of significant conservation concern because they have high bycatch rates and high value fins. The great hammerhead has been assessed as endangered and the smooth hammerhead as Lower Risk / Near Threatened by the IUCN Redlist. There is no information on the population structure of either species to inform management and conservation efforts. We report on an ongoing assessment of the global population structure of both species using nuclear microsatellite markers and complete mitochondrial control region (mtCR) sequences (approximately 1098 nucleotides) from 78 great and 85 smooth hammerheads. Great hammerhead samples analyzed thus far included 59 North Atlantic and 6 Indo- Pacific individuals. Smooth hammerhead samples analyzed included 14 Atlantic, 23 North Pacific, 28 Southeast Pacific and 19 Indo-Pacific individuals. Analyses of the great hammerhead mtCR revealed strong geographical subdivision into two distinct evolutionary lineages with little exchange of haplotypes between the lineages (FST 0.704, P< 0.005) and little to no detectable genetic structure within either lineage. Smooth hammerhead mtCR revealed strong geographical subdivision into four separate populations with no evidence of gene flow between the populations (FST= 0.802, P< 0.00000) and little to no detectable genetic structure within the populations. Analyses of microsatellite loci from both species are currently underway. Despite the modest regional distribution of samples analyzed thus far, the data suggest that genetic population subdivision in these species may be extensive, making it likely that proper management will require a multi-regional approach.

 

Jacqueline E. Thrasher, John F. Morrissey

Ontogenetic variation in effect of ration size on growth of Scyliorhinus retifer

Hofstra University, Hempstead NY, United States

Chain catsharks, Scyliorhinus retifer, are continental shelf- and slope-dwelling elasmobranchs of eastern North and Central America. This species has been relatively unstudied and it is important to understand some of the basic elements of their natural history to comprehend the larger roles they play, such as their ecologic impact as predators within an ecosystem. The main purpose of this study is to determine how daily maintenance ration will affect growth and gross conversion efficiency during ontogeny. Previous studies have examined how different daily ration levels affect growth and gross conversion efficiency of teleost fishes; however, few studies have dealt with this issue in cartilaginous fishes, and no studies have examined the ontogenetic variation in this relationship for any shark species. This study examines a cold-water species with a considerably slower metabolism compared to similar studies on other cartilaginous fishes. We used four feeding regimes in juveniles and adults to examine the relationship between food intake and growth. We hypothesize that the percentage of food intake that will be used for growth will be highest in juveniles and lowest in adults. We also hypothesize that gross conversion efficiency will peak at an optimum ration that will lead to a decrease in increasing rations beyond this optimum point.

 

John Tyminski1, Jim Gelsleichter1, Philip Motta2

Androgen Receptors In The Bonnethead Shark (Sphyrna tiburo): A Means To Understanding The Functional Role Of Steroids In The Male Reproductive Tract

1Mote Marine Laboratory, Sarasota, Florida, United States, 2University of South Florida, Tampa, Florida, United States

Androgens and the androgen receptor (AR) play important roles in virilization, spermatogenesis, and sexual behavior in vertebrates. An understanding of the distribution and levels of expression of the ARs on the cellular and tissue level demonstrates the pattern of responsiveness to the androgenic hormones in a given organism. In this study, the ARs of the reproductive tract of the male bonnethead shark, Sphyrna tiburo, were detected on a cellular level using in situ hybridization (ISH) and immunocytochemistry (ICC) while levels of AR expression were measured using relative quantitative PCR. ISH results localized the AR RNA in the interstitial cells, Sertoli cells, and developing sperm of the testes, and mature spermatozoa within the seminal vesicles and the epididymides. The ICC methods used to detect the AR protein using a rabbit polyclonal antibody, PG-21, produced comparable results in the shark testes but did not yield positive results in the seminal vesicles or the epididymides. However, the Leydig gland, whose secretions contribute to the seminal fluid, demonstrated consistent AR immunoreactivity. The use of relative PCR revealed that these organs have variable levels of AR gene expression that significantly differ with the stage of the shark’s seasonal reproductive cycle. Additionally, the presence of steroidogenic enzymes, such as 17β-hydroxysteroid dehydrogenase, was detected cellularly as a measure of androgen synthesis using ICC. Serum steroid hormone levels are often presumptively correlated with reproductive events whereas knowledge of the cognate receptors provides insight into the cells and processes that are regulated by the hormones. By characterizing AR distribution in the reproductive tract and the steroidogenic enzymes in the testes of male S. tiburo, this study provides the basis for future research on the direct and indirect effects of androgenic hormones in this species. These results, along with comparisons of AR distribution in other elasmobranch species, will be discussed.

 

Senzo Uchida, Minoru Toda, Yosuke Matsumoto


Captive Records of Manta Rays in Okinawa Churaumi Aquarium

Okinawa Churaumi Aquarium, Motobu-cho, Okinawa Pref., Japan

From thirty years, from 1978 to 2008, we have kept a total of 19 Manta Rays (Manta birostris) in captivity at the Okinawa Expo Aquarium and its immediately adjacent successor, the Okinawa Churaumi Aquarium. We are the first Aquarium in the world to keep manta rays successfully, and as of January 20, 2008, we hold the world record for the longest time in captivity of a single individual, 15 yrs. 8 months. A female manta pup, the first-ever conceived and born in captivity, was born here on June 17, 2007. For 24 years, until 2001, 14 of these rays were kept either in the 1,100 m3 tank or the open-sea pen associated with the Expo Aquarium. In 2001, when the new 7,500 m3 tank was ready at Churaumi, four of these rays were transferred directly to it, where they have been kept until now. The large Churaumi tank was built to serve as both a display and experimental tank, with the twin goals of exhibiting Whale Shark and Manta Ray feeding behaviors, and studying their reproduction in captivity. We have been fortunate to make observations on mating and birthing behavior of captive adult Manta Rays, and to collect reproductive data, such as size and age at reproductive maturity, gestation time, litter size, size and weight of newborn, most of which is information new to science. Our observations and data, including data on survival times in captivity, are reported and discussed in this report. Among the four species in the Family Myliobatidae kept in our Aquarium (including Manta birostris, Mobula japonica, M. diabolus, M. tarapacana ), Mantas have shown the best adaptability to captive settings. Because of our demonstrated ability to keep and observe animals successfully over long periods of time, we believe keeping wild animals in captivity can lead to making valuable contributions to understanding their biology.

 

Jeremy Vaudo, Michael Heithaus

Factors Influencing the Abundance of Sympatric Ray Species over a Shallow Sandflat in Shark Bay, Western Australia

Florida International University, Miami, FL, United States

Shallow habitats of tropical regions often support diverse ray communities, but few studies have investigated how they may partition habitats or resources. Between 2006 and 2008 we examined spatiotemporal variation in ray species composition and abundance over a shallow sandflat in Shark Bay, Australia using belt transects. At least nine species of rays were observed over the flats. More species and individuals were observed when water temperatures were high. The most common species were the giant shovelnose ray (Rhinobatos typus), reticulate whipray (Himantura uarnak), cowtail ray (Pastinachus sephen), and blackspotted whipray (H. toshi). Factors influencing species abundance varied. Blackspotted whipray abundance increased with increasing temperatures but was equal among microhabitats and across tidal heights. Abundances of giant shovelnose rays, reticulate whiprays, and cowtail rays, however, were affected by water temperature, microhabitat, and tidal height. These rays were most common in a narrow band close to shore and increased in abundance only within this microhabitat as temperature increased. These three species also increased in abundance at lower tidal heights when temperatures were high. Feeding pit densities were highest closest to shore, despite preliminary evidence that prey densities are no higher in this microhabitat than other microhabitats and contrary to predictions of behavioral thermoregulation, rays tended to rest in the warmest water available. The patterns exhibited by giant shovelnose rays, reticulate whiprays, and cowtail rays could be driven by predation risk from great hammerhead and tiger sharks, which are common at higher temperatures, but cannot access shallow habitats at low tidal heights.

 

Jonelle Verdugo, Juan M. Ezcurra, John B. O'Sullivan

Captive Biology ofthe Pygmy Devil Ray (Mobula munkiana) at the Monterey Bay Aquarium

Monterey Bay Aquarium, Monterey, California, United States

Relatively little is known about the captive biology and husbandry care of the devil rays (family Mobulidae). In 2005 the Monterey Bay Aquarium embarked on a collection trip to the Sea of Cortez, Baja California Sur, Mexico. One pygmy devil ray (Mobula munkiana) was held for one year and seven months at the Tuna Research and Conservation Center. During this time we learned animal handling and feeding techniques for this species and gathered some initial information on captive biology. A pilot respirometry study was conducted to measure routine metabolic rate; preliminary results indicate a mean MO2 of 136.2 + 5.0 (S.E.) mg O2/kg/hr at 21 oC. We hope to continue more respirometry and bioenergetics studies in the future, as well as continuing to develop husbandry techniques for these active rays.

 

Jon Walsh1, David Ebert2

A new species of angelshark, Squatina sp. nov., from the western North Pacific (Chondrichthyes: Squatiniformes, Squatinidae)

1Moss Landing Marine Laboratories, Moss Landing, CA, United States, 2Pacific Shark Research Center, Moss Landing, CA, United States

A recent taxonomic study (Walsh and Ebert, 2007, Zootaxa, 1551: 31-47) redescribed and confirmed the occurrence and validity of four squatinid species (Squatina formosa, S. japonica, S. nebulosa, and S. tergocellatoides) in the western North Pacific (WNP). These squatinids can be distinguished from each other by several distinctive characters including: the relationship of the pelvic fin tips to the first dorsal fin origin, pelvic girdle width, upper lip arch shape, and the presence or absence of mid- back thorns and ocelli on the pectoral fins. Examination of a squatinid species caught off the Philippine Islands, previously identified as S. formosa, was found to reveal several distinct characters inconsistent with other WNP squatinids. These distinctions include differences in the head width, pelvic insertion and pelvic base length, and unique caudal and upper lip arch shapes. We contend that these differences warrant designation of a new species of WNP squatinid. A revised dichotomous key for the region is presented that now includes all five known WNP squatinid species.

 

Christine Ward-Paige

Counting Elasmobranchs


Dalhousie University, Halifax, Nova Scotia, Canada

Recent widespread evidence documenting large-scale shifts in elasmobranch populations has changed the perspective of research methodology from observational studies to a more predictive framework based on meta-analysis of fisheries data and population modelling. However, this shift has not effectively addressed the fundamental problem with censusing elasmobranch populations which is that long-lived and potentially rare and declining species continue to be decimated, and in some cases they are removed for the sole purposes of censusing. Given that many shark species have declined to dangerously low levels of abundance at alarming rates, there is an need to implement non-destructive methods of censusing these highly vulnerable species. I synthesize methods used to count marine fishes, with an emphasis on elasmobranchs, and make the argument that volunteer scuba divers can provide valuable data that should be used in the assessment of global elasmobranch populations. I first review the most commonly used methods for censusing elasmobranch populations. Then I cover non-extractive methods- how they work, and their ability to include elasmobranchs. Subsequently, I present results of a model that simulated fish and divers in the three most commonly used underwater visual census (UVC) methods, roving-diver technique, belt-transect technique, and stationary-point count. Here, I discuss the accuracy of these UVC methods for estimating fish density at different fish speeds and investigate the best method for censusing fish at low densities. Finally, I review the utility of Citizen Science and present the North American Breeding Bird Survey (BBS) as an example of a successful application of volunteer surveys. Using the BBS as an analogy, I propose that marine scientists employ volunteer scuba divers to report elasmobranch sightings in a way that can be valuable for monitoring and conservation.

 

Nicholas Wegner1, Chugey Sepulveda2, Jeffrey Graham1

The Intrinsic Elasmobranch Gill Design Potentially Limits Gas Exchange and the Aerobic Performance of the Shortfin Mako, Isurus oxyrinchus, a Lamnid Shark

1Scripps Institution of Oceanography, La Jolla, CA, United States, 2Pfleger Institute of Environmental Reseach, Oceanside, CA, United States

The lamnid sharks (family Lamnidae) demonstrate a remarkable evolutionary convergence with tunas (family Scombridae) for high-performance swimming. Analysis of gill structure and function in the shortfin mako, Isurus oxyrinchus, a lamnid shark, reveals similarities to tunas in the presence of specializations to maintain gill rigidity during ram ventilation and to permit the O2 transfer required for fast, sustainable swimming. However, mako and tuna gill specializations have structurally different bases due to intrinsic differences in the gill design of elasmobranchs and teleosts. The elasmobranch gill has a more tortuous water pathway, and in vivo measurements of mako gill resistance suggest that this design limits total gill surface area in comparison to some teleosts. Thus, while mako gill areas are larger than non-lamnid shark species, they are significantly less than those of tunas. The larger size of elasmobranch erythrocytes also increases mako respiratory lamellar thickness and gas diffusion distances in comparison to tunas. These intrinsic characters limit gas exchange and may prevent lamnid sharks from reaching the scope of sustainable aerobic performance achieved by tunas.

