AES Oral Presentation Abstracts
Hofstra University, Department of Biology, Hempstead, NY 11549, USA
Prey capture kinematics of the chain catshark Scyliorhinus retifer
Past studies of feeding kinematics in the elasmobranchs (sharks, skates and rays) have focused on easily accessible species inhabiting the epipelagic portion of the ocean. Thus, our knowledge of feeding behavior in deeper dwelling elasmobranch fishes is strictly limited. The chain catshark (Scyliorhinus retifer) is a member of one of the most well researched groups of elasmobranchs (order: Carcharhiniformes), but this particular species inhabits a deep-sea environment and its feeding strategies are therefore unknown. In an attempt to better understand the feeding biology of S. retifer we utilized high- speed videography to document the kinematic events during prey capture. Sharks were filmed feeding on pieces of Atlantic silversides (Menidia menidia) scaled to the mouth diameter (large prey) and one-half the mouth diameter (small prey). Frame-by-frame analysis of kinematic variables indicated that the chain catshark utilizes mild suction to capture benthic prey items. Univariate ANOVAs found that prey size did not significantly affect the majority of kinematic variables. Though kinematic displacement measurements differed significantly between individuals, the timing of most movements did not. Only two timing variables, time to minimum lower jaw angle and time to maximum hyoid displacement, were found to vary significantly between large and small prey items. However, a MANOVA of principal components found no significant differences when simultaneously analyzing all derived kinematic variables for the effect of prey size. These results suggest that S. retifer exhibits stereotypical feeding behavior when capturing benthic prey. The feeding behavior of the chain catshark shows a strong connection to the basic pattern of kinematic events described in feeding studies of other carcharhiniform sharks. Nonetheless, stark differences in RSI values and the timing of upper jaw protrusion between this species and Cephaloscyllium ventriosum indicate that multiple prey capture strategies exist within the family Scyliorhinidae.
(MPA) Programa de Pos-Graduacao em Zoologia e (PC, MPA, RBB) Setor de Ictiologia, Campus de Pesquisa, Museu Paraense Emilio Goeldi, Av. Perimetral, 1901, Terra-Firme, Belem, Para, Brazil, 66077-530; (ASV) Curso de Engenharia de Pesca, Universidade Federal Rural da Amazonia, Av. Perimetral, s/n, Terra-Firme, Belem, Para, Brazil, 66077-530; (PC) Programa de Pos-Graduacao em Ciencias Biologicas (Zoologia) e Laboratorio de Ictiologia, Departamento de Sistematica e Ecologia, Centro de Ciencias Exatas e da Natureza, Cidade Universitaria, Universidade Federal da Paraiba, Joao Pessoa, Paraiba, Brazil, 58059-900.
Reproductive biology of Potamotrygon scobina Garman, 1913 (Chondrichthyes: Potamotrygonidae) in the Marajó Bay region, Pará, Brazil
Potamotrygonids present a reproductive mode described as matrotrophic viviparity withtrophonemata. This study presents the results on the reproductive aspects of the freshwater stingray Potamotrygon scobina in the Marajó Bay region. The specimens (n = 244) were sampled in the Colares Island region in the years 2000 through 2002. Males (n = 120) and females (n = 124) had their main reproductive characteristics analyzed in the field and in laboratory. All reproductive organs and embryos were fixed in formaldehyde solution (10%) and preserved in ethanol (70%). The HSI and GSI were also calculated for juveniles, sub-adults and adult specimens of both sexes. HSI values varied from 2.75 – 4.86 for males and 3.48 – 7.34 for females. GSI values varied from 0.17 – 0.65 for males and 0.16 – 0.45 for females. The Pearson Correlation Coefficient (r) of the disc width and clasper length was of 0.80. Abundant semen and spermatophores were present in 20.83% of the males sampled and were only observed at a minimal disc width of 358 mm. Embryos (n = 162) were present in 41.33% (n = 31) of the adult females sampled and were only observed at a minimal disc width of 387 mm. Adult females presented an average ovarian and uterine fecundity of around 5. The Pearson Correlation Coefficient (r) of the disc width and number of embryos was of 0.66. Slight salinity changes seem to play an important role as a trigger for reproduction in the P. scobina population of this region. The results obtained indicate that the reproductive cycle of P. scobina is closely related to the hydrologic cycle of the Amazon Estuary region. (Supported by CNPq, CAPES and WWF – Brazil grants).
(MA) Departamento de Ciencias del Mar, Universidad Arturo Prat, Avda. Arturo Prat 2120, 111-0939 IQUIQUE, Chile; (LAC) Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Casilla 160-C, Concepción, Chile
Elasmobranchs grow in length according to a two-phase growth model
Often, it is assumed that the von Bertalanffy growth model (VBGM) is appropriate to describe growth in length of elasmobranchs. However, a review of the literature suggests that a two-phase growth model could better describe growth in elasmobranchs. In this paper, we compare the two-phase growth model (TPGM) with the VBGM for 18 data sets of elasmobranch (16 species), by fitting the models to 36 age-length data pairs available (female, male and both sexes pooled). The Akaike Information Criteria (AIC) and the difference in AIC between both models revealed that in 23 cases (from 36) the probability that the TPGM was correct =50%. The VBGM tends to estimate larger Linf values than the two-phase growth model, while the K parameter tends to be underestimated. We show growth rate in length tends to decrease near the age at first maturity in several species of elasmobranch. This growth pattern seems to be a characteristic of elasmobranchs. The importance of the TPGM lies in that it appropriately describes this aspect of the life history of the species. In this context, we conclude that the VBGM is not appropriate to describe the growth of elasmobranchs, and that the TPGM should not be overlooked, particularly in stock assessment models.
(DA, GMC, AHA) Moss Landing Marine Laboratories, California State University, 8272 Moss Landing Rd, Moss Landing, CA 95039, USA; (LJN) NOAA Fisheries Northeast Fisheries Science Center, Narragansett Laboratory, 28 Tarzwell Drive, Narragansett, RI 02882, USA; (LAK) University of Maryland Center of Environmental Science, Chesapeake Biological Laboratory, P.O. Box 38, 1 Williams Street, Solomons, MD 20688, USA; (TAB) Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA
Application of bomb radiocarbon chronologies to Shortfin Mako (Isurus oxyrinchus) age validation
Age estimation is an issue for the shortfin mako (Isurus oxyrinchus) because of ongoing disagreement on the periodic deposition of vertebral growth bands. A band pair is defined as a set of opaque and translucent bands in vertebral centra. Using four age determination techniques, Pratt and Casey (1983) concluded two band pairs formed annually; however, Cailliet et al. (1983) assumed one band pair per year. To evaluate the validity of both interpretations, a new technique was applied using radiocarbon measured in shark vertebrae. In the 1950-1960s, thermonuclear testing released large amounts of radiocarbon into the atmosphere, which reacted to form 14CO2 and entered the ocean through gas exchange over the following years. This influx created a time-specific marker in the marine environment that can be used in age validation. In the first application to elasmobranchs, Campana et al. (2002) validated the vertebral ageing methodology for the porbeagle (Lamna nasus) and assayed four samples from one shortfin mako vertebra, suggesting annual deposition of one band pair for both species. In the present study, band-counting age estimates from 54 shortfin mako vertebrae collected in 1950-1984 ranged in age 1-31 years. Bands in early stages of life appeared broad and clear and became less defined with age. Ageing error between readers was consistent, with 76% of the estimates ranging within two years of each other. Twenty-one radiocarbon values from vertebrae of eight shortfin makos (collected in the Western North Atlantic in 1963-1984) ranged between -160.2‰ and 86.8‰. The resulting concordance with the porbeagle indicated shortfin mako has longevity of at least 31 years and supports annual deposition of a single pair of growth bands. This work was performed, in part, under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.
(ACS) Semmelweis University, Budapest, 1094, Tûzoltó utca 58., Hungary; (CJP) Lisbon Aquarium, Lisbon, Portugal
A study on the learning and sensory capabilities of a captive Manta birostris(Mobulidae)
A female Manta birostris (4 m wingspan) was observed in the Lisbon Aquarium over an 18 day period during September 2004. Her presence in her feeding square, the position of the cephalic fins and surfacing behavior were recorded by the EthoLog softver before and during regular feedings, as well as at random times between feedings. These behavioral elements were also recorded to test the effects of (1) the presence of a person on a bridge above the feeding square, as well as (2) the empty feeding bucket, (3) a bucket not usually used for feeding, (4) shrimp soup and (5) normal feeding bucket with shrimp soup , each in the water separately. The Manta’s normal behavior and her responses to these stimuli were also observed in another square of the tank, different than her usual feeding square. The results showed the presence of a person on the bridge didn’t change her usual swimming behavior. However, the presence of the empty feeding bucket and the other bucket or the shrimp soup, all attracted her to the feeding square, where she spent more time and showed surfacing behavior in an attempt to feed. The most significant response was recorded after the empty feeding bucket was placed into the water at her feeding square. These results suggest that this Manta birostris has learned to appear in order to get her food in response not only to olfactory but visual cues as well.
(NA) Texas A&M University, Department of Biology, College Station, TX 77843-3258, USA; (JDM) Texas A&M University, Department of Wildlife and Fisheries Sciences, College Station, TX 77843-2258, USA
A phylogenetic analysis of Batoidea (Elasmobranchii) based on morphological data
Although monophyly of the batoids (electric rays, sawfishes, guitarfishes, skates, and stingrays) is widely accepted and well corroborated, the interrelationships within batoids remain controversial. The most contentious issues concern the phylogenetic position of the Torpediniformes (electric rays) and the Pristiformes (sawfishes), and the composition of the Rhinobatiformes (guitarfishes). A phylogenetic analysis based on 81 anatomical characters of representatives of 32 of the 72 genera of batoids and four outgroups revealed that batoids comprise three major clades: Torpediniformes, Rajiformes, and Myliobatiformes. Rajiformes include Pristidae, Rhina, Rhynchobatus, Rhinobatidae, and Rajidae. Myliobatiformes include Platyrhinidae, Zanobatus, and Myliobatiformes (in a traditional sense). The derived myliobatiforms comprise two major clades: Gymnura and the pelagic rays, and the benthic rays. The terminal benthic rays form two clades: 1) Indo-PacificHimantura, New World Himantura, and potamotrygonids, and 2) Dasyatis kuhlii,Taeniura, Pteroplatytrygon, and Dasyatis. Neither Himantura nor Dasyatis, as presently conceived, are monophyletic. Several West African species of Dasyatis are more closely related to Indo-Pacific Himantura than to Dasyatis.
(ACA,FSD) Tasmania Aquaculture and Fisheries Institute, Nubeena, Crescent, Taroona, Tasmania, 7053, Australia; (ACA,SJD) CSIRO Marine Research, GPO Box 1538, Hobart, Tasmania, 7001, Australia
Movement patterns of the draughtboard shark Cephaloscyllium laticeps using acoustic telemetry and conventional tagging
The draughtboard shark Cephaloscyllium laticeps (Duméril, 1853) is the most common catshark in coastal areas of southern Australia. We have been using a combination of acoustic and conventional tagging technology to provide a greater insight into the behavior of this species. Between January 2000 and February 2004, 375 conventionally tagged sharks were released in an isolated reef study site in the Derwent Estuary, Tasmania, Australia. To date, 121 sharks have been recaptured with 36% recaptured on multiple occasions. The large amount of multiple recaptures within the reserve suggests a high degree of site fidelity. Larger longer-term movements of up to 200km have been recorded. The longest period between tagging and recapture was 39 months. Between January-July 2003, 25 sharks were fitted with acoustic tags. Acoustic receivers were deployed in the study site, along the Derwent Estuary and in an adjacent bay. Acoustic tag results also demonstrated the high affinity that draughtboard sharks have for the study site. The analysis of the acoustic data also provided information on residency periods and behavior that could not be obtained from conventional tagging studies.
(ACA,FSD) Tasmania Aquaculture and Fisheries Institute, Nubeena, Crescent, Taroona, Tasmania, 7053, Australia; (PN) Faculty of Science Engineering and IT, James Cook University, Townsville, QLD, 4811, Australia; (ACA,SJD) CSIRO Marine Research, GPO Box 1538, Hobart, Tasmania, 7001, Australia
Endocrine correlates of the reproductive biology of the oviparous catshark,Cephaloscyllium laticeps (Duméril, 1853)
The draughtboard shark Cephaloscyllium laticeps is an oviparous species that inhabits the coastal waters off Southern Australia where it is a common bycatch species in commercial trap, net and hook fisheries. We addressed the reproductive condition of this species based on the level of steroid hormones in the plasma. We tested four hormones, Estradiol (E2), Testosterone (T), 11-Ketotestosterone (11-KT) and Progesterone (P4). 11-KT was not detectable in any shark. T, E2 and P4 were present in females although P4 and E2 were only found in low concentrations in males. Correlations of reproductive development with the level of gonadal steroids were obtained and subsequently used to assess the maturity of sharks caught and released in a scientific reserve. Results from this study demonstrate that assessment of reproductive biology in elasmobranchs can be achieved without harm to the shark. The development of a non-destructive sampling technique has benefits for sampling sharks that do not need to be killed, such as endangered species, species in marine protected areas, nursery areas or bycatch species. This study has significant implications for future elasmobranch research and also advances our knowledge on endocrinology of marine fish.
(IEB) University of Florida, Department of Fisheries and Aquatic Sciences, 7922 NW 71st St, Gainesville, FL 32653, USA; (BLW) Fish and Wildlife Research Institute, 100 8th Ave SE, St. Petersburg, FL 33701, USA; (NEK) National Marine Fisheries Service, Northeast Fisheries Science Center, 28 Tarzwell Drive, Narragansett, RI 02882, USA; (JJM) Fishery Sampling Branch, NEFSC, 166 Water Street, Woods Hole, MA 02543, USA
Differences in the ratios of fin to carcass weight among fourteen species of sharks
The practice of shark finning, or the harvest of a shark’s fins without the carcass (meat), was prohibited by federal law in 1993. To regulate and minimize shark finning, federal rules were enacted that allowed fins to be landed if the total weight of the fins was no more than five percent of the total weight of the landed dressed carcasses. Although many different species are harvested for their fins, the “five percent rule” was established using data from only sandbar sharks, Carcharhinus plumbeus, due to a lack of data for other shark species. Fin weight ratios were calculated for several commercially valuable shark species from coastal waters of the U.S. Atlantic Ocean and Gulf of Mexico using standardized data collated from state and federal databases. Analysis of variance procedures, Scheffe’s multiple comparison analysis, and student’s t-tests were used to test for statistical differences in the fin weight ratios of 14 species of sharks. Comparisons were made among species for which comparable size data were available; therefore large coastal and pelagic sharks were analyzed separately from small coastal sharks and dogfishes. The fin weight ratio of the sandbar shark (5.33%) was the largest of the 14 species examined, while the silky shark, Carcharhinus falciformis, exhibited the lowest ratio at 2.53%. The fin ratio of the sandbar shark was significantly higher than most of the other large coastal species we examined, and the bonnethead shark, Sphyrna tiburo, had a fin weight ratio (4.91%) that was significantly higher than other small coastal species examined. Fin ratios were not different between juveniles and adults for most species, suggesting an isometric growth relationship. The variation in ratios among the species we examined suggests that species-specific management of shark finning in U.S. waters should be further explored
University of California, Irvine, Dept. Ecology and Evolutionary Biology, Irvine, CA, 92696-2525, USA
What makes and breaks cartilaginous jaws: The biomechanics and biochemistry of shark jaw cartilage
All vertebrates begin with a cartilaginous skeleton in the embryonic stage. As they mature, most convert their cartilaginous skeletons into bone. However Chondrichthians (sharks, ratfish, and rays) maintain a cartilaginous skeleton and thrive in the same niches as bony fish. In most vertebrates cartilage is a soft connective tissue that serves two purposes; a low-friction bearing surface and contour filler. Fish with cartilaginous skeletons can function at extremes (growing big, swimming fast, and eating hard-prey) which suggest that the skeletons of these animals are stronger than originally assumed. We also believe that the biochemical properties (collagen, proteoglycan, and water contents) affect the mechanical properties of the cartilage. We examined the biomechanics and biochemistry of shark jaw cartilage from four shark species; Carcharhinus falciformis, Carcharhinus plumbeus,Sphyrna zygaena, and Isurus oxyrinchus. Multiple 8.0 mm or 10.0 mm cylindrical plugs were tested by compressing the plug three times to ten percent of its initial thickness (=0.10) at 2 mm/sec. Properties differed between species (p<0.001). Shark cartilage was also stiffer than mammalian cartilage (5.2×107 vs. 2.0×107 Pa). Shark and mammalian cartilage was similar in strength. The plugs were lyophilized and collagen and proteoglycan was measured with hydroxyproline and DMMB assays. The average value for water content was consistent with mammalian cartilage (85% vs. 75%). Collagen content was much lower than mammalian cartilage (13% vs. 50% DW). Further biochemical studies will investigate why shark jaw cartilage, which has very little collagen content, is as strong as mammalian cartilage.
(DMB, JKC, EC) NOAA Fisheries Service, Southeast Fisheries Science Center, Panama City Laboratory, 3500 Delwood Beach Road Panama City Beach, FL 32408 USA; (LHW) California State University Long Beach, Biology Department, Peterson Hall 1-109, 1250 Bellflower Blvd, Long Beach, CA 90840 USA; (CAM, JG) Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236 USA
Latitudinal variation in the diet and daily ration of the bonnethead shark Sphyrna tiburo from the eastern Gulf of Mexico
Bonnethead Sphyrna tiburo diet and daily ration were determined for three major areas in the eastern Gulf of Mexico: northwest Florida (latitude ≈30oN), Tampa Bay (≈28oN), and Florida Bay (≈25oN). In each area, diet was assessed size classes (40-60, 61-80, and 81-100+ cm TL) and quantified using six indices: percent by number, percent by weight, frequency of occurrence, the index of relative importance (IRI), IRI expressed on a percent basis (%IRI), and %IRI based on prey category (%IRIPC). In northwest Florida, a mix of decapod crabs, decapod shrimps, and crustaceans other than lobster were found in stomachs of sharks 40-60 cm TL (n=78). Stomachs of sharks 61-80 cm TL (n=60) and 81-100+ cm TL (n=51) contained mostly decapod crabs. The same trend was observed in Tampa Bay for the larger two size classes of sharks (n=103 and n=61, respectively). In Florida Bay, sharks 40-60 cm TL (n=27) fed on crustaceans and cephalopods, sharks 61-80 cm TL (n=90) took fewer decapod crabs and shrimps and more lobsters and cephalopods, while the diet of sharks 81-100+ cm TL (n=38) was dominated by cephalopods, lobsters, and decapod crabs. Correlation and simple correspondence analysis showed diets from northwest Florida and Tampa Bay to be similar; diets of sharks from Florida Bay were different. A bioenergetic model was constructed to estimate daily ration using diet data from this study and species-specific inputs from other studies. Daily ration was different among areas and life stages. Daily ration was highest for young-of-the year sharks and lowest for adult sharks.
(JJB, WDS) Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Rd., Moss Landing, CA 95039, USA; (JFM-F) Instituto Nacional de la Pesca, Programa Tiburón, Centro Regional de Investigación Pesquera, Calle 20 Sur, 605, CP 85400 Guaymas, Sonora, Mexico; (REH) Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Pkwy., Sarasota, FL 34236, USA
Reproductive biology and fishery aspects of the golden cownose ray, Rhinoptera steindachneri (Evermann and Jenkins, 1891) from the Gulf of California and Pacific coast of Baja California Sur, Mexico
The golden cownose ray, Rhinoptera steindachneri (Evermann and Jenkins, 1891), is widespread in coastal waters of the tropical and subtropical eastern Pacific. It was among the most abundant species taken in artisanal elasmobranch fisheries of the Gulf of California and Bahía Almejas (Baja California Sur), Mexico, during 1998-2000. In the northern Gulf of California, R. steindachneri landings peaked during summer months and were negligible during winter. In Bahía Almejas, this species was frequently landed in August and uncommon in June, a trend also noted in CPUE (#individuals/vessel/trip; August =1.13, June=0.13). Size segregation and schooling behavior was evident from landings in both regions. Disc width (DW) of R. steindachneri harvested in the Gulf of California ranged from 39-98 cm and averaged 64.2 cm for males (n=585) and 64.4 cm for females (n=505). The largest male (96 cm DW) and female (104 cm DW) were recorded at Bahía Almejas. Size at first maturity and 50% median maturity were similar for males (64 cm, 69.9 cm DW) and females (65 cm, 70.0 cm DW). The largest immature male was 78 cm DW and the largest immature female was 72 cm DW. Fecundity was determined to be one offspring per female with larger females carrying larger embryos. Parturition was estimated to occur from late June to August at 39-45 cm DW after a gestation period of 10-12 months. Bahía Almejas served as a nursery ground for neonate R. steindachneri and a likely breeding location for adults. The conservative reproductive strategy of R. steindachneri, in which a single pup is produced annually after maturity is reached at a relatively large size, suggests that this species is of low productivity and highly susceptible to overexploitation.
(MB, BG) Southern Seas Ecology Laboratories, Darling Building DP 418, School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA 5005, Australia; (MB, TW) Primary Industries Research Victoria, P.O. Box 114 Queenscliff, Vic 3225, Australia
Reproductive parameters for population assessment of Squalus megalops
Population assessments of chondrichthyan species require several key parameters of their reproductive biology, which were estimated for Squalus megalops. For both sexes, length-at-maturity differed depending on the criterion adopted for defining maturity. For males, length-at-maturity is smallest when condition of seminal vesicles is adopted as a maturity criterion. For females, length- at-maturity is smallest when the largest follicle diameter >3 mm is adopted as the criterion for maturity; this is appropriate only as an indicator of the onset of maturity. Mature males are capable of mating throughout the year. Females have a continuous asynchronous reproductive cycle. The sex ratio of embryos is 1:1 and litter size and near-term embryo length increase with maternal length. Females have an ovarian cycle and gestation period of two years. This is reflected in the differences found between the maturity and maternity ogives. Although all females are mature at 600 mm, only 50% of them contribute to annual recruitment each year. Hence, for chondrichthyan species with reproductive cycles of two, three or more years, if maturity ogives are used in population assessments instead of maternity ogives, the models would over-estimate recruitment rates.
National Marine Fisheries Service, Highly Migratory Species Management Division, 1315 East-West Highway, Silver Spring, MD 20910, USA
Atlantic shark species-specific management: Is it possible?
In 2002, the stock assessment for Atlantic large coastal sharks determined that the two primary species in the fishery, sandbar and blacktips, were rebuilding and rebuilt, respectively, and that the complex as a whole was still overfished. In the 2003 Amendment 1 to the Atlantic Tunas, Swordfish, and Shark Fishery Management Plan, the National Marine Fisheries Service (NMFS) established quotas for the large coastal shark complex as a whole rather than for the individual species. This decision was made in part due to the inability of some fishermen and dealers to identify sharks correctly and in part due to the paucity of data regarding the ability of fishermen to target one or two species while avoiding other species. NMFS is currently analyzing alternatives to improve the ability of fishermen to identify sharks. However, little or no research is being done regarding the ability of fishermen to target specific sharks. Gear research in the Atlantic pelagic longline fishery has indicated that sea turtle takes can be significantly reduced by modifying hook types and using certain types of bait. Similar research is needed in the commercial shark fishery, primarily for bottom longline and gillnet gears, to determine if the bycatch of unwanted sharks, finfish, and sea turtles can be avoided or reduced. Such research could protect the more vulnerable species while still allowing for a sustainable fishery on other species and could allow quotas to be established on a more species-specific basis.
University of Zurich, Institute of Zoology, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
Insight into migration patterns of bull sharks in the South Pacific
Data on habitat use and seasonal movements are essential for designing conservation strategies, yet such data are rarely available for large marine animals such as sharks. In this study we equipped eleven bull sharks, Carcharhinus leucas, from a Fijian population with pop-up satellite tags to test the hypothesis that bull sharks migrate into nursery grounds. Individual tags remained attached for two to seven months. The pop-up locations give insight into movement patterns and distribution of bull sharks in the South Pacific. They further underscore the need for international cooperation in devising conservation plans.
San Juan College, 4601 College Boulevard, Farmington, NM 87402-4699, USA
Morphology and phylogenetic implications of Recent and fossil carcharhiniform shark vertebral centra
The cross-sectional anatomy of secondary calcifications of shark vertebral centra has featured in phylogenetic hypotheses, although never in a rigorous cladistic framework. In this study, the internal calcification patterns, along with the external morphology, of fossil and Recent shark centra of the Order Carcharhiniformes have been coded and subjected to a cladistic analysis to address the utility of centrum features for revealing relationships. Carcharhiniform sharks were selected as a study group because they are a monophyletic clade with reasonably well understood intraordinal relationships, a rich fossil record, and readily available Recent comparative skeletal material. The external characters evaluated include centrum proportions, the presence and distribution of cartilage canals, and the size, shape, and spacing of the foramina for the basidorsal and basiventral arch components. The internal calcification features evaluated include the morphology and spacing of the four intermedialia, the four noncalcified areas, and the four diagonal calcifications. Centrum characters were analyzed both separately and combined with additional morphological characters from previous analyses. Results of the cladistic analysis show that shark centrum characters are useful for elucidating phylogeny. Tree topology was very similar for both analyses, and similar to recent molecular databased phylogenies. The addition of centrum data to shark phylogenetic analyses will allow for a more objective means of determining the interrelationships of fossil and extant carcharhiniform sharks than studies based on teeth alone, with their well-documented difficulties. The data gathered will also be important for future studies to interpret the relationship between centrum morphology and swimming characteristics in extant, and ultimately, extinct taxa.
(GMC, WDS, HFM) Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039 USA; (KJG) Department of Biology, Jackson State University. 1400 J.R. Lynch Street, P.O. Box 18540, Jackson, MS 39217 USA
Chondrichthyan growth studies: An updated review, stressing terminology, sample size sufficiency, validation, and curve fitting
Validated age and growth estimates are important for constructing age-structured population dynamics models of fishes, including chondrichthyans, especially those that are exploited. We will review, correct, and supplement the results from the recent chondrichthyan ageing summary chapter, stressing the structures (both traditional and novel) utilized to estimate ages and synthesize the terminology used to describe their growth features. We will discuss validation approaches, concentrating on edge and marginal increment analyses. We will propose methods to assess size-specific sample sufficiency. We will review the mathematical approaches used to produce and interpret validated growth parameters, stressing the incorporation of size at birth (L0). We will briefly summarize results from recent studies among taxonomic groups, stressing the patterns in growth and longevity parameters, how useful they are for age-structured models and resulting management policies for assessing the status of exploited chondrichthyan populations.
(SEC) Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia, Canada B2Y 4A2; (CJ) Center for Quantitative Fisheries Ecology, Old Dominion University, Norfolk, VA 23508, USA; (GAM) Pacific Biological Station, Nanaimo, British Columbia, Canada V9R 5K6; (SM) Institute of Marine Research, P.O. Box 1870 Nordnes, N-5817 Bergen, Norway
Bomb dating and age determination of spiny dogfish
Bomb radiocarbon has previously been used to validate the age of large pelagic sharks based on incorporation into vertebrae. However, not all sharks produce interpretable vertebral growth bands. Here we report the first application of bomb radiocarbon as an age validation method based on date-specific incorporation into spine enamel. Our results indicate that the dorsal spines of spiny dogfish (Squalus acanthias) recorded and preserved a bomb radiocarbon pulse in growth bands formed during the 1960s. Through comparison of radiocarbon assays in young, known-age dogfish collected in the 1960s and 1970s with the corresponding growth bands in old dogfish collected later, we confirm the validity of spine enamel growth band counts as accurate annual age indicators to an age of at least 45 yr. Radiocarbon incorporation into North Sea dogfish spines occurred in similar years as those in the northeast Pacific, although the amount of radiocarbon differed in keeping with the radiocarbon content of the water. Based on the age-validated spines, the growth rate of spiny dogfish in the northwest and northeast Atlantic is substantially faster, and the longevity is substantially less, than that of dogfish in the northeast Pacific.
(ABC, GMC) Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039, USA; (AK) BLM/DOI California Coastal National Monument, and NOAA/DOC National Marine Protected Areas Center, Science Institute, 99 Pacific St., Monterey, CA 93940, USA; (JSB) Washingon Sea Grant Program, 3716 Brooklyn Avenue NE, Seattle, WA 98105, USA
Long-term trends in elasmobranch catch composition from fishing derbies in Elkhorn Slough, California
Long term trends in the elasmobranch assemblage in Elkhorn Slough, Monterey Bay, California, were analyzed by documenting species composition and catch-per-unit-effort (CPUE) from 55 sport fishing derbies during May, June and July, from 1951 until 1995. The most abundant species, bat rays (Myliobatis californica), shovelnose guitarfish (Rhinobatos productus) and leopard sharks (Triakis semifasciata), were also analyzed for size-weight relationships, trends in size class distributions, stage of maturity, and sex ratios. Changes in species composition over the course of the derbies included the near complete disappearance of shovelnose guitarfish by the 1970s and a slight increase in the abundance of minor species (mainly smoothhounds, Mustelus spp., and thornbacks,Platyrhinoidis triseriata) starting in the mid-1960s. The proportion of bat rays in the catch steadily increased over the years while the abundance of leopard sharks has declined slightly during the last two decades. A peak in overall CPUE was evident during the mid to late fifties. Leopard shark and bat ray size class distribution data showed no obvious changes. The catch of bat rays and leopard sharks was consistently dominated by immature individuals, while the catch of shovelnose guitarfish was heavily dominated by adults. Female bat rays and shovelnose guitarfish were larger than their male counterparts, and outnumbered males nearly 2:1. Female and male leopard sharks were more nearly equal in size and sex ratio. Changes in species composition are likely due to shifts in the prevailing oceanographic conditions and habitat alteration in Elkhorn Slough. The sex ratios, stage of maturity, and size class distributions provide further evidence to the theory that Elkhorn Slough functions as a nursery ground for bat rays and leopard sharks.
