AES Oral Presentation Abstracts
(*=presenter; G=Gruber Best Student Presentation Award Winner)
National Marine Fisheries Service, Southeast Fisheries Science Center, 3500 Delwood Beach Dr., Panama City, FL 32408, USA
Preliminary reproductive parameters of the Atlantic Angel Shark with a potential example of reproductive senescence
The Atlantic Angel Shark, Squatina dumerili, is a benthic species inhabiting deep waters of the Gulf of Mexico and the Atlantic Ocean. This species is listed as prohibited by the Fisheries Management Plan for Atlantic Tunas, Swordfish, and Sharks due to the lack of biological data and a precautionary approach for species thought to be highly susceptible to exploitation. Reproductive parameters were determined for 164 sharks (76 females, 88 males) captured in the Gulf of Mexico from fishery independent and dependent sources. Males were considered mature if they possessed calcified claspers and the epididymis was tightly coiled. Mature females had well developed left ovaries with large (>10 mm) oocytes and prominent nidamental glands. Reproduction occurs by aplacental viviparity; embryos examined in utero were umbilically attached to individual yolk sacs. Both resting and gravid females occur simultaneously in the population, indicating a biennial reproductive cycle. The gestation period is approximately 10 months in duration with an average litter size of 8 (+/- 1.82) pups, and the size at birth is approximately 25 cm fork length (FL). Near term embryos and neonates of similar sizes were collected from January through December, suggesting that parturition is protracted. The median length at maturity was 88.7 cm for males and 83.5 cm FL for females. In addition, one large female (112 cm FL) was examined which had no typical signs of maturity (ovary was smooth and undeveloped, uteri were contracted, no developed ova), indicating that this female was either reproductively sterile or had reached senescence. Reproductive senescence, a state at which older individuals in a population cease to reproduce, has not been documented in elasmobranchs to date.
(ASB, PJM) University of South Florida, Dept. Biology, 4202 East Fowler Ave., SCA 110, Tampa, FL 33620, USA; (MRH, REH) Mote Marine Laboratory, Center for Shark Research, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA
Movement patterns of the Cownose Ray within Charlotte Harbor, Florida: A preliminary assessment
Cownose rays (Rhinoptera bonasus) occur throughout the coastal Gulf of Mexico and are abundant residents of Florida estuaries, including Charlotte Harbor where they are present throughout the year. Historical data indicate that R. bonasus are more abundant within this estuary during the spring and summer months. Although frequently observed, little data exist regarding R. bonasus movement patterns or habitat use. Acoustic hydrophones deployed in Charlotte Harbor were used to monitor an approximate area of 100 km2. Five R. bonasus (57-80 cm DW) were fitted with external acoustic transmitters and were monitored over periods ranging from 1-82 days. The longest uninterrupted track was for an immature male and lasted 34 days. This same animal was tracked moving through lower Charlotte Harbor, exiting Pine Island Sound to enter the lower Caloosahatchee River. Minimum convex polygons were used to calculate activity spaces for each animal, and ranged between 10.1 km2 and 89.95 km2. Average activity space for these tagged animals was 42.58 km2. Quantitative analysis of habitat use will be discussed, along with ecological implications and goals for this ongoing project.
(GWB) Middle Tennessee State University, Department of Biology, P.O. Box 60, Murfreesboro, TN 37132, USA; (SAB) The University of Southern Mississippi, Department of Coastal Sciences and Gulf Coast Research Laboratory, 703 East Beach Drive, Ocean Springs, MS 39564, USA
Infectious agents and the liberation of captive elasmobranchs: A prespective
The animal health ramifications of liberating captive elasmobranchs into natural waters theoretically range from favorable to deleterious. Little practical knowledge exists regarding this topic. However, when this topic is addressed more generally by considering all organisms, examples of the aforementioned extremes are few compared to the diversity and number of organisms that have been released from captivity. Nevertheless, some notable deleterious examples include liberated teleosts whose parasites have destabilized wild populations thereby affecting commerce and attracting considerable negative publicity. Elasmobranchs host a wide variety of parasites, few of which are considered pathogens in captivity. Furthermore, in spite of casual references to infectious pathogens, i.e., those not stemming from controlled experiments, one could argue that a life-threatening or health-limiting infectious pathogen has yet to be demonstrated from a feral elasmobranch. A protocol for routine, pre-release, health-screening of elasmobranchs could be developed to reduce the intraspecific and interspecific risks of deleterious, post-release effects. However, given the limitations of detecting potential pathogens, the scientific value of such screening may be diminished when single or small numbers of elasmobranchs are being liberated. Ultimately, it is likely that decisions regarding the liberation of captive animals will always be based on an incomplete scientific understanding of potential risk. This likely reality makes management decisions political and prone to negative public outcry if, for example, local stocks or communities experience or are perceived to have experienced a demise after animals are liberated.
(DMB, JKC, MS) NOAA, National Marine Fisheries Service, Southeast Fisheries Science Center, Panama City Laboratory, 3500 Delwood Beach Road, Panama City Beach, FL 32408, USA; (JAB) Department of Zoology, North Carolina State University, Center for Marine Sciences and Technology, 303 College Circle, Morehead City, NC 28557, USA
Ontogenetic and habitat related trends in the diet of the Atlantic Sharpnose Shark (Rhizoprionodon terraenovae)
Stomach contents of Atlantic sharpnose sharks (Rhizoprionodon terraenovae) taken from fishery independent surveys in two areas of the northeast Gulf of Mexico were examined to test for differences in diet with ontogeny and habitat use. In the first area, Crooked Island Sound, young-of-the-year (n=56) were found to feed on a mix of teleosts and invertebrates (mostly Opisthonema oglinum and cephalopod squid), juveniles (n=185) fed mostly on Cynoscion spp. and Brevoortia spp., and adults (n=105) on Micropogonias undulatus. In the second area, the gulf side of St. Vincent Island, young-of-the-year (n=201) fed mainly on decapod shrimp, juveniles (n=25) on sciaenids (mostly Micropogonias undulatus), and adults (n=74) on Brevoortia spp.. Spearman correlation analysis indicated ontogenetic diet shifts within each location. In addition, simple correspondence analysis showed that life stage diet differed between locations. Crooked Island Sound is an enclosed, shallow barrier island system, consisting of seagrass and sandy bottom; whereas, the gulf side of St. Vincent Island is an area highly influenced by currents and tidal changes, consisting of hard, muddy bottom. Crooked Island Sound is more diverse in potential prey species (Shannon-Weiner diversity index, H=3.17) than the gulf side of St. Vincent Island (H=2.91). Variations in diet composition within and between the two areas are likely due to differences in overall habitat structure and availability of potential prey species.
Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Rd., Moss Landing, CA 95039, USA
Diet, feeding ecology, and ecomorphology of the dominant ray species in Bahía Almejas (Baja California Sur, Mexico)
Despite the importance of trophic relationships in understanding community structure and stability, little is known about the feeding ecology of most elasmobranch species. This is especially true of rays, which typically occupy high trophic levels in low-latitude marine coastal ecosystems. In Bahía Almejas, specimens were collected between 1998 and 2002 from an artisanal gillnet fishery targeting rays during summer months. Diet and ecomorphology of the feeding apparatus were examined for the most abundant species, including: the Shovelnose Guitarfish (Rhinobatos productus), Diamond Stingray (Dasyatis dipterura), Cortez Electric Ray (Narcine entemedor), California Butterfly Ray (Gymnura marmorata), and Pacific Cow-nose Ray (Rhinoptera steindachneri). Sample size sufficiency was examined using cumulative prey curves and a priori power analyses. Compound indices (%IRI, GII) were used to characterize diet. Ontogenetic, intergender, and temporal differences in diet were analyzed using parametric or multivariate statistics, whenever possible. Interspecific comparisons of dietary overlap, using both general (e.g., crabs, teleosts, polychaetes) and species-specific prey categories, were compared using Spearman Rank correlation. Trophic level was calculated using a technique modified from Cortés (1999). An Index of Foraging Habitat was created based on known habitat associations of prey items. Morphological and meristic aspects of the feeding apparati of each species were compared intraspecifically with principal component analysis and interspecifically with discriminant function analysis. Canonical correlation analysis was used to investigate associations between morphological variables and diet composition. Results of these analyses will be presented and the trophic roles of these species in Bahía Almejas assessed. The diets and morphologies of these species did not exhibit a high degree of similarity, potential facilitating their coexistence in this region.
(JKB) Department of Geography and Anthroplogy, Howe-Russell Geoscience Complex, Louisiana State University, Baton Rouge, LA 70803, USA; (MAM, JKB) International Aquatic and Terrestrial Conservation Medicine and Biotelemetrics Research Laboratory, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA; (GBS, RF) Massachusetts Division of Marine Fisheries, Martha’s Vineyard Research Station, P.O. Box 68, Vineyard Haven, MA 02568, USA
The physiological effects of propofol on wild caught sharks
Limited data are available on the effects anesthesia on elasmobranch physiology. Additionally, only a single study is available on the effects of propofol, an intravenous anesthetic, on captive bamboo sharks, Chiloscyllium plagiosum. This study was designed to determine the value of propofol as an anesthetic for wild caught sharks. The objectives of the study were to: 1) successfully induce anesthesia in wild benthic sharks, 2) monitor the cardio-respiratory and blood-based physiological effects of capture/handling stress and propfol anesthesia, and 3) monitor post-release survivorship in the benthic sharks using acoustic telemetry. Smooth dogfish, Mustelus canis, were collected from Vineyard Haven Harbor, Massachusetts using a 0.75 km longline. Three sharks were captured and anesthetized in 2002 and five sharks were anesthetized in 2003. All sharks were bled immediately following capture to establish relative capture stress levels using pH and blood gas values. Sharks were then placed in aerated holding bins on deck of the capture vessel, propofol dosages were calculated (2.0-4.0 mg/kg), and the drug administered. Sharks were monitored for clinical signs of anesthesia and blood samples were collected at 30, 90, and 150 minutes post-induction to monitor physiologic stress. Additionally, two dogfish were captured and handled in a manner similar to the sharks receiving propofol and served as controls. Two propofol sharks, one propofol control, and a single shark that underwent no on-deck trials were all released with acoustic tags to monitor post-release survivorship. All sharks that underwent anesthesia survived. The two anesthetized sharks that were tracked survived for at least 25 days post-release when the signals from the transmitters were lost. Results from the pH and blood gas data suggest that dogfish are sensitive to capture and handling stress. Sharks that underwent anesthesia did not undergo more stress relative to controls, but did exhibit slower stress recovery times.
(JMB, BMG) University of Adelaide, Southern Seas Ecology Laboratories, School of Earth and Environmental Sciences, Adelaide, SA, 5005, Australia; (JMB, TIW) Marine and Freshwater Resources Institute, P.O. Box 114 Queenscliff, VIC, 3225, Australia
Dietary composition of three shark species in southeastern Australia
Dietary composition, as determined by stomach contents analysis, is a straightforward approach for determining the links between sharks and other species. Understanding these links contributes to a better appraisal of the role and function of the components of marine ecosystems and the structure of marine food webs. Determining the species linkages is also essential for trophodynamic ecosystem modeling. The present study analyzes the dietary composition of the Sharpnose Sevengill Shark (Heptranchias perlo), a deep-water predator, the Broadnose Sevengill Shark (Notorynchus cepedianus), a coastal top predator, and the Piked Spurdog (Squalus megalops), a demersal shark and one of the most abundant shark species of the southern Australian continental shelf. The Sharpnose Sevengill Shark preyed exclusively on deep-water teleosts and to a lesser extent on cephalopods. The Toothed Whiptail (Lepidorhynchus denticulatus) and the Cardinalfish (Apogonops anomalus) were the most important prey items in number, mass and occurrence. Chondrichthyans (Mustelus antarcticus, Callorhynchus milii and Urolophus cruciatus) and teleosts (Sillago flindersi) were the most important taxa in the diet of the Broadnose Sevengill Shark. The Piked Spurdog fed on several groups: teleosts, squids, octopus, hermit crabs and polychaetes. The overlap in the diet of the three species will be discussed from an ecosystem management viewpoint.