 

Kevin Weng2, Heidi Dewar1, Suzanne Kohin1, Oscar Sosa-Nishizaki3, Erick Cristóbal Oñate González3, Barbara Block4, David Holts1, James Wraith1

Migration and Habitat Use of Blue Sharks in the Eastern North Pacific Ocean

1NOAA Fisheries, La Jolla, CA, United States, 2University of Hawaii at Manoa, Honolulu, HI, United States, 3CICESE, Ensenada, Baja California, Mexico, 4Hopkins Marine Station, Stanford University, Pacific Grove, CA, United States

The blue shark is the most abundant pelagic shark in the world and is likely to be an important predator in open ocean ecosystems. Blue sharks have been captured in enormous numbers in high seas fisheries over many decades, sustained only by the wide distribution and high fecundity of the blue shark, but major reductions in abundance have occurred in some ocean basins and the IUCN lists the species as ‘Lower Risk Near Threatened’. Knowledge of the biology of this species is important to help us understand how pelagic communities function, and why some elasmobranch species are more vulnerable to overexploitation and extinction than others. We studied the spatial ecology of blue sharks via satellite telemetry by tagging sharks in two locations within the California Current System of North America. Sharks made extensive use of the rich upwelling system off Baja California, California and Oregon, and also made long distance movements into oligotrophic regions of the subtropical gyre and the eastern tropical Pacific. Blue sharks did not appear to undertake movements in a coordinate manner as they dispersed from the tagging locations. Blue sharks inhabited cool upwelled waters, warm tropical waters to near 30°C, and waters beneath the thermocline to 7°C. The sharks undertook extensive diving to depths in excess of 700 m. Diving was frequently greatest during daytime, but sharks undertook dives at all times of the day. Knowledge of the movements and habitat usage of this abundant pelagic shark will improve our understanding of pelagic ecosystems and inform the development of high seas fishery management schemes.

 

William White1, Dharmadi Dharmadi2, Ian Potter3

The Bycatch Fishery for Mobulid Rays in Eastern Indonesia


1CSIRO Marine & Atmospheric Research, Hobart, Tasmania, Australia, 2Research Centre for Capture Fisheries, Jakarta, West Java, Indonesia, 3Centre for Fish and Fisheries Research, Murdoch University, Perth, Western Australia, Australia

Although mobulids are taken in a variety of fisheries throughout much of their range, details of these fisheries are poorly documented. In Indonesia, mobulid rays are landed as bycatch by artisanal gillnet fishers targeting skipjack tuna. Between April 2001 and March 2006, more than 20 surveys of Indonesian fish landing sites were carried out to determine the species, size and sex compositions of the chondrichthyan catches. This study contributes to the limited knowledge on biological aspects and fisheries information for the Mobulidae. The data were derived from 409 mobulids that were examined during the fish landing site surveys. At one particular landing site, it was estimated that 1575 mobulid rays (equivalent to ~320 tonnes) are landed annually. The most abundant of the five species was Mobula japanica (~50%), followed by Mobula tarapacana (~24%), Manta birostris (~14%), Mobula thurstoni (9%) and Mobula cf kuhlii (2%). The four most abundant species were represented by a wide size range of each species and, in the case of Mobula japanica, by embryos, neonates and fully-mature individuals. The disc width at maturity (DW50) of males, derived from the proportion of males at each size class with fully- calcified claspers, ranged from 1538 mm for M. thurstoni to 3752 mm for M. birostris. In recent years, there has been an increasing demand for various body parts of mobulids. Branchial filter plates, which are used for traditional Chinese medicines, are the most valuable, fetching as much as 30 $US a kilo (dry weight). The skins are dried and deep fried and the flesh salted and dried and these are used for human consumption, while cartilage is dried for export as a filler for shark-fin soup. The very low fecundity of the large and probably long-lived mobulid rays make the stocks of their species particularly susceptible to further increases in fishing.

 

Lisa B. Whitenack, Philip J. Motta

Correlated Evolution of Selachian Tooth Morphology, Diet, and Ecology

University of South Florida, Tampa, FL, United States

Due to the cartilaginous nature of the skeleton, the fossil record for sharks is overwhelming composed of teeth. Hypotheses regarding diet, feeding habit, and evolution are therefore usually inferred from a combination of qualitative dentition characteristics and the possible prey items that are contemporaneous in the fossil record. To date, a rigorous evolutionary analysis of the above characters has not been undertaken. The goal of this study is to assess the correlated evolution of tooth morphology, diet, and ecology in extant selachian families using independent contrast analysis. Each family was represented by one to four species, dependant on the degree of tooth morphology variation in the family, with filter-feeding species excluded. For each species, a series of morphometric measurements were taken on teeth on the right side of the upper and lower jaws of up to five individuals. These measurements were used to calculate quantitative tooth morphology characters, including cusp aspect ratio, notch angle, cusp inclination indices, and percent of tooth base overlap. Data about ecology and diet were taken from the literature. The above characters were mapped onto an existing phylogeny. Independent contrast analysis was then used to search for correlated evolution of these characters, with branch lengths set to unity. Preliminary results indicate no phylogenetic pattern for teeth of the upper jaw. These teeth tend to be highly variable in morphology intraspecifically, even within families such as Lamnidae and Carcharhinidae. However for teeth in the lower jaw, families with cusps that are less broad tend to have teeth that are also angled more distally relative to the jaw symphysis and deeper notches. There appears to be no pattern for degree of tooth base overlap in either the upper or lower jaws; this instead appears to be correlated with prey handling behaviour.

 

Naeem Willett1, Dewayne Fox1, Brad Wetherbee2

Not All Nursery Areas Are Created Equal: The Importance of Small Scale Nursery Habitat for Delaware Bay Sandbar Sharks

1Delaware State University Department of Agriculture and Natural Resources, Dover, Delaware, United States, 2University of Rhode Island Department of Biological Sciences, kingston, Rhode Island, United States

Due to declines in sandbar shark populations, efforts are underway to better understand habitat use in nursery areas for rebuilding depleted stocks. Large numbers of young-of-the-year (YOY) and age 1+ juvenile sandbar sharks reside in Delaware Bay from early summer through early fall. We utilized an automated telemetry array (Vemco VR-2) to monitor sandbar shark habitat utilization patterns during their residency in Delaware Bay. We hypothesized that our principal receiver array was near or within primary nursery habitat based on previous studies. Additional receivers were attached to navigational buoys within Delaware Bay. We monitored the movement patterns of 59 sandbar sharks that were surgically implanted with coded acoustic transmitters during the summers of 2005 and 2006. In total over 46,000 detections of telemetered sandbar sharks were recorded. The vast majority (92%) of total detections occurred within the hypothesized nearshore primary nursery habitat compared to receivers located in deeper waters and at the entrance to Delaware Bay. Site fidelity for returning sandbar sharks was high (42%) in years following the implantation of transmitters. Of the returning individuals (n=25), a high proportion (80%) were comprised of age 1+ juvenile sandbar sharks. The low rate of returning YOY sandbar sharks to Delaware Bay suggests either a high mortality rate during the first year of life or low fidelity to Delaware Bay in the second summer. The high degree of site fidelity and abundance of near shore detections illustrate the importance of such a small portion of Delaware Bay to juvenile sandbar shark stocks. Data from this research may improve the protection and understanding of sandbar shark habitat while residing in Delaware Bay.

 

Kara Yopak, Larry Frank

A Neural Basis for a Shark’s Motor Repertoire? Quantifying the Complexity of the Cerebellum using Magnetic Resonance Imaging (MRI)

University of California San Diego, Center for Scientific Computation in Imaging, San Diego, CA, United States

The cerebellum appeared at the onset of the chondrichthyan radiation and is known to be essential for executing fast, accurate, and efficient movement, yet there is still much controversy surrounding its absolute function, which remains unresolved. Comparative data on cerebellar anatomy from cartilaginous fishes with disparate behavioral repertoires can provide critical information on cerebellar function and development, and ultimately vertebrate evolutionary trajectories. Recent work has shown patterns of brain organization in sharks that are correlated with ecological parameters. Cerebellum size has strong allometric correlations, but there exists significant interspecific variation in corpus folding. We have previously developed a visual grading method, ranging from 1-5, which provided a classification scheme for cerebellar foliation. When applied to a range of species (n=81), the highest foliation levels (4-5) were found in agile predators that lived in 3D environments, such as Isurus oxyrinchus, Alopias vulpinus, and Sphyrna mokarran. However, visual classification is limited as it does not parameterize structural variations, and thus does not provide a quantitative method for characterization and comparison of foliation; these methods can often miss subtle but important differences between species that may have high evolutionary significance. Here we provide such a quantitative method using Magnetic Resonance Imaging (MRI) in conjunction with shape analysis methods. The degree of foliation was quantified using three different measures of geometric variation following image segmentation: (1) local tissue curvature (2) cortical flattening, and (3) spherical harmonic decomposition. These methods were preliminarily applied to 5 shark species with varying levels of foliation (based on the visual classification scheme). These methods greatly extend the visual foliation index by providing quantitative methods for interpreting and analyzing the architecture and surface structure of chondrichthyan brains. Through these, we plan to explore the extent to which adaptive, developmental, and phylogenetic processes are driving neural evolution. 

POSTERS

Sabrina Albrecht

Target-Training in the Brownbanded Bamboo Shark (Chiloscyllium punctatum) and Nurse Shark (Ginglymostoma cirratum)

Coastal Carolina University, Conway, South Carolina, United States

The capability of sharks learning repetitive tasks was undertaken in this experiment. One male bamboo shark Chiloscyllium punctatum (63 cm TL) and one male nurse shark Ginglymostoma cirratum (110 cm TL) held in captivity since the beginning of 2007, were used in this experiment. Between September 2007 and April 2008, 61 trials were conducted to determine if these sharks could distinguish between colors (black square vs. white square targets), and shapes (white circle vs. white square targets). The sharks were trained to correctly identify with the targets using a reward system. The rewards were obtained when the sharks correctly hit their snout against the white square target for distinguishing between color and shape. The bamboo shark could obtain a maximum of eight pieces of fish, whereas the nurse shark was allowed a maximum of three, consistent of a normal regimen used by the aquarium. The bamboo shark correctly identified both the color and shape targets 437 out of 488 opportunities (89.5%), the nurse shark had a success rate of 167 out of 183 (91.2%). The assumption that some species of sharks rely on their barbels: as a means of identifying objects, rather than sight was also investigated. Initial response time varied, but decreased over time. The sharks appear to rely more on their eyesight for color distinction than on tactile behavior for shape discrimination. (Supported funding Ripley’s Aquarium, South Carolina, Advisor Dr. Dan Abel)

 

Marcela Bejarano Alvarez, Felipe Galvan Magaña

Reproductive Biology of Hammerhead Shark Sphyrna lewini in Salina Cruz, Oaxaca, Mexico

Centro Interdisciplinario de Ciencias Marinas,Cicimar, La Paz, B.C.S., Mexico

The hammerhead shark Sphyrna lewini was the most caught shark in Oaxaca. However the reproductive aspects of the specie in this area of Mexico are unknown. Samples and data were collected every week at the artesanal fishing between September 2004 and June 2006. A total of 991 hammerhead sharks (342 females and 649 males) also juveniles (45 to 160 cm TL) and adults (170 – 288 cm TL) were sampled. Sex ratio in adults was 1F:2M. The hammerhead shark was present all year but the biggest abundance was in May to July, this is the season when the pregnant females appear. Size of first maturity for females was 220 cm TL (increase in diameter of the oocyte, width of the oviductal gland). The histologycal analysis showed that males have diametric testes, sperm in epididymis, ductus deferens and compound spermatozeugmata in seminal vesicle, which suggests a size of first maturity for males at 180 cm TL. We don’t found sperm storage in the oviductal glands of females but this condition has been confirm for the specie. We recorded 40 pregnant females with an interval of 6 to 40 embryos. Births were in July to August and the birth size was between 41 to 51 cm TL. We propose Salina Cruz, Oaxaca as a nursery area for hammerhead shark Sphyrna lewini.

 

Csilla Ari

The Brain of Mobula japanica (Spinetail Devilray, Myliobatiformes, Elasmobranchii) in Gross Morphological and Ecological Perspectives

Semmelweis University, Budapest, Hungary

The difference in brain mass among different taxonomic radiations is one important measure of brain evolution. In the present study the brain mass to body mass ratio and external morphological features of Mobula japanica’s (spinetail devilray) brain are described. M. japanica extended the upper boundary of the minimum convex polygon described earlier by other authors for batoids, which is plotted on a double logarithmic scale of brain to body mass. The new data had high leverage to the regression, compared to other batoids, causing some change in the allometric coefficient. The encephalization quotient was higher than unity, therefore it can be concluded that the actual brain mass is greater than expected by the given body mass. The most prominent brain parts were the huge and high telencephalon, giving 61 % of the total brain mass and the convoluted, strongly foliated cerebellum, with 19 %. M. japanica had the highest percentage of telencephalic mass from all batoids studied so far, while squalomorph sharks are represented by 24-31 %, galeomorph sharks 35-66 %, and batoids 33-51.1 %. The cerebellum of the Mobula was most similar to that of lamniform and advanced carcharhiniform sharks, which had extremely high foliation, and the cerebellum could be divided into 3 lobes with deep sulci. A structural dimorphism of cerebellar foliation was detected between genders, albeit with a small sample size. No such gender-related dimorphism was detected in brain mass/body mass ratio. Other brain parts were similar to those of other elasmobranch species. The data are dicussed in terms of their systematic or evolutionary significance.

 

Michael Bennett, Andrea Marshall

The Reproductive Ecology of Manta birostris off Southern Mozambique

University of Queensland, St Lucia, QLD, Australia

Manta birostris is common in southern Mozambican coastal waters with 450 individual rays identified, based on their unique dorsal and ventral markings, in the area around Inhambane since 2003. Manta rays are present year-round and use many inshore reefs as cleaning stations. Observation of this population over five years has revealed previously unreported aspects of their reproductive biology and behaviour. The study population in southern Mozambique is sexually segregated, with a female to male sex bias of 3.5:1. Sexual dimorphism in size is apparent between the sexes. The high re-sighting rate (40%) of individuals infers a semi-resident local population that has allowed the reproductive condition of known individuals to be regularly assessed. Male rays appear to transition from immaturity to maturity around a disc width (DW) of 3 meters, whereas females mature at about 4 m DW based on observed pregnancies and reproductive pectoral fin scarring. Pregnancies have been observed in over 60 individuals. Courtship and mating behavior typically occurs between October and January, but appears to be punctuated. Parturition occurs in the summer months, from late November to early February. Typically a single pup is born per litter. The smallest free-swimming individual accurately measured in the field was 1.5 m DW, while a 1.3 m DW pup was extracted in early October from a dead specimen. Preliminary data suggests that the gestation period in this population is 12-13 months. While at least four females were seen to be pregnant in consecutive years, the majority of individuals had a biennial or even triennial reproductive cycle.

