Aversa, Marina Ileana; Dans, Silvana Laura; Crespo, Enrique Alberto
Age Determination and Growth in the Beaked Skate, Dipturus chilensis, in Northern Patagonia
Centro Nacional Patagonico (CONICET), Puerto Madryn, Chubut, Argentina
Age and growth of the beaked skate were estimated from bands in the vertebral centra of 405 individuals obtained from incidental catches of the Argentine hake (Merluccius hubbsi) fishery. It was assumed that the relationship between a hyaline plus an opaque ring corresponds to one year age. All skates collected were sexed, sized and weighted and a section of the vertebral column including the first 20 elements was removed. The histological technique used to enhance the growth bands on the vertebral centra was found to be satisfactory used for ageing marine mammals and some elasmobranches species. Stained sections provided repeatable and consistent bands counts though marginal crowding in the centra of older skates may leaded to underestimate the number of rings. The oldest male was 16 yr old and 101 cm of total length; the oldest female was 24 yr old and 133 cm of total length. Gompertz and von Bertalanffy growth models were fitted to the age and length data (L) and to age and disc width data (DW). Both growth models fit the data well. Maximum likelihood tests indicated that models constructed for males and females separately described growth data of the beaked skate better than one with both sexes combined. The von Bertalanffy growth curves derived from this technique indicate that female beaked skates reach greater size in length as well as in disc width (L∞=138 cm; DW∞= 102 cm) and have a lower growth rate (K=0.08) than males (L∞=110 cm; DW∞= 81 cm; K= 0.117). Beaked skates in northern Patagonia had lower estimates of L∞ than their conspecifics in the Pacific Ocean.
Bethea, Dana; Hollensead, Lisa; Carlson, John
Distribution and Abundance of Early Life Stages of Shark Species in the Panhandle of Florida, 2003-2006
NOAA Fisheries Panama City Laboratory, Panama City, FL, United States
Identification and conservation of essential fish habitat are important components of providing adequate management and conservation for shark populations. This is of particular importance when attempting to understand the dynamics of young sharks in coastal nursery areas to provide better information for juvenile shark distribution and abundance. Gillnets were fished in four areas in the panhandle of Florida (~29o40’N, 85o13’W) from April through October 2003-2006: St. Andrew Bay, Crooked Island Sound, St. Joe Bay, and the gulf-side of St. Vincent Island. A total of 563 sets were made. Captured sharks species were measured, sexed, and assessed for life history stage (young-of-the-year, juvenile, and adult), and when in good condition, tagged and released. Differences in size distribution were observed between areas. In St. Andrew Bay, Crooked Island Sound, and St. Joe Bay (three protected areas), the most abundant species-life stage combinations were Atlantic sharpnose shark juveniles (37-74 cm FL, mean=54.5, n=551) and young-of-the-year (25-54 cm FL, mean=38.5, n=230) and bonnethead young-of-the-year (43-52 cm FL, mean=43.7, n=129). However, on the gulf-side of St. Vincent Island, the most abundant sharks were blacktip juveniles (50-107 cm FL, mean=78.1 cm FL, n=195), finetooth juveniles (50-105 cm FL, mean=84.9 cm FL, n=146), and spinner juveniles (56-104 cm FL, mean=79.0, n=83). Habitat profiles were relatively similar among areas and species. In general, young-of-the-year are more often collected in shallower water with higher temperature, lower salinity, and more turbid conditions compared to juveniles. Catch per unit effort (# sharks per set per hour) was measured against several categorical factors. Factors found to effect relative abundance were area, season, and depth, depending on species and life stage. Recapture data indicated that most species do not range far and return to areas initially tagged, in some cases after many years at large.
Bruce, Barry; Stevens, John; Bradford, Russell
Satellite Tracking of Sharks in Australian Waters – Current Research and Challenges
CSIRO Marine & Atmosphheric Research, Hobart, Tasmania, Australia
Satellite-based data collection technologies have provided enormous improvements in our understanding of the spatial dynamics, movement patterns, habitat preferences and behaviour of sharks across a variety of ecosystems. These techniques have been applied in Australian waters to species as diverse as sawfishes in fresh and estuarine habitats, white, grey nurse and tiger sharks moving throughout coastal waters and the open ocean spatial dynamics of whale sharks, mako and blue sharks. Each species present specific challenges related to handling, tag application (sometimes with implications for tag design), predation events on tags and general tag retention. In some cases, where retention issues have been resolved, tag bio- fouling has presented some further challenges that require resolution to avoid deleterious effects on tagged sharks. Satellite-based data sets have also presented challenges and rewards in terms of data acquisition and handling, data processing, analysis, interpretation and visualisation. This talk will examine current Australian research on sharks that uses satellite-based techniques and illustrate examples of some of the above challenges and, where achieved, how these challenges have been tackled or the plans to do so.
Brunnschweiler, Juerg1; Pierce, Simon2; Marshall, Andrea2; Baensch, Harald3; Dudgeon, Christine4
Preliminary Whale Shark Sighting Data From Tofo Beach, Mozambique, And Depth And Temperature Data From A Whale Shark Crossing The Mozambique Channel
1University of Zurich, Zurich, Switzerland, 2Manta Ray & Whale Shark Research Centre, Tofo Beach, Mozambique, 3The Open University, Milton Keynes, United Kingdom, 4School of Integrative Biology, The University of Queensland, Australia
The area around Tofo Beach, Mozambique, has become a prime site for whale shark encounters in recent years. We provide preliminary results from photographic identification work that started in October 2005. In the first season (October 2005 to March 2006), a total of 163 whale sharks were sighted, of which 27 were females ranging from 5 to 10 m estimated lengths (mean = 7.13 m) and 88 were males ranging from 4.5 to 10 m estimated lengths (mean = 6.9 m). Of these males, 13 were mature. The total resight rate was 21%, with 19% of females resighted and 27% of males. The maximum duration between resights was 95 days (mean = 26.6 days) for females and 116 days (mean = 45 days) for males. In order to get insight into large scale movement patterns of whale sharks found in the Tofo Beach area, in February 2006, a male and a female whale shark were equipped with pop-up archival satellite tags. Within 91 days, the female whale shark crossed the Mozambique Channel and the tag popped up on the south-east coast of Madagascar. The shark spent most of its time near the water surface but showed occasional deep dives to a maximum depth of 1286 m. This depth is the deepest diving depth ever directly recorded for this species. Ambient temperatures were 3.38 to 29.9 °C (mean = 23.98 °C). The results suggest that the Tofo Beach area is an important feeding area for juvenile whale sharks, with a consistently high number of sightings year-round.
Henderson, Aaron1; Calosso, Marta2; McClellan, Katherine2
Elasmobranch Utilisation of the Waters Around South Caicos, Turks & Caicos Islands
1Sultan Qaboos University, Muscat, Oman, 2School for Field Studies, Salem, MA, United States
The island of South Caicos lies at the eastern edge of the Caicos Bank, at the southern end of the Bahamian Archipelago. The surrounding marine environment offers diverse habitats ranging from coral reefs to shallow seagrass beds and mangrove fringed sandflats, which serve as nursery grounds for numerous invertebrate and vertebrate species. Among the latter, sharks and rays are arguably the most conspicuous inhabitants of these shallow waters. Unfortunately, the development of tourism on South Caicos threatens to alter the local marine environment, through land-based development and increased recreational utilisation of its coastal waters. The present study was therefore undertaken to identify what elasmobranch species utilise these areas, with a view to determining what role the marine habitats around South Caicos play in the respective life-cycles of the species occurring there. Juvenile Negaprion brevirostris, Ginglymostoma cirratum, Dasyatis americana were found to utilise the shallow seagrass and sandflat habitats, as did adult Ginglymostoma cirratum, Dasyatis americana, Aetobatus narinari, Carcharhinus acronotus and Sphyrna tiburo. Adult Galeocerdo cuvier and Sphyrna mokarran were also observed in these areas but to a far lesser degree than the aforementioned species. The coral reefs to the south and east of the island were inhabited by adult and juvenile Ginglymostoma cirratum, Dasyatis americana and Carcharhinus perezi, in addition to adult Aetobatus narinari and Sphyrna mokarran. Negaprion brevirostris was by far the most commonly encountered species, with juveniles and neonates evidently using the area as a nursery ground.
Carlson, John1; Cortes, Enric1; Siegfried, Katie1; McCandless, Camilla3; Neer, Julie1; Beerkircher, Lawrence2
Should Night Sharks Be Listed as a Species of Concern to the Endangered Species Act?
1NOAA Fisheries Service, Panama City, FL, United States, 2NOAA Fisheries Service, Miami, FL, United States, 3NOAA Fisheries Service, Narragansett, RI, United States
Night sharks are an oceanic species generally inhabiting outer continental shelf waters in the northwest Atlantic Ocean including the Caribbean Sea and Gulf of Mexico. Although not targeted, night sharks make up a segment of the shark bycatch in the pelagic longline fishery. Historically, night sharks comprised a significant proportion of the artisanal Cuban shark fishery but today are rarely caught. Anecdotal evidence also suggests declines in the abundance within the pelagic longline fishery and data from billfish tournaments. Although information from some fisheries has shown a decline in night sharks, it is unclear whether this decline is due to changes in fishing tactics, market, or species identification. Despite the uncertainty in the decline, the night shark is currently listed as a Species of Concern (i.e. candidate species) to the Endangered Species Act due to purported declines in abundance resulting from fishing effort (i.e., overutilization). To assess their relevance to the species of concern list, we collated all available information on the night shark to provide an analysis of its status. Night shark landings were likely both over- and under-reported and thus probably did not reflect all commercial and recreational landings, and overall have limited relevance to the current status of the species. Average size information has not changed considerable since the 1980’s based on information from the pelagic longline fishery when corrected for gear bias. Analysis of biological information indicates night sharks are fairly productive (r=10%/year) and should be able to withstand reasonable levels of fishing effort. An analysis of trends in abundance from multiple data sources gave conflicting results with one series in decline; two series increasing and one relatively flat. Meta-analysis was applied to time series analysis to provide an overall trend estimate. Based on the analysis of all current available information, we believe the night shark does not qualify as a species of concern but should be retained on the prohibited species list as a precautionary approach to management until a more comprehensive assessment of the status of the stock can be conducted (i.e. stock assessment).
Global Population Structure of the Tope (Galeorhinus galeus), as Inferred by Mitochondrial Control Region Sequence Data
Nearshore Marine Fish Research Program, California State University, Northridge, Northridge, CA, United States
The tope, Galeorhinus galeus, is a medium sized member of the order Carcharhiniformes (family: Triakidae), currently distributed globally in temperate waters. Global populations of G. galeus are considered to be in decline due to the exploitation of shark fisheries over the past 80 years. Little is known of the northeastern Pacific population of G. galeus, and recent observations off the California coast indicate an increase in numbers. To determine the genetic structure of northeastern Pacific G. galeus populations, and the levels of gene flow among globally distributed populations, samples (n = 96) were collected and analyzed from five geographically dispersed populations (Argentina, Australia, California, South America, and the U.K.). A 1006-bp section of the 1068-bp mitochondrial control region (mtCR) revealed 33 polymorphic sites with 20 transitions, 11 transversions, and 2 deletions producing 28 haplotypes. Haplotypes were unique to their geographic location with only one haplotype shared between Africa and Australia. Overall, populations demonstrated high levels of haplotype diversity (0.9004 +/- 0.0172), low levels of nucleotide diversity (0.0065520 +/- 0.003458), and significant genetic structure (FST = 0.27151 and φST =0.85642; P < 0.001). Based on the results of this study, increasing numbers of G. galeus in the northeastern Pacific can be best explained by local recruitment and not input from geographically distant populations.
Chapman, Clint; Renshaw, Gillian
Anoxia Tolerance and Haematological Strategies in Two Closely Related Reef Sharks: The Epaulette Shark (Hemiscyllium ocellatum) and the Grey Carpet Shark (Chiloscyllium punctatum)
Griffith University, Gold Coast, Australia
Within elasmobranchs, only the epaulette shark (Hemiscyllium ocellatum) has been characterised as possessing significant tolerance to prolonged periods of hypoxia and even anoxia. This species is periodically exposed to cycles of increasingly severe hypoxia on coral reef flats, which it survives by entering into an energy protective state of ventilatory depression, bradycardia and neuronal hypometabolism. In comparison, the closely related grey carpet shark (Chiloscyllium punctatum) has a broader distribution and is not common on hypoxic coral reef flats. Therefore the ability of this species to tolerate oxygen deprivation had not been investigated. Ventilation rates and the time to loss of righting reflex were recorded in both species, in an open ended anoxic challenge. Haematological measurements were taken in both shark species to a standardised 1.5 hours of anoxia followed by 12 hours of re- oxygenation by measuring hematocrit, erythrocyte counts, haemoglobin concentration, plasma glucose and lactate levels. During anoxia, no ventilatory depression was observed in the grey carpet shark and the mean time to loss of righting reflex was 36.42 minutes (+/- 6.4 std. dev.) in juveniles and 153.84 minutes (+/- 36.42 std. dev.) in adults. The epaulette shark showed a mean time to loss of righting reflex of 178.13 minutes (+/- 30.5 std. dev.). In response to 1.5 hours of anoxia, the epaulette shark had a significant increase in hematocrit and MVC however there was no change in erythrocyte or haemoglobin concentrations, indicating an increase in erythrocyte volume. Alternatively, the grey carpet shark showed a significant hemoconcentration. This was indicated by significant increases in erythrocyte and haemoglobin concentrations, while mean corpuscular volume (MCV) and mean corpuscular haemoglobin concentrations (MCHC) indicated no changes in cell size or haemoglobin content. This hemoconcentration may be a result of either increased urine flow or the release of erythrocytes from a storage organ such as the spleen during oxygen deprivation. Within both species plasma lactate levels increased significantly, immediately following anoxia, while plasma glucose concentrations significantly increased after 2 hours of re-oxygenation in normoxia, a response not previously found in other elasmobranch species.
Chapman, Demian2, Shivji, Mahmood1
Tracking the Fin Trade: Genetic Stock Identification of Endangered Western Atlantic Scalloped Hammerhead Sharks
1Guy Harvey Research Institute and Oceanographic Center, Nova Southeastern University, Dania Beach, FL, United States, 2Current: Pew Institute for Ocean Science, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, United States
Dried fins from the scalloped hammerhead shark (Sphyrna lewini) are among the most highly-valued in the international fin trade, often fetching wholesale prices of over $100/kg. As a result of escalating market demand and fisheries overexploitation, Western Atlantic populations of this species have collapsed and are now classified as “Endangered” by the International Union for the Conservation of Nature (IUCN). While estimated global landings of this species are currently around 1-3 million sharks per year, the genetic stock structure and contribution of endangered Western Atlantic sharks to the total landings are unknown. Analyses of mitochondrial control region sequences (548 bp) from 105 animals reveal that Western Atlantic scalloped hammerheads comprise at least three distinct management units (MU’s: U.S.A., Central American/Caribbean and Brazil; overall φST=0.64) that will each be largely reliant on intrinsic reproduction rather than immigration for rebuilding. These MU’s are sufficiently differentiated from each other and eastern Atlantic and Indo-Pacific stocks to permit genetic assignment of fins to geographic origin, thus facilitating an improved assessment of the impact of the fin trade on regional scalloped hammerhead populations. Stock of origin determined for 57 scalloped hammerhead fins sampled from 11 traders in the Hong Kong market showed that the contemporary trade is globally-sourced, with a substantial presence of fins from imperiled Western Atlantic stocks. Results are used to formulate regional management recommendations and to develop monitoring strategies for the Asian fin trade that could dramatically improve global conservation of scalloped hammerheads and serve as a template for other sharks impacted by this trade.
The Effects of an Absence of Live Prey on the Predatory Abilities of Whitespotted Bamboosharks, Chiloscyllium plagiosum
University of Miami, Coral Gables, FL, United States
Because certain prey species may be very abundant at some times, yet very scarce at others, a predator that has become efficient at catching and eating this prey during periods of abundance would benefit if it retained efficiency during periods of scarcity. To determine whether hatchling whitespotted bamboosharks, Chiloscyllium plagiosum, are able to retain the ability to capture and eat prey after a period of prey absence, sharks were given experience foraging on one type of live prey, either polychaete worms or ghost shrimp, for twenty days (age= 2-21 days) and were then denied access to live prey for 18 days during which time they were fed small cubes of fresh tuna. They were allowed to forage on their initial prey species again after the absence period, and the predatory efficiency of sharks before and after the absence period were compared. The predatory efficiency of sharks after the absence period of were also compared to sharks of the same age that either had an equivalent amount experience without the absence period or were naïve to predation. When the prey was polychaete worms, the predatory efficiencies of sharks before and after the absence period were not different nor were they different from those of experienced sharks of the same age; however, sharks after the absence period were more efficient than naïve sharks. When the prey was ghost shrimp, the predatory efficiencies of sharks were higher after the absence period than before it. The predatory efficiencies of sharks after the absence period were not different from those of experienced sharks of the same age; however, sharks after the absence period were more efficient than naïve sharks. Hatchling whitespotted bamboosharks do retain the ability to catch and consume prey after a short period of prey absence.
Cocks, David; Clarke, Leon; Hussey, Nigel; Kennedy, Hilary
Testing the thermodynamic partitioning of Ba, Sr, and Ca in sharks teeth sampled from commercially operated aquaria
University Wales – Bangor, Bangor, Gwynedd, North Wales, United Kingdom
Elemental partition ratios, expressed as Ka-wSr/Ca, Ka-wBa/Ca, and Ka-wSr/Ba, have been shown to vary with temperature between synthetically precipitated apatite (a) and water (w) over the range 5 to 60oC. As such, these elemental ratios have been suggested as potential proxies for aquatic temperature and water-mass reconstruction. However, application of such geochemical proxies, to both recent and fossilised remains, requires confirmation of thermodynamic relationships in biogenic, as well as synthetic, apatite materials. This study investigated the partitioning of Ba, Sr, and Ca between aquaria water and sharks teeth, under constrained temperature conditions within three commercially operated aquaria. The elemental concentrations of 32 teeth and several water samples were determined by ICP-MS and ICP-AES and two hypotheses investigated: i) whether there is a temperature dependant elemental partitioning in sharks teeth and; ii) whether any species-specific elemental fractionation occurs in sharks teeth. Differential partitioning by temperature was tested using sand tiger (Carcharias taurus) teeth obtained from three aquaria: the London Aquarium (main tank mean temperature 23.24 ± 0.31oC; holding tank 24.39 ± 0.77oC); Deep Sea World (15.41 ± 1.04oC); and The Deep (24.09 ± 0.36oC). From the ICP-MS data a significant difference was found between The Deep and the other two aquaria for the elemental partition ratios Ka- wBa/Ca and Ka-wSr/Ba. Species-specific fractionation was tested using sand tiger, sand bar (Carcharhinus plumbeus), and black tip reef (Carcharhinus limbatus – within holding tank) sharks teeth from the London Aquarium. A significant difference was found between the black tip reef and the other two species for Ka-wSr/Ca and Ka-wSr/Ba ratios from ICP-MS data. The preliminary data suggest different temperatures do influence element partitioning in sand tiger teeth, but no significant statistical correlation between aquaria temperatures and partitioning ratio was found. High elemental variability within the London Aquarium teeth may be a confounding factor. Despite such high variability, a significant difference in the black tip reef shark Ka-wSr/Ca and Ka wSr/Ba ratios indicates a possible species-specific elemental fractionation, relative to both sand tiger and sandbar sharks. Recommendations will be made for improving experimental methodology, and for reducing variability in the analysis of shark tooth samples using these techniques.
de Sabata, Eleonora1; Clò, Simona2
A Six-Year Photo-Identification Study of a Population of Sandbar Sharks (Carcharhinus plumbeus) in the Mediterranean Sea Provide Evidence of Their Strong Philopatry on an Annual Cycle and over Multiple Years
1MedSharks, Rome, Italy, 2CTS, Rome, Italy
A population of sandbar sharks (Carcharhinus plumbeus) congregates in May and June in a small bay on the Turkish Aegean coast, Eastern Mediterranean sea. In 2001 the MedSharks project started a study of this population through underwater observations, photo-identification, dart- and PAT tagging, which is still underway. Observations indicate the presence of a population composed exclusively of sexually mature sharks. Only few males were seen; most of the sharks are large females with conspicuous abdomens. Some show fresh bite marks, with blood still visible. Underwater photo-identification was performed every year, creating a dataset of 3000 photographs and 10 hours of video. Natural distinctive marks were used for individual recognition. Photos were manually sorted and individuals identified using at least two independent characteristic features (e.g. fin shape, pigmentation marks, scars, tags). We were thus able to identify at least 50 different animals. Some natural marks were stable for a period of five years, providing a reliable way to identify individual sharks over time. Here we present a catalogue of identified animals and of confirmed re-sightings over the years. These re-sightings provide evidence of strong site-specific philopatry in this group of sharks, on an annual cycle and over multiple years. This catalogue will be the base for a population estimate. This is the first field study of any shark species ever undertaken in the Mediterranean sea.
Delius, Bryan; Heithaus, Michael
Do Bull Sharks Mediate Upstream Nutrient Transport in the Florida Coastal Everglades?
Florida International University, Miami, FL, United States
The Florida Coastal Everglades is an atypical estuary because limiting nutrients are supplied mainly from the ocean rather than from freshwater. One important question, then, is how these nutrients move against the flow of water to reach the low-salinity mangrove-sawgrass ecotone. Large consumers, such as juvenile bull sharks (Carcharhinus leucas), are one possible vector for such upstream transport. We used stable carbon and nitrogen isotopic analysis to determine if bull sharks could play a role in upstream nutrient delivery in the Shark River of the Florida Coastal Everglades. Sharks were captured using 400 m longlines at five sites 2 to 27 km from the mouth of the river. Small blood and muscle samples were collected from each shark to assess stable nitrogen and carbon isotopic ratios which provided information on trophic position (nitrogen) and whether sharks were feeding in marine- or freshwater-based food webs (carbon). More than 70 bull sharks were captured between the river mouth and 27 km upstream and in salinities ranging from 0.2 to 26.3 ppt. Preliminary analyses suggest that catch rates are unaffected by salinity and instead are driven by distance from the river mouth with a peak at ca. 22 km. Neither carbon nor nitrogen signatures varied between tissue types and were not affected by distance from the river mouth or shark size (range = 70-180cm TL),. Comparison with primary producers in the Shark River and adjacent coastal waters indicates that sharks are feeding in marine food webs and near the third trophic level. Thus, juvenile bull sharks likely mediate upstream nutrient flow in the Shark River, but it is still unclear whether they actively transport nutrients (by swimming to marine habitats to feed) or trap nutrients in the ecotone region (by feeding on other consumers moving upstream).
DiBattista, Joseph1; Feldheim, Kevin2; Gruber, Samuel3; Hendry, Andrew1
Are Indirect Genetic Benefits Associated with Polyandry? A Test in a Natural Population of Lemon Sharks
1McGill University, Montreal/Quebec, Canada, 2Field Museum, Chicago/Illinois, United States, 3Rosenstiel School of Marine and Atmospheric Science, Miami/Florida, United States
Multiple mating has clear fitness benefits for males, but the benefits for polyandrous females are less certain. We tested for such benefits in a population of lemon sharks (Negaprion brevirostris) by combining mark-recapture studies with genetic sampling and pedigree data. Specifically we followed the fates of individuals in six cohorts (450 age-0 and 255 age-1 fish) in relation to their genetic variation, and whether they were the product of polyandrous or monoandrous matings. We tested these hypotheses by using microsatellite markers to estimate genetic diversity (multi-locus standardized heterozygosity) or parental relatedness (internal relatedness). We found that offspring from polyandrous matings did not have a greater genetic diversity or survival than the offspring of monoandrous matings. We also found no evidence of positive associations between either individual offspring genetic diversity, or the level of parental similarity, and our surrogate measure of fitness (i.e., survival). In fact, age-1 individuals with fewer heterozygous microsatellite loci and more genetically similar parents (more inbred) were more likely to survive to age-2. Multiple mating by female lemon sharks does not appear to be adaptive from the perspective of indirect genetic benefits to offspring. Instead, it may simply result from a conflict between the sexes, with females allowing matings to avoid continued harassment. Our inability to find indirect genetic benefits of multiple mating despite detailed pedigree and survival information suggests the need for similar assessments in other natural populations.
Dicken, Matt; Smale, Malcolm; Booth, Anthony
Dynamics of the Raggedtooth Shark (Carcharias taurus) along the East Coast of South Africa
Straits Research, PE, South Africa
Understanding the population dynamics of raggedtooth sharks (Carcharias taurus) is crucial in defining abundance, habitat use and evaluating the effects of exploitation and anthropogenic activities. Between 1984 and 2004, a total of 1107 juvenile (< 1.8 m TL) and 2369 maturing and adult (> 1.8 m TL) C. taurus were tagged and released along the east coast of South Africa. A total of 125 juvenile and 178 maturing and adult C. taurus were recaptured, representing recapture rates of 11.2% and 7.5%, respectively. A Cormack-Jolly-Seber model was developed to estimate abundance, survival and probability of capture for both size classes of shark. The mean annual abundance of juvenile sharks was 6 800 (CV = 13%) and adult sharks 16 700 (CV = 9%). The accumulated effect of tag loss, non-reporting and post-release mortality were to reduce the overall estimate of juvenile and adult abundance by approximately 50%. The adjusted estimate of population size for both juvenile and adult sharks over the last decade appears to have remained constant (P > 0.05). This is one of the first applications of an open population model to any shark species worldwide.