(KB, HS, CR) National Marine Fisheries Service, Highly Migratory Species Management Division; (SF1), 1315 East-West Highway, Silver Spring, MD 20910, USA; (GF) National Marine Fisheries Service, Highly Migratory Species Management Division, 9721 Executive Center Drive, St. Petersburg, FL 33702, USA
The status of United States shark management in the Atlantic Ocean
The Highly Migratory Species (HMS) Management Division of the National Marine Fisheries Service (NOAA Fisheries) is responsible for the management of the Federal Atlantic shark fisheries including the Gulf of Mexico and Caribbean Sea. In late 2003, the HMS Management Division completed Amendment 1 to the Fishery Management Plan (FMP) for Atlantic tunas, swordfish, and sharks. Amendment 1 revised the rebuilding plan for large coastal sharks, established a method of calculating quotas, updated essential fish habitat (EFH) for five shark species, and made several changes to the commercial and recreational regulations including adjustments to bag and size limits and establishment of a time/area closure. The HMS Management Division is now beginning to work on Amendment 2. Amendment 2 will likely focus not only on ongoing issues that were not addressed in Amendment 1 such as the pelagic shark quotas and updating EFH for the remaining species, but also on issues regarding how stakeholders want the fishery to look in the future such as the potential for quota allocations between directed, incidental, and recreational permit holders and the need for species identification workshops for fishermen. The alternatives in Amendment 2 will be based on the results of the latest stock assessments as well as comments received during public scoping meetings that will likely be held in April and May 2004.
University of Zurich Zurich, Switzerland CH-8057
Natural stomach eversion in Carcharhinus perezi
Stomach eversion is a known but rarely observed phenomenon in elasmobranch fishes. A vomiting reflex has been induced in rays and dogfish under laboratory conditions and everted stomachs have been reported by fishermen that caught sharks with line and net. Anecdotal evidence exists that stomach eversion and swallowing occurs naturally in carcharhinid shark species. I here present video footage of naturally occurring stomach eversion and swallowing in an elasmobranch species, the Caribbean Reef Shark, Carcharhinus perezi. I discuss the ecological context in which it occurred as well as possible functions of natural stomach eversion in sharks.
(JKC) National Marine Fisheries Service, Southeast Fisheries Science Center, 3500 Delwood Beach Rd., Panama City, FL 32408, USA; (JAN, KAR) Coastal Fisheries Institute and Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, LA 70803, USA
Are summer nursery areas optimal for juvenile shark growth and survival?
Conventional theory assumes that nursery areas provide the most advantageous habitat for the growth and survival of young sharks. Beginning in spring in northwest Florida, age 0 bonnethead sharks recruit to summer inshore areas from offshore waters. According to catch per unit effort data, as the summer progresses CPUE decreases from a high in May of 1.8 sharks per hour to 0.5 sharks per hour in August and remains relatively similar until November when sharks emigrate offshore. The large reduction in CPUE over the summer suggests that sharks have either left coastal habitats or perished. To better assess this hypothesis, a generalized bioenergetic model based on species-specific experimental data was constructed to determine the energetic demands of residing in a coastal area. Our preliminary model suggests that energy requirements of individuals were lowest in spring and highest in summer when water temperatures approach 30 C. Moreover, a simulation of 1000 individuals suggests that average weight is 0.35 kg at immigration, reaches a maximum of 0.64 kg on day 70 (early June), declines to a minimum of 0.42 kg on day 144 (mid-Aug), and increases to 0.75 kg at emigration. Further, a condition factor of a hepatosomatic index, weight, and energy content of the liver, determined from field collected sharks mirrored results from the bioenergetic model. Sharks had the highest condition factor in spring and fall and lowest in summer. Gutfullness was also highest in summer when sharks would need to consume more to meet their energetic needs. Results suggest that inshore habitats are demanding on young sharks and may not be the optimal habitat that theory suggests.
University of South Florida, College of Marine Science, St. Petersburg, FL 33701, USA
The hearing abilities of the Nurse Shark, Ginglymostoma cirratum, and the Yellow Stingray, Urobatis jamaicensis.
The hearing thresholds of two species of elamobranchs, the Nurse Shark, Ginglymostoma cirratum, and the Yellow Stingray, Urobatis jamaicensis, were examined using the Auditory Brainstem Response (ABR) to better understand the hearing abilities of elasmobranchs. Audiograms were completed for both species (n=5 for each species) at 1m from the transducer where both sound pressure and particle velocity were measured. ABR measurements were also made with 5 m separation between the fish and the transducer to test the effects of varying the ratio between sound pressure and particle velocity on evoked potential levels. The results show that these species detected low frequency sounds from 100-1000 Hz with best sensitivity from 100-400 Hz. The narrow hearing bandwidth supports the hypothesis that these fish are hearing generalists, without any special hearing adaptations. These results are similar to previous laboratory measurements of shark hearing and have implications for shark sound attraction experiments conducted in the field.
(DC, MS) Guy Harvey Research Institute, Oceanographic Center, Nova Southeastern University, 8000 North Ocean Drive, Dania Beach, FL 33004, USA; (EL) Center for Conservation and Research, Henry Doorly Zoo, Omaha, NE 68107, USA; (PP) Biology and Biochemistry, The Queen’s University, 97 Lisburn Rd., Belfast, N. Ireland, UK.
A genetic investigation into a shark ‘virgin-birth’: Asexual reproduction, inter-specific hybridization or long-term sperm retention?
Asexual reproduction via parthenogenesis is relatively rare among chordates and has never been recorded in the class Chondrichthyes. In December 2001, a female Bonnethead Shark, Sphyrna tiburo, gave birth in captivity to a single female pup, despite having been separated from any male S. tiburo for a period of at least three years. Widespread media attention quickly led to this case being billed as “the shark-virgin birth” (i.e., asexual reproduction), however other explanations (sexual reproduction coupled with long-term sperm storage, inter-specific hybridization with a male leopard shark, Triakis semifasciata, tank-mate) could not be ruled out. We present the results of a genetic investigation aimed at ruling out these alternatives and determining whether this birth is the first known case of asexual reproduction in this ancient lineage.
Virginia Institute of Marine Science, Fisheries Science Department, 1208 Greate Road, Gloucester Point, VA 23062, USA
Nursery habitat and migratory patterns of juvenile sandbar sharks, Carcharhinus plumbeus, in the Eastern Shore of Virginia seaside bays and lagoons
Sandbar sharks are the principal species caught in both the recreational and commercial shark fisheries of the Atlantic coast. The definition and protection of both winter and summer nursery areas is critical for the rebuilding of sandbar shark stocks. The bays and lagoons of the Eastern Shore of Virginia provide a summer nursery habitat for these sharks. Longline and gillnet sampling were conducted in this region during the summers of 2002 and 2003 to delineate the temporal and spatial use of this nursery habitat by sandbar sharks. Short and long term activity patterns of sharks were studied during the summer of 2003 using an acoustic telemetry system consisting of an array of 15 fixed location listening stations. Acoustic transmitters were implanted in 27 juvenile sandbar sharks which were tracked intermittently from 3 hours to over 65 days. Additional information regarding both summer and winter nursery area use was obtained by attaching 21 satellite transmitters to large juvenile sandbar sharks captured while in this nursery area. Longline and acoustic sampling will continue in the summer of 2004 in order to further define how this nursery area is used by neonate and juvenile sandbar sharks.
NOAA Fisheries, Panama City Laboratory, 3500 Delwood Beach Road, Panama City, FL 32408, USA
Effects of temporal variability on population viability analysis of an elasmobranch
Population viability analysis (PVA) is concerned with identifying the minimum population size that will produce a reasonable probability for a population to survive in the future. Temporal variability or stochasticity is one of the main causes of population vulnerability through its effect on vital rates and ensuing population growth rates. Demographic stochasticity is a form of temporal variation in population growth dictated by random variation in the fate of individual animals that can introduce substantial variability at low population sizes. The effect of considering temporal variability and demographic stochasticity on viability metrics associated with the probability of quasi-extinction was investigated using published data on population size estimates of the White Shark (Carcharodon carcharias) in South Africa as an illustration. First, a PVA that considers annual temporal variability in vital rates was compared to a time-invariant projection model often used in demographic analyses of elasmobranchs. Second, the time-dependent population-based PVA model was compared to an individual-based model incorporating demographic stochasticity. In each case, predicted mean population size and the probability of population size being below a minimum threshold of 50 individuals after approximately three generation times were computed for several initial population sizes and age distributions (stable vs. non-stable). For the population-based models, survival and birth rates were described by a beta and truncated lognormal distribution, respectively. For the individual-based models, the probability of survival was modeled as a uniform distribution as often done in conservation contexts and, alternatively, as a binomial distribution, whereas the number of births was modeled following a discrete Poisson distribution. In all cases, age at maturity and longevity were drawn from uniform distributions. Results indicated that demographic stochasticity starts having a marked effect at a population size of about 50 females and that disregarding temporal variability in vital rates tends to underestimate population performance.
(MND) Ecology and Evolutionary Biology, University of California, 321 Steinhaus Hall, Irvine, CA 92697, USA; (MMK & TJK) Skeletal Biology, Shriners Hospital for Children, Tampa, FL 33612, USA
Extracellular matrix composition in the rostral gel of Squalus acanthias: A non-cartilaginous skeletal element
Vertebrate skeletal elements are diverse and include loose gels (nucleus pulposus of intervertebral joints), fibrous bands (tendons and ligaments), stiff but compressible cartilages and hard mineralized bone. Some taxa incorporate all of these elements (e.g., tetrapod taxa); in others, one tissue predominates. The chondrichthyan fishes have been considered an example of the latter due to the perceived uniformity of their skeleton. While it is clear that the chondrichthyan skeleton is primarily cartilage and lacks bone, the behavioral diversity of these fishes suggests heterogeneity in skeletal structure. Variations in the composition and properties of supporting skeletal tissues may result as adaptations to specific mechanical requirements. We have found a novel gel-like skeletal element in the cranium of the dogfish, Squalus acanthias, filling a dorsal trough in the rostrum. Preliminary compositional analyses of extracellular matrix macromolecules indicate that the gel is a unique skeletal element rather than a modified form of cartilage. Compared with cranial cartilage, collagen makes up only a small proportion of the extracellular matrix of the gel. Also, the rostral gel exhibits particularly high levels of hyaluronic acid and relative proportion of unsulfated chondroitin disaccharides. These observations suggest that the cells within the elasmobranch skeletal system, presumably chondrocytes, have the potential to express and assemble distinct extracellular matrices adapted for a range of biomechanical requirements. The rostral gel likely acts as a space filling material, but may also function biomechanically to strengthen the rostral element or provide shock absorption and resiliency.