 

Diego Bernal1, Dave McGillivray2, Scott Aalbers3, Douglas Syme2, Jeanine Donley4, Chugey Sepulveda3

In-vivo Muscle Dynamics of Thresher Sharks During Sustained Swimming

1University of Massachusetts, Dartmouth, Dartmouth, MA, United States, 2University of Calgary, Calgary, Canada, 3Pfleger Institute of Environmental Research, Oceanside, CA, United States, 4MiraCosta College, Oceanside, CA, United States

This study presents the first phase of a collaborative research project that investigates several aspects of locomotor muscle function and design in the thresher sharks (Alopiidae). Threshers are a group of large, pelagic sharks easily recognized by their elongate upper caudal lobe. The alopiids represent the only genus to contain species with both lateral and medial positions of the red aerobic locomotor muscle (RM). Thus, the alopiids provide the ideal system in which to test the hypothesis that the medial RM position in the common thresher shark (Alopias vulpinus) provides the basis for a propulsion mechanism similar to that found in the lamnid sharks and different from sharks with lateral RM. Field studies captured common thresher sharks and used sonomicrometry to quantify the in-vivo muscle dynamics of the red and white muscle (WM) during sustained swimming. Preliminary data on RM strain (at first dorsal fin), at a tailbeat frequency of 0.5Hz, was consistently greater than that of the WM and decreased significantly during simulated swimming movements (when the RM was not stimulated; i.e., passive swimming). By contrast WM strain did not differ between active and passive swimming. A comparison of RM and WM phase during swimming showed instances in which RM shortening both led and trailed that of the surrounding WM, with no phase difference observed during the passive swimming experiments. This finding suggests that, similar to lamnid sharks, the common thresher RM sheers relative to the WM. Therefore, these results suggest that the common thresher may exhibit a similar uncoupling of RM shortening and local body bending as seen in the thunniform lamnids.

 

Maria-del-Pilar Blanco-Parra1, Fernando Márquez-Farías2, Felipe Galván- Magaña3

Description of the Banded Guitarfish Reproductive Tract and Embryos Development

1Posgrado en Ciencias del Mar y Limnología, UNAM, Mexico City, Mexico, Mexico, 2Instituto Nacional de la Pesca, SAGARPA, Mazatlán, Sinaloa, Mexico, 3Centro Interdisciplinario de Ciencias Marinas (CICIMAR-IPN), La Paz, Baja California Sur, Mexico

No information is known about the reproductive tract anatomy in the banded guitarfish. Males possess two functional compound-type lobulate testes. In immature individuals, testes appear as a small pink structure attached in the anterior portion of the epigonal organ ranging in length between 10 to 80 mm. Testes of mature individuals range from 40 to 100 mm. Microscopic examination of testes indicate that banded guitarfish possess multiple germinal zones located on the dorsal surface. Females posses two functional external type ovaries. Immature females have undeveloped ovaries with small, clear, yolkless oocytes less than 5 mm in diameter, the uterus appear narrow and the oviducal gland is difficult to distinguish from the rest of the oviduct. In mature females vitelogenic oocytes range from 5 to 25 mm. Embryos were found to be equally distributed in each uterus. At the beginning of the gestation, all fertilized oocytes in each uterus are contained in a single, thin, amber colored envelope that remain until the embryos complete their development. At the second month of development (April) embryos start to be distinguishable with a mean total length of 26 mm and without coloration; three months later, embryos reach the birth size 186 mm TL and the yolk was completely absorbed.

 

Mark Bond1, Steven Kessel1, Rupert Perkins1, Samuel Gruber2, Tristan Guttridge3

Identification by Video Surveillance of Species-specific Bait Manipulation by Lemon Sharks, Negaprion brevirostris and its Influence on Capture Susceptibility

1Cardiff University, Cardiff, United Kingdom, 2Bimini Biological Field Station, Bimini, Bahamas, 3Leeds University, Leeds, United Kingdom

Anyone familiar with shark fishing knows that some species can successfully remove bait from a hook without getting caught. This ability whether through species- specific mouthing techniques or individual differences in bait manipulation has potentially significant implications for fisheries management. If catch rate is affected by behavioural differences in bait handling this can lead to a species-specific bias with regard to, abundance estimates and CPUE., This could erroneously imply that there are greater or fewer numbers of a particular species. We investigated the question of capture susceptibility in the field using a 30 m long section of long line with a single baited gangion. An underwater video camera placed near the rig enabled us to record the behaviour of each lemon shark approaching and interacting with the baited hook. Analysis of the video records provided materials to identify inter- and intraspecific variations in bait handling behaviour which in turn influenced whether a shark became hooked or not. One objective of the study was to examine whether the negative stimulus of capture could result in rapid learning whereby a shark would actively avoid a baited hook as a result of being hooked. We investigated this by first marking juvenile lemon sharks with colour-coded dart tags at the study site (Bimini lagoon). Their interactions with baited hook were also observed and videotaped from a 16ft tower. Data collected included approach duration, number of approaches, as well as a number of bait-handling behaviours. We thus determined if a shark that was previously caught (i.e. negatively conditioned), actively avoided the baited hook or displayed caution (slower approach time) on subsequent trials over a period of months. Supported by grants from the Hoover Foundation, BBFS, National Science Foundation and Leverhulme Foundation.

 

Simon Brown1, Joe Bizzarro2, Mariah Boyle1, David Ebert2, Gregor Cailliet1

Diet Composition of Four Abundant Skate Species of the Gulf of Alaska

1Moss Landing Marine Labs, Moss Landing, CA, United States, 2Pacific Shark Research Center, Moss Landing, CA, United States

Stomach content analysis is being performed on four of the most abundant skate species in the Gulf of Alaska. Through participation on fishery independent trawl surveys (National Marine Fisheries Service and Alaska Department of Fish and Game), stomach samples of Raja rhina, R. binoculata, Bathyraja aleutica, and B. interrupta were collected and preserved immediately at sea for high resolution stomach content analysis. Preliminary results suggest commercially important species such as tanner crab (Chionoecets bairdi) and northern pink shrimp (Pandalus eous) are a significant dietary component of the larger species (R. rhina, R. binoculata, and B. aleutica), whereas a diversity of smaller-sized prey were found within the stomachs of B. interrupta. Future work will focus on intra- and interspecific variation in diet as sample sizes become sufficient for quantitative statistical analyses. The results of this study will help to determine the trophic interactions of these common demersal predators in the Gulf of Alaska ecosystem.

 

Felipe Carvalho1, Paulo Oliveira2, Fabio Hazin2, Bruno Macena2, Andrew Piercy1, George Burgess1, Debra Murie1

Ecology of Three Elasmobranch Species in the Atol das Rocas Biological Reserve, off Northeast Brazil

1University of Florida, Gainesville, FL/Southeast, United States, 2Universidade Federal Rural de Pernambuco, Recife, PE/Northeast, Brazil

Atol das Rocas, a unique atoll in the South Atlantic Ocean, was the first designated marine reserve in Brazilian waters. From August 1999 to December 2007, 28 surveys, averaging 20 days each, were carried out in the Atol das Rocas Biological Reserve aimed at studying the population demographics and behavior of three common elasmobranch species present in the area. Visual censuses were used to document the use of habitat and population structure of nurse shark (Ginglymostoma cirratum) and southern stingray (Dasyatis americana). In addition, a tag-recapture study estimated the population size and growth of young lemon sharks (Negaprion brevirostris). A total of 73 young lemon sharks were caught, without mortality, ranging in total length (TL) from 60- 70 cm for females and 70- 80 cm for males. The population size of young lemon sharks in the region was estimated at 147±36 individuals. Females and males showed an increase in TL of 12.7 cm/year and 12.4 cm/year, respectively. A total of 184 rays were sighted in the visual censuses. Of these, 85% presented some distinguishing marks that were photographed. The population of southern stingray in the Atol das Rocas, based on the analysis of re-sightings in different surveys, was estimated at 99.2 ± 17.1 individuals. Mean number of nurse sharks sighted in each expedition was 123.34 ± 48.75, with TL's ranging from 42-293 cm. The extreme tidal regime present in the Atol das Rocas has a significant influence on the behavior of these three elasmobranch species. The area hosts unique populations of these species, underscoring the need to implement proper conservation and management measures.

 

Florencia Cerutti-Pereyra1, Frazer McGregor3, Guy Stevens5, Corey Bradshaw4, Mark Meekan2

Photo Identification of Manta Rays in the Indo-Pacific Ocean

1Charles Darwin University, Darwin, NT, Australia, 2Australian Institute of Marine Science, Darwin, NT, Australia, 3Murdoch University, Perth, WA, Australia, 4University of Adelaide, Adelaide, SA, Australia, 5Four Seasons Resort, Maldives, Maldives

Mark-recapture (or sight-resight) studies are one of the most prevalent and widely tested methods of estimating demographic parameters such as population size, survival, movement rate, and age/sex structure. This method uses natural skin pigmentation patterns, marks or scars present on animals, which makes it less disruptive to the animal and their environment than conventional tagging techniques. Photo-id libraries from the Maldives, Ningalooo Reef, WA and Yap Islands are being used to study population parameters and migration of manta rays from the Indo-Pacific Ocean. The aim of this study is to identify if there is a “typical” aggregation of manta rays and which size and /or sex is the most common. Cleaning stations and feeding grounds have been identified as the most important aggregation sites in each location but the number of mantas participating in them and the reasons why they are grouping in such places are some of the questions we intend to answer. Using libraries with photos from several years, it is possible to determine residency of individuals and site fidelity, which helps in the understanding of population dynamics and sexual-biased migrations. The understanding of manta ray population traits and migration patterns is essential to 1) maintain the ecotourism industries that these rays support in hot spots like Ningaloo Reef, W.A. or Maldives Islands, and 2) to improve the local management plans and regulations. Moreover, the ongoing long-term project this study is a part of will improve the general understanding of manta ray movement through international waters, allowing the possibility of designing protected areas in international and shared waters.

 

Florencia Cerutti-Pereyra1, Felipe Galvan-Magaña2, John O’Sullivan3

Abundance, Seasonal Occurrence, and Biological Information of Devil Rays (Batoidea:Mobulidae) in the Gulf Of California, Mexico.

1Charles Darwin University, Darwin, Australia, 2Centro Interdisciplinario de Ciencias Marinas, :a Paz, Baja California Sur, Mexico, 3Monterey bay aquarium, Monterey, California, United States

Devil rays have been harvested to an unsustainable level due to a strong fishery in the Gulf of California. The life strategy of this group, make them very vulnerable to over fishing, so studies are necessaries for management and conservation plans in the area. Two fishery camps were sampled during May to July of 2002 and from February to October of 2004. A total of 356 organisms were caught, 135 of Mobula japanica (74 females, 61 males), 112 of Mobula munkiana (50 females, 62 males) and 109 of Mobula thurstoni (51 females, 58 males). Mobula japanica occurs mainly on summer months, we found that the most abundant size was 210 cm disc width (DW) and 61% of the organisms sampled were smaller that the estimated size at maturity (ESM); we also found gravid females. Mobula munkiana is known to be a winter species; however, we found it from February to July. The most abundant size was 50 cm DW and we found that 78% of the sample is smaller than the ESM; we also found gravid females and small organisms with the size suggested for birth. Mobula thurstoni occurs all year- round with a seasonal size segregation. The most abundant size in this study were 130 and 150 cm DW; 60% of the catch were organisms smaller that the ESM. Also gravid females were found in this species. The presence of juveniles, neonates and/or gravid females of the three species on the nets, make evident not only that this area have been used by these mobulids as mating and nursery ground, but also that the fishery is targeting on juveniles, which may collapse populations in a short period of time as happened with other species of elasmobranchs in the world.

 

Taylor Chapple1, Scot Anderson3, Salvador Jorgensen2, A.Peter Klimley1, Barbara Block2

A Validation for the Use of Fin Photographs for Individual Identification of White Sharks (Carcharodon carcharias) off California and a Comparison between Two Analysis Methods

1University of California-Davis, Davis CA, United States, 2Hopkins Marine Station, Stanford University, Pacific Grove CA, United States, 3Inverness CA, Inverness CA, United States

One of the most widely used techniques to determine population and demographic information is the mark-recapture method. Non-invasive techniques to identify and mark individuals of rare species provide an easier method to collect these data with minimal impact to the animals. The behavior of the white shark, Carcharodon carcharias, and identifying markings on the trailing edge of the dorsal fin permit individual identification via high-resolution photographs. These photographs can be obtained either above or below water allowing greater probability of identification than other body markings. Here we used fin photographs from a 20 year study period in central California to validate the use of these markings as an individual identifier while comparing the accuracy of manual and computer-assisted identification methods. Manual identification required a reader to visually compare and match all known fins within the database, whereas computer-assisted techniques utilized DARWIN, a program developed to identify dolphin fins, to match the photographs. Results from the two methods were tested against the true matches determined from known secondary traits.