Investigating Abundance and Distribution of Nearshore Sharks in the Northern Gulf of Mexico
1NOAA/NMFS MS Labs, Pascagoula, MS, United States, 2Dauphin Island Sea Lab, Dauphin Island, AL, United States
In 1995 the NMFS Mississippi laboratory initiated a bottom longline survey to assess population characteristics of sharks in the Atlantic Ocean and Gulf of Mexico. Qualitative analyses of the Gulf of Mexico data suggest a faunal break for sharks located near Mobile Bay. A monthly nearshore bottom longline survey was initiated in May of 2006 to investigate the potential faunal break as well as to gather information on sharks found in shallower waters (<20 m) along the coasts of Mississippi and Alabama (waters inaccessible to the vessels used during the above mentioned NMFS longline survey). To date 11 species representing nearly 800 individuals have been sampled from the nearshore bottom longline survey. Blacknose (Carcharhinus acronotus), sharpnose (Rhizoprionodon terraenovae) and blacktip (C. limbatus) sharks make up greater than 80% of the catch with CPUEs of 2.9, 2.8 and 2.2 sharks/100 hooks, respectively. No sharks were caught during the months of December through February, suggestive of migrations to warmer waters offshore. One difference observed between this nearshore survey and the initial NMFS survey was a greater abundance of finetooth sharks (C. isodon) in coastal waters than in deeper waters, indicating a possible nearshore habitat preference for this species. This study provides the fine scale distribution and abundance data necessary for robust stock assessment and future implementation of ecosystem based management plans.
Ebert, David; Bizzarro, Joseph
Distribution and Habitat Associations of Skates (Rajiformes: Arhychobatidae) along the Eastern Bering Sea Continental Slope
Moss Landing Marine Laboratories/Pacific Shark Research Center, CA, United States
Skates are an important component of the Bering Sea demersal fish community and are commonly caught in groundfish fisheries throughout Alaska. Despite the abundance and diversity of skates in this region, very little is known about their basic life history and ecology. To address this information gap, the distribution and habitat associations of the eastern Bering Sea continental slope (EBSCS) deep-water skate assemblage (Bathyraja spp.) were investigated. Data were collected during Alaska Fisheries Science Center bottom trawl surveys along the EBSCS during June- July 2002 and June-August 2004. The survey area extended from northwest of Unalaska Island (55° 95’N, 168° 52’W) to the southern Navrin Canyon (60° 16’N, 179° 68’W) in depths ranging from 200 to 1,200 m. The EBSCS can be characterized by three distinct mega-habitats; a broad, gentle, sloping area referred to as shelf habitat; areas bisected by submarine canyons referred to as canyon habitat; and regions of steep profile referred to as slope habitat. Trawls were conducted at six distinct locations of uniform habitat type. A total of 3,600 specimens comprised of nine species were examined for reproductive information and classified as juveniles, sub- adults, or adults. Distribution and habitat associations of each life stage of these species were analyzed in relation to location and depth. The results presented are part of an ongoing, broad-based, study of the demersal chondrichthyan fauna in the eastern North Pacific and Bering Sea.
Schultz, Jennifer1; Feldheim, Kevin2; Gruber, Samuel3; Ashley, Mary4; Bowen, Brian1
Coastal Habitat Preference Isolates Transatlantic Populations of the Lemon Shark (Negaprion brevirostris)
1University of Hawaii at Manoa, Kane’ohe, HI, United States, 2Field Museum, Chicago, IL, United States, 3University of Miami; Bimini Biological Field Station, Miami, FL; Bimini, Bahamas, United States, 4University of Illinois at Chicago, Chicago, IL, United States
The lemon shark (Negaprion brevirostris) inhabits shallow, inshore waters on either side of the Atlantic, with a relict population in the eastern Pacific; a sister species, the sicklefin lemon shark (Negaprion acutidens) is widely distributed throughout the Indo-West Pacific. To test for genetic connectivity among transatlantic N. brevirostris populations, we analyzed mitochondrial and microsatellite loci of individuals from Bimini, Bahamas, Atol das Rocas, Brazil and Bijagos, Guinea-Bissau. Genetic isolation is greater among transatlantic populations separated by 2,600 kilometers (Brazil-Guinea-Bissau) than among populations separated by 5,870 kilometers of coastal habitat (Brazil-Bahamas). Oceanic habitat, rather than distance, restricts gene flow, indicating strong coastal dependence. We used a molecular clock calibrated with the Isthmus of Panama and coalescence analyses to determine whether past vicariance events best account for the transoceanic distribution of this coastal shark. Comparisons with the eastern Pacific N. brevirostris population and the Indo-Pacific sister species, N. acutidens, indicate dispersal and speciation approximately 9-13 million years ago across the East Pacific Barrier (more than 4,000 kilometers of open ocean) and subsequent dispersal across the Atlantic 150,000-400,000 years ago. While an affinity for coastal habitat has primarily influenced lemon shark phylogeography, rare transoceanic dispersal has resulted in colonization, and in one instance speciation, across formidable barriers.
Effect of Changing Salinity on Urea and Trimethylamine-oxide Levels in Blood Plasma of Atlantic Stingray (Dasyatis sabina)
University of West Florida, Pensacola, FL, United States
Atlantic stingrays tolerate salinities ranging from 0‰ in Lake Jessup, Florida to more than 70‰ in the Laguna Madre, Texas. Like most elasmobranches Atlantic stingrays regulate plasma urea levels to reduce the osmotic gap. Trimethylamine oxide (TMAO) is also kept high to ameliorate urea’s deleterious effect on protein function. While several studies have investigated osmotic responses of Atlantic stingrays to decreasing salinities, little is known of how urea and TMAO levels change at salinities above 35‰. My project examined changes in plasma urea and TMAO levels of Atlantic stingrays exposed to salinities of 5, 20, 35, 50, and 65‰. Mean urea and TMAO values showed significant changes between salinity treatment groups (P < 0.05); however, plasma levels of these osmolytes did not demonstrate a linear relationship with ambient salinity. Plasma osmolality of stingrays in our experiments were hyper-osmotic at 35‰ seawater, showing a 33% difference between blood and water osmolality. At 5‰, however, stingrays became increasingly hypersaline showing a 440% increase between blood and water osmolality indicating that a minimum urea/TMAO level is required for normal physiological function. Under hypersaline conditions, Atlantic stingrays maintained plasma osmolyte concentrations only slightly higher than ambient water with only a 4% difference. Interestingly, we did not find a 2:1, Urea:TMAO ratio sometimes reported in the literature, rather ratios remained relatively constant at approximately 10:1and showed no significant difference (P < 0.05) between treatment salinities, suggesting that compounds other than TMAO make up the remaining osmotic gap. The ability to regulate and maintain consistent osmolyte:urea levels in the face of salinities approaching 200% seawater is the key adaptation making Atlantic stingrays to be one of the most euryhaline elasmobranch species known.
Figueroa, Daniel Enrique1; Martos, Patricia2; Reta, Raúl2; Cousseau, María Berta1; Díaz de Astarloa, Juan Martín3
Temperature and Salinity in SW Atlantic Waters Inhabited by Skates
1Universidad Nacional de Mar del Plata (UNMdP), Mar del Plata, Argentina, 2UNMdP and Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), Mar del Plata, Argentina, 3UNMdP, INIDEP and Consejo Nacional de Investigaciones Científicas y Técnicas, Mar del Plata, Argentina
Skates (Rajidae) are bentic fishes that are found worldwide. They are absent in waters of the inner continental shelf at tropical to warm temperate latitudes. Therefore they are well represented in the surveyed area. For the present paper we considered 613 fishing hauls, carried out by R/V of the National Institute for Marine Research and Development (INIDEP), between 34° and 55°S and from the coast to the continental slope, from 1993 to 1999. Oceanographic data (included CTD profiles) in the place of the haul were obteined and the captures were determined, following McEachran and Dunn (1998), Menni et al. (1984) and Stehmann (1978). In the study area there are 7 genera, Atlantoraja, Rioraja and Sympterygia inhabit warmer and generally shallow waters in the northern (Group 1), Dipturus and Psammobatis present extensive distribution in the continental shelf (Group 2), and Bathyraja and Amblyraja dwell patagonian shelf and slope, and deeper waters to the north (Group 3). Group 1 is the most stenothermic and euryhaline of the region. On the contrary, Group 3 is the most eurythermic and stenohaline. Group 2 shows an intermediate behaviour. Considering the subantarctic water genus Bathyraja, four species of them (B. albomaculata, B. brachyurops, B. macloviana and B. magellanica) are more eurythermic as well as euryhaline, while the other three B. griseocauda, B. multispinis and B. scaphiops show a strict-stenothermous-stenohaline behaviour.Within Psammobatis genus, P. lentiginosa is stenohaline and relatively stenothermal; both P. bergi and P. extenta are relatively warm stenothermal. Psammobatis spp. are relatively cold-stenothermal. P. bergi, P. extenta and Psammobatis spp are euryhaline species.
Franks, Bryan1; Gruber, Samuel2
A Mother’s Right to Choose: Ecological Partitioning of Nursery Areas at Bimini, Bahamas and its Implications for Conservation Strategies
1School of Bioscience and Biotechnology, Drexel University, Philadelphia, PA, United States, 2Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, United States
We studied a population of neonate and juvenile lemon sharks within two primary nursery areas at Bimini, Bahamas using both active and passive telemetry-tracking to examine movement patterns and habitat selection with the goal of understanding how predation risk and prey availability interact to affect space use. Between July 2002 and December 2005 we implanted transmitters in 55 lemon sharks; actively tracking 39 individuals and monitoring 16 using bottom mounted acoustic receivers. Eight individuals were tracked for longer than one year and one individual was monitored for the entire 3-year study. Results analyzed to date show that sharks younger than 4 years of age had relatively small home ranges (x̅ =0.76 km2, range = 0.17 – 3.02 km2) and were highly site attached when examined using Monte Carlo simulated random walks. The shortest direct, underwater distance between the North Sound nursery and the South Bimini nursery is only 8.9 km. Yet, there was no immigration or emigration in juvenile sharks between the two nursery areas studied. Although we tracked individual sharks travelling up to 38 km within their home range in a 24 hour period, sharks from one nursery never ventured to the other nursery. Thus the two lemon shark nurseries studied at Bimini must be considered entirely separate and distinct nursery grounds rather than a single continuous unit. This finding must be taken into account when designing and implementing conservation strategies. The decision by a full-term shark of exactly where parturition occurs may have important implications for the long term survival and fitness of cohorts. Even small-scale destruction or degradation of nursery habitat may have far reaching implications to populations if nurseries are geographically separated within a small area. In conclusion, a large area that supports juvenile sharks may well consist of many small geographically and ecologically distinct primary nurseries. These results demonstrate the importance of fine-scale studies of shark nurseries to accurately delineate space use by juvenile sharks and how such results may affect conservation strategies.
Gelsleichter, Jim1; Szabo, Nancy2
Are Bull Sharks on Drugs? Preliminary Observations on Human Pharmaceutical Exposure and Uptake in Juvenile Bull Sharks (Carcharhinus leucas) Residing in Wastewater-impacted Freshwater Habitats
1Center for Shark Research, Mote Marine Laboratory, Sarasota, FL, United States, 2Analytical Toxicology Core Laboratory, University of Florida, Gainesville, FL, United States
Recently, there has been growing concern about the ecological and human health risks posed by pharmaceutical-related pollutants originating from human excretion. These compounds can have unexpected and often profound effects on non-target species because many drugs function by altering biological processes that are common in most organisms. Since these contaminants enter the natural environment primarily through domestic and industrial wastewater discharge, they pose their greatest threats to wildlife residing in aquatic habitats bordering highly populated regions. However, there has been very little research conducted on the exposure to and uptake of these pollutants in aquatic species. In this presentation, we discuss preliminary data on the presence and concentrations of 7 widely prescribed human pharmaceuticals in juvenile bull sharks (Carcharhinus leucas) residing in wastewater- impacted Florida rivers. The compounds that were examined include 17α- ethynylestradiol (EE2), the synthetic estrogen commonly used in human contraceptives, and the active components (listed in parentheses) of the anti- depressant agents Celexa (citalopram) Luvox (fluvoxamine), Paxil (paroxetine), Zoloff (sertraline), Effexor (venlafaxine), and Prozac (fluoxetine). Several of these compounds have been detected in surface waters of aquatic ecosystems and the tissues of aquatic organisms in previous studies. Two of these compounds, EE2 and fluoxetine, have also been shown to be capable of altering reproduction and/or embryonic development in aquatic vertebrates. Juvenile bull sharks depend on freshwater and brackish rivers as “nursery grounds,” areas that are believed to provide young fish with protection from predators and abundant food to sustain high survival and rapid growth to maturity. Since these habitats are increasingly contaminated by wastewater-related pollutants including human pharmaceuticals, it is important to assess the risks that these contaminants pose to this unique species By doing so, our larger study will contribute valuable data on a non-fishing related human activity that may adversely affect Essential Fish Habitat for C. leucas.
Gleiss, Adrian C.; Wilson, Rory P.; Gruber, Samuel H.
What Can Cutting-edge Data-Loggers Tell Us About Behavior? A Preliminary Test on Captive Sharks at Bimini, Bahamas
1University of Wales, Swansea, Swansea, West Glamorgan, United Kingdom, 2Bimini Biological Field Station, Miami, Florida, United States
Elucidation of the behavioral-ecology of elasmobranchs is essential to further our understanding of the role of these important animals in marine ecosystems and therefore facilitate their conservation. Methodologies employed so far often rely heavily on untested assumptions, as to the behavioural function of an animal’s movement, highlighting the importance of a new technology able to resolve elasmobranch behaviour in the field. Semi-captive trials were conducted on two Lemon sharks (Negaprion brevirostris) in the Bahamas. Animals were equipped with state-of-the-art archival-tags, measuring 13 parameters (tri-axial acceleration, tri-axial magnetic field strength and a suite of other environmental factors). Using tri-axial acceleration and tri-axial magnetic field strength, three simple behaviours could be distinguished, steady-swimming, resting and fast-start swimming. Each behaviour could be defined by parameters measured and stored by the tags (frequency and amplitude of acceleration peaks, changes in compass orientation etc.). During steady swimming, animals displayed a wide range of tail-beat frequencies (0.4-1.2 Hz) and tail-beat acceleration amplitude (0.002-0.16 G). Overall dynamic body acceleration (ODBA), a parameter that has eluded reliable estimates of activity-specific metabolic rate in other taxa, showed a positive linear relationship with tail-beat frequency, thus indicating the potential for ODBA to be used as a proxy for energy expenditure in sharks. Comparison of ODBA for four distinct behaviours revealed it to be highest for fast-start swimming, while the ODBA measured during resting phases is lowest. The potential of these data-loggers, as well as their limitations are compared to other technologies presently employed in the study of elasmobranch behaviour. Supported by the Bimini Biological Field Station and the University of Wales, Swansea.
Goldman, Kenneth1; Musick, John2
Demographic Analysis of Sand Tiger Sharks in the Western North Atlantic
1Alaska Department of Fish and Game, Homer, Alaska, United States, 2Virginia Institute of Marine Science, Gloucester Point, Virginia, United States
The majority of demographic analyses on elasmobranch fishes have used deterministic life-tables (or Leslie matrix models) to calculate intrinsic rates of population increase and other demographic parameters. Density-dependent compensation is a standard concept in ecology and fisheries biology, however incorporating the effect of uncertainty in vital rates into demographic analyses of elasmobranch fishes is a relatively new and extremely useful approach to demographic modeling. We used life-table models incorporating uncertainty into vital rate estimates by establishing probability distributions for maximum age, age at first reproduction, fecundity and survivorship at age for sand tiger sharks in the western North Atlantic. Monte Carlo simulations were used to generate population growth rates, generation times, net reproductive rates, mean life expectancies, population doubling or halving times, and fertility, juvenile and adult elasticities. In order to utilize life-table models for analyses where fishing mortality was included, density-compensation values generated from the Intrinsic Rebound Potential model (of Au and Smith) were incorporated into our life-table models. The goals of this research are to provide new demographic parameter estimates for sand tiger sharks in the western North Atlantic based on recently published revised life history parameter estimates, and to observe whether the Intrinsic Rebound Potential model adequately predicts the necessary degree of compensatory survival in sub-adult age classes to keep population growth rates and other demographic parameter estimates stable under various levels of fishing mortality.
Graham, Rachel1; Gongora, Mauro2; Burgess, George3
Sharks and Rays of Belize: Results From Assessments of Abundance and Distribution and Fisher Interviews
1Wildlife Conservation Society, Punta Gorda, Belize, 2Belize Fisheries Department, Belize City, Belize, 3Program for Shark Research, UFL, Gainesville, Florida, United States
Shark populations are in decline globally through overfishing, and Belize is no exception. Interviews conducted with fishers throughout Belize and in neighbouring Guatemala suggest a dramatic decrease in shark diversity, abundance and size of sharks captured in Belize. The fishery targets primarily carcharhinid species, several of which are listed by the World Conservation Union as “Endangered”. As preferred species such as hammerheads (Sphyrna spp.) become increasingly scarce other shark species such as nurse sharks (Ginglymostoma cirratum) and rays (Dasyatis spp. and Himantura spp.) are increasingly captured to supply nearby countries with meat for the Lenten season and fins for the Asian market. Nets and, secondarily, longlines are gears of choice in a shark fishery conducted primarily between November and March. In southern Belize, fishing pressure originates mostly from neighbouring countries where shark populations have been overfished and coastal populations are significantly higher, demand is greater and gas half the price of that sold in Belize. Fisher survey results are further supported by a broad field survey conducted throughout southern Belize from January through October 2006 that has yielded low catch per unit effort. Results further reveal a notable absence of coastal sharks where patriarch fishers indicate previous higher diversity and abundance. Results from this study will be incorporated into the National Plan of Action for Sharks, which will form the basis for management of sharks and rays in Belize.
When Boat-based Tracking Is Not an Option: The Trials and Tribulations of Using Amazing (and Sometimes Frustrating) Satellite Telemetry on Several Shark Species in Two Ocean Basins
Wildlife Conservation Society, Punta Gorda, Belize
Long gone are the days where boat-based tracking provided the primary means of studying sharks in their element. The advent of satellite telemetry to study the behaviour and environmental preferences of sharks has expanded rapidly in the past decade and spawned a new generation of computer-savvy armchair behavioural biologists. As tag makers perfect their wares and collaborate with teknowledgeable field biologists, a dynamic and iterative tag development process has resulted in cost-effective tags that are increasingly demand- versus supply-driven. Much of the pioneering effort in satellite telemetry has focused on planktivorous sharks such as basking and whale sharks due to their predictable surface-based feeding behaviour. Studies conducted with 32 whale sharks in both the Indian Ocean and the Caribbean Sea have highlighted successes and shortfalls of both archival and location-only satellite tags. Satellite tracked whale sharks have revealed common patterns of environmental preferences and movements, results which have led to conservation successes and increased interest in the application of satellite telemetry to a range of other elasmobranchs. Lessons learned from the whale shark research have been shared broadly to maximize success in studies involving other elasmobranch species, particularly species those under heavy fishing pressure. Satellite telemetry can further identify the timing and location of undocumented shark fishing in relation to marine protected areas as revealed in a recent Belize-based study of elasmobranchs.
Guttridge, Tristan1; Gruber, Samuel2; Croft, Darren4; Sims, David3; Krause, Jens1
Size-assortment in Groups of Wild Juvenile Lemon Sharks, Negaprion brevirostris, Based on Evidence from Gill Net Captures
1University of Leeds, Yorkshire, United Kingdom, 2Bimini Biological Field Station, South Bimini, Bahamas, 3Marine Biological Association, Plymouth, United Kingdom, 4University of Wales Bangor, Bangor, United Kingdom
Group living in sharks is a widespread phenomenon but relatively little is known about the composition and organization of these groups. To study the natural composition and size-assortment of juvenile lemon sharks, N. brevirostris, records spanning an 11 year study were analyzed. One-hundred-forty-one individuals were caught as pairs with 70 different gill nets, set in three nursery areas in Bimini, Bahamas. All netted sharks were measured, sexed, tagged and released. Results demonstrated that pairs of sharks were significantly more size-assorted than would be expected due to random associations between individuals. The implications of this assortment for group living of wild sharks are discussed, along with the potential passive and active mechanisms that may contribute to the observed patterns. Supported by the NSF and Florida Department of Education.
Ha, Daniel1; Musick, John2
Comparison of Shark Long-Line Catch in New Jersey Across Forty Years
1West Chester University of Pennsylvania, West Chester, PA, United States, 2Virginia Institute of Marine Science, Gloucester Point, VA, United States
Researchers conducted a long-line survey off the coast of New Jersey in 1961-62, using gear virtually identical to that still used by the Virginia Institute of Marine Science’s (VIMS) long-line survey. The New Jersey study offers a rare opportunity to compare shark catch per unit effort (CPUE) for the same locations over a more than forty year time span using the same fishing gear and methods. The 1961-62 data were obtained from the National Marine Fisheries Service, and a sub-sample of the 1961 sites were resampled using the same type of gear in July of 2005. The mean biomass per standard set of the long-line in 2005 was 14% of the same in 1961. The most common species in both years was C. plumbeus, while the rarest species in both years was A. vulpinus. Of the six species that occurred in both 1961 and 2005, four had lower mean sizes and narrower size distributions in 2005 than in 1961. The CPUE of two of the six species, C. obscurus and G. cuvier, declined between 1961 and 2005. Mean weight per shark declined significantly in three of the six species (C. plumbeus, C. obscurus, and I. oxyrinchus). These findings provide separate corroboration of the patterns found in the more detailed Virginia data set, suggesting that any trends in abundance and/or mean body mass are not unique to Virginia or to the sampling period. To estimate a 1961 point in the VIMS data set, the New Jersey CPUE ratio (1961/2005) was multiplied by 2004 (2003 for G. cuvieri) Virginia long- line CPUE’s for the sharks under study. This showed dramatic 1961-1973 declines in Virginia in all species except C. plumbeus., and the Large Coastal Species complex. This implies that declines in shark populations began before the advent of recorded commercial fishing pressure.
Haas, Diane L.; Ebert, David A.
Torpedo formosa sp. nov., a New Species of Electric Ray (Chondrichthyes: Torpediniformes: Torpedinidae) from Taiwan
Pacific Shark Research Center, Moss Landing Marine Laboratories, Moss Landing, CA, United States
A new species of torpedo ray, Torpedo formosa, sp. nov., is described from specimens collected from northeastern Taiwan. The new species is placed in the subgenus Tetronarce based on a uniform purplish dorsal coloration and the absence of papillae around the spiracles. It is distinct from the sympatric T. tokionis, the only other known Torpedo (Tetronarce) species from the western North Pacific, by a disc that is wider than long, a shorter tail, a greater number of spiral valve turns, and its dorsal coloration. It has been misidentified as T. nobiliana, but is distinguished from it by having longer snout and spiracle lengths, a lower vertebral count, and a caudal fin height that is greater than the distance from the first dorsal origin to the caudal fin origin. The distribution of T. formosa appears to be somewhat restricted as it is currently known only from the northeast coast of Taiwan, with no known reports from Japan or the Philippines. An overview on the distribution of Torpedo (Tetronarce) species is given.
Harahush, Blake; Hart, Nathan; Fritsches, Kerstin; Collin, Shaun
Retinal Development of the Visual System in the Brown Banded Bamboo Shark, Chiloscyllium punctatum (Hemiscylliidae)
University of Queensland, Brisbane, Queensland, Australia
The growth and development of the retina of the oviparous elasmobranch Chiloscyllium punctatum is examined in the embryonic, hatchling, juvenile and adult stages. The eye of C. punctatum begins its formation early in development at around 27 days post deposition (dpd) with retinal progenitor neurons present from 58 dpd. Retinal cell differentiation begins around 82 dpd with the ganglion and Muller cells, followed by the amacrine, horizontal, and bipolar cells and finally the photoreceptors (rods and cones) at 115 dpd. The bases of the rod photoreceptor outer segments (OS) also begin to accumulate visual pigment (rhodopsin) at this time, with equivalent concentrations of pigment throughout the OS present at 119 dpd. Microspectrophotometric analysis reveals the rods possess a peak spectral sensitivity of 500 nm, which does not alter post-hatching. By 124 dpd, the retina is fully differentiated and all synaptic connections are formed, approximately one month prior to hatching. Rates of retinal cell differentiation are not constant throughout embryogenesis with pronounced increases in cell proliferation and cell death. The retina continues to grow throughout life, although post-hatching rates are much slower than during embryogenesis. The distribution of ganglion cells varies throughout development and a specialised retinal region of high density forms across the horizontal meridian upon hatching. This study reveals that C. punctatum may possess functional vision up to 30 days prior to hatching and possesses a mature retina well-adapted for both scotopic and photopic vision as it emerges from its egg case.