National Marine Fisheries Service-Mississippi Laboratories P.O. Drawer 1207 Pascagoula, MS 39568, USA; Louisiana State University Baton Rouge, LA 70803, USA
Age, growth and maturation of the Finetooth Shark, Carcharhinus isodon off the southeastern United States
The life history of the Finetooth Shark, Carcharhinus isodon, in the coastal waters off South Carolina was studied by determining age, growth and size and age at maturity. Finetooth sharks were collected from the near shore and estuarine waters of South Carolina from April 2002 through August 2003. Cervical vertebrae were extracted from 168 finetooth specimens (71 males and 97 females), ranging in size from 376 to 1262 mm fork length (FL), and were prepared for age analysis using standard techniques. Sex specific von Bertalanffy growth model curves were generated using observed length at age data and yielded the following von Bertalanffy growth equations: Females: Lt = 1321 mm FL (1-e-.18(t-(-2.32))) Males: Lt = 1152 mm FL (1-e-0.33(t-(-1.53))) The oldest female was 12.3 years and the oldest male was 10.3 years. Theoretical longevity estimates were 18.8 years for females and 10.6 years for males. Median length at which 50% of the population was mature was 1021 mm FL for females, equivalent to 5.1 years old and 1015 mm FL for males, equivalent to 5.0 years old. Data from this study were compared to finetooth sharks from the Gulf of Mexico. Finetooth sharks in the western Atlantic Ocean were older, reached larger theoretical maximum sizes and had lower growth coefficients than conspecifics in the Gulf of Mexico, yet showed similar theoretical ages at zero fork length and sizes at birth. Results from this study indicate finetooth sharks show life history parameters that are intermediate to other sharks in the small and large coastal complexes.
(KMD, GHD) University of Hawaii, Dept. Zoology, HIMB and EECB, 2538 The Mall, EDM 152, Honolulu, HI 96822, USA; (APM) Dept. Environmental, Population and Organismic Biology, University of Colorado, Boulder, CO 80309, USA; (BWB) Hawaii Institute of Marine Biology, PO Box 1346, Kaneohe, HI 96744, USA
Genetic survey of nursery habitats in the Scalloped Hammerhead Shark, Sphyrna lewini
Scalloped hammerhead sharks spend much of their life offshore, but use nearshore bays for partuition and nursery habitat. To understand this nursery behavior, we examined the genetic structure of this species using a 600 bp fragment of maternally inherited mtDNA. Maximum likelihood analyses revealed three lineages worldwide, distinguished by approximately 6-7% sequence divergence. These lineages overlapped in some locations, indicating historical dispersal between ocean basins. For example, lineages that predominate in the Atlantic and Pacific co-occur in Thailand, and specimens from Baja California included both a Pacific lineage and an Indian Ocean lineage. However, there is also evidence for contemporary population subdivision and isolation by distance. Some nurseries, like Kaneohe Bay in Hawaii, are characterized by a single haplotype, indicating a founder event and/or population isolation. We conclude that dispersal among regions occurs over deeper evolutionary time, but that homing to nurseries may still predominate over the timescale relevant to fishery managers. Our subsequent research will quantify isolation among nursery areas, to resolve the level of site fidelity in reproductive females. This information is an essential foundation for management of hammerhead sharks. We are still seeking samples from a few key locations to complete this work.
Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039, USA
From the Bering Sea to southern Africa: An overview of skate (Chondrichthyes: Rajiformes) reproductive biology
Skates are an important component of the demersal fish community in many temperate and deepsea ecosystems. Similar to other chondrichthyans, most skates have life history characteristics that make them vulnerable to over-exploitation. Recently, skates have become a concern to fishery agencies due to the preponderance of these elasmobranchs caught as bycatch in groundfish fisheries and as a directed fishery. Although they may comprise a significant component of the overall catch, general biological information on skates is scare. Current studies by researchers at the Pacific Shark Research Center (PSRC) reveal that skates exhibit variable and complex life history parameters. Presently, a long-term, broad-based study is underway to elucidate aspects on the life history, ecology, and systematics of skates in three different ecosystems. These aspects include age and growth, demography, distribution, feeding ecology, habitat utilization, systematics, and reproductive biology. Data will be presented from the age, growth, and reproductive biology portions of this study that includes a total of 43 species representing 12 genera and three families. Among the findings to be presented, it is important that skate studies, (1) determine the correct identity of the species involved, (2) identify to species those taken as bycatch and/or in directed fisheries, (3) standardized the methods of determining maturity, (4) critically review age and growth studies, and (5) determine and identify discrete populations through genetics and quantitative life history studies. Finally, it is concluded that skate life history parameters need to be studied on a localized basis and not on a global basis. This is especially true for management purposes.
Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Rd., Moss Landing, CA 95039, USA
Distribution and reproductive biology of deep-sea scyliorhinids off central California
These findings are part of a broad-based ecological investigation into the life history of three deep-sea catsharks (Scyliorhinidae), Apristurus brunneus, A. kampae and Parmaturus xaniurus, in the eastern North Pacific. Preliminary results on the distribution and reproductive biology of these species off central California will be presented. Specimens were collected from trawl and longline survey cruises by the National Marine Fisheries Service (NMFS) from June 2002 through December 2003 from Año Nuevo to Point Sur, California. Distribution and occurrence of the three species were analyzed to identify trends associated with season, depth, maturity, and sex. Longline hauls were mainly comprised of P. xaniurus, with an occasional catch of gravid female A. brunneus. Conversely, trawl cruises were primarily comprised of Apristurus spp. Apristurus brunneus were typically found between 300-942 m, while A. kampae occurred deeper than 1,005 m. The total lengths at 50% reproductive maturity were determined for males and females of all three species. It was determined that both A. brunneus and P. xaniurus reproduce year-round based on the occurrence of gravid females and gonadosomatic (GSI) and hepatosomatic indices (HSI) for both males and females. Gravid A. kampae females were found from July through December.
(BRF, JRS) School of Bioscience and Biotechnology, Drexel University, Philadelphia, PA 19104, USA; (SHG) Bimini Biological Field Station, Bimini, Bahamas and Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149, USA; (BMW) Dept. of Biological Sciences, University of Rhode Island, 100 Flagg Rd., Kingston, RI 02881, USA
The spatial ecology and habitat utilization of juvenile lemon sharks (Negaprion brevirostris) in Florida, Brazil, and the Bahamas
The Magnuson-Stevens Fishery Conservation and Management Act (1996) requires the collection of data related to essential fish habitat. A major component of determining essential fish habitat is characterizing the extent and utilization of nursery areas. Lemon sharks as with many other shallow water or coastal sharks use nursery areas during their early years of life. Studies suggest that nursery areas are chosen because of low predation rates, high abundances of prey, and suitable habitat. A combination of manual and automated acoustic tracking is being used to determine the movement patterns and habitat utilization of juvenile and subadult lemon sharks. GIS models are being constructed using water temperature, salinity, bathymetry, dissolved oxygen, biotope, prey availability, water currents, and predator presence as layers in the model. The three sites being studied: Bimini, Bahamas; Marquesas Key, Florida; and Atol das Rocas, Brazil are all lemon shark nursery areas but each nursery has unique characteristics that will be discussed. The GIS models will be used to examine habitat selection, mortality rates, and movements of juvenile lemon sharks within the nursery areas. The movement parameters will be compared for sharks of different age classes and sharks living in different nursery areas. The major objective of this study is to determine if juvenile lemon sharks select specific habitats within the nursery areas in order to maximize benefits such as prey availability and minimize threats such as predator encounters. Preliminary results and proposed research will be discussed.
Coastal Carolina University, Dept. of Marine Science, POB 261954, Conway, SC 29528, USA
Differences in the shark population of Winyah Bay, South Carolina, in drought and wet years
Shallow coastal waters and estuaries may constitute critical habitat as feeding and nursery grounds for sharks. As part of a long-term study of the ecology of sharks in Winyah Bay, a relatively shallow 155.4 km2 coastal plain estuary whose shark fauna has not been systematically studied, we set 259 bottom longlines from May 2002 through November 2003 throughout the bay and at a variety of salinities. In 2002, a drought year, 199 sharks (adults, juveniles, and pups) of 11 species were caught, whereas 82 sharks comprising 5 species were captured in 2003. All species showed declines from 2002 to 2003, including: Sandbar sharks (Carcharhinus plumbeus), n = 79 and 55, respectively; Blacktip (C. limbatus), 37 and 1; Atlantic Sharpnose (Rhizoprionodon terraenovae), 36 and 16; Finetooth (C. isodon) 38 and 0; and Bull (C. leucas) 3 and 0. Shark abundance (Catch per Unit Effort, or CPUE) correlated with salinity, water temperature, depth, and tide. These results also suggest that Winyah Bay may constitute essential fish habitat for some species of sharks (as defined in the Magnuson-Stevens Fishery Conservation and Management Act). (Supported by the Georgetown County Environmental Protection Society).
(JG, CJW) Center for Shark Research. Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA; (NJS) Analytical Toxicology Core Laboratory, University of Florida, Box 110885, Gainesville, FL 32611, USA; (LELR) Department of Chemistry, Biochemistry, and Molecular Biology, Oregon Graduate Institute, P.O. Box 91000, Portland, OR 97291, USA; (SH) Department of Natural Sciences, New College of Florida, 5700 North Tamiami Trail, Sarasota, FL 34243, USA
Exposure levels and effects of organochlorine contaminants in Atlantic stingrays from Florida’s St. Johns River
Populations of the Atlantic Stingray (Dasyatis sabina) residing in Florida’s St. Johns River represent the only permanent freshwater elasmobranchs in North America. Despite their persistence in this unique habitat, previous research has indicated that these populations may be threatened by as yet unknown ecological factors. Reproductive failure and health anomalies have been documented to occur in D. sabina inhabiting Lake Monroe, a degraded component of this river system. Furthermore, serum concentrations of steroid hormones responsible for regulating reproduction were found to be several times greater in an estuarine population of D. sabina than levels in Lake Monroe stingrays. These abnormalities are consistent with the known effects of organochlorine (OC) contaminants, pollutants that have been linked with health disorders in other central Florida wildlife. With this in mind, the goal of this study was to examine exposure levels and potential effects of OC contaminants in St. Johns River stingrays. Liver concentrations of 30 OC pesticides and polychlorinated biphenyls (PCBs) were examined in D. sabina from 4 central Florida lakes. Reproductive health was examined in mature male and female D. sabina from 3 of these sites, representing low, moderate, and high levels of OC contamination. Possible effects of OC contamination on stingray immune function also were examined.