 

Patricia Charvet-Almeida1, Ana Julia Silva2, Mauricio Almeida1, Anderson Viana3, Ana Luisa Albernaz1

Diet of the Freshwater Stingray Potamotrygon motoro (Potamotrygonidae) in the Brazilian Amazon River Channel

1Museu Paraense Emilio Goeldi, Belem, Para, Brazil, 2EMATER, Vigia de Nazare, Para, Brazil, 3Universidade Federal do Para, Belem, Para, Brazil

Potamotrygon motoro is a widely distributed species in the Brazilian Amazon Basin. It is polychromatic and valued in the international ornamental trade. This study is a contribution to the feeding biology of this species in the Solimoes / Amazonas River channel. The samples (n = 50) were obtained throughout the Brazilian portion of the Solimoes / Amazonas River, in 2003. Specimens were subject to anesthesia and sacrificed. Stomachs were removed, fixed in formaldehyde solution (10%), preserved in ethanol (70%) and then had its content analyzed in the laboratory. Percentage of Frequency of Occurrence (% FO), Weight (% W), Number (% N) and Index of Relative Importance (IRI and %IRI) were calculated for each food item. Digestion and repletion levels were observed too. Results indicated that these stingrays in the 93 study area feed mainly on bony fish (Siluriformes and Peciformes), crustaceans (Decapoda, Palaemonidae), gastropods (Gastropoda) and insects (Isopoda). Fragments of plant tissue were observed among stomach contents. Repletion level showed that most (59%) stomachs had little content. Digestion level observation indicated that most items (62%) were highly digested (fragments only). Conclusively, P. motoro can be considered a piscivorous species that also includes other food items on its diet but on lower proportions.

 

Tim Clark1, Keller Laros2

Sixteen Years of Photo-Identification of Hawaiian Manta Rays (Manta

birostris)


1University of Hawaii, Honolulu, Hawaii, United States, 2Manta Pacific Research Foundation, Kailua-Kona, Hawaii, United States

Manta rays (Manta birostris) have been a tourist attraction in Kona, Hawaii for over 25 years, where over 11,000 divers per year observe manta rays feeding at night. However, little is known about their basic biology. Data has been collected from dive instructors on the presence of individual manta rays at two dive sites along the Kona coast in order to investigate their life history, population structure, and site fidelity. One hundred and thirty five individuals have been identified in Kona since 1992. Manta rays in Kona appear to have a high site fidelity to certain feeding areas, long life, and low reproduction.

 

Elizabeth Cuevas-Zimbrón1, Oscar Sosa-Nishizaki1, John O’Sullivan2

Preliminary Study on the Age and Growth of the Spinetail Mobula, Mobula japanica, (Müller and Henle, 1941), with Comments on its Vertebral Column Structure

1CICESE, Ensenada, B.C., Mexico, 2Monterey Bay Aquarium, California, United States

This study provides the first information on the age and growth of any species of the Mobula genus, and contributes to the knowledge of the life history of Mobula japanica. We analyzed 55 longitudinal vertebral sections from organism caught in southern Gulf of California. Disc width (organism’s size, DW) ranged between 1095 mm to 2400 mm. Using dissection and radiographic analysis of the vertebral column, we found that vertebrae only appeared at the posterior region, being the most adequate for age determinations the vertebras below the dorsal fin. We found a significant linear relationship between disc width and vertebral size (radium), suggesting a proportional growth. In order to enhance the growth bands in the vertebrae, a modification of the Violet Crystal staining technique was used. The average percent error (APE) and the percent of agreement (PA) between readers were high. The oldest observed age was 14 bands (female with 2300 mm DW), while the youngest was 1 band (female with 1210 mm and a male of 1390 DW size). The preliminary von Bertalanffy growth equation estimated was DWt = 2338.07 (1 – e –0.2771 (t – 1.676)).

 

Tobey Curtis

Management of Skate Fisheries off the Northeastern United States


National Marine Fisheries Service, Gloucester, MA, United States

A number of skate species (Family Rajidae) are widely distributed across the continental shelf off the northeastern United States, and are subject to fishing mortality in the region’s extensive commercial fisheries. Historically, skates were commonly caught as bycatch in trawl and dredge fisheries targeting other, more valuable species, such as cod, flounder, monkfish, and sea scallops. Catches were largely discarded. In recent years, however, the value of skate products has increased in domestic and foreign markets, resulting in increases in landings and the emergence of localized targeted fisheries. In response, the New England Fishery Management Council (Council) drafted the Northeast Skate Complex Fishery Management Plan (FMP) that was implemented by the National Marine Fisheries Service (NMFS) in 2003. The FMP included management measures for seven skate species: winter (Leucoraja ocellata), barndoor (Dipturus laevis), thorny (Amblyraja radiata), smooth (Malacoraja senta), little (Leucoraja erinacea), clearnose (Raja eglanteria), and rosette (Leucoraja garmani). Among its measures, the FMP included establishment of an open access Federal permit to possess skates, biological reference points for determining stock status, prohibitions on possession of overfished skates (barndoor, thorny, and smooth skates), possession limits for the skate wing fishery, and an exemption program for vessels targeting small skates for bait markets. In 2007, NMFS declared that winter skate had become overfished, triggering the need to initiate Amendment 3 to the FMP, which would establish a stock rebuilding program for winter skate, and contribute to the rebuilding of other overfished skate stocks. The amendment is currently under development by the Council, but progress has been hampered by a lack of data on skate biology, population dynamics, and species- specific trends in fishing mortality.

 

Brad Daw1, Frazer McGregor2

Management of Manta Ray (M.birostris) Interactive Tours in the Shallow Lagoonal Waters of Ningaloo Reef, Western Australia – A Global Benchmark for Tourism Interactions

1Department of Environment and Conservation, Exmouth, Western Australia, Australia, 2Murdoch University, Perth, Western Australia, Australia

A comprehensive ‘Code of Conduct’ for manta ray interactions is being implemented at Ningaloo Reef Western Australia to reduce unnecessary pressures upon manta rays and ensure the long term, year-round sustainability of eco-tourism. In the shallow lagoonal waters of Bateman Bay, interactive snorkelling tours to swim with manta rays have become so popular that they take more people per annum than those targeting the iconic whale shark. Commercial operators use light planes to locate manta rays within the <50km2 bay, where they can be observed year-round targeting specific food items, mating and giving birth. Current pressure is significant and potential for further increases in pressure is high. The tourism industry is concerned with current pressures and there have been several incidents where mantas have physically rammed or breached upon swimmers. In response to this, the WA Department of Environment and Conservation with community consultation has formulated a ‘Code of Conduct’ for manta ray interactions. This follows on from the highly successful Western Australian Closed Season Notice for Whale Sharks (CSNWS), (a legal mechanism to control interaction activities) which has become a global benchmark. The ‘code of conduct’ for manta ray interactions includes conditions similar to the CSNWS such as minimum distances, time limits, and controls of total passenger and in water numbers. It also has specific clauses to protect ‘cleaning stations’ and mating aggregations. It is hoped that implementation of this code for manta rays will ensure a sustainable in-water viewing industry and allow manta rays to continue visiting important habitats (such as Bateman Bay in the Ningaloo Reef Marine Park) with minimal interference.

 

Moeava de Rosemont

Observation and Sighting Description of the Manta Birostris, in BoraBora Island (French Polynesia – South Pacific)

NOAA, California, United States

Manta Birostris are permanent resident inside BoraBora's lagoon. In order to know more about its population, an ID program and a sighting survey have been monitored since August 2002 till June 2005. The method: each dive has been done with a digital video equipment to record mantas behaviour. Then the footages are played to identify (when it is possible) the black belly pattern of each individual. Each new manta sighted has its own file and every interesting behaviour is archived on tape. In June 2005, we did formally identified 43 females and 42 males. With this empiric method and recurrent sightings, we discovered that there was a resident colony inside the lagoon, and some mantas cruising the lagoon occasionally, mostly during the mating season. In the same time, as we could regularly sight the same individuals, we could deduce that the pregnancy time does not exceed 12 months. Other basic biology have been monitored as the growth of a new born manta ray, the healing process (when wounded) and the question of the albinos individuals. Some interrogations have occurred as the presence and use of pheromone mostly during the mating process. Since June 2005, the Mantas have disappeared from the place they used to clean, and the survey has been interrupted. Hotels constructions nearby and tourism activities are probably one explanation. Fortunately, they came back since July 2007 and we hope that we will be able to assist again to the manta's mating dances for the next season.

 

Mark Deakos

Using Paired-Laser Photogrammetry for Measuring Manta Ray (Manta birostris) Sizes. Are Maui’s Mantas Horizontally Challenged?

1The Hawaii Association for Marine Education and Research, Inc, Lahaina, Hawaii, United States, 2University of Hawaii, Manoa, Hawaii, United States

Paired-laser photogrammetry was used to measure the disc width (DW) of 78 manta rays (Manta birostris) from a nearshore Maui population. The mean ratio of DW to disc length (DL) for 43 of these individuals was 2.30 (N=43, SD=0.10). The mean ratio for mature males (determined by the claspers extending beyond the pelvic fins) was not significantly different than that for immature males (t (14)=0.59, p=0.56) indicating that the DW to DL proportion remains constant throughout development. DL measurements were more reliable and more easily obtained than DW measurements using paired-laser photogrammetry. Given this, DL measurements were used and converted to the more conventional DW measurement equivalent using the ratio of 2.30. Female DW ranged from 2.42 m to 3.70 m (mean=3.22 m, N=40). The maximum female DW in this population is 25% smaller than the maximum reported for a female in Indonesia (White et al., 2006), and as much as 59% smaller than that reported in other parts of the world (Last & Stevens, 1994). Male DW ranged from 1.98 m to 3.18 m (mean=2.80 m, N=33). The maximum male DW in this population is 22% smaller than the maximum DW reported for a male in Indonesia (White et al., 2006). Males were sexually mature at a DW greater than 2.79 m, (N=20), 26% smaller than what has been reported for males in Indonesia. These results support paired-laser photogrammetry as a non-invasive and precise method for sizing manta rays in the field and suggest that manta rays in Maui mature and grow to a much smaller body size than what is observed in Indonesia and other populations worldwide.

 

Gabriela Delpiani1, Ezequiel Mabragaña2, Daniel Figueroa1

Dentition of the Southern Thorny Skate, Amblyraja doellojuradoi (Pozzi, 1935): Qualitative Analysis and Anomalies

1Universidad Nacional de Mar del Plata, Mar del Plata, Buenos Aires, Argentina, 2Museo del Mar, Mar del Plata, Buenos Aires, Argentina

Dentition analysis of cartilaginous fishes is an important tool for determining species, establishing phylogenetic relationships between extinct and living taxa, and describing ontogenetic morphological changes. This work constitutes the first description of Amblyraja doellojuradoi`s dentition. The jaws (n = 72) were extracted, cleaned and prepared with two different treatments. Some of them were dried and whitened with 30% diluted hydrogen peroxide; while the tooth plates of others were taken and pasted on a vegetal paper. In the Southern thorny skate the dentition was gradient monognathic heterodonty. In the upper jaw, the symphysial teeth and approximately the two rows on both sides of them have low cusps, but their size increases in lateral teeth and reduce again in the commissural teeth. In the lower jaw, the cusps from the symphysial teeth are larger and arched, reducing their size to the commissural teeth. A. doellojuradoi presented ontogenetic heterodonty, having the juvenils cusps with little development, while adults have too much developed and sharp-pointed cusps. This ontogenetic change was manifest both in males and females, although in the first one was more conspicuous. Two kind of anomalies were observed in some specimens: (1). an additional incomplete row between two complete rows, and (2) an increasing tooth base size and division of their cusp until the tooth divided completely in the same row. Gradient monognathic heterodonty as well as ontogenetic heterodonty is common in skates ́ dentition. Indistinct sexual heterodonty observed in A. doellojuradoi was also recorded in A. radiata and Dipturus batis whereas other species exhibit marked sexual heterodonty or absence of heterodonty. Regarding anomalies in tooth arrangement, this is the first record of that kind of malformation in skates ́ dentition.

 

Juleen Dickson2, Anabela Maia1, Paolo Domenici3

Three Dimensional Escape Response in the White-spotted Ratfish,

Hydrolagus colliei

1University of Rhode Island, Kingston, RI, United States, 2California State Univeristy Fullerton, Fullerton, CA, United States, 3CNR IAMC, Torregrande, Italy

Escape responses are vital to the survival of prey during predator-prey interactions. This study documented the kinematics of the escape responses of white spotted ratfish, Hydrolagus colliei (Chimaeriformes). Three H. colliei (345-460 mm TL) were trawled off the coast of San Juan Island, WA and housed in flow through aquaria at the University of Washington, Friday Harbor Laboratories. Seven escape responses were elicited with a forceful tap on the caudal region and recorded using a high speed camera at 250 fps. The video sequences were digitized for both lateral and dorsal views, obtained simultaneously from a mirror suspended at a 45° angle above the tank. Video analysis was based on displacement of center of mass, calculated from straightened frozen specimens. Escape responses generally included a large vertical excursion which corresponded to 77 ± 14% (mean ± SEM) of the horizontal displacement. Large vertical excursions in escape locomotion are relatively unusual in fish, although they have has been observed in previous work (e.g. hatchet fish, Carnegiella strigata, and knifefish, Xenomystus nigri). The potential advantages of this type of response may lie in eluding predators that have little vertical maneuverability. The average latency time to response was about 200 ms (108- 332 ms), which is higher than the latency values commonly observed in teleosts (10-50 ms). This was unexpected, since ratfish are the only chondrichthyans whose adults are known to have Mauthner cells, the giant neurons largely responsible for the fast response time. The average head turning rate during stage 1 was 1515 ± 548 deg. s-1, which is in line with results on other fish. Maximum acceleration was 75.3 ± 19 m s-2 and maximum speed was 3.01 ± 0.45 m s-1. Overall, locomotor performance appears to be higher than that observed in the only other chondrichthyan species studied (Squalus acanthias).