Hayes, Christopher; Jiao, Yan
Stock Assessment and Management of Scalloped Hammerheads (Sphyrna lewini) in the Northwestern Atlantic Ocean.
Virginia Tech, Blacksburg, VA, United States
NOAA Fisheries Service recently completed an assessment of large coastal sharks (LCS), the Southeastern Data Assessment and Review 11. It was determined that the nine species aggregate was not overfished (N/NMSY > 1), but the review panel recommended that NOAA Fisheries Service conduct species-specific assessments of large coastal sharks. This study investigates the population dynamics of one species within the LCS complex: scalloped hammerhead sharks (Sphyrna lewini). Scalloped hammerheads are a slow growing species that exhibits relatively low fecundity, making them vulnerable to over-exploitation. Because catch data are not partitioned by size or age, we used an age-aggregated surplus-production model. We investigated the goodness of fit of models with three productivity curves: Schaefer (1954), Fox (1970), and Pella-Tomlinson (1969) using Akaike Information Criterion (AIC). The biological implications of these three curves and the AIC were used to select the Pella-Tomlinson model. Multiple scenarios were constructed to test the influence of 1) abundance index weighting and standardization, 2) species composition change over time, and 3) anomalies in the catch data. The population experienced severe overfishing prior to 1996, but has grown since the mid-1990s as fishing pressure decreased. Current population size is just under half (0.47) of the estimated population size prior to fishing. Bootstraps were used to demonstrate uncertainty in the estimated parameters. Incorporating that uncertainty, we projected the population thirty years into the future at various management-relevant fishing levels: FMSY, (0.75)FMSY, F2005, and (0)FMSY, and we estimated the risk of the population being overfished in 30 years under those fishing-levels.
Hollensead, Lisa; Bethea, Dana; Carlson, John
Bioenergetic Condition of Juvenile Scalloped Hammerheads (Sphyrna lewini) in Two Coastal Habitats in the Northeastern Gulf of Mexico
NOAA National Marine Fisheries Service, Panama City, FL, United States
There are many different estuarine habitats throughout the Gulf of Mexico that may serve as a nursery area for sharks. The bioenergetic condition of juvenile scalloped hammerheads (Sphyrna lewini) in two habitats in the northeastern Gulf of Mexico was examined. Tests were conducted to determine any differences in growth and daily ration between juvenile scalloped hammerheads in a relatively shallow, protected area (Crooked Island Sound, FL) and river-influenced estuarine environment (gulf- side of St. Vincent Island, FL). Sharks were collected using gillnets May-August, 2000-2004. Livers were weighed to calculate the hepatosomatic index (H.S.I). Stomachs were emptied and individual prey items were separated, identified to the lowest possible taxon, counted, and weighed, and then used to calculate the index of relative importance on a percent basis (%IRI). Bioenergetic models were used to obtain daily ration and growth rate. In Crooked Island Sound, fish dominated the diet (flounder, 83.9 %IRI). On the gulf-side of St. Vincent Island, shrimp were more important May-July (62.7 %IRI), but sciaenids (e.g., Stellifer lanceolatus) dominated the diet in August (40.3 %IRI). In Crooked Island Sound, daily ration was 1.4 % body weight day-1. On the gulf-side of St. Vincent Island, daily ration was higher (1.8 % body weight day -1). H.S.I. values decreased during the hottest months of the summer in both areas, indicating that sharks may be living off liver reserves for increased energetic demand. Overall, there were no differences in growth rate between areas.
Hueter, Robert1; Tyminski, John1; Simpfendorfer, Colin1; de la Parra, Rafael2; Trigo Mendoza, Montserrat2
Satellite-Based Tracking of Whale Sharks (Rhincodon typus) Tagged off Quintana Roo, Mexico: Movement Patterns, Hypotheses and Challenges
1Center for Shark Research, Mote Marine Laboratory, Sarasota, Florida, United States, 2CONANP-SEMARNAT, Cancun, Quintana Roo, Mexico
Between mid-April and September each year, large numbers of whale sharks (Rhincodon typus) aggregate to feed in the coastal waters off Mexico’s Isla Holbox and Isla Contoy, where the northwestern Caribbean Sea meets the southeastern Gulf of Mexico. Biological studies of these sharks to document their distribution, ecology and behavior began off Quintana Roo in August 2003, and have continued into 2007. In addition to using conventional visual tags with which we have tagged over 550 sharks at the site, our migration studies have deployed satellite-linked pop-up archival transmitting tags (PATs). So far a total of 13 PATs have been attached to immature and mature sharks of both sexes with total lengths ranging from 4.5 to 8.5 m. Archived information has been recovered from eight of these tags to date. After using the upwelling-fed, nutrient-rich waters off Isla Holbox and Isla Contoy as a summer feeding area, the sharks appear to disperse in multiple directions in the fall. The satellite tag data have documented geographic movements of nearly 900 km in one month from the tagging site westward into the Gulf of Mexico, southward into the Caribbean Sea, and eastward towards the Straits of Florida. Utilization of both inshore and offshore habitats is evident. Once off the continental shelf, the archived PAT data have revealed regular diel vertical movements and dives to at least 1,376 m. During these vertical movements the sharks may experience ambient temperature changes of over 25 ̊C in as little as one hour’s time. These results, hypotheses about the sharks’ movement patterns and challenges in the use of satellite tagging to track these huge animals will be discussed.
Hussey, Nigel; McCarthy, Ian; Mann, Bruce
Use of a Long Term Tag-recapture Data Set on the Dusky Shark (Carcharhinus obscurus) in South East Africa to Determine Spatial and Temporal Movements and Growth Rates
School of Ocean Sciences, University of Wales – Bangor, Menai Bridge, Anglesey, United Kingdom
KwaZulu-Natal (KZN) in Southern Africa is an important nursery area for dusky sharks (Carcharhinus obscurus). The recreational fishery is well developed and previous studies have expressed concern over fishing mortality rates. Through a long term tag recapture programme (1983-2006) initiated by the Oceanographic Research Institute and WWF South Africa, a total of 9541 individual sharks have been tagged. This study aimed to determine spatial and temporal movement patterns with specific focus on elucidating information on large scale movements undertaken by juvenile animals. As of December 2006, a total of 620 sharks had been recaught, principally juvenile animals, through the involvement of recreational fishers and captures in beach protection nets. The majority of recaptures were within 100 km of tagging in the core nursery area in KZN. A total of 48 animals (7.7%) undertook movements >200km and a clear southward movement pattern was identified between KZN and the Eastern/Southern Cape (E/SC). Large scale movement (>200km) in a southerly direction occurs between June (mid autumn/winter season) and November (beginning of spring/summer season) with no significant difference in minimum migration speed detected across months. Seasonal northerly migration patterns (E/SC to KZN) were less well defined. The largest movement recorded in a southerly direction was 1323 km (mean ± S.E; 806.4 ± 54.4) and in a northerly direction 1374 km (mean ± S.E; 623 ± 102.0). Of animals moving <100km south from KZN, a notable increase in displacement occurred between June and October suggesting these animals may have been caught as they began their migration to E/SC. A significant pattern of increasing speed with increasing displacement was observed, although no significant difference was found in migration speed between sharks moving >100km in a northerly or a southerly direction. The maximum speed of travel recorded in this study was 32.4 km/day for a shark travelling from KZN to E/SC. Growth rates calculated from the tag-recapture data using both Fabens (1965) and Francis (1988) models agree with current literature values. The information obtained on migration patterns and growth rates of dusky sharks in this study highlights the value of long- term monitoring programmes in understanding the ecology of the coastal life- stage/s of shark species.
Imhoff, Johanna; Gruber, Samuel; Lankford, Thomas
Evaluation of Ultrasonic Accelerometry as a Technique for Studying Foraging Behavior in Juvenile Lemon Sharks (Negaprion brevirostris)
1University of North Carolina Wilmington, Wilmington, NC, United States, 2University of Miami Rosenstiel School of Marine and Atmospheric Science, Miami, FL, United States, 3University of North Carolina Wilmington, Wilmington, NC, United States
Shallow lagoons surrounding Bimini, Bahamas serve as important nurseries for juvenile lemon sharks (Negaprion brevirostris). Although the movement patterns and food habits of juveniles within these nurseries have been well-studied, information regarding specific foraging locations or habitats is lacking. Investigation of foraging locations of the juvenile lemon shark would provide greater insight into its early life history, and a basis for understanding its movement patterns. Knowledge of foraging locations of apex predators could also be useful for management, specifically regarding placement of marine protected areas. The objective of this study was to evaluate the ability of a newly developed ultrasonic accelerometer transmitter to detect foraging-related accelerations made by juvenile lemon sharks. Transmittered sharks (n=7; FL=69-90 cm) were observed in captivity with and without live fish prey. Alarm events signalled by the transmitter and associated behaviors were recorded under four different sensitivity levels (1.5g, 1.7g and 1.9g in all directions, and 2.1g in the forward and reverse directions/3.0g in the side to side direction; 1g = 9.8 m/s2). Transmitter performance was evaluated by comparing frequencies of positive alarms (associated with pursuit, capture or handling of prey) and false positives (associated with non-foraging behaviors) across trials. The most sensitive transmitter (1.5g) detected 85% of chases, 100% of handling behaviors, and 100% of captures. Though the overall detection of foraging attempts, defined as the occurrence of one or more foraging behaviors, was 80%, this transmitter also had the highest false positive rate (.194 per minute). The less sensitive transmitters (1.7g, 1.9g and 2.1g/3.0g) produced few alarms overall, most of which were false positives. With further adjustment of accelerometer sensitivity to reduce false positive alarms, and continued captive trials, this technology has the potential to be useful for studying the foraging habits, physical locations of foraging attempts, and foraging success of large marine predators.
Jones, Lisa1 Quattro, Joe2; Driggers, William1; Hubbell, Gordon3
Use of Mitochondrial DNA Sequence Data to Identify Morphologically Similar Species of Triakid Sharks in the Northern Gulf of Mexico
1NMFS/SEFSC/Pascagoula Laboratories, Pascagoula, MS, United States, 2University of South Carolina, Columbia, SC, United States, 3Jaws, Int, Gainesville, FL, United States
Historically, two shark species within the genus Mustelus (Family Triakidae, smoothhounds) have been recognized in the northern Gulf of Mexico: the smooth dogfish, Mustelus canis, and the Florida smoothhound, M. norrisi. In a recent revision of the genus a new species (M. sinusmexicanus) was described from the northwestern Gulf of Mexico. Differentiating M. sinusmexicanus from M. canis is difficult and based primarily on dermal denticle morphology, vertebral counts, and vertebral morphology. Thirty seven specimens (four M. canis, five M. norrisi, and 28 M. sinusmexicanus) were identified and independently verified to examine the usefulness of reported characters for use in field identifications. After morphometric and meristic measures were obtained, DNA was isolated from fin clips from each specimen. While three species were identified using accepted morphological characters, direct sequencing of the mitochondrial control region (d-loop) revealed the presence of only two species. Of the four haplotypes found, three were unique to M. sinusmexicanus and a single haplotype was shared by M. canis and M. norrisi.
Jorgensen, Salvador1; Weng, Kevin1; Perle, Chris1; Anderson, Scot3; Van Sommeron, Sean4; Klimley, A. Peter2; Block, Barbara1
Satellite Tracking of Lamnid Sharks in the North Pacific Ocean
1Tuna Research and Conservation Center, Hopkins Marine Station of Stanford University and Monterey Bay Aquarium, Pacific Grove, CA, United States, 2Department of Wildlife, Fish, & Conservation Biology, 1334 Academic Surge, University of California at Davis, Davis, CA, United States, 3Invernes, CA, United States, 4Pelagic Shark Research Foundation, Capitola, CA, United States
Understanding the ecology and physiology of sharks of the family Lamndiae with satellite-based tracking is a major focus of the Tagging of Pacific Pelagics (TOPP) research program. We have tagged 91 white sharks with Pop-up satellite archival tags (PAT), and 94 salmon sharks with Smart Position or Temperature tags (SPOT), 78 of the salmon sharks were ‘double-tagged’ with PAT tags. The SPOT tags have provided over 36,000 positions, and PAT tags have logged over 12,500 days of data from both species. Results to date have revealed some similarities in the annual offshore migratory patterns of these Lamnid congeners, while demonstrating geographic niche partitioning in the north eastern Pacific. Both species have long- term migrations and display fidelity back to the coastal regions of tagging. White sharks undertook consistent yearly migrations offshore away from northern California coastal habitats. Records from deployments over eight months in duration demonstrate individuals consistently return to specific sites, known elephant seal rookeries, along northern California after a pelagic phase that lasts approximately 6 months. This site fidelity facilitates the recovery of the PAT tags that are scheduled to pop up near-shore at the end of the migratory cycle. This results in the retrieval of full archival records detailing pressure, ambient temperature and light in 60 second intervals. Seven of these archival records (mean duration 257±18 days) have revealed detailed diving behavior at two white shark pelagic hotspots, a region of the central north Pacific gyre dubbed the ‘white shark café’, and a second region just south of the Hawaiian Islands. Oscillatory diving behavior was consistent among individuals in the central eastern pacific hot spot but distinctive at either location. Salmon sharks displayed two modes of migration with some individuals over-wintering in Alaskan waters, or migrating large distances to the tropics or subtropics, presumably to pup. SPOT tag deployments on Salmon sharks have provided continuous records for up to 3 years revealing strong fidelity to particular coastal regions in Alaska. Individuals also returned to the same southern regions in successive years. Both Lamnids occupy a large home range together comprising most of the eastern north Pacific, however, relatively little geographic overlap occurs with the notable exception of regions of the productive California current.
Kajiura, Stephen1; Fitzgerald, Timothy2
Response of Juvenile Scalloped Hammerhead Sharks to Electric Stimuli
1Florida Atlantic University, Boca Raton, FL, United States, 2Environmental Defense, New York, NY, United States
All elasmobranchs possess an electrosensory system that enables them to detect electric fields in their environment. Although their exquisite sensitivity to weak electric fields is legendary, the determination of their sensitivity (ie. voltage gradient detection threshold) is often derived by extrapolating from a mathematical model of the charge distribution for an ideal dipole. This study empirically measured the electric field intensity of a dipole in seawater and confirmed the close correspondence with the model. From this, it is possible to predict how the sharks will respond to dipolar electric fields comprised of differing parameters. We tested these predictions by exposing sharks to different sized dipoles and levels of applied current that simulated the bioelectric fields of their natural prey items. The sharks initiated responses from a significantly greater distance with larger dipole sizes but did not respond from a significantly greater distance with increasing levels of electric current; a result that may be due to the limited range of currents tested. This study is the first to ground-truth a popular model and test predictions about how sharks will respond to a variety of different electric stimuli.
Kessel, Steven; Gruber, Samuel; Perkins, Rupert; Grubbs, Dean
Exploratory Longlines on the Slope of the Great Bahama Bank off Bimini
1Cardiff University, Cardiff, United Kingdom, 2University of Miami, Miami, FL, United States, 3Virginia Institute of Marine Science, Gloucester Point, VA, United States
Since May 2005 a number of deep longline sets have been conducted at Bimini, Bahamas (25°44N, 79°16W), with the purpose of assessing the abundance and diversity of the shark assemblages on the western slope of the Great Bahama Bank. The set location is 2 nm west of Bimini on the edge of the Gulf Stream. Each set involves a single weighted bottom line at a depth of ~300 m. Sets are monitored continuously at the surface for a period of ~12 hrs from dusk till dawn. Gangions extend from the main line and include 18/0 circle hooks for larger sharks and 12/0 circle hooks for smaller sharks. During the hauling process sharks are identified, sexed and measured (pre-caudal, fork and total length) and all individuals over 140 cm fitted with a NOAA/NMFS M-type dart tag. To date six different species have been captured, Galeocerdo cuvier, Hexanchus nakamurai, Carcharhinus altimus, C. signatus, Squalus cubensis and Mustelus canis insularis. These sets may allow evaluation of movements of G. cuvier between the deeper slope waters and the shallow Great Bahama Bank. This species is common on the shallow water sets conducted twice monthly on the Bahama Bank (<3 meters depth). All G.cuvier from slope waters were mature (>300cm in total length) and mature specimens have also been captured on the shallow sets. Recaptures of tagged individuals may reveal movement between slope and bank waters for this species. Past sets have revealed a relatively high abundance of H. nakamurai, previously thought to be uncommon in these waters. It is likely that more species will be encountered with future sets, further increasing understanding of Bimini’s deep water shark populations.
Le Port, Agnès1; Sippel, Tim2; Lavery, Shane2; Montgomery, John. C1
Dispersal of Short-tailed Stingrays (Dasyatis brevicaudata) Determined from Satellite Tagging and Mitochondrial DNA (mtDNA)
1Leigh Marine Laboratory, University Of Auckland, Leigh, New Zealand, 2School of Biological Sciences, University Of Auckland, Auckland, New Zealand
The short-tailed stingray (Dasyatis brevicaudata) is a large temperate stingray solely distributed in the southern hemisphere, and has been recorded in New Zealand, southern Australia and South Africa. In summer, this species forms conspicuous aggregations at some off-shore islands, such as the Poor Knights Islands (NE New Zealand). Movements and reproduction related migrations in short-tailed stingrays are poorly understood. Here, we present movement data for stingrays using a new technique of PSAT tag attachment developed for ray species. Two female short-tailed stingrays were tagged for 62 and 151 days in total, to investigate their long-term movements and environmental (depth, temperature) preferences. In particular, the species’ potential for long-distance seasonal migrations was examined. Our results do not provide evidence for seasonal migrations away from offshore islands. However, tagged stingrays showed a shift to deeper waters towards winter and decreased time spent at shallow depths. More detailed examination revealed a more heterogeneous behaviour. The rays showed very different daily vertical movements, only one displaying a strong diel vertical migration, while the other spent the majority of its time in deep waters (> 100m) both day and night. We suggest that diel vertical movements observed in one of the stingrays may be due to behavioural thermoregulation reflecting the particular environmental (currents, depth) conditions of its surroundings. Preliminary results from mtDNA analyses investigating large scale connectivity of short-tailed stingray populations will also be discussed.
Lisney, Thomas; Collin, Shaun
Retinal Topography in Elasmobranchs: Implications for Behavioral Ecology and Spatial Resolving Power
School of Biomedical Sciences, Vision, Touch and Hearing Research Centre, The University of Queensland, Brisbane, Queensland, Australia
The topographic distribution of retinal ganglion cells in fishes is strongly correlated with behavioral ecology. These cells are organized into one or more species-specific, specialised regions of increased cell density, which serve to sample particular regions of visual space with a higher spatial resolving power. In comparison to bony fishes, the topography of retinal ganglion cells in cartilaginous fishes has received little attention. We have assessed the retinal topography of ten species of elasmobranch, based on counts of Nissl-stained, presumed retinal ganglion cells in retinal wholemounts. These new data have been combined with information from the literature in order to present an overview of retinal ganglion cell topography in cartilaginous fishes. The prominent feature of most elasmobranch retinas is an elongated horizontal band or ‘streak’ of increased cell density, which reflects the importance of scanning the horizon (the substrate-water or air-water interfaces, or the horizontal gradient of light in the water column). However, variation in the position of the streak (i.e. in the dorsal, central, or ventral retina) reflects interspecific differences in behavioral ecology. As the retinal ganglion cells and their axons provide the only link between the eye and the brain, the spatial resolving power of an eye can be estimated using retinal ganglion cell spacing and a measure of the focal length of the eye. Estimates of the upper limits of spatial resolving power for elasmobranchs range from approximately 2.0 to 10.6 cycles per deg. Active benthopelagic and pelagic sharks, especially some coral reef associated and oceanic species, tend to have a higher spatial resolving power than benthic sharks and rays. Presenting author’s current address: Department of Biology, Queen’s University, Kingston, Ontario, Canada.
Movement Patterns of Grey Reef Sharks at Johnston Atoll and Palau, Pacific Ocean
Boston Univ., Boston, MA, United States
The movement patterns of the grey reef shark, Carcharhinus amblyrhynchos, was examined at Johnston Atoll and in Palau. The objective was to determine whether this shark species exhibited any measurable degree of local site fidelity or if they just wandered widely and haphazardly. At Johnston Atoll, the question concerned the degree of exposure to individual sharks that were found in reef habitats contaminated with PCBs and Dioxins. At Palau, the question concerned if and how far individual sharks wander beyond the boundaries of the marine protected area at the Blue Corner dive site. Sharks were captured by baited hook, promptly tagged and released. Tags were banded onto a shark’s caudal peduncle and tracked by underwater loggers strategically deployed at up to 17 locations. The study at Johnston Atoll was during 1999 to 2003. The Palau study was from 2003 to 2006. The presentation will show maps of shark movements with an analysis of diel patterns of habitat use.
Lowe, Christopher; Mull, Christopher; Zemel, Hayley
Occurrence and Distribution of Stingray-related Injuries at Seal Beach, California
California State University Long Beach, Long Beach, CA, United States
An average of 275 stingray-related injuries are reported annually at Seal Beach, California, a small (1.5 km long) urban beach, located south of Los Angeles. The round stingray (Urobatis halleri) is a common ray along nearshore sandy beaches and bays in southern California and is thought to be responsible for a majority of these injuries to beach goers. Analysis of Seal Beach lifeguard injury reports from 1997 to 2005 indicated that most injuries occurred during summer months and in areas closest to the San Gabriel River mouth. Beach seine sampling indicated that rays were most abundant near the San Gabriel River mouth where water temperatures were highest and finer sediments were most common. Reported injuries by activity indicated that board surfers (16%), swimmers (11%) and waders (21%) constituted the greatest proportion of injuries reported at Seal Beach. A majority of injuries were reported on feet and lower legs (> 96%); however, injuries were also reported on hands, buttocks, and knees. A stingray education program has been instituted by Seal Beach lifeguards in attempts to reduce the number of injuries.
Mandelman, John W.1; Skomal, Gregory B.2
Blood Acid-base Status in Longline-caught Carcharhinids: Links Between Interspecific Differences and Observer Reported At-vessel Mortality
1New England Aquarium, Boston, MA, United States, 2Massachusetts Marine Fisheries- Massachusetts Shark Research Program, Vineyard Haven, MA, United States
Fisheries observer data have revealed interspecific differences in the at-vessel mortality rates of several carcharhinid sharks captured either directly or as bycatch on demersal longlines off of the southeastern US. As current regulations mandate the release of many of these fish, interspecific variation in physiological resiliency also carries substantial ecological and management implications. To investigate the species-specific relationship of longline-induced mortality to physiological perturbations, we analyzed whole blood acid-base status (pH, pCO2, pO2, lactate anion) in sandbar (Carcharhinus plumbeus; n = 44), dusky (C. obscurus; n = 24), blacktip (C. limbatus; n = 10), tiger (Galeocerdo cuvier; n = 49), and Atlantic sharpnose (Rhizoprionodon terraenovae; n = 24) sharks captured alive on standardized commercial-style demersal longline gear during three-hour sets on four NMFS longline surveys conducted off the southeastern US from 1996-2004. We found significant (p < 0.0001) species-specific differences in all blood acid-base indicators. Moreover, differences in mean blood pCO2 and lactate levels indicated that the extent to which depressions in blood pH could be attributed to metabolic and/or respiratory acidoses differed by species. Pair-wise comparisons of mean blood chemistry parameters revealed that tiger sharks exhibited the lowest perturbation, followed by sandbar sharks. Mean blood pH was lowest in the blacktip shark, followed by the dusky and sharpnose sharks. Higher blood lactate levels in the latter two species, however, implies enhanced anaerobiosis and a greater metabolic contribution to the blood acidemia, while elevated pCO2 in the blacktip was indicative of a greater respiratory component. These differences in blood biochemistry correlate well with species-specific mortality rates observed during commercial longline fishing activities. Thus, mortality induced by longline capture is closely associated with species-specific differences in respiratory and metabolic physiology. Although closely related, these carcharhinids possess intrinsic physiological mechanisms that differ markedly and contribute to varying levels of longline-induced mortality.