(ABC, GMC, DAE) Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039, USA; (RMS) University of California Sea Grant Extension Program, Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039, USA
Spatial and temporal patterns of movement and habitat utilization of female leopard sharks in Elkhorn Slough, California
The leopard shark (Triakis semifasciata) is one of the most abundant nearshore sharks in California and is commonly found in bays and estuaries. Elkhorn Slough is a shallow tidal embayment at the edge of Monterey Bay that is extensively utilized by leopard sharks of all ages and is believed to function as a nursery ground for the species. Due to the important role of the Slough in the life history of leopard sharks, understanding how sharks utilize this environment is important. Patterns of movement and habitat use of female leopard sharks in Elkhorn Slough were examined using acoustic tags and a combination of manual tracking and passive monitoring techniques between May 2003 and February 2005. Ten leopard sharks (91-132 cm TL) were tagged and manually tracked for 20-71.5 hours. An additional 13 leopard sharks (78-140 cm TL) were tagged and monitored for 4-443 days using an array of acoustic receivers. Analyses done to date indicate that the Elkhorn Slough National Estuarine Research Reserve marsh restoration site is important for leopard sharks in Elkhorn Slough. Tagged sharks spent extensive amounts of time in several specific areas during the pupping season, providing evidence of the value of the reserve as a nursery ground. Shark movements and habitat use appeared to be tidally influenced, because movements of tagged animals were restricted to channels and tidal creeks at lower tides. As the tide increased, they moved out of the channels onto intertidal mudflats where they appeared to utilize low intertidal mudflats. When in the main channel of Elkhorn Slough, shark movements showed more diel periodicity. Tagged animals moved up and down the Slough at relatively regular intervals, in which the sharks primarily occurred in the lower slough during night.
(JKC) Southeast Fisheries Science Center, NOAA Fisheries Service, 3500 Delwood Beach Rd., Panama City, FL 32408, USA; (IEB) Department of Fisheries and Aquatic Sciences, University of Florida, Gainesville, FL 32611, USA
Growth dynamics of the Spinner Shark, Carcharhinus brevipinna, off the United States Southeast and Gulf of Mexico coasts: a comparison of methods
The age and growth dynamics of the Spinner Shark in the northwest Atlantic Ocean off the Southeast United States and in the Gulf of Mexico were examined and four growth models were used to examine variation in the ability to fit size-at-age data. The von Bertalanffy growth model, an alternate equation of the von Bertalanffy growth model with a size-at-birth intercept, the Gompertz growth model, and a logistic model were fitted to sex-specific observed size-at-age data. Considering the statistical criteria (e.g. lowest MSE, high coefficient-of-determination, and greatest level of significance) we desired for this study, the logistic model provided the best overall fit to the size-at-age data while the von Bertalanffy growth model gave the worst. When considering biological validity, the von Bertalanffy model for female sharks provided estimates similar to those reported in other studies. However, the von Bertalanffy model was deemed as inappropriate for describing the growth of male spinner sharks because estimates of theoretical maximum size suggested a size much larger than that observed in the field. However, the growth coefficient (k=0.14) from the Gompertz model provided an estimate most similar to that reported for other large coastal species. The analysis of growth for spinner shark in this study demonstrate the importance of fitting alternate models when standard models fit the data poorly or when growth estimates do not appear to be realistic.
University of South Florida, College of Marine Science, 140 7th Avenue South, St. Petersburg, FL 33701, USA
Dipolar hearing measurements in the Horn Shark, Heterodontus francisi
The hearing abilities of elasmobranchs have been measured using sounds broadcasted from an underwater speaker in several different experiments. While these experiments have produced complete audiograms for the species tested, many scientists have questioned whether a monopole stimulus (such as an underwater speaker) is appropriate for measuring hearing and determining what sounds sharks are attracted to in the field. It has been suggested that a dipole stimulus that mimics the acoustic disturbances caused by prey moving through water would be a more relevant stimulus for measuring shark hearing abilities. A vibrational shaker was used to produce a dipole stimulus for testing the hearing of four horn sharks, Heterodontus francisi. Hearing tests were also conducted in the same setup on the same individuals using an underwater speaker to directly compare the dipole stimulus with a monopole stimulus. In both cases, evoked potentials were obtained in response to the stimuli using the auditory brainstem response method and audiograms were produced. The relevance of monopole versus dipole stimuli when referencing the hearing of elasmobranchs and how these relate to their ability to detect sounds from a distance will be examined.
(ALFC, ALB, SAK) Dept. of Biology, SCA 110, University of South Florida, 4202 E Fowler Ave, Tampa, FL 33620, USA; (BSS, SGW) Hubbs-SeaWorld Research Institute, 2595 Ingraham Street, San Diego, CA 92109, USA; (MGM) Australian Institute of Marine Science, Darwin, NT 0811, Australia; (REH) Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA; (BWB) Hawaii Institute of Marine Biology, SOEST, University of Hawaii, PO Box 1346, Kaneohe, HI 96744, USA
Preliminary information on the population genetics of the whale shark (Rhincodon typus)
In recent years tagging studies, including satellite transmitters, have increased our knowledge of the migratory behavior of whale sharks. These findings reinforce the perception of a mobile species that can move thousands of kilometers in short time periods. Based on the perception of high vagility, we hypothesized that inter-region or inter-ocean genetic differences for whale shark populations would be slight. Here we use mitochondrial DNA control region sequences to assess the genetic connectedness of whale sharks sampled from different oceans. We found 37 polymorphic sites (including insertions and deletions) resolving 18 haplotypes in complete mtDNA control region sequences from 30 whale sharks (10 from Gulf of Mexico; 7 from Sea of Cortez; 4 from Ningaloo Reef, Western Australia; 4 from Taiwan; 3 from South Africa; and 1 each from Maldives and Philippines). We found no significant genetic subdivision and sharing of haplotypes among ocean basins. Our data are consistent with a single global population. This inference, however, is subject to two caveats; low statistical power associated with small sample sizes, and life history considerations. First, there are marked differences observed among haplotypes, including base substitutions and gaps of 17 to 164 nucleotides, indicating that sufficient variation exists to detect population subdivision, pending larger sample sizes. Second, most samples were collected from whale shark feeding aggregations, where reproductively segregated populations could co-occur. Mixing of cohorts could contribute to the lack of phylogeographic subdivision detected here. More sequence data are being gathered to provide a statistically rigorous analysis of genetic variation among biogeographic regions, including microsatellite approaches for analysis of fine-scale breeding system.
California State University, Northridge, Dept. of Biology, 18111 Nordhoff St., Northridge, CA 91330-8303, USA
Population genetics of the Tope Shark (Galeorhinus galeus) in response to California fishery pressures
The Tope Shark (Galeorhinus galeus) has been the subject of intense overfishing over the last 74 years (Ripley 1946, FAO.org). Millions of sharks were harvested during the 1940s primarily for their vitamin A rich livers (Ripley 1946, Leet et al. 2001). This intense exploitation collapsed breeding areas within the San Francisco and Tomales bays (Leet et al. 2001). Currently all sharks face a new global threat, that of shark finning. Unfortunately, only well-qualified estimations exist on how many sharks inhabit the world’s oceans. Without exact population data, the impact of overfishing on shark species can only be assumed. Because empirical estimation of true population sizes of pelagic shark species is unrealistic, a method of determining shark population health is sorely needed. The tope shark provides an excellent model because the species was historically overfished (Leet et al 2001). By analyzing and comparing the mtDNA of present day tope sharks with the mtDNA of specimens preserved prior to 1940, evidence of inbreeding and the possible existence of a population bottleneck may be established.
(DDC, MSS) Guy Harvey Research Institute, Oceanographic Ctr, Nova Southeastern University, 8000 N. Ocean Dr, Dania Beach, FL, 33004, USA; (PAP) The Queens University of Belfast, MBC, 97 Lisburn Rd, Belfast, BT97BL, Northern Ireland, UK; (JG) Elasmobranch Physiology and Environmental Biology Program, Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Pkwy, Sarasota, FL 34263, USA
Mating systems of the bonnethead and scalloped hammerhead sharks in the southeast United States, as revealed by microsatellite DNA profiling
Just as DNA-profiling has revolutionized our understanding of the reproductive biology of many animal groups, this technology has begun to provide significant new insights into the mating practices and parentage of free-living sharks. Genetic profiling of two shark species (nurse [Ginglymostoma cirratum] and lemon [Negaprion brevirostris]) have revealed almost ubiquitous multiple paternity of litters within the sampled study populations. In contrast, our recent studies have revealed that female bonnethead sharks (Sphyrna tiburo; Family Sphyrnidae [hammerhead sharks]) demonstrate a relatively low frequency of multiple paternity within a given reproductive cycle (p<20% of 22 litters directly tested by microsatellite genotyping). Collectively, these studies indicate diversity in the mating systems of sharks, raising interesting questions as to what factors drive the evolution of female promiscuity and multiple paternity in these ancient fishes. To further explore this issue, we have expanded our analysis of parentage in S. tiburo to include a total of 70 litters (>650 embryos), originating from breeding grounds along the Gulf coast of Florida and South Carolina. Despite an increase in sample size, multiple paternity remained low overall and we tested the hypothesis that it is more common in larger females. We also genotyped 20 litters (>400 embryos) of scalloped hammerheads (S. lewini), a larger, ecologically dissimilar congener of S. tiburo. Although we document the first records of multiple paternity in S. lewini, the mating system of this species appears to be more akin to that of S. tiburo than it is to that of N. brevirostris and G. cirratum.
(PC) Programa de Pos-Graduacao em Ciencias Biologicas (Zoologia) and Laboratorio de Ictiologia, Departamento de Sistematica e Ecologia, Centro de Ciencias Exatas e da Natureza, Universidade Federal da Paraiba, Joao Pessoa, Paraiba, Brazil, 58059-900; (MPA) Programa de Pos-Graduacao em Zoologia, (PC) Setor de Ictiologia and (ALMA) Coordenacao de Ciencias da Terra e Ecologia, Museu Paraense Emilio Goeldi, Av. Perimetral 1901, Terra-Firme, Belem, Para, Brazil, 66077-530
Distribution of elasmobranchs in the Brazilian Amazon River floodplain
The Amazon River floodplain is associated with white water rivers and presents seasonal changes that are closely linked to the hydrologic cycle. The information available on the elasmobranch species and respective distribution in the Solimões- Amazonas River system was very limited. An expedition was organized in September and October 2003 to collect data on the distribution of elasmobranchs, among other species groups. Twenty-six points of sampling were spread along over 3,000 km in the Brazilian portion of the Amazon River floodplain. Daily bottom long-line fisheries (captures), direct observation of specimens (registers) and interviews (reports) were used to provide evidence on the local elasmobranch species. Frequency of occurrence and biomass were calculated for each species. Water parameters were also noted. The results correspond to a unique specific study on the diversity of elasmobranchs present in this aquatic system. Information related to three elasmobranch families were obtained, namely: Pristidae, Carcharhinidae and Potamotrygonidae. The species that presented a wider distribution were: Paratrygon aiereba, Plesiotrygon iwamae, Potamotrygon motoro, Pristis perotteti andCarcharhinus leucas. Some potamotrygonid species were only observed in certain areas. It is suggested that some of the tributary rivers directly influence the Amazon River system by creating a water transition area close to their mouths that consequently may affect distribution patterns. The results indicated the presence of four linked but distinct biogeographical regions. A fifth region could be considered the estuarine area with the seasonal influence of higher salinity levels and the register of occurrence of dasyatids. Biological data on species distribution along the Amazon River floodplain is essential for adequate conservation planning in this dynamic and threatened river system. (Supported by Pró-Várzea – IBAMA- PNUD BRA/00/008 / MPEG / FADESP and CAPES).
(PC, RSR) Programa de Pos-Graduacao em Ciencias Biologicas (Zoologia) and Laboratorio de Ictiologia, Departamento de Sistematica e Ecologia, Centro de Ciencias Exatas e da Natureza, Universidade Federal da Paraiba, Joao Pessoa, Paraiba, Brazil, 58059-900; (MPA) Programa de Pos-Graduacao em Zoologia and (PC, MPA) Setor de Ictiologia, Campus de Pesquisa, Museu Paraense Emilio Goeldi, Av. Perimetral 1901, Terra Firme, Belem, Para, Brazil, 66077-530
Paratrygon aiereba: A multi-species complex (Chondrichthyes: Potamotrygonidae)
Neotropical freshwater stingrays belong to a single family that is considered monophyletic by several authors. The Potamotrygonidae family is comprised of three valid genera, namely: Plesiotrygon, Potamotrygon and Paratrygon. A fourth genus is currently under description. Two of these genera have been considered monotypic and are represented by the species Plesiotrygon iwamae and Paratrygon aiereba. On the other hand,Potamotrygon includes 18 described species but there are approximately 8 other species being described or under study. The recent increment in collecting and research activities carried out with potamotrygonids has brought up clear evidence that Paratrygon aierebacorresponds to a multi-species complex and that Paratrygon is not a monotypic genus. The preliminary analyses indicate that the Paratrygon genus comprises at least two or possibly three distinct species. It is likely that future sampling in some Amazonian river drainages still might alter this number. These species are distinguished by external and internal morphological characteristics, as well as morphometric differences. Intra-specific polychromatism was also evidenced, as in other species belonging to this family. The ecological aspects associated with river drainages seem to play an important role in these species geographical distribution. Paratrygon thayeri (Garman, 1913), currently treated as a synonym of Paratrygon aiereba, might be revalidated, pending on a more detailed study of morphometric and distributional data. Meanwhile, studies are under way and more specimens are being collected to elucidate this multi-species complex and to provide the required descriptions and redescriptions. (Supported by CNPq and CAPES grants).
(ABC, PJM) University of South Florida, Department of Biology, 4202 E. Fowler Avenue, SCA 110, Tampa, FL 33620, USA; (MRH, REH) Mote Marine Laboratory, Center for Shark Research, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA
Diet of the Atlantic Cownose Ray Rhinoptera bonasus in Charlotte Harbor, Florida, USA
Cownose rays are benthic, suction feeders whose foraging activities have been implicated in severe damage to commercial shellfish industries and seagrass habitat. With jaws highly modified for durophagy, it has been assumed that they are crushing specialists, feeding primarily upon hard molluscan prey. Stomach contents from cownose rays caught within the Charlotte Harbor estuary between July 2003 and July 2004 were analyzed using the index of relative importance (IRI). A total of 92,576 prey items from 38 families fell into 9 distinctive groups: bivalves, gastropods, crustaceans, brachiopods, chordates, echinoderms, nematodes, polychaetes, and detritus. Adult and juvenile diets showed significant overlap (Schoener’s index = 0.69). Crustaceans, polychaetes, and bivalves were the dominant groups present over all stomachs examined. Crustaceans (%IRI = 56.85) and polychaetes (%IRI = 25.90) were the most important prey groups, with cumaceans (Cyclaspis sp. andOxyrinchus smithii) accounting for the majority (94%) of crustaceans and Pectinaria gouldii representing the bulk (70%) of the polychaetes. Bivalves were the least abundant of the three dominant groups (% IRI = 12.93). Cyclaspis sp., O. smithii and P. gouldii are prevalent benthic invertebrates within Charlotte Harbor and can occur in extremely high densities. All cumaceans and polychaetes within ray stomachs were intact, indicating capture through suction feeding. All larger, hard prey (bivalves, echinoderms, and brachiopods) showed evidence of crushing (fractured and broken shells). Although currently believed to be a hard prey specialist, these results suggest the cownose ray may behave as an opportunistic generalist, modifying feeding behavior to consume any readily available prey.
(ABC, PJM) University of South Florida, Department of Biology, 4202 East Fowler Avenue, SCA 110, Tampa, FL 33620, USA; (MRH, REH) Mote Marine Laboratory, Center for Shark Research, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA
Tracking the cownose ray Rhinoptera bonasus within a southwest Florida estuary: Evidence for residence?
The Atlantic cownose ray Rhinoptera bonasus is present within the Charlotte Harbor estuary throughout the year. Although believed to be highly migratory, transient residents of coastal inshore waters, minimal quantitative data exist regarding their distribution, movement patterns, or abundance. Between July 2003 and April 2005, 27 cownose rays (18 adults and 9 juveniles) were tagged and tracked within Pine Island Sound and the Caloosahatchee River using passive acoustic telemetry. Minimum convex polygons (MCP) and kernel utilization distributions (KUD) were calculated to demonstrate the extent of an animal’s home range and core areas of use. Animals were monitored within the study area for periods of 1-223 days (mean = 42 days). Nine individuals were observed moving regularly between Pine Island Sound and the Caloosahatchee River, maintaining activities over a wide range of salinities (5.0 -30.0 ppt) and habitat. Rays within the Caloosahatchee River were typically present for longer continuous periods, while rays tracked in Pine Island Sound tended to move in and out of the study area more frequently. Daily MCPs ranged between 0.01 and 25.8 km2. As highly mobile, pelagic swimmers capable of traversing large distances, these data show that cownose rays may also remain within very small areas for extended periods. Total core areas of use (50% KUD) were located over sand or mud bottom for 23 of the 27 tracked rays. Only 4 rays had core areas that significantly overlapped seagrass habitat, contrasting with existing suspicion that they heavily utilize grass beds. These tracking results provide insight to R. bonasus use of a south Florida estuary and allow predictions regarding the impact of this species in similar environments.
Virginia Institute of Marine Science, PO Box 1346, Gloucester Point, VA 23062, USA
Investigations into the activity patterns and space use of juvenile sandbar sharks,Carcharhinus plumbeus, in the Eastern Shore of Virginia summer nursery area
The sandbar shark is the most abundant large coastal shark found in the waters off the East Coast of the United States and is the principal species caught in the commercial shark fishery off the Atlantic coast. Examining the habitat use and activity patterns of juvenile sandbar sharks of this population while they occupy summer nursery areas is an important research need for current and future management efforts. During the summer of 2003, 15 stationary acoustic receivers were anchored in Wachapreague Inlet, Virginia and 27 sandbar sharks were surgically implanted with coded acoustic transmitters. Each time a receiver detected a transmitter it recorded the date, time, and identification of that transmitter. Data was downloaded every week from the receivers throughout the summer from July 7th when the first shark was captured and implanted with a transmitter to the last shark’s departure from the area on September 30th. During the summer of 2004, the array was expanded to include 21 receivers and an additional 37 sharks were implanted with transmitters. In addition, 10 sharks implanted with transmitters in 2003 returned to the area and were detected by the array in 2004 and were tracked for various periods of time. During 2004, the receivers were placed in the field June 2nd and remained in place until the last shark’s departure on October 4th. Preliminary data on the activity patterns and habitat use of juvenile sandbar sharks in this summer nursery area will be presented.
Florida Atlantic University, Dept. of Biological Sciences, Boca Raton, FL 33431, USA
Ecomorphology of shark electroreceptors
Sharks are found in nearly every marine habitat and possess numerous adaptations that enable them to survive in a multitude of ecosystems. I examined whether morphological differences in the electrosensory system of sharks correlate with their environment and ecology. By quantifying the number, density, and distribution of electrosensory pores for a large number of species, I have been able to elucidate trends in the ecomorphology of shark electroreceptors. This study consisted of two separate analyses. I examined the electrosensory system of species from the same family that inhabit different environments as well as species from different families that inhabit the same environment. This was done to determine whether similarities in the electrosensory system result from phylogenetic constraint or evolutionary convergence from a common environment. Pelagic species were found to possess relatively few electrosensory pores (450-900) with the majority of species having over 60% of the pores on the ventral surface of the head. Deepwater species have electrosensory pore counts that range from 250-1150 with 38-59% of the pores located on the ventral surface of the head. Shallow coastal species exhibit wide variation in pore counts ranging from 430-3000 electrosensory pores. The distribution of pores ranges from 43-66% on the ventral surface. Several species were examined from the order Carcharhiniformes. This taxa has greater pore counts overall, with most species possessing over 1400 electrosensory pores. The carcharhinids typically have an even distribution of electrosensory pores on the dorsal and ventral surfaces. The results reveal that both phylogenetic constraint and convergence from a common environment have acted in concert in the development of the elasmobranch electrosensory system.
(EC) NOAA Fisheries Service, NMFS, Panama City Laboratory, 3500 Delwood Beach Road, Panama City, FL 32408, USA; (MA) Departamento de Ciencias del Mar, Universidad Arturo Prat, Avda. Arturo Prat 2120, 111-0939 Iquique, Chile
Bayesian hierarchical meta-analysis of elasmobranch age and growth data
Describing the relationship between age and growth is central to understanding fish population dynamics and conducting stock assessments. Growth curves for elasmobranchs are often unavailable for populations of a given species or for related species and there is often uncertainty surrounding parameter values, all of which ultimately hinder progress in assessment and conservation of this group of fishes. By combining data sets of related populations or species, Bayesian hierarchical analysis can be used to predict parameter values for populations or species for which no age and growth data are available. This approach takes into account both model form (the ubiquitous von Bertalanffy growth function in our case) and parameter uncertainties. Here, we explore the use of this methodology for elasmobranch age and growth data by considering several case studies involving species of sharks for which age and growth data from several populations or studies are available, and one case study for several related species of carcharhinid sharks. We then predict von Bertalanffy parameters for populations/species for which no data exist while taking account of natural and methodological variability. In this application of a Bayesian hierarchical analysis, which was previously applied to stock-recruit data for salmon, we first assume that the von Bertalanffy parameters of the individual growth curves for each population or species are related and assigned a prior probability distribution. We then use the relationships between the von Bertalanffy parameters of the individual growth curves to predict parameter values for populations or species for which no data exist.
(DLC) Auke Bay Laboratory, National Marine Fisheries Service, 11305 Glacier Highway, Juneau, AK 99801-8626, USA; (SG) Alaska Fisheries Science Center, National Marine Fisheries Service, 7600 Sand Pt Way NE, Bldg. 4, Seattle WA 98115-0070, USA; (JB)UW/NOAA Joint Institute for the Study of Atmosphere and Ocean, Alaska Fisheries Science Center, 7600 Sand Point Way NE, Bldg. 4, Seattle WA 98115-0070, USA; (KJG) Jackson State University, Department of Biology, P.O. Box 18540, Jackson, MS 39217, USA; (CT) School of Fisheries and Ocean Sciences, Juneau Center, University of Alaska Fairbanks, 11120 Glacier Highway, Juneau, AK 99801-8677, USA
Shark bycatch in Alaskan federal waters
Three shark species commonly occur in Alaskan waters: Pacific sleeper shark, Somniousus pacificus, spiny dogfish, Squalus acanthias, and salmon shark, Lamna ditropis. Information on the distribution, stock structure, and life history characteristics of these species is extremely limited. There are currently no directed commercial fisheries for sharks in Alaskan federal waters, but sharks are captured incidentally as bycatch in federally managed commercial fisheries for other species and some shark bycatch is now being retained. Limited available data from the commercial fishery observer program and from fishery independent surveys indicate that bycatch of sharks in Alaskan federal waters is low (p<3%) relative to targeted catch. However, shark bycatch is considered a nuisance, and there is a perception by some that shark numbers are increasing in Alaskan waters. As a consequence there is increasing pressure to open directed commercial fisheries targeting some shark species, particularly spiny dogfish. Establishing sustainable catch limits under the current federal management regime requires either a catch history, or a reliable point estimate of biomass combined with a natural mortality estimate; none of these exist for shark species in Alaskan waters. As a consequence, alternative management strategies need to be developed and implemented for these potentially vulnerable species if targeted fisheries are permitted.
Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, USA
Distribution and movements of juvenile bull sharks, Carcharhinus leucas, in the Indian River Lagoon System, Florida.
The Indian River Lagoon system along Florida’s Atlantic coast is a nursery ground for bull sharks (Carcharhinus leucas). Since bull sharks are a component of Florida’s shark fisheries, proper management requires a better understanding of their ecology within their vital nursery areas. A sampling program utilizing longlines and rod and reel has been initiated to estimate the current abundance and distribution of bull sharks in this estuary. Tagging and acoustic telemetry are being used to investigate the movements and habitat use of the young sharks. To date, sampling efforts have yielded the capture of 20 young-of-the-year and juvenile bull sharks (54-94 cm FL). They were captured over a broad range of salinities, depths, and oxygen concentrations, and only in temperatures > 20°C. Four sharks have been actively tracked, providing over 65 hours of movement data. Based on these preliminary results, the daily movements of these sharks appear to be confined to comparatively small core use areas (p< 4 km2). There were no obvious changes in movement patterns between day and night. Continued tagging and tracking efforts will provide a clearer understanding of how this important predator utilizes its nursery habitats.
Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, USA
The occurrence of white sharks, Carcharodon carcharias, off the southeastern United States, and their presence in fisheries
White sharks, Carcharodon carcharias, are sparsely distributed throughout the western North Atlantic Ocean, typically found in cold and temperate shelf waters. They are only occasionally encountered in the warmer waters off the southeastern U.S. and in the Gulf of Mexico. Though considered a leading cause of mortality in this globally threatened species, little has been documented on the bycatch of white sharks in fisheries. Since the white shark is now a prohibited species in the U.S. Atlantic, catches often go unreported. We have compiled 56 credible records of white shark occurrences between Cape Hatteras, North Carolina and Cape San Blas, Florida in the Gulf of Mexico from the period of 1974 to 2005, including 40 individuals incidentally caught in commercial fisheries. White sharks were most common in this region between December and April when sea surface temperatures are at their seasonal lows. Over 70% of the individuals encountered were immature based on total length. Although white sharks are relatively rare catches in the Atlantic shark bottom longline fishery (1 per 3,800 sharks), there are seasonal peaks in catch rate along certain sections of coastline. Hooking mortality rates are high (>60%). The continental shelf waters off Florida’s Atlantic coast may be an important winter feeding ground for subadult white sharks. Their presence in this region makes them vulnerable to commercial longlining operations, which may be a significant source of mortality for this species in the north Atlantic.
(TSDE) University of Hawaii at Manoa, Dept. of Zoology, 2538 The Mall Edm. 152, Honolulu, HI, USA; (KNH, RDG, RJT, BWB) Hawaii Institute of Marine Biology, P.O. Box 1356, Kaneohe, HI, USA
Multiple paternity assessments for three species of congeneric sharks (Carcharhinus) in Hawaii
Multiple paternity is expected to increase fitness and should be particularly common when females cannot evaluate males, as is the case for the brief copulatory encounters typical of most elasmobranchs. We tested for multiple paternity in single litters of three congeneric species of carcharhinid sharks found in Hawaiian waters: the sandbar shark (Carcharhinus plumbeus), bignose shark (Carcharhinus altimus), and Galapagos shark (Carcharhinus galapagensis). Based on eight microsatellite loci, we observed evidence of multiple paternity in both sandbar and bignose, but not Galapagos sharks. Multiple paternity may maintain genetic diversity, especially in populations that are inherently small or have undergone population decline. Hawaii provides a unique setting for this study because it hosts near pristine populations of these sharks, and can provide insight into the reproductive health of top marine predators that are susceptible to depletion.
University of Aberdeen, School of Medical Sciences, Cell and Developmental Biology Research Program, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, Scotland, UK
The early evolution of viviparity in elasmobranch fishes leads to extreme remodelling of the vertebrate follicle
The elasmobranch fishes are the oldest surviving extant jawed vertebrates. Their early acquisition of functional jaws and dentition placed them in a role of apex predator early on in their evolutionary history. This role favours a life history strategy which produces: large animals, that are relatively long-lived, and which produce few offspring. To maximise their survival, offspring are relatively large and precocial. Producing large offspring requires more maternal input to the developing embryos either in the form of increased yolk, (lecithotrophy) or as extra nutrition supplied by the mother to the embryo throughout gestation, (matrotrophy). This favours a switch from an egg laying mode of reproduction to that of live bearing, (viviparity). Modes of viviparity in elasmobranch fishes include: lecithotrophy, oophagy, adelphophagy, placental analogues, and ultimately the yolk sac placenta. A first step in producing larger offspring would be that of extended egg retention which eliminates the need for large robust egg cases, thus more nutrients can be stored in the egg for use by the embryo. These egg cells can only reach a finite size as they have to confirm to certain physical and physiological parameters: i.e. gas exchange, acquiring enough nutrients, and maintaining their integrity during oogenesis and upon ovulation, where they lose the support afforded by the follicle. Here we show that remodelling of the follicle does facilitate the production of large eggs. We also indicate for the first time that some of the microvillar extensions between the oocyte and the follicle cells, (zona radiata) may go through a major remodelling: increasing dramatically in size, may take on a role in a novel transport system, and ultimately in supporting extremely large eggs during ovulation.
Ecology & Evolutionary Biology, University of California Irvine, 321 Steinhaus Hall, Irvine, CA 92697, USA
Uniform strain in broad muscles: A new twist on tendons
Myofilament overlap determines tension generation in all vertebrate skeletal muscle. The range of muscle fiber strains used to generate a given movement (i.e., sarcomere lengths) is therefore linked to force production. As a result, regions of a muscle experiencing different strains operate in different regions of the length-tension curve, likely decreasing whole-muscle force output. The anterior jaw adductor muscle of the cartilaginous fish, Hydrolagus colliei, exhibits a morphological solution to ensuring similar strains. The muscle’s tendon flips 180 degrees on its longitudinal axis, such that anterior fibers insert more posteriorly and vice versa. Since insertions closer to the jaw joint experience smaller excursions during mouth opening, the anterior face of the muscle strains less than in an unflipped tendon system (the inverse is true for the posterior face). This results in nearly homogenous strain across the muscle with a flipped tendon, compared with a 10% inhomogeneity between anterior and posterior faces in the unflipped condition. We illustrate that Hydrolagus‘ morphology functions effectively in strain homogenization. The human latissimus dorsi muscle exhibits a similar morphology, indicating that this may be an ideal anatomical mechanism for strain homogenization in broad muscles attached to rotating structures and inserting relatively far from the joint.