 

Wallice Duncan1, Marise Sakuragui2, Cleverson Ramos2, Tayrine Benze2, Oscar Costa1, Marisa Fernandes2

Functional Morphology of the Gills of Amazonian Freshwater Stingrays (Elasmobranchii: Potamotrygonidae)

1Federal University of Amazonas, Manaus/Amazonas, Brazil, 2Federal University of Sao Carlos, Sao Carlos/Sao Paulo, Brazil

The aim of this study was to describe the epithelial morphology of gills in potamotrygonid species. The Na+/K+-ATPAse-rich cells are numerous on the filament epithelium, but they may also appear relatively abundant on the lamellae of the gills of Potamotrygon schroederi. In addition, a multicellular complex of chloride cells is usually found on the afferent edge of the gill filament of Potamotrygon sp. (a new species). Interestingly, these two species are endemic of acidic and ion-poor blackwater of the Rio Negro (Central Amazon Basin). The gill morphology of those species differs in some aspects from the others potamotrygonid (Paratrygon aiereba, Potamotrygon motoro, P. aff. orbignyi, P. scobina and P. orbignyi). In all potamotrygonid rays, the mitochondria-rich cells (MRC) lacks the tortuous basolateral tubular system, instead does have moderate infoldings. In addition, they apical membrane is characterized by dense microvilli with intra- and interspecific variation. In contrast to MRC, the pavement cells (PVC) cover almost all gill epithelial. The apical membrane of PVC is characterized by the presence of microvilli or microridges which differ between species. The most conspicuous features of the PVCs are the presence of subapical secretory vesicules that contains mucous PAS-positive. The gill arch epithelium also has numerous large glandular mucous cells which are strongly PAS-stained. These morphological features probably allowed to the Potamotrygonidae family evolve their freshwater tolerance from marine incursion during the Early Miocene. Financial support: FAPEAM.

 

Colombo Estupiñan-Montaño1, Luis G. Cedeño-Figueroa1, Felipe Galvan-Magaña2

Feeding Habits Of The Scalloped Hammerhead Sphyrna lewini, in Ecuadorian Pacific

1Universidad Laica “Eloy Alfaro” de Manabí (ULEAM), Manta, Manabi, Ecuador, 2Centro Interdisciplinario de Ciencias Marinas, La Paz, Baja California Sur, Mexico

The research on biology of Scalloped hammerhead Sphyrna lewini in Ecuador are scarce. To know more on this worlwide shark we review 116 stomach contents from sharks caught in the ecuadorian Pacific and unloaded in Manta, Ecuador from January to December 2004. This shark is caught yearround with the higher catches from January to June. The Scalloped hammerhead feed on cephalopods, fishes and crustaceans. Using the Index of Relative importance (IRI), we found that the cephalopods Histioteuthis spp (22.7%) and Dosidicus gigas (21.9%) were the main prey, following by the fishes Merluccius gayi (6.5%) and Anchoa spp. (4.3%). S. lewini is an oceanic predator because predate more on oceanic cephalopods from the families Histioteuthidae and Ommastrephidae; however also consume fishes from the benthic zone as Merluccius gayi.

 

Michelle Evans, Daniel Abel, Sam Gary, Damien Wilkinson

Demographics and Habitat Partitioning of Elasmobranchs in Port Royal Sound, South Carolina: Preliminary Results

Coastal Carolina University, Conway, SC, United States

A longline and rod-and-reel survey for elasmobranchs was conducted in Port Royal Sound, a south-eastern South Carolina deep water embayment, from June – August 2007. This long-term project has four main objectives: (1) to determine which species of elasmobranchs are utilizing Port Royal Sound as habitat, (2) to determine if species partition themselves spatially, temporally, by sex and/or size, (3) to determine if Port Royal Sound is a nursery ground for elasmobranchs, and (4) to determine if species assemblages are unique by comparing results with previous studies in South Carolina. Three generalized areas were sampled regularly along with episodic wild card sites. Twenty adult lines (16/0 hooks) and twenty pup lines (12/0 hooks), baited with Boston mackerel were bottom-set concurrently during slack tides throughout the summer. Elasmobranchs were identified, measured, tagged (only sharks) and released. We caught 174 elasmobranchs (n = 61 on long-lines, 113 on rod-and-reel) comprising ten species: Rhizoprionodon terranovae (n = 129), Carcarhinus limbatus (17), Dasyatis sabina (12), C. acronotus (4), C. plumbeus (4), D. americana (3), C. isodon (2), Galeocerdo cuvier (1), Sphyrna lewini (1), and S. tiburo (1). Most individuals captured were young-of-year or immature. Catch per unit effort (CPUE, #sharks.100 hooks.-1 h-1) for adult and pup lines was 2.7 ± 0.63 (x ± SE) and 12.1 ± 1.83 (x ± SE), respectively, for all areas. Port Royal Sound or nearby areas may represent Essential Fish Habitat for a number of species of sharks and rays. Next sampling season we are expanding the effort and we will investigate habitat partitioning. This is the first large-scale comprehensive survey for elasmobranchs in Port Royal Sound.

 

Vicente Faria1, Bruno Jucá-Queiroz2, Jones Santander-Neto2, Manuel Furtado-Neto2

Elasmobranch Fisheries off Northeastern Brazil, Western Equatorial Atlantic

1Instituto de Ciências do Mar, Universidade Federal do Ceará, Fortaleza, CE, Brazil, 2Departamento de Engenharia de Pesca, Universidade Federal do Ceará, Fortaleza, CE, Brazil

The conservation status of elasmobranchs is of worldwide concern since examples of rapid population declines caused by fisheries pressure have become commonplace. In Northeastern Brazil, interest in elasmobranch products has grown in the recent years, due to the increased value of shark fins and batoid sub-products. The goal of the present study was to provide preliminary data on both the identity and the quantity of elasmobranchs captured off Northeastern Brazil. Captures were recorded during industrial and small-scale fisheries landings in Fortaleza, CE. The industrial fisheries employing longlines ranged from 25 to 168 m in depth on the continental 149 slope off Northeastern Brazil (1°00’S, 9°00’S). Twenty-one landings were monitored between November 2004 and November 2006. Overall, 1873 dressed shark carcasses were landed, including Carcharhinus spp. (n=661), Ginglymostoma cirratum (n=582), and Carcharhinus acronotus (n=445). 674 batoid carcasses were landed, primarily Dasyatis spp. (n=656). Small-scale fisheries, employing hook and line, and gillnets ranged from 10 to 100 m in depth on the continental shelf off Ceará State coast (03°23’S, 38°05’W; 03°25’S, 038°48’W). Landings were monitored weekly from September 2006 to March 2008. A total of 795 sharks were landed, including Rhizoprionodon spp. (n=427), Ginglymostoma cirratum (n=124), and C. limbatus (n=95). 1227 batoids were recorded, including Dasyatis americana (n=1073), and D. guttata (n=115). Results will be presented and discussed in light of shark fisheries monitoring and management.

 

Jasmine Fraurer, Shaara Ainsley, Dave Ebert, Gregor Cailliet

Preliminary Results on the Life History of Four Bering Sea Skate Species, Genera Bathyraja and Rhinoraja

Moss Landing Marine Laboratories, Moss Landing, CA, United States

The eastern Bering Sea is an area of high skate abundance and diversity. Relative to their abundance, however, little is known about the basic life history traits for most of the skate species living there. Researchers from the Pacific Shark Research Center at Moss Landing Marine Laboratories are continuing their efforts to collect, analyze, and synthesize important life history information, including age, growth, and reproduction, of various chondrichthyans and other fishes, to be used for fisheries management. The four species in the current study include the commander skate, Bathyraja lindbergi, whiteblotched skate, Bathyraja maculata, whitebrow skate, Bathyraja minispinosa, and mud skate, Rhinoraja taranetzi. Samples have been, and will continue to be, collected during NOAA Fisheries survey cruises in the eastern Bering Sea and through the observer program. At this time, more than 230 B. lindbergi, 170 B. maculata, 215 B. minispinosa and 145 R. taranetzi have been collected. Vertebrae, caudal thorns, and reproductive organs from each species will be used to estimate age and maturity. Preliminary estimates of total length at 50% maturity are: B. lindbergi females 77.9 cm and 84.2 cm for males, B. maculata females 96.0 cm and 98.0 cm for males, B. minispinosa females 66.38 cm and 68.85 cm for males, and R. taranetzi females 61.4 cm and 57.9 cm for males.

 

Carlos Polo-Silva, Felipe Galván-Magaña, Angélica Barrera-García

Trophic Ecology of Thresher Sharks A. pelagicus Nakamura 1935 and

Alopias superciliosus (Lowe, 1839) in Ecuadorian Pacific


Centro Interdisciplinario de Ciencias Marinas, La Paz, B.C.S., Mexico

The thresher sharks Alopias pelagicus and Alopias superciliosus are species found in oceanic waters of tropical and subtropical seas. There is few biological information on trophic studies of these sharks worldwide. In Ecuador both species were the 37% of the total shark capture in Manta, Ecuador. Our objective is to know the ontogeny changes in the feeding habits in both thresher sharks in the Ecuadorian Pacific from an analysis of stomach contents and isotopic analysis (δ13C and δ15N) in vertebrae. The stomach contents of 233 thresher sharks were analyzed, which 111 correspond to A. pelagicus and 122 to A. superciliosus. The individuals of each species were separated by sex and maturity stages (mature and immature). Finding 24 preys in A. pelagicus and 27 in A. superciliosus. According to the relative importance index (IIR), the main prey of A. pelagicus were Dosidicus gigas (IIR= 33 %) Benthosema panamense (IIR= 15 %) and Sthenoteuthis oualaniensis (IIR= 1.5 %) keeping the same preys by sex and mature stage. Whereas for A. superciliosus the main prey were: Larimus argenteus (IIR = 58.4%), Merluccius gayi (IIR= 13.0%), D. gigas (IIR = 11.0%) and B. panamense (IIR = 9.3%). We found few differences between sex and stage mature in the A. superciliosus diet. According to isotopic analysis, the mean values of δ13C and δ15N in vertebrae of A. pelagicus were: -16.7 ± 0.38 (δ13C) and 9,4 ± 034 (δ15N); whereas in A. superciliosus was -16,7 ± 0,54 (δ13C) and 10.1 ± 0.33 (δ15N). Using the Levin index, A. pelagicus like A. superciliosus were specialist predators, where A. pelagicus had more affinity to feed in oceanic areas; while A. superciliosus feed more on coastal and oceanic areas. This data on trophic habitat was corroborated with the isotopic values of δ13C.

 

Ana Bricia Guzmán Castellanos, Ana María Torres Huerta, José Alberto Montoya Márquez

Morphological Variation in the Dwarf Round Ray Urotrygon nana (Miyake & McEachran, 1988) from the Gulf of Tehuantepec, Mexico

1Instituto Politecnico Nacional, Oaxaca, Oax., Mexico, 2Universidad del Mar, Oaxaca, Oax., Pto.Ángel, Mexico

In order to describe morphologic variation in the dwarf round ray Urotrygon nana we examined 468 individuals from the shrimp trawl fishery of the Gulf of Tehuantepec. We determined the sex and state of maturity, and 9 morphometrics measures: total length (TL), disc length (DL), disc width (DW), preorbital length (POL), interorbital distance (IOD), preoral length (PoralL), internasal distance (IND), tale length (LC) y mouth length (LB) for each sampled individual. The number and total length of embryos was determined for pregnant females. Factor analysis was used to identify the meristics responsible for variation in body shape. Additionally three statistical models were tested to analyze for allometry in morphometrics relationships; the potential model produced the best fit in the majority of cases (R2 greater value). Discriminant analysis was used to identify sexual dimorphism in adults. Females ranged between 8.2 and 37.6 cm TL, and males between 8.0 and 29 cm TL. The shape of the dwarf round ray is determined by three dimensions (factors, 70% of the total percentage of the explained variance) related to disk (24.8%), eye- mouth-nose region (50.9%) and mouth width (69.8%). Most morphometric relationships showed negative allometry significant. Urotrygon nana presents sexual dimorphism in total length (λp= 0.620), disc width (λp= 0.598), internasal distance (λp= 0.592), interorbital distance (λp=0.579), preoral length (λp= 0.578) and dentition morphology. Females have molariform teeth, but neonate and young males present cuspidate teeth and adult males acute cuspidate teeth.

 

Blake Harahush1, Kathryn Green2, Rick Webb2, Shaun Collin1

Assessing the Ultrastructure of the Elasmobranch Retina: The Application of Microwave and High Pressure Freezing Techniques

1School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia, 2Centre for Microscopy and Microanalysis, University of Queensland, Brisbane, Queensland, Australia

Numerous studies have examined the ultrastructure of the vertebrate retina. However, few have examined the retina in elasmobranchs, an ancient group that has existed for more than 400 million years. In order to trace the evolution of the vertebrate retina and optimise the ultrastructural detail that has been lacking in previous studies, we examined the retina of the brown banded bamboo shark (Chiloscyllium punctatum) using a range of techniques including standard chemical fixation (CF), microwave chemical fixation (MCF) and high pressure freezing (HPF, using either a Leica EM PACT2 or a Bal-Tec HPM 010). Following anaesthesia with MS222 (1:2,000 in sea water), the eye was enucleated and retinal tissue was immediately extracted. For HPF, retinal samples were rapidly processed in hexadecene, elasmobranch Ringer, DMEM (Dulbecco’s Modified Eagle’s Medium) Ringer, or with no preincubation, with and without prior oxygenation. HPF samples were freeze substituted with 2% OsO4 + 0.5% uranyl acetate in 100% acetone (dry). CF and MCF fixed samples were fixed in Karnovsky’s fixative and post-fixed with 1% OsO4. The quality of the retinal ultrastructure after the various fixation processes was assessed based on the integrity of cellular organelles, membrane contrast and fixation artefacts (if present). The ultrastructural definition of cone photoreceptors was of particular interest, since traditional histological processing has previously revealed substandard morphology. Various trials resulted in the elasmobranch Ringer being the most effective with or without oxygenation. MCF and HPF using the Leica EM PACT2 proved to be the most effective techniques for revealing superior ultrastructure. Membrane contrast was best using HPF, and mitochondria with visible cristae and Golgi complexes were clearly discernible using only this technique. MCF using DMEM Ringer resulted in large gaps in the tissue and very low membrane contrast. The Bal-Tech HPF technique and HPF with no ringer proved to be ineffective methods.