Mara, Kyle R.1; Motta, Philip J.1; Huber, Daniel R.2
Durophagy in the Bonnethead Shark, Sphyrna tiburo: An Ecomorphological Conundrum
1University of South Florida, Tampa, FL, United States, 2University of Tampa, Tampa, FL, United States
Bite force, used as a measure of performance, may be used to link an organism’s cranial morphology with its biological role. As such, bite force may be predictive of dietary constraints or lack thereof. The bonnethead shark, Sphyrna tiburo, is a durophagous member of the family Sphyrnidae. Its diet in south Florida waters consists almost entirely of juvenile blue crabs which are either crushed or ingested whole during ram feeding. This abundant coastal predator has a feeding mechanism specialized for the consumption of hard prey, including a modified jaw adductor activity pattern, and molariform teeth. The goal of this research was to characterize the biomechanical basis of durophagy in S. tiburo (68-96 cm TL) by determining the leverage of its jaw adducting mechanism (mechanical advantage) and its bite force. Theoretical maximum bite forces were estimated from three-dimensional musculoskeletal modeling and compared to those gathered during manually restrained biting and electrical stimulation of the jaw adducting musculature in anesthetized sharks. Preliminary data indicate that the average theoretical bite force ranged from 13.7 N at anterior teeth to 52.6 N at the posterior teeth. Average bite force from restrained individuals was 10.9 N at the front of the jaws and average anterior bite force during electrical stimulation was 9.1 N. Mechanical advantage ranged from 0.29–1.27 from the anterior to posterior teeth. Compared to other durophagous bony fishes and elasmobranchs, S. tiburo has a surprisingly low bite force given the proportion of hard prey in its diet. These findings are discussed in relation to the force required to crush crabs and prey capture behavior.
McCandless, Camilla T.1; Pratt, Jr., Harold L.4; Kohler, Nancy E.1;. Merson, Rebeka R.3; Recksiek, Conrad W.2
Movements and Migrations of Juvenile Sandbar Sharks, Carcharhinus plumbeus, Tagged in Delaware Bay
1NOAA Fisheries, Narragansett, RI, United States, 2University of Rhode Island, Kingston, RI, United States, 3Rhode Island College, Providence, RI, United States, 4Mote Marine Lab, Summerland Key, FL, United States
Delaware Bay is one of two principal nursery grounds for the sandbar shark, Carcharhinus plumbeus, in United States coastal waters, with the second one located in Chesapeake Bay. Tagging studies were conducted for juvenile sandbar sharks in Delaware Bay during their summer nursery seasons from 1995 to 2000 using gillnet (1995-2000) and longline (1997-2000) gears. These studies were designed to aid fishery managers in defining essential fish habitat for juvenile sandbar sharks tagged in Delaware Bay by determining spatial and temporal distributions, overwintering nursery areas, and if natal homing occurs in sandbar sharks born in Delaware Bay. A total of 2066 juvenile sandbar sharks were caught in Delaware Bay from 1995 to 2000 and 87% of the sharks sampled were tagged before release. Of these tagged sharks, 156 (9%) have been recaptured through 2005. Mark-recapture data from the NMFS Cooperative Shark Tagging Program were also used to supplement the data obtained from this study. These include 143 recaptures of sandbar sharks originally tagged in Delaware Bay from 1964 to 2005 as juveniles. The majority of these sharks were tagged by NMFS biologists (69%) and recreational fishermen (18%). The remaining sharks in this database were tagged by other biologists (6%), fisheries observers (4%) and commercial fishermen (3%). Recaptures indicate that the majority of sandbar sharks born in Delaware Bay return to their natal nurseries for up to five years following birth (and potentially up to 12 years of age), overwinter off North Carolina, and eventually expand their range south to the east coast of Florida and into the Gulf of Mexico as they get larger. This study also provides the first evidence of mixing between the juvenile sandbar shark populations that utilize Delaware and Chesapeake Bays during the summer nursery seasons.
McComb, Mikki; Kajiura, Stephen
Visual Fields Of Four Batoid Fishes: A Comparative Study Florida Atlantic University, Boca Raton, FL, United States
The visual system of elasmobranchs has been the subject of much interest dating back well over 200 years. However, fundamental aspects of the visual system, such as the size and extent of the visual field, remain largely unexplored. The functional visual field is an integral component of the visual sensory system and is central to an organism’s perception of its environment. The goal of this study was to quantify the horizontal and vertical visual fields of four morphologically dissimilar and phylogenetically distinct batoid species. We asked two primary questions: (1) Do visual fields differ among species that possess different head morphology, eye position, and behavioral ecology? (2) Are visual field similarities retained in related, yet phylogenetically distinct batoid species? To address these questions we assessed the visual fields of four batoid species from four families: the clearnose skate (Raja eglanteria), Atlantic stingray (Dasyatis sabina), yellow spotted stingray (Urobatis jamaicensis), and cownose ray (Rhinoptera bonasus). The extent of the visual field was determined using an electroretinogram (ERG) technique. A slit of light illuminated an intact dark adapted eye, and elicited an electrical response from the retinal photoreceptors. An electrode positioned on the eye captured the electrical signal. The light was freely rotated around the eye vertically and horizontally and a positive ERG response was the criterion used to establish the limits of the functional visual field. The horizontal and vertical visual fields significantly differed among the four batoid species and each corresponded to individual aspects of feeding and swimming behavior. All species achieved anterior and dorsal binocular convergence. This study demonstrates the importance of determining the 3- dimensional visual field to understand how organisms perceive their environment.
McElroy, W. David1; McCandless, Camilla T.2; Kohler, Nancy E.1
Diet Overlap and Feeding Patterns of the Two Dominant Shark Species in Delaware Bay
1Department of Fisheries, Animal and Veterinary Science, University of Rhode Island, Kingston, RI, United States, 2Apex Predators Investigation, NOAA/NMFS, Narragansett, RI, United States
The Delaware Bay ecosystem is a large estuary that is a major nursery for both sandbar sharks, Carcharhinus plumbeus, and smooth dogfish, Mustelus canis, though a wide range of sizes occur. These are the two most abundant sharks in the Bay, which coexist during the summer months. The diet of both species was characterized and compared for three different size classes. The diet of the smooth dogfish is dominated by crustaceans, especially in the adults, whereas the sandbar shark feeds predominately on teleosts, increasingly in larger juveniles. There is some overlap in diet, and multidimensional scaling plots and spearman rank correlation revealed that adult dogfish and young of the year sandbar sharks have the greatest similarity in food habits. Prey groups important to both are Majid, Pagurid, and Portunid crabs; additionally some predation on similar fish species occurs. Analysis of similarity tests performed using multiple dietary indices found significant differences in diet between all size classes of the two species. Feeding patterns differ between the species with greater proportional mass and numbers of prey items occurring in smooth dogfish stomachs. No distinct diel patterns in feeding were found in either species by examining percent body weight of prey, stage of digestion values, or occurrence of empty stomachs. Smooth dogfish do not show any significant patterns in feeding between months, whereas sandbar sharks show significant patterns that vary between size classes. Smooth dogfish in the Bay are continuous feeders preying predominately on a variety of crustaceans, along with mollusks and other invertebrates. Sandbar sharks are intermittent feeders feeding on crustaceans but primarily on teleost prey, especially in larger sharks. Discerned differences in diet and feeding patterns are major factors that allow these top predators to coexist during the summer months in Delaware Bay.
McElwain, Andrew; Benz, George
In the Nose of Jaws: Patterns of Infection of the Copepod, Kroeyerina elongata on Blue Sharks
Middle Tennessee State University, Murfreesboro, TN, United States
Elasmobranch olfactory sacs are comprised of a series filaments and lamellae which create a series of small, heterogeneously structured habitats where some parasites live. Although no detailed published studies exist on the distribution of copepods in the olfactory sacs of fishes, casual observations suggest that some copepods infect specific places within the olfactory sacs of sharks. Building on results of a pilot study, we investigated the infection patterns of 3,278 K. elongata in the olfactory sacs of 20 blue sharks. The number of copepods per olfactory sac ranged from 0 to 213 (mean = 82.7 ± 10.07; n = 40) with females typically outnumbering males. Within the olfactory sacs, about 78% of all copepods faced upstream relative to the flow of water through the olfactory sac. There was no linear relationship between shark fork length and copepod intensity (r2 = 0.114, P = 0.275) and no significant difference was discovered between copepod intensity in left vs. right olfactory sacs (t = 0.002, P = 0.998). Adult female copepods typically occupied the central chambers of the olfactory sac while adult males typically infected distal chambers nearest the nares. Within olfactory sac chambers, females were usually found attached to the base of the rachis or within the first third of the excurrent water channel while males were usually attached to or between olfactory lamellae. When considered with respect to the pattern of water flow through the olfactory sac, these results can be used to propose a lifecycle for K. elongata.
McGowan, Dave; Kajiura, Stephen
Electroreception in Euryhaline Elasmobranchs
Florida Atlantic University, Boca Raton, FL, United States
The elasmobranch electrosensory system evolved to function optimally in an electrically conductive marine environment, yet there are numerous species of euryhaline elasmobranchs that inhabit freshwater systems. Whereas obligate freshwater elasmobranchs, such as the Potamotrygonid stingrays, have evolved significant morphological changes in their electrosensory system to enable them to function in an electrically resistive freshwater environment, the morphology of the electroreceptors in euryhaline elasmobranchs remains similar to marine species. Nonetheless, euryhaline elasmobranchs retain electroreceptive capabilities in freshwater. This study determined the electrosensitivity of a euryhaline elasmobranch in both a highly conductive marine environment and a high impedance freshwater environment. The euryhaline Atlantic stingray, Dasyatis sabina, is locally abundant in the tidally-dynamic Indian River Lagoon system (IRL) of east Florida, where salinities range from freshwater to full-strength seawater. A separate population of Atlantic stingrays in the St. Johns River system (SJR) complete their entire life history in freshwater. We tested whether stingrays from the freshwater SJR differed in their electroreceptive capabilities compared to stingrays from the marine IRL environment. We quantified the behavioural response of the stingrays to prey-simulating electric stimuli in freshwater (0 ppt), brackish (15 ppt), and full strength seawater (35 ppt). Stingrays tested in the 15 and 35 ppt treatments did not differ significantly and demonstrated a mean response threshold of 0.004 μVcm–1. In contrast, stingrays from either population tested in freshwater demonstrated a mean response threshold of 1.189 μVcm–1. Thus, stingrays tested in the marine environment demonstrated an electrosensitivity more than two orders of magnitude greater than those tested in a freshwater environment. Stingrays from the two populations did not differ when tested at the same salinity. We also determined that the salinity at which a stingray was captured in the IRL had no effect on how it responded when tested in a different salinity. Additionally, we failed to uncover the previously hypothesized differences in electrosensitivity due to the size and sex of the stingray.
Mejía-Falla, Paola Andrea1; Hleap, Jose Sergio1; Payán, Luis Fernando1; Navia, Andrés Felipe2
Habitat Use by Whitetip Shark (Triaenodon obesus), Whale Shark (Rhincodon typus) and Manta Ray (Manta birostris), in the Gorgona Island, Pacific Ocean off Colombia
1Fundación SQUALUS, Cali, Valle del Cauca, Colombia, 2Universidad del Valle, Departamento de Biología, Grupo de Investigación en Ecología Animal, Cali, Valle del Cauca, Colombia
Monthly immersions between June 2005 and August 2006 in four diving zones of Gorgona Island National Natural Park were performed to study the habitat use and population dynamic of Triaenodon obesus, Rhincodon typus and Manta birostris, using photo-identification procedure as methodology. The northern zone presented greater percentage of sighting but a less number of individuals; this zone is the only site where the three species are found. The southern and western zones are used preferentially by Triaenodon obesus which are found in groups of females and males in different growth stages. This species was recorded during almost all year and some pregnant females were observed during the second semester of the year. Also, through photos a pregnant female was identified in September 2004 (“marked”) and in July 2005 (“re-captured”) suggesting a maximum reproductive cycle of 12 months. Manta birostris and Rhincodon typus may be seasonal species in the Gorgona Island occurring between March and July.
Mejía-Falla, Paola Andrea; Navia, Andrés Felipe
Life History Aspects Of Round Stingrays Urotrygon rogersi Of The Pacific Ocean Off Colombia
Fundación SQUALUS, Cali, Valle del Cauca, Colombia
Life history aspects of 285 individuals of round stingray Urotrygon rogersi were studied. Specimens were captured from the by-catch of shrimp artisan fishing in the Colombian Pacific between March and November 2006. The weight-size relationship presented significant differences between males and females, the latter having a greater weight to the same total length starting from 18 cm. Males reach maturity between 21 and 23 cm; females become mature at 19 cm and hold embryos after reaching 20.5 cm of length. The sexual proportion of males and females was: adults 1:1.4 and embryos 1:1. The maximum fecundity was 4 embryos per uterus and two uteri were functional (mainly the left). The high percentage of mature individuals in the zone and the presence of embryos during all months, allow us to suggest: 1. U. rogersi presents reproduction all year (non-seasonal). 2. U. rogersi presents a trade-off between fecundity and reproductive cycle and 3. The monitored zones are important areas of nursery and reproduction to Urotrygon rogersi.
Montano, Melinda1; Gelsleichter, Jim2
Ethoxyresorufin-O-deethylase (EROD) Activity as a Biomarker for Pollutant Exposure in Bonnethead Sharks (Sphyrna tiburo) and Atlantic Stingrays (Dasyatis sabina)
1Eckerd College, St. Petersburg, FL, United States, 2Elasmobranch Physiology and Environmental Biology Program, Center for Shark Research, Mote Marine Laboratory, Sarasota, FL, United States
Exposure to some environmental pollutants, such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and dioxins, has been associated with reproductive toxicity and endocrine disruption in aquatic wildlife. Since these compounds are capable of inducing production of the enzyme, Cytochrome P450A (CYP1A1), increased presence or activity of CYP1A1 is commonly used as a biomarker of exposure to these contaminants. The aim of this study was to measure exposure to and effects of CYP1A1-inducing pollutants in bonnethead sharks (Sphyrna tiburo) and Atlantic stingrays (Dasyatis sabina) using ethoxyresorufin-O-deethylase (EROD) activity, an enzyme assay for CYP1A1. To validate the use of this technique as a measure for pollutant exposure in these species, EROD activity in sharks and stingrays was measured in animals treated with β-napthoflavone (BNF), a known CYPIA-inducer, and compared with control animals. Hepatic EROD activity in BNF-treated sharks and stingrays was nearly 7 times higher than that in control animals. Following validation, hepatic EROD activity was examined in bonnethead sharks from 8 sites on the Atlantic and Gulf coasts and in Atlantic stingrays from 4 sites in Florida’s St. Johns River. Hepatic EROD activity was nearly 10 times greater in St. Johns River stingrays collected near Jacksonville than in stingrays from all other St. Johns River sites. These results corresponded with known differences in pollutant exposure levels in this river system. Bonnethead sharks from Atlantic populations had significantly higher EROD activities than Gulf coast populations. These data agreed with recent comparisons of CYP1A1-inducing contaminants in Atlantic and Gulf coast sharks. Increased EROD activity was not observed in stingray or bonnethead populations in which reproductive complications (e.g., infertility) have been previously reported. Therefore, CYP1A1-inducing contaminants do not appear to be responsible for these abnormalities. Nonetheless, evidence of elevated EROD activity in some of the populations examined justifies additional research on these animals, which should be geared toward determining if organismal-level effects of pollutant exposure are also experienced.
Morgan, Alexia; Burgess, George
Regional and Taxonomic Differences in Bycatch Caught in the U.S. Bottom Longline Fishery
University of Florida, Gainesville, FL, United States
Bottom longline fishing is a relatively non-selective commercial fishing technique that catches both targeted and non-targeted (bycatch) species. From 1994-2005, the Commercial Shark Fishery Observer Program (CSFOP) placed fishery observers aboard bottom longline fishing vessels targeting sharks along the Atlantic coast and Gulf of Mexico from New Jersey to Texas. During this period, the CSFOP collected data on targeted sharks and all bycatch caught by these monitored vessels. A two way ANOVA test using year as a block effect and region and taxa as factors was performed to look for differences by region and bycatch taxon. Three regions (Gulf of Mexico, South Atlantic and Mid Atlantic Bight) and two time periods (1994-2001 and 2002-2005) were used for this analysis. All bycatch species were divided into seven taxonomic categories (Anguilliformes, Batoidea, Carangididae, Lutjanididae, Serranidae, other Osteichthyes, and other Vertebrata (Chelonia, Cetacea and Aves) for each of the regions and time periods. There was a significant difference between regions (P < 0.0001, F = 16.55, α = 0.05), taxa (P < 0.0001, F = 13.89, α = 0.05), and years (P = 0.0042, F = 7.38, α = 0.05) but no significant difference (P= 1.00, F = 0.02, α = 0.05) was found between the regions-taxa interaction.
Motta, Philip, Davis, Ray; Hueter, Robert; Maslanka, Michael; Mulvany, Samantha
Whale Shark Filter Feeding: Morphology, Mechanism and Consumption
1University of South Florida, Tampa, Florida, United States, 2Georgia Aquarium, Atlanta, Georgia, United States, 3Mote Marine Laboratory, Sarasota, Florida, United States, 4Georgia Aquarium, Atlanta, Georgia, United States, 5University of South Florida, Tampa, Florida, United States
The world’s largest fish, the whale shark Rhincodon typus, utilizes ram and suction filter feeding to engulf planktonic and small pelagic prey. The ram filtering feeding behavior was investigated in situ at feeding aggregations of whale sharks off Isla Holbox, Quintana Roo, Mexico. Sharks were feeding on dense aggregations (4.3 g/m3) of plankton, primarily composed of calanoid and cyclopoid copepods. Filter rates based on mouth morphometrics and swimming speeds were calculated, and together with plankton tows gave an approximate estimate of biomass consumption of 2.2kg/h. To investigate the mechanics of feeding, the filtering apparatus was dissected on a 7 m TL specimen. Small, denticulated teeth ring the jaw, and a double buccal valve posterior to the jaw reduces water backflow out of the mouth. A novel filtering apparatus consists of a series of twenty filtering pads that lie dorsally and ventrally on either side of the branchial apparatus at an angle to the incoming water. These pads, which completely occlude the branchial arches, have pores of varying diameter. A mechanism of crossflow filtration whereby particles are entrained posterior to the pads is proposed. After passing through the pads an elaborate system of channels directs water within the branchial pad, through what appear to be collimator vents, and over the gill lamellae before exiting the pharyngeal slits.
Mull, Christopher; Lowe, Christopher; Young, Kelly
Sexual Segregation and Utilization of Coastal Saltmarsh Mitigation by Pregnant Female Round Stingrays (Urobatis halleri)
Department of Biology, Cailfornia State University Long Beach, Long Beach, CA, United States
Despite a large seasonal aggregation of round stingrays (Urobatis halleri) in Seal Beach, CA, no behavioral or physical evidence of mating has ever been observed. Mating in this population is thought to occur in nearby Anaheim Bay estuary, which is part of the Seal Beach National Wildlife Refuge (SBNWR). SBNWR is composed of 1.1 km2 of estuary and four mitigation ponds. With muted tidal flushing, the mitigation ponds experience very seasonal temperature ranging from 10.9oC in winter to 29.3oC in summer. Round stingrays were sampled every other week from June 2005 to September 2006. All captured rays were weighed, sexed, and examined for mating scars as evidence of recent breeding behavior. From June 2006 to September 2006 blood was sampled via the caudal vein from a subset of rays and analyzed for progesterone using radioimmunoassay. Rays exhibited strong sexual segregation with only one male being captured out of 428 rays sampled throughout the study period. There was little variance in size of adult females captured, with averages ranging from 188 – 203.5 mm disc width (p>0.05). The majority of round stingrays collected were mature females (disc width>160mm), with most showing evidence of mating. Progesterone levels were elevated in females sampled through July and August (0.75 ng/ml) and levels decreased significantly to 0.16 ng/ml by September. Progesterone levels of females from the SBNWR were higher than those sampled off Seal Beach where the highest level of 0.1 ng/ml progesterone was observed in June 2005. We believe that the presence of round stingrays in the estuary is regulated by temperature, and that pregnant female round stingrays may be using these warm shallow ponds to increase the gestation rate, purported to be three months, which is relatively short for a live bearing elasmobranch.
Navia, Andrés Felipe1; Mejía-Falla, Paola Andrea1; Zapata, Luis Alonso2; Rubio, Efraín3
Preliminary Results on the Biology of Elasmobranchs Caught as Bycatch in a Tropical Prawn Trawl Fishery-Shrimp in the Pacific Ocean off Colombia
1Fundación SQUALUS, Cali, Valle del Cauca, Colombia, 2Fondo Mundial para la Naturaleza, WWF-Colombia, Cali, Valle del Cauca, Colombia, 3Universidad del Valle, Departamento de Biología, Sección Biología Marina, Cali, Valle del Cauca, Colombia
Biological aspects of elasmobranchs accidentally captured by commercial prawn trawls in the Pacific Ocean off Colombia were studied between July and December 2001. A total of 231 individuals belonging to seven families, nine genders and eleven species (five sharks, three skates and three rays) were collected. Zapteryx xyster was the dominant by-catch species and Carcharhinus porosus presented the lowest frequency. The species studied were distributed between 9 – 59 m depth, Urotrygon aspidura was captured in the shallowest waters and Mustelus lunulatus in the deepest. A total of 21 prey items were identified for five elasmobranchs species, where squids, shrimps and fishes were the most representative in the diet, while crabs, gastropods and bivalves were occasional. The value of niche breadth indicated to M. lunulatus as specialist predator of a particular food (Squilla panamensis) and to Z. xyster as the most generalist species. All species studied present an isometric growth and their size varied between 37 and 210 cm. Pregnant females of M. lunulatus, Rhinobatos leucorhynchus and Raja velezi were found.
Neer, Julie1; Cortes, Enric1; Brooks, Liz2
Status of the Large Coastal Shark Management Complex, Sandbar and Blacktip Sharks in US Atlantic Waters
1NOAA Fisheries Service, Panama City, FL, United States, 2NOAA Fisheries Service, Miami, FL, United States
Sharks of US Atlantic waters (including the Gulf of Mexico) are currently managed by the Highly Migratory Species (HMS) Division of the National Marine Fisheries Service. Since 1993, federal management plans have been in place to monitor and regulate the commercial and recreational harvest of many shark species. Currently, managed species fall into one of four management groups: Large coastal sharks (LCS), Small coastal sharks, Pelagic sharks, and Prohibited species. Since the inception of shark management, HMS has relied on the Southeast Fisheries Science Center (SEFSC) to conduct periodic assessments to determine the status of the managed species, particularly the LCS complex, the primary component of the commercial shark fishery in US waters. In early 2005, HMS requested that SEFSC conduct an assessment for the LCS complex, as well as species-specific assessments for blacktip and sandbar sharks, as the two species comprise ~85% of the recorded commercial landings. The assessments followed the procedure known as SEDAR (SouthEast Data Assessment and Review) utilized by the SEFSC and its associated Management Councils for its teleost stock assessments. The LCS SEDAR process began in Nov 2005 and was completed in June 2006. We will present an introduction to the SEDAR process, discuss the assessment methods and results, and discuss the conclusions of the independent Peer Review Panel. The major results were that sandbar sharks were found to be overfished and overfishing is occurring; blacktip sharks in the Gulf of Mexico were not overfished and no overfishing was occurring; and that the status of blacktip sharks in the Atlantic Ocean and the LCS Complex is unknown.
Nielsen, Anders; Sibert, John R.
Errors in Light Based Geolocation and How to Fix Them
Pelagic Fisheries Research Program, Joint Institute for Marine and Atmospheric Research, University of Hawaii at Manoa, Honolulu, HI, United States
We briefly explore the sources of errors in estimating geographic position from solar irradiance time-series. Some previous approaches to reconstructing tracks from light- based position estimates using state-space models are briefly presented. We then present a new, coherent model to estimate the most probable track of geographic positions directly from a series of light measurements. This is performed without making any light-level threshold assumptions, or constraining the movement of the tag between dawn and dusk. The new model generates two estimates of geographic positions per day (at dawn and dusk). The covariance structure of the model is designed to handle high correlations between light measurements, such as might be caused by local weather conditions. The yearly pattern in latitude precision is estimated by propagating the data uncertainties through the geolocation process. The model has been applied to simulated data, mooring studies, and real deployments on swimming and diving fish. We demonstrate that tracks can be reliably estimated, even in cases where the other methods have completely failed and have produced misleading position estimates. The importance of open collaboration for the future development and application of electronic tags cannot be overemphasized. The models discussed in this paper were developed because a broad network of collaborating tag users and manufacturers generously shared their time, data, and ideas. All of these models are in the public domain and can be freely downloaded from https://www.soest.hawaii.edu/tag-data/software/
O’Connell, Craig1; Stroud, Eric1; Herrmann, Michael1; Rice, Patrick1; Gruber, Samuel2
Evaluation of Barium-Ferrite Permanent Magnets on the Behavior of Four Species of Elasmobranchs
1SharkDefense LLC, Oak Ridge, NJ, United States, 2Bimini Biological Field Station and University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, FL, United States
Avoidance behavior in the presence of magnetic barriers was evaluated in four species of elasmobranchs at the Bimini Biological Field Station, South Bimini, Bahamas. Barriers were composed of grade C8 Barium-Ferrite (BaFe12O19) permanent magnets, each exerting a magnetic flux of 55 Gauss at the pole. In the first investigation involving adult southern stingrays (Dasyatis americana) and juvenile nurse sharks (Ginglymostoma cirratum), permanent magnets were arranged just under the sandy substrate in maze-like patterns. In the second investigation involving juvenile lemon sharks (Negaprion brevirostris), and one juvenile tiger shark (Galeocerdo cuvier), a fence-like barrier with two 70 cm2 openings was constructed using polyethylene mesh (3.2 cm x 3.2 cm). One opening was bordered with permanent magnets, and the other with sham magnets composed of polyurethane cardboard covered in black duct tape. All subjects demonstrated greater avoidance behavior (i.e. accelerations away from, 90 ̊ or 180 ̊ turns) to the region containing permanent magnets when compared to the controls. Negaprion brevirostris had 136 avoidance behaviors towards the magnets, while having only 16 avoidance behaviors towards the control. Galeocerdo cuvier displayed 19 avoidance behaviors towards the treatment, while having only 2 towards the control. Avoidance behaviors were observed to be more violent as the individuals approached the magnetic fields. Preliminary results suggest that the test subjects detected and were sensitive to the magnetic flux and were apparently repelled by the magnetic barriers.