(KJG) Jackson State University, Department of Biology, P.O. Box 18540, Jackson, MS 39217, USA; (JAM) Virginia Institute of Marine Science, Route 1208, Greate Road, Gloucester Point, VA 23062, USA
Growth and maturity of salmon sharks in the eastern and western North Pacific, with comments on back-calculation methods
Age and growth estimates for salmon sharks, Lamna ditropis, in the eastern North Pacific were derived from 182 vertebral centra collected from sharks ranging in length from 62.2 to 213.4 cm precaudal length (PCL), and compared to previously published age and growth data for salmon sharks in the western North Pacific. Eastern North Pacific males and female salmon sharks were aged to 17 and 20 years, respectively. von Bertalanffy growth parameters derived from vertebral length-at-age data are Linf = 207.4 cm PCL, k = 0.17 yr-1, and to = -2.3 years for females, and Linf = 182.8 cm PCL, k = 0.23 yr-1, and to = -1.9 years for males. Age at maturity was estimated to range from six to nine years old for females (median precaudal length of 164.7 cm PCL) and from three to five years old for males (median precaudal length of 124.0 cm PCL). Weight length relationships for female and male in the eastern North Pacific are W = 8.2×10-05 x L2.759 (r2 = 0.99) and W = 3.2×10-06 x L3.383 (r2 = 0.99) respectively. Our results show that male and female salmon sharks in the eastern North Pacific possess a faster growth rate, reach sexual maturity earlier and attain greater weight-at-length than their same sex counterparts living in the western North Pacific. The variability in these life history parameters may be due to ecological differences between the eastern and western North Pacific or due to population (stock) structure. This variability along with the strong sexual segregation exhibited by this species across the North Pacific basin and an unknown rate of current bycatch all complicate management issues for this species.
(JMG) Department of Biological Sciences, University of New Orleans, New Orleans, LA 70148, USA; (CAA, JMQ) Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
Concordant mitochondrial and nuclear evidence of lineage diversification among hammerhead sharks (Sphyrna)
Comprehensive genetic surveys have refuted the general hypothesis of panmixia for many cosmopolitan marine species. Deep phylogenetic divergences indicative of historical separation have been recovered in diverse marine taxa. Unfortunately, comprehensive genetic surveys are uncommon for cosmopolitan species, including elasmobranch fishes, and the potential for deep genetic divergences within species remains largely untested. Exploitation and habitat degradation threaten the sustainability of elasmobranch fisheries and the continued existence of certain species, making genetic studies invaluable conservation and management tools. Phylogeographic surveys of mitochondrial and nuclear gene variation were used to test for deep phylogenetic divergences within the Scalloped Hammerhead, Sphyrna lewini. Mitochondrial control region variation was partitioned by ocean basin for S. lewini, which is nearly circumtropical in distribution. Atlantic and Pacific populations did not share haplotypes, which averaged 5% sequence divergence. Surprisingly, a similar level of mtDNA divergence was recorded among Atlantic Ocean samples. Three Atlantic haplotypes were recovered, two restricted to specimens from coastal South Carolina and one found throughout the basin. The South Carolina haplotypes differed by one transition but averaged 5.1% sequence divergence from the widely distributed Atlantic haplotype. Control region gene trees place the South Carolina haplotypes basal within S. lewini. To test the mtDNA hypothesis of phylogeographic structure within and among basins, scalloped hammerhead samples were screened for variation at an evolutionarily independent nuclear locus, LDHA6. Nuclear variation was not highly structured between basins, with two of six alleles common among scalloped hammerhead samples and widely distributed across basins. However, samples with the South Carolina control region haplotypes were fixed for a divergent LDHA6 allele that also was limited to these specimens. Like the control region gene trees for S. lewini, the South Carolina LDHA6 allele is basal to other alleles in the LDHA6 gene trees.
(EDG)St, Joseph’s University, Dept. of Biology, 5600 City Ave., Philadelphia, PA 19131, USA; (RL) Carnegie Museum, 18 Hillside Rd., Mount Holly, NJ 08060, USA
Diversity and evolution of Paleozoic chondrichthyans
The Paleozoic chondrichthyans are divided into three main assemblages or tribes; the elasmobranchians (paleoselachians plus a smaller group with closer ties to the Euselachii), the non-holosytylic Euchondrocephali and the Holocephalimorpha. The latter two assemblages are the fishes assigned to the Euchondrocephali and make up the majority of the chondrichthyans (ca. 29% and 45% respectively). Elasmobranchs represent only 25% of the Class. Over all, the ecological and morphological aspects of the chondrichthyan community show fine niche partitioning on the basis of both feeding and propulsive specializations. The nature and range of this diversity is the main focus of this talk. The divergent trends in neurocranial proportions, types of dentition, the structure and support of the visceral skeleton, and select postcranial features are considered in light of possible developmental processes underlying chondrichthyan diversity and evolution. This and other research indicates that, in contrast to the osteichthyans, the range of morphological diversity in chondrichthyans results from the modification of suites of characters rather than individual characters. Elasmobranchs are interpreted as a highly specialized and derived branch of the total chondrichthyan adaptive radiation.
Southern Illinois University, Fisheries and Illinois Aquaculture Center, Carbondale, IL 62901, USA
Genetic concerns associated with the release of captive elasmobranchs
The release of captive-reared fishes has resulted in considerable damage to gene pools of native freshwater and anadromous fishes. Such damage includes a loss of fitness attributed to outbreeding depression and a reduction in the genetic effective population size (Ne) of wild stocks following the release of too many offspring from few captive breeders. Both of these effects are unlikely following the captive release of elasmobranchs for a number of reasons. For reductions in Ne to occur a large number of captive-reared fish must enter the wild gene pool. Based on elasmobranch life histories (low fecundity and high parental investment) and the difficulty and expense of rearing large numbers of elasmobrachs in captivity, it is unlikely that sufficient numbers of offspring from few enough parents could be raised in captivity to significantly affect a healthy wild stock. However as more elasmobranch stocks face depletion in the wild it is conceivable that captive rearing facilities may be used to supplement wild stocks. If so, well-established methods of maintaining sufficient Ne should be practiced. For outbreeding depression to occur stocks that have evolved in reproductive isolation such that significant adaptive or co-adaptive evolution has occurred. Genetic studies performed to date indicate that there is generally a large amount of gene flow among geographically distant populations of several elasmobranch species, precluding the evolution of adaptive and co-adaptive differences among stocks. However, there is evidence of significant genetic divergence among some oceanic stocks of highly vagile species and at finer scales in some demersal species. While the genetic risks to native stocks of elasmobranchs following captive release appear minimal based on the above considerations, a principled and prudent approach would be to avoid releasing captive-reared elasmobranchs into the wild, and to release wild-caught elasmobranchs only into their population of origin.
(EJH) Southern Illinois University Carbondale, Fisheries and Illinois Aquaculture Center, Carbondale, IL 62901, USA; (JCC) Albion College, Albion, MI 49224, USA; (HLP) Mote Marine Laboratory, Summerland Key, FL 33042, USA
Estimating the number of sires and inferring paternal genotypes in Nurse Shark (Ginglymostoma cirratum) litters.
Nurse sharks have been shown to exhibit polyandry based on restriction fragment analysis of major histocompatibility complex loci. The presence of polyandry in nurse sharks is not surprising considering previous field observations of free-living nurse sharks frequently encountered multiple males involved in courtship and mating activities with individual females. We used multiple DNA microsatellite loci to investigate polyandry in nurse sharks by genotyping three complete litters ranging in number from 29 to 39 pups. All three litters exhibit polyandry with a minimum of five to six sires per litter based on the number of multilocus paternal haplotypes. Litters were sorted into full- sib groups based on analysis of kinship among littermates allowing for a more accurate estimate of the true number of sires and the contribution of each to the litter. Identification of full-sib groups also permits the identification of both paternal alleles at many loci and provides very high exclusion probabilities that can be used to unambiguously identify the sires of each full-sib group. This project is part of an ongoing study of nurse shark reproductive ecology in the Dry Tortugas, Florida. The unrivaled access to all life stages of nurse sharks, including mating groups and neonates, coupled with the very limited lifetime home ranges of nurse sharks, make this species ideal for studies of reproductive ecology.
Marine Biology Program, Florida International University, 3000 NE 151 St, North Miami, FL 33181, USA; Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Pkwy, Sarasota, FL 34236, USA
Catch rates and movements of bull and great hammerhead sharks in the lower Florida Keys
Bull sharks (Carcharhinus leucas) and hammerhead sharks (Sphyrna mokarran) are top predators in coastal waters of the Caribbean and the Gulf of Mexico, but little is known about their habitat use patterns or movements. We conducted a preliminary study of the distribution and movements of these sharks in near-shore habitats of the lower Florida Keys using catch rates, fixed-location acoustic monitoring systems and satellite telemetry. Catch rates of both bull and hammerhead sharks were influenced by habitat type and bait type. Despite being sympatric in many habitats, the few individuals monitored with acoustic telemetry and satellite telemetry as well as recaptures by fishermen suggest markedly different movements over the period of days. Generally, bull sharks made more localized movements over a period of weeks while four hammerhead sharks equipped with satellite transmitters moved several hundred kilometers east in a matter of days, and one shark made a dive to at least 300 meters depth. Bull sharks however, spent the majority of their time in much shallower water.
Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA
Does freshness count? Movements and habitat use by young bull sharks in the Caloosahatchee River
The use of freshwater habitats by bull sharks, Carcharhinus leucas, has been widely reported in the literature. This species is known to utilize habitats far up rivers and into large lakes. There has been little data, however, concerning how bull sharks use these habitats. This presentation will examine the use of the Caloosahatchee River as a nursery area for neonate and young-of-the-year C. leucas. To examine habitat use and home range size 18 C. leucas were captured in the Caloosahatchee River in August 2003, and fitted with acoustic transmitters. The movement patterns of all 18 individuals were monitored via a series of 20 acoustic hydrophones. Monitored sharks had a restricted home range (c. 4 km2) near the river mouth for the first two months of the study. No sharks were caught outside this region although data from surveys in previous years have shown that young C. leucas are commonly found farther upstream at this time of year. Rainfall levels during the summer of 2003 were higher than average, causing lower than normal salinities within the Caloosahatchee River study site. Salinity at the mouth of the river in the first two months of the study averaged 0.2 ppt. By October salinity levels at the mouth of the river had increased to 11.2 ppt and shark home ranges had increased to over 27 km2. In December of 2003 salinity levels at the mouth of the river were 16.8 ppt and shark home ranges size had expanded to the full extent of the monitoring array, over 69 km2. These results suggest that habitat use by C. leucas in the Caloosahatchee River was altered by salinity regime during the heavy rainfall of 2003. Detailed examination of home range and habitat use through time will be presented.
California State University Long Beach, Dept. of Biological Sciences, 1250 Bellflower Blvd., Long Beach, CA 90840, USA
Distribution and abundance of round stingrays (Urobatis halleri) at Seal Beach, California.
On average 250 stingray-related injuries occur to beachgoers at Seal Beach, California each year. This small 1.5 km long urban beach is bordered by coastal river with several power-generating plants 2 km upstream that discharge heated seawater into the Seal Beach area. Large numbers of round stingrays, Urobatis halleri, are known to inhabit Seal Beach and it has been hypothesized that U. halleri are attracted to thermal effluent; however, nearshore distribution and abundance of U. halleri and seafloor water temperatures at Seal Beach or adjacent areas are unknown. Distribution, abundance, and density of U. halleri were compared between two sites at Seal Beach (outfall sites) and also at adjacent Surfside (reference site ~ 2 km away) using diving surveys and beach seines. Diving surveys conducted from June-October of 2002 and 2003 indicated significantly higher stingray densities within 30 m of the surfzone, but densities decreased significantly 31-60 m from the surfzone. Concurrent seafloor water temperatures during diving surveys were significantly higher at Seal Beach than at Surfside, and were also higher within 30 m of the surfzone than 31-60 m from the surfzone. Stingray density from dive surveys was also positively correlated with seafloor water temperature at the Seal Beach sites, but not at Surfside. Stingray abundance obtained during monthly beach seines conducted from July 2002 through November 2004 was consistently higher at Seal Beach compared to Surfside Beach. These results suggest that U. halleri prefer warm nearshore habitats close to the surfzone at Seal Beach to cooler, ambient water temperatures further from the surfzone.