(BMD, CWR) Department of Fisheries, Animal, and Veterinary Sciences, University of Rhode Island, 20A Woodward Hall, 9 E Alumni Ave, Kingston, RI 02881, USA; (CTM, NEK) Apex Predators Program, NOAA/NMFS, 28 Tarzwell Drive, Narragansett, RI 02882, USA; (BMW) Department of Biological Sciences, University of Rhode Island, 100 Flagg Road, Kingston, RI 02881, USA
Distribution of sharks in the U.S. Virgin Islands with an emphasis on nursery areas
Local commercial catch data in the United States Virgin Islands (USVI) on sharks is non-existent, and biological baseline data on the status of near shore sharks is very limited. As anthropogenic influences on the USVI coastline continue to increase, understanding coastal shark nursery habitat in these areas is becoming increasingly critical. Longline surveys were conducted around the islands of St. Thomas and St. John, USVIs to attempt to quantify the distribution and movements of neonate and juvenile sharks. The survey will also be used to provide a baseline assessment of shark populations. To date, the study has recorded neonates of three large coastal shark species utilizing five locations. Over all, seven large coastal and two small coastal shark species have been recorded. Catch per unit effort (CPUE) per bay has ranged from 0 – 25.8 elasmobranchs per 100 hook-hours. This data will aid federal and territorial marine managers in accurately assessing and managing elasmobranch fishes and essential fish habitat.
(JDD, APH) McGill University, Redpath Museum and Department of Biology, 859 Sherbrooke St. W., Montréal, QC, H3A 2K6, Canada; (KAF) The Field Museum, Pritzker Laboratory for Molecular Systematics and Evolution, 1400 South Lake Shore Drive, Chicago, IL 60605, USA; (SHG) Rosenstiel School of Marine and Atmospheric Science, Division of Marine Biology and Fisheries, 4600 Rickenbacker Causeway, Miami, FL 33149, USA
Juvenile lemon sharks, Negaprion brevirostris, do not form kin-based associations in a tropical nursery lagoon at Bimini, Bahamas
As part of an ongoing long-term life history study, a lemon shark nursery site at Bimini, Bahamas has been exhaustively sampled annually from 1995 to 2004. Morphological measures were obtained from approximately 200 lemon sharks each year, of which 60 to 100 are young of the year (y-o-y), and fin samples were removed for subsequent genetic analyses. Using previously developed microsatellite markers, parent/offspring and sibling relationships between sampled individuals can be inferred by assigning y-o-y to distinct litters and reconstructing genotypes of the parental generation. While much has been gleaned about the mating system of lemon sharks using this genetic approach, little is known about their social behaviour and potential association within nursery areas. Therefore, the aim of this study was to detect the presence of kin-biased behavioural patterns, testing the hypothesis that nursery-bound juveniles patrol with related conspecifics more often than with unrelated ones. Using the existing genetic database, pairs of sharks spatially and temporally captured together in gill nets were identified. The relatedness of individuals within each pair was assessed using a categorical approach coupled with a chi-square analysis, while a matrix of relatedness values (r) was generated using Kinship 1.3. Juvenile sharks caught together were related in only 4 out of 91 pairs over a five year span (1996-2000), not significantly greater than expected by chance alone. Interestingly, when broken down by year, no individuals caught together were related in 1996, 1999, and 2000. As previously shown in natural salmonid populations, a complete lack of kin-association suggests kin competition may be influencing the distribution and interaction of sharks at this study site. Future applications of the existing genetic database to examine heritability of early life-history traits such as growth rates, mortality rates and litter size in lemon sharks will also be discussed.
Californa State University Fullerton, Dept. of Biological Science, 800 N. State College Blvd., Fullerton, CA 92831, USA
The contribution of mitochondrial proton leak as a heat source in lamnid sharks
Endothermic fishes can elevate the temperature of certain tissues above ambient temperature because the tissues are served by counter-current heat exchangers that conserve metabolic heat. In lamnid sharks, warming of the locomotor musculature, visceral organs, and eye/brain is associated with lateral retia, the suprahepatic rete, and orbital retia, respectively. Whether these tissues are also specifically modified for thermogenesis remains unknown. This study examines the contribution of mitochondrial proton leak as a potential heat source in two endothermic tissues in the shortfin mako shark. Proton leak is an intrinsic property of the inner mitochondrial membrane whereby protons bypass ATP synthase and diffuse back into the matrix to dissipate energy. We compared mitochondrial proton leak rates in the red muscle and liver of three shark species and hypothesized that the endothermic shortfin mako would have higher proton leak rates than the ectothermic blue shark and leopard shark. Respiration rate and membrane potential in isolated mitochondria were measured simultaneously using a Clark-type oxygen electrode and a lipophilic probe (TPMP+), respectively. Succinate-stimulated respiration rate was titrated with inhibitors of the electron transport chain to demonstrate a non-linear relationship between respiration rate and membrane potential. Although the proton leak rate in red muscle was higher than in liver for all three species, the rate did not differ significantly between endothermic and ectothermic sharks for either tissue. The results suggest that red muscle and visceral endothermy in lamnids is achieved principally through the presence of heat exchangers and not through an increase in energetically wasteful thermogenic pathways such as proton leak. (Supported by NSF and NIH.)
(WWD) Virginia Institute of Marine Science, present address: Wildlife, Fish, and Conservation Biology, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, USA; (RWB, JAM) Virginia Institute of Marine Science, 1208 Greate Road, Gloucester Point, VA 23062-1346, USA; (PGB) Department of Biological Sciences, Indiana University South Bend, 1700 Mishawaka Ave., South Bend, IN 46634-7111, USA
Metabolic rates and bioenergetics of juvenile sandbar sharks (Carcharhinus plumbeus) in the lower Chesapeake Bay
We measured the standard and routine metabolic rates (SMR and RMR) of juvenile sandbar sharks (Carcharhinus plumbeus) over the range of body sizes and temperatures characteristic of northwestern Atlantic coastal summer nursery areas. The allometric equations relating SMR (mg O2/hr) to body mass (kg) were: SMR=65 (+/-15) x M0.73 (+/-0.14), SMR=120 (+/-17) x M0.79 (+/-0.08), and SMR=207 (+/-28) x M0.63 (+/-0.07) at 18C, 24C, and 28C, respectively. The overall SMR Q10 was 2.9+/-0.2. The allometric equation for RMR was: RMR = 213 (+/-38) x M0.79 (+/-0.11) at 24-26C. RMR averaged 1.8+/-0.1 times the SMR. The estimated additional costs of swimming in a curved path was 7.7+/-1.1%. When corrected for this effect, the mean ratio of RMR to SMR equaled 1.6+/-0.1. There was no significant correlation between body mass and the ratio of RMR to SMR. Assuming maximum metabolic rate is two to three times SMR (as in other elasmobranchs), sandbar sharks use approximately 50-80% of their metabolic scope to sustain their routine continuous activity, leaving limited potential increase in oxygen delivery to fuel somatic growth and reproduction. We then estimated daily ration and seasonal prey consumption rates for six age-classes of juvenile sandbar sharks in the lower Chesapeake Bay summer nursery area using a bioenergetics model with habitat-specific data on growth rates, diet composition, water temperature (range 16.8-27.9C), and population structure. The predicted mean daily rations ranged between 2.17+/-0.03 (age-0) and 1.30+/-0.02 (age-5) percent body mass per day. These daily rations are higher than earlier predictions for sandbar sharks, but are comparable to those for ecologically similar shark species. The total nursery population of sandbar sharks was predicted to consume approximately 124,000 kg of prey during the 4.5 month stay in the Chesapeake Bay nursery, an insignificant top-down effect on the Chesapeake Bay ecosystem in comparison with teleost piscivores and humans.
Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039, USA
Reproduction, diet, and habitat utilization of leopard sharks, Triakis semifasciata, in Humboldt Bay, California, U.S.A.
The leopard shark, Triakis semifasciata (Girard), endemic to the eastern North Pacific, is one of the most common elasmobranch species found along the California coast. Several northern California bays and estuaries, including Humboldt Bay, are important nursery areas for this species. A total of 312 females were sampled in Humboldt Bay during the spring over three successive years. All females examined were determined to be mature and ranged in size from 120-154 cm LT. Only three adult males were caught in the study area and all were tagged and released. Overall, of the 153 females examined in early spring 130 contained term-embryos. Each embryo was encapsulated in a clear membranous sac and all appeared to be near-term. The number of embryos per female ranged from 1-37 with the trend being that larger females had more embryos. A total of 1,446 embryos were sexed with a male:female ratio of 1:0.93 that was not significantly different than a 1:1 ratio (P > 0.05). Embryos ranged from approximately 17-20 cm LT. Of the 159 individuals examined in late spring no females with embryos were found and all, with the exception of four individuals, were observed to be ovulating. A total of 239 stomachs were examined, of which 196 (82.0%) contained prey items. Overall, fish eggs (Atherinopsis californiensis), at 48.0%, had the highest %IRI, followed by the cancrid crabs, Cancer antennarius(29.8%) and C. magister (11.6%). All other prey items were of relatively minor importance, cumulatively representing 10.6% of the overall diet. Leopard sharks were observed foraging and this behavior is described.
(KBE, GVC) Boston University, Dept. of Biology, Boston, MA 02215, USA; (RM, MEH) Woods Hole Oceanographic Institute, Woods Hole, MA 02543, USA
Development of the Little Skate (Raja erinacea) as an in situ bioindicator of environmental spermatotoxicants
Epidemiological and wildlife studies have implicated environmental pollutants in declining sperm production, but few of the 87,000 chemicals added to the environment have been tested for spermatotoxicity. To detect and localize the presence of spermatoxicants in the natural environment, the little skate was selected for its potential as an in situ bioindicator species. Skates are nonmigratory and widely distributed in coastal waters. Also, the simple organization of the elasmobranch testis facilitates stage-by-stage analysis of spermatogenesis. Skates were collected from a highly polluted Superfund site (New Bedford Harbor, NBH, MA) and four different reference sites (ME, NH, MA). Analysis of testicular cross-sections showed that NBH skates, when compared to reference skates, had significantly fewer spermatocysts (germ cell/Sertoli cell clones) in the spermatocyte and early spermatid stages of development. Although the number of spermatogonial cysts did not differ, the percentage with apoptotic cells was significantly greater in NBH than in reference skates (24 vs. 14%). Moreover, although apoptosis was restricted to spermatogonial stage cysts in controls, apoptotic gonocytes were seen in the germinal zone of two NBH skates. Consistent with high levels of PCBs known to be present in NBH, P4501A1 mRNA (a marker of arylhydrocarbon receptor activation) was highly induced in muscle of all NBH skates and in testis of 6 skates from the same group (n, 9), when compared to reference skates (n, 12). Also, testicular aromatase mRNA was elevated ≈2 fold in NBH, but -tubulin mRNA and other markers showed no clear site-related differences. These results provide clear evidence of spermatotoxicity and altered gene expression in skates resident in a highly polluted environment, and further suggest that the defect involves the developmental advance of spermatogonial clones into meiosis and spermiogenesis. Supported by NIEHS (P42ES07381); EPA (STAR R825434); NOAA (MIT Sea Grant); and NICHD (2T32 HD073897).
(NE) New York Aquarium, 502 Surf Ave, Brooklyn, NY 11224, USA; (JFM) Hofstra University, Hempstead, NY 11549, USA
Age and growth determination of a deep-sea centrophorid shark, Centrophorus cf.uyato, from the Cayman Trench, Jamaica, W.I.
Over the two-year period between August 2000 and March 2002, 54 specimens ofCentrophorus cf uyato were captured (7 males and 47 females) from depths of 400-913m. Both anterior and posterior dorsal fin spines were cross-sectioned for analysis. Readings between the first and second dorsal spines were compared within and between spines. The average percent error was determined for anterior and posterior spines individually, as 7.15% and 5.33%, respectively, and for the accepted readings between the two spines as 15.3%. Overall, ring visibility in the posterior spines was greater than in the anterior spines yielding higher values and more accurate results. Growth curves were constructed and size and age at maturity were determined and compared between both anterior and posterior dorsal fin spines using all readable samples.
Nova Southeastern University Oceanographic Center, 8000 North Ocean Drive, Dania Beach, FL 33004, USA
Activity patterns, distribution and population structure of the yellow stingray,Urobatis jamaicensis in Southeast Florida
The yellow stingray, Urobatis jamaicensis is a commonly observed elasmobranch in coastal waters of Southeast Florida. Despite their frequent occurrence the ecology of yellow stingrays remains poorly understood. Acoustic tracking and extensive visual point counts were conducted to determine the short-term movements, seasonal distribution and population structure of yellow stingrays in Broward County, Florida. Diel activity patterns displayed intermittent movements throughout the day; however, nocturnal movements exhibited a significant increase in both rates of movement and space utilization. Total daily movements were confined to relatively small areas (mean = 21,403m2 +/- 10,696 SEM) and demonstrated strong site fixity, which implies a possible display of home ranging behavior. However, intermittent tracking across several days indicates that yellow stingrays may not utilize their full range on a daily basis. Landscape topography demonstrated considerable influence on the space utilization of stingrays and movements varied with proximity to the reef edge/sand interface. Yellow stingrays remained permanent residents within the study site with no indication of varying inshore/offshore seasonal distribution. Apparent gender segregation was noted during spring months (March, April, May) with females dominating the inshore region 20F:8M. Average individual size of the population was 333mm total length (TL), with females dominating the larger size classes (>350mm TL). The occurrence of increased numbers of intermediate size classes (250-299mm to 300-349mm TL) on the offshore reef suggests a potential ontogenetic shift to deeper water or range expansion. Field observations of gravid females occurred throughout the year, however, the annual reproductive cycle remains unclear. Reports of a 3-month gestation rate and observed peaks in non-gravid females during the months of February and October suggest two separate ovulatory cycles. Preliminary results from an on-going reproductive study further indicate a biannual cycle with an undetermined number of broods produced per female each year.
(VVF) Iowa State University, Dept. of Ecology, Evolution, and Organismal Biology, Ames, IA 50011, USA; (MTM) 3371 Turnberry Circle, Charlottesville, VA 22911, USA
Trying again two centuries later: an essay on the various species of sawfish (Chondrichthyes, Pristiformes)
The sawfishes, family Pristidae, is comprised of seven nominal species: Anoxypristis cuspidata, Pristis pectinata, P. zijsron, P. clavata, P. perotteti, P. microdon and P. pristis. However, due to considerable taxonomic confusion this number may in fact vary between four and ten. Among the reasons for this taxonomic disarray is that many of the original species descriptions were extremely abbreviated, and in some cases not even based on specimens, or based only on isolated anatomical parts; only two of the six type specimens are available for examination today; poor representation of specimens in collections, which mostly consist of dried rostra or very young specimens; and scarcity of these animals in their natural habitat due to overfishing. In the present study we reviewed sawfish taxonomy based on evidence from (1) morphological (external morphometric and meristic characters) and molecular data (DNA sequence from one mitochondrial gene, NADH-2) of representative specimens, (2) museum records and historical specimens, (3) distributional information derived from archaeological remains and anthropological artifacts and (4) review of the primary literature. Inferences based on our results are discussed in the context of sawfish diversity, geographical distribution and historical taxonomy.
(AF) Warnell School of Forest Resources, University of Georgia, Athens, GA, USA; (AS, KM, HJ, AB) Department of Environmental Chemistry, Stockholm University, Stockholm, Sweden; (GT) Freshwater Institute, Department of Fisheries and Oceans, Winnipeg, MB, Canada; (JS) Institute of Biology, University of Iceland, IS-108 Reykjavík, Iceland; (OP) Ergo Research, Hamburg, Germany
Everything under the sun: Contaminants in the Greenland shark
Anthropogenic contaminants are a continuing concern for marine life, particularly higher trophic level organisms that can accumulate high levels due to biomagnification. Although many sharks feed at or near the top of food webs, we know very little about levels and effects of contaminants in these fish. The Greenland shark (Somniosus mircocephalus) is a large, long-lived, cold water species that feeds throughout the marine food web and thus has the potential to have high concentrations and a wide variety of contaminants. Samples of liver were collected from Greenland sharks from Iceland and the Canadian Arctic to examine a large list of contaminants and their metabolites in this species. Levels of legacy organochlorine contaminants (e.g., PCBs, DDT. chlordanes) were very high in the shark from both Iceland and the Canadian arctic, and were similar to other higher trophic level arctic organisms. These sharks were also found to contain metabolites of PCBs and DDT, dioxins, and heavy metals, as well as new contaminants of interest brominated (including a number that are believed to be naturally produced) and fluorinated compounds. This study represents the most comprehensive examination of contaminants in an elasmobranch species to date. The contaminant pattern in the Greenland shark is very unique and raises questions about the source of these contaminants, levels of contaminants in sharks, and the biotransformation capacity of elasmobranchs.
(BEF) Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039, USA; (EA) University of Massachusetts, Biology Department, 221 Morrill South, 611 North Pleasant St., Amherst, MA 01003, USA
The radial muscle: A new chapter in shark tails
The swimming kinematics and hydrodynamics of heterocercal tails in elasmobranchs have been the focus of a number of recent studies. However, the locomotor functions of the internal morphological structures of the heterocercal tail remain unexplored. In this study we examine the morphology and function of the radial muscle or radialis during swimming in the spiny dogfish Squalus acanthias. The radialis consists entirely of red muscle fibers and is located ventral to the segmented axial myomeres in the most distal region of the caudal fin, originating on the ventral processes of the vertebral column and inserting along the horizontal septum. Individual muscle fibers are arranged dorsoposteriorly at angles ranging from 14 to 88 degrees relative to the vertebral column. The muscle fibers of the radialis share a similar fiber orientation and lie in close association with the deepest layer of the subdermal connective tissue sheets. Electrical stimulation of the radialis in anesthetized sharks results in visible movement of the ceratotrichia of the dorsal lobe of the caudal fin.. Using sonomicrometry, we found that muscle fibers shortened by p<1% of their resting length during stimulated contractions. Finally, we combined bilateral electromyography of the radialis with simultaneous video to determine the point of activation of the radialis within the tailbeat cycle. Our results indicate that the radialis is active immediately after maximum lateral excursion of the caudal fin to the ipsilateral side. We also find that the activity patterns of the radialis on the right and left side of the body are approximately 180 degrees out of phase. Morphology and motor patterns of the radialis suggest that this muscle is acting as postural reinforcement, and controlling the orientation of the dorsal lobe of the caudal fin during steady swimming.
Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, Dickinson Hall Museum Rd., Gainesville, FL 32611, USA
Geographical and temporal variation in length distributions of six species of shark taken in the bottom longline fishery off the southeastern United States
For any species subject to commercial fishing, changes in size distribution over time may indicate larger population-wide trends such as over-fishing and compensation. Thus, accurate data on catch size are important for assessment of current fishery management strategies. Seasonal changes in size may also indicate sex or size specific aggregation or be reflective of migratory patterns. We present an annual and monthly analyses of fork length (FL) distributions by sex of six coastal commonly targeted shark species in the bottom longline fishery off the southeastern United States. Length-frequency for Carcharhinus plumbeus, C. limbatus, C. leucas, Sphyrna lewini, S. mokarran, and Rhizoprionodon terraenovae were collected by the Commercial Shark Fishery Observer Program (CSFOP) between 1994 and 2004. Data were analyzed for differences in FL for males and females based on the fishing region, month and year. Significant differences in length frequency distributions were determined over time and between geographic areas. Factors influencing seasonal and regional patterns as well as long- term shifts in size classes will be discussed.
National Institute of Water and Atmospheric Research Ltd, Private Bag 14901, Wellington 6003, New Zealand
Morphometric minefields – towards a measurement standard for cartilaginous fishes
Size measurements are crucial for studies on the growth, maturation, maximum size, and population structure of cartilaginous fishes. However different researchers may use a variety of measurement techniques even when working on the same species. Accurate comparison of results among studies (e.g. time series of measurements on the same population, cross-population comparisons) is only possible if (a) the measurement technique used is adequately defined, and (b) in situations where different techniques are used, a conversion equation can be derived. These conditions have not always been met, leading to invalid comparisons and incorrect conclusions. Using data for shortfin mako shark (Isurus oxyrinchus) and an Antarctic skate (Amblyraja georgiana), I explore the morphometric relationships among different measurement techniques and the complications presented by allometric growth. The pros and cons of various body measurements on sharks, skates and chimaeras are discussed. Suggestions are provided for selecting an appropriate measurement technique, recording additional measurements on a subsample of the fish to develop conversion regression relationships, and the establishment of an international database of conversion equations.
(BRF) Bimini Biological Field Station, Bimini, Bahamas and School of Bioscience and Biotechnology, Drexel University, Philadelphia, PA 19104, USA; (SHG) Bimini Biological Field Station, Bimini, Bahamas and Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149, USA; (JRS) School of Bioscience and Biotechnology, Drexel University, Philadelphia, PA 19104, USA
The movements and habitat selection of juvenile lemon sharks, Negaprion brevirostris, in Bimini, Bahamas over a spatiotemporal scale
We are studying a population of nursery-bound juvenile lemon sharks at Bimini, Bahamas using both manual and automated tracking to answer questions about movement patterns and habitat selection within two primary nursery areas. To date, 48 nursery-bound and 3 non-nursery bound juvenile lemon sharks have been tracked both continuously and intermittently. Seven of these sharks have been in the study for longer than one year. Research questions being investigated include: Do lemon sharks exhibit habitat selection within the primary nursery areas; do environmental factors affect the movements of juvenile sharks; are movements within the nursery correlated with areas of low predation risk and/or high prey availability; does time of day, season, age of shark, or site affect either activity patterns or habitat preference; is the shift from primary to secondary nursery area gradual; is there immigration or emigration by juvenile sharks between primary nursery areas? Answers to these questions will help define the role of nursery grounds in the early life history and evolution of lemon sharks. Initial results suggest that juvenile lemon sharks have clearly defined home ranges with a strong correlation between the size of the shark and size of the home range. The size of the 95% kernel home range averages 47.7 hectares in the South Bimini nursery and 90.7 hectares in the North Sound nursery. Preliminary analyses of the data indicate that sharks disproportionately use areas within the nursery with 91% of all locations being obtained within 200 meters of the shoreline signaling some type of habitat selection. Tracking data support the hypothesis that there is essentially no emigration of lemon sharks from their natal nursery area during the first three years of life. We will discuss the results of data from all 51 sharks investigated over the past 28 months.
Irish Sea Fisheries Board, PO Box 12, Crofton Road Dun Laoghaire, Co. Dublin, Ireland
The use of caudal thorns as ageing structures on the thorny skate Amblyraja radiata
Thorny skate (Amblyraja radiata) were collected off Greenland during a research cruise in November 2004, primarily to establish whether caudal thorns could be used as effective ageing structures. In total 52 specimens were collected, 28 male, and 24 female, covering the full size range from pre-hatching to fully mature. Age estimates were derived from crystal violet stained sagittal vertebral sections and silver nitrate stained whole caudal thorns. Age bias plots and coefficient of variation indicated that both structures provided similar unbiased and precise age estimates. However thorns generally scored higher on readability scores, which indicated that band resolution was higher on thorns compared to vertebrae. Poor thorn band resolution was however noted on larger specimens, particularly near the periphery where bands were crowded and also near the apex where thorn wear was evident. Vertical transverse sections of silver nitrate stained thorns revealed the underlying band morphologies and growth processes. The study reveals that caudal thorns can be used as effective ageing structures for the thorny skate.
College of William and Mary, Virginia Institute of Marine Science, P.O. Box 1346, Rt. 1208 Greate Rd, Gloucester Point, VA 23062, USA
Using demographic models to determine sustainable fishing for elasmobranchs: Pitfalls, advances and applications
Leslie matrices and life history tables are demographic simulation models that are commonly used to evaluate the ability of specific elasmobranch life history strategies to sustain given levels of fishing pressure. In many cases, the application and interpretation of model results are presented without a clear logical basis. Estimates of maximum population growth rates (r-intrinsic) and therefore maximum sustainable fishing mortality are being used to evaluate extinction risks to depressed stocks and guide management decisions. However, neither a Leslie matrix nor a life table can be used to estimate r-intrinsic without additional information. In this paper, we first review the logic of demographic analysis, show basic relationships and discuss what can and cannot be inferred. We then discuss how models can be extended and what additional inferences can be made when additional information is available. We derive and apply methods for estimating r-intrinsic for the barndoor skate (Dipturus laevis) and obtain an estimate of 0.33 to 0.50 yr-1. For the lemon shark (Negaprion brevirostris), r-intrinsic is estimated to be between 0.04 to 0.06 yr-1.
Elasmobranch Physiology and Environmental Biology Program, Center for Shark Research, Mote Marine Laboratory, Sarasota, FL 34236, USA
Vitellogenin as a biomarker of xenoestrogen exposure in the bonnethead shark,Sphyrna tiburo
Vitellogenin is a large glycolipophosphoprotein that serves as the precursor to egg yolk in sexually mature, female non-mammalian vertebrates. Vitellogenin is produced in the liver in response to stimulation by the gonadal steroid, 17b-estradiol, and is secreted into the bloodstream for delivery to developing oocytes. Although the production of this protein is generally female-specific, male non-mammalian vertebrates are also capable of synthesizing vitellogenin in response to exposure to natural estrogens and environmentally relevant, estrogen-mimicking environmental contaminants or “xenoestrogens.” Because of this, vitellogenin protein and gene expression assays have become valuable approaches for detecting xenoestrogen exposure and effects in a broad range of animal taxa. In this presentation, we discuss recent efforts to develop a species-specific gene expression assay for vitellogenin in the bonnethead shark, Sphyrna tiburo. The production of vitellogenin was induced in male S. tiburo by estradiol treatment. A putative cDNA fragment of S. tiburo vitellogenin was obtained from reverse transcribed liver RNA of estradiol-treated sharks using the polymerase chain reaction with degenerate primers based on conserved regions of vertebrate vitellogenins. Similarity analysis of sequence data confirmed the identity of this product as vitellogenin. A digoxigenin-labeled riboprobe for bonnethead shark vitellogenin was prepared via in vitro transcription using the cDNA template. The riboprobe was used to develop semi-quantitative assays for characterizing vitellogenin gene expression in liver of field-sampled sharks. Additionally, sequence data was used to identify a 19-amino acid fragment of the bonnethead shark vitellogenin protein that was suitable for the production of polyclonal antibodies. This peptide sequence was commercially synthesized and used to generate protein-specific probes, which will be used to develop non-lethal assays for detecting vitellogenin in shark plasma.
(SPG) University of Rhode Island, Department of Biological Sciences, 100 Flagg Rd, Kingston, RI 02881, USA; (MND) University of California Irvine, Ecology and Evolutionary Biology, 321 Steinhaus Hall, Irvine, CA 92687-2525, USA
Force transmission of the adductor mandibulae complex across the jaw symphysis in sharks
The symphyses are fibrous midline connections between the halves of the jaws; the morphology of these joints has a profound effect on feeding mechanics. Fusion of the symphyses facilitates durophagy by strengthening the jaws or stiffening them to allow more efficient force transfer to the balancing-side, yet this sacrifices maneuverability that may be important in prey processing. This study examined the effect of flexible symphyses on force transmission across the jaws in two shark species (Mustelus canis, Squalus acanthias) by comparing working-side, balancing-side and symphyseal bite forces during in vivo muscle stimulation. Although both species have unfused symphyses, the diet of M. canis includes hard prey, indicating a feeding mechanism that is both flexible and strong. In a jaw with a non-rigid midline connection, we would expect force to decrease with distance from the working-side. However, while bite force in M. canis decreased to approximately 50% at the symphysis, balancing-side forces nearly equaled working-side values. Stimulation of the same jaw muscles in S. acanthias revealed a similar decrease in forces at the symphysis and considerable variation at the balancing-side of the jaw. These differences are likely rooted in interspecific variation either in jaw shape or muscle physiology. To discriminate between these hypotheses, we calculated the mechanical advantage of the preorbitalis and dorsal quadratomandibularis muscles at sequential locations along the jaw. The mechanical advantage of the muscles differed between species, indicating that the muscular anatomy influenced bite force more than the shape of the jaw.
(BJG) University of Rhode Island, Dept. Fisheries, Animal, and Veterinary Sciences, Kingston, RI 02881, USA; (LJN) NOAA National Marine Fisheries Service, Northeast Fisheries Science Center, 28 Tarzwell Drive, Narragansett, RI 02882, USA
Age and growth of the thresher shark, Alopias vulpinus, in the northwest Atlantic Ocean
Age and growth estimates were generated for the thresher shark, Alopias vulpinus, in the western North Atlantic using vertebral centra from 173 female, 135 male, and 11 individuals of unknown sex ranging in size from 56 cm to 264 cm FL. Males and females were aged to 22 (228 cm FL) and 24 (244 cm FL) years respectively. Male and female growth was similar until approximately age 8 (185 cm FL), after which male growth rate slowed. Female growth slowed at a later age than males (approximately 10 years). von Bertalanffy growth parameters generated from the vertebral data using a set size at birth provided the best fit for the band counts: Linf = 226.7 cm FL and K = 0.16 for males and Linf = 263.5 cm FL and K = 0.11 for females.
Florida Program for Shark Research/ Florida Museum of Natural History, University of Florida, Dickinson Hall, Museum Road, Gainesville FL 32611, USA
Regional bycatch composition of the commercial shark bottom longline fishery of the southeast United States.