Oliver, Simon P.; Hussey, Nigel E.; Turner, John R.; Beckett, Alison J.
Oceanic Sharks Risk Visiting Coastal Waters
University of Wales, Bangor, Menai Bridge, Isle of Anglesey, United Kingdom
The pelagic thresher shark, Alopias pelagicus, is an oceanic species whose biology is little known. These sharks regularly visit Monad Shoal, a shallow seamount in the Philippines, to be cleaned by cleaner wrasses Labroides dimidiatus and Thalassoma lunare. Symbiotic cleaning behaviour between sharks and teleosts has never been investigated in the wild before but the observable interactions seen at this site explain why these mainly oceanic sharks venture into shallow coastal waters, where they are vulnerable to human disturbance from fisheries and dive tourism. Pelagic thresher sharks visited Monad in greater abundance during the early hours of the morning, though there was no evidence for differential cleaning site selection based upon size or sex of individuals (N = 66). Cleaning interactions were organized into ‘Natural’ (devoid of influence, anthropogenic or otherwise) and ‘Perturbed’ (influenced by the presence of divers or other animals) events, which in turn were deconstructed into segments and hits. High resolution video analysis of four complete events showed that observed thresher sharks demonstrated specific behavioural patterns to facilitate cleaning interactions with cleaner fishes. Circle and Clean was described as a new behavioural unit to elasmobranch ethology. Cleaning behaviour (N = 167) was quantified within six anatomically delineated zones established on the shark client (Head, Dorsal, Caudal, Pelvic, Ventral, Pectoral) with significance found in the number of cleans registered in and around the cloaca. The location of cleaning interactions may be related to the potential presence of Echthrogaleus sp. (Pandaridae, Copepoda) parasitic upon the shark client and/or its need for wound healing. New methods for observing pelagic sharks in situ were developed through the practical application of a predictability system in conjunction with the use of a remote video camera. Shoal areas with cleaning stations are recognized as important habitats for the region’s pelagic thresher sharks and assessed in need of protection.
Piercy, Andrew1; Gelsleichter, James2; Boyer, Stephanie1; Murie, Debra3
Reproduction of the Sandbar Shark (Carcharhinus plumbeus) in the Northwest Atlantic and Gulf of Mexico
1Florida Museum of Natural History, University of Florida, Gainesville, FL, United States, 2Center for Shark Research, Mote Marine Laboratory, Sarasota, FL, United States, 3Department of Fisheries and Aquatic Sciences, University of Florida, Gainesville, FL, United States
We examined aspects of the reproductive biology of sandbar sharks (Carcharhinus plumbeus) captured in the Northwest Atlantic and Gulf of Mexico (N=750). Specimens were obtained through fishery-dependent and -independent sampling from January 2003 to December 2006. Gross observations of the gonads and reproductive tracts of male and females sharks were gathered. Additionally, we examined histological preparations of testes, epididymides, seminal vesicles, and nidamental glands. Preliminary data indicate a distinct seasonal trend in both male and female reproductive events. While mature male sandbar sharks are capable of reproducing annually, our data indicate that mature female sandbar sharks exhibit a rest period of at least one year in between reproductive events.
Ramírez-González, Jorge1; Bojórquez, Francisco3; Escobar-Sánchez, Ofelia1; Elizalde-Hernández, José Arturo1; Ahuja, Paul1; Rangel-Acevedo, Rodrigo1, Villavicencio-Garayzar, Carlos2
Bioeconomic Importance of Elasmobranches in the Artisanal Fishery of Punta Lobos, Baja California Sur
1Iemanya Oceanica A.C., La Paz, Baja Californa Sur, Mexico, 2Univesidad Autónoma de Baja California Sur, La Paz, Baja California Sur, Mexico, 3Sociedad Cooperaiva de Producción Pesquera Ejidal Punta Lobos, Todos Santos, Baja California Sur, Mexico
The elasmobranches have biological characteristics that make them extremely vulnerable to fishing efforts. In Mexico, they also have a significant economic importance. They are fished by the artisanal fishery, which is multi-specific, so it is very difficult to identify management units. The objective of this project is to evaluate the importance of the elasmobranchs in the artisanal fishery and identify if they are an objective, alternative or secondary group. The Index of Bioeconomic Importance (IBI) was used to rank the fishing resources in Punta Lobos, Baja California Sur. Also field trips were conducted to identify the elasmobranches species, their reproductive condition and the fishing gear used. Our preliminary results show that in Punta Lobos the fishermen capture 12 species of elasmobranches. Mustelus henlei and Raja velezi are the most important. The fishermen use bottom gillnets of 6 and 8 inches of mesh size and fragmented loglines called “simpleras” to catch elasmobranches. The IBI indicates that the elasmobranches are in fourth place; as such they are part of the alternative group for the Punta Lobos fishery. In conclusion, the elasmobranches, for its economic importance and vulnerability, must be a priority in the management of artisanal fisheries.
Richards, Vincent; Henning, Marcy; Witzell, Wayne; Shivji, Mahmood
Multilocus Molecular Evidence Supports the Recognition of at Least Two Species of Spotted Eagle Ray (Aetobatus narinari)
1National Coral Reef Institute and Guy Harvey Research Institute, Oceanographic Center, Nova SE University, Dania Beach, Florida, United States, 2National Marine Fisheries Service, SEFSC, Miami, Florida, United States
The spotted eagle ray (Aetobatus narinari), a batoid of conservation concern (Near Threatened IUCN category), is currently described as a single, circumglobally distributed species. However, geographic differences in parasite diversity have raised suspicions that A. narinari may constitute a species complex. Here we assessed the validity of A. narinari as a single cosmopolitan species using 1570bp of sequence data from two mitochondrial genes (cytochrome b and COI) and the nuclear ribosomal ITS2 locus. Specimens from three major geographic regions were examined: the Caribbean and Florida, West and Central Pacific, and the East Pacific. Phylogenies for each locus described three distinct lineages with no genetic exchange among regions, and genetic distances among the most divergent lineages were comparable to batoid and bony fish congeners. Using combined genealogical concordance and genetic distance criteria, we recommend that the West/Central Pacific population be recognized as a distinct species from populations in the Caribbean, Florida, and East Pacific. We further recommend that the Caribbean/Florida and East Pacific populations, separated by the Isthmus of Panama, be given subspecies status. Dramatically higher nucleotide diversity and sequence divergence coupled with a basal position in multiple phylogenetic analyses support an Indo-West Pacific origin for the A. narinari species complex with subsequent migration into the Atlantic. Evolutionary relationships among lineages suggest a westerly migration around the southern tip of Africa, with intensification of the Benguela coldwater upwelling system a possible vicariant mechanism underlying speciation.
Romine, Jason1; Grubbs, R. Dean1; Conrath, Christina2; Musick, Jack1
Growth estimates for the sandbar shark, Carcharhinus plumbeus, in the Northwest Atlantic through tag-recapture methods.
1Virginia Institute of Marine Science, Gloucester Point, VA, United States, 2Florida Museum of Natural History, Gainesville, FL, United States
Growth estimates for the sandbar shark, Carcharhinus plumbeus, in the Northwestern Atlantic were estimated using a reparameterized von Bertalanffy growth model. Sharks were tagged in Virginia waters with roto-tags and double return nylon dart tags from 1992 to 2006 by the shark longline survey of the Virginia Institute of Marine Science. Captured sharks were measured, tagged, and released by VIMS scientists. Dart tags were inserted at the base of the first dorsal fin on the left side of the animal. Over the time period, 37 recaptured sharks with reliable length at recapture information were reported. Time at liberty ranged from 26 to 3,561 days. Pre-caudal length at tagging ranged from 41 to 81 cm and pre-caudal length at recapture ranged from 43 to 147 cm. Growth increments ranged from 0.10 to 66 cm. The fitted model estimated growth rates of 11 cm*yr -1 for 45 cm pre- caudal length sharks and 7 cm*yr -1 for 75 cm pre-caudal length sharks.
Schaaf-Da Silva, Jayna; Ebert, David
A Taxonomic Revision of the Western North Pacific Swell Sharks, Genus Cephaloscyllium Gill 1862 (Chondrichthyes: Carcharhiniformes: Scyliorhinidae), with Descriptions of two New Species
Moss Landing Marine Laboratories, Moss Landing, CA, United States
Until recently, the genus Cephaloscyllium Gill, 1862 (Chondrichthyes, Carcharhiniformes, Scyliorhinidae) had only one species recognized, C. isabellum [= C. umbratile (Jordan and Fowler, 1903)], from the western North Pacific (WNP), with one dubious, species, C. formosanum, having been described by Teng ( 1962). Not long ago, two additional species were described, C. sarawakensis (Yano, Ahman, and Gambang, 2005) and C. parvum (Inoue and Nakaya, 2006) from this region. Here we present a revision of this genus, including a re-description of C. umbratile based on the holotype, a re-examination of the two recently described species, and a description of two additional new species collected from southeastern Taiwan. Cephaloscyllium umbratile can be distinguished from its congeners based on body size, length of first dorsal fin base, anal-caudal fin space, and dorsal-caudal fin space. Furthermore, we conclude, based on a comparison of C. parvum and C. sarawakensis, that the former is a junior synonym of the latter species. Finally, we present a revised key to the WNP Cephaloscyllium recognizing six species: C. circulopullum, C. fasciatum, C. sarawakensis, C. umbratile, and two new species.
Satellite and Archival Telemetry of Shark Movements and Behaviour in Relation to Environment: Achievements, Challenges and Future Perspectives
Marine Biological Association Laboratory, Plymouth, United Kingdom
Sharks play a key role in shaping the structure, distribution and abundance of prey populations, which in turn has important consequences for the functioning of ecosystems. Characteristically, sharks search widely for resources and concentrate activity in productive habitats with associated high biodiversity. As such, they have the potential through their movement and behaviour patterns to signal wider-scale changes in marine ecosystem status. Therefore, knowledge of shark movements, activity and habitat selection in relation to variations in the physical and biotic environments will help resolve how natural and human-driven environmental changes affect marine populations. However, tracking shark movements is difficult because they often range widely and spend most, of not all, their time below the water’s surface and beyond direct observation. Indirect methods of following their behaviour, such as satellite and archival telemetry has revolutionised our view of these enigmatic predators. Sharks were first tracked using satellite-based techniques in the late 1970s but more recent advances in technology and its progressive miniaturisation have allowed a wider range of species and greater numbers of individuals to be monitored. Despite these successes, there remains a general lack of understanding about movement patterns, where sharks go, what they do when they get there, and, crucially, why they select particular habitats over others at certain times. Determining when and why sharks conduct certain behaviours will help us to predict how these predators will respond to environmental change. In this paper I will briefly review the principal achievements in the field of shark satellite telemetry, and then identify the main challenges that lie ahead. I will discuss how in the near future this field will mature to incorporate new advances in movement ecology and embrace new developments such as dynamic integration of satellite-derived behavioural data with environmental remote-sensing, key steps forward that offer real opportunities to tackle the ‘why’ question.
Stroud, Eric1; Herrmann, Michael1; Rice, Patrick1; O’Connell, Craig1; Gruber, Samuel2
Observations of Repellent Behavior Using Highly Electropositive Metals.
1SharkDefense LLC, Oak Ridge, NJ, United States, 2Bimini Biological Field Station and University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, FL, United States
A shark repellent based on an electrochemical process is proposed. Highly electropositive metals, particularly the early Lanthanides and certain Group I, II, and III metals produced violent aversive reactions in juvenile lemon sharks (Negaprion brevirostris) and juvenile nurse sharks (Ginglyostoma cirratum). Pure electropositive metal ingots ranging from 70g to 100g terminated tonic immobility in juvenile lemon sharks (Negaprion brevirostris) and juvenile nurse sharks (Ginglyostoma cirratum) at distances of 2cm to 20cm from the side of the head, despite lack of a visual cue. The most violent reactions using Group III metals were observed using Praseodymium, Lanthanum, and Cerium. Of the Group II metals studied, Magnesium, Calcium, and Strontium produced the most violent reactions, with Magnesium being the most stable and practical metal from this group for prolonged use. Group I metals are too reactive to be considered practical; however, Lithium ribbon did produce a violent response in one juvenile lemon shark studied. In a closed system containing seawater electrolyte, an electropositive metal anode, and a shark fin clipping as the cathode, electromotive forces of 1.24eV to 1.46eV were measured with an electrode gap of 5cm at 25 degrees Celsius. A direct correlation between the standard oxidation potential of the metal and intensity of the behavioral response from the shark has been found. Published standard oxidation potentials greater then 2.30eV appear to hold the most promise for a selective electrochemical shark repellent.
Testerman, Christine1; Richards, Vince1; Francis, Malcolm2; Pade, Nicholas3; Jones, Catherine3; Noble, Les3; Shivji, Mahmood1
Global Phylogeography of the Porbeagle Shark (Lamna nasus) Reveals Strong Genetic Separation of Northern and Southern Hemisphere Populations
1Nova Southeastern University, Dania Beach, FL, United States, 2NIWA, Wellington, New Zealand, 3Aberdeen University, Aberdeen, Scotland, United Kingdom
The commercially exploited, epipelagic porbeagle shark (Lamna nasus) occurs in temperate waters of the North Atlantic and southern hemisphere but is absent from warmer equatorial waters. This species is of high conservation concern, being assessed by the IUCN as Vulnerable globally and Endangered or Critically Endangered in the North Atlantic. We report on the global population genetic structure of porbeagle sharks using complete mitochondrial control region sequences (1063 nucleotides) from individuals (n=280) throughout the species range, with 2 collection sites in the North Atlantic and 5 collection sites in the southern hemisphere. Analyses revealed strong geographical subdivision with two genetically distinct populations (one in the North Atlantic and one throughout the southern hemisphere), no exchange of haplotypes between the two populations (φST=0.82, P<0.00001), and the highest levels of diversity (122 haplotypes, h=0.95, π = 0.015) reported in a global population study of sharks to date. There was no detectable genetic structure within either hemisphere. Coalescent analyses using shark mitochondrial control region mutation rates indicate an origin in the North Atlantic during the Pliocene and expansion into the southern hemisphere during the early Pleistocene, timelines that are consistent with the fossil record. Comparison of the genetic distance between the northern and southern hemisphere porbeagle populations with interspecific lamnid genetic distances indicates that the two populations are not sufficiently divergent to be considered separate species.
Thorson, James1; Simpfendorfer, Colin2
Gear Selectivity and Sample Size Effects on Growth Curve Selection in Shark Age and Growth Studies
1Virginia Tech, Blacksburg, VA, United States, 2James Cook University, Townsville, Qld, Australia
Growth and length data is often obtained from fitting known growth curves to field data. However, most gear types select for particular lengths, so these field samples may yield significantly biased estimates of growth and maximim length. To study this, we simulated four populations of Dusky shark (Carcharhinus obscurus) and Atlantic sharpnose shark (Rhizoprionodon terraenovae) in stable-age distribution using different generating models. We then simulated field samples using a variety of sample sizes and gear types with known length-selection probabilities. Gompertz, von Bertalanffy (two and three parameter versions), Logistic, and Schnute growth curves were fitted to the simulated field data. Using the Akaike Information Criteron (AIC), we explored which growth curves provided either (1) parsimonious fit or (2) good estimates of generating parameters for different gear types. We also explored the use of model combination and multi-model inference in improving parameter estimation. We found that the two-parameter von Bertalanffy curve functioned well with small samples sizes and logistic selectivity associated with trawls. Meanwhile, the Schnute curve gave accurate parameter estimates for most sample sizes and gear types, and multi-model parameter estimation improved accuracy under most regimes. The results suggest that, within a single species and population, different growth curves will produce the best fit for studies using different sample size and gear selectivities. We also found that AIC does not always distinguish which model most accurately estimates life-history parameters.
Ubeda, Armando J.; Simpfendorfer, Colin A.; Heupel, Michelle R.
Movements of Bonnetheads, Sphyrna tiburo, in Response to Salinity Changes in a Large Florida Estuary
Center for Shark Research at Mote Marine Laboratory, Sarasota, FL, United States
The movement of bonnetheads, Sphyrna tiburo, within a large estuarine system on the Gulf of Mexico coast of Florida was examined to define response to salinity change. Shark presence and movements were evaluated by acoustic monitoring and gillnet sampling. Acoustic monitoring data were used to investigate active selection of different zones within the estuary based on differences in salinity among zones. Sharks were monitored for 187 days in 2003 and 217 days in 2004. Monitoring data supported the hypothesis that salinity played a role in the distribution and movement of S. tiburo. Catch per unit effort (CPUE) data obtained from gillnet sampling were examined to determine affinity or avoidance of specific salinities within the study site as calculated using an electivity index. Electivity analysis showed almost no affinity or avoidance for specific salinity values. The difference in results between the CPUE and acoustic monitoring in relation to the potential effects of salinity likely relate to the nature of the data, with acoustic monitoring providing continuous data and CPUE providing snapshot location data. The results of this study suggest that although bonnetheads are collected within a wide range of salinity levels, salinity may affect movement and distribution. Salinity effects may be more pronounced during periods of prolonged and/or large changes in salinity as detected by long-term monitoring.
Walsh, Jonathan1; Ebert, David 2
A Review of the Systematics of Western North Pacific Angel Sharks, Genus Squatina, with Redescriptions of Squatina formosa, S. japonica, and S. nebulosa (Chondrichthyes: Squatiniformes: Squatinidae)
1Moss Landing Marine Laboratories, Moss Landing, CA, United States, 2Moss Landing Marine Laboratories & Pacific Shark Research Center, Moss Landing, CA, United States
Squatinids are quite distinct from other shark-like fishes, but are difficult to differentiate amongst each other. Four of the 16 known valid squatinid species reported occur in the western North Pacific (WNP). Differences among the WNP species complex have traditionally relied upon the nasal barbel shape, interorbital and interspiracle distances, ocelli patterns, number of dermal folds about the mouth, and the presence of midback thorns. Unfortunately, many of these characters are difficult to distinguish, hindering identification of individuals. Using WNP squatinid specimens and photographs, both from field expeditions and museums, we confirm the validity of four species in the area. Additionally, the resulting information obtained also corrects mistakes present in S. formosa type material, clarifies differences in the particularly challenging distinction between S. formosa and S. nebulosa, and is the basis for a revised dichotomous key for the region that includes all four known valid WNP squatinid species.
Wetherbee, Bradley M.1; Fox, Dewayne2
Site Fidelity and Patterns of Habitat Use of Sandtiger Sharks (Carcharias taurus) in Delaware Bay
1University of Rhode Island, Kingston, RI, United States, 2Delaware State University, Dover, DE, United States
Worldwide populations of the sandtiger shark (Carcharias taurus) have declined dramatically over the past several decades as a result of high rates of harvest in commercial and recreational fisheries. Populations along the US East coast may have decreased by as much as 80% over this time period and sandtiger sharks have been grouped among the “prohibited species” category in the NMFS FMP for Atlantic Tunas, Billfish and Sharks. Sandtiger sharks are of particular concern because they give birth to only two offspring every other year and thus have a reproductive output that rivals the lowest among any species of elasmobranch in the world. Despite this high level of protection, there is very little information upon which to base assessment of sandtiger shark stocks and for monitoring progress of stock recovery. Additionally, there is a paucity of information on basic aspects of the life history of sandbar sharks in US waters, including details of their migrations, seasonal use of large bays and essential habitat. This study examines site fidelity, habitat requirements and movement patterns of sandtiger sharks in Delaware Bay. Sandtiger sharks remained in Delaware Bay throughout the majority of the summer, spending considerable time in shallow, nearshore waters, but moved throughout the bay and occasionally left the bay.
Whitenack, Lisa B.; Simkins, Daniel C.; Motta, Philip J.
Three-Dimensional Finite Element Analysis of Selachian Teeth
University of South Florida, Tampa, FL, United States
While teeth are a vital component of the shark feeding apparatus, their role in feeding has largely been ignored. Most shark tooth studies are qualitative in nature. Applying engineering techniques to shark tooth functional morphology can potentially reveal insights into evolution undiscovered by traditional qualitative methods. The goal of this study is to explore the link between form and function for selachian teeth using Finite Element Analysis (FEA). FEA is a computational method for solving many types of engineering equations. FEA is particularly well-suited to determining mechanical stress and strain for various loading conditions. This technique is often utilized on shapes too complex to be modelled analytically. We built three-dimensional FE models of individual teeth of four carcharhinid species to visualize stress distribution during puncture and draw. Initial results indicate that during puncture events, stress is concentrated at the tooth tip, decreasing greatly with distance from the tip. However, with increasing penetration the stress would rapidly dissipate as more of the cusp contacts the prey. During draw events, narrow teeth, such as those of Carcharhinus limbatus, concentrate stress along the edges. Broader teeth, exemplified by C. leucas, show lower stress concentrations during draw than puncture, indicating that these teeth are better engineered for draw. Notched teeth from Galeocerdo cuvier primarily concentrate stress at the notch during both draw and puncture. Despite these stress concentrations, broken shark teeth are rarely seen. We therefore hypothesize that shark teeth have high safety factors, and their flexible attachment may further inhibit stress concentration by distributing stress through the collagenous Sharpeys fibers that anchor the tooth to the dental lamina.
Wilborn, Rachel; Bennett, Wayne
Swimming Performance and Metabolic Costs of Exertion in three Species of Juvenile Elasmobranchs
The University of West Florida, Pensacola, Florida, United States
Maximum swimming velocity (UCrit), oxygen consumption, and blood lactic acid levels are useful indicators for evaluating maximum metabolic performance in fish. Unfortunately, most previous studies evaluate only a single indicator, or fail to account for differences among species or life stage. In addition, most studies focus on bony fishes and largely ignore elasmobranchs. I evaluated comparative swimming performances in three juvenile species of elasmobranchs (blue-spotted ribbontail stingrays, Atlantic stingrays, white-spotted bamboo sharks), and quantified metabolic costs of exertion. Critical (UCrit) and maximum (Vmax) swim velocities (cm sec-1) were determined for 28 animals with both Atlantic and ribbontail stingrays obtaining greater absolute (cm sec-1)and relative (body lengths per second) speeds than bamboo sharks. Changes in pre- and post-exertion oxygen consumption and lactic acid values (mmol L-1) were statistically indistinguishable in all three species, and ventilation rates (opercula counts min-1) recovered rapidly post-exertion indicating minimal use of anaerobic metabolism for locomotion. My study suggests that swimming performance endpoints and metabolic responses to exertion correlate to habitat preference and predator avoidance tactics in juvenile elasmobranchs. Performance and metabolic results indicate that both batoid species are capable of short intervals of accelerated aerobic velocities enabling them to reach the nearest seagrass bed or sand flat. Conversely, bamboo shark swim performance endpoints and metabolic data indicate a greater dependence on three-dimensional structure and a limited ability for elevated swimming velocities.
Willett, Naeem1; Fox, Dewayne1; Wetherbee, Bradley2
Monitoring Site Fidelity and Habitat Utilization of Juvenile Sandbar Shark (Carcharhinus plumbeus) Within Essential Nursery Habitat of Delaware Bay
1Delaware State University, Dover, DE, United States, 2University of Rhode Island, Kingston, RI, United States
Due to declines in sandbar shark populations over the past several decades, efforts are underway to better understand habitat use in nursery areas for rebuilding of depleted stocks. Large numbers of young-of-the-year (YOY) and juvenile sandbar shark reside in Delaware Bay from early summer through early fall. We utilized an automated telemetry array (Vemco VR-2) to monitor sandbar shark habitat utilization patterns during their residency in Delaware Bay. We hypothesized that our array was near or within primary habitat based on previous studies. Sixty sandbar shark were fitted with coded acoustic transmitters during the summers of 2005 and 2006. Telemetered sandbar shark were detected over 40,000 times during the course of this project. Sandbar shark tagged in 2006 were detected less frequently than those during 2005; although in 2006 they were tagged a full month earlier, indicating higher site fidelity in 2005. Sandbar shark tagged in 2006 were also more frequently detected on receivers in deeper water than in 2005. Of 12 age 1+ juvenile and 18 YOY sandbar shark tagged in 2005, 50% and 6% respectively returned to Delaware Bay the following year. These findings suggest either a high mortality rate during the first year of life or low fidelity to Delaware Bay during their second summer. The high degree of site fidelity of a large number of sandbar sharks within a relatively small portion of Delaware Bay suggests that this area is essential to the survival and development of juvenile sandbar shark. At a minimum, habitat degradation of the core nursery area of sandbar shark activity in Delaware Bay should be avoided.