(DRH, PJM) University of South Florida, Dept. of Biology, Tampa, FL 33620, USA; (REH) Center for Shark Research, Mote Marine Laboratory, Sarasota, FL 34236, USA
Crushing and gouging: A bite performance analysis of durophagous and piscivorous sharks
Biting performance was investigated in the Horn Shark Heterodontus francisci and the Lemon Shark Negaprion brevirostris in order to identify behavioral differences associated with their divergent feeding mechanisms. H. francisci is durophagous, primarily consuming molluscs and echinoderms, whereas N. brevirostris is a piscivore. Five individuals of each species were trained to bite prey off of a custom-designed force transducer. Bite performance trials were simultaneously filmed at 250 fields/s with a Redlake Motionscope digital video system. Eight performance variables related to the magnitude, duration, and rates of change of force application were quantified using LabVIEW 6.1 software. Heterodontus francisci’s bite performance variables were significantly greater than those of N. brevirostris in nearly all cases. Maximum bite force of H. francisci and N. brevirostris were 70 N and 8 N respectively, while mean durations of force application were 450 and 154 ms respectively. Each bite performance variable indicates that bite force application by H. francisci is greater in magnitude and longer in duration than that by N. brevirostris, and indicative of a diet consisting of hard prey. Feeding performance by N. brevirostris is notably enhanced by head-shaking during prey capture however. While in the past it could only be conjectured as to whether sharks with different feeding mechanisms bite in different ways, this study provides conclusive data that this is in fact the case. Feeding performance studies such as this provide a new avenue to understanding how differences in morphology and behavior among taxa translate into differences in resource acquisition.
(NEH, JRT) School of Ocean Sciences, University of Wales, Bangor, Menai Bridge, Anglesey, LL59 5EY, Wales, UK; (SHG) Bimini Biological Field Station and University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, FL 33149, USA
Biotope mapping of the Bimini Islands as a base for defining Negaprion brevirostris nursery habitat
Conservation efforts to protect the marine environment are critical as extensive development is planned for The Bimini Islands, North Bahamas. Neonate, juvenile and sub-adult lemon sharks (Negaprion brevirostris) are dependent on the Bimini lagoonal complex. For effective management and conservation an accurate knowledge of early life history of resident sharks is required in order to define Essential Nursery Habitat. Integrating Geographical Information Systems and remote sensing has proved to be effective in achieving this. The study aimed to map the biotopes of the Bimini Islands, and two lemon shark nursery grounds within the Bimini setting. Landsat 7 ETM+ imagery was used alongside extensive groundtruthing to obtain data on the assemblage of conspicuous species, environmental parameters, biological zones and substrata. Data was standardized and statistically analysed to define biotopes which reflected the varying density of the dominant Turtle Grass (Thalassia testudinum) and environmental characteristics of the three main lagoons: (1) semi intertidal, North Sound Basin, part enclosed, limited tidal flushing and consequent stunted productivity; (2) Western Lagoon with restricted tidal flow; and (3) Eastern Lagoon opening out on to the Grand Bahamas Banks. The North Sound ecosystem appears most fragile with respect to environmental/ecological disturbance proposed by the resort development, which includes extensive mangrove removal and dredging. Marked effects on the survival of young lemon sharks in the North Sound caused by siltation due to unregulated dredging (pre-development) have been published. Although accuracy assessment has yet to be undertaken, field observations indicate that Landsat is suitable for medium/coarse resolution maps. Complex optical parameters within the water column however, presented problems during classification. Within the nursery grounds, boundaries may be inaccurate due to the sensors spatial resolution. The biotope maps will enable preliminary statistical analysis of habitat, with data on prey item and juvenile shark location and abundance to identify essential nursery habitat.
(DBK, EJH) Southern Illinois University, Fisheries and Illinois Aquaculture Center, Department of Zoology, Carbondale, IL 62901, USA; (MH, REH) Center for Shark Research, Mote Marine Laboratory, Sarasota, FL 34236, USA
Genetic structure of Blacktip Shark, Carcharhinus limbatus, populations
The circumtropical Blacktip Shark, Carcharhinus limbatus, utilizes coastal nursery areas throughout the world. Although many coastal elasmobranch species have widespread distributions, the genetic relatedness among populations is poorly known. Most previous investigations have been limited to sharks of multiple age groups collected from a single geographic region and have failed to detect genetic structure among sampled locales. We examined the fine-scale structure of blacktip continental nurseries in the western Atlantic Ocean and Gulf of Mexico using mitochondrial control region sequences and multiple microsatellite markers scored in neonate and young-of-the-year blacktip sharks. In addition, mitochondrial control region sequences were employed to investigate the genetic relationships of widespread populations from several locations in the eastern Atlantic and Indo-Pacific. Our data support female philopatry to natal nursery regions throughout the western Atlantic, Gulf of Mexico, and Caribbean Sea with higher levels of male-mediated gene flow within this region, producing population structure with microsatellites at larger geographical scales versus mitochondrial DNA. Nurseries along the Florida Gulf coast are genetically similar, suggesting the presence of straying among geographically proximate nurseries. A worldwide pattern consisted of two distinct clades: a western Atlantic, Gulf of Mexico, and Caribbean Sea clade and an eastern Atlantic and Indo-Pacific clade. Limited sharing of haplotypes among populations may reflect genetic structure within each region. Straying among proximate nurseries could serve as a dispersal mechanism and may have been interrupted by a vicariant event, such as the rise of the Isthmus of Panama, resulting in the two observed clades. This scenario implies historical dispersal across the Pacific Ocean, supported by the recovery of identical haplotypes from the Philippines, Hawaii, and the Gulf of California, and an oceanic barrier to migration across the Atlantic.
(RL) Carnegie Museum, 18 Hillside Road, Mt. Holly, NJ 08060, USA; (EDG) Biology Department, Saint Joseph’s University, 5600 City Ave, Philadelphia, PA 19131, USA
The quest for the stem chondrichthyan condition
New paleontological finds across the globe and new data on chondrichthyan biostratigraphy and community assemblages have significantly expanded the available information on the history of the Chondrichthyes and features of the chondrichthyan stem group. These new data also suggests that chondrichthyan researchers may need to reconsider commonly held interpretation(s) of the primitive condition of select anatomical and dental features. For example, the primitive chondrichthyan tooth condition has been presumed to be an in-line multicuspid tooth with no basal specializations (e.g., Diademodus Harris 1951) yet, the stratigraphic data indicate this is not an early tooth form. New chondrichthyan specimens exhibit intracranial fissures, features otherwise typically seen in osteichthyan neurocrania. Suspensorial and branchial morphologies display a range of diversity and indicate a history of ecomorphological adaptations that extends to the earliest levels of chondrichthyan diversification. Data resulting from these research programs have been used to expand our cladistic database of 320 million year old Bear Gulch and other chondrichthyan fishes. The results of this phylogenetic analysis are presented and show that regardless of the polarizations, characters, or modes of character analysis chosen, multiple origins and/or reversals of major character complexes are a striking feature of the early chondrichthyan radiation.
Warnell School of Forest Resources (Fisheries), University of Georgia, Athens, GA 30602, USA
Variable uptake and elimination of nitrogen stable isotopes in freshwater stingrays
Stable isotope analyses are frequently used in ecological studies to describe food-web structure and estimate trophic position, but few studies have considered the tissue kinetics of stable isotopes. While uptake of 15N has been quantified, no studies have examined its elimination. To address this issue, ocellate river stingrays (Potamotrygon motoro) were fed a high (222.5 ± 23.9; uptake), followed by low (7.3 ± 0.7; elimination), d15N diet. The rate of d15N increase during uptake varied among liver (3.2 d-1), muscle (1.3 d-1) and cartilage (0.84 d-1); unexpectedly, d15N in blood remained at 11.5 (±0.1) for the entire experiment. During the elimination phase, d15N values decreased in liver, but at a slower rate than during uptake; d15N values in muscle and cartilage showed little elimination of 15N. These results show that the behaviour of nitrogen isotopes is more complex than has been assumed previously. Following a diet switch, observed d15N values in fishes will depend both on the direction of the change (uptake vs. elimination) and the tissues examined (e.g. muscle, liver). Provided they are well understood, nitrogen stable isotope kinetics can potentially expand the range of ecological information available from fish tissues.
(CTM, NEK) USDOC/NOAA/NMFS, 28 Tarzwell Drive, Narragansett, RI 02882, USA; (HLP) Mote Marine Laboratory, 24244 Overseas Summerland Key, FL 33042, USA
Monitoring the juvenile Sandbar Shark, Carcharhinus plumbeus, population in the Delaware Bay nursery grounds
Delaware Bay is one of the principal pupping and nursery grounds for sandbar sharks, Carcharhinus plumbeus, in the East Coast waters of the United States. To provide information for effective management of this essential Sandbar Shark habitat, we need to understand and monitor its use by this species. Researchers from the National Marine Fisheries Service (NMFS) and the University of Rhode Island have been conducting gillnet and/or longline surveys for juvenile sandbar sharks in Delaware Bay since 1995. In 2001, a random stratified sampling plan based on depth and geographic location was initiated to assess and monitor the juvenile sandbar shark population. The geographic regions and depth strata ranges were chosen based on differences seen during historical sampling for juvenile sandbar sharks in Delaware Bay by NMFS from 1995 to 2000. Catch per unit effort in sharks per hour was used to examine the temporal and spatial relative abundance and distribution of sandbar sharks in Delaware Bay during the summer nursery seasons. Population estimates of juvenile sandbar sharks were also created using the catch data from the random stratified sampling plan and an estimate of gear sampling area that incorporates a simple Gaussian odor plume model. This model takes into account the rate of odor production by bait and the chemosensory threshold of the target species with respect to current velocity and gear saturation time.
(LJM, GC) School of Biology, University of St Andrews, Bute Medical Buildings, St Andrews, Fife, KY16 9TS, UK; (CC) Dept. Biology, Georgia Southern University, Georgia Avenue, Statesboro, GA 30460, PO Box 8042, USA; (NH) Gatty Marine Laboratory, School of Biology, University of St Andrews, St Andrews, Fife, UK
Osmoregulation and the sodium pump in the Bull Shark, Carcharhinus leucas from the Brisbane River, Queensland
The Bull Shark, Carcharhinus leucas, is rare amongst the elasmobranchs in that it is able to tolerate both seawater and freshwater environments. The body fluids of C. leucas can range between 600 and 1100 mOsm kg-1, but are always hyperosmotic to either the seawater (around 900-1000 mOsm kg-1) or freshwater (less than 100 mOsm kg-1) environment in which they are acclimated. Despite this variability in osmotic concentration, the plasma salt concentrations are maintained at levels similar to that of marine teleosts. This is achieved by efficient transport and regulation of water and ions which requires the expression and function of a number of membrane transporters which are fundamental to osmoregulation, including the Na, K-ATPase (sodium pump). Using RT-PCR and 5′- and 3′ RACE techniques we have amplified, cloned and sequenced cDNAs encoding the bull shark Na, K-ATPase alpha and beta subunits. The nucleotide and putative amino acid sequences have been analysed and compared to those published for other species including other stenohaline and euryhaline elasmobranchs. Further immunohistochemical and molecular studies are presently being conducted to characterise the expression and distribution of Na, K-ATPase alpha and beta subunits within the osmoregulatory tissues of bull sharks acclimated to FW or SW environments.