Since 1994, the Commercial Shark Fishery Observer Program (CSFOP) has been placing fishery observers aboard bottom longline boats along the Atlantic coast and Gulf of Mexico from New Jersey to Louisiana. During this time the CSFOP has collected data on all sharks and bycatch caught aboard monitored vessels. From 1994-2004 the CSFOP monitored 1,259 sets representing over 777,984 hooks and 11,184,639 hook hours. Observations were made on 63,257 sharks and bycatch consisting of 3139 other vertebrate animals. The bycatch was dominated by batoids and bony fishes with limited sea turtle (52 individuals, 29.7% mortality), cetacean (2, 1 dead, 1 escaped), and seabird (1, released) catches. The major groups of bycatch were serranids (33.6%), batoids (19.1%) and anguilliforms (14.7%). Bycatch was not evenly dispersed over the range of the fishery. The Florida Key region in particular had a high amount of bycatch, representing over 40% of the entire fishery total. Over 75% of the batoid bycatch was caught in Atlantic waters, while over 80% of serranids, lutjanids, anguilliformes, and carangids were recorded in the Gulf of Mexico. The high percentage of bycatch in the Florida Keys reflects the fishing methodology of fishers, who frequently set on or near hard bottom, and welcomed the addition of valuable groupers and snappers in their catches.
(KJG) Jackson State University, Department of Biology, 1400 J.R. Lynch St., P.O. Box 18540, Jackson, MS 39217 USA; (SB) National Marine Fisheries Service, 9721 Executive Center Drive North, Koger Building, Suite 201, Saint Petersburg, FL 33712 USA; (JAM) Virginia Institute of Marine Science, Route 1208, Greate Road, Gloucester Point, VA 23062 USA
A re-examination of the age and growth of sand tiger sharks, Carcharias taurus, in the western North Atlantic
Age and growth estimates for sand tiger sharks, Carcharias taurus, in the western North Atlantic were derived from 96 vertebral centra collected from sharks ranging from 94 to 277 cm total length (TL), and compared to previously published age and growth data. The oldest female and male sand tiger sharks aged in this study were 17 and 15 years of age, respectively. von Bertalanffy growth parameters derived from vertebral length-at-age data are Linf = 295.8 cm TL, k = 0.11 yr -1, and to = -4.2 years for females, and Linf = 249.5 cm TL, k = 0.16 yr -1, and to = -3.4 years for males. Sexual maturity is estimated to be 9-10 years for females and 6-7 years for males. Weight-to-length relationships for female and male sand tiger sharks in the western North Atlantic are; W = 1.3×10-04 x L2.4 (r2 = 0.84, n=55) and W = 9.0×10-05 x L2.5 (r2 = 0.84, n=47) respectively, and 7.9×10-05 x L2.5 (r2 = 0.84) for the sexes combined. Our results show sand tigers possess a slower rate of growth than previously thought. This information is crucial for accurately assessing this populations ability to recover, and further justifies the need for this species to be fully protected.
Virginia Institute of Marine Science, College of William and Mary, P.O. Box 1346, Gloucester Point, VA 23062-1346, USA
Analysis of fall migration of cownose rays, Rhinoptera bonasus, using pop-up satellite archival tags
The life history of the Cownose Ray, Rhinoptera bonasus, has been well studied in the Chesapeake Bay, which serves as a primary nursery for young-of-year pups during the summer months. In order to further the understanding of the population biology of the cownose ray, fall migration of cownose rays was examined and the wintering grounds identified. Seven adult female cownose rays were tagged with Pop-up Satellite Archival Tags (PSATs) in the lower Chesapeake Bay in early September 2003. The tags were programmed to release and begin data transmission after six months. Data collection by the tags was excellent; however, data transmission was very poor. Three tags were found on Florida beaches and returned for download of archival data. Comparison of tag data to oceanographic sea surface temperature (SST) data and coastal bathymetry contours showed that the rays had very similar migratory behavior in terms of temperature and depth preferences. They moved from Chesapeake Bay down the South Atlantic Bight at a migration rate of approximately 6.7 NM/d arriving in southern Florida around late December. Based on SST comparisons, none of these rays migrated south of 27 °N. Two potential gestational patterns have been suggested for cownose rays-semi-annual reproduction vs. annual reproduction with mid-gestation diapause. In contrast to the estuary- based summer grounds, cownose rays remained off-shore during the winter months near the continental shelf break where it approaches the Florida coastline. The energy required for long-distance migration plus the stark contrast of the wintering grounds to the rays’ summer residence make a winter nursery unlikely.
Virginia Institute of Marine Science, College of William and Mary, P.O. Box 1346, Gloucester Point, VA 23062-1346, USA
Quantification of forces imposed by Pop-up Satellite Archival Tags and estimation of metabolic cost
The recent development of the Pop-up Satellite Archival Tag (PSAT) has allowed the collection of information on a tagged animal including geolocation, pressure (depth) and ambient water temperature. The success of early studies on pelagic fishes has spurred increasing interest in using these tags on a large variety of species and age groups. However, some species and age groups may not be suitable candidates for carrying a PSAT due to its relatively large size and the consequent energy cost to the study animal. Potential energetic costs of carrying a tag in the cownose ray, Rhinoptera bonasus, were examined. Two forces act on an animal tagged with a PSAT: lift from the PSAT’s buoyancy and drag as the tag is moved through the water column. In a freshwater flume, a spring scale measured the total force exerted by a PSAT at flume velocities from 0.00 – 0.60 m/s. By measuring the angle of deflection of the PSAT at each velocity, the total force was separated into its component forces, lift and drag. The power required to carry a PSAT horizontally through the water was then calculated from the drag force and velocity. Using published metabolic rates, the power for a ray of a given size to swim at a specified velocity (i.e. swimming power) was estimated. For each velocity, the power required to carry a PSAT was compared to the swimming power expressed as a percentage, %TAX. A %TAX greater than 5% was felt to be energetically significant. Our analysis indicates that a ray larger than 14.8 kg can carry a PSAT without exceeding this criterion. The approach can be applied to other species allowing a researcher to decide the suitability of a given study animal for tagging with a PSAT.
Virginia Institute of Marine Science, PO Box 1346, Gloucester Point, VA 23062, USA
Insights from analysis of 30 years of Virginia shark long-line survey data
The Virginia Institute of Marine Science has been conducted shark long-line surveys with standard gear in Viginia waters since 1973. Only one analysis of these catch data have been presented to date. In this paper we present the results of analysis of trends in abundance over the last 30 years of Virginia sharks species. We also examine patterns of abundance with physical parameters, and examine size distribution data for changes in the last 30 years. Our analysis shows a clear decline in abundance of virtually all shark species caught often enough for statistical analysis. Sandbar (Carcharhinus plumbeus), dusky (C. obscurus), sand tiger (Carcharias taurus), and tiger (Galeocerdo cuvieri) all show significant declines. Only small shark species such as the Atlantic sharpnose shark (Rhizoprionodon terraenovae) and the smooth dogfish (Mustelus canis) show equivocal trends. Breakdown of sandbar shark abundances into size classes show trends in abundance to be driven by juvenile sharks, with adults virtually not appearing in recent years of our survey. Physical parameters examined include bottom and surface temperatures, times of day lines were set and retrieved, month of survey, location, and depth. Bottom temperature is the most consistently significant parameter in our models, with month of survey being significant in certain cases. Time of set and retrieval are virtually never significant. Size-distribution curves can only be studied for the most abundant species collected in this survey, and, to date, only the most abundant, the sandbar shark, has been studied in this manner. These results show loss of larger individuals over the course of the survey, with some less obvious trends still to be teased out. Future work will include analysis of additional physical data, analysis of larger-scale meterological data, including North Atlantic oscillation data, and analysis of trends in catches of other elasmobranchs (batoids) caught as bycatch.
California State University, Northridge, Department of Biology, Nearshore Marine Fish Research Program, 18111 Nordhoff St., Northridge, CA 91330 USA
Aspects of the life history of the Brown Smoothhound, Mustelus henlei, from southern California
Various aspects of the life history of the Brown Smoothhound, Mustelus henlei, are being examined in a Southern California population from Catalina Harbor, Catalina. Age and growth of the adolescent and adult specimens will be described using the Von Bertalanffy growth function, as well as the species fecundity and length at birth. I am also examining the age and growth of M. henlei fetuses, as well as the sex ratio at birth. The diet of the brown smoothhounds from Southern California is also being examined. Preliminary data indicates that the diet of the brown smoothhounds from Catalina Island is dominated by Teleosts, including juvenile Atractoscion nobilis, crustaceans, and cephalopods.
California State University Long Beach, Dept. Biological Sciences, Long Beach, CA 90840, USA
Elemental signatures in vertebral cartilage of the round stingray, Urobatis halleri, from Seal Beach, California br />
Elemental analyses (x-ray spectrometry, electron microprobe analysis) have been used to verify ages in elasmobranchs by examining seasonal peaks of elements in cartilage growth. These studies found that there were annual cycles of calcium and phosphorus that corresponded with age estimations. In the current study, a new technique for elemental spatial analysis involving time-of-flight inductively-coupled-plasma-mass spectrometry (TOF ICP-MS) has been used to assess the potential of verifying age estimates and seasonal banding patterns in the vertebral centra of the round stingray, Urobatis halleri. This technique uses a high-energy UV laser to ablate a sample, which is then swept into the ICP-MS by a pressurized argon stream. The spatial distribution of elemental signatures was compared to the annual and seasonal periodicity of growth bands used for age estimation. Vertebral centra were sectioned sagittally producing 0.5 mm thick bow-tie sections. The sample sections were pre-ablated with the laser to remove external contamination and the ICP-MS chamber was purged to remove leftover gaseous elements. Each sample was laser ablated across the whole vertebral corpus calcareum at a speed of 10 micrometers sec-1 with a laser spot size of 30 micrometers. Calcium, phosphorus, magnesium, and strontium were the main elements screened in the vertebral sections. Preliminary results show that spatial peaks in calcium, phosphorus, strontium, and magnesium concentrations may correlate with growth bands in the vertebral centra. In addition to verifying age estimates, this analysis could be applied to determine possible location of nursery grounds that may possess distinct elemental characteristics and dispersal patterns of the round stingray.
California State University Long Beach, Dept. Biological Sciences, Long Beach, CA 90840, USA
Age and growth of the round stingray, Urobatis halleri, at Seal Beach, California
The round stingray, Urobatis halleri, is the most common nearshore elasmobranchs in southern California and is particularly abundant at Seal Beach, California. The popularity of Seal Beach for both beachgoers and stingrays, results in 200-500 round stingray-related injuries each year. However, it is unclear why round stingrays aggregate at Seal Beach. Because of the desire to reduce the number of round stingray-related injuries, knowledge of the age and growth of this species is important for management. Round stingrays were collected monthly in beach seines at Seal Beach, California in 2003 and 2004 (n=171). Vertebral centra were sectioned and age was estimated by two readers. Growth models were fit to the estimated age-at-disc width data and age estimations were applied to frequencies of disc widths of round stingrays. The parameters estimated by the von Bertalanffy growth model were a maximum disc width of 348 mm for males and 251 mm for females, k= 0.06 year-1 for males and 0.11 year-1 for females, and t0= -4.61 for males and -5.38 for females. The maximum disc width estimated was comparable to other batoids like Urolophus lobatus and Trygonoptera personata. The age structure of the population of round stingrays at Seal Beach consisted of mostly older, mature males and females. Age at maturity (150 mm disc width) corresponded to an average age of 3.8 years for females and 3.75 years for males. The maximum estimated age was 14 years old at a disc width of 239 mm for males and 213 mm for females. Males were more numerous than females throughout the year with the highest frequency of occurrence in August; however from May through September females outnumbered males. Based on the age structure of this population, round stingrays are likely aggregating at Seal Beach for reproductive purposes and this species may be sensitive to control measures.
(NH) Pew Institute for Ocean Science, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida, 33139, USA; (RAM) Fish Museum, University of British Columbia, Department of Zoology, Vancouver, BC V6T 1Z4, Canada; (CF) Apex Images CC, 14 Thibault Walk, Marina Da Gama, Cape Town, 7945, South Africa
White Shark (Carcharodon carcharias) predation on Cape fur seals (Arctocephalus pusillus pusillus) at Seal Island, South Africa: Present knowledge and future directions
Predator-prey interactions between white sharks (Carcharodon carcharias) and Cape fur seals (Arctocephalus pusillus pusillus) were studied at Seal Island in False Bay, South Africa, from 1997 to 2003. 2088 predatory attacks on seals were recorded during the study period and frequency and success rate were analyzed according to 13 biotic and abiotic factors. Attacks were primarily on lone in-coming young of the year seals, were spatiotemporally clustered at the primary pinniped entry/exit point at the south terminus of the Island, and occurred almost exclusively during winter (May-September), mostly within two hours of sunrise. Predatory success rate averaged 47%, but increased to 55% under scotopic conditions and decreased to 40% under photopic conditions. Shark attack frequency is high, averaging 5.6 per day, with as many as 26 recorded in a single day. Experiments using infrared video imaging demonstrated that both seals and white sharks can be detected in darkness by their thermal signatures and helped document that seal movement about the Island is greater at night than during the day. Sharks may control seal populations through top-down trophic affects by directly causing significant seal mortality as well as by indirectly altering seal foraging behavior due to predation risk. Current work is aimed at determining the ecological role of the white shark in False Bay and evaluating its impact on ecosystem structure and function.
(MRH) Department of Biological Sciences, Florida International University, 3000 NE 151 St, North Miami, FL 33131 USA; (AJW, LMD) Department of Biological Sciences, Simon Fraser University, Burnaby, BC V5A 1S6 Canada; (IMH) Department of Behavioural Ecology, Zoology Institute, University of Bern, Wohlenstrasse 50a, CH-3032 Hinterkappelen, Switzerland
Microhabitat use of tiger sharks in Shark Bay, Western Australia: Predator-prey interactions at multiple spatial scales
Tiger sharks (Galeocerdo cuvier) are important predators in a variety of nearshore communities, including the seagrass ecosystem of Shark Bay, Western Australia. Growing evidence suggests that they may have profound impacts on the habitat use decisions made by a variety of prey species in Shark Bay, but the possibility that these effects occur over multiple spatial scales has not been investigated. We used catch rates and acoustic tracking to determine tiger shark microhabitat use, and conducted surveys of bottlenose dolphin (Tursiops aduncus) distribution and captures of green sea turtles (Chelonia mydas) to assess their responses to predation risk. Sharks preferred shallow habitats over deep ones, but preferred shallow edge microhabitats over shallow interior ones. The use of shallow edges likely increases encounter rates with potential prey, but prey are more likely to escape an encounter with a tiger shark in these microhabitats than they are within interior ones. Interestingly, turtles with good body condition and dolphins select edge microhabitats over interior ones when tiger sharks are present. This suggests that intrinsic habitat risk (probability of death in an encounter situation) is more important than shark density in determining microhabitat use of prey. The dynamics of predator-prey interactions over multiple spatial scales in Shark Bay may have important consequences for the dynamics of the Shark Bay seagrass ecosystem through indirect effects transmitted by grazers, like green turtles, that are common prey of tiger sharks.
Guy Harvey Research Institute, Oceanographic Center, Nova Southeastern University, 8000 North Ocean Drive, Dania Beach, FL 33004 USA
Streamlined genetic identification of ridgeback sharks for fisheries management and conservation
The burgeoning market for shark products, including high demand for shark fins, has raised widespread concerns about ecologically harmful exploitation of many shark species, and prompted calls for better management and conservation of sharks on a species-specific basis. Despite the desired goal of species-specific management, the U.S. Atlantic shark fishery is currently managed on the basis of species groups mainly because of difficulties identifying many of the requiem sharks (family Carcharhinidae) common in the fishery. We report a highly streamlined, rapid multiplex PCR method for identifying ridgeback carcharhinid shark carcasses and other body parts to species level. Our multiplex PCR assay comprises eight species-specific nested in between two universal primers simultaneously to discriminate the seven ridgeback sharks (night [Carcharhinus signatus], dusky [C.obscurus], Caribbean reef [C. perezi], sandbar [C. plumbeus], bignose [C. altimus], silky [C. falciformis], and tiger [Galeocerdo cuvier]) in U.S. and global commercial fisheries. The primers are designed based on fixed, species-specific variations in the nuclear ribosomal ITS2 locus. Assessment of intra-specific DNA sequence variability in this locus on a global scale indicates extremely high conservation within species, making the ITS2 locus very useful for potential shark DNA barcoding applications. Use of this assay to screen fins from the Hong Kong market reveals the presence of fins from most of these ridgeback species in the international fin trade.
Biological Programs Department, National Aquarium in Baltimore, Pier 3, 501 East Pratt Street, Baltimore, MD 21202, USA
Boys will be boys: Sexual conflicts in captive sand tiger sharks, Carcharias taurus
Precopulatory behavior in captive sand tiger sharks, Carcharias taurus, has previously been documented. Reproductive behavior or sexual conflicts were documented from 1998 to 2003 in a colony of sand tiger sharks at the National Aquarium in Baltimore. These observations corroborate much of the previous information. Of note however, is that the dominance hierarchy in males is associated with additional behaviors not previously described. Physical separation of males resulted in a cessation of sexual conflicts. The results suggest that in this colony at least the dominance hierarchy in males is not based strictly upon size, the speed and food intake patterns are indicative of position in the hierarchy, and that the most dominant and most subordinate males are key sharks within the hierarchy.
Mote Marine Laboratory, Center for Shark Research, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA
Can MPAs be effective for managing a mobile shark population?
The presence and movements of a population of young blacktip sharks (Carcharhinus limbatus) was monitored via a series of acoustic hydrophones over a period of three years to examine their use of a coastal nursery area. Data from this project were used to investigate the efficacy of hypothetical marine protected areas (MPA) for this population. Small and large reserve designs were used to determine which would provide better protection for this population. The small reserve (c. 1.5 km2) provided consistent levels of protection across years with sharks receiving good protection early in the summer season, but with declining protection thereafter. The large reserve (c. 3.5 km2) provided less consistent levels of protection across years, but provided protection for a greater portion of time than the small reserve. Excursions from the small reserve were high early in the season and declined as sharks used this region less through the later portion of the summer. Excursions from the large reserve did not show any consistent pattern, but were also high early in the season and decreased through time as sharks used less of the reserve area. These results were coupled with previously calculated mortality estimates to examine whether these reserve areas provided reliable protection for sharks during their periods of highest mortality. The large reserve provided better protection for sharks during this period than the small reserve, suggesting the large reserve design may have provided sufficient protection for young sharks. Although there are currently no protected areas directed at shark nurseries, these results suggest that time-area closures for nursery populations of highly mobile shark species may be of value. Directed MPAs may be useful for mobile populations during select times of their life history or in select locations along their migratory routes.
(DRH) University of South Florida, Dept. Biology, Tampa, FL 33620, USA; (MND, APS) University of California, Irvine, Ecology and Evolutionary Biology, Irvine, CA 92697, USA
The crushing bite of the water bunny Hydrolagus colliei
Holocephalans, the sister group to the sharks, skates and rays, have their upper and lower dentition fused into a bony beak well suited for crushing hard prey. The upper jaw is not free, as in elasmobranchs, but fused to the cranium, providing mechanical stability during feeding. These morphological novelties have functional implications for durophagy. We therefore quantified bite force over ontogeny in the white spotted ratfish, Hydrolagus colliei, using tetanic stimulation of the jaw adductor musculature, and compared these data to theoretical bite force estimates based on a 3D model of jaw and muscle architecture. Bite force increased with positive allometry by virtue of increasing mechanical advantage of the jaw adduction mechanism, and ranged from 12-87 N in 21-44 cm H. colliei. Size specific bite force of H. colliei is greater than that of non-durophagous chondrichthyan fishes, and is comparable to that of the hard prey eating horn shark Heterodontus francisci. As in previous studies the maximal forces predicted from muscle architecture exceeded those achieved by stimulation. Fatigue rate in the bite force of H. colliei was compared to that of the spiny dogfish Squalus acanthias to identify physiological adaptations in the jaw adductor musculature that allow H. colliei to continually graze benthic prey.
Directed Shark Fisheries, Inc., PO Box 11604, Daytona Beach, FL 32120-1604, USA
Commercial shark industry perspective about large coastal sharks (LCS) of the Atlantic Ocean region
The Atlantic Shark fishery management plan (FMP) was implemented during April 1993, by the National Marine Fisheries Service (NMFS). The large coastal shark (LCS) management complex was established and consists of twenty-two (22) species of LCS. This shark industry document will be providing illustrations as to the past and current fishing status of these 22 individual LCS species based upon the historical experience of the Atlantic shark fishery participants and known sources of mortality. The past dozen years of federal shark management have benefited all of the LCS species in the US Atlantic Ocean region, as per the opinion of the commercial shark fishing industry. LCS Species Assessment List The following 22 LCS species are listed in alphabetical order by scientific name: I will however refer to each LCS species by the common name in this document. Scientific name Common name 1. (Carcharhinus altimus) Bignose shark 2. (Carcharhinus brachyurus) Narrowtooth shark 3. (Carcharhinus brevipinna) Spinner shark 4. (Carcharhinus falciformis) Silky shark 5. (Carcharhinus galapagensis) Galapagos shark 6. (Carcharhinus leucas) Bull shark 7. (Carcharhinus limbatus) Blacktip shark 8. (Carcharhinus obscurus) Dusky shark 9. (Carcharhinus perezi) Caribbean Reef shark 10. (Carcharhinus plumbeus) Sandbar shark 11. (Carcharhinus signatus) Night shark 12. (Carcharias taurus) Sand Tiger shark 13. (Carcharias noronhai) Bigeye Sand Tiger shark 14. (Carcharodon carcharias) Great White shark 15. (Cetorhinus maximus) Basking shark 16. (Galeocerdo cuvieri) Tiger shark 17. (Ginglymostoma cirratum) Nurse shark 18. (Negaprion brevirostris) Lemon shark 19. (Rhincodon typus) Whale shark 20. (Sphyrna lewini) Scalloped Hammerhead shark 21. (Sphyrna mokarran) Great Hammerhead shark 22. (Sphyrna zygaena) Smooth Hammerhead shark.
(RH, JT) Mote Marine Laboratory, Center for Shark Research, 1600 Ken Thompson Pkwy., Sarasota, FL 34236, USA; (JGC, FRS, RP, JPR) CONANP-SEMARNAT, Blvd. Kukulcan Km. 4.8 Zona Hotelera, C.P. 77500, Cancun, Quintana Roo, Mexico
Whale shark summer feeding grounds where the Gulf of Mexico meets the Caribbean Sea
In summer months, large aggregations of whale sharks (Rhincodon typus) inhabit nearshore waters off Mexico and Cuba in the southeastern Gulf of Mexico and northwestern Caribbean Sea. Biological studies of these sharks to document their distribution, number, size, sex, behavior and migration began off Quintana Roo, Mexico, in August 2003, and are continuing. Research methods include a combination of on-water and aerial surveys, tagging and tracking, and collaborations with local fishermen and guides. The sharks begin to appear in the area in mid-April and remain more or less continuously through September, apparently feeding on plankton associated with a summer upwelling. A total of 875 on-water sighting records (22 in 2003, 853 in 2004) has been accumulated along with results of three aerial surveys in late June, mid-August and mid-September 2004. To date 191 individual sharks have been tagged (18 in 2003, 173 in 2004). All data indicate that several hundred sharks are present in the area each summer. Estimated sizes of observed sharks range 2-13 m TL; tagged animals range 3.5-12 m TL, with an average size of 6.7 m TL. Sex ratio of tagged sharks is 3.1M:1F. Mature and immature animals are present. Resightings of tagged animals to date have been reported over 300 nm away from the tagging site. Off the northwest coast of Cuba, whale sharks are reported by tuna fishermen and biologists to be present in the fall months. Studies of the sharks in these waters have been initiated to determine their relation to the Mexican shark complex. This area where the Gulf of Mexico meets the Caribbean Sea may comprise one of the most important population centers for whale sharks in the western hemisphere.
(SBI, LJBL) School of Ecology and Environment, Deakin University, PO Box 423 Warrnambool Victoria, Australia 3280; (SBI, JDS) CSIRO Marine Research, GPO Box 1538 Hobart Tasmania, Australia 7001
Age, growth and maturity of Etmopterus baxteri (Squaliformes: Etmopteridae) from southeastern Australia
In Australia, Etmopterus baxteri is one of about 12 deepwater dogfish species that are regularly caught as bycatch/byproduct to demersal trawl fisheries. Recently introduced regulation through a basket-quota management regime (which amalgamates eight commercial deepwater dogfish species) has introduced a TAC of 200 t for 2005. However, high-grading of E. baxteri is likely as other species offer more commercial return. The vertebral centra of E. baxteri are small and deep-coned. Numerous preparation techniques, including silver nitrate, ninhydrin and alizarin red, were investigated, although no bands were found. The second dorsal spine of E. baxteri is about 50% larger than the first dorsal spine. The relationship between spine length and animal length indicated that the spines continue to grow throughout life, making them a suitable structure for age examination. Bands on the external surface of the second dorsal spine were enhanced with a derivative of alizarin red. Transverse sections at the apex of the pulp cavity yielded bands within the inner dentine layer. The number of bands in each area increased with animal size, although they were dissimilar. The relationship between the two growth zones was compared and we suggest that bands in the inner dentine stop forming and may therefore underestimate age. Length-at-age data from external bands were considered to be more accurate, and were used to estimate longevity, growth and the age at maturity. Male longevity is 48 years with an A50 of 20 years. Female longevity is 57 years. Females matured (A50) at 30 years, although the youngest female with candled uteri was 35 years, and the youngest female with near-term embryos was 39 years. Litter size increases with animal size although the length of gestation is unknown. However, if a 3-year reproductive cycle (from follicle development to parturition) is assumed, the lifetime fecundity for each female is about 81. Male and female growth was similar until the onset of male maturity. The VBGM for each sex is as follows: Male: 64.57(1-e-0.065(t+4.36)) r2 = 0.82; n = 83 Female: 83.6(1-e-0.038(t+4.98)) r2 = 0.80; n = 158.
NOAA/NMFS SEFSC, Pascagoula Laboratories, P.O. Drawer 1209, Pascagoula, MS 39567-1209, USA
Age and growth of the smooth dogfish and the Florida smoothhound in the U.S. Gulf of Mexico.
The smooth dogfish and the Florida smoothhound are common in the U.S. Gulf of Mexico. Here we report on the preliminary results of an investigation into the life history of both species. Specimens were collected during all months of the year from southwest Florida to Texas by commercial fishermen and during National Marine Fisheries Service trawl and longline surveys. Ages were obtained by analyzing growth bands on vertebral centra. Age estimates were used to generate sex-specific von Bertalanffy growth models for each species. The annual deposition of growth bands was validated up to an age of 8 for females of and 6 for males. The periodicity of growth band deposition was verified using marginal increment analysis. Reported results also include size at parturition and size and age at maturity.
University of California, Los Angeles, Dept. Ecology and Evolutionary Biology, Los Angeles, CA 90095, USA
How are habitat and prey preference of batoid fishes reflected in sensory anatomy and prey capture?
Feeding behavior in elasmobranch fishes has frequently been studied in sharks rather than their batoid relatives. The present study is focused on the feeding behavior of three species of rays. Rays are ancestrally benthic fishes though some groups have evolved a pelagic lifestyle and have separated themselves either partially or completely from the benthos. The transition to pelagic life coincided with a transition from undulatory to oscillatory modes of locomotion with modified body designs in some species, as well as a shift in diet. Species which remain intermediate to the benthic and pelagic habitats, termed benthopelagic, are powerful swimmers and can swim large distances over deep water but remain tied to the benthos for feeding. A benthic, Urobatis halleri, a benthopelagic, Myliobatis californica, and a pelagic ray, Dasyatis violacea, are compared to investigate differences in anatomy and prey capture behavior. Typical prey and preferred prey are also compared between ray species to see if prey characteristics and habitat are reflected in prey detection and capture. The electrosensory and mechanosensory systems are compared between the three species through mapping and quantification of electroreceptor and lateral line pore and canal distributions. Analysis of body and jaw movements are included to characterize and compare prey capture strategies as they relate to habitat and preferred prey. Future studies will identify behavioral responses as indicators of detection thresholds of the lateral line and electroreceptor systems. Underwater video of feeding in the field will also be used to supplement lab studies of feeding behavior.
(SMK) Florida Atlantic University, Biological Sciences, 777 Glades Rd, Boca Raton, FL 33431, USA; (TCT) University of Hawaii at Manoa, Zoology Dept, 2538 The Mall, Honolulu, HI 96822, USA; (JBF, APS) University of California, Irvine, Ecology & Evolution, 321 Steinhaus Hall, Irvine, CA 92697, USA
Olfaction in sphyrnid sharks
Hammerhead sharks (Family Sphyrnidae) are characterized by a unique head morphology in which the olfactory capsules of the cartilaginous neurocranium are laterally expanded. The enlarged olfactory capsules contain correspondingly large olfactory organs. It has been hypothesized that the widely spaced incurrent nares and large olfactory organs of sphyrnid sharks might confer directional localization of odors and enhanced olfactory sensitivity compared to their carcharhinid relatives. We tested these hypotheses by comparing the morphology of the peripheral olfactory system in all eight extant sphyrnid species as well as two carcharhinid species. The distinct prenarial grooves, characteristic of most sphyrnid species, channel water from along the anterior margin of the cephalofoil laterally into the incurrent nares. This effectively reduces the separation distance between left and right nares to a distance comparable to that of carcharhinid sharks. In addition, although sphyrnid sharks typically possess a greater number of olfactory lamellae than carcharhinid sharks, the dorso-ventrally compressed cephalofoil contrains the proportions of the lamellae such that the total lamellar surface area does not differ between comparably sized scalloped hammerhead sharks, Sphyrna lewini, and sandbar sharks, Carcharhinus plumbeus. An electro-olfactogram technique was employed to quantify the response of juvenile scalloped hammerhead sharks to a variety of proteinogenic amino acids. The amino acids differed significantly in their ability to elicit responses from the olfactory epithelium of the sharks. Aspartic acid and proline yielded the lowest magnitude responses in the scalloped hammerhead with minimum detectable concentrations around 10-5 molar. Cysteine and serine yielded the greatest response magnitudes with minimum detectable concentrations less than 10-7 to 10-8 molar. These values are comparable with values for other elasmobranch fishes and, taken in conjunction with the morphological data, seem to indicate that sphyrnid sharks might not possess any extraordinary olfactory capabilities.