 

Fabio Hazin1, Teodoro Vaske1, Paulo Oliveira1, Bruno Macena1, Felipe Carvalho2, George Burgess2

Ecological Aspects of the Whale Shark (Rhincodon typus) at Saint Peter and Saint Paul Archipelago, Brazil

1Universidade Federal Rural de Pernambuco, Recife, Pernambuco/Northeast, Brazil, 2University of Florida, Gainesville, Florida/Southeast, United States

The first record of a whale shark in Brazilian waters was in the coast of Bahia State in 1921. Since then, additional sightings have been reported along the Brazilian coast, but knowledge on the species biology and ecology in the region has remained poor. Whale sharks are most frequent observed at the Saint Peter and Saint Paul Archipelago (SPSPA), a small group of rocky islands located on the mid-Atlantic Ridge, just north of the Equator. In July 1998, the Brazilian Navy established a scientific research station in the Archipelago, which allowed researchers to remain in the area for more extended periods and enabled the study of local whale sharks. After compiling all existing data on the whale sharks recorded in the SPSPA, we proceeded to observe locations of occurrence, estimated the lengths of those sharks, analyzed the trends in occurrence over the last nine years, and investigated possible ecological factors that might influence their distribution and seasonal occurrence. Sharks ranged in total length from 2.0-14.0 m and sightings were most common from January to March. The higher density of whale sharks in the Archipelago during this time period appears to be associated with an increase in the abundance of eggs and larvae of flying fish (Exocoetidae), which spawns in the area at this time of year.

 

Fiona Hogan1, Steve Cadrin2, Ken Oliveira3

Age Validation of Little Skate and Winter Skate Using Tetracycline Marking at both Egg and Adult Stages

1University of Massachusetts School for Marine Science, Dartmouth, Massachusetts, United States, 2NOAA/UMass Cooperative Marine Education and Research Program, Dartmouth, Massachusetts, United States, 3University of Massachusetts Dartmouth, Department of Biology, Dartmouth, Massachusetts, United States

The northeastern American skate complex is a data poor fishery resource. For example, age data are not available for all skate species in all areas. As part of an age validation study on multiple skate species, individuals were treated with tetracycline at egg and adult life stages. The main focus of this study is to validate the periodicity of vertebral bands in adult specimens that were given an intraperitoneal injection of tetracycline. Adult little and winter skates are currently being maintained in a seawater laboratory facility for a minimum of one year. Subsamples were sacrificed early and mid-way through the experiment to confirm that incorporation of tetracycline into the vertebrae occurred in each treated species. As part of a preliminary study attempting to validate the formation of the birthmark, egg cases of little and winter skates were injected with tetracycline. The birthmark is often defined as the change in angle of the corpus calcareum, but is not consistently formed. Alternatively, defining the birthmark as the first visible band in the centrum may underestimate the true age. Two trials of injections were conducted: (a) tetracycline directly injected into the yolk-sac; and (b) tetracycline injected into the cavity of the egg case. After each treatment, egg cases were maintained at ambient water temperatures in separate tanks. Newly hatched individuals will be immersed in an alizarin complexone waterbath, in an attempt to mark the hatch mark. Successfully hatched skates will be maintained for various time periods to determine if the tetracycline was incorporated in the notochord. If this treatment is successful, it may be applied to other skate species in the complex to validate age determination.

 

Robert Morgan, Luz Patricia Hernandez

Distribution of Muscle Fiber Types within Chondrichthyan Muscles

George Washington University, Washington, DC, United States

Vertebrate morphologists have long appreciated the importance of muscle fiber type composition. Although they vary widely in their size and distribution, different isoforms of slow and fast myosins comprise the bulk of all skeletal muscle tissue. Combined, these different myosins coordinate to perform a variety of important functions associated with locomotion, feeding and breathing. Evolutionarily, amniotes and anamniotes have shown a remarkable disparity in muscle fiber type distribution. In amniotes and adult amphibians muscle fibers show a mosaic distribution with interspersed slow and fast fibers. In fishes, as well as in larval amphibians, muscle fibers show a zoned distribution whereby specific fiber types group together within muscles. Here we describe the distribution and relative proportion of fast and slow fibers in adult shark and skate muscles. Muscles were stained for a variety of specific myosins using standard immunohistochemical methods. Antibodies considered to stain all vertebrate myosins (based on data from a large number of amniotes and anamniotes) did not recognize myosins within many irregularly shaped muscle fibers in skate. While our results do not indicate the mosaic pattern seen in amniotes, they also do not fully support the strictly zoned fast and slow regions seen in most anamniotes. Antibodies against slow myosin stained the peripheries of certain larger muscle fibers, but stained entire smaller diameter fibers in other muscles as seen in anamniotes. Thus skate muscles may be comprised of a number of intermediate fiber types and consist of a unique pattern of distribution. It is likely that a range of intermediate muscle fiber types may be an ancestral character. We discuss the functional, evolutionary, and developmental implications of our data.

 

Lisa Hollensead1, Dana M. Bethea1, Mark Grace2, Ken Siprell1

NOAA Southeast Fisheries Science Center Elasmobranch Tagging Management System: One Database to Bind Them All

1SEFSC NOAA Fisheries Panama City Laboratory, Panama City, FL, United States, 2SEFSC NOAA Fisheries Mississippi Laboratories, Pascagoula, MS, United States

The Panama City Laboratory and Mississippi Laboratories of the NOAA Southeast Fisheries Science Center (SEFSC) and our collaborators have tagged over eleven- thousand elasmobranchs in the Gulf of Mexico and southeast Atlantic Ocean since 1996. Elasmobranchs are tagged with dart-like or loop tags inshore through the GULFSPAN program, offshore via fishery-independent surveys on NOAA research vessels, and commercial vessels carrying an observer. Elasmobranches are also being tagged with satellite pop-off tags and acoustic tags. Recognizing the need to standardized data collection, we have been developing an elasmobranch tagging management system for the SEFSC. The ultimate goal of the database is to provide managers, researchers, and the public involved in elasmobranch tag and recapture in the Gulf of Mexico and southeast Atlantic Ocean with a system to enter and process elasmobranch tag and recapture data. Capture and recapture data include: date, time, and location (latitude and longitude) of capture, gear type used as well as specific abiotic conditions such as temperature, salinity, dissolved oxygen, and turbidity. We plan to have the database fully searchable for NOAA researchers and collaborators by January 2009 and online for public use January 2010.

 

Natalia Hozbord, Julieta Jañez

Age and Growth Estimates for the Smallnose Fanskate, Sympterygia bonapartii in the South-west Atlantic and Derived from Captive Born

1Instituto Nacional de Investigación y Desarrollo Pesquero, Mar del Plata/ Buenos Aires, Argentina, 2Fundacion Temaiken, Escobar/ Buenos Aires, Argentina

The smallnose fanskate, Sympterygia bonapartii is common endemic skate specie from south-west Atlantic. Although the relative abundant and broad geographical distribution few studies were conducted on biology of the smallnose fanskate. In order to provide insight into the life history of S. bonapartii, age and growth were estimated using vertebral centra from skates captured from research cruises conducted by Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP) in Uruguay and north Argentina coastal waters (34°-42°S). As well, the reproductive success of smallnose skate at Temaiken aquarium provided an opportunity to obtained data on growth between 0-2 years under constant temperature (16.4-18.2°C) and fed daily. Both captive and wild size at age data were fitted to Gompertz growth model. Vertebral age estimates ranged from 0- 12 years for females and 0- 8 years for males. Age at 50 % maturity estimated to be 7.03 years (63.5 cm TL) for females and 8.51 years (62.3 cm TL) for males. From the 25 born in captive skates measured monthly, the parameters estimated for females and males were L =83.90 cm, k =1.00 cm year-1 and L =72.78 cm, k =1.08 cm year-1, respectively. Female size at maturity was reached at 61 cm Lt (1.78 years), considered at the moment of oviposition. Captive females and males grew an average of 25.44 cm year-1 22.78 cm year-1, respectively. Theoretical longevity was estimated between 14.12- 14.32 years for wild population and 3.28- 3.62 years for captive skates. This study is the first contribution to estimate age and growth for S. bonapartii. This information greatly improves the understanding of smallnose fanskate biology, and will be applicable to the stock assessment and management of this species in Uruguay and north Argentina coastal.

 

David Kacev1, Rebecca Lewison1, Suzanne Kohin2, Andrew J Bohonak1, Louis W Botsford1

Length Based Population Dynamics Analysis of Mako Sharks on the West Coast of North America

1San Diego State University, San Diego, California, United States, 2Southwest Fisheries Science Center, La Jolla, California, United States, 3University of California, Davis, Davis, California, United States

Mako sharks, Isurus oxyrinchus, on the West coast of the Unite States and Baja California are impacted by commercial, recreational, and artisanal fishing pressures. Despite these pressures, little is known about the population sizes and dynamics of makos in this region. This study will endeavour to use genetic analysis to determine population structure of mako sharks in the region. This analysis will involve microsatellite genotyping of samples collected in conjunction with NMFS. We will then use length-based matrix models to determine population growth rates. The parameters for these models will be estimated based on both fisheries dependent and independent data as well as from available literature. We will then run elasticity analyses to determine which parameters have the greatest impacts on the population growth rate. Preliminary model runs suggest that the mako stocks are shrinking (lambda < 1) and that the parameter to which model output is most sensitive is the survivability of large, reproductive sharks.

 

Tom Kashiwagi1, Takashi Ito2, Jennifer Ovenden3, Michael Bennett1

Population Characteristics of Manta birostris Observed in Yaeyama, Okinawa, Japan, 1987-2006

1University of Queensland, St. Lucia, QLD, Australia, 2Marine Service Ito, Kohama Island, Okinawa, Japan, 3Queensland Department of Primary Industries and Fisheries, St. Lucia, QLD, Australia

Encounter-history records and biological observations of manta rays at Yaeyama, Okinawa, Japan have been compiled for over 4500 dives conducted on over 2400 days in the period from 1987 to 2006. A photo-identification methodology based on the unique skin patterns of individual rays was used to identify 303 different manta rays. The disc widths of the smallest free swimming individuals was 0.9m. Maximum disc widths observed were 3.6 m for male and 4.3m for female. The age at first pregnancy appeared to be about ten-years of age, with mature females appearing to give birth on a three or four year cycle. Newborn rays have been observed on many occasions, but preliminary analysis suggests that mortality or emigration from the study site is relatively high over the first three years of life. The longest period between the first and last sighting of a single individual was 27 years, for a female ray identified in 1980 that was still alive at the end of the study. Quantitative analyses indicate that this Japanese manta ray population is either stable or has increased over the study period.

 

Robert D. Rubin, Katherine R. Kumli

Photo-Identification of the Manta Ray, Manta birostris, in the Revillagigedos Islands, Mexico

Santa Rosa Jr. College, Santa Rosa CA, United States

Photographic samples have been obtained for a population of manta rays for the past three decades. Based on differences in color and marking pattern we have established the presence of two forms, referenced here as chevron and black morphs. Chevron and black animals compose 70.2% and 29.8% respectively of the known population and do not differ significantly in either size or sex ratio. Dissimilar individual markings occur in both morphs and do not appear to change over time. The use of a four-point grid matching technique of the ventral surfaces has allowed us to recognize 225 individuals to date. Seventy-one (32.5%) of the animals have been resighted and one individual has been seen 13 times. Three are known for a period of fifteen years. Females represent 55.9% and males 44.1% of the sexed individuals (n= 111). Known populations of manta rays in the Pacific and Indian Oceans appear to lack the black morph. Chevron individuals in these populations show recognizably different markings on both the surfaces which appear to be regionally specific. They are also of smaller body size and seem to reach reproductive maturity at sizes well below those of this population. These differences may suggest ecotypes as a function of differences in food availability or character displacement as well as the absence of gene flow.

 

Peter M. Kyne1, Jeff W. Johnson2, Kathy A. Townsend1, Michael B. Bennett1

Mobula japanica (Müller & Henle, 1841) in Australian Waters

1The University of Queensland, Brisbane, Queensland, Australia, 2The Queensland Museum, Brisbane, Queensland, Australia

The Japanese devil ray Mobula japanica (Müller & Henle, 1841) has a circumtropical distribution in warm temperate and tropical waters of the Atlantic, Pacific and Indian Oceans. It has been documented in Australian waters from only four specimens and two live sightings, all from the east coast (between approx. 15°S and 33°S), in the Southwest and Western Central Pacific zones. The first record is from a specimen collected inshore from the estuarine waters of Lake Macquarie in New South Wales (32°59’S, 151°35’E) in April 1968. The head of this specimen is lodged in the Australian Museum, Sydney. Accompanying photographs show distinguishing characteristics of the species and original collection notes indicate a size of 1880mm disc width (DW). More recent records come from beach-washed specimens in southern Queensland. A 1088mm DW immature male was beach-washed on Eurong Beach, Fraser Island in August 2000; a 2224mm DW mature male was beach-washed on Flinders Beach, North Stradbroke Island in September 2007; and, a ~3100mm DW unsexed individual was beach-washed north of McLaughlan Rocks, Fraser Island in October 2007. Additional live sightings (verified from photographs) have been reported off Southport, southern Queensland and from the northern Great Barrier Reef. Mobulids are not well represented in museum collections due to their large size and irregular capture by most fishing and sampling techniques. The number of recent beach-washed records of M. japanica, together with live sightings, indicates that the species is likely more common than previously documented in the waters of eastern Australia. The family Mobulidae is represented in Australian waters by four species (Manta birostris, Mobula eregoodootenkee, M. japanica and M. thurstoni).