Florida Museum of Natural History, University of Florida, Florida Program for Shark Research, Gainesville, FL 32611, USA
Monitoring the East Coast bottom long line fishery through the Commercial Shark Fishery Observer Program
Since 1994, the Commercial Shark Fishery Observer Program (CSFOP) has been placing fisheries observers aboard bottom long line vessels directed at large coastal sharks from New Jersey to Louisiana. Fisheries observers have collected a large array of biological and fishery specific information that has served as a keystone data set utilized in the management process. The CSFOP has monitored 1140 sets representing 86,056 hooks and 10,153,396 hook hours aboard 42 vessels, documenting the capture of 34 species and 55,138 individuals from all four management categories. About 2-4% of the commercial bottom long line landings were monitored each fishing season. We report on species catch and landing composition and disposition, catch per unit effort, fishing and total mortality, size of individuals, and bycatch composition. Two species, Carcharhinus plumbeus (35.9% of catch) and Rhizoprionodon terraenovae (27%), are caught most frequently in this fishery. While C. plumbeus (56.7%) is routinely carcassed and landed for sale, R. terraenovae is rarely landed (10.9%). Yearly catch per unit effort (number of sharks per 10,000 hook hours) data varied within the large coastal and small coastal management groups, and within species, reflecting trends in population levels and movement patterns. At vessel fishing mortality was extremely high in some marketed species, e.g., Sphyrna mokarran (96.1%) and Sphyrna lewini (92%), while relatively low in others, e.g., Galeocerdo cuvieri (6.8%). However total fishing mortality was highest for Carcharhinus limbatus (99.6%) and R. terraenovae (99.3%), market and bait species, respectively. Length frequency histograms reveal variations between years, seasons and regions for many species, including two high interest sharks, C. obscurus (a protected species) and C. plumbeus (the cornerstone species of the fishery). Bycatch is not high in the fishery, most commonly Epinephelus morio (545), Dasyatis spp. (179) and Sciaenops ocellatus (126).
(PJM, DL, MPM, LBW, APW) University of South Florida, Dept. Biology, 4202 East Fowler Avenue, Tampa, FL 33620, USA;(REH) Mote Marine Laboratory, Sarasota, FL 34236, USA; (TCT) University of Hawaii, Dept. Zoology, Honolulu, HI 96822, USA; (APS) University of California Irvine, Dept. Ecology and Evolutionary Biology, Irvine, CA 92697, USA
A sucker is born every time: A story of suction prey capture in the nurse shark, Ginglymostoma cirratum
The functionally specialized Nurse Shark Ginglymostoma cirratum is representative of a group of sharks that are obligate suction feeders with apparently limited modulatory ability. Analyzing its food capture behavior by electromyography, high speed videography, and pressure recording, we determined that capture is invariably by suction, generating sub-ambient pressures as low as -98 kPA. Mouth opening occurs in 32-56 msec with a total bite time of 100-164 msec. Buccal pressure determined from semi-captive animals show two distinctly different pressure profiles that are perhaps related to the two-stage suction pump mechanism of the jaws and hyoid. A suite of anatomical features for effective suction feeding includes a small terminal mouth that is laterally bounded by enlarged and reinforced labial cartilages that pivot forward during jaw opening to form a tubular orifice. Jaw opening and buccal expansion is mediated by a conservative group of muscles similar to that of other sharks, but unlike most sharks the preorbitalis and levator palatoquadrati muscles appear to play no role in palatoquadrate protrusion. Upper jaw protrusion apparently has little functional utility during its suction prey capture, which appears at odds with its unique biomechanical design, perhaps reflecting its shared phylogenetic history with other orectolobid sharks.
Va. Inst. Mar. Sci., Greate Rd., Gloucester Pt., VA 23062, USA
Evolution of reproductive modes in elasmobranchs
Evidence is presented to support the hypothesis that yolksac viviparity, not oviparity, is the plesiomorphic reproductive mode in modern elasmobranchs. Yolksac viviparity is the most widespread mode occuring in most modern orders. In addition yolksac viviparity is the principal mode of reproduction in the oldest or most primitive members of the Batoidea, Squalomorphii, and Galeomorphii. Oviparity is the only mode in the Heterodontiformes an early offshoot from the Galeoids.However the earliest heterodontifoms were contemporaneous (lower Jurassic) with the most primitive order of galeoids, the brachaelurid Orectilobiformes which have yolksac viviparity. More advanced forms of viviparity, i.e. histotrophy, oophagy, placental viviparity, are all derived from yolksac viviparity. Elasmobranch oviparity is also derived from yolksac viviparity primarily as an adaptation for small species to increase fecundity, and as a bet hedging strategy to offset the probabilty of high predation on small pregnant females. Morphological and physiological data are also presented that support the yolksac viviparity hypothesis. In addition the yolksac viviparity hypothesis is more parsimonious from an evolutionary perspective. Plesiomorphic oviparity requires the independent evolution of viviparity nine or ten times and oviparity (as reversals) at least twice. Plesiomorphic viviparity requires the independent evolution of oviparity four or five times with no reversals.
(JAN, BAT) Coastal Fisheries Institute, Louisiana State University, Baton Rouge, LA 70803, USA; (JKC) National Marine Fisheries Service, 3500 Delwood Beach Road, Panama City, FL 32408, USA
Oxygen consumption of the Cownose Ray, Rhinoptera bonasus
Standard oxygen consumption rate (VO2) was determined for 19 cownose rays (Rhinoptera bonasus) using flow-through respirometry. Rays ranged in size from 0.4 to 8.25 kg (350 mm to 790 mm DW). Respirometry experiments were conducted at temperatures from 19.0 to 28.8o C, salinities ranging from 17.1 to 30.8 ppt and run within two hours of sunrise. Estimates of mass-dependent VO2 ranged from 55.88 mg 02 kg-1hr-1 for an 8.25 kg ray to 332.75 mg 02 kg-1 hr-1 for a 2.2 kg animal at 22 to 25o C. Multiple regression analysis was used to examine the effect of temperature, salinity, and mass on standard mass-independent VO2. Temperature had a significant effect on oxygen consumption (p = 0.0096), as did log (mass) (p = less than 0.0001), whereas salinity was insignificant (p = 0.5585). The final predictive regression model was: VO2 = temperature*0.05 + log(salinity)*0.55 + log(mass)*0.87 + 0.13 (p = less than 0.0001; Adj. r2 = 0.83). The Q10 was calculated to be 2.2.
(SPN, RDH) University of Plymouth, Department of Biological Sciences, Plymouth, Devon, PL4 6PW, England; (SPN, SHG) Bimini Biological Field Station, Bimini, Bahamas; (SHG) Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Florida, USA
Prey preference of nursery-bound juvenile Lemon Sharks, Negaprion brevirostris, at Bimini, Bahamas.
Prey preference was determined by quantitatively comparing the dietary composition of juvenile lemon sharks with concurrent sampling of prey communities at Bimini, Bahamas, between March 2000 and March 2003. Six hundred and forty-two juvenile lemon sharks were caught (averaging 54.7 ± 0.3 cm precaudal length, mean ± S.E., range 43.5 to 90.0 cm), of which 396 (62 %) contained stomach contents. Juvenile lemon sharks were predominately piscivorous (96 %IRI, index of relative importance), with the primary prey Yellowfin Mojarra, Gerres cinereus (70 %IRI). Extensive sampling of prey communities identified 175 species, of which only 49 (29 %) were preyed upon by juvenile lemon sharks. Prey recovered from shark stomachs were measured where possible, or original size calculated using predictive bone length regressions. Original size was obtained for 350 dietary items, with 85 % calculated using predictive bone regressions. Juvenile lemon sharks demonstrated a degree of selective feeding at Bimini, with proportions of prey families and prey sizes in the diet significantly different to those found in the environment (c2, P < 0.001 and Kolmogorov-Smirnov test, P < 0.001 respectively). The most preferred prey of juvenile lemon sharks (in rank order) were: toadfish > barracuda > parrotfish > filefish > mojarra. Yellowfin Mojarra were consumed in proportion to the distribution of fish lengths in the environment, suggesting that their importance in the diet may be due to preferred sizes in the environment as well as their ease of capture. Juvenile lemon sharks demonstrated a preference for slower-moving prey that were easier to capture (e.g. mojarras, toadfish, parrotfish and filefish), while avoiding larger, faster and harder to catch species. The degree of selection exhibited by juvenile lemon sharks was greatest when prey were more abundant, suggesting that lemon sharks conform to the optimal foraging theory.
(JWO, DES, GRH) NOAA, National Marine Fisheries Service, Alaska Fisheries Science Center, RACE Division, 7600 Sand Point Way NE, Seattle, WA 98072, USA; (JDM) Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX 77843, USA
Bathyraja parmifera (Rajidae: Arhynchobatinae) and related species, including preliminary data on a new species from the Aleutian Islands
Bathyraja parmifera is the most common skate on the eastern Bering Sea shelf, where it is widespread. Wide variation in spination and color, as well as the purported presence of the related western Pacific species, B. smirnovi, in the eastern Bering Sea led to this review. Bathyraja parmifera belongs to the Arctoraja group, which contains six nominal species, perhaps four of which are valid. Bathyraja simoterus has been considered a synonym of B. parmifera, however morphological evidence suggests the need for further examination of the species validity. The group is characterized by distinct characters of spination, claspers, and vertebrae. The dorsal thorn row in B. parmifera specimens from the Bering Sea shelf ranges from complete to interrupted, having a wide naked area between nape and tail. Specimens of the Aleutian Islands west of Amukta Pass possess an invariably complete dorsal row with a higher thorn count, coupled with a unique spotted color pattern and a less wide disc. Claspers also appear to exhibit distinct internal and external morphological features. Internal structures of the claspers differ in the shapes of the ventral marginal, axial, and dorsal terminal 2 cartilages. Bivariate plots of morphological characters revealed differences in disk width, tail length at the dorsal fins, as reflected in interdorsal length and the distance from dorsal-fin origins to the caudal-fin tip, and differences in pelvic-fin lobe proportions. When all morphometric data were subjected to a principal components analysis, significant differences were apparent between B. parmifera from the eastern Bering Sea and B. cf. parmifera from the Aleutian Islands.
8272 Moss Landing Rd. Moss Landing, CA 95039, USA
Age, growth, and maturity of the Sandpaper Skate, Bathyraja kincaidii
The Sandpaper Skate, Bathyraja kincaidii is commonly taken as bycatch in trawl fisheries off central California although there is no life history information known for this species. To assess age, growth and maturity, 393 Bathyraja kincaidii have been collected from commercial samplers, monthly trawl surveys and slope surveys conducted by the National Marine Fisheries Service since January 2002. Sexes were equally represented, with females comprising 50.1% and males 49.9%. Females ranged from 199-610 and males from 195-635 mm total length (TL). For age and growth analysis, sectioned vertebrae were read 3 times and APE (0.08), CV (0.13) and D (0.07) precision values calculated. Ages were assigned based on agreement of at least two independent estimates, with an additional read if necessary. Marginal increment analysis was unsuccessful, therefore centrum edge analysis is being investigated. Age estimates indicate a minimum longevity of 17 years for female and 18 years for male B. kincaidii. Females grow faster (Linf=533.9 mm; k=0.245; n=100) but males reach a larger size (Linf=580.387mm; k=0.187; n=90). Analysis of residual sum of squares indicated no difference (p = 0.089) between male and female von Bertalanffy growth curves, and combined sexes produced values of Linf=554.2mm and k=0.213. Females first mature at 450 mm (4 years), while males first mature 440 mm TL, 1 year earlier. However, 50% maturity was similar between sexes: 467 mm and 7.0 years for females and 492 mm and 7.5 years for males.