University of California, Irvine, Dept. Ecology and Evolutionary Biology, 5230, 5309 Biological Sciences II 2525, Irvine, CA 92697, USA
Sharks: The skinny
How shark skin structure relates to function is still uncertain. Shark skin is covered in many tooth-like structures called denticles embedded in the dermis and projecting through the epidermis. How this structure affects the material properties is a question of interest. The two objectives of this study were to determine the differences in strength and stiffness of the skin and also to describe the mineral content between and within species. I also tested whether the material properties are correlated with degree of mineralization. Shark skin from 4 species (Isurus oxyrinchus, Mustelus lunulatus, Prionace glauca, andCarcharhinus plumbeus) was biomechanically tested and data were analyzed to compute strength and stiffness. Skin samples were then heated to 500 degrees C in a muffle furnace for 3 hours to remove organic matter. The remaining material determined mineral content, 16%, 28%, and 24%, respectively. Mineral content differed between species (p< 0.0001) but not within species (p > 0.05). Both the skin strength and stiffness differ between species (p p< 0.0001). Stiffness ranged between 1×10^5 to 1×10^7 Pa. However, only stiffness differed within species (p p< 0.0001), whereas strength did not (p > 0.05). These results suggest that mineral content, strength, and stiffness of shark skin are independent of each other. It is possible that the other skin materials, such as collagen fibers, contribute greatly to strength and stiffness. The mineralized denticles in the skin may instead be more involved in locomotion.
(LAK) Chesapeake Biological Laboratory, University of Maryland Center of Environmental Science, P.O. Box 38, 1 Williams Street, Solomons, MD 20688, USA; (AHA, GMC, KHC) Moss Landing Marine Laboratories, California State University, 8272 Moss Landing Road, Moss Landing, CA 95039. USA; (TAB) Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94551,USA
Investigations of δ14C, δ13C, and δ15N in vertebrae of white shark (Carcharodon carcharias) from the eastern Pacific
Age and growth estimates from vertebral band counts of the white shark (Carcharodon carcharias) from the eastern Pacific Ocean indicate a relatively long life and slow growth rate; however, these estimates have not been validated. To obtain reliable age, growth, and longevity estimates useful for stock assessment and fishery models, validation of age estimation is essential. However, because not all sharks deposit annual growth zones in their vertebrae, nor are they easily discernable in all species; it is necessary to validate the periodicity of these growth zones by an independent method. Radiocarbon (14C) age validation uses the discrete 14C signal produced from thermonuclear testing in the 1950s and 1960s retained in skeletal structures as a time-specific marker. The goal of this study was to evaluate validation of age estimation procedures and gain a better understanding of the carbon source to white shark vertebrae. Annual growth zones of vertebrae spanning the 1930s to 1980s were cored and analyzed for δ14C, δ13C, and δ15N. Stable isotopes provided useful trophic information, however validation of age estimates was confounded by the combined influence of the dietary source of carbon to the vertebrae, large-scale movement patterns of white sharks, and steep radiocarbon gradients present within the northeast Pacific Ocean. This work was performed, in part, under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.
(STK) Cardiff University, School of Earth, Ocean and Planetary Sciences, Main Building, Park Place, Cardiff, CF10 3EY, UK; (SHG) University of Miami, Rosentiel School of Marine and Atmospheric Sciences, 4600 Rickenbacker Causeway, Miami, FL 33149-1098, USA; (BRF) Drexel University, Department of Biosciences and Biotechnology, 3141 Chestnut Street, Philadelphia, PA 19104, USA; (GTJ) Bimini Biological Field Station, Shark Lab, South Bimini, Bahamas; (SK) University of Gothenburg, School of Sciences, Box 100, Gothenburg, 405 30, Sweden
Community structure of the resident and nomadic shark populations, Bimini, Bahamas
A twice-monthly long-line schedule has been implemented at Bimini, Bahamas (25°44N, 79°16W) since July 2003. Designed to sample the resident and nomadic adult shark populations and closely match the methodology of past research expeditions between 1981 and 1989, thus allowing comparisons between catches. Five lines, approximately 400m in length are set, four running north to south to the east of the main lagoon; the fifth in a new location each time. The bottom-set main lines are anchored at each end and have 15 baited gangions interspersed with floats, checked every three-five hours. Captured specimens are secured to the boat, measured (pre-caudal, fork and total length) and individuals over 140cm fitted with a NOAA/NMFS M-type dart tag. All lemon sharks (Negaprion brevirostris) receive a PIT tag and a DNA sample is taken. Eight species, Carcharhinus acronotus, C. leucas, C. limbatus, Ginglymostoma cirratum, Galeocerdo cuvier, N. brevirostris, Rhizoprionodon terraenovae, Sphyrna mokarran, have been captured in the current regime, whereas 13 species were recorded during the 1980s campaign. The four dominant populations, as proportions of total catch, are G. cirratum (34%), C. limbatus (25%), G. cuvier (22%) and N. brevirostris (14%). This is in stark contrast to the 1980s catches, G. cirratum (12%), C. limbatus (2%), G. cuvier (7%) and N. brevirostris (74%), with the latter displaying an alarming 83% decline in CPUE over the past 20 years. Of the present populations N. brevirostris and G. cirratum show the highest rates of recapture, 33% and 9% respectively, suggesting that these dominate the resident sharks, while C. limbatus and G. cuvier dominate the nomadic. Results further suggest the apparent massive decline in N. brevirostris may be due to local anthropogenic influences, highlighting the urgent need for an in-depth investigation into the specific causes for these drastic changes in shark assemblages.
(SKM) Coastal Carolina University, Department of Marine Science, P.O. Box 261954, Conway, SC 29528, USA; (MC) Director, Center for Undergraduate Research, Xavier University of Louisiana, 1 Drexel Drive, New Orleans, LA 70125, USA
Correlations between the distributions of the Atlantic Stingray (Dasyatis sabina) and the Southern Stingray (Dasyatis americana) and salinity profiles in Winyah Bay, South Carolina
Both the Atlantic, Dasyatis sabina, and the Southern stingray, Dasyatis americana, are common estuarine species found in South Carolina. Both species are found in S.C. sounds, estuaries and rivers at some part of the year. D. sabina has been found to frequent and even reside in low salinity waters while D. americana prefers waters that are marine salinities. The purpose of this study was to determine if the existing distributions of either or both D. sabina and D. americana, in Winyah Bay, S. C., vary according to salinity profiles. Winyah Bay watershed is the third largest watershed along the east coast of the United States and it serves as the freshwater drainage of four major rivers. Salinity within the bay can vary dramatically with up to 20 ppt difference between the surface and bottom water masses depending on the amount of fresh surface water entering the bay through the four rivers. Stingrays were captured May through September using longlines with 16/0 hooks for adults and 12/0 hooks for juveniles. In addition, lines were set during both tidal cycles and set 60 min. for adults and 30 min. for juveniles. This pilot study showed distinct differences between D. sabina and D. americana for salinity preferences. Initial results showed D. americana seemed to prefer higher salinities in the lower reaches of the bay (21-32 ppt), low tide and high tide respectively, while D. sabina preferred lower salinities in the upper portion of the bay (9-16 ppt) where the four major rivers input freshwater. D. americana exhibited average CPUE’s of 8.5 in salinities of 19-25 ppt, whereas D. sabinaexhibited average CPUE’s of 12.7 in salinities of 5-10ppt. This year this study will be continued for a second sampling season in order to further compare these two stingrays within this estuary.
(AL, JCM) Leigh Marine Laboratory, University of Auckland, PO Box 349, Warkworth 1241, New Zealand; (AL, JCM, SL) University of Auckland, School of Biological Sciences, Private Bag 92019, Auckland, New Zealand
Population genetics of short-tailed stingrays, Dasyatis brevicaudata
Short-tailed stingrays (Dasyatis brevicaudata) have been recorded in New Zealand, Australia and South Africa. They are widely distributed in New Zealand and at times form conspicuous aggregations at some off-shore islands, such as the Poor Knights Islands (NE New Zealand). Despite anecdotal evidence of seasonal migrations, nothing is known about the current levels of connectivity of these widespread populations, or the genetic relatedness among populations. Population genetics were used to investigate the relationship between the Poor Knights Islands aggregation and other New Zealand coastal and island locations. From March 2004 to March 2005, 60 short-tailed stingrays were sampled around New Zealand on SCUBA using a pole-mounted biopsy head. We analyzed geographic patterns of variation in mitochondrial DNA from short-tailed stingrays to investigate genetic relationships within and among locations. Here, we present results of preliminary analyses of short-tailed stingray samples collected from 6 locations around New Zealand. Short-tailed stingray gene flow, its relationship to movement and migration, and implications this has for management and conservation of this species in the Poor Knights Marine Reserve will be addressed.
San Diego State University, Dept. Biology, San Diego, CA 92182, USA
The genetic population structure of the leopard shark (Triakis semifasciata)
Leopard sharks (Triakis semifasciata) are one of several cartilaginous fishes commonly found in the coastal waters of California. Despite their relative abundance, very little is known about the movement, dispersal and population structure of this species. Like other k-selected predators, this species is susceptible to population depletion. By learning more about the genetic population structure of leopard sharks, it may be possible to make better-informed management decisions regarding this ecologically significant predator. Cartlaginous fishes are slowly-evolving and have extraordinarily large amounts of genomic DNA. The first question addressed in this study is: What is the genetic population structure of leopard sharks? Answers provided by this investigation may reveal relative dispersal capabilities and general movement patterns. The second question to be addressed in this study is: What molecular markers can be used to assess population structure? Preliminary research has shown that inter simple sequence repeats (ISSRs) are useful for screening large amounts of genetic material for polymorphic loci within a species. This technique may prove to be broadly applicable and useful for other population genetic studies involving little-studied vertebrate species.
(PSL) Boston University Marine Program, Marine Biological Lab., Woods Hole, MA 02543, USA; (LKL) University of Massachusetts, Biology Dept. Boston, MA 02125-3393, USA
Movement patterns of the grey reef shark, Carcharhinus amblyrhynchos, at Johnston Atoll and Palau.
Acoustic telemetry was used to study movement patterns of the grey reef shark,Carcharhinus amblyrhynchos at two coral reef locations in the Pacific. The focus of the Johnston Atoll (JA) study was to examine contaminant uptake in a top predator. The focus of the study in Palau was to identify shark residency patterns and to explore implications relative to conservation issues, particularly the domain needed for a marine protected area aimed at reef shark protection. At the Palau site, Blue Corner, the key question was whether the sharks seen by divers on a daily basis are the same ones over a long time. If so, we wanted to determine how large a domain was necessary to be delineated as the marine protected area (MPA) in order to best protect those sharks. Individual C. amblyrhynchoswere outfitted with acoustic tags to determine their frequency of return to certain key reef sites where underwater acoustic loggers were deployed. At Johnston Atoll, the sites of concern were where sediment and reef fish contamination (e.g. PCBs, dioxins, heavy metals) were greatest. In Palau, the key site is Blue Corner, one of the main destination scuba dive locations for the ecotourism industry. The question for sharks at both locations was: how long do individuals remain at or routinely visit a particular reef location? At JA, we found higher than expected levels of contaminants in the shark tissues indicating that individuals may have been more site specific/frequent than previously anticipated. At both locations, we found that individual sharks were much more site specific than expected. Overall, our study objective is to learn more about the natural history of C. amblyrhynchoson Pacific reefs and to apply this knowledge to the conservation of the species.
South Carolina Dept. of Natural Resources, Marine Resources Research Institute, 217 Fort Johnson Road, Charleston, SC 29412, USA
Satellite pop-up tagging provides a first look into the diel migration patterns of the night shark, Carcharhinus signatus.
Five night sharks (Carcharhinus signatus) caught off the coast of South Carolina were fitted with satellite pop-up tags on 26 June 2003. One specimen suffered from immediate post-release mortality, but the other four carried tags for 90 to 120 days. The tags were programmed to record hourly depth, temperature and light readings throughout the deployment interval. Data recovered from the tags indicated all specimens made a net northeastward movement of 195 to 575 km during the deployment. Analysis of depth and temperature data demonstrated a consistent pattern of diel vertical migration in all specimens. This vertical migration pattern bore a strong resemblance to that observed for swordfish (Xiphias gladius) in the same region, though swordfish rose to shallower waters at night and dove deeper during the day. Night sharks spent daylight hours in approximately 260 to 380 m of water in mean temperatures of 10.0 to 10.6 C. Nocturnal behavior was marked by an ascent to shallower waters of 60 to 90 m and approximately 20.0 to 24.5 C. This is believed to be the first electronic tagging study of any type on this species.
(CGL) Dept. of Biological Sciences, California State Univ. Long Beach, CA 90840, USA; (AF) NOAA/NOS/NCCOS/CCMA-Biogrography Program, Waimanalo, Hawaii 96795, USA; (JB) Department of Marine Science, Univ. of Hawaii at Hilo, Hawaii, 96720, USA; (JC) Marine Science Institute, Univ. of CA, Santa Barbara, CA 93106, USA; (YP) Hawaii Institute of Marine Biology, Univ. of Hawaii at Manoa, Kaneohe, HI 96744, USA
Movements of blacktip reef sharks (Carcharhinus melanopterus) in lagoons at Palmyra Atoll
Palmyra is a remote, pristine, undeveloped atoll where minimal human activity and fishing has occurred over the last 60 years. Site fidelity and movement patterns of blacktip reef sharks were determined using acoustic telemetry monitoring (VR2) in lagoons at Palmyra. Fifteen adult sharks (mean TL 110 ± 11 cm) were monitored for up to 411 days (mean 233 ± 144 days). Four of the 15 sharks were only detected for up to 75 days. Sharks were found to move through all three major lagoons at Palmyra, moving at least 6 km between monitors. The longer sharks were detected the more likely they were observed to move to different lagoons. Several short-term, fine-scale acoustic tracks indicated that sharks move along reef edges during low tide, but move up onto the reef flats at high tide. This behavior corresponds with observed movement patterns of bonefish and other teleost prey, which use the reef flats to forage during high tide.
University of South Florida, Department of Biology, Tampa, FL 33620, USA
Ontogenetic development of feeding behavior in two elasmobranchs: do anatomical constrains canalize behavioral capacity?
Early ontogeny is a time of rapid anatomical, physiological, and behavioral development and the degree of synchrony between anatomy and behavior during this period can influence individual survival. Understanding the ethomorphological development of feeding during early ontogeny is important because nutrient acquisition influences every aspect of organismal biology. A one-year longitudinal feeding study was conducted for two elasmobranch species: the whitespotted bambooshark Chiloscyllium plagiosum and the leopard shark Triakis semifasciata. To quantify changes in cranial anatomy and morphology, several external characters associated with the feeding apparatus were measured weekly. To quantify feeding behavior, individuals were filmed weekly using a high-speed digital video camera as they consumed various prey types. The cranial morphology of C. plagiosum exhibited primarily isometric growth and little change in shape through ontogeny. The cranial morphology of T. semifasciata, however, was dominated by allometric growth, producing greater changes in shape. These changes included an anterior displacement of the mouth and the development of a relatively narrow, shallow head profile. Although intraspecific differences both at discrete times and when comparing trajectories across ontogeny complicated comparison, modulation in response to prey attributes was clearly evident in T. semifasciata (e.g. faster, less ram-dominated kinematics for live prey) but was broadly absent in C. plasiosum. The capacity to perform diverse feeding behaviors throughout ontogeny is not constrained by anatomical development in T. semifasciata but tends to be canalized toward greater stereotypy in C. plagiosum. A plastic, functionally-generalized feeding apparatus and repertoire may benefit T. semifasciata, a common denizen of estuaries, by allowing exploitation of diverse prey in variable environments using different behaviors over ontogeny. Morphological conservation of the feeding apparatus throughout ontogeny in concert with honing of its feeding repertoire, however, may allow C. plagiosum to exploit numerous crevice-dwelling reef organisms throughout ontogeny using a single specialized behavior.
Boston University, Department of Biology, Boston, MA 02215, USA
The elasmobranch epigonal-ovarian complex (EOC): Regulation of leukocyte turnover by sex hormones
In mammals, it is well known that sex hormones affect both the innate and acquired immune systems by up- or down-regulation of the cells and factors they produce. It has been shown that, in general, estrogens hypersensitize the immune system while androgens and progestins are thought to down-regulate immune function. The cartilaginous fish (sharks, skates, and rays) offer a novel approach to the study of endocrine-immune interactions. These are the only species in which the gonads are directly associated with an autonomous immune tissue, the epigonal organ. Furthermore, the constant turnover of immune cells, via regulation of leukocyte proliferation and apoptosis, is critical for maintenance of homeostasis. To test whether sex hormones have an effect on cellular turnover of the epigonal organ, we utilized immunohistochemical (IHC) techniques to investigate apoptosis (TUNEL) and proliferation (proliferating cell nuclear antigen, PCNA Ab) of this unique leukopoietic tissue from reproductively active (RA) vs. non-reproductively active (NRA) little skates (Leucoraja erinacea). IHC analyses showed that that RA animals exhibited greater apoptosis than NRA animals, while the opposite was true for proliferation, suggesting a potential effect of sex hormones. We then used in vitro experiments to test the effects of 10-5M estradiol (E2), progesterone (P4), testosterone (T), and dexamethasone (Dex) on apoptosis and proliferation of epigonal leukocytes. Tritiated thymidine incorporation, DNA fragmentation, and labeling of leukocytes with caspase-3 Ab demonstrated a significant influence of sex hormones on immune cell turnover. This is the first study to demonstrate a reproductive endocrine-immune interaction in an elasmobranch species. It is likely that this association illustrates, in part, how these animals have survived for over 400 million years to become the oldest extant jawed vertebrates. Investigation of this novel association offers insight into the mechanisms behind both physiological and pathophysiological influences of sex hormones in higher vertebrates, including humans.
Florida Atlantic University, Dept. Biological Sciences, Boca Raton, FL 33431, USA
Electric organ morphometrics of the lesser electric ray, Narcine brasiliensis
All elasmobranchs have the ability to detect electricity, however only the Rajiformes are capable of bioelectrogenesis. Within this order, skates use their small electric organs to emit weak electric organ discharges (EODs) involved in communication, whereas electric rays of the subfamily Torpedininae emit strong EODs from their large, kidney-shaped electric organs during prey-capture. The lesser electric rays of the subfamily Narcininae are capable of producing both strong and weak EODs from their large, kidney-shaped main electric organs and their small accessory organs respectively; however, the function of both of these types of discharges remains unknown. My goal is to characterize the main electric organ discharge and to determine how both the main and accessory EODs are employed behaviorally. Requisite to this goal is a morphometric study to examine possible sexual dimorphisms or ontogenetic changes in the electric organs. Morphometrics obtained from the representative species, Narcine brasiliensis, include: disc width, total length, total mass, main electric organ mass, accessory electric organ mass and number of main electric organ electroplaques. The proportion of EOD generating mass relative to the total body mass, herein referred to as the electro-somatic index (ESI, expressed as percent), was calculated for both main and accessory electric organs (MESI and AESI respectively). Mean MESI of N. brasiliensis was 13.69 ± 0.63% SE (n=15) and mean AESI was 0.10 ± 0.01% SE (n=15). Main and accessory electric organ masses and the number of electroplaques in the main electric organ correlate positively with size morphometrics. In addition, the AESI demonstrates a positive allometry with body size, whereas the MESI is negatively allometric. None of the morphometric characters were sexually dimorphic. Future electrophysiological and behavioral experiments will investigate the function of the main and accessory electric organs to elucidate how they are employed in the natural history of this species.
(MAM) School of Marine Science and Technology, Ridley Building, University of Newcastle, Newcastle upon Tyne, NE1 7RU, UK; (GBS) Martha’s Vineyard Marine Fisheries Field Station, Massachusetts Division of Marine Fisheries, PO Box 68, Vineyard Haven, MA 02568, USA; (ATF) Warnell School of Forest Resources, University of Georgia, Athens, GA 30602, USA
Tissue types reflect trophic inferences from stable isotopes in sharks
Food-web relationships in marine systems have traditionally been defined through stomach-content analysis but biochemical techniques have recently emerged to validate and broaden temporal diet patterns. Stable-isotope analysis has become a practical tool for evaluating these relationships in aquatic systems, however, routine sampling of muscle tissue captures only part of the trophic information available from each animal. We compared 15N and 13C values among liver, muscle and cartilage in blue shark (Prionace glauca), shortfin mako (Isurus oxyrinchus), and common thresher (Alopias vulpinus) from the northwest Atlantic to show how multiple-tissue sampling captured feeding relationships which would have been invisible to muscle tissue alone. Specifically, we demonstrated evidence of a known spring cephalopod to bluefish (Pomatomus saltatrix) diet switch in shortfin mako, and found that blue shark and common thresher have consistent diets throughout the year. We concluded that consistency observed among stable-isotope values in multiple tissues implied that the fish were in steady-state with the isotope ratios of their diet and that multiple tissues should be used in trophic assessments of large pelagic fishes. Further experiments to quantify the turnover of stable isotopes in different tissues and species are needed to improve the accuracy of stable-isotope analyses.
Guy Harvey Research Institute, Oceanographic Center, Nova Southeastern University, 8000 North Ocean Dr., Dania Beach, FL 33004, USA
Efficient genetic identification of species and geographic origin of body parts from CITES and/or legislatively protected shark species
Heavy exploitation of sharks globally to satisfy the demands of the international fin market have resulted in trade in a few species considered particularly sensitive being restricted or controlled by national legislation or international accord (e.g. CITES). Despite these conservation efforts, however, trade in these species continues because law enforcement monitoring and surveillance is hindered by species identification problems. We present the development and application of a highly streamlined, robust, multiplex PCR assay for identification of basking shark (Cetorhinus maximus; CITES Appendix II) and sand tiger shark (Carcharias taurus; protected in the U.S. and Australia) body parts in trade. Given the spatially “patchy” nature of national protective efforts for some species, identifying the geographic origin of the traded products will be needed for legal enforcement, and will be informative for assessing geographic trends in exploitation pressure. To this end, we will present preliminary data on development of a combined nuclear and mitochondrial locus, multiplex PCR assay that simultaneously distinguishes species and ocean-basin of origin for the sand tiger shark. The reslts suggest that if appropriate levels of population genetic structure exist, it should be possible to simultaneously determine species and population of origin of shark body parts with a single tube PCR.
(AM, HNC) Universidade de Lisboa, Faculdade de Ciências, Departamento de Biologia Animal & Instituto de Oceanografia, Campo Grande, 1749-016 Lisboa, Portugal; (NQ) Faculdade de Ciências da Universidade do Porto, Departamento de Zoologia e Antropologia, Praça Gomes Teixeira, 4099-002 Porto, Portugal; (JPC) Oceanário de Lisboa, SA, Esplanada D. Carlos I – Doca dos Olivais, 1990-005 Lisboa, Portugal
The Shortfin Mako Shark, Isurus oxyrinchus, from Portuguese waters – foraging ecology, population dynamics and reproduction
The shortfin mako, Isurus oxyrinchus, is caught in the eastern North Atlantic as a steady bycatch of the surface drift longline fishery, directed to swordfish, Xiphias gladius. Teleosts showed to be the principal component of this shark’s diet, occurring in 87% of the 112 stomachs sampled (vacuity index 12%) and accounting for over 90% of the weighted contents. Crustaceans and cephalopods are also common prey of I. oxyrinchus, while other elasmobranchs were present in its diet in low percentages. Young-of-the-year and juveniles show less constancy in diet composition throughout seasons when compared to adults. Reproductive traits revealed median length at maturity for males to be 185 cm fork length, with only 9 mature males caught. The only mature female was 290 cm and the larger immature female 210 cm fork length, suggesting maturity is reached in this interval. Cohort analysis indicates summer as the most probable parturition season, with smallest sharks (64 and 66 cm fork length) caught in July. Individuals larger than 120 cm fork length present sexual size dimorphism with larger females and sex ratio is biased towards males 1.8:1 (M:F) among juveniles. Sexual size dimorphism may account for the low number of mature females sampled, making them unavailable to fishing gear, rather than being absent from the study area.
(RBM) WA Marine Research Laboratory, PO Box 20, North Beach, WA 6920 Australia and Center for Ecosystem Management, School of Natural Sciences, Edith Cowan University, 100 Joondalup Drive, Joondalup, WA 6027 Australia; (CAS) Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236 USA; (JAC, RRA, SJN) WA Marine Research Laboratory, PO Box 20, North Beach, WA 6920 Australia. (GAH) Center for Ecosystem Management, School of Natural Sciences, Edith Cowan University, 100 Joondalup Drive, Joondalup, WA 6027 Australia
Validated age and growth of the Sandbar Shark, Carcharhinus plumbeus, (Nardo, 1827) in western Australian waters
Age and growth of the sandbar shark, Carcharhinus plumbeus, were examined using vertebral ageing techniques and tag- recapture data. Growth curves were derived from consensus counts by three readers of growth-bands from the vertebrae of 238 individuals, ranging in size between 47 and 154cm FL. The annual periodicity of growth-band formation was validated using vertebrae from tagged sharks injected with oxytetracycline (n=10) and calcein (n=25), at liberty for between 31 and 2,723 days. The oldest female was 25 years and the oldest male was 19 years. The ages at which 50% of female and male sharks were mature were estimated to be 16 years and 14 years, respectively. Growth increment data from 95 tagged C. plumbeus, at liberty for between 1 and 2,723 days, were used to construct growth curves for comparison with those derived by vertebral analysis. The two methods yielded noticeably different results. Based on a known size at birth of 42.5cm FL, von Bertalanffy parameters estimated using length at age data from vertebral analysis were: K= 0.039 yr-1 and Linfinity= 245.8 cm; K= 0.044 yr-1 and Linfinity= 226.3 cm and K= 0.040 yr-1 and Linfinity= 239.6 cm for females, males and combined sexes, respectively. The von Bertalanffy parameters derived from tag-recapture data were: K= 0.169 yr-1 and Linfinity= 134.9 cm for combined sexes. As the growth parameters estimated from tag recapture data were biologically unrealistic, the results from vertebral ageing were determined to provide a more accurate description of age and growth in this study. These results confirm that C. plumbeus is a slow-growing and late maturing species that is vulnerable to overfishing and would take considerable time to recover from overexploitation. These results will provide the basis for detailed age-structured stock assessments that will be used in developing management strategies for the fisheries that target this stock.
(DMM) Florida Atlantic University, 777 Glades Road, Boca Raton, FL 33431, USA; (JG, CAM) Elasmobranch Physiology and Environmental Biology Program, Center for Shark Research, Mote Marine Laboratory, Sarasota, FL 34236, USA; (RPB, CLB) Florida International University, 3000 NE 151st Street, North Miami, FL 33181, USA
Comparative thyroid hormone concentration in maternal serum and yolk of the bonnethead shark (Sphyrna tiburo)
Hormones are chemical messages within the body that can produce and coordinate anatomical, physiological, and behavioral changes within an animal. In mammals, thyroid hormone regulates the basal metabolic rate, initiates differentiation of the central nervous system, and is vital to successful early development. As in mammals, thyroid hormone has been found to regulate growth and development in teleost fish, however, its role within cartilaginous fish is poorly understood. This study examined the presence of thyroid hormone in the maternal serum and egg yolk of developing bonnethead sharks, (Sphyrna tiburo), within two sites along the Florida coast. Samples were taken during different developmental periods, including pre-ovulatory, post-ovulatory, and yolk-dependent stages in order to establish a developmental profile of thyroid hormone. The concentration of thyroid hormone increased as development proceeded which is similar to the pattern seen in yolk of teleosts, avians and reptiles. Histological assessments were made on the embryonic thyroid gland to determine if embryos were capable of endogenous thyroid hormone production. Embryos that were greater than 5.9 cm in total length did have thyroid follicles that possessed characteristics of active secretion. The concentrations of thyroid hormone within yolk and serum were found to differ within developmental periods as well as within sites. The concentration of thyroid hormone was highest in the area that supported higher growth rates, and size at maturity, which suggests possible plasticity in maternal provisioning.
The Living Seas, Epcot®, Walt Disney World® Resort, 2016 N. Avenue of the Stars, EC-Trl W-251, Lake Buena Vista, FL 32830, USA
Behavioral observations on captive sandtiger sharks, Carcharias taurus, at The Living Seas
The object of this study was to determine baseline behaviors of captive sandtiger sharks,Carcharias taurus, inhabiting the 21.5 million-liter saltwater environment of The Living Seas. Concurrently, the presence of scuba divers was also evaluated for its effect on these behaviors. After their introduction, two female sharks were simultaneously observed for 6 weeks, under five different scuba diving conditions: (1) no divers, (2) three divers, (3) six divers with food present, (4) three staff divers and 12 guest snorkelers, and (5) three staff divers and 12 guest scuba divers. Each shark was observed for a total of sixty, 30-minute sessions. A total of 22, species-typical, motor patterns and postures were recorded during the study. Three additional behaviors were observed outside of sessions. Overall, a solitary behavioral pattern was seen for each animal, swimming on average 91.7% of their time alone in a relatively “straight line” pattern. Conversely, during intra-species interactions, a dominance relationship was suggested between the two sharks. Dominance was inferred by one animal yielding when the two animals passed each other, and “tailing,” characterized by closely following and restricting the tail movement of the lead shark. Site fidelity was observed for both sharks, spending 68.8% of their time in two of the nine defined areas within the environment, which coincided with feed location. During guest dive programs, however, the sharks were observed utilizing other areas of the environment more often. Other behaviors influenced by the presence of divers include the sharks’ activity levels and behavioral range and frequency. This study provided descriptive techniques to determine basic behaviors of sandtiger sharks in a captive environment and assessed the effects of divers within the habitat on the behavior of the sharks.