 

Thomas Lisney

The Visual Biology of Holocephalans: A Review


Queen's University, Kingston, Ontario, Canada

The holocephalans (commonly referred to as chimaeroid fishes or ratfish) are an ancient group of fishes commonly found in temperate deepwater habitats of the continental shelves and slopes. In contrast to their close relatives, the elasmobranchs, many aspects of their biology are poorly understood. Holocephalans are generally described as having large eyes and are assumed to rely heavily on vision. However, the visual biology of these animals has received little attention. This study aims to present a review of the available literature alongside new data on relative eye size. The relative size of the eyes and the optic tectum (the part of the brain that receives the majority of sensory input from the eyes) is large, suggesting that holocephalans rely heavily on vision. Holocephalan retinas have been reported to contain rod photoreceptors and a reflective tapetum lucidum, both adaptations for increasing visual sensitivity in low-light levels. The topographic organization of the retinal ganglion cell layer in two species of Hydrolagus has revealed a dorsal horizontal streak of increased cell density, which indicates that viewing the substrate-water interface is important in these fishes. The peak absorbance (lambda max) of rod visual pigments correlates with the photic environment. Species found in deepwater (Chimaera, Hydrolagus) have rod visual pigments with lambda max values around 480nm, whereas the more shallow-dwelling Callorhinchus callorhynchus has a rod visual pigment with a lambda max of 499nm. Similar differences are also seen in relative eye size, with deepwater species having relatively larger eyes than species found in shallower habitats.

 

Andrea Marshall, Michael Bennett

Cleaning Behaviour of a Photographically Identified Population of Manta Rays in Southern Mozambique

University of Queensland, St. Lucia, QLD, Australia

Cleaning behaviour in reef fishes has been studied in detail both in the field and experimentally. Manta rays, Manta birostris, are widely known by SCUBA divers to visit inshore reefs to be cleaned by small host cleaner fish. The areas that they frequent are often referred to as ‘hot spots’ or ‘aggregation sites’. In some locations, these cleaning stations are active year-round, while in other locations the presence of manta rays at inshore reefs is seasonal or erratic. Details of the cleaning behaviour between cleaner hosts and manta ray clients have yet to be reported in the literature in detail. The frequency with which manta rays visit these designated cleaning stations has also not yet been explored. Such valuable information could heavily influence local eco-tourism industries, highlight the need to protect potentially critical habitats, and have implications on the management of manta rays populations worldwide. Our study aimed to gain a preliminary understanding of the habitat usage, in respect to cleaning, of a semi-resident population of manta rays in southern Mozambique. Through the examination of frequently used cleaning stations on inshore reefs we provide rough estimates of both the frequency with which they visit these stations and the total time individuals spend cleaning per day. These estimates offer new insights into how important these sites are to the daily and seasonal activity of these rays. Additionally, having used minimally intrusive photographic and observational techniques over a four-year period, we report on the diversity and behaviour of cleaner fish species specifically associating with manta rays in this region.

 

Luis Mejía-Salazar, Agustín Hernández-Herrera, Felipe Galván-Magaña

Reproductive Biology of the Pacific Sharpnose Shark, Rhizoprionodon longurio (Jordan & Gilbert, 1882), in the Mexican Pacific Ocean

Centro Interdisciplinario de Ciencias Marinas, La Paz, B.C.S, Mexico

The Pacific sharpnose shark, Rhizoprionodon longurio, is a specie of commercial importance in some places of the Mexican Pacific coast with reproductive migrations through this coast. Its distribution goes from Southern California to Perú. Samples were obtained from the fishing camps of Bahía de La Paz, B.C.S., Punta Arenas, B.C.S., Mazatlán, Sin., in the Gulf of California; and Ensenada Chipehua, Salina Cruz, Oax., in the Gulf of Tehuantepec, from March 2004 to September 2006. The reproductive biology of 387 Pacific sharpnose shark was examined. Their total length (TL) ranged from 46 cm to 123 cm. Five new-born of sizes between 36 and 46.5 cm TL were captured incidentally in Bahía de La Paz. The overall sex ratio was 1.18:1 males per female. Ovarian egg diameters and the presence of uterine eggs or developing embryos show that female maturation occurs at about 80 cm TL, while clasper development suggests that males mature at about 82 cm TL. Forty four pregnant females and 24 with uterine eggs were captured, with fecundity between 2 to 10 embryos. The smallest embryos were found during August and new-born during May and September. The gestation period was estimated in 11-12 months. The mating time in Bahía de La Paz apparently occurs from May to August.

 

Sara Melo, Lisandro Vieira, Maria Lúcia Araújo

Paratrygon aiereba (Chondrichthyes: Potamotrygonidae) Fisheries at Purus River, Brazil

1Universidade Federal do Acre, Rio Branco, Acre, Brazil, 2Universidade Federal do Acre, Rio Branco, Acre, Brazil, 3Universidade Federal do Amazonas, Manaus, Amazonas, Brazil

Purus River is an important fishery area in Amazon basin. This river system is responsible for almost 30 % of the fishing production landed in Manaus market. In the last decade the stocks of commercially important teleost fish such as Colossoma macropomum is decreasing and freshwater stingrays species can be observed in the captures. The propose of this work is describe the freshwater stingray fishery at Purus River system, Information was collected from catch landed at local markets from 2006 through 2007. At least three species of potamotrygonid were observed at market: Potamotrygon motoro, P. scobina and Paratrygon aiereba. The latter species is the main target species due to its greater biomass, despite its low abundance. The fishing effort is concentrated on main channels of Purus river, on the preferential habitat of Paratrygon aiereba adult specimens. The fishing activities occur during the reproduction season. The highest captures were obtained at lower Purus because following factors: (i) the proximity of the capture locations to consumer markets; (ii) larger autonomy and load capacity of fishing boats at lower Purus River; (iii) the higher abundance of this species in places around confluence areas among main rivers system in the Amazonian basin. A management plan for Paratrygon aiereba in this area should be considered urgently by regional and national regulatory environmental agency.

 

Eli Michael, Tim Clark, Victoria Newman

Measuring the Size Distribution of Mantas Rays Seen Along the Kona Coast of Hawaii

Manta Pacific Research Foundation, Kailua-Kona, HI, United States

Knowledge of the growth rate of a species is critical for its proper management. We use a system of parallel lasers mounted to an underwater camera to measure the size of manta rays present along the Kona coast of Hawaii. We discuss our measuring techniques and their limitations. Some of the older female rays have disk widths as large as 4.2 meters, while the younger males can be half that size. Knowing approximate birth dates for many of these rays (first sightings of new born pups), the Von Bertalanffy growth function was used to estimate the growth of the population over time. With a high resight rate for these mantas, continued long term observations will allow us to measure explicit growth rates.

 

Craig O'Connell1, Eric Stroud3, Patrick Rice2, Samuel Gruber4

Evaluation of a Magnetic Barrier on Juvenile Negaprion brevirostris: Preliminary Results

1Coastal Carolina University, Conway, SC, United States, 2University of Miami, Miami, FL, United States, 3Seton Hall University, South Orange, NJ, United States, 4Bimini Biological Field Station, Bimini, Bahamas, Bahamas

Nets used to protect human-populated beaches from sharks are a significant contributor to elasmobranch mortalities. Mechanisms that can reduce these types of mortalities are then desirable. Recent evidence suggests that elasmobranches avoid strong magnetic fields. We investigated the behavior of captive juvenile lemon sharks (Negaprion brevirostris) towards a magnetic barrier dividing a pen enclosure. This barrier was constructed along the diameter of the cylindrical pen and contained two 0.25 m2 openings on either end of the fence. The magnetic opening (treatment) was surrounded by four C8 BaFe2O4 permanent magnets which measured approximately 400 Gauss at the surface. The control opening was surrounded by four clay bricks of similar size and shape to the magnetic treatment with no measurable magnetic field. The sharks were encouraged to swim from one side of the pen to the other by introducing fish juice (blood, fish oil, etc.) into the region of the pen opposite the sharks. Results indicated that N. brevirostris detected and were sensitive to the magnetic flux and avoided the magnetic treatment while swimming through the control a greater number of times. The sharks demonstrated greater avoidance behavior (i.e. accelerations away from, 90o or 180o turns) to the region containing permanent magnets when compared to the controls. These data suggest that a selective shark exclusion magnetic barrier, in addition to the shark-nets on human populated beaches, may reduce elasmobranch mortality associated with shark-nets.

 

D. Gigi Ostrow1, Matt Salomon1, Ann Marie Clark1, Jeff Kneebone2, James Sulikowski3, Paul Tsang2

Population Genetic Patterns among Phenotypically Divergent Thorny Skate (Amblyraja radiata) Populations from the Western Gulf of Maine

1University of Florida, Gainesville, Florida, United States, 2University of New Hampshire, Durham, New Hampshire, United States, 3University of New England, Biddeford, Maine, United States

Within the western Gulf of Maine, we have identified two different size groups of the thorny skate, Amblyraja radiata: a larger group of sexually mature skates that has an average total length of 91.5 cm, an average weight of 16.5 lbs, and an average age of 15.1 years, and a smaller group of sexually mature skates that has an average total length of 59 cm, an average weight of 4 lbs, and an average age of 9.4 years. In order to determine whether these two groups are genetically isolated from each other or from populations in Canada that are phenotypically similar to the small Gulf of Maine group, we developed microsatellite loci to examine population genetic structure. The following two hypotheses were investigated: 1) smaller, early- maturing thorny skates are migrating from Canadian waters into the Gulf of Maine, and 2) large and small size groups of sexually mature thorny skates are reproductively isolated and do not belong to a single genetically cohesive species. Preliminary data from 5 microsatellite loci suggest that the two Gulf of Maine groups are not genetically isolated from one another nor is either group distinct from the Canadian skates (FST= 0.013). Data from additional microsatellite loci will be incorporated, and the levels of exchange between the two Gulf of Maine phenotypic groups between the Gulf of Maine and Canada will be reported. (Supported by the New Hampshire Sea Grant Program)

 

Ana Palmeira, Getulio Rincon

Reproductive Aspects of the “Mariquita” Stingray, Dasyatis marianae, of the Northeast Brazil

Conselho Nacional de Pesca e Aquicultura, Brasilia, DF, Brazil

The mariquita stingray, Dasyatis marianae, is a small species with a restricted distribution along the shallow and reef waters of Northeast Brazil. Although this is a regular catch compound of the local artisanal fisheries, only recently it was recognized as a valid species and formally described. As part of a larger program to provide biological information on poorly known batoid fishes under fishery effort, we started to sample specimens from the artisanal fishery of Almofala beach, State of Ceará, Brazil. Seventy seven specimens (22 males and 55 females) were daily sampled from October/2007 to March/2008 and preserved in formalin for laboratorial analysis of reproductive and feeding aspects. Males ranged in size from 148 to 295 mm disc width-DW and females from 140 to 366 mm DW. Females mature at 300 mm DW and males mature between 240-255 mm DW (based on clasper growth). Birth seems to occur when embryos reach 140 mm DW (the smallest free swimming specimen recorded was 140 mm DW and the largest embryo was 150 mm DW). Uterine fecundity was always only one embryo per litter, and ovarian vitellogenesis was concomitant with pregnancy. Only the left ovary and the left uterus develop for reproduction, while the right counterparts remain undeveloped. These reproductive features allied to its high endemism bring concern on the conservation of the species and possible local extinctions where it is presently exploited.

 

Andrew Piercy, Christina Walker

Maternal Influences on Embryonic Condition and the Occurrence of Runts in Viviparous Sharks

Florida Program for Shark Research, Gainesville, FL, United States

Pregnant Sandbar (N=26) and Atlantic sharpnose (N=20) sharks were collected from the north-western Atlantic Ocean and Gulf of Mexico. No significant relationship between litter size and maternal length was detected for either species. Equal numbers of embryos were noted in the right and left uterus of pregnant sandbar sharks. Pregnant Atlantic sharpnose sharks had significantly more embryos in the left than the right uterus. Embryonic lengths and weights were recorded and relative condition values were calculated. Runts were observed in 85% of sandbar and 45% of Atlantic sharpnose shark litters examined. Variation in embryonic relative condition was noted and potential causes were examined. Mean relative condition values of sandbar shark embryos increased over the duration of the gestation period. No relationship between litter size and mean or range of embryonic relative condition values were detected for either species. Mean embryonic relative condition values did not vary significantly with maternal length for either species. No relationship between maternal length and the range of embryonic relative condition values was detected for Atlantic sharpnose sharks. An inverse significant relationship between maternal length and the range of embryonic relative condition values was noted for the sandbar shark. This constriction of the range of relative condition values suggests that larger pregnant sandbar shark may be better able to provide consistent nourishment for all embryos. Embryos with greater relative condition values may exhibit lower natural mortality.

 

Marloes Poortvliet2, Jeanine Olsen2, Donald Croll1, Giacomo Bernardi1, Kelly Newton1

Population Genetics of Devil Rays

1UCSC, Santa Cruz, California, United States, 2RUG, Groningen, Netherlands

The lack of information on devil ray populations precludes the development of a realistic management program. Almost nothing is known about basic aspects of their ecology , population biology , movement patterns, and migration. A vailable information is typically anecdotal or based on dead specimens, providing little insight into the biology of living manta rays. In this light, population genetic studies can provide important information for conservation of a species by helping to define conservation units on the basis of genetic stocks, and provide information on size and direction of migration, mating system and other topics. Using genetic techniques, we will attempt to answer the following questions, focusing on M. japanica and M. munkiana: 1) What is the spatial scale and connectivity of genetically defined populations or stocks of the mobulids M. japanica and M. munkiana; 2) How do indirect estimates of dispersal and connectivity of M. japanica and M. munkiana based on genetic data compare to direct estimates based on tagging data; 3) What insights about the mating system (especially sex biased dispersal) of M. japanica and M. munkiana can be obtained from the genetic data; 4) Parentage analysis of same- size schools of M. munkiana; 5) What are the phylogenetic relationships within the family Mobulidae, and what characteristics (life history or other) are important in the separation of these species? This project is in early stages: currently we are trying to collect samples of both devil rays from locations in the Gulf of California and on the Pacific side of Baja, mainland Mexico, Costa Rica, Panama and Peru; samples of M. japanica will additionally be collected from Hawaii, New Zealand and the Philippines.