(ANP, FFS) Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, P.O. Box 117800,Gainesville, FL 32611, USA; (JG) Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA
Morphological and histological changes in the genital ducts of the male Atlantic stingray, Dasyatis sabina, associated with the seasonal reproductive cycle.
Changes in the morphology and histology of the epididymis and seminal vesicle in male Atlantic stingrays (Dasyatis sabina) were examined in relation to the seasonal reproductive cycle. Observations on the size and structure of these organs were accompanied by measurements of cell proliferation in genital duct epithelia using proliferating cell nuclear antigen (PCNA) as a marker for mitotic activity. No signs of reproductive tract growth or histological alteration were apparent during the initial stages of spermatogenesis. However, increased PCNA expression in the seminal vesicle epithelium was observed during this period, suggesting that this organ begins to undergo preparatory changes at an early stage in the reproductive cycle. During late spermatogenesis, heightened expression of PCNA in epithelial cells of the epididymis and seminal vesicle was observed in conjunction with dramatic increases in size and semen content of these organs. Extensive changes in the histological architecture of the genital ducts also were evident at this time, including regression of the stroma and increased size and secretory activity of the epithelium. Although the epididymis regressed in size and structure shortly after sperm production was completed, the seminal vesicle retained its appearance and activity for the duration of the 7-month copulatory period. Afterwards, immune cell content increased considerably in both ducts, likely reflecting clearance of residual spermatozoa in preparation for the subsequent reproductive season. The present study provides a basis for future reports on the physiological regulation of reproductive tract function in elasmobranchs, and establishes PCNA immunocytochemistry as a novel tool for such investigations.
(HLP) Mote Marine Laboratory, 24244 Overseas Highway, Summerland Key, FL 33042, USA; (JCC)Albion College, Department of Biology, Albion, MI 49224, USA
Reproductive competition and cooperation in male Ginglymostoma cirratum: Patterns and strategies
Ginglymostoma cirratum mating events generally involve one single male approaching a female that is resting or swimming in a shallow (less than 1m) refuge. The male orally grasps the chosen female’s pectoral fin as it attempts to mate. Female mating avoidance behavior is common. Single events are successful 7.2 % of the time. A small proportion of observed events (about 15 %) involve multiple males. During these events, two to at least ten males enter a shallow refuge from deeper water. They arrive together as a loose group behind the females, circle into position and attempt a pectoral grasp on one selected female. As the female reacts and begins to move toward shallower water or rolls to avoid or shake off an initial grasp, the group of males increases in speed, circling and pursuing as the female is herded or physically carried by them to the edge of the flats and into the channels (less than 2m), where water is deep enough to permit copulation. During this time, competition becomes obvious and intense with all males but one trying for the unshakable grasp of the female’s pectoral fin that makes copulation possible. Males nudge, bump and push each other as they grasp one or both female fins. One attendant non-competitive male facilitates mating from the very first encounter by positioning himself in front of the mating sharks (blocking). Videography shows that this role is determined even before the pectoral grasp is attained or the identity of the copulating male is decided by competition. Group mating is successful 24 % of the time.
(CMP) Duke University, Nicholas School of the Environment, Durham, NC 27708, USA; (DCA) Coastal Carolina University, Marine Science Dept., Conway, SC 29528, USA
A longline assessment of shark nursery grounds in two South Carolina estuaries
Surveys of sharks along the southeast coast have shown declines in several species. While these declines are generally attributed to overfishing, reliance of sharks on specific mating and nursery areas may be a contributing factor. As part of a long-term study, longline surveys were conducted from spring 2002 through fall 2003 in Murrells Inlet, a heavily human-impacted estuary, and nearby North Inlet, a relatively pristine system. Shark faunas of both sites have not been systematically studied. North Inlet had a higher CPUE (0.0735) than Murrells Inlet (0.0068), as well as higher species diversity. Juvenile and neonates of Rhizoprionodon terraenovae, Carcharhinus plumbeus and C. isodon were caught in North Inlet but not Murrells Inlet. Environmental variables (salinity, temperature, turbidity, DO) were similar. Polycyclic aromatic hydrocarbons, which are significantly higher in Murrells Inlet, may be a factor. Although data are based on only a single full sampling season, findings suggest that human impact is a deterrent to the utilization of Murrells Inlet as a nursery ground. (Supported by Georgetown County Environmental Protection Society, Project COASTSPAN, and the Edna Bailey Sussman Fund).
(NQ, FL, SP, PR, JPC) Rua Jorge Castilho 1613, 7C, 1900-272 Lisboa, Portugal; (AMS) Dept. de Zoologia e Antropologia, Faculdade de Ciências da Universidade do Porto, Portugal
Biological data on sharks landed in Portugal
There are 47 species of sharks and 28 species of rays off the Portuguese coast. Although several of them have substantially elevated commercial value and despite the drastic decrease in landings during the last few years, there is a lack of governmental regulations to protect these species or regulate the fisheries. In March 2003 a monitoring program was started on the four main Portuguese fishing landing docks, aiming to obtain relevant biological information so to propose adequate conservation measures. So far more than 1.200 individuals have been sampled, belonging to five of the most valued and frequently landed species: Centrophorus granulosus, Centrophorus squamosus, Centroscymnus coelolepis, Isurus oxyhinchus and Prionace glauca. Preliminary results on length/weight, size at maturity and seasonality of reproduction are presented.
(JGR, JAM) Virginia Institute of Marine Science, Fisheries Science Laboratory, Gloucester Point, VA 23062, USA; (RDG,KNH )Hawaii Institute of Marine Biology, PO Box 1346, Kaneohe, HI 96744,USA
Age and growth of the Sandbar Shark, Carcharhinus plumbeus, in Hawaii.
Age and growth of the sandbar shark, Carcharhinus plumbeus, in Hawaiian waters were investigated by examining annuli deposited in the vertebral centra from wild animals. Previous research has suggested rapid growth rates not typically associated with sandbar shark congeners throughout the world. Previous researchers estimated von Bertalanffy growth parameters of K=0.37 and Linf =149 for females and K=0.37 and Linf =139 for males. These growth estimates were obtained from captive sharks and may not be representative of growth rates exhibited by the wild population. Preliminary results portray much lower von Bertalanffy growth parameter estimates. Estimates for both sexes combined were: Linf =148, K=0.11, and t0 =-3.67.
Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA
Distribution of immature bull sharks (Carcharhinus leucas) in a southwest Florida estuary
The distribution and salinity preference of immature bull sharks (Carcharhinus leucas) was examined based on the results of longline surveys in three adjacent estuarine habitats in southwest Florida: the Caloosahatchee River, San Carlos Bay and Pine Island Sound. Size frequency distributions were significantly different between each of these areas indicating the occurrence of age-based habitat partitioning. Neonate and young-of-the-year animals occurred in the Caloosahatchee River and juveniles older than 1 year occurred in the adjacent embayments. The existence of habitat partitioning may reduce intra-specific predation risk, and so increase survival of young animals. The catch rates of juvenile C. leucas were highest in areas with salinities between 10 and 20 ppt. Thus although they are able to osmoregulate in salinities from fresh to fully marine, juvenile, C. leucas may, have a salinity preference. Reasons for this preference are unknown, but need to be further investigated.
(GS) Massachusetts Division of Marine Fisheries, Martha’s Vineyard Research Station, P.O. Box 68, Vineyard Haven, MA 02568, USA; (LN) National Marine Fisheries Service, 28 Tarzwell Dr., Narragansett, RI 02882, USA
Ultrasonic tracking of the porbeagle shark, Lamna nasus, in the Gulf of Maine.
Ultrasonic telemetry was used to investigate short-term horizontal and vertical movements of the Porbeagle Shark, Lamna nasus, in the Gulf of Maine. In August of 2000, two longline-caught porbeagle sharks were outfitted with pressure sensitive transmitters and tracked for periods of 48 hours. The sharks, which differed in size, exhibited dramatic differences in habitat preferences. Porbeagle 1, a 92.5 cm fork length female less than 1 year in age, traveled a total distance of 97 km and remained in the nearshore coastal waters of Maine with 82% of the total track time in water depths less than 60m. Although the shark moved through depths ranging from the surface to 64.2 m, 88% of the track was spent in the top 15 m of the water column. Over the duration of the track, porbeagle 1 moved through water temperatures ranging from 10-17ºC, but 93% of the track was spent in the discrete water temperature range of 15-17ºC. Porbeagle 2, an immature 203 cm fork length female of 12+ years, moved progressively east across the Gulf of Maine over a distance of 117 km. In contrast to porbeagle 1, this shark remained offshore over waters 71-250 m deep and moved through broader depth and temperature ranges of 0-85.5 m and 7-18ºC, respectively. Moreover, this shark swam deeper and in cooler water than the smaller shark, with 63% and 58% of the total track time at depths and temperatures of 15-45 m and 9-12ºC, respectively. This shark also exhibited diel differences in vertical behavior and its average rate of movement (0.676 ± 0.028 m s-1) was significantly higher (p less than 0.01) that that of porbeagle 1 (0.576 ± 0.026 m s-1). The behavioral differences exhibited by these two sharks may be indicative of size-specific habitat preferences in this species.
Moss Landing Marine Laboratories, Pacific Shark Research Center, 8272 Moss Landing Road, Moss Landing, CA 95039, USA
Population dynamics of a commercially exploited stingray, Dasyatis dipterura
Rays are commonly taken in western Mexico’s artisanal elasmobranch and industrial trawl fisheries. Dasyatis dipterura, the Diamond Stingray, is one of the most commonly landed species in their directed elasmobranch fisheries. Demographic analyses of D. dipterura from the Magdalena Bay lagoon complex, B.C.S., Mexico, were performed to estimate population growth characteristics and potential responses to fishing pressure. Age-structured life history tables and Leslie matrices were calculated using empirical fecundity, longevity, and maturity values. Monte Carlo simulation was incorporated to introduce demographic variability and uncertainty in age at maturity, fecundity, survivorship, and longevity. Ten models were developed from static (4) and Monte Carlo (6) approaches based on maximum observed age (28), theoretical maximum age (63), and variable longevity (25-39) under unexploited and exploited (F=0.05) conditions. Elasticity analyses determined the relative contribution and impact of changes in fertility, juvenile, and adult survival to population growth rates (l). Annual survivorship probabilities ranged between 0.71-0.94. Projections generated by incorporating Monte Carlo simulations produced mean l of 1.05-1.06 (5-6% increase) per year, net reproductive rates per generation (Ro) of 2.4-3.0, and generation times (A) from 14.4-15.2 years. Mean values of l obtained applying variable vital rates were similar to those recently calculated for several large, coastal carcharhinids. Introducing relatively low fishing mortality into population models produced a maximum l value under an optimal, static scenario of 1.09 and a minimum value of 1.01 annually under varied models. These D. dipterura populations thus have relatively low productivity and low resilience to fishing pressure. Elasticity analysis indicated that population growth rates of D. dipterura are more strongly influenced by survival of the juvenile and adult stages than survival of neonates or changes in fecundity. This elasticity pattern is similar that those observed among species of sharks and other long-lived marine vertebrates.