The Living Seas, Epcot®, Walt Disney World® Resort, Lake Buena Vista, FL 32830, USA
Behavior of spotted eagle rays, Aetobatus narinari, in captivity at The Living Seas
Although commonly found throughout the coastal surface waters of the world’s warm and tropical oceans, limited information is available on the behavior and ecology of spotted eagle rays (Aetobatus narinari). This study focused on describing and quantifying species-typical motor patterns and postures of 3.1 spotted eagle rays in a 21.5 million liter, semi-natural display aquarium at The Living Seas. Study subjects were two adult rays, one male and one female, measuring ≈1.2 meters in disc width. A total of 81 hours of data (40.5 hours/ray) were collected during five, two-week sessions occurring between January and December 2002. Rays were observed simultaneously by divers for 30-minute periods, once per day. Occurrence and frequency of behaviors, as defined on a pre-established ethogram, were recorded. Additionally, vertical and horizontal positions were also recorded at timed intervals enable to establish space use patterns. An additional 10 hours of observations were made during the introduction of two juvenile males. Out of the 21 behaviors defined by the final ethogram (7 states and 14 events), 18 behaviors were recorded during the study with the three remaining behaviors observed outside of sessions. The average specific duration (in seconds) of 11 of the 18 behaviors was also determined. Behavior varied between the rays and by season. The rays spent an average of 67.7% of their time alone; swimming in a baseline pattern (sustained, relaxed forward movement), and conversely spending an average of 24.7% of their time within 3 meters of another spotted eagle ray. Analysis on spatial usage of the environment indicated that one of the nine spatially defined areas was utilized significantly more than other areas (34.8%, p<0.05). However, space use varied by ray, time of day, and time of year. These observations expand the previous repertoire of behaviors in spotted eagle rays. Future studies will evaluate the social significance of these findings.
(WDM, CWR) Department of Fisheries, Animal and Veterinary Science, University of Rhode Island, 20A Woodward Hall, 9 East Alumni Ave, Kingston, RI 02881, USA; (CTM, NEK, KAD) Apex Predators Program, Narragansett Laboratory, NOAA/NMFS, 28 Tarzwell Dr., Narragansett, RI 02882, USA; (BMW) Department of Biological Sciences, University of Rhode Island, 100 Flagg Rd., Kingston, RI 02881, USA
Diet, gastric evacuation, and feeding ecology of juvenile sandbar sharks,Carcharhinus plumbeus, and smooth dogfish, Mustelus canis, in Delaware Bay
Sandbar shark (Carcharhinus plumbeus) and smooth dogfish (Mustelus canis) are common coastal shark species along the U.S. Atlantic coast. Both species use coastal estuaries as nursery areas, and Delaware Bay is one of the largest nursery areas for both species along the U.S. east coast. This study characterizes the diet of sandbar and smooth dogfish sharks in the Delaware Bay nursery. Sharks were caught using bottom longlines and gillnets at locations throughout the bay. Stomachs were everted and contents were collected using non-lethal techniques. Stomach contents were weighed and identified to the lowest taxon possible. A total of 217 smooth dogfish was sampled, with stomachs of 212 (97.7%) sharks containing food. Weight of stomach contents represented a mean of 1.29% of their body weight (%BW). Smooth dogfish in Delaware Bay consumed mostly crustaceans (82% based on index of relative importance – IRI), followed by molluscs (11% IRI), and smaller quantities of annelids, and teleosts. The dominant crustaceans were a variety of crabs, with Majid and Cancrid occurring most frequently, and Portunid and Pagurid crabs also common. Changes in the diet with ontogeny were observed, with annelids, shrimp, and molluscs (primarily razor clams), occurring more frequently in stomachs of younger sharks. Larger smooth dogfish consumed larger prey and had a more diverse diet that included several teleost species. For sandbar sharks, 441 of 822 (53.7%) stomachs examined contained prey items. The mean quantity of food present in stomachs of sandbar sharks represented 0.51%BW. The diet of sandbar sharks was dominated by teleosts (78% IRI), followed by crabs (22% IRI). The teleost component of the sandbar shark diet contained many benthic, but few pelagic species. This study represents a portion of a project on the feeding ecology of these sharks in Delaware Bay, which will include measures of gastric evacuation and estimates of daily ration for these two species.
School of Biology, University of St Andrews, Bute Medical Buildings, St Andrews, Fife, KY16 9TS, UK
An extremely tolerant shark: Osmoregulation in the bull shark, Carcharhinus leucas
The bull shark, Carcharhinus leucas, is a true champion of salinity tolerance. It can survive in water ranging from 0 to 53 ppt by precisely controlling the composition of its body fluids. This is achieved by the expression, function and coordination of several ion transporters and channels including the Na, K-ATPase. Bull shark Na, K-ATPase alpha and beta subunit isoforms have been amplified, cloned and sequenced. Northern blotting has been used to quantify messenger RNA expression in the rectal gland, gill, kidney and intestine of both FW- and SW-acclimated sharks. Using antibodies raised to the known sequences of both subunits, protein expression of Na, K-ATPase alpha and beta subunits have been compared in the gill, kidney and intestine. In addition, immunohistochemistry has been used to show the distribution of Na, K-ATPase within the osmoregulatory tissues.
Laboratorio de Bases Biologicas, ESCA,Av. Carvalho Leal, 1777, Cachoeirinha, CEP 69065-001, Manaus, AM, Brazil
Freshwater stingrays fisheries (Chondrichthyes:Potamotrygonidae) at black and clear water river systems in the Brazilian Amazon
Potamotrygonids are elasmobranchs that exhibit the same complexity of life cycle as marine elasmobranchs. Freshwater stingrays presently are not among the main target species for the ornamental fish industry, and until recently, neither for the commercial fishery fleet in the Brazilian Amazon region. In the last two years this picture is changing and at least frozen meat of two species of freshwater stingrays Paratrygon aiereba and Potamotrygon motoro has become common in some specialized fish market in Amazonas and Pará State. In both ornamental and commercial fisheries, fishing trips in two different rivers systems (Rio Tapajós Basin and Rio Negro Basin) were conducted in collaboration with local fishermen during the fishing season to obtain capture and effort data. Potamotrygon motoro is the only species common in both fisheries activities. CPUE of this species to ornamental fishing at Rio Negro Basin (black water river system) has not been decline in the last 06 years. The CPUE has been around 16,36 individuals/fishermen/year (s.e ± 5, 3). In the last two years in Rio Negro basin, the rising of fishing effort to artisanal fisheries for food purpose using hook and line is causing a decline of individuals of high classes of disc width from 70 cm to 65,0 cm. The stingray in this kind of fishing is mutilated and discarded. At Rio Tapajós Basin, P. motoro is being fishing as target species to artisanal fisheries for food purpose using hook and line. The fleet is new and probably will grow in the future years, because the traditional stocks of teleosts fishes are collapsing in the area.
(AMM) NOAA Corps., National Marine Fisheries Service, Southeast Fisheries Science Center, 3500 Delwood Beach Road, Panama City, FL 32408, USA; (JKC) National Marine Fisheries Service, Southeast Fisheries Science Center, 3500 Delwood Beach Road, Panama City, FL 32408, USA; (JAN) Coastal Fisheries Institute and Dept. of Oceanography & Coastal Sciences, Louisiana State University, Baton Rouge, LA 70803,USA
A revised age and growth model for blacknose shark from the eastern Gulf of Mexico using x-ray radiography
Underestimates of age can seriously bias any resulting demographic or stock assessment models. In a previous study on blacknose shark, Carcharhinus acronotus, in the eastern Gulf of Mexico, elucidation of bands using thin sections of vertebrae resulting in poor readability and the most successful technique was to count bands on vertebrae half sections. The utilization of half sections can be problematic because of the difficulty in discerning bands on the edge. Consequently, the oldest aged shark from that study was 4.5+ years although tag-recapture data indicated that sharks could be much older. To develop more accurate age estimates, we reexamined the original samples using x-ray radiography and developed a revised age and growth model for blacknose shark in the eastern Gulf of Mexico. Estimates of the von Bertalanffy growth model using revised counts are Linf=1360 mm fork length, k =0.10/yr, and to = -3.22 yr for females and Linf=1053 mm fork length, k = 0.22/yr, and to = -2.04 yr for males. These results were significantly different from the previous estimates. Moreover, the oldest aged sharks are 11.5+ and 9.5+ years for females and males, respectively.
Moss Landing Marine Laboratories, Moss Landing, CA 95039-9647, USA
A review of age and growth, reproductive biology, and demography of the white shark, Carcharodon carcharias
The von Bertalanffy growth function (VBGF) is given by L(t) = Loo – (Loo – Lo) exp (-kt), where Lo is mean size at birth, Loo is mean maximum size, and k is a rate constant with units of reciprocal time that is best interpreted in terms of longevity or number of half-lives (ln2/k). The time (t) it takes to reach the fraction x of Loo is given by t = 1/k ln[(Loo-Lo)/Loo(1-x)]. If we choose x = 0.95 and Lo = 0.2Loo, then longevity is given by 2.77/k = 4.0 ln2/k. The value of L(t) has reached 95% of Loo in four half-lives. Growth functions for three populations of white shark from California, South Africa, and Australia will be reviewed and compared. A pregnant white shark was caught on 13 October 1997 in a set-net off Baisolane, Taiwan with 8 embryos of TL between 0.5 and 0. 6 m. Time of capture and length of embryos fit an existing but tentative growth curve that predicts a gestation time of around 15-18 months. Uterine width data of pregnant white shark suggest that female maturity is around 5 m TL and 15 yr. Matrix population models of white shark will be reviewed and an integrodifference equation model explored.
Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA
A new seawater facility for experimental research on large elasmobranchs and other marine species
Mote Marine Laboratory’s Center for Shark Research recently completed construction of a new research facility dedicated to the experimental study of large elasmobranchs and other marine species. This facility is designed to serve the needs of residential and visiting researchers, including collaborating scientists and students. The facility includes two large, oval-shaped tanks, one 9 m x 17 m x 2 m with 280,000 L capacity and the other 6 m x 12 m x 2 m with 152,000 L capacity. Both tanks are equipped with observation windows, access platform, independent filtration and heater/chiller units and an overhead web-accessible video system for experimental observation is planned. Four smaller round tanks (2 m and 2.5 m) with independent life support systems provide space for smaller elasmobranchs. Capital improvements to seawater supply and treatment systems guarantee availability of high quality seawater, especially during periodic red tide events. These improvements include two 15hp seawater pumps, new pipelines, improved storage tank volume and filtration/sterilization systems providing 1,520,000 L of raw seawater daily for open loop operations and 380,000 L of sterilized seawater storage for closed loop operations. The facility has been designed and constructed to support many types of elasmobranch research including physiological, behavioral and environmental studies and technology development. Since the facility’s completion, large specimens of four shark species (Sphyrna mokarran, Carcharhinus limbatus, C. leucas and C. plumbeus) have been successfully maintained in captivity. Currently, graduate students are conducting research on feeding mechanisms and morphology of the great hammerhead shark using the facility, and studies on elasmobranch electroreception, orientation and navigation are planned. Applications to use this new research facility are encouraged from scientific colleagues, graduate students, undergraduate student interns, and educators. Please contact Robert Hueter (email@example.com or 941-388-4441) at the Center for Shark Research, Mote Marine Laboratory to submit a research proposal.
(PJM, DRH, DL, KRM, MPM, LBW) University of South Florida, Dept. Biology, Tampa, FL 33620, USA; (REH) Mote Marine Laboratory, 1600 Thompson Parkway, Sarasota, FL 34236, USA; (APW) US Fish and Wildlife Service, 4001 N. Wilson Way, Stockton, CA 95206, USA
Suction performance and feeding biology of the nurse shark Ginglymostoma cirratum
To investigate the relationship between suction performance, morphology and prey capture in the obligate suction feeding nurse shark Ginglymostoma cirratum, pressure recordings were taken both internally and externally on laboratory and field- tested sharks. Food capture, which is invariably by suction, is relatively stereotyped, rapid, and explosive, generating the lowest sub-ambient suction pressures (-110 kPA) recorded for any aquatic vertebrate. Similar to other suction feeding fishes, the duration of buccal expansion, which occurs in approximately 32-56 msec, is inversely proportional to sub-ambient suction pressure measured at the oral aperture. The suction pressure is on average -7 kPa greater at the mouth than within the buccopharyngeal cavity as expected due to the restricted oral aperture. Buccopharyngeal pressure starts to decline 33 msec before the mandible starts to depress, and peak internal sub-ambient pressure coincides with peak mandibular depression. The rate of buccal and pharyngeal expansion appears to be the primary determinant of the magnitude of sub-ambient suction pressure. Upper jaw protrusion, which reaches peak anteroventral excursion during the compressive phase of the bite and is predominantly confined within the buccal cavity, has no apparent function during prey capture, other than to grasp large prey. Due to the rapidly diminishing influence of suction in front of the mouth, the nurse shark must closely approach its prey to entrain it within the water being sucked into the mouth. We hypothesize that the specialized morphology and suction performance of the nurse shark permits prey capture by stalking, ambushing, and hunting by expectation within reef crevices, particularly at night when it can closely approach unsuspecting prey.
(LJN, NEK) NOAA/NMFS, 28 Tarzwell Dr., Narragansett, RI 02882, USA; (DA, GMC, HM) Moss Landings Marine Labs. 8272 Moss Landing Rd., Moss Landing, CA 95039, USA; (SW) Natal Sharks Board, Private Bag 2, Umhlanga Rocks, 4320, South Africa
Validated age estimates for the shortfin mako, Isurus oxyrinchus, in the North Atlantic Ocean
Age and growth estimates for Isurus oxyrinchus derived from vertebral centra of 258 specimens (118 males, 140 females), ranging in size from 64 to 340 cm fork length (FL) were compared with data from 22 tag-recaptured individuals (74-193 cm FL) and length-frequency data from 1,822 individuals (1,035 males, 787 females; 65-215 cm FL). Annual band pair deposition, confirmed by a concurrent bomb radiocarbon validation study, was used as the basis for band interpretation. Validation was further confirmed with a tetracycline-injected male shortfin mako recaptured after being at liberty off South Africa for one year and aged at 18 years. Growth rates from tag-recapture analysis were higher than those derived from vertebral annuli and were only available from sharks up to 193 cm FL. Modal length- frequency data were used to verify the first four age classes. Growth curves were fitted using both von Bertalanffy and Gompertz methods. The 3-parameter version of the von Bertalanffy growth function produced more reasonable values for males (Linf = 253 cm FL, K = 0.125 yr-1 (estimated longevity = 21 yr), and Lo = 72 cm). The 3-parameter version of the Gompertz growth function produced more reasonable estimates for females (Linf = 366 cm FL, K = 0.087 yr-1 (estimated longevity = 38 yr) and Lo = 88 cm. Males and females were aged to 29 (260 cm FL) and 32 years (335 cm FL), respectively. Both sexes grew similarly to age 11 (207 cm FL, 212 cm FL for males and females, respectively) when growth rates decreased in males and remained constant in females. Age at 50% maturity was estimated at 8 years for males (185 cm FL) and 18 years for females (275 cm FL). The species grows slower, matures later and has a longer life span than previously reported in North Atlantic waters.
Dirac Science Library, Florida State University, Tallahassee, FL 32306-4120, USA
Reconciling phylogenies – Contrasting molecular and morphological phylogenies of sharks
There are significant discrepancies between phylogenetic analyses of modern elasmobranchs founded upon morphological and molecular data. Stratigraphic data (heavily biased toward isolated teeth) are more compatible with the molecular tree, suggesting that the neoselachian fossil record contains a few gaps of relatively short duration. By contrast the morphological trees predict numerous lengthy gaps exist in the fossil record of many modern elasmobranch lineages, and that a major radiation of numerous modern elasmobranch lineages occurred prior to the early Jurassic. I will discuss approaches to character reconciliation between morphological and molecular data sets. This involves identifying use of inappropriate molecular evolutionary models in sequence data and homology mis-specification in morphological data sets.
Coastal Fisheries Institute, Louisiana State University, Baton Rouge, LA 70805, USA
Incorporating variability in size at birth into growth models for elasmobranchs: Does it make a difference?
In order for age models to be considered accurate regarding the growth dynamics of a species, multiple models or various formulations of the same model may be required to determine which most accurately describes the growth of that species. Historically, the von Bertalanffy growth model (VBGM) with a to parameter has been the model applied most to elasmobranchs. More recently, some studies have begun to apply modified versions of the von Bertalanffy growth model. An alternate model introduced by Fabens (1965) reparameterizes the VBGM by removing the to parameter and forcing the model through the Y-intercept (e.g., hypothesized size-at-birth). While this model may be more applicable when there is an inadequate sample of very small individuals, the model still relies on one estimate of size-at-birth when, in reality, size-at-birth varies. To address the issue of variability in size-at-birth, a Monte Carlo simulation was incorporated into the size-at-birth intercept. The details of the methodology will be presented using the bull shark,Carcharhinus leucas, as a case study. Results of the analysis will be discussed for the bull shark, as well as several other species such as the finetooth shark, C. isodon, blacktip shark, C. limbatus, Atlantic sharpnose shark, Rhizoprionodon terraenovae, and the bonnethead shark, Sphyrna tiburo. This study provides the first attempt to incorporate variability at size-at-birth and provide measures of variability around the individual parameter estimates for elasmobranchs. sets.
(CHZN, AJL) University of Hull, Dept. Biological Sciences, Cottingham Road, Hull, HU6 7RX, UK; (DG) The Deep, Hull, HU1 4DP, UK
Captive mating in sand tiger sharks (Carcharias taurus)
Mating of sand tiger sharks (Carcharias taurus) was observed and filmed at the Blue Planet Aquarium, Ellesmere Port, England, in May of 2004. The shark tank where the 5 sand tigers are kept is an irregular polygon approximately 25 meters wide, 36 meters long, averaging 3 meters in depth, and with a maximum depth of 6 meters. The tank holds 2.8 million liters of water with the whole system containing 3.8 million liters. Water is heated to mimic natural conditions with a minimum water temperature of 22°C and a maximum temperature of 26°C. On May 3rd a 240 cm male sand tiger was observed courting a 270 cm female. The male followed the female then nosed her, coming from behind and underneath the female, and placing his snout just below the cloaca. The initial bite was to the right pelvic fin of the female. The pair then spiraled in a clockwise direction for 14 seconds with the female shark trying to bite the male. His grip held and he remained out of her reach so was not bitten. The female then submitted. Still biting her pelvic fin the male slowly swam them both around the tank and worked his grip up to the right pectoral fin. This lasted 1 minute. The female was then turned onto her back as the male inserted his right clasper into her cloaca. The male was also upside down during copulation, which lasted 32 seconds. After the male withdrew, he swam off with his claspers crossed. The female remained in the bottom of the tank for twenty-four minutes before turning herself into an upright position and swimming off. Mating of sand tigers in the wild has not been observed, and to our knowledge this the only time when such behavior has been filmed in captivity.
Hofstra University, Department of Biology, Hempstead, NY 11549, USA
Histological comparison of the retinal structure of deep-water and epipelagic sharks
Morphological characteristics of the retina of a deep-water shark of the order Squaliformes were compared to three epipelagic sharks (one carcharhinoid and two lamnoids) to investigate visual adaptations in elasmobranchs living at different depths. The three epipelagic species (Alopias vulpinus, Isurus oxyrinchus, and Prionace glauca) have well- developed eyes, with retinas composed of both rod and cone photoreceptors in ratios of 13:1, 12:1, and 14:1, respectively, whereas Centrophorus cf. uyato, a mesobenthic species found at depths greater than 400 m, has a retina composed solely of rods. The rod-rich, relatively cone-poor retinas of these four elasmobranchs yield low visual acuity and rather high sensitivity, enabling them to detect an object against contrasting background in dim light. Further histologic investigations into eight different regions of the retinas, four central and four peripheral, exhibited no indication of intraretinal variation within each species in terms of photoreceptor abundance, distribution, outer-segment length, inner-segment length, or width, suggesting that there is no specific area of increased visual acuity or sensitivity in the photoreceptor layer of these species. As expected, interspecific variation in these characteristics was observed between the deep-water squaloid and the three epipelagic sharks, whereas little variation was observed between the ecologically and taxonomically related A. vulpinus and I. oxyrinchus. These variations in retinal structure are discussed in terms of the ecologic and taxonomic relationships of these sharks.
(YPP) Department of Zoology, Hawaii Institute of Marine Biology, University of Hawaii at Manoa, 46-007 Lilipuna Rd., Kaneohe, HI 96744, USA; (CGL) Department of Biological Sciences, California State University Long Beach, 1250 Bellflower Blvd., Long Beach, CA 90840, USA; (KNH) Hawaii Institute of Marine Biology, University of Hawaii at Manoa, 46-007 Lilipuna Rd., Kaneohe, HI 96744, USA
Variations in the response of gastric acid secretion during periods of fasting between shark species
Elasmobranchs are the earliest known vertebrates to develop an acid secreting stomach and also exhibit a variety of foraging modes. Inter-specific differences in the response of gastric acid secretion during periods of fasting are thought to exist amongst elasmobranchs, although the causative factors behind these differences are unknown. We have measured gastric pH continuously, using autonomous pH data-loggers, in free swimming leopard (Triakis semifasciata), nurse (Ginglymostoma cirratum), and blacktip reef sharks (Carcharhinus melanopterus) and found that leopard and blacktip reef sharks continuously secrete gastric acid, while nurse sharks periodically cease acid secretion while fasting. Measurements of acid secretion rates, pepsin levels and a mathematical model of gastric digestion, suggest that maintaining a continuously acidic stomach may decrease digestion time of a subsequent meal by 5-7 hours in leopard sharks. We hypothesize that frequently feeding shark continuously secrete gastric acid as it provides antiseptic conditions, while reducing digestion time of a subsequent meal. Infrequently feeding sharks may periodically shut down acid secretion as an energy conserving mechanisms while fasting.
(KTP,SPN,RDH) University of Plymouth, Dept. Biology, Plymouth, Devon, PL4 8AA, UK; (SHG) Rosenstiel School of Marine and Atmospheric Science, 4600 Rickenbacker Causeway, Miami, FL 33149-1098, USA; (KTP,SPN,SHG) Bimini Biological Field Station, Bimini, Bahamas
Exposure of nursery-bound lemon sharks, Negaprion brevirostris, to dietary non-essential trace metals at Bimini, Bahamas
Dredging and removal of mangroves may result in increased availability of non-essential trace metals (NTMs) to marine food webs. NTMs are not required by sharks and may be toxic at high levels, resulting in reduced growth. Mangrove removal and sediment dredging at North Bimini, Bahamas (25°44’N 79°16’W) since 1999 coincided with reduced growth rates in nursery-bound lemon sharks (Negaprion brevirostris). Subsequently, we investigated arsenic, mercury, nickel, lead and uranium concentrations in sediments (n = 29) and major prey of juvenile lemon sharks (n = 153, 8 families) from the impacted nursery and an unimpacted control nursery at Bimini. All NTM concentrations were higher in sediments from the impacted nursery, with significantly greater levels of arsenic and mercury (Kolmogorov-Smirnov tests, P = 0.01). Concentrations of NTMs in lemon shark prey were similar in both nurseries. Mojarra (Gerreidae) dominate the diet of juvenile lemon sharks at Bimini, and consistently contained some of the highest levels of NTMs. All NTM concentrations increased slightly with mojarra total length, although none were significant. Dietary composition and daily ration estimates were used to predict NTM dietary exposure in lemon sharks. Shark consumption rates and prey size increase with shark length and therefore dietary exposure to NTMs further increases as sharks grow. Dietary exposure to NTMs may contribute to the reduced growth rate observed in juvenile lemon sharks at North Bimini, although further studies are required. The potential release of sequestered metals from North Bimini sediments may result in trophic bioaccumulation of NTMs within this essential fish habitat over the next several years. These baseline sediment and prey metal data can be used to monitor impacts of continued habitat degradation at Bimini on the life history of lemon sharks.
(AP, TF, FS) Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, Gainesville FL 32611, USA
Analysis of variability in vertebral morphology and growth ring counts in two Carcharhinid sharks
This study examined the variability in morphology and growth ring counts of vertebral centra taken from two regions of the vertebral column from two shark species, Carcharhinus plumbeus and C. limbatus. Sets of five adjacent vertebrae were removed from the vertebral column above the branchial region and below the first dorsal fin. Medial lateral breadth, caudal-cranial length, and dorso-ventral heights were measured for each vertebra. Additionally, a subset of vertebrae was sectioned and growth rings were counted. Intra- and inter-regional differences in morphology and growth ring counts were determined using multiple regression analysis.
(ANP FFS) Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, USA; (JJG) Elasmobranch Physiology and Environmental Biology Program, Center for Shark Research, Mote Marine Laboratory, Sarasota, FL 34236, USA
Morphological changes in the clasper gland of the Atlantic Stingray, Dasyatis sabina, associated with the seasonal reproductive cycle
The clasper gland of the Atlantic stingray, Dasyatis sabina, was examined over a one-year period, covering an entire reproductive cycle. Changes in clasper gland tissue architecture, fluid production, and cell proliferation were assessed. No changes in tissue architecture were observed. Evidence of cell proliferation in the gland epithelium was not detected using immunocytochemistry for Proliferating Cell Nuclear Antigen, a cellular marker of mitosis. Epithelial cells were not observed to undergo mitosis, and cell membranes remained intact. The lack of structural changes and epithelial cell proliferation supports the proposed merocrinal mode of fluid secretion. Rays captured in non-breeding months had clasper glands that exhibited tubules with reduced lumens. In contrast, rays caught during the breeding season had clasper gland tubules with enlarged lumens. Clasper gland fluid production was quantified through measurements of the fluid area and tubule area calculated from digital images. Clasper gland fluid production was significantly higher during the mating period than during months not associated with copulatory activity. These data support the notion that the clasper gland is involved in stingray copulatory activity. This study adds to the paucity of literature focused on this poorly understood component of reproduction in skates and rays.
Ecology and Evolutionary Biology, University of California, Irvine, 321 Steinhaus Hall, Irvine, CA 92697-2525, USA
A hole in the head: Spiracle morphology and importance during exercise
Spiracles are vestigial first gill slits bringing seawater through a narrow passage from the dorsal body wall into the oropharynx. Several proposed hypotheses explain the function of spiracles : 1. Spiracles are presumed to function in ventilation at rest and while feeding. 2. Spiracles may function in O2 exchange supplying oxygen to the brain and eye. 3. The spiracular organ may be part of the lateral line system and serve as proprioceptors monitoring the position of the hyomandibula. A fourth possibility is that current spiracle distribution is due to phylogenetic relationships. In this study, we examined hypotheses 1 and 4. We looked at the effect of exercise on the rate of buccal and spiracular ventilation in the spiny dogfish, Squalus acanthias. We exercised dogfish in a racetrack flume and measured spiracular ventilation and buccal ventilation. Based on previous data, rate of buccal ventilation and spiracle opening were expected to exhibit a 1:1 relationship at rest and increase with swimming velocity. Buccal ventilation rate and spiracle opening both increased with swimming velocity (F1,144=15.755, p<0.001 and F1,73=106.47, p<0.001, respectively) and the ratio of spiracle movement to buccal ventilation rate did not change with speed (p= 0.172). This coupling suggests both spiracular and buccal ventilation are important to animals at rest and while swimming at the moderate speeds. However, spiracular ventilation may be less important in extremely fast swimming. We examined spiracle morphology in 15 familes in 7 order of cartilaginous fishes. Spiracles are found in all batoids and many basal sharks, but are very reduced or absent in the larger, fast-swimming sharks (e.g., carcharhinids, lamnids). Phylogeny is a strong predictor of spiracle morphology, and our data suggest sedentary/benthic sharks have ovoid rather than circular spiracles.
Fisheries Department,Virginia Institute of Marine Science, College of William and Mary, PO Box 1346, Gloucester Point, VA 23062, USA
Detection of polyandry and reproductive periodicity in the sandbar shark,Carcharhinus plumbeus
Understanding aspects of life history, such as lifetime fecundity and individual reproductive success, are critical to effective management of exploited species. Sandbar sharks,Carcharhinus plumbeus, are a major component of the directed shark fishery in the western North Atlantic. Females are thought to mate with multiple males in large aggregations off Florida before returning to specific nursery grounds every two years for pupping. These traits may make the species particularly susceptible to localized stock depletion and loss of genetic variation. As part of a larger study examining the population condition of C. plumbeus in the western North Atlantic and gene flow among populations, I set out to investigate philopatry and polyandry while determining reproductive periodicity in females utilizing the Virginia eastern shore lagoons and lower Chesapeake Bay as nursery grounds. Seven novel polymorphic microsatellite markers allowed for the resolution of familial relationships among individuals sampled in the summers of 2003 and 2004. Kin groups of three or more individuals across cohorts were taken as evidence of philopatric behavior in female sharks. Periodicity was then inferred by assessing the year of birth for all individuals placed within a given kin group through size at age relationships. Polyandrous mating was confirmed by examining genotypes at each locus across individual litters. Detection of more than four parental alleles at two or more loci within a litter was taken as evidence of multiple sires. Multilocus genotypes of a mother and her progeny were then used to determine the minimum number of fathers per litter. Independent methods of assessing paternal contribution were compared and manual inspection of genotype arrays ensured that no full sibling group contained more then four alleles per locus. Results are discussed in terms of management concerns and evolutionary significance.