Wueringer, Barbara E.1; Squire, Lyle Jnr.2; Hart, Nathan S.1; Collin, Shaun P.1
Sensory Biology and Prey Manipulation Behavior in Sawfishes
1University of Queensland, Brisbane, Queensland, Australia, 2Cairns Marine Aquarium Fish, Cairns, Queensland, Australia
The family of pristid sawfish face a global crisis, with all species listed as critically endangered on the IUCN Redlist. One characteristic that all species have in common may also be a major factor contributing to their decline; the elongated rostrum that bears lateral teeth (the ‘saw’). As the saw becomes easily entangled in fishing gear and is also a valuable trophy, sawfish are regularly taken as by-catch. However, the use of the saw has never been studied. The aim of this study is to identify the use of the saw in the context of prey manipulation, prey capture behaviour and reactions elicited by different sensory stimuli. An ethogram of the range of behaviors displayed by freshwater sawfish, Pristis microdon, is presented in the context of prey manipulation and social interaction. The most common interaction between individuals, the caudal or dorsal ‘push’ with the saw, results in two subsequent (and different) behaviors displayed by the resting sawfish; ‘continue in position’ or ‘position abandon’. ‘Position abandon’ can be sometimes followed by ‘floor raking’. The sawfish initiating the push either ‘retains swimming’ or ‘adopts position’ with respect to the resting sawfish. Preliminary results on diurnal variation in activity, presumably driven by visual cues, and the use of electroreception during prey capture reveal that these sensory modalities play important roles. Detailed knowledge of sawfish behaviour is crucial for maintaining optimal health of these endangered species in captivity and alleviating future fishing pressure.
Wyffels, Jen1; Itoh, Yoshiaki1; Sakai, Junichi1; Masuda, Motoyasu2
Characterization and Dynamics of the Extra-embryonic Egg Case Contents of Scyliorhinus torazame
1Aichi Medical University, Nagakute, Aichi, Japan, 2Hekinan Seaside Aquarium, Hekinan, Aichi, Japan
Scyliorhinus torazame is an oviparous elasmobranch and its embryos require 214±26 days to complete development at 14-16°C. Within the egg case the ovum is suspended by chalazae in an egg jelly secreted by the oviducal gland. There are three layers of egg jelly differing in proximity to the ovum and viscosity. The embryo moves freely in the closest, liquid layer. This liquid is surrounded by a clear viscous colloid jelly. Finally, the terminal ends of the egg case contain a dense plug of semi-translucent solid jelly. The egg case has four respiratory slits, two on the dorsal side and two on the ventral side of the egg case. The respiratory slits are sealed with solid jelly until 103±6 days at 14-16°C after oviposition. The carbohydrate composition of each layer of egg jelly was investigated by HPLC analysis of acid-hydrolyzed samples. Six sugars, N-acetylgalactosamine, N- acetylmannosamine, N-acetylglucosamine, fucose, galactose and mannose, were detected by this method. The highest concentration of carbohydrate was measured in solid jelly followed by colloid and finally liquid. The monosaccharide with the highest concentration in both the solid and colloid was galactose. The water content of the colloid and solid egg jelly layers was 94.2±0.7 % and 84.1±1.9 % respectively. Egg jelly hydration was affected by the osmolarity of the surrounding seawater. Protein and carbohydrate measured in the liquid jelly increased in concentration until egg case eclosion.
Yopak, Kara1; Lisney, Thomas2; Collin, Shaun2; Montgomery, John3; Frank, Lawrence3
The Batoid Brain: Correlations with Ecology, Locomotory Mode, and Fin Morphology
1UCSD Center for Scientific Computation in Imaging, La Jolla, CA, United States, 2School of Biomedical Sciences, Vision, Touch and Hearing Research Centre, The University of Queensland, St. Lucia, QLD 4072, Australia, 3University of Auckland, Leigh Marine Laboratory, Leigh 0941, New Zealand
The widespread variation in both brain size and complexity previously reported in sharks also occurs in batoids. The relative brain mass of a species is dependent upon the relative enlargement or regression of individual brain structures, some of which can be identified with different sensory modalities and behaviors. The relative development of five major brain areas (the telencephalon, diencephalon, mesencephalon, cerebellum, and medulla) was assessed in over 20 species of skate and ray from a range of families, which inhabit a number of different habitats. Structural assessment using traditional (transverse cross-sections) and newly emerging (Magnetic Resonance Imaging – MRI) methodologies will be discussed. Some images (MRI) were acquired on a GE Signa 3T Clinical scanner with a home built radio-frequency coil using a 3D spoiled gradient echo sequence with flip angle of 30degrees, an echo time of TE=4.5ms, and a TR of 10ms. A cerebellar foliation index was also used to quantify the variation in the structural complexity of the corpus cerebellum. Brain variation appears to be strongly correlated with phylogeny. Basal groups have smaller brains and less structural hypertrophy and members of the same family tend to exhibit similar patterns in brain size, organization, and cerebellar foliation. However, the relative development of the five major brain areas is likewise similar in species that occupy similar habitats and use similar modes of locomotion. Species with an active lifestyle and complex primary habitat, such as Dasyatis brevicaudata and Aetobatus narinari, demonstrate a relatively increased brain size, telencephalon size, and cerebellar foliation. Less-active benthic species, such as Dipturus innominatus and Aptychotrema rostrata, show an enlarged mesencephalon and medulla, with a smooth cerebellar corpus. The structural development of the cerebellum is also correlated with locomotion and pectoral fin skeletal structure, with species specializing in the use of either the oscillation or undulation of the pectoral fins for locomotion having higher foliation than species that use an intermediate swimming strategy or rely more heavily on axial-based locomotion.
Ainsley, Shaara M.; Ebert, David A.; Cailliet, Gregor M.
Age, Growth and Reproduction of the Bering Skate, Bathyraja interrupta (Gill & Townsend, 1897), from the Gulf of Alaska
Pacific Shark Research Center & Moss Landing Marine Laboratories, Moss Landing, CA, United States
An increase in skate landings, as well as the development of skate fisheries in the Gulf of Alaska, has amplified interest in the management of skates in the eastern North Pacific. Skates are taken in large numbers as bycatch in Alaskan commercial bottom trawl and long-line fisheries. Vertebrae and caudal thorns were taken from 705 individuals and reproductive tracts were collected from 281individuals in the Gulf of Alaska between the months of April and September of 2005-06. Observed total lengths ranged from approximately 16-82 cm for males and from 18-87 cm for females. Vertebral centra grow proportionately with total length (n = 103, r2 = 0.934). Total lengths at 50% maturity were approximately 68 cm for males and 70 cm for females. Estimated ages at 50% maturity range from 6 to 9 years for both males and females. Ages estimated from vertebral centra show a minimum longevity of 12 years for males and 13 for females. Growth model parameters will be presented. Gravid females appear in all months sampled at both locations with no discernable peak. A similar life history study is in process examining B. interrupta collected from the Bering Sea.
Ajemian, Matthew1; Powers, Sean1; Geraldi, Nate1; Murdoch, Thaddeus2
Movements of Spotted Eagle Rays (Aetobatus narinari) in Harrington Sound, Bermuda
1University of South Alabama and Dauphin Island Sea Lab, Dauphin Island, AL, United States, 2Bermuda Biodiversity Project, Bermuda Zoological Society, Flatts, FL BX, Bermuda
Rays and small shark species are a central component of marine and estuarine foodwebs as a result of their role as predators on benthic invertebrates. Because may of these species for dense schools, their potential impact on invertebrate prey population may be large. The reported increase in the abundance of these mesopredators, in particular Myliobatidae rays, may pose problems for fisheries management because many of their prey items include exploitable shellfish species (oysters, scallops, conchs). One such myliobatid species, the cownose ray (Rhinoptera bonasus), has already been demonstrated as integral to the destruction of some temperate shellfish industries on the east coast of the United States. The spotted eagle ray Aetobatus narinari is another myliobatid which has not been investigated with respect to ecological role, but is common in subtropical Bermuda. Populations of these rays may be increasing with the loss of sharks in the area and is raising concerns for resource managers and conservationists as they are prime predators of economically valuable queen conch (Strombus gigas). In our research effort, we aim to evaluate the role of A. narinari in Bermudian waters through studies of food consumption, movements, and predator-prey interactions. Here we present preliminary data on the movements of this species within Harrington Sound, a semi- enclosed water body dominated by seagrass habitat.
Bizzarro, Joseph J.1; Compagno, Leonard J.V.2; Ebert, David A.1
Aspects of the biology and distribution of the sixgill sawshark, Pliotrema warreni (Regan 1906), in South African waters
1Pacific Shark Research Center, Moss Landing Marine Laboratories, Moss Landing, CA, United States, 2Shark Research Center, Iziko – South African Museum, Cape Town, South Africa
The sixgill sawshark, Plitotrema warreni, is one of five sawshark species (Pristiophoridae) and the only member of its genus. Endemic to the southwestern Indian Ocean, this species has been reported from Cape Algulhas, South Africa to southern Mozambique, including waters off Madagascar, at depths of 26-455 m. Available biological information about P. warreni is extremely limited and largely anecdotal. Seventy-seven individuals (44 females, 33 males) were collected from fishery independent trawl surveys conducted between False Bay and Port Elizabeth, South Africa, facilitating an assessment of this species’ reproductive biology, diet composition, and distribution. Size at birth was determined to be approximately 35- 38 cm total length (TL). Maximum size of females and males was 136.4 cm TL and 112.0 cm TL, respectively. Size at first maturity ranged from 109.0 cm TL in females to 91.1 cm TL in males. Fecundity was estimated at 5-7 per litter. The largest immature female was 123.6 cm TL, whereas the largest immature male measured 104.4 cm TL. Females matured at a larger size than males and also reached a larger maximum size. Diet composition consisted primarily of small demersal fishes and shrimps. The occurrence of P. warreni was extremely localized and it was captured infrequently in survey trawls. This shark is commonly taken as bycatch by commercial trawlers and, like sawfishes, is probably especially susceptible to capture in net gear because of its long, toothed rostrum. Given the low fecundity, large size at maturity, and restricted range of P. warreni, this species may be vulnerable to fishery exploitation and habitat degradation.
Bubley, Walter; Fagan, Erin; Koester, David; Sulikowski, James; Tsang, Paul
Assessing Alternate Techniques to Enhance Visualization of Growth Increments to Estimate Age in Spiny Dogfish, Squalus acanthias
1University of New Hampshire, Durham, NH, United States, 2University of New England, Biddeford, ME, United States
The spiny dogfish (Squalus acanthias) is a cosmopolitan shark species found in temperate coastal waters of the Atlantic and Pacific Oceans. There are discrepancies in the literature using second dorsal fin spines as the structure for estimating age with this shark, with the estimated maximum age being anywhere from 25 – 38 years old in the Atlantic, a difference of over 50%. Therefore, the goal of our present study was to develop a new method for the accurate estimation of age in the spiny dogfish population within the Gulf of Maine, by first determining the structure and preparation method from which repeatability in the counts of growth increments is most consistent. We will accomplish this by comparing age estimates using the traditional dorsal fin spine method of age determination to the vertebral centrum method, one commonly used with many other elasmobranchs, to ascertain which structure produces the most accurate and reliable correlation between age and total length in spiny dogfish. Vertebrae were removed just anterior to the first dorsal fin, with each vertebra being sectioned and prepared using a different technique. Vertebrae were randomly selected to be unstained, stained with alizarin red, crystal violet, or silver nitrate, or processed using histological techniques developed for elasmobranchs and stained with hematoxylin. The second dorsal fin spines were removed at the level of vertebral attachment, will be examined whole, and horizontal sections will be taken and prepared using the same stains used for the vertebrae. In randomized and blinded trials, two readers will independently age all centra and spines twice, and results are calculated for within and between readers using Average Percent Error and Coefficient of Variation. These values will be used to determine the method which yielded the greatest amount of repeatability between counts. The standardization of an aging technique will allow for more accurate life history parameters and thus, more successful management of the spiny dogfish population in the western Atlantic. (Supported by NH Sea Grant College Program, NOAA # NA060AR4170109)
Buch, Robert1; Sanford, Christopher2; Burgess, George1; Castro, Jose3; Cotton, Chip4; Galbraith, John5
A Morphometric Analysis of the Genus Centrophorus in the Northwestern Atlantic
1Florida Program for Shark Research, Gainesville, Florida, United States, 2Hofstra University, Hempstead, N.Y., United States, 3Mote Marine Laboratory, Sarasota, Florida, United States, 4VIMS, Gloucester Point, VA, United States, 5NOAA, Woods Hole, Mass., United States
Morphometrics of deep-sea squalid specimens, genus Centrophorus, from the Northwestern Atlantic were analyzed in an effort to determine species validity. Initially, Discriminant Function Analysis (DFA) was performed using 65 morphological measurements of 59 museum specimens and 25 newly caught specimens from Jamaican waters. The key characters separating these 84 specimens are associated with snout length, pelvic fin inner margin length, length of the subterminal margin, and length of the caudal fin. Morphometrics of twelve specimens (provided by Jose Castro and Mote Marine Laboratory), also collected from the Northwestern Atlantic, were then compared with results from the analysis of the initial 84 specimens. The DFA was performed a second time using all 96 Centrophorus specimens and the 12 most diagnostic measurements. Study results indicate that there are at least 6 different species of Centrophorus in the Northwestern Atlantic. Moreover, the DFA supports the validity of Centrophorus acus, C. granulosus, and C. uyato.
Cartamil, Daniel1; Santana, Omar2; Sosa-Nishizaki, Oscar2; Graham, Jeffrey1
A Survey of the Artisanal Elasmobranch Fisheries along the Pacific Coast of Baja California Norte: Preliminary Results
1Scripps Institution of Oceanography, La Jolla, CA, United States, 2Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, Ensenada, Baja California, Mexico
The Pacific coast of Baja California Norte has one of the fastest-growing elasmobranch fisheries in Mexican waters. However, little data exist for the region with regard to the extent of these fisheries or their impact on elasmobranch populations. A collaborative research program, led by the Scripps Institution of Oceanography (SIO) and the Centro de Investigacion Cientifica y de Educacion Superior de Ensenada (CICESE), has recently been established to survey the traditional, or artisanal, camps of the region and collect data on species catch composition, fishing effort, location, gear types, and seasonal fishery activity. Approximately twenty-two artisanal camps operate in the region, using primarily inshore gillnets (targeting coastal elasmobranchs and teleosts) or longlines (for pelagic shark). Preliminary analyses indicate that landings of inshore elasmobranchs are dominated by banded (Zapteryx exasperata) and shovelnose (Rhinobatus productus) guitarfish (22% and 27% of total observed catch, respectively), while pelagic elasmobranch landings are dominated by mako (Isurus oxyrinchus) and blue (Prionace glauca) shark (12% and 14% of total observed catch). Common thresher shark (Alopias vulpinus) become more abundant in inshore fisheries with increasing latitude. Over 50% of common thresher shark landed are juveniles (i.e., <100 cm FL), indicating that the region may be an important nursery area for this species, at least on a seasonal basis. Collaborative efforts between SIO, CICESE and other institutions have led to the formation of the Southern California Bight Elasmobranch Consortium, which will address issues relevant to the conservation and management of shared elasmobranch resources in U.S. and Mexican Pacific waters.
Chapple, Taylor; Botsford, Louis
Determination of Effect of Fishing on the Status of the Common Thresher Shark, Alopias vulpinus, off of the Coast of California
University of California, Davis, Davis, CA, United States
Sharks are critical to many marine systems and are more prone to overexploitation than bony fish; thus, only a few species are able to support fishery. In 1978, the common thresher shark. Alopias vulpinus, was first targeted in Californian waters during a springtime drift gillnet fishery. Over the next 13 years there was a significant decline in the catch per unit effort (CPUE). In response, California implemented various seasonal and area closures during this period to protect pregnant females. By 1990, drift gillnet fishing was either completely prohibited or severely limited in the months that had previously provided 50% of shark catch. During the fishery, CPUE data, size distribution of the catch and total landings were recorded. Though the population showed evidence of significant declines, the available information was never utilized to make a formal assessment of the common thresher shark population on the west coast. In our study, we created a model of the A. vulpinus population using a Leslie matrix and known demographic characteristics. We then fit this model to the CPUE data and determined a least squares estimate of the mortality due to fishing that would result in the extent of decline evident in the fishery data. In addition, we simulated the population at stable age distribution at virgin biomass and then transformed this age distribution into a size distribution. We compared our simulated distribution with the actual distribution after fishing occurred. These results allowed us to determine the effect of fishing on the structure of the population and to describe a stock recruitment relationship for the thresher shark and its vulnerability to fishing pressure.
Conrath, Christina; Burgess, George
Investigations into the Activity of Ray Species in the Indian River Lagoon System, Florida
University of Florida, Gainesville, FL, United States
The primary objective of this project is to investigate the movement and residency patterns of ray species found within the Indian River Lagoon (IRL) system. An acoustic array of 27 Vemco VR-2 receivers was strategically deployed within the Mosquito Lagoon portion of the IRL to maximize spatial coverage within this area. Rays of four species were captured via tangle net and outfitted with coded V-13 transmitters. During the spring and summer of 2006, 15 bluntnose stingrays (Dasyatis say), 11 smooth butterfly rays (Gymnura micrura), 1 cownose ray (Rhinoptera bonasus) and 1 spotted eagle ray (Aetobatus narinari) were tracked for periods of time ranging from 12 hours to 217 days (intermittently). Despite a lack of detection of these animals within the winter months, there was little evidence of emigration out of the area either into the southern portion of the IRL via Haulover Canal or into coastal waters via Ponce Inlet. The detection rate of both bluntnose stingrays and smooth butterfly rays within the lagoon system was highest within the southern portion of the lagoon, particularly at two receivers 3.2 and 4.4 km southeast of Haulover Canal, indicating a preference for this locality with over 50% of all detections occurring at these two receivers. During the upcoming summer, movement studies within the IRL will continue and an additional 32 transmitters will be deployed on rays within this area.
Cotton, Charles F.; Musick, John A.
Aging Chondrichthyan Fishes Using Dorsal Fin Spines: Utility Or Futility?
Virginia Institute of Marine Science, Gloucester Point, VA, United States
Chimaeras (Holocephali) and dogfishes (Elasmobranchii: Squaliformes) are commonly caught as bycatch or targeted in several fisheries worldwide for meat and valuable squalene. Age and growth data are lacking for most squaliform species, in part because traditional aging methods rely on vertebral centra which are not suitably calcified to record growth in these species. All holocephalans and most squaliform species possess dorsal fin spines which have been shown to record both internal growth bands, visible in a transverse section, and external growth bands, visible on the spine base. Recent studies of two squaloid species suggest that internal bands cease formation when the animal reaches a certain size, while external bands continue formation until death. This raises the possibility of age underestimation when using a transverse section of the spine. Given this uncertainty, future age and growth studies using dorsal fin spines should examine the relationship of internal and external banding patterns to determine if this discrepancy is unique to certain taxa or universal among chondrichthyans bearing fin spines. In ongoing collections we have accumulated fin spines from 2 holocephalan species (Hydrolagus affinis and H. pallidus) and 10 squaliform species (Squalus cubensis, Centroscyllium fabricii, Etmopterus bigelowi, E. princeps, Centrophorus cf. niaukang, C. squamosus, Deania hystricosa, Centroscymnus coelolepis, C. owstoni, and Centroselachus crepidater). External bands were not obvious on freshly cleaned spines of any of these species. We present the results of external band readability under various staining techniques for all of these species. Additionally we compare internal and external banding patterns for those species yielding good readability. Although our sample sizes at this stage of collection are too small to generate growth equations for these species, these data will be useful in determining the suitability of fin spines for aging and whether discrepancy exists between the observed number of external and internal bands in these species.
Curtis, Tobey; Snelson, Franklin; Burgess, George
A Comprehensive Review of the Distribution and Habitat Use of Bull Sharks, Carcharhinus leucas, in the Indian River Lagoon System, Florida
University of Florida, Gainesville, FL, United States
Bull sharks (Carcharhinus leucas) are a component of the United States Atlantic large coastal shark fishery, which has been depleted over the last 30 years. To more effectively manage the species in this fishery, increased knowledge and more detailed descriptions of their essential habitats are necessary. Here we present a synthesis of 30 years of bull shark catch data from Florida’s Indian River Lagoon (IRL) system, to comprehensively describe their distribution and habitat utilization within this intracoastal environment. We collected bull shark catch and direct observation data from the scientific literature, fishery-independent surveys, fisherman interviews, and other personal communications from 1976-2005. Over 350 individual bull shark records were compiled, predominantly comprised of young-of- the-year and juvenile specimens. Immature bull sharks were determined to be present in the IRL year round, but were far more abundant between March and November. Adult bull sharks, predominantly gravid females, were rare, but mostly present in the early summer. The sharks were found to occur in a broad range of available habitats including freshwater creeks, seagrass beds, dredged channels, power plant outfalls, ocean inlets, in depths of 0.2-4.0 m, temperatures of 18.5-37.0° C, salinities of 1.2-31.1 ppt, in dissolved oxygen concentrations of 1.5-9.2 mg/L, and in water clarity levels as low as 0.7 m. Data from the IRL was compared to data available from other potential bull shark nursery areas throughout the Gulf of Mexico. This information will help us to better define the habitats that are important to the growth and development of the sharks that utilize these productive coastal systems. Prudent management within such areas will help to rebuild depleted shark resources in the Atlantic.
Clò, Simona1; de Sabata, Eleonora2
Remarkable Presence of Basking Sharks (Cetorhinus maximus) throughout Sardinia Island (Mediterranean Sea)
1CTS, Roma, Italy, 2MedSharks, Roma, Italy
Important new records from North Sardinia have recently been reported and give a new distribution of basking shark in Italian waters. The presence of basking shark, Cetorhinus maximus (Gunnerus, 1765), throughout Sardinia Island was investigated collecting information from military authorities, professional and recreational fishermen and from Marine Protected Areas. More than 50 records of information on basking sharks were collected, with records dating from 1910 to 2006. Data revealed the presence of specimens of quite different sizes that range from very young (about 2 m TL) to large adults (8 m TL). Numerous records registered in the last two years are related to an increasing scientific and public interest on the species but also to variation in zooplankton abundance. The present study aims to compile data on the presence, distribution, seasonal changes in number, length frequency of basking sharks in Sardinia Island. The knowledge on the distribution and population structure of basking sharks in the Mediterranean basin plays an important role in the implementation of conservation measures of such protected species.
Dean, Mason1; Bizzarro, Joseph2; Summers, Adam1
Evolutionary History of Feeding Morphology of Batoid Fishes
1Ecology & Evolutionary Biology, University of California, Irvine, CA, United States, 2Pacific Shark Research Center, Moss Landing Marine Laboratories, Moss Landing, CA, United States
We examine the evolutionary history of feeding morphology and diet in the batoid fishes (stingrays, skates and their allies), the most speciose group of cartilaginous fishes, through comparisons of the anatomies and geometries of their head skeletons. By illuminating the feeding mechanism in a phylogenetic context we aim to demonstrate the importance of specific morphological features in the ecological success of this group, and selective pressures that led to more “extreme” feeding modes (e.g., hard prey crushing, filter feeding). We CT-scanned (0.4-0.75 mm slice thickness) 40 museum specimens, representing approximately 54% of batoid genera, and compared seven variables of cranial anatomy relating to the feeding mechanism. Associations among these morphological variables, as well as among morphological and dietary characters were investigated in terms of phylogeny using pairwise comparisons. Only two variables (gape height and the ratio of gape height and width) were significantly associated, indicating independence of the majority of our chosen variables. Three morphological variables were significant predictors of certain diets, allowing us to infer the diets of several species for which there is currently no dietary information. Reconstruction of the morphology and diet of the common ancestor, from squared-change parsimony and maximum likelihood estimates, indicates that the basal batoid was likely benthodemersal and fed on mechanically complex and elusive prey such as shrimp or squid. Our data illustrate that the evolution of impressive trophic diversification can be explained by simple and subtle changes in the morphology of cranial elements.