 

Jose A. Sanchez-de Ita, Felipe Glavan-Magaña

Age and Growth of the Silky Shark, Carcharhinus falciformis, on the West Coast of Baja California Sur, Mexico

Centro Interdisciplinario de Ciencias Marinas, La Paz, Baja California Sur, Mexico

The age and growth of the silky shark, Carcharhinus falciformis, caught from August 2000 to October 2002 on the west coast of Baja California Sur, Mexico, are described. In total 252 sharks were registered, mainly between June and November. The ages of 145 organisms were estimated using vertebra growth marks. The females were between 88 and 230 cm total length (TL), and the males between 142 and 260 cm TL. The relationship of vertebra radius to TL showed a rectilinear tendency with a coefficient of determination r2 = 0.94, indicating that vertebrae are useful for age estimates and description of growth in this species. It was assumed that growth marks have annual periodicity and that the opaque band is formed during summer and fall. The estimated age for females was between 2 and 16 years, and for males between 3 and 14 years. No significant difference between sexes in size or age was detected. The estimated parameters for the growth model of von Bertalanffy for combined sexes were L = 240 cm TL, k = 0.138 year-1 and t0 = -2.98 years. According to the growth model, the silky shark averages 20 cm growth in the first year of life; 16 cm/year between 2 and 4 years; 10 cm/year from 5 to 7 years; 6 cm/year in the next 4 years and 3 cm/year or less after 11 years of age. It was determined that females and males reach sexual maturity between 7 and 8 years of age.

 

Marcelo Santos, Otávio Oliveira, Akemi Shibuya, Oscar Costa, Maria Lúcia Araújo

Histology of Lateral Line in Embryos of Potamotrygon motoro (Chondrichthyes: Potamotrygonidae)

1UFAM, MANAUS, Brazil, 2INPA, Manaus, Brazil

Potamotrygon motoro is a stingray restrict to freshwater environment. It exhibit benthonic habits, unrelated with morphological findings of neuromast pore channel distribution on the lateral line. The purpose of this study was examined by light and scanning electron microscopy the lateral-line sense organs in the embryos skin of freshwater stingray Potamotrygon motoro in four different stages of embrionary development. The neuromast is composed by a sensory hair cell, surrounded by support cell, mantle cell, and a jelly cupula. Some degenerated sensory cell was presented, and this fact is related with cell turnover. As the animals develop toward later embryo stages, the epidermis surface becomes thickened and the number of neuromasts higher. The neuromast morphology is similar in stage 3 and 4 of embrionary development.

 

Akemi Shibuya1, Sho Tanaka2, Jansen Zuanon3, Maria Lucia Araujo4

Comparative Study of Prey Capture Mechanisms in Freshwater and Marine Stingrays

1Instituto Nacional de Pesquisas da Amazônia, Manaus, Amazonas, Brazil, 2Tokai University, Shimizu, Shizuoka, Japan, 3Instituto Nacional de Pesquisas da Amazônia, Manaus, Amazonas, Brazil, 4Universidade Federal do Amazonas, Manaus, Amazonas, Brazil

The feeding behavior in elasmobranchs has been well documented for shark species; however, the knowledge for batoids still remains scarce. The aim of this study is to provide a comparison of feeding mechanisms between freshwater and marine stingrays under captive conditions. Specimens of Potamotrygon motoro (Potamotrygonidae) and Dasyatis akajei (Dasyatidae) were maintained in two acrylic aquariums. Video recordings were made using two high-speed cameras at 250 field s- 1 positioned at the side and under the aquarium. Twenty-eight video sequences were obtained (13 for P. motoro and 15 for D. akajei). Ram, bite manipulation, suction capture and suction transport composed the feeding behavior of both species; however, each species adopted somewhat distinct feeding tactics. After capturing the prey by suction or jaw protrusion, P. motoro manipulated the prey by expelling and engulfing it two or three times before suction transport. For D. akajei, the feeding behavior included prey capture by jaw protrusion and suction transport, usually without the expelling and suctioning phase. Apparently the manipulation phase occurred only for large preys. Anatomical details (e.g. relative mouth size and oral musculature) may explain the differences observed in prey manipulation by the stingray species.

 

Drayton Smith1, Eileen Grogan1, Richard Lund2

Mineralization of Meckel’s Cartilage in the Shark, Squalus acanthias: Histological Observations and the Role of Mechanical Stress

1Saint Joseph's University, Philadelphia, PA 19131, United States, 2Carnegie Museum of Natural History, Pittsburgh, PA 15213, United States, 3Academy of Natural Sciences, Philadelphia, PA 19103, United States

The chondrichthyan (sharks, skates, rays and chimaeras) skeleton is composed of hyaline cartilage surrounded by peripheral units of mineralization known as tesserae which provide strength while allowing for flexibility. Previous observations of Squalus acanthias skeletal tissue have shown differences in the development and localization of tesserae across a single cartilage element. We hypothesize that mechanical force and the resultant stresses imparted upon the cartilage may be one factor that influences their formation. To test this hypothesis two groups of sharks were fed different diets for 12 – 13 weeks, to impart high versus low stress levels on the jaw cartilage during feeding. The first group was fed whole mackerel to stimulate active bite feeding, which requires greater use of the adductor mandibulae complex for an extended period of time. The second group was fed small pieces of chopped mackerel to promote suction feeding and invoke less adductor mandibulae use. Calcein, a fluorescent marker, was injected intramuscularly at the beginning of the study to trace newly mineralized cartilage. A stress-strain gauge affixed to the Meckel’s cartilage near the insertion of the quadratomandibularis ventral (QMV) muscle was used to measure the magnitude of jaw cartilage stress imparted by muscles during feeding using. Electromyography provided simultaneous quantification of muscle activity. Demineralized and non-demineralized samples of Meckel’s cartilage, individually stained with Alizarin Red S, Verhoeff’s, Villanueva Osteochrome and for ALP/TRAP activity, were evaluated for the structure and distribution of tesserate mineralizations and evidence of cellular activity. Fluorescence microscopy revealed new mineralization in the cap and base of the body using calcein and Alizarin Red S for both treatment groups. Other features of jaw mineralization are presented for sharks subjected to the different feeding regimes. Collective histological observations support previous reports of different mechanisms of mineralization in the cap versus body zone of the tessera.

 

Kristine Stump1, John McManus1, Samuel Gruber2

Applying an Individual-Based Modeling Approach to Address Potential Impacts of Habitat Loss in a Lemon Shark Nursery

1University of Miami - Rosenstiel School of Marine and Atmospheric Science, Miami, FL, United States, 2Bimini Biological Field Station, Bimini, Bahamas

Mangroves provide critical habitat for many species, often during juvenile life stages. In Bimini, Bahamas, the mangrove-fringed lagoon between the two main islands comprises several important parturition sites and nursery areas for lemon sharks (Negaprion brevirostris). Within the North Sound nursery, juvenile lemon sharks are afforded abundant prey, as well as protection from larger predators. A significant volume of research exists concerning the life history, physiology, feeding and diet, bioenergetics, growth and behavioral ecology of lemon sharks in Bimini, as well as numerous studies on the ecosystem itself. The growing field of individual-based modeling has helped researchers begin to understand complex ecological patterns that develop from individuals’ behaviors and interactions with each other and their environment. In an individual-based computer model, “agents” representing individuals are assigned rules that dictate their behaviors and influence interactions with other agents and the environment. This type of model can be a powerful heuristic tool to explain ecosystem complexity. After multiple iterations of the model, population- and ecosystem-level patterns may emerge from interactions of independently-acting agents. The goal is to develop the model such that emergent patterns reflect patterns of interest observed in the field. This study will utilize over twenty years of data to create an individual-based model that combines the behavior and bioenergetics of juvenile lemon sharks with that of the sharks’ prey and predators as they interact within the North Sound ecosystem. The field-validated model will ultimately be used to address actual and potential ecological impacts of mangrove removal in the nursery area. In addition, the model will help elucidate the roles of this high-level predator in a mangrove-fringed lagoon ecosystem, as well as the potential consequences of a decline or loss of this predator. Supported by grants from NSF, Hoover Foundation, CPB Environmental Foundation and the Bimini Biological Field Station.

 

Lydie Couturier, Kathy Townsend, Scarla Weeks, Michael Bennett

Oceanic Conditions, Chlorophyll-a and Zooplankton; Exploring the Reasons for Seasonal Migrations of Manta birostris in Southern Queensland Waters.

The University of Queensland, Brisbane, Queensland, Australia

Manta rays occur in coastal waters around North Stradbroke Island in southern Queensland in the Austral spring/summer, arriving in October and leaving in March. It is hypothesised that the appearance of Manta birostris at this site coincides with rising water temperatures and increases in primary production in the coastal waters, leading to zooplankton blooms that provide a rich source of food for these rays. The departure of manta rays is hypothesised to be due to a significant decline in either the quality or quantity of available zooplankton, and is likely to be correlated with measurable oceanic conditions. We used satellite imaging to map sea surface temperatures and concentrations of chlorophyll-a along the Queensland coast and, in particular, around the study sites at North Stradbroke Island throughout the year. Plankton tows were conducted at specific sites where manta rays are known to aggregate seasonally. These tows occurred at the same locations in the months prior to the arrival of manta rays, during their presence and after they had left. Plankton species were identified, counted and the total sample was analysed for lipid content, ash fraction and energetic content on a monthly basis. Information on the presence or absence of manta rays at the study sites was collected to explore possible links with measurable biotic and abiotic environmental factors.

 

Karla Tribuzy1, Rodney Bassanezi1, Moisés Cecconello1, Maria Lúcia Araújo2, Luiz Alberto Monjeló2, Nilomar Oliveira2

Using Fuzzy Model to Age Estimation of Freshwater Stingrays Species from Rio Negro Basin, Brazil

1UNICAMP, Campinas, Brazil, 2UFAM, Manaus, Brazil

Accurate assessment of elasmobranch age is necessary to obtain estimates of growth, mortality and longevity rates The purpose of this study was through Fuzzy method developed a model for noninvasively determining the age of two species of freshwater stingrays from Rio Negro Basin: Potamotrygon motoro e P. cf histrix. One of assumption of the model is that the first maturation occurs in the point of inflection of length and weight curve obtained in the model crisp. The Fuzzy model incorporates the variations that in fact happen in the experimental data. The feasibility of estimating the age by a computer model based on a Fuzzy system was previously reported to teleost fish. The result obtained through Fuzzy model to Potamotrygon cf histrix provide a significant fit to observed data for capture and release studies. Nevertheless the first maturation age of Potamotrygon motoro is overestimated using this method, and a model adjustment it is necessary.

 

Armando Ubeda1, Colin Simpfendorfer2, John Tyminski1, Robert Hueter1

Re-examination of Growth Rates of Female Bonnethead (Sphyrna tiburo) from Two Different Populations from the Eastern Gulf of Mexico Based on Tag-Recapture Data

1Center For Shark Research at Mote Marine Laboratory, Sarasota, Florida, United States, 2James Cook University, Townsville, Queensland, Australia

Juvenile and adult Sphyrna tiburo were tagged with external nylon-barbed tags and released along Florida’s Gulf coast beginning in November of 1991. Length and time- at-liberty data from 105 usable recaptures were used to examine growth rates of female sharks from the eastern Gulf of Mexico. The time at liberty ranged from 2 to 2,029 days while the measured growth increments ranged from -5.4 to 29.8 cm. A maximum likelihood approach was employed for the analysis of the growth increment data derived from this tagging and recapture study. This approach allowed for the estimation of von Bertalanffy parameters as well as measurement error, growth variability, and uses mixture theory to provide an objective way of dealing with outliers. A bootstrapping method was utilized to estimate confidence limits of the parameters. Analyses were performed combining all usable samples from all areas and by separating them in two different populations based on previous studies that concluded that there is latitudinal variation in growth rates for this species. These results will be discussed and compared with previous published results from age-at-length data for female bonnetheads inhabiting similar regions of Florida.

 

Kevin Weng1, David Foley3, James Ganong2, Christopher Perle2, George Shillinger2, Barbara Block2

Migration of a High Trophic Level Predator, the Salmon Shark, Between Distant Ecoregions

1University of Hawaii at Manoa, Honolulu, HI, United States, 2Hopkins Marine Station, Stanford University, Pacific Grove, CA, United States, 3NOAA Fisheries, Pacific Grove, CA, United States

Knowledge of how animals move through the environment, and the characteristics of habitats they select, are essential to understanding the ecological functions they are fulfilling in each habitat, which in turn is necessary to predict responses to environmental change. High trophic level organisms are known to exert structural influences through the food web, so understanding the range, migration and foraging strategy of abundant predators is necessary to understand ecosystem function. As a result of the difficulty of studying pelagic marine animals, our knowledge of their life history and ecology has developed slowly. Recent advances in monitoring technologies have enabled researchers to remotely follow individual animals over seasonal and multi-year timescales, revealing long-distance migrations in a variety of marine taxa. In this study, satellite telemetry is used to monitor the behaviour of salmon sharks, and remote sensing to characterize their environment, thereby obtaining both animal behaviour and habitat data. Salmon sharks undertook long-range migrations wherein behavioural indices were correlated with regional habitat characteristics. Quantitative movement analyses to determine speed, path straightness and first passage time revealed focal area behaviours in northern and southern regions, with transiting behaviours at mid-latitudes. Individuals migrating to a highly productive southern region stayed longer than those moving to a low productivity region. The combination of multi-year time-series of animal behaviour with synoptic environmental data allows us to understand how the habitats that animals select differ from one another, the key factors influencing habitat selection, and the likely responses to change.