(BCP) Sarasota High School, 1000 South School Ave., Sarasota, FL 34237, USA; (KBR, JG, CAL) Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA
Analysis of the antibiotic properties of the epidermal mucus of the Atlantic stingray, Dasyatis sabina, conferred by associated bacterial symbionts
To survive in contaminated environments and in microflora-rich seas, estuaries, and riverine systems, elasmobranch fishes have had to evolve efficient host defense mechanisms. Although the capacity of mucus to act as mechanical protection, hydrodynamic lubrication, an anti-parasitic agent, and in osmotic regulation is well established, its potential as a source of novel antibiotic compounds is virtually unexplored. To investigate the role of epidermal mucus in protection against environmental pathogens, samples of mucus from three individuals from a freshwater population of Atlantic stingray, Dasyatis sabina, were obtained and antibiotic properties of mucus-associated bacterial symbionts were examined. This was accomplished through the culture of bacterial symbionts to allow antibiotic producers to effuse their antibiotics. A set of tester strain bacteria were then grown on top of the first cultures, and four zones of inhibition were observed. Growth inhibition was shown to be strongest against methicillin-sensitive Staphylococcus aureus ATCC 43300 andEnterococcus faecalis ATCC 10471. Sixteen symbionts believed to be unique to freshwater Atlantic stingray were selected for identification. Three of these are believed to produce antibiotics. DNA extractions and PCR amplifications of 16S rRNA genes were successful on bacterial symbionts. Phylogentetic placement of bacterial species by means of GenBank BLAST searches against known 16S rRNA genes is currently on going. Results of preliminary searches show the presence of bacteria belonging to genera Shewanella, Flectobacillus, and Staphylococcus.
(NQ,FL,PAR,AMS) Centro de Investigação em Biodiversidade e Recursos Genéticos, Campus Agrário de Vairão, Rua Padre Armando Quintas, 4485-668 Vairão, Portugal; (AM) Universidade de Lisboa, Faculdade de Ciências, Instituto de Oceanografia, Campo Grande, 1749-016 Lisboa, Portugal; (JPC) Oceanário de Lisboa, SA, Esplanada D. Carlos I – Doca dos Olivais, 1990-005 Lisboa, Portugal
Growth and reproduction of Centroscymnus coelolepis, Centrophorus squamosusand Prionace glauca off the Portuguese coast
In March 2003 a monitoring program was implemented on the four main Portuguese landing docks, aiming at obtaining growth and reproduction data on the most frequently landed benthic (Centroscymnus coelolepis and Centrophorus squamosus) and pelagic (Prionace glauca) shark species. While length-frequency analyses failed to produce a good estimate of age and growth for benthic species due to lack of smaller individuals, growth parameters for P. glauca were estimated as: K=0.11, Linf=238.29cm (for females) and K=0.18, Linf=221.60cm (for males). C. squamosus males are sexually active throughout the year and maturation occurs between 96 and 105cm total length; C. coelolepis male maturation occurs around 85-90cm TL. A summer breeding season for P. glauca is proposed for the north-east Atlantic, with males maturating at 198cm fork length. These species have a late maturation and 95% of the landed sharks were immature.
University of Rhode Island, Dept. Biological Sciences, Kingston, RI 02881, USA
Dental biomechanics in the Whitespotted Bamboo Shark (Chiloscyllium plagiosum): A novel mechanism for varying tooth function
Whitespotted bamboo sharks (Chiloscyllium plagiosum) feed upon soft prey, fishes and squid, and possess the characteristic clutching type dentition that is well suited for grasping and holding such prey. In contrast, they also feed upon hard prey, such as crabs, repeatedly crushing and breaking them into several pieces prior to swallowing. The ability to process hard prey is not typically associated with clutching-type dentitions. Tooth mechanics during capture and processing of these contrasting prey types (hard and soft bodied) requiring functionally different tooth morphologies is presented in C. plagiosum based on anatomical dissection and manual manipulation of teeth and associated tissues. Teeth of C. plagiosumare loosely attached to the jaws allowing movement in both sagittal and frontal planes; a feature noted in many other species of elasmobranchs, including carcharhinid sharks and white sharks, Carcharodon carcharias. During prey capture, the spike-like tooth cusps are used for piercing the flesh of captured soft prey, thereby preventing escape. Tension generated in the dental ligament during jaw protrusion and adduction may counter the flexible tooth attachment and fix the teeth in an erect position; facilitating the puncture of soft prey. Alternatively, when feeding on prey harder than the teeth can pierce, the teeth passively fold inward towards the oral cavity (depress) such that the broad flat labial faces of the teeth are nearly parallel to the surface of the jaws and are used as a crushing surface. Movement into the depressed position increases the tooth surface area contacting prey and decreases the total stress applied to the tooth; therefore, decreasing the risk of structural failure. This mechanism suggests that flexible tooth attachment may be a functionally beneficial adaptation in C. plagiosum that allows for an increase in dietary breadth, and is not merely a by-product of rapid tooth replacement.
(EAR, DMS) Dynamac Corporation, Mail Code: Dyn-2, Kennedy Space Center, FL 32899, USA; (DHA) Florida Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute, 1220 Prospect St., Suite 285, Melbourne, FL 32901, USA
The discovery of an important winter nursery for the lemon shark, Negaprion brevirostris, at Cape Canaveral, Florida
The lemon shark, Negaprion brevirostris, is a large coastal carcharhinid with tropical affinities whose early life history has been extensively studied. Along the east coast of North America, known high-value nurseries for this species consist of quiescent lagoons and shallows of south Florida and the Bahamas. Recently, a sizeable population of juvenile lemon sharks has been observed along the Atlantic beaches of Cape Canaveral on the central east coast of Florida. These juveniles aggregate within relatively sheltered longshore troughs along an otherwise high-energy coastline, a behavior that facilitates both visual counts and collection. Biweekly visual surveys along a fixed nine kilometer beach transect have demonstrated that lemon sharks are present in the littoral zone year-round but are most common (in groups occasionally exceeding 300 animals) from November until April. To date, 160 sharks have been captured using cast nets and hook and line. Sizes ranged from 48 – 149 cm precaudal length, with estimated ages of 0.5 to 8.7 years. Limited tag returns demonstrate that a portion of this population is migratory, traveling as far as North Carolina (645 km). The local conditions that facilitate such large aggregations are unknown but Cape Canaveral is considered a climactic transition zone and possesses the most expansive sub-littoral shoals along the Florida east coast. Further, these aggregations are currently protected from harvest within the Kennedy Space Center no-entry security zone. Given the high number of sharks documented and the small area of suitable habitat surveyed to date, Cape Canaveral may eventually be recognized as one of the most important nursery areas for lemon sharks in the United States.
Guy Harvey Research Institute, Oceanographic Center, Nova Southeastern University, 8000 N. Ocean Drive, Dania Beach, FL 33004, USA
Strong population genetic structure in the southern stingray, Dasyatis americana, revealed by mtDNA control region sequences
Although over half of all known elasmobranchs are batoids, with many species exploited and several of conservation concern, little is known of their population genetic structure and intraspecific evolutionary history. We report here an assessment of gene flow among geographic populations of the southern stingray (Dasyatis americana), a large, recreationally important, demersal batoid that ranges from New Jersey, USA and the northern Gulf of Mexico to southern Brazil. Sequence variation in 648bp of the mitochondrial control region was used to infer patterns of gene flow among Florida and Caribbean populations. Out of 229 animals sampled from six locations, 56 haplotypes were identified and AMOVA results revealed high levels of population structure (overall ST=0.47). Gene flow between the Everglades National Park, Florida, and Antigua separated by 2,200km was highly restricted (ST=0.82). Restricted gene flow was also apparent over much shorter geographic distances, as a comparison between two Belizean populations separated by just 120km produced a ST of 0.21. Our results highlight that populations of the southern stingray need to be managed as distinct evolutionary units.
Dept. Zoology, University of Hawaii at Manoa, 2538 McCarthy Mall, Edmondson 152, Honolulu, HI 96822
Functional subunit hypothesis in the Scalloped Hammerhead Shark, Sphyrna lewini
The functional subunit hypothesis proposes that ampullary canals of the elasmobranch electrosensory system are organized into subgroups with distinct spatial projections that serve different biological functions (electric navigation/orientation, prey and conspecific detection, predator avoidance). The prediction of unique projections was tested by measurement of the spatial coordinates of ampullary pores and corresponding subdermal ampullae on the head of a 2.3 m TL scalloped hammerhead shark, Sphyrna lewini, and calculation of each canal vector in 3D space. Ampullary clusters were categorized into four groups: superficial ophthalmic anterior (SOa), superficial ophthalmic posterior (SOp), buccal (BUC) and mandibular (MAN). The dorsal SOp contains the longest canals (3.9-15.2 cm) with horizontal projections almost exclusively at 0° and 135° (ref 0°=rostral, 90°=lateral, 180°=caudal, 270°=medial), and a graded dorsolateral projection up to 60° vertical. Because this subcluster has the longest (and most sensitive) projections in both the vertical and horizontal planes, it is a potential candidate for detection of weak uniform electric fields. In contrast, the ventral SOp has short and long canals that project radially from the cluster. The SOa contains 55% of the canals in the entire array with strong rostral, dorsal and ventral projections. Due to their extreme rostral position and orientation, the SOa and ventral SOp should mediate orientation to dipole fields of prey positioned near the snout. The BUC cluster at the lateral edge of the cephalofoil contains dorsal and ventral canal projections (0.6-9.3 cm) that show a continuous rotation from 20°-270°. This arrangement may guide turning behavior towards dipole fields that originate from prey or conspecifics. These results are consistent with predictions of the functional subunit hypothesis and await behavioral and physiological confirmation.
(AR-V) University of Nebraska, Lincoln, Dept. Biological Sciences, Manter Hall 314, Lincoln, NE 68588-0118, USA; (AAP) Universidad Nacional de Colombia, Bogota, Colombia; (AAP, ODS) Instituto de Investigaciones Marinas y Costeras, INVEMAR, Cerro de Punta Betin, Santa Marta, Colombia
A new born Whale Shark (Smith, 1828) from the Golfo de Morrosquillo, Colombia
An offspring of whale shark, with a few hours born was collected in the Golfo de Morrosquillo, Colombia. This individual is the smallest new born specimen recorded so far: 53 cm total length. The previous record was from 300 fetal specimens, ranging in length from 42 to 63 cm in 1995, in a female that was harpooned off the eastern coast of Taiwan. This finding proves, finally, the ovoviviparity of whale shark. The catch was accidentally made during the dry season (January-May) of 2002, by fishermen with a gill net in the Tinajones mouth of the Sinũ River, in the Colombian Caribbean (75°55’26″W, 9°27’03’N). The sample was deposited in the collection of the Natural Marine History Museum of Colombia (INVPEC 3664). The whale shark in some parts of the world is well protected, while in some areas is intensively hunted for its fins and meat. It is listed as “Vulnerable” by the International Union for Conservation of Nature and Natural Resources (IUCN). This discovery opens a new window about the possibility of the southern waters of the Caribbean being a birthing area during the north summer months.
Moss Landing Marine Laboratories, Pacific Shark Research Center, 8272 Moss Landing Rd., Moss Landing, CA 95039, USA
Food habits of the Longnose Skate, Raja rhina (Jordan and Gilbert, 1880), in central California waters
The Longnose Skate, Raja rhina, is one of the most important incidental species landed in central and northern California demersal fisheries. However, life history information is extremely limited for this species and aspects of its diet and feeding habits are unknown. Feeding ecology studies can provide researchers with important insights towards understanding potential fishery impacts on marine systems. The primary objective of this study was to analyze the feeding ecology of R. rhina off the coast of central California. Specimens of R. rhina were collected between September 2002 and August 2003 from fisheries-independent trawl surveys conducted by the National Marine Fisheries Service, Santa Cruz Lab (NMFS-SCL). Of 1,193 longnose skates caught, 527 were female and 666 were male. To date, 116 R. rhina stomach samples have been processed, and all prey items identified to lowest possible taxa. For every stomach, the percentage of each prey item by number (%N) and weight (%W) were calculated and averaged to obtain a mean value. These measures were combined with the overall percent frequency occurrence (%FO) to determine the Index of Relative Importance (IRI), represented as %IRI. Preliminary results indicate that the five most important prey items are Neocrangon resima (31.7% IRI), Octopus rubescens (11.6% IRI), unidentified euphausiids (11.4% IRI), unidentified teleosts (10.7% IRI), and unidentified shrimp (9.6% IRI). Raja rhina diet will be further analyzed through comparison of the following intraspecific variables: gender (male/female), depth (shelf/slope), and size class (<600 mm/>600 mm).
(JGR, JAM) Virginia Institute of Marine Science, PO Box 1346, Gloucester Point, VA 23062, USA; (RDG, KNH) Hawaii Institute of Marine Biology, University of Hawaii PO Box 1346, Kaneohe, HI 96744, USA
Age and growth of the sandbar shark, Carcharhinus plumbeus, in Hawaii
Age and growth of the sandbar shark, Carcharhinus plumbeus, in Hawaiian waters were investigated by examining annuli deposited in the vertebral centra from wild animals and mark-recapture methhods. Previous research has suggested rapid growth rates not typically associated with populations of sandbar sharks throughout the world. Previous researchers estimated von Bertalanffy growth estimates of K=0.37 and Linf=149 for females and K=0.37 and Linf=139 for males. These growth estimates were obtained from captive sharks and may not be representative of growth rates exhibited by the wild population. Preliminary results portray much lower von Bertalanffy growth parameter estimates. Estimates for both sexes combined were: Linf=148, K=0.11, and t0= -3.67. Available tag-recapture data support these estimates.
CICESE, Dept. Biological Oceanogrphy, Ensenada, BC, 22860, Mexico
Genetic structure of batoid fish populations from the Gulf of California and the Pacific Baja California coasts
Batoid fishes play an important roles in the population control of the other marine species; as links in the flow of energy and matter of the marine ecosystem; and as fishing resources in the coasts of the Mexican Pacific. The Pacific coast of Baja California and the Gulf of California harbor a rich and diverse assemblage of batoid fauna, because of its recent and geologically active history during the last 6 million years, this region is of particular interest to study the effect of dispersal and viacariant events and possible processes of incipient speciation in marine and terrestrial biotas. The aim of this work is to examine the relationship between the levels of diversity and genetic structure with the mobility and fecundity in five species of batoid fishes (Myliobatis californica, Rhinobatos productus, Rhinoptera steindachneri, Narcine entemedor and Gymnura marmorata) collected from the Gulf of California and the Pacific Coast of Baja California. PCR- RFLPs of the mitochondrial NADH2 gene revealed variable levels of haplotype and nucleotide diversities ranging from 0 to 0.51 and 0 to 3.41%, respectively. No relationship was found between levels of fecundity and genetic diversity of the species. The degree of differentiation and genetic isolation between populations assessed with AMOVA, varied from none to extremely high levels (0 < ST < 0.94). There was no relation between species mobility and levels of the genetic structure. No general phylogeographic concordance was found between Gulf and Pacific populations but at least two species showed significant Pacific/Gulf differentiation.
(CS) Hofstra University, Department of Biology, Hempstead, NY 11549, USA; (CW) University of Rhode Island, Biologicical Sciences Department, 100 Flagg Road, Kingston, RI 02881, USA
The effects of suction generation on prey capture in bamboo sharks
Suction feeding is the most common means of prey capture in fishes. In contrast to the large body of literature on suction feeding in teleosts, sharks have received little attention. No studies have yet explored how suction pressures generated in the mouth cavity during inflow of water translate to pressure changes in front of the mouth at the position of the prey. Furthermore, we have no idea of how predator size affects this relationship. Whitespotted bamboo sharks, Chiloscyllium plagiosum, are strong suction feeders and feed readily while resting on the substrate. Suction pressure at the position of the prey was recorded at specific locations in front of the mouth of three different size classes of shark. Predator and prey positions were recorded simultaneously using high speed video. Maximum drop in pressure at the prey was achieved quickly during suction feeding and on average was smaller in magnitude than in the mouth cavity. Mean suction pressure attenuates rapidly with distance from the front of the mouth. However, a drop in pressure, and therefore water velocity, is still evident at much greater distances than that reported for teleosts using other techniques. The magnitude and duration of suction pressure scales positively with predator size. Interestingly, the mean pressures generated at the prey do not vary significantly when the pressure transducer is positioned in an arc from a line directly in front of the mouth indicating that the water inflow into the mouth is uniform and not anteriorly directed. Thus, the angular position of the prey relative to the front of the mouth will have a minimal impact on feeding success.
University of California, Irvine, Dept. Ecology and Evolutionary Biology, Irvine, CA 92697-2525, USA
Structural properties of calcification in batoid elasmobranch cartilage
As in all elasmobranchs, the cartilage skeleton of batoids functions as a stiff ultrastructure for muscle actuation during swimming. However, elastic cartilage is a suboptimal skeletal material, and must therefore be stiffened for efficient force transmission. Batoid swimming styles range from oscillatory (flapping) to undulatory (wiggling). These different locomotor modes place different stresses on the wing skeleton during motion. Because of this, we might expect that morphological adaptation would occur, maximizing the efficiency of the musculoskeletal swimming apparatus for each particular style. We have found several morphological differences, occurring at many different scales that appear to stiffen the skeleton in areas specific to swimming style. At the smallest scale, the calcification patterns of the individual skeletal elements (radials) of the wing vary between a sheath of calcified plates (crustal calcification) in oscillatory swimmers to dorsal and ventral struts (catenated calcification) in undulatory swimmers. To explore the structural contributions of calcification style to the stiffness of the skeleton, we measured the stiffness of radials and joints from two species of batoids, one oscillator and one undulator. We hypothesized that crustally calcified radials of the oscillator would be stiffer than the catenated radials of the undulator. We further hypothesized that the joints between the radials would be a great deal more flexible than the radials themselves. Preliminary results show that crustal calcification is on average two orders of magnitude stiffer than catenated calcification, while the joints are on average nine orders of magnitude more flexible than the radials. This confirms that nearly all of the sometimes considerable bending of the batoid wing is occurring in the inter-radial joints. It also implies that the skeletons of oscillatory rays may be subjected to much greater stresses than those of the undulatory species.
(JCS) Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, PO Box 117800, Gainesville, FL 32611, USA; (GRP) Florida Marine Research Institute, Florida Fish and Wildlife Conservation Commission, Charlotte Harbor Field Laboratory, 1481 Market Circle, Unit 1, Port Charlotte, FL 33953-3815 and Department of Biological Sciences, Florida Institute of Technology, 150 West University Boulevard, Melbourne, FL 32901-6975, USA
Non-fishery related anthropogenic and natural effects on the smalltooth sawfish (Pristis pectinata) in Florida, with a summary of these effects on sawfishes worldwide
Bycatch mortality in commercial net fisheries was the major reason for the decline of the endangered smalltooth sawfish, Pristis pectinata, in the United States. Although these net fisheries have been reduced or eliminated in some states, including Florida, other anthropogenic factors such as interactions with debris and rostrum removal may slow recovery of the sawfish population. We obtained entanglement, injury, and mortality data on P. pectinata not associated with net fisheries by soliciting information from anyone who encountered this species in Florida. Each informant was asked a series of questions including overall health of the fish, date and location of encounter, and estimated total length. Of the 3,240 encounters reported to us through 2004, 42 indicated an entanglement, injury, or mortality. Direct and indirect anthropogenic effects were most commonly reported (79%). These included individuals damaged by debris such as polyvinyl chloride pipes and elastic bands, caught without their rostra, killed by powerheads, and shot with arrows. Natural effects were less commonly reported (21%). Reports included attacks on P. pectinata by sharks as well as a mortality that coincided with a red tide event. Demand for sawfish parts for use in religious offerings, traditional medicine, and the fin trade have also affected sawfishes in other parts of the world. Sawfishes have been preyed on by sharks, crocodiles and dolphins, and have been trapped in drying water bodies in other parts of the world. Despite recent legislation, human activities remain a threat to P. pectinata in Florida and probably to sawfishes worldwide. Many people are still not aware of the endangered status of this species in the United States, but this can be ameliorated by incorporating education and awareness efforts as part of the management process. This study shows that although natural effects apparently do not present a major threat to sawfish in Florida, they should be monitored. In addition, more research and monitoring is needed to better understand the biology and ecology of P. pectinata, and the recovery obstacles faced by this species.
División Ictiología, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Av. ángel Gallardo 470, (C1405DJR) Buenos Aires, Argentina
Reproductive biology of Mustelus schmitti Springer, 1939 (Triakidae: Carcharhinidae) from Buenos Aires province, Argentina
In the present study the reproductive biology of M. schmitti collected from the commercial bottom trawl fishery operating in Puerto Quequén, Argentina was investigated. The specimens were sampled during 2003-2004 seasonally. The number of sharks collected was 637 (298 males and 339 females). There were 190 pregnant females that contain 1,103 embryos. The size ranged from 419 to 819 mm total length (TL) for males and from 417 to 951 mm TL for females. The relationship of TL and body weight was different between sexes (P<0.05). In contrast, the embryos did not show differences between sexes (P>0.05). The size frequency showed that females attain larger length and weigh than males. Fifty percent (50%) of maturity size showed that males mature at a lower TL (567 mm) than females (598 mm). We found that the left testis reached larger weigh and length than the right one (P<0.01). The average values of the IG and IH per season varied significantly for males and females. The average values of the white and yellow ova per season showed significant differences (P<0.05). The maximum diameter of the left oviducal gland was greater than the right one (P<0.05). At greater TL the females had more embryos per brood (P<0.01) than bigger puppies (P>0.05).
(KIS) University of California, Dept. of Environmental Studies and the Center for Stock Assessment Research, 1156 High Street, Santa Cruz, CA 95064, USA; (BS) University of California, Applied Math and Statistics, Santa Cruz, CA 95064, USA
A Bayesian approach to estimating asymptotic size without age data
The von Bertalanffy growth equation is commonly used in ecology and fisheries management to model individual growth of an organism. Generally, a nonlinear regression is used, with length-at-age data, to recover key life history parameters: Linf (asymptotic size), k (the growth coefficient), and t0 (the time when size is zero). However, age data are often unavailable for many species of interest, which makes the regression impossible. To tackle this problem, we have developed a Bayesian model to find Linf using only length data. We use length and age data for female Blue shark, Prionace glauca, and although we are only using lengths in our model, we use the corresponding age data to perform the traditional regressions. Our method is not specific to Blue shark, but rather it is a general model that can be used with any length data. Preliminary comparisons of our model output and the results of a nonlinear regression using the von Bertalanffy growth equation show similar estimates of Linf. Our work will facilitate more detailed stock assessments of species for which age data are sparse.
(CAS) Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA; (SFJD) Natal Sharks Board, Private Bay 2, Umhlanga Rocks, 4320, South Africa
Population status of 14 shark species caught in the KwaZulu-Natal beach protection program
Shark nets have been set off the beaches of KwaZulu-Natal, South Africa, since 1952 to minimize risk of shark attack. The nets fish in fixed localities 400 m from shore and both directly impact local shark populations and act as fisheries- independent monitoring devices. Reliable catch information at the species level was available for the period 1978-2003. Trends in catch rate and size were used to assess the population status of 14 commonly caught shark species. In addition, a demographic modeling approach was used in conjunction with the catch information to assess the potential impact of the nets. Catch rates of four species (Carcharhinus leucas, C. limbatus, Sphyrna lewini and S. mokarran) showed a significant decline, as did the mean or median length of three species (Carcharhinus amboinensis, C. limbatus and Carcharodon carcharias). The catch rate of Galeocerdo cuvier increased. For most species that showed declining catch rates or median length the potential impact of the shark nets was assessed to be low, suggesting that other sources of catch were responsible for the declining status. The potential impact of the shark nets was assessed to be high for two species (neither of which showed declines in catch rate or median length), because of very low intrinsic rates of population increase.
(GS) Massachusetts Marine Fisheries, Martha’s Vineyard Marine Fisheries Field Station, P.O. Box 68, Vineyard Haven, MA 02568, USA; (JC) Massachusetts Marine Fisheries, New Bedford Office, 838 South Rodney French Blvd., New Bedford, MA 02744, USA; (EL) Massachusetts Marine Fisheries, Annisquam River Marine Fisheries Field Station, 30 Emerson Ave., Gloucester, MA 01930, USA
The occurrence of a Great White Shark, Carcharodon carcharias, in a southern New England tidal estuary
On September 21, 2004, a great white shark, Carcharodon carcharias, entered a shallow southern New England coastal estuary in Naushon Island, Massachusetts. The tidal estuary of approximately 0.03km2 has a maximum depth of 6m and two inlets, a narrow (8m) bridge-covered channel to the north and a broader (35m), yet shallow (<1m), southern outlet. The white shark, an immature female with an estimated total length and weight of 430cm and 770kg, respectively, remained in the estuary for 14 days. During this period, the shark repeatedly traversed the estuary, occasionally swimming into very shallow depths (<1m), yet seemingly unwilling to exit the estuary, regardless of the tide. After close observation of the animal over several days, it became apparent that the shark was not likely to exit the area through either point of egress. Hence, actions were taken to motivate the shark to leave the estuary. First attempts involved the less obtrusive use of methods that appealed to its visual, chemosensory, and electrosensory capabilities, yet the shark demonstrated little to no reaction to a number of stimuli. Ultimately, the shark was herded through the shallow southern channel and into the open water of Vineyard Sound with the combined use of weir netting and water pumps. Although the shark was tagged with a standard NMFS tag and a pop-up archival transmitting tag, the latter shed prematurely. Archived depth data collected by the tag showed that the shark exhibited a marked semi-diurnal preference for deeper depths that correlated closely with tide and currents in the estuary. This behavior may be indicative of an energetic response associated with swimming in a tidal estuary with high current velocities.
Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039, USA br />
Growth of the California skate, Raja inornata: Assessment of multiple ageing structures and somatic growth models
Elasmobranch size-at-age estimates are predominantly derived from vertebral band counts and modeled using a three parameter von Bertalanffy growth function. However, alternative ageing structures and growth models may provide improved descriptions of species’ growth. The objectives of this study were to examine the applicability of non-traditional calcified structures as reliable size-at-age estimators and to describe the somatic growth characteristics of Raja inornata, a nearshore skate species for which no previous life history information has been published. Relationships between ageing structure and specimen sizes were used to assess the assumption that the structures increase proportionally to specimen size. Precision among caudal thorn, neural arch, and vertebral centrum age estimates were evaluated using tests of symmetry and analysis of variance to determine the most suitable structure. The temporal periodicity of band deposition was examined using modified centrum edge and marginal increment ratio analyses as semi-direct methods of validation. Disc width-, total length-, and weight-at-age estimates were fitted to polynomial, two parameter von Bertalanffy, three parameter von Bertalanffy, Gompertz, and Schnute growth functions. Models were developed from female and male size-at-age data separately and combined and analyzed by analysis of residual sums of squares to determine if calculated parameters are equivalent between the sexes. The most appropriate growth model was selected based on parsimony and goodness-of- fit using Akaike’s information criterion and standard errors of model estimates.
(EMS, MMH) SharkDefense LLC, PO Box 2593, Oak Ridge, NJ 07438, USA; (SHG) Bimini Biological Field Station and University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, FL 33149, USA
An improved qualitative method for detecting and isolating shark-repelling semiochemicals
We have developed an improved qualitative method for detecting and isolating shark-repelling semiochemicals utilizing reverse-phase liquid chromatography and gradient elution. The method employs a reverse-phase column and acetic acid gradient with spectral detection range between 240nm to 340nm. Samples are deproteinized using perchloric acid, neutralized with potassium hydroxide, centrifuged, and filtered prior to injection into the column. Two groups of early eluting (less than 6 minutes) and very late eluting (greater than 25 minutes) peaks characterize the compound of interest. Degradation of the semiochemical from heat or inadequate storage is a recurrent problem and is readily evaluated by observing the areas under these characteristic peaks. Compounds which have been shown to loose efficacy in field trials reveal the absence of certain characteristic peaks when using this qualitative method. We used the same method reverse-phase to observe primary and secondary amines in the semiochemical extract using derivatization with w/w ninhydrin, pre-column. Derivatized samples were allowed to develop color for 1 hour prior to injection with detection for secondary amines at 440nm while that for primary amines was at 570nm. Comparison of the spectra for extracts from Carcharodon carcharias, Negaprion brevirostris, Carcharhinus limbatus, Ginglymostoma cirratum, Squalus cubensis, Galeocerdo cuvier, and Dasyatis americana between 200nm to 800nm show absorption commonalities. The greatest absorptions were found in extracts from the head ofC. carcharias. A 500ml sample of head extract from C. carcharias was tested for repellency on six C. perezi and two C. acronatus. Sharks were attracted to the test site using fish heads and chum, and a 500ml seawater control was delivered. The control did not affect feeding behavior. When 500ml of the head extract was presented, C. perezi andC. acronatus displayed aversive behavior within 2 minutes of dosage. Both C. acronatus subjects departed visual range and four of six C. perezi subjects departed visual range. The remaining two C. perezi were disinterested in food for the next 10 minutes.