Dempsey, Adair1; Janech, Michael2; Lacy, Eric3; Miller, Donald4, Ploth, David2, Fitzgibbon, Wayne2
Localization of Facilitated Urea Transporters to Tubular Segments in the Bundle and Sinus Zones of the Kidney of the Euryhaline Stingray, Dasyatis sabina
1Grice Marine Laboratory, College of Charlston, Charleston, SC, United States, 2Division of Nephrology, Medical University of South Carolina, Charleston, SC, United States, 3Marine Biomedicine and Environmental Sciences Center, Medical University of South Carolina, Charleston, SC, United States, 4Cell and Molecular Pharmacology and Experimental Therapeutics, Medical University of South Carolina, Charleston, SC, United States
The principle component of the osmoregulatory strategy of marine elasmobranchs is the maintenance of high concentrations of urea in their body fluids. The reabsorption of filtered urea by the renal tubules is the primary mechanism underlying the retention of urea. Urea movement across the renal tubular epithelium occurs, at least in part, via specific phloretin-sensitive, facilitated transport proteins. We have identified two members of a urea transporter (UT) family from the kidneys of the Atlantic stingray, Dasyatis sabina. To clarify the role of these UTs, we utilized immunohistochemistry to identity the tubular sites at which they are expressed. Stingrays were maintained in harbor water (850 mOsmol/kg H2O) and fed a diet of shrimp for at least 2 weeks prior to study. They were anesthetized with MS-222 in buffered harbor water and perfused with elasmobranch Ringer’s followed by 4% paraformaldehyde. The kidneys were blocked in paraffin. Six micron sections were incubated with an affinity-purified antiserum generated to a sequence common to the 2 UTs (strUT-1 and strUT-2). Localization of UT expression was visualized using DAB stain. The specificity of the signal was confirmed by incubation of adjacent sections with the antiserum preincubated with the immunizing peptide. We also examined the expression of 2 other membrane transporters. Tubular segments were identified from the criteria reported by Lacy and Reale (1985). Numerous positively stained tubular segments were observed in both bundle and sinus zones in the presence of anti-strUT. In the sinus zone, strong immunoreactive signal was observed in the Proximal-III tubular segment while weak staining was found in one of the intermediate segments. In the bundle zone, immunoreactive signal was observed in the Distal-I segment. Signal for the co- transporter, NKCC, was localized to the apical membrane of tubular segments in both the bundle and sinus zones. In contrast, Na+-K+-ATPase was localized to the basolateral membranes of a number of segments within the bundle zone but to only one of the intermediate segments in the sinus zone. Our findings indicate that the strUTs are expressed in tubular segments in both the bundle and sinus zones. The expression of UTs in the bundle zone supports a role for countercurrent exchange in urea reabsorption. The mechanism(s) by which urea is reabsorbed via UTs in segments in the sinus zone remain to be identified.
Di Santo, Valentina; Bennett, Wayne A.
Effects of Temperature on Elasmobranch Fishes: Overview and Future Prospects
University of West Florida, Pensacola, FL, United States
Temperature is the most important factor affecting the physiology of fishes, and while many studies have evaluated temperatures’ effect on bony fishes, very little data are available for elasmobranchs. The purpose of our review was to evaluate the role of temperature on elasmobranch ecology based on studies made over the last six years at the University of West Florida Ecological-Physiology Laboratory and supported by other contemporary literature. Direct observations of captive or free- swimming animals show that seasonal and/or diel vertical and horizontal movements of lemon sharks (Negaprion brevirostris), Atlantic stingrays (Dasyatis sabina), bat rays (Myliobatis californica) and dogfish (Scyliorhinus canicula) are likely temperature influenced. Likewise, laboratory studies suggest that selection of a preferred temperature enhances digestion efficiency, growth, gestation times and metabolism in several species. Temperature also plays a role in abundance and geographic distribution of some elasmobranchs including round stingrays (Urobatis halleri) and Greenland sharks (Somniosus microcephalus). Temperature tolerance limits remain largely unknown in elasmobranchs. Only a single published study (on Atlantic stingray) has evaluated the complete thermal niche for an elasmobranch, however, experiments in progress have found that thermal niche requirements are much more narrow for elasmobranchs than for bony fish. Further studies could elucidate ways in which temperature influences other important physiological processes in cartilaginous fishes.
Dowd, Wes1; Harris, Breanna3; Kültz, Dietmar2; Cech, Jr., Joseph1
Leopard Sharks Modulate Physiology and Behavior in Response to Salinity Change
1University of California-Davis, Dept. Wildlife, Fish and Conservation Biology, Davis, CA, United States, 2University of California-Davis, Dept. Animal Science, Davis, CA, United States, 3Ohio University and Bodega Marine Laboratory REU Program, Bodega Bay, CA, United States
Physiological responses to environmental changes can occur at several organizational levels (molecular, cellular, organismal) and over several time-scales. Behavioral responses may complement or override physiology, requiring an integrative approach to relate laboratory results to ecological consequences. Here, we assess both physiological and behavioral responses of leopard sharks (Triakis semifasciata) to salinity changes. Sharks were acclimated to 60%, 80%, or 100% seawater for 48 hours (short-term) or 3 weeks (long-term). Plasma samples were analyzed for osmolyte concentrations. To assess underlying molecular mechanisms, we identified several proteins that were up- or down-regulated in osmoregulatory tissues (gill, rectal gland) during salinity change using a proteomics approach (i.e., 2- dimensional electrophoresis and mass spectrometry). The functions of these proteins were assessed using bioinformatics databases and pathway analysis software. Behavioral responses (e.g., swimming) were monitored using focal animal surveys. Plasma osmolality and chloride concentrations decreased with decreasing salinity over 48 hours, and the osmotic gradient between shark and environment was greatest at 24 hours. Sharks remained hyperosmotic but hypoionic to the medium in short and long-term experiments. Individuals in 60% seawater in the long-term treatment responded behaviorally by reducing their activity by ~50%, suggesting a long-term behavioral tradeoff for increased costs of osmoregulation. These multi- level laboratory results provide a baseline for comparison with proposed field studies to evaluate tradeoffs between physiology and behavior in wild sharks inhabiting estuaries.
Gary Jr., Samuel; Abel, Daniel; Howington, Eric; Gandy, Dave; Garwood, Jason; Gocke, Kelsey; Knott, Lisa; Marcus, Emily; Maxwell, Katie; McDonough, Mollie; Provaznik, Jennifer; Travaline, Mario; Yednock, Bree
Sharks of Winyah Bay, SC: Results after 5 Years
Coastal Carolina University, Conway, SC, United States
We conducted a longline survey from 2002 – 2006 in Winyah Bay SC, a 65 km2 partially-mixed coastal plain estuary, to characterize shark fauna and investigate habitat partitioning. We caught 484 sharks comprising 12 species, including adults and juvenile Carcharhinus plumbeus (241), Rhizoprionodon terraenovae (117), Carcharhinus limbatus (50), and Carcharhinus isodon (44). Juvenile Sphryna lewini were also captured. Annual average CPUE (sharks/100 hooks, ± SEM) ranged from 2.23 – 4.70 for 16/0 lines and 1.26 – 6.13 for 12/0 lines. Greatest abundance and diversity occurred in June (102 sharks/9 species,) July (84/8) and August (129/8), respectively. There was a higher mean monthly CPUE for juvenile C. plumbeus (1.07 ± 0.18) than adult (0.13 ± 0.03) (p < 0 .001) for all months, with peak adult CPUE occurring in October. Both middle and lower bay consistently produced higher CPUE for juvenile C. plumbeus (1.06 ± 0.36, and 1.17 ± 0.26, respectively) than adults (0.05 ± 0.02, 0.23 ± 0.06) (middle bay p = 0.021, lower bay p = 0.008). Recursive partitioning showed that depth, month, and salinity were important factors correlated with catch rate. Regression analysis showed a significant relationship between mean CPUE and mean day length (April 1 – November 30, p = 0.009, R2 = 0.392) and CPUE and water temperature (April 1 – November 30, p = 0.031, R2 = 0.291). Winyah Bay thus represents habitat and potential summer nursery grounds for numerous shark species.
Gomes, Amanda Piraice1; Shibuya, Akemi2; Marques Barcellos, José Fernando1; Góes Araújo, Maria Lúcia1
Distribution of Lateral Line System in Embryos of Potamotrygon Species (Chondrychthyes: Potamotrygonidae)
1Universidade Federal do Amazonas, Manaus, Amazonas, Brazil, 2Instituto Nacional de Pesquisas da Amazônia, INPA, Manaus, Amazonas, Brazil
Studies on the lateral line canals are focused solely on marine species. The knowledge of the mechanosensorial system in freshwater stingrays is scarce, especially during the embryo development. The purpose of this study is to obtain information about the development of lateral line system in embryos of Potamotrygon motoro (n=9) and P. orbignyi (n=5). The samples were collected at Rio Negro Basin, Amazonas, Brazil. The specimens were fixed in 10% formalin and conserved in 70% ethanol solution. Lately, they were dissected. Dorsal and ventral surface had pores and vesicles of Savi counted. The distribution and shape of sensorial canals were analyzed. The following canals were considered: hyomandibular, supraorbital, infraorbital and posterior lateral line. The dorsal canals of both species exhibit bilateral symmetry. They are interconnected and present pores in all canals. The number of pores varied in P. motoro from 230 to 258, and from 220 to 285 in P. orbignyi. The ventral surface has exhibited non-pored canals, except the hyomandibular canal, whose pores are concentrated in rostrum region. The number of pores varies from 34 to 44 in P. motoro and from 30 to 36 in P. orbignyi. The vesicles of Savi are located in bilateral rows on the rostrum midline. The number of vesicles of Savi varied from 10 to 14 in P. motoro and from 6 to 10 in P. orbignyi. These variations can be related to the difference on the habitat and feeding habits on the species. The number of pores has a direct relationship with the embryo development exclusively in P. orbignyi.
Cultural Importance of Elasmobranchs in the Fishing-Gatherers Groups of the Sao Paulo Coast, Brazil
1Nucleo de Pesquisa e Estudo em Chondrichthyes, Santos, Sao Paulo, Brazil, 2Museu de Arqueologia e Etnologia da Universidade de Sao Paulo, Sao Paulo, Sao Paulo, Brazil
Nowadays, many people see sharks as killers, but in the past they were admired by coastal societies that used the marine organism for subsistence. In the shell mounds funeral offerings that have been studied on the Sao Paulo coast, we observe an association between materials or abstracts shark images used as ritualistic symbols. The study was based on the analysis of 15.447 faunal remains of elasmobranches (teeth, spines and vertebras) of already existing collections of archaeological sites of the coast of Sao Paulo (Maratuá shell mound, Mar Casado shell mound, Buracão shell mound, Piaçaguera shell mound, Cosipa shell mound, Mar Casado site and Tenório site) and present at the Museu de Arqueologia e Etnologia da Universidade de Sao Paulo – MAE-USP. The main shark faunal remains identified in the offerings are teeth and vertebrae of the white shark (Carcharodon carcharias), tiger shark (Galeocerdo cuvier), bull shark (Carcharhinus leucas) and sand tiger shark (Carcharias taurus). We can consider the sharks as sacred fishes due to their behavior, and the elements of them that were used as protective adornment talisman in pre-historic society. The association between elasmobranchs and young men and women (mainly 20 and 30 years old), may represent a fertility symbol, as they do in records from Mexico and Panama. The teeth and vertebrae present in most of the burials could indicate the different status among individuals in the society. Sharks and rays, like some others animals, were considered gods in all the Pacific islands and only lost their status after the introduction and stabilization of Christianity during the colonization periods in these lands. The Christian domination occurred in most coastal groups around the world, and changed the culture and belief of the people from considering sharks as gods in pre-historic society, to demonizing them in current society.
Ecology and Use of Pristis (Elasmobranchii, Pristidae), by Fishing- Gatherers on the Coast of Sao Paulo, Brazil
1Núcleo de Pesquisa e Estudo em Chondrichthyes, Santos, São Paulo, Brazil, 2Museu de Arqueologia e Etnologia da Universidade de São Paulo, São Paulo, São Paulo, Brazil
Artifacts made from rays (rostral teeth and spine) are very common in shell mounds on the coast of Sao Paulo, Brazil. The presence of the genus Pristis among the studied species of elasmobranch fishes in this shell mounds reinforces the hypothesis these animals occurred in southeastern Brazil, and were used by fishing-gatherers. This study was based on the analysis of the materials from the collection of Museu de Arqueologia e Etnologia of Universidade de São Paulo (MAE-USP), collected from studies conducted in seven shell mounds from São Paulo State: Piaçaguera, Cosipa 2, Mar Virado, Tenório, Buracão, Mar Casado and Maratuá. The dates of these archaeological sites range from 4930 and 1875 YBP. Were analyzed twelve rostral teeth of the genus Pristis from shell mounds. The teeth have artificial marks left from making arrows and harpoons. The basic function of the teeth found in these shell mounds was the production of tools and ornaments. From the analyzed teeth, ten (83%) were associated to the faunal remain and two (17%) were associated with burials, and they can be considered as ceremonial or votive elements. There had been no new records of occurrence of the genus Pristis on the coast of Sao Paulo State in Brazil, and there are a few studies on the use of their products in many ancient and contemporary human communities. This paper provide data about the distribution of rays of this genus in archaeological sites and the use of this resource by fishing- gatherers on the coast of Sao Paulo.
Haas, Diane L.; Ebert, David A.; Cailliet, Gregor M.
Age, Growth, and Reproduction of the Aleutian Skate, Bathyraja aleutica (Gilbert, 1896), in the Eastern Bering Sea
Pacific Shark Research Center, Moss Landing Marine Laboratories, Moss Landing, CA, United States
The Aleutian skate (Bathyraja aleutica) is a large deep-water species that commonly occurs in bycatch of Alaskan trawl and longline fisheries. Although it dominates the eastern Bering Sea slope skate biomass and the softnose skate biomass in the Gulf of Alaska, minimal biological information exists for B. aleutica. Knowledge of life history, including age, growth, and reproductive biology, is necessary for effective management of this potentially vulnerable species. Since 2004, more than 600 skates were collected in the eastern Bering Sea during NMFS-AFSC exploratory trawl surveys and by the NMFS-AFSC Fisheries Observer Program. Gonads were examined using visual and histological analyses for maturity stage and reproductive seasonality. For age determination, banding patterns in vertebral thin sections and caudal thorns were examined and compared. Male age estimates ranged from 0 to 16 and females 0 to 17 years. Preliminary size (age) at 50% maturity was estimated at 123 cm TL (~10 years) for males and 124 cm TL (~10 years) for females. Growth model parameters and maximum age estimates will be presented. A comparative life history analysis of B. aleutica from the Gulf of Alaska is currently under investigation.
Preliminary Analysis of the Diet of the Tiger Shark, Galeocerdo cuvier, from the South Atlantic and Gulf of Mexico
NOAA Fisheries, Panama City, FL, United States
The tiger shark, Galeocerdo cuvier, is an important top-level predator in the pelagic ecosystem and is considered to be a generalistic scavenger with a widely varied diet. Very little diet information is available for the tiger shark in the Atlantic Ocean and Gulf of Mexico, with only limited observations from historic fishing tournaments and fishery independent sampling of a small number of tiger sharks providing colloquial data. This is a preliminary analysis of the diet of the tiger shark caught in the bottom longline fishery sampled by the shark bottom longline observer program. Samples were frozen by the observer and diet was classified at NOAA Fisheries Panama City Laboratory. Prey items were identified to lowest possible taxa and quantified using six indices: percent by number (%N), percent by weight (%W), frequency of occurrence (%O), the index of relative importance (IRI), IRI expressed on a percent basis (% IRI), and % IRI based on prey category (% IRIPC). All prey items identified as bait were excluded from analysis. Preliminary results (n = 10, 0 empty) indicate teleosts (including sailfish, Istiophorus platypterus, yellowedge grouper, Epinephelus flavolimbatus, and catfish) make up 72.2 % IRIPC with crustaceans (predominantly portunid crabs) making up 23.95 % IRIPC. Also present in the diet were elasmobranchs, sea turtles, mollusks, sea birds, cnidarians, and plant material. Further quantification of the diet will help determine the trophic role the tiger shark plays in its ecosystem as well as identify any patterns or changes in diet with maturity or location.
Hogan, Fiona; Cadrin, Steve; Oliveira, Ken
Age Determination of Skate Species in Massachusetts Waters
University of Massachusetts School of Marine Science, New Bedford, MA, United States
Landings of elasmobranchs account for an increasing percentage of commercial fishery harvests in New England. Despite this, demographic information (e.g., age, growth, and life history parameters) for many elasmobranch species is limited. In this study, we are investigating the validity of presumed annular marking on skate vertebrae for use in age determination of individuals. This is being accomplished by injecting live individuals of various skate species collected in Massachusetts waters with tetracycline and then holding these animals in captivity for a minimum of a year. Age determination will subsequently be accomplished by examining the vertebral bands of these individuals using a staining technique, a number of which will be tested to determine the most effective technique. Image analysis software will also be used to automate and enhance the accuracy of the age determinations. As well, growth data are being obtained from individual fish to determine relationships between age and other life history characteristics such as length, weight, and fecundity.
Form and Function of Stingray Mechanosensory and Electrosensory Systems (Elasmobranchii: Batoidea)
University of California, Los Angeles, Los Angeles, CA, United States
Elasmobranch fishes (sharks, skates, and rays) demonstrate remarkable sensory capabilities which are used for a variety of purposes including locating and capturing prey. This study compares the sensory anatomy to detection capabilities of the mechanosensory lateral line system and the electrosensory system in the benthic feeding round stingray, Urobatis halleri, and bat ray, Myliobatis californica. These systems allow elasmobranchs to locate prey through detecting water movements and electrical fields respectively. Predictions based on detailed maps of the sensory anatomy were tested in behavioral detection experiments. U. halleri feeds primarily on small epifaunal benthic invertebrate prey and the lateral line of this species shows a high proportion of ventral non-pored canals while the electrosensory pores are highly concentrated around the mouth. M. californica feeds primarily on infaunal benthic invertebrates as well as some more mobile invertebrates and fishes. The lateral line system in this species is highly branched with a large number of pores per branch. The electrosensory system shows a high pore number and is highly concentrated anteriorly. Both systems in M. californica have dramatic lateral extension toward the wing tips on the anterior edge of the pectoral fins. Responses of both species to water jets at 10cm/s are compared, M. californica responds to water jets over a significantly greater proportion of its disc width. Responses to weak electrical fields were comparable to those observed for sharks with minimum responses below 1 nanovolt. Implications of these results are discussed within the context of the ecology of these species.
Kacev, David1; Cartamil, Daniel2; Sosa-Nishizaki, Oscar3; Lewison, Rebecca1; Bohonak, Andrew1
Genetic Analysis of Common Thresher Shark Nurseries in the Southern California Bight
1San Diego State University, San Diego, CA, United States, 2Scripps Institution of Oceanography, San Diego, CA, United States, 3Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, Ensenada, BCN, Mexico
Common thresher sharks, Alopias vulpinus, are the most commercially harvested elasmobranch on the California coast; they are also the target of a seasonal recreational fishery. Despite this high fishing pressure, relatively little is known about their biology and life history. The Southern California Bight (SCB) has long been considered a nursery area for this pelagic species, and recent, preliminary data from the Southern California Bight Elasmobranch Consortium suggests that there may be two distinct nursery sites within the Bight; one located in the northern SCB, the other off the Pacific coast of Northern Baja California, Mexico. In this study, we will use genetic analyses to determine if these two proposed sites are in fact, distinct nursery areas, or represent the latitudinal extremes of distribution of one large migrating juvenile population. Fin clip and muscle samples are being collected in Northern Baja with the assistance of artisanal fishers and in the northern SCB in conjunction with the annual NMFS juvenile thresher shark survey. We are also collecting samples from three other sites that are not proposed nursery areas. We intend to use primers that amplify the mitochondrial control region of the sharks and compare the haplotype diversities among the sampled sites using ΦST and other analyses. If the two sites are nurseries, we expect to find less haplotype diversity within them than in the non-nursery areas, where individuals pupped in multiple nursery sites can mix. Here we compare the haplotype diversities between the two nursery sites to determine if they are different enough from one another to conclude that there are two distinct breeding populations. This information can then be shared with fisheries managers to create more effective policies for ensuring sustainable stocks.
MacDonald, Alyssa1; Stokesbury, Kevin2
Estimating Spatially Specific Abundance and Size Distribution of Skate in the Northwest Atlantic Ocean
1University of Massachusetts Dartmouth, North Dartmouth, MA, United States, 2School for Marine and Science Technology, New Bedford, MA, United States
The Federal Fisheries Management Plan for the skate complex (Amblyraja, Dipturus, Leucoraja, Malacoraja and Raja spp.) in New England waters was developed in 2003 and is reviewed annually. The skate stock assessment is based on a relative index of abundance developed from a multispecies groundfish survey. This assessment could be strengthened with the addition of an absolute estimate of skate abundance using the SMAST video survey. The video survey was designed to estimate scallop abundance from Georges Bank to the Mid Atlantic, but also provides data on fishes, macroinvertebrates and benthic substrates. To use the video survey required estimating the sampling error for skates, in particular are skates attracted or repelled to the video sampling pyramid. We developed a method to quantify the impacts of sampling on skate behavior within the video samples and applied the results to our research. We mapped skate distributions and calculated an absolute estimate of abundance of the skate complex. Future research will examine the effects of abiotic factors on skate distribution. These data provide spatially and temporally specific information required for ecosystem based fisheries management.
Mejía-Falla, Paola Andrea1; Navia, Andrés Felipe1; Mejía, Luz Marina3; Rubio, Efraín2; Acero, Arturo3
Marine and Freshwater Elasmobranchs of Colombia: A Review
1Fundación SQUALUS, Cali, Valle del Cauca, Colombia, 2Universidad del Valle, Departamento de Biología, Sección Biología Marina, Cali, Valle del Cauca, Colombia, 3Instituto de Investigaciones Marinas y Costeras, INVEMAR, Santa Marta, Magdalena, Colombia
An extensive revision of species of sharks, skates and rays registered for marine and continental waters of Colombia indicated that our country comprises 176 species of elasmobranchs. 61 species of sharks and 57 of skates and rays have been confirmed through photographic records and biological collections while the remaining has only been supported by bibliographical references. This inventory includes 66 genera (34 sharks and 32 skates and rays) and 33 families (19 sharks and 14 skates and rays). Four new species and 20 new reports for Colombian waters have been published in the last 25 years; seven species are deposited in internationals museums but have not been reported by scientific literature. These results indicated that Colombia is a rich country in elasmobranchs, including approximately 15.3% of species, 36.7% of genders and 55% of families of elasmobranchs of the world. Such richness must call the attention of the community to carry out protection and conservation actions.
How Well Do Yellow Elasmobranchs Smell?
Florida Atlantic University, Boca Raton, Fl, United States
The olfactory capabilities of elasmobranchs are legendary. Although they are reputed to demonstrate remarkable sensitivities, this is based on surprisingly little empirical evidence. Olfaction plays an important role in the localization of prey, and amino acids in particular are known to be effective odorants for elasmobranchs. However, the threshold sensitivity has been assessed for only four elasmobranch species using a handful of amino acids. Literature values for these species indicate threshold sensitivities to be approximately 10-7 to 10-8M. In this study, I investigated the olfactory capabilities of juvenile lemon sharks, Negaprion brevirostris, and yellow spotted stingrays, Urobatis jamaicensis. These phylogenetically distant species occur sympatrically but occupy different ecological niches. Negaprion brevirostris is a carcharhinid shark that actively swims throughout the near shore environment whereas U. jamaicensis is a benthically associated Urolophid that often buries in the sand. To determine how the olfactory abilities of these sympatric species compared, I examined both their olfactory morphology and physiology. The olfactory organs (rosettes) were dissected from both species and the total surface area of the olfactory lamellae was quantified. The lemon sharks averaged 48.4 ± 2.3 cm2 of lamellar area compared to 28.7 ± 2.1 cm2 for the yellow spotted stingrays. I also employed an electro-olfactogram (EOG) technique to assay the sensitivities of the species to a suite of twenty proteinogenic amino acids. Although there were significant differences in the response magnitudes among the amino acids, the most stimulatory amino acids were similar for both species; these were alanine, phenylalanine, tyrosine, serine, and methionine. The threshold sensitivities to these amino acids were also similar, with both species detecting amino acids down to a concentration of approximately 10-8 M with some individuals reliably detecting concentrations as low as 10-10 M. These results support the threshold sensitivities demonstrated by the previously tested elasmobranch species and illustrate that elasmobranchs are perhaps no more sensitive than teleost fishes.