Moss Landing Marine Laboratories, Pacific Shark Research Center, 8272 Moss Landing Road, Moss Landing, CA 95039, USA
Reproductive biology of California (Raja inornata) and longnose (R. rhina) skates off central California
Skates have long been a common component of bycatch and discard among eastern North Pacific trawl fisheries, however, very little is known of their biology, distribution, or abundance in this region. California skate landings have markedly increased since the early 1990’s, but associated species and population-level effects are unknown. Fishing pressure has notably impacted the abundance, population structure, and distribution of skates in the North Atlantic, emphasizing the need for baseline biological information of this poorly known group. Since September 2002, members of the Pacific Shark Research Center have been working in collaboration with the National Marine Fisheries Service (NMFS) Santa Cruz Laboratory to investigate the life history, ecology, and systematics of central California skates. Data are being collected from monthly NMFS longline and trawl surveys across five depth strata ranging from 18-823 m. Here we report on the reproductive biology of the two most common skate species collected in these surveys, California (Raja inornata) and longnose (R. rhina). Raja inornata ranged from 17.3 to 72.2 cm TL with an F:M sex ratio of 1:0.8 (n = 299). Size at first maturity was observed at 54.5 cm TL among females and at 50.1 cm TL for males. Raja rhina ranged from 16.3 to 131.0 cm TL with an F:M sex ratio of 1:1.3 (n = 1,176). Size at first maturity was 73.1 and 61.9 cm TL for females and males, respectively. These results, and several other preliminary findings on skate reproduction, are part of an ongoing, broad-based study developed to determine critical life history parameters that are essential for effective management of these and other chondrichthyan species.
(DES, JWO, GRH) National Marine Fisheries Service, Alaska Fisheries Science Center, 7600 Sand Point Way NE Bldg. 4, Seattle, WA 98115, USA; (JDM) Department of Fisheries and Wildlife Sciences, Texas A&M University, College Station, TX 77843, USA
A new species of skate (Rajidae: Arhynchobatinae) from the Aleutian Islands
During the 2002 Aleutian Islands groundfish bottom trawl survey conducted by the Resource Assessment and Conservation Engineering (RACE) Division of the U. S. National Marine Fisheries Service, eleven specimens of a new species of Bathyraja were collected from Seguam Pass in the eastern Aleutian Islands. Seven additional specimens were later collected from Tanaga Pass and Petrel Bank in the central Aleutians. This new species is herein described and its geographic and bathymetric range documented. The new species is similar to B. violacea and Rhinoraja taranetzi in its moderate maximum size and absence of thorns on the disc. However, it can be clearly distinguished from B. violacea by its distinctive color pattern, uniform covering of fine denticles, and clasper morphology. It can be distinguished from R. taranetzi and other similar western North Pacific species by the lack of a pseudosiphon on the clasper as well as by differences in various morphometric and meristic characters.
EMS, MMH) SharkDefense Chemical Repellents and Research, PO Box 2593, Oak Ridge, NJ 07438, USA; (SHG) Bimini Biological Field Station and University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, FL 33149, USA
Semiochemicals as shark repellents – identification and behavioral responses
Multiple extracts of decayed shark carcasses were analyzed using HPLC, GC-MS, and fluorimetry in order to identify semiochemicals. Various semiochemicals were identified, and a mixture of these semiochemicals was prepared for evaluation as a chemical shark repellent. Feeding populations of up to twelve Caribbean reef sharks (Carcharhinus perezi) were significantly reduced within 180 seconds when a 200ml dose of the semiochemical mixture was delivered into the feeding zone. Aversive behavior was observed with as little as 1%w/w of the semiochemical mixture per 200ml dose. Favorable results were found with the semiochemical mixture when evaluated against the Johnson-Baldridge effective concentration model.
(JS, JK, SE, HH) University of New Hampshire, Zoology Department, Spaulding Hall, 46 College Road, Durham, NH 03824, USA; (JJ) Yankee Fishing Coop, Route 1A, Seabrook NH 03874, USA; (PD) University of Maryland, Department of Biology, College Park, MD 20742, USA; (PT) University of New Hampshire, Department of Animal and Nutritional Sciences, Kendall Hall, 129 Main St, Durham, NH 03824, USA
The reproductive cycle of the Thorny Skate, Amblyraja radiata, from the western Gulf of Maine.
The Thorny Skate (Amblyraja radiata) is a large species of skate that is endemic to the waters of the western north Atlantic in the Gulf of Maine. Because the biomass of thorny skates has recently declined below threshold levels mandated by the Sustainable Fisheries Act, commercial harvests from this region are prohibited. In order to address this problem, we have undertaken a comprehensive study to gain insight into the life history of this species. To this end, the present study describes and characterizes the reproductive cycle of female and male thorny skates, based on monthly samples taken off the coast of New Hampshire, USA, from May 2001 to May 2003. Reproductive parameters, such as gonadosomatic index (GSI), shell gland weight, follicle size and the presence of egg case formation, were assessed for 48 female skates. In general, these reproductive parameters remained relatively constant throughout most of the year. However, a transient but significant increase (p less than 0.05) in GSI and shell gland weight was revealed in specimens captured in October. Furthermore, within the cohort of specimens sampled monthly throughout the year, a subset of females always had large, presumptive preovulatory follicles present in their ovaries. In addition, with the exception of June and September specimens, egg cases undergoing various stages of development were observed in the uteri of specimens captured during all other months of the year. For males (n=48), histological stages III through VI (SIII-SVI) of spermatogenesis, GSI and hepatosomatic index (HIS) were examined. While there appeared to be monthly fluctuations in spermatogenesis, GSI and HIS, no significant differences were found. However, the production and maintenance of mature spermatocysts (SVI) within the testes was observed throughout the year. When combined with the observation that egg case production also occurred in females captured during most months of the study, our findings collectively suggest that the thorny skate represents an oviparous elasmobranch species that is reproductively active year round.
California State University, Long Beach, Department of Biological Sciences, Long Beach, CA 90840, USA
Movements and site fidelity of the Round Stingray, Urobatis halleri, at Seal Beach, California
The Round Stingray, Urobatis halleri, is a common nearshore elasmobranch in southern California waters. At Seal Beach, California, round stingrays are found in high densities and are responsible for approximately 300 injuries to beachgoers each year. Despite their abundance and negative interactions with humans, little is known about their movements or residence time in the Seal Beach area. Fine-scale movements and site fidelity of round stingrays at Seal Beach were examined using acoustic telemetry. Ten rays were manually tracked for up to 90.5 h, and 25 rays have been monitored using automated acoustic receivers for up to 480 d. Manually tracked rays generally exhibited limited nearshore movement, with greater distances traveled at night when the tide was ebbing than during the day with ebbing tides. Acoustically monitored rays typically remained off Seal Beach for weeks after they were tagged and six of 10 rays tagged in September 2002 were detected approximately one year later, with one individual detected at Seal Beach 15 mo after being tagged. Most detections of acoustically monitored rays occurred during the summer and early fall. These rays were recorded more often in the warm waters of the San Gabriel River mouth than adjacent beaches, with rays often returning to Seal Beach after periods of absence. Most male rays tagged were not detected during the winter, but returned the following spring, indicating a clear seasonal pattern. Overall, females were detected far less than males, but were more often detected during the winter. Both sexes co-occurred during June, corresponding with the mating season. Unlike other elasmobranchs that have been shown to exhibit strong diel movement patterns, round stingrays show movements related to a combination of tidal and diel periodicities with aperiodic movements away from Seal Beach.
(PWW, HRH) The Field Museum, 1400 S. Lake Shore Drive, Chicago, IL 60605, USA; (DM) Statistical Research Inc., 5331 Meadedale Drive, Burnaby, BC, V5B 2E6, Canada
Maya bloodletting rituals and stingray spines: The point of combining ichthyology, archaeology, and anthropology
Fishes played an important role in the everyday life and mythology of the ancient Maya civilization. An infamous example is Maya bloodletting rituals, where stingray spines were often used to perforate a ruler’s tongue, ear, or genitals to provide blood to inveigle the gods. Recent work has suggested that fresh spines may have been used and that the symptoms resulting from envenomation (most notably pain) were an important part of the bloodletting ritual. However, stingray toxins pose a more serious threat to human health than mere pain and inflammation. Medical studies conducted to track injuries resulting from stingray attacks report that up to two-thirds of all cases result in tissue necrosis. Yet the presence of stingray spines in ritual contexts and inclusion in bloodletting rituals as seen on Lintels 15 and 25 from Yaxchilan is indisputable. Case studies also show that even spines that appear clean may still retain necrotic properties. Reconciliation of these two disparate factors is crucial if we are to understand how the Maya viewed toxic marine materials and why they incorporated them into their ritual behaviors. Correlations between political events and stingray spine use may hold the key for understanding how these objects were articulated into the larger social and political sphere. Combining insights from the disciplines of ichthyology, archaeology, and anthropology can be mutually enlightening.
(SW) Natal Sharks Board, PBX2, 4320 Umhlanga Rocks, South Africa; (LN) Narragansett Lab, Northeast FSC, 28 Tarzwell Dr, RI 02882, USA; (FJ) Göteborg Natural History Museum, Box7283, 40235 Göteborg, Sweden; (GB) Florida Program for Shark Research, FMNH, Box117800, FL 32611, USA; (PC) Dep. Zoology, The Natural History Museum, London SW75BD, UK; (ADM) via L. Ariosto 4, 20145 Milano, Italy; (SG) South East FSC, 75 Virginia Beach Dr, MI, USA; (FCF) Dip. Scienze della Terra, Parco Area delle Scienze, Uni di Parma, 43100 Parma, Italy; (DE) PSRC, MLML, 8272 Moss Landing Road, CA 95039, USA; (JF) Dep. Ichthyology, CAS, Golden Gate Park, CA 94118, USA; (FH) Laboratoire Ecologie et Environnement, FSB, USTHB, BP39 El Alia, Algiers, Algeria; (FHM) Meistraat 16, 2590 Berlaar, Belgium; (SV) Museo di Storia Naturale dell’Università, Sezione di Zoologia, Via Romana, 17-50125 Firenze, Italy; (LVC, BH) Shark Research Center, SAM, Box61, 8000 CT, South Africa; (AWM) Umhlanga Radiology, PBX09, 4320 Umhlanga R., South Africa
Preliminary investigation of vertebral growth rings in the basking shark Cetorhinus maximus (Gunnerus)
Vertebral samples of 10 females (260.6-686 cm total length (TL)), 15 males (311-840 cm TL) and 9 unknown sex (375.9-853.4 cm TL) C. maximus were sourced through museums and institutional and private collections. A total of 101 vertebrae, including 58 vertebrae from a 260.6 cm TL animal, were used. In addition, different size vertebrae from a further eight animals were available. X-radiography was used to enhance the visibility of vertebral growth rings and a total of 153 x-radiographs were produced. Of those, 94 were scanned and growth ring counts were done both manually and using Digital Image Analysis. There was a linear relationship between vertebral diameter and TL and Von Bertalanffy parameters based on observed and back-calculated values will be presented.