Morris, John; Simpfendorfer, Colin
Satellite Tag Retention on Large Coastal Sharks of the Eastern Gulf of Mexico
Mote Marine Laboratory, Sarasota, FL, United States
Pop-up archival tags have become a popular research tool in ecological studies of billfish, tuna, sharks and rays. However, the use of these tags has produced only marginal success when applied on large coastal sharks of the Gulf of Mexico. To investigate the premature detachment of satellite tags on coastal sharks, dummy tags were attached to a captive sandbar shark (Carcharhinus plumbeus) in a 60,000-gallon research tank. Two attachment methods were tested: 1) tethered to the first dorsal fin by a fin tag and length of plastic-coated wire; and 2) tethered to the body by a metal headed dart tag and a length of plastic coated wire. To test whether sharks may be rubbing the tags off, a hard substrate consisting of two 100 lb concrete reef balls were positioned in the middle the tank. Video cameras were set up to record the animal’s behavior and verify if the animal uses the hard bottom to remove the tags. In addition, the animals were monitored for up to 6 weeks to document behavioral changes and tag performance. Within 1 – 2 weeks both tag attachments areas became swollen and inflamed. By the end of 2 weeks the metal-headed dart attachment had shed. The area of attachment had become infected and developed a 3.5cm lesion. Similarly, the roto-tag attachment was detached during week 6 while containing the animal. In both trials, the attachment areas were swollen and infected and a pungent smell of necrotic tissue was observed. Neither tag attachment trial induced rubbing behavior or tag loss associated with intentional rubbing. This implies that shark behavior was not affected, but tag loss did occur during both trials due to infection and development of necrotic tissue of the attachment area. This was attributed to the constant movement and rotation of the tether caused by the excessive buoyancy and drag of the tag and the normal swimming behavior of the shark. Modification of the attachment method to eliminate dependency on intra-musculature tissue to retain the tag will improve retention success. In addition, the reduction of tag buoyancy and drag will reduce the elliptical movement of the tag, there-by reducing the tension and friction at the attachment area created by the roto-tag and plastic-coated wire tether.
Navia, Andrés Felipe; Mejía-Falla, Paola Andrea
Notes on the Distribution and Biology of Narcine leoparda in the Colombian Pacific Coast
Fundación SQUALUS, Cali, Valle del Cauca, Colombia
Between March and November 2006, 65 individuals of Narcine leoparda in the Colombian Pacific coast were collected. Specimens were captured between 1.8o N y 4o N, showing a depth range of 1.8 to 33 m and a latitude range of 166000 km2, which increases the distribution of this specie one degree north latitude. Maximum length of capture was 28.7cm; the weight-length relationship was described for the equation: Wt = 0.005-Lt 2.8444, of isometric type. Narcine leoparda presented an aplacental yolk sac viviparity, an average fecundity of 2 embryos per female and the average maturity size of females and males was 20 cm and 14 cm, respectively; the birth size is near to 5 cm. This study also indicates that Narcine leoparda is an endemic species of the Colombian Pacific.
Plank, Susanne; Lowe, Christopher; Brusslan, Judith
The Population Genetics of Round Stingrays (Urobatis halleri) from Southern California Assessed by Microsatellite Markers
California State University Long Beach, Long Beach, CA, United States
This study aims to determine whether the genetic population structure of round stingrays near a warm water outfall in Seal Beach, CA shows either seasonal or inter- annual variation. It also aims to elucidate if a homogeneous population structure exists in the Southern California Bight, utilizing samples that have been collected from the Seal Beach Naval Weapons Station (SBNWS) wetlands and San Diego Bay, CA. Highly polymorphic STR primer pairs have been developed for four loci, and analysis is nearly complete for one of the loci, Uha 170. This locus shows no variation over seasons or over 5 years (F=0.7221, p=0.6534) at Seal Beach. Partial analysis of the SBNWS and San Diego samples indicate similar allele distributions to that of Seal Beach suggesting a large, homogeneous population. Primary data from the other three loci thus far show similar results to the Uha 170. Tissue samples from round stingrays found across geographic barriers (north of Point Conception, the Gulf of California, and Santa Catalina Island) are also currently being collected and will be tested to determine if they display different allelic frequencies to those found in the Southern California Bight.
Effective Number of Breeders for Sandbar Sharks, Carcharhinus plumbeus (Nardo, 1827), Using Two Nursery Areas in the Western North Atlantic
Virginia Institute of Marine Science, Gloucester Point, VA, United States
Sandbar sharks, Carcharhinus plumbeus, in the western North Atlantic mate off the coast of Florida. Females migrate to nursery areas from Cape Canaveral, FL to Long Island, NY for parturition, with the larger nurseries situated between North Carolina
and Delaware. Litter sizes are relatively small (x̅ = 8.4) and females have biannual reproductive cycle. The species is heavily exploited by the commercial fishery, making up as much as 2/3 of the yearly landings in the directed shark fishery. The combination of low fecundity and proposed female philopatry may make the species susceptible to localized extirpation in the face of exploitation. In addition, their may be differences between nursery areas in their contribution to the adult stock, with some being more important than others. Therefore it is important to determine the number of individuals contributing their genes to cohorts in different nursery grounds both within and across years. This can be accomplished using a molecular approach to estimate the effective number of breeders and effective population size. Young of the year sharks were sampled from 2003-2006 in the eastern shore lagoons of Virginia and from 2004-2006 in Delaware Bay. Individuals were genotyped at eight polymorphic microsatellite loci. Pairwise FST values were used to investigate whether individual cohorts taken at each nursery ground should be considered separately when estimating the effective number of breeders. The linkage disequilibrium method was used to estimate the effective number of breeders contributing to each cohort in each nursery. In addition the Jorde and Ryman temporal method was also used to examine the effective size of each nursery from consecutive cohorts. Results are discussed in a conservation and evolutionary context.
Press, Michelle; Vigliotti, Tabitha; Conrath, Christina; Burgess, George
Sexual Dimorphism in Tooth Morphology of the Roundel Skate, Raja texana, from the Gulf Of Mexico, USA
University of Florida, Gainesville, FL, United States
Differences in the tooth morphology of male and female batoids (skates and rays) are observed in several species. However, few comprehensive studies have been conducted on this phenomenon. Previous studies suggest that the differences in morphology may be due to diverse prey preferences or an adaptation for males to more effectively grasp females during mating. Such morphological differences are suspected in R. texana. Jaws were removed from 114 (74 female: 40 male) R. texana, and morphological variations of male and female teeth were quantified. To account for intra-jaw tooth variations, lower jaw teeth were extracted using a dental pick at two locations (toward the back of the jaw and at the center). Teeth from both locations were photographed under magnification, and morphology software was used to denote landmarks and curves within each tooth. A procrustes analysis was performed on these data to standardize differences in tooth size and orientation. Analysis of Variance and Principal Components Analysis techniques were used to quantitatively compare the tooth shape from both jaw localities of male and female roundel skates.
Rinewalt, Christopher1; Ferry-Graham, Lara1; Ebert, David2; Cailliet, Gregor1
The Importance of Intra-specific Differences in the Tooth And Jaw Morphology of the Sandpaper Skate, Bathyraja Kincaidii: Food or Mates?
1Moss Landing Marine Laboratories, Moss Landing, CA, United States, 2Pacific Shark Research Center, Moss Landing, CA, United States
The sandpaper skate, Bathyraja kincaidii, is a small batoid endemic to the eastern North Pacific. The diet from specimens collected throughout its range indicated this species is a trophic generalist, feeding mainly on krill, shrimp and polychaetes but also taking various other invertebrates and teleosts. The results of that study determined there were significant intra-specific differences in the diet between sexes, maturity states and among geographic zones. To examine possible reasons for these differences, the feeding morphology and dentition of the sandpaper skate were examined. A total of 179 skates was collected and mouth width, pre-oral length, upper jaw protrusion, tooth crown length, crown width, cusp height and cusp length were measured. A multivariate analysis of variance (MANOVA) revealed there were significant differences in these measurements among the three factors (sex, maturity, and zone) and their interactions. Most notable was the extreme morphology of mature males. This group displayed significantly smaller pre-oral lengths and tooth crown widths, but significantly greater protrusion, larger tooth cusp heights and cusp lengths than both immature males and females of both maturity states. No major prey categories displayed a similar change in importance among the factors as those displayed by the morphological measurements, indicating that the intra- specific differences in morphology were not correlated with differences in diet. It is well known that the teeth and jaws of skates play several roles, one of which is mating. Therefore, the system is one of trade-offs and compromises. Our data suggest that reproduction is more important than prey capture in shaping this morphological system. A shorter snout and increased protrusion combined with larger tooth cusps likely facilitates the grasping of females which occurs during mating. These differences have persisted because they do not prohibit capturing prey such as the items listed above.
Scaravelli, Dino1; De Sabata, Eleonora2; Clò, Simona3
Shark Decline in the Northern Adriatic Sea
1University of Bologna, Bologna, Italy, 2MedShark, Roma, Italy, 3C.T.S., Roma, Italy
The coastal and central north-eastern part of Adriatic sea, in the Mediterranean, is characterized by shallow water and a strong pressure form human activities as far as pollution and overfishing. Centuries of fishing effort dramatically change the faunal composition of this area that is also characterized by semiclose water circulation and, in the last decades, a freshwater adduction of heavily polluted main rivers of north Italy. Thanks to historical reports we know that the area was typically an euthrophic sea with a high diversity of elasmobranch. Close to 50 species were cited for the area from the 19 century. Actually a revision of shark presence give us a total list of 28 species, but numbers and sightings draw a dark scenario. Checking, for a first attempt, 5 markets on northern coast, that land from1,5 to 7,8 million kg each, the percentage of elasmobranches vary from 0,01 to 1,30% of the meat, with a rapid decline in the last 4 year. The number of species actually landed vary on these market between 3 and 7, but only Mustelus spp. can be considered a typical prey (around 46400 kg per year in the 5 market, the 86% of all the sharks and rays). The small Scyliorhinus spp. for example disappeared in another controlled marked in 2001 and until now just isolated specimens were landed. The area was considered in the last decade a nursery area for Alopias vulpinus and Prionace glauca, that also were frequently caught in fish competitions and as a bycatch. Meanwile also a very rapid decline also interested these species and now they are really rare all around this sea. Despite the rare sights of Cetorhinus maximus, Squatina squatina, Hexanchus griseus and Carcharhinus plumbeus the situation in the area is clearly close to a collapse. Distribution of information and relative abundance of the different group, from markets and also from various information, are presented to describe the actual level of crisis.
Modeling Physical Properties of Joint Arrays in Batoid Wings
Univ. Calif., Irvine, Irvine, CA United States
The pectoral fins (wings) of batoid elasmobranchs (rays, skates, guitarfish) are formed by arrays of serially repeating skeletal elements (radials). They provide the opportunity to study the effects of small-scale morphological changes on large-scale structural properties. I used the spatial arrangement of the radials as a basis for models of local and whole-wing stiffness as well as the passive bending properties of the wing. Both analyses focused on single inter-radial joints as points of action, and summed local and global interactions. Stiffness calculations were based on a constrained linear spring model minimized for stored energy after perturbation. Direction of passive bending was based on the spatial relationship between neighboring joints. Comparing data from the wings of six species of batoid fishes, whole wing stiffness is higher in oscillatory swimmers than in undulatory swimmers. There was substantial variation in stiffness in different areas of the wing, with leading edges of oscillators being stiffer than trailing edges and the wind of undulators being divided into separate medial and lateral bands of stiffness. It appears that the spatial arrangement of radials can be linked to swimming performance in a way that might have application in robotics and deployable structures.
Shibuya, Akemi1; Zuanon, Jansen1; Góes Araújo, Maria Lúcia2; Tanaka, Sho3
Comparative Study of the Orobranchial Musculature in Potamotrygonidae Species from Rio Negro Basin, Amazonas, Brazil
1Instituto Nacional de Pesquisas da Amazônia, INPA, Manaus, Amazonas, Brazil, 2Universidade Federal do Amazonas, Manaus, Amazonas, Brazil, 3Tokai University, School of Marine Science and Technology, Skimizu, Shizuoka, Japan
The feeding behavior has received an increase attention in elasmobranchs, contributing to understanding the mechanisms involved in the capture and processing of prey. The purpose of this study is to provide a comparison of the relative size of the oral muscles in Potamotrygonid species, relating to their feeding habits. The specimens were obtained from the middle rio Negro basin, Amazonas State, Brazil. The samples were fixed in 10% formalin and preserved in 70% ethanol solution. The head skin was discarded to visualize the muscles. Ten muscles were considered in the analysis of the cephalic musculature, involved in the feeding (Adductor mandibulae, Depressor mandibularis, Depressor hyomandibularis, Spiracularis, Coracohyomandibularis, Levator palatoquadrati, Preorbitalis, Coracohyoideus, Levator hyomandibulae and Coracomandibularis). The muscles were removed and dried at 37oC to constant weight and their relative proportions (%Wm) compared among the species. Preliminary results were obtained from Potamotrygon motoro (n=3) and P. orbignyi (n=5). Five muscles presented significant differences (p<0.05). The muscles Adductor mandibulae and Depressor mandibularis had higher proportional values in P. motoro. We suggest that the higher relative proportions of these muscles are probably related to the processing of large and hard-shelled preys, such as crabs. Depressor hyomandibularis, Spiracularis, and Coracohyoideus showed proportionally higher contributions for P. orbignyi. They seem to be associated to its insectivorous habits. These muscles are involved in the expansion of the orobranchial cavity in the beginning of the suction movement. The diet composition of these species seems to corroborate our findings on the characteristics of their oral musculature.
Shimabukuro, Valeria Mercedes1; Scenna, Lorena Beatriz2; Barbini, Santiago Aldo3; Figueroa, Daniel Enrique1; Díaz de Astarloa, Juan Martín4; Cousseau, María Berta1
Feeding Habits of the White-dotted Skate, Bathyraja albomaculata (Chondrichthyes, Rajidae), on the Argentinean Continental Shelf
1Universidad Nacional de Mar del Plata (UNMdP), Mar del Plata, Argentina, 2UNMdP and Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina, 3UNMdP and Comisión de Investigaciones Científicas, Buenos Aires, Argentina, 4UNMdP, CONICET and Instituto Nacional de Investigación y Desarrollo Pesquero, Buenos Aires, Argentina
The white-dotted skate, Bathyraja albomaculata (Norman, 1937), is a medium size species in the Magellan region, from Uruguay in the Atlantic to central Chile in the Pacific. Diet composition, changes with sex and maturity status, and feeding strategy of this species were investigated in Argentinean waters (35°-55°S) through stomach contents analyses. Specimens were collected from research cruises carried out by Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP) between September 2003 and May 2005. Stomach contents were fixed in formalin 4%. Prey were counted, weighted, and identified to the lowest possible taxonomic level. Of a total of 184 stomachs examined, 95.1% contained food. All the sample sizes were sufficient for comparison, as the cumulative curves of diversity reached an asymptote. According to the Index of Relative Importance expressed as a percentage, polychaetes (67.97%) were the most important prey group in the diet of B. albomaculata followed by amphipods (23.78%) and isopods (8.13%). Cumaceans, crabs, euphausiids, teleosts, ophiuroids, hydrozoans and priapulids were not important in the diet (IRI<1%). The highest dietary overlap (Simplified Morisita Index) was found between mature males (n=55) and mature females (n=40) and the lowest similarity was observed between immature skates (n=80) and mature males. The graphical method of prey-specific abundance against frequency of occurrence suggested that the white-dotted skate is a polychaete specialized feeder. However, immature specimens seem to prey upon a greater proportion of amphipods than mature individuals of both sexes. These results were part of a study about ecology, biology and biodiversity of Bathyraja species on the Argentinean continental shelf.
Smith, Joshua; Musick, John
Resource Partitioning of Two Dasyatid Stingrays in the Coastal Lagoons of Virginia
Virginia Institute of Marine Science, Gloucester Point, VA, United States
Elasmobranch fishes (sharks, skates, and rays) are K-selected marine animals characterized by slow growth, late ages at maturity, and the production of relatively few offspring (Compagno, 1990; Musick et al. 2000). Assessments of elasmobranch biology and population dynamics are generally focused on sharks because they are targeted by recreational and commercial fisheries. Stingrays have not been studied as thoroughly in the United States because they are typically discarded as bycatch. However, stingrays may have significant impacts on predator-prey dynamics and overall ecosystem energy budgets as they are some of the largest predators in their ecosystems. Knowledge of their role in ecosystem function is critical as fisheries science shifts to ecosystem-based management plans. The bluntnose stingray, Dasyatis say, and the southern stingray, Dasyatis americana, are seasonal migrants into the coastal lagoons of Virginia that may play a important role in energy flow of the lagoon ecosystem. This study looked to assess the manner in which these closely related species partition the resources available within a lagoon ecosystem. Catch data and acoustic tracking data from the Hogg Island Bay coastal lagoon ecosystem indicated some temporal and spatial overlap in habitat use. However, stomach content analysis provides evidence that food preference is one way in which these similar species divide available resources. The results from this study provide insight on factors important in determining Essential Fish Habitat for marine animals with vulnerable life history characteristics.
Thrasher, Jacqueline; Morrissey, John
Effect of Ration Size on Growth of Scyliorhinus retifer: An Ontogenetic Approach
Hofstra University, Hempstead, United States
Many studies have examined the effect of daily ration on growth and gross conversion efficiency of teleost fishes, whereas few such studies have been conducted with cartilaginous fishes, and no study has examined this relationship during the ontogeny of any chondrichthyan. The objective of this study is to determine the relationship between ration level and a) growth, b) gross conversion efficiency, and c) gastric evacuation period in hatchling, adolescent, and adult chain catsharks, Scyliorhinus retifer. We will conduct feeding experiments that will vary ration levels to examine the relationship between food intake and growth during ontogeny. A fecal analysis also will be completed to determine ontogenetic variation in absorption efficiency of this species. We hypothesize that assimilation will be highest in hatchlings and lowest in adults, and that ovigerous adult females will consume a proportionately greater amount of food than adult males. We also hypothesize that gross conversion efficiency will peak at an optimum ration level for each ontogenetic stage in the life history of S. retifer.
Toffoli, Daniel; Hrbek, Tomas; Góes de Araújo, Maria Lúcia; Pinto de Almeida, Maurício; Charvet-Almeida, Patricia; Pires Farias, Izeni
Testing DNA Barcoding in the Potamotrygon (Potamotrygonidae: Myliobatiformes) Radiation in South America
1Universidade Federal do Amazonas, Manaus, Amazonas, Brazil, 2University of Puerto Rico, San Juan, Puerto Rico, Puerto Rico, 3Universidade Federal do Pará, Belém Pará, Brazil, 4Universidade Federal da Paraíba, João Pessoa, Paraíba, Brazil
The goal of DNA barcoding is the utilization of one or more genes to i) assign individuals to its species and ii) enhance discovery of new species. Barcoding is based on two assumptions: i) monophyly of species in respect to the molecular marker used and ii) intraspecific genetic variability must be much lower than interspecific genetic distance. In this study we use a segment of COI to test the efficiency of barcoding in delimiting eight freshwater stingray species of Potamotrygon. Three broadly distributed species of the Amazon basin are not reciprocal monophyletic (P. motoro, P. orbignyi, and P. scobina). Monophyly of the other five is statistically supported but relationships among them are not. One specimen collected in Orinoco basin grouped with P. schroederi, a species endemic of Negro River. The color and color pattern of the Orinoco specimen most closely resembles P. orbignyi, and differs sharply from P. schroederi. Although a number of sister species occur on either side of the Orinoco/Negro divide, the Orinoco P. cf. orbignyi and the Negro P. schroederi are separated by lower genetic distance than proposed species barcode thresholds, and much lower than that found between reciprocally monophyletic potamotrygonid sister species. The weakly supported phylogenetic relationships, coupled with short branch lengths suggest that Potamotrygon went through a rapid radiation. Our results invalidate the use of genetic distance thresholds proposed by barcoding to separate species that went through a recent radiation, and corroborate criticisms about usefulness of barcoding for delimiting and discovering species. Under an evolutionary perspective, there is no natural genetic divergence threshold in the same way as there is no threshold of morphological divergence, a point in which a population becomes a distinct species. Species are dynamic evolutionary entities and not static classes to which a single delimiting criterion can be applied.
Verissimo, Ana; Cotton, Chip
In Deep Dark Waters – Revision Of The Genus Centrophorus (Squaliformes) In The Western North Atlantic
Virginia Institute of Marine Science, Gloucester Point, VA, United States
The alpha taxonomy of the genus Centrophorus has been problematic throughout its history. This can be attributed to the poor resolution of the chosen diagnostic morphological characters; the absence or poor condition of the holotypes; and the lack of detail in the original species descriptions. As a result, identification of species is problematic. Misidentifications are widespread in the field as well as in museum collections. There is therefore a pressing need for basic taxonomic clarification within the genus, essential to the cataloging of museum specimens as well as fisheries management. This poster presents preliminary morphometric and molecular data on the Centrophorus species found in the western North Atlantic and Gulf of Mexico. Detailed morphometric data of several nominal species, collected from multiple localities, were obtained from specimens held in museum and research institute collections. Molecular data (mitochondrial COI gene sequences) were also obtained from a few of these species, and from different localities. The two databases were explored independently and then compared for consistency of groupings. The results suggest that some species names, such as C. granulosus, are often incorrectly assigned to multiple species based on the geographical location of collection and not on the actual morphological characters. The grouping discrimination analysis suggests a high diversity of Centrophorus morphotypes in the western North Atlantic and Gulf of Mexico, and some of these might include undescribed species.
Waghmode, Saket; Diamond, Sandra; Strauss, Richard; Mulligan, Kevin
Staying Single or Getting Ready to Mingle: Examination of Whether Sexual Segregation Exists in Atlantic Sharpnose and Blacktip Sharks in the Gulf of Mexico using GIS Analysis
Texas Tech University, Lubbock, Texas, United States
Sexual segregation occurs in terrestrial as well as marine animals, including some species of sharks. In the Gulf of Mexico, the Atlantic sharpnose shark (Rhizoprionodon terraenovae) is the most abundant small coastal species, while the blacktip shark (Carcharhinus limbatus) is the most abundant large coastal species. In both species, females are bigger than the males. Our goal is to compare the segregation rates of the two species in the Gulf of Mexico on the basis of sex and size. GIS methods will be used to map areas of high male and female population density in a given year. Preliminary results demonstrated little sexual segregation in the Atlantic sharpnose shark while blacktip sharks exhibit a high amount of sexual segregation.
Wegner, Nicholas C.1; Sepulveda, Chugey A.2; Graham, Jeffrey B.1
Gill Morphology of the Shortfin Mako, Isurus oxyrinchus, and Blue Shark, Prionace glauca
1Scripps Institution of Oceanography, UCSD, La Jolla, CA, United States, 2Pfleger Institute of Environmental Research, Oceanside, CA, United States
Lamnid sharks (family Lamnidae) and tunas (family Scombridae) demonstrate a remarkable evolutionary convergence for high-performance swimming. This study examines the gill structure of the shortfin mako (Isurus oxyrinchus), a lamnid shark, to determine what extent mako gills differ from other elasmobranchs and approach those of tunas for specializations to maintain gill rigidity during ram ventilation and to permit the O2 transfer required by fast, sustainable swimming. Examination of fixed gill tissue and microvascular casts reveals several structural specializations in the mako not present in the blue shark, Prionace glauca, a non-lamnid pelagic species which occupies a similar ecological niche. Gill surface area is 2-3 times greater in the mako than the blue shark, and mako diffusion distances are significantly shorter. Makos also possess a suite of gill microvascular specializations including a unique blood flow pattern through the lamellae which likely minimizes vascular resistance through the gills and increases gas exchange.
Wiley, Tonya1; Simpfendorfer, Colin2; Faria, Vicente3
Rostral Tooth Count of the US Smalltooth Sawfish (Pristis pectinata) Population
1Mote Marine Laboratory, Sarasota, Florida, United States, 2James Cook University, Townsville, Queensland, Australia, 3Iowa State University, Ames, Iowa, United States
The taxonomy of sawfish has been a long-lasting unsettled situation. Rostral tooth counts are one of the most useful characteristics for identifying species of sawfish. However, there is inconsistency in the accepted rostral tooth counts for many of the species including Pristis pectinata. Therefore, in order aid taxonomic clarification, a rostral tooth count range for the remnant US population of P. pectinata is provided. Eighty-two rostral tooth counts were taken on smalltooth sawfish captured in Florida and Georgia from 2000-2007. This study finds the number of rostral teeth present on US smalltooth sawfish is 22-29 per side and 45-56 total. Examination of bilateral asymmetry and sexual dimorphism in Pristis pectinata rostral tooth counts will also be presented.
Examination of Smalltooth Sawfish (Pristis pectinata) Movements Using Pop-Up Archival Satellite Tags
Mote Marine Laboratory, Sarasota, FL, United States
The smalltooth sawfish (Pristis pectinata) is the only elasmobranch species listed as federally endangered within United States waters. The implementation of conservation measures is being severely hampered by the lack of scientific data on this species. The NOAA Fisheries Smalltooth Sawfish Recovery Plan draft acknowledges the necessity to identify habitat utilization, aggregations, local abundance, and behavioral ecology of adult sawfish. These research areas are considered necessary to prevent extinction or an irreversible decline of the population. To address these concerns an on-going tagging study using satellite technology was initiated. Results for three pop-up archival transmitting (P A T) tags deployed on smalltooth sawfish in Florida Bay will be presented.