(EMS, MMH) SharkDefense LLC, PO Box 2593, Oak Ridge, NJ 07438, USA; (SHG) Bimini Biological Field Station and University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, FL 33149, USA
Effects of magnetic fields exceeding 50 Gauss on tonically immobilized sharks
Sharks are well known to detect electric and magnetic fields from the work of Kalmijn, Tricas, Klimley and others yet there is still controversy as to the mechanism of magnetic field detection. To evaluate the potential of strong magnetic fields as a repellent we exposed three species of sharks to rare earth magnets. We observed that magnetic fields exceeding 50 Gauss terminated tonic immobility (TI) in juvenile lemon sharks, Negaprion brevirostris, nearly adult blacktip sharks, Carcharhinus limbatus, and juvenile nurse sharks, Ginglymostoma cirratum. Grade N48 and N50 nickel coated, permanent, neodymium-iron-boride magnets with a residual induction of 1 Tesla (10,000 gauss) were utilized in a series of trials. These magnets were 100 mm diameter cylinders with a 25 mm height. A digital gauss meter was used to measure the strength of the magnetic field relative to the experimental subject. In one series of trials, immobilized sharks were held stationary relative to the magnet’s axial (flat) face and the magnet moved toward the shark. In a second series, tonically immobilized sharks were moved relative to the stationary magnet. In both series, immobilized sharks awakened from tonic immobility at a distance of between 10 and 20 cm from the magnet’s face. Sharks were positioned both axially (nose-first) and laterally (eye-first) to the magnet. Tonically immobilized sharks turned away from the magnet, despite the direction of the approaching magnetic field. In a separate set of trials, two 12 volt DC-powered electromagnets, 75W and 360W with magnetic fields of approximately 2 gauss and 20 gauss respectively, failed to terminate TI even at distances less than 1 cm from the shark. Attempts were made to shield the sharks by blocking the magnetic field using mu-metal and bismuth metal covers. Both 12.5 mm thick folded Mu-metal foil and a bismuth metal block were apparently ineffective at shielding the magnetic field and did not inhibit a shark’s response. We noted that diamagnetic bismuth metal alone will occasionally terminate tonic immobility at a range of 10 cm or less.
(JAS) Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, POB 117800, Gainesville, FL 32611, USA; (SE, JK) University of New Hampshire, Department of Zoology, Spaulding Hall, 46 College Road, Durham, NH 03824, USA; (PCWT) University of New Hampshire, Department of Animal and Nutritional Sciences, Kendall Hall, 129 Main Street, Durham, NH 03834, USA
The reproductive cycle of the smooth skate, Malacoraja senta, in the western Gulf of Maine
The smooth skate (Malacoraja senta) is common to the waters of the western north Atlantic, ranging from the St. Lawrence River south to George’s Bank. To date, very little biological data has been collected for this species, leaving many questions unanswered. Furthermore, recent stock assessments in the Gulf of Maine indicate the biomass of smooth skates has declined below threshold levels mandated by the Sustainable Fisheries Act. Thus, the synergistic lack of biological data and overall population decline has prompted the National Marine Fisheries Service to prohibit the possession of this species in this region. As part of a large study goaled at documenting life history parameters of M. senta, the present study describes and characterizes the reproductive cycle of female and male smooth skates, based on monthly samples taken off the coast of New Hampshire, USA, from May 2001 to April 2002. Gonadosomatic index (GSI), hepatosomatic index (HSI), shell gland weight, follicle size and egg case formation, were assessed for 79 female skates. In general, these parameters remained relatively constant throughout most of the year, with the exception of a transient increase (p<0.05) in GSI in August. Moreover, developing or fully developed egg cases were observed in the uteri of specimens captured in seven out of the twelve sampling months. For males (N=81), histological stages III through VI (SIII-SVI) of spermatogenesis, GSI and HSI were examined. No significant differences were found throughout the year for any parameter. However, the production and maintenance of mature spermatocysts (SVI) were observed within the testes throughout the year. Based on these observations, it appears as though the smooth skate is capable of reproduction year round.
(JS) Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, POB, Gainesville, FL 32611, USA; (JK, SE, HH) University of New Hampshire, Zoology Department, Spaulding Hall, 46 College Road, Durham, NH 03824, USA; (PT) University of New Hampshire,Department of Animal and Nutritional Sciences, Kendall Hall Durham, NH 03824, USA
Determination of age and size at sexual maturity for the thorny skate, Amblyraja radiata, using morphological, histological and steroid hormone analyses
The thorny skate (Amblyraja radiata) is a large species of skate that is endemic to the waters of the western north Atlantic. Current stock assessments in the northeast U.S. indicate the biomass of A. radiata is below threshold levels mandated by the Sustainable Fisheries Act. Due to this circumstance, commercial harvest of this species is now prohibited from this region. In order to gain insight into the life history of this skate from the western Gulf of Maine, age at size was linked to maturity by using criteria from three endpoints; steroid hormone concentrations, gross morphological examination of reproductive tracts and histological examination of spermatogenesis. Age bias plots and the coefficient of variation, from vertebral band counts, suggests that our ageing method represents a non-biased and precise approach to the age assessment of A. radiata. Maturity ogives for males (n=67), predict that 50% maturity occurs at a total length of 875 mm and at 11 years. For females (n=69), maturity ogives predict that 50% maturity occurs at a total length of 865 mm and 11 years of age. Collectively, our results suggest that analyzing a combination of reproductive parameters offers an accurate determination of sexual maturity in the thorny skate. An additional outcome of the present research is that analysis of circulating hormone concentrations (a relatively non-invasive approach, i.e. without sacrificing the skate) provides an accurate means to determine size at sexual maturity.
(APS) University of California, Irvine, CA 92697; (TJK)Shriners Hospital for Children, Tampa, FL, USA
Hot and cold skeletons – the effect of temperature on the properties of cartilage
The chondrichthian skeleton is made of lightly mineralized cartilage. Since the material properties of gels vary with temperature and cartilage is a fiber reinforced gel, we tested whether temperature has an effect on the properties of shark skeletons. The sleeper shark (Somnoisus pacificus) typically lives in cold water of the northern Pacific. Mobula thurstoni inhabits warmer waters of the central pacific. Using a small environmental chamber we performed dynamic compressive tests at four temperatures between 4 and 30 degrees C. Cartilage is stiffer at colder temperatures and sleeper shark cartilage is less stiff than Mobula cartilage at 30 degrees.
Tokai University, School of Marine Science and Technology, Shizuoka, 424-8610, Japan
Comparison between elemental microanalysis and traditional staining methods of growth zones in calcified structures of elasmobranches
We have used mainly their vertebral centra and dorsal spines for ageing elasmobranches. Recently, neural arches and caudal thorns also have been used for the ageing structures. These ageing structures have growth zones composed of opaque and translucent bands. Several methods for enhancing these bands are described by many scientists, namely immersion and impregnation, sectioning and staining, X-radiography, etc. Elements, Ca and P, of growth zones in the centra of some sharks have been analyzed with X-ray spectrometry or electron microprobe. We compared between elemental microanalysis and traditional staining methods of growth zones in calcified structures of elasmobranches. Growth zones of vertebral centra, dorsal spines, neural arches and caudal thorns collected from some elasmobranches were observed alone or by means of sectioning and staining, and X-radiography. These calcified structures were also sectioned, polished and analyzed with electron microprobe (JOEL; JX A-8900R WD/ED Combined Microanalyzer). Fluctuation of Ca and P in the growth zones coincided nearly with the appearance of bands enhanced with the staining methods. The process of making samples for electron microprobe, however, was much time-consuming and specialized. Effective use of elemental microanalysis and staining methods based on data will be discussed.
(JET, GS) Department of Biology, Grice Marine Laboratory, College of Charleston, 205 Fort Johnson Rd., Charleston, SC 29412, USA; (GFU) South Carolina Department of Natural Resources, 217 Fort Johnson Rd. Charleston, SC 29412, USA
Seasonal and spatial patterns of Atlantic Sharpnose Shark (Rhizoprionodon terraenovae) captures in South Carolina coastal waters
Seasonal population trends of Atlantic sharpnose sharks (Rhizoprionodon terraenovae) were analyzed from 4684 specimens collected by the South Carolina Department of Natural Resources from coastal waters surrounding the greater Charleston area between March 1998 through December 2002. Specimens were collected using longlines, gillnets, and hook and line method. Preliminary analyses of the data show strong seasonal fidelity of adults and pups to certain locations. Pups were most abundant within estuaries during the spring and summer months, and adults were most commonly captured in nearshore oceanic waters during the spring, summer, and fall. Males were more abundant than female adult sharks, indicating the possible sexual segregation of adult Atlantic sharpnose sharks in certain coastal environments. Data on fishing gear selectivity and geographical GSI spatial analyses of female and male adult and pup spatial distributions will be further examined.
University of Queensland, Center for Marine Studies, St.Lucia, Queensland, 4072, Australia
Prey discrimination and foraging behaviours of the Bluespotted Stingray, Dasyatis kuhlii (Muller and Henle, 1841) in Moreton Bay, Australia
The Bluespotted Stingray, Dasyatis kuhlii is a benthic elasmobranch that is common in Moreton Bay. Prey selection, foraging efficiency and foraging behaviours of 10 rays were observed in controlled laboratory experiments in which a selection of prey species and sizes were offered at depths of either 1 cm or 5 cm in sand. Additional experiments were also conducted to test their ability to discriminate artificial electric fields of different strength and depth, and to determine the relative dominance of olfactory, electrical or mechanical cues in stingray foraging. Bluespotted stingrays discriminate species and size of buried prey (p<0.01, p<0.03 respectively), though depth did not influence prey selection (p>0.05, p>0.05 respectively). Rays often excavated prey species that they did not subsequently consume suggesting that they are not accurately able to discriminate among buried prey. All sizes of their preferred prey were consumed once acquired, although rays were unable to determine prior to excavation if buried prey are too large to consume. Among sensory modalities tested, there was a clear preference for electrical stimuli (p<0.02), although olfaction was also important in prey detection. Rays did not discriminate between electric fields of different strength and depth (p<0.05) indicating that blue spotted maskrays are unable to resolve the interaction between prey depth and prey size. The implications of these finding for the foraging biology of stingrays are considered.
(JTA, TIW, RWD) Zoology Department, The University of Melbourne, Victoria 3052, Australia; (JTA, TIW) PIRVic Centre Queenscliff, Victoria, Australia 3225; (JTA) Instituto Nacional de la Pesca, México
Reproduction of Port Jackson sharks off south-eastern Australia
The Port Jackson shark (Heterodontus portusjacksoni) is a common demersal shark off southern Australian waters. Tagging studies suggest the existence of different populations along the Australian coasts. General information about its reproduction has also been reported, but possible differences in the reproductive parameters of sharks from different areas have never been studied. The aim of the present investigation was to determine the reproductive parameters of the populations off south-eastern Australia. Sex, total length (TL), clasper length and maturity condition were recorded from sharks collected from commercial catches; and used to estimate length at maturity. Ovarian fecundity was recorded and compared to the number of eggs laid by sharks held in captivity. The reproductive cycle was determined based on the proportion of females with completely developed follicles and the size of the follicles through time. Biological data from the 712 Port Jackson dissected sharks indicated that males mature at around 800 mm TL and females between 850 and 1000 mm TL on the east coast of Victoria. This species has an annual reproductive cycle. Ovulation time is strongly correlated with water temperature, starting at the beginning of spring. Females have a long egg laying period (Late August to March) and lay up to 18 eggs per reproductive season. Egg hatching takes place in winter. Differences in the size at maturity were found between males from the east and the west coast of Victoria, suggesting the presence of at least two populations.
Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039, USA
Population structure of thresher sharks (Alopias spp.) based upon mitochondrial DNA control region sequence data
The family Alopiidae is comprised of three species: the pelagic (Alopias pelagicus), bigeye (A. superciliosus), and common (A. vulpinus) thresher sharks. Alopias pelagicus is found only in the Pacific and Indian oceans, while the other two species are distributed worldwide. Despite growing conservation concerns, genetic relatedness among thresher shark populations is poorly known. We examined the population genetic structure of each species using DNA sequences from the mitochondrial control region. Samples of A. pelagicus, A. superciliosus, and A. vulpinus were collected from the East (n = 0, 15, 14) and West (n = 0, 6, 39) coasts of the United States, Gulf of California (n = 23, 1, 0), Clipperton Atoll (n = 3, 0, 0), Ecuador (n = 22, 14, 0), Hawaii (n = 0, 13, 0), Taiwan (n = 5, 11, 5), Indonesia (n = 25, 0, 0), New Caledonia (n = 1, 0, 0), New Zealand (n = 0, 0, 5), South Africa (n = 0, 1, 5), and France (n = 0, 1, 5). Despite their high dispersal potential, our data indicate limited gene flow among thresher shark populations, but geographic patterns of genetic variation differ among species. Gene flow in A. pelagicus is limited across the Pacific Ocean, but is extensive among locations in both the eastern and western Pacific. In A. superciliosus, genetic heterogeneity was detected among Pacific and Atlantic populations, but not among populations spanning the entire Pacific Ocean. Results for A. vulpinus indicate genetic heterogeneity among all sampled populations, both within and between the Atlantic and Pacific oceans. Taken together, our data indicate that intra-specific biological and ecological differences among thresher sharks are sufficient to cause variable patterns of inter- specific genetic population structure. This study also highlights the need for international cooperation in management of thresher shark populations.
(MAT, LJBL) School of Ecology and Environment, Deakin University, PO Box 423, Warrnambool, Victoria, 3280, Australia; (MAT, JDS) CSIRO Marine Research, GPO Box 1538, Hobart, Tasmania, 7001, Australia
A comparison of different methods and structures for age determination of skates in Australian waters
Skates are a common by-catch/by-product of both State and Commonwealth demersal fisheries that operate around Tasmania, Australia. Two large-bodied skates, D. whitleyiand D. gudgeri are harvested for their flesh on the domestic market. In the south-east trawl and non trawl fishery about 55% of D. whitleyi and 22% of D. gudgeri are retained. The total catch of skates is essentially unregulated with very little recorded on a species-specific basis. Little is known of the life history of any of the skates found in southeastern Australia. The vertebrae and caudal thorns of seven skate species were collected from commercial fishers from around Tasmania and examined for ageing readability. Various ageing techniques were trialed on these different structures. Dipturus gudgeri (n=300) andD.whitleyi (n=73) showed the most promising band formations in both structures using two different methods: whole and sectioned vertebrae and whole and sectioned caudal thorns. A strong correlation between caudal thorn length, width, height and the animals total length indicated that caudal thorns continue to grow throughout the animals life. This was also apparent with the vertebral centra. The two largest vertebrae and two least worn caudal thorns from each animal were prepared for ageing. Centra were sectioned longitudinally and the caudal thorn was sectioned both transversally and diagonally to assess the apex of the thorn. Bands present on the surface of the thorn and those in thorn sections were compared with vertebral whole and sectioned counts. Variable differences between the number of bands on/in the caudal thorn and the vertebrae were found. Growth increments derived from whole and sectioned vertebrae were insignificant. Difficulties were found in reading the deeply coned vertebrae of D. gudgeri and counting bands near the edge of whole vertebrae for both species. Consistency was found in surface and internal band counts of caudal thorns.
(CAT) School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, 11120 Glacier HWY, Juneau, AK 99801, USA; (CAT, VFG) School of Aquatic and Fishery Sciences, University of Washington, 1122 NE Boat St, PO Box 355020, Seattle, WA 98105-5020, USA; (PS) Integrative Fish Biology Program, Northwest Fisheries Science Center, 2725 Montlake Blvd East, Seattle, WA 98112, USA; (GB) Washington State Department of Fish and Wildlife, 600 Capitol Way N, Olympia, WA 98501-1091, USA
Reproductive Endocrinology and Estimation of Demographic Parameters of Puget Sound Spiny Dogfish
A one year study was undertaken to investigate reproductive parameters and endocrinology of spiny dogfish (Squalus acanthias) in Puget Sound, WA to aid management of the commercial fishery. Size at maturity, fecundity and reproductive timing were estimated from 416 females and 185 males sampled from a commercial trawl catch. Size at 50% maturity was estimated at 89.9cm for females and 66.6cm for males, fecundity was an average of 6.85. The pupping season was determined by the stage of embryonic development and found to peak in September and October. Serum samples were collected from 203 females and 144 males. Samples were assayed for concentrations of estradiol and progesterone (females), and testosterone (males). The results presented here show that distinct reproductive stages can be identified by the hormone concentrations alone with greatest accuracy at the most critical management stages. Sampling blood from live dogfish is less invasive and costly (both economically and timely) than sacrificing and dissecting dogfish to determine reproductive state, making monitoring the reproductive cycling of a population less of a process for fishery managers.
(FIT, TIW) Department of Primary Industries Victoria, Queenscliff Centre P.O. Box 114 Queenscliff, Victoria. Australia 3225; (FIT, LL, PJ) Deakin University, P.O. Box 423, Warrnambool, Victoria, Australia 3280
Demographic biology of the sparsely-spotted stingaree Urolophus paucimaculatusfrom south eastern Australia
Studies of the reproduction of Urolophus paucimaculatus in south eastern Australia were undertaken at several sites including Port Phillip Bay, Lakes Entrance and Western Bass Strait during August 2002-March 2005. Ovarian follicle development and seasonal embryonic growth indicate a 1-year gestation period in synchrony with a 1-year ovarian cycle. Litter size increases with maternal length with a maximum of six offspring per pregnancy. U. paucimaculatus exhibit aplacental viviparity with trophonemata, the embryos utilize the yolk from the yolk sac early during gestation and histotroph during the later phase of embryonic development. Parturition occurs during September-December. Maximum embryo size is 161 mm TL and 42 g mass. There is no obvious mating season or seasonal trend in hepatic somatic index or gonadosomatic index. For the female population, 50% are mature at 270 mm TL, and for the male population 50% are mature at 278 mm TL. The maternal length where 50% of the population is contributing to the next year recruitment is 358 mm TL.
Mote Marine Laboratory, Center for Shark Research, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA
Cloning the androgen receptor protein in the Bonnethead Shark (Sphyrna tiburo)
Steroid hormones are essential for proper reproductive development in all vertebrates. Androgens are sex steroids secreted by the gonads that regulate virilization, spermatogenesis, and sexual behavior. These physiological actions require the binding of androgen to a specific receptor protein. Androgen receptors (AR) are ligand-activated transcription factors that bind to a specific nucleotide sequence of DNA and positively or negatively regulate transcription. Knowledge of these receptors in elasmobranch fishes, being the oldest living animals that possess an archetypical vertebrate pattern of reproductive endocrinology, may provide insight into the evolution of steroid hormone receptors in general. An understanding of the distribution and levels of expression of the elasmobranch ARs on the cellular and tissue level demonstrates the pattern of responsiveness to the androgenic hormones. In order to assess this distribution using molecular methods, efforts were initiated to clone and sequence a fragment of this gene in the bonnethead shark, Sphyrna tiburo, an elasmobranch species with a well-defined annual reproductive cycle. Degenerate primers were utilized in a nested PCR reaction to amplify a 325-base pair fragment from reverse-transcribed testicular bonnethead RNA. This fragment was ligated into a plasmid vector and transformed into competent E. coli cells. After growing transformants in liquid sub-culture, plasmid DNA was extracted and cut with a restriction endonuclease to confirm the presence of an appropriately sized insert. Sequencing of the plasmid/insert and subsequent analysis by BLASTX confirmed the identity of the insert as AR. This sequence most closely resembled that of an amphibian (Xenopus laevis) and a bird (Gallus gallus). In future, the cloned AR fragment will be used to construct an RNA probe to characterize AR gene expression in this species using in situ hybridization (ISH) and northern blotting techniques which should lead to a greater understanding of the functional role of androgenic hormones in elasmobranchs.
Mote Marine Laboratory, Center for Shark Research, Sarasota, FL 34236, USA
Relative abundance and long-term movement patterns of juvenile blacktip sharks,Carcharhinus limbatus, in three Florida Gulf coastal nursery areas, 1995-2004
The decline in recent decades of many U.S. shark stocks has led to the implementation of management plans with the goal of stock recovery. Because fishery-independent surveys are a valuable source of data to assess stock decline or recovery, the Mote Center for Shark Research initiated surveys in 1995, in three Florida Gulf coast nurseries (Yankeetown, lower Tampa Bay and Pine Island Sound), to estimate the relative abundance of juvenile blacktip sharks, Carcharhinus limbatus, a key species in the U.S. southeast commercial and recreational fishery. Monthly, random stratified sampling by bottom gill net was conducted within two geographically fixed 10 km2 grids for each of the three areas which were selected based upon the consistent blacktip catches observed during previous exploratory studies. All shark catch was identified, sexed, categorized by maturity, measured and weighed, and all live sharks were tagged and released. A total of 970 quantitative gill nets sets were made between 1995 and 2004 resulting in the capture of 8,257 sharks of thirteen species, of which 3,842 were juvenile blacktips. Recaptures have been reported from 149 of the tagged sharks comprising 5 species. First-year blacktips have demonstrated movements of more than 280 nautical miles after leaving their summer nursery grounds. Recapture data further indicates a pattern of sharks returning to their natal nursery areas the following season and in subsequent years. A general linear model was used to standardize the CPUE data. Significant differences in the juvenile blacktip catch were found between years, nursery areas, and between grids within a nursery area. When looking at the blacktip catch rates over the entire 10-year period, there were no apparent trends that would be indicative of population level changes. Possible reasons for this lack of a clear trend as well as other relevant aspects of this dataset will be discussed.
(CJW, CAL) Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA; (ABB, TRS) Department of Animal and Veterinary Sciences, Clemson University, Clemson, SC 29634, USA; (YW) Clemson University Genomics Institute, Clemson University, Clemson, SC 29634, USA
Further characterization of tumor cell growth inhibitory activity in epigonal conditioned medium (ECM) from bonnethead shark, Sphyrna tiburo
Previous work in our laboratory has demonstrated that media conditioned by short-term cultures of bonnethead shark (Sphyrna tiburo) epigonal cells (epigonal conditioned medium, ECM) possessed potent growth inhibitory activity against several tumor cell lines, including human malignant melanoma (A375.S2), murine fibrosarcoma (WEHI 164), breast carcinoma (MCF-7), and Burkitt’s B-cell lymphoma (Daudi). Continued studies have focused on 1) characterization of preferential inhibition of ECM toward malignant versus non-malignant cells, and 2) isolation and purification of bioactive ECM proteins and peptides with increased specific activity. To evaluate the specificity of ECM for malignant cells, a normal/tumor cell line pair, derived from human primary ductal carcinoma (HCC38) and normal peripheral blood cells (HCC38 BL), was used. ECM demonstrated preferential cytotoxicity towards malignant cells, with approximately 2 to 4.5 times more growth inhibition of malignant cells than non-malignant cells. Efforts to purify bioactive compounds included application of crude ECM to Bio-Rex 70 cation exchange chromatography, with bioactivity residing in bound material eluted with 0.8 M NaCl. Further separation of the salt-eluted fraction using AcA 34 molecular exclusion chromatography resulted in protein fractions with approximately three-fold increase in bioactivity over that of crude ECM. Separation of ECM proteins based on hydrophobicity using reverse-phase C18 HPLC resulted in fractions with approximately 10 to 20-fold increase in growth inhibitory activity. Fractions with greatest bioactivity were subjected to in-liquid tryptic digestion, with resulting peptide fractions isolated by reverse-phase HPLC and assayed against human breast carcinoma cell line MDA-MB-435. Two fractions, shown by mass spectrometry to contain at least two unique peptides, demonstrated significant inhibitory activity at concentrations as low as 1.0 ug/ml, representing an approximately 500 to 1000-fold increase in specific activity compared with crude ECM.br />
University of South Florida, Dept. of Biology, 4202 E. Fowler Ave., SCA 110, Tampa, FL 33620, USA
Performance of shark teeth during puncture: implications for the mechanics of cutting
Feeding performance plays an important role in overall fitness. Tooth morphology contributes to feeding performance; however this component has largely been ignored in functional morphological studies of elasmobranch feeding. The goal of this study is to explore the evolution of selachian teeth in a biomechanical and functional context. Here we report the results of preliminary testing of teeth during puncture for nine species of carcharhinid and three species of lamnid sharks. Teeth were driven into prey items at a rate of 400 mm/s using a MTS MiniBionix II universal testing system and force and pressure at initial penetration, maximum force, and work to fracture were analyzed. Results indicate that during unidirectional puncture, teeth with a wider triangular cusp produce more force and pressure than a tooth with a narrow cusp. Narrow anterior teeth of Isurus oxyrinchusrequired an average of 15.03 N of maximum penetration force, while the largest average maximum penetration force (40.35 N) was for an upper anterior tooth of Carcharhinus leucas, occurring after the cross sectional area of the tooth abruptly increases proximal to the distal notch. Results also indicate that serrations play a role in the overall dynamics of performance due to binding of material between individual serrations. As the tooth moves through the material, binding occurs as tooth serrations increase in size towards the base, causing high stresses on the tooth and prey. As the shark engages in head shaking, fibers are broken causing a decrease in stress on the tooth. Notching, seen in the teeth of C. leucas and Galeocerdo cuvier, can be thought of as an extreme serration, providing more tensile stress to the fibers during head shaking. These results have implications for studies of fossil chondrichthyans, where typically tooth morphology is used to predict feeding ecology in the absence of performance data.
Mote Marine Laboratory, Center for Shark Research, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA
Elasmobranchs of Everglades National Park
Few directed studies have been conducted on the elasmobranch fauna of Everglades National Park, so little is known of their importance in this area. Data on elasmobranchs captured during surveys for smalltooth sawfish in Everglades National Park were used to examine species occurrence, distribution and movement patterns. Surveys were conducted utilizing bottom set longlines, gillnets, seine nets and rod and reel from July 2000 to February 2005. A total of 1015 elasmobranchs of 12 species were identified within the Park (Carcharhinus acronotus, C. isodon, C. leucas, C. limbatus, Dasyatis spp.,Galeocerdo cuvier, Ginglymostoma cirratum, Negaprion brevirostris, Pristis pectinata, Rhizoprionodon terraenovae, Sphyrna mokarran and S. tiburo).Carcharhinus leucas (n=302), N. brevirostris (n=239), C. limbatus (n=126) and G. cirratum (n=112) were encountered most frequently. Data from Mote Marine Laboratory’s tag/recapture database showed that 20 C. leucas, three C. limbatus, eight G. cirratum, 16 N. brevirostris and two S. tiburo were tagged and/or recaptured within the park after periods at liberty of 1 to 1099 d. All 16 N. brevirostris were tagged and recaptured within the boundaries of the park (44 to 1061 d at liberty). Carcharhinus leucas, C. limbatus and G. cirratum were tagged or recaptured as far north as Tampa Bay on Florida’s west coast. No recaptures were reported from Florida’s east coast or south of the park boundary. The salinity, temperature, depth and dissolved oxygen data were analyzed to determine any environmental preferences. The distribution, seasonal occurrence and size/frequency distribution of common shark species will be presented.
(CW) University of Rhode Island, Biological Sciences Department, 100 Flagg Road, Kingston, RI 02881, USA; (CS) Department of Biology, 114 Hofstra University, Hempstead, NY 11549, USA
Mechanics of suction generation during feeding in bamboo sharks
Although recent studies have increased our understanding of suction generation during feeding in teleosts, similar studies on elasmobranchs are lacking. The kinematics of selected internal head and branchial structures in bamboo sharks, Chiloscyllium plagiosum, are measured using sonomicrometry to quantify elements that are directly responsible for internal expansion of the orobranchial cavity, and therefore the generation of suction inflow. Simultaneous pressure recordings inside the orobranchial cavity were used to assess pressure flow at strategically important locations during feeding. A compressive preparatory phase occurs prior to the expansive phase in half of the capture events. An anterior to posterior progression of expansion occurs in the gape, hyoid, and pharyngeal cavities during suction feeding. Pressure in the gape and hyoid regions decrease rapidly as the mouth opens and peak subambient pressures are reached at approximately the same time as peak gape. Peak subambient pharyngeal pressure is less extreme and occurs prior to that in the buccal and hyoid cavities. Hyoid depression appears to be a dominant feature of generating suction in sharks. A major advantage of sonomicrometry is continuous quantification of moving structures that are not visible externally or have moved out of camera view. Sonomicrometry reveals that interhyal distance decreases and the hyoid arch is drawn anteriorly during feeding. In contrast to preliminary evidence using videography that shows the onset of upper jaw protrusion following peak gape, sonomicrometry reveals that upper jaw protrusion actually begins much earlier, shortly after the onset of lower jaw depression.
(ATW, SMK) Biological Sciences, Florida Atlantic University, 777 Glades Road, Boca Raton, FL 33431, USA; (JBF, APS) Ecology & Evolution, 321 Steinhaus Hall, University of California, Irvine, CA 92697, USA; (TJK) Shriners Hospital for Children, 12502 North Pine Drive, Tampa, FL 33612, USA
Sexually dimorphic skate snouts
Although sexual dimorphisms in head shape are well documented among teleosts, only a single example of sexually dimorphic head shape is documented in elasmobranch fishes. The rostral cartilages of male bonnethead sharks, Sphyrna tiburo, elongate concomitantly with the clasper cartilages at sexual maturity creating a distinct bulge along the anterior margin of the cephalofoil. To determine if this phenomenon is unique to S. tiburo or widespread among the elasmobranchs, we examined rostral cartilage length and head shape among deep water and coastal skate species (Rajidae) from both the Atlantic and Pacific basins. We sampled individuals of both sexes across a range of sizes. We photographed the dorso-ventrally compressed skates using backlighting to facilitate visualization of the rostral cartilages thus precluding the need to x-ray the heads. Twelve homologous landmarks on the head were digitized and a Procrustes analysis was employed to create a consensus model for each species. A principal components analysis was used to quantify departure of the individuals from the consensus model and test for differences between the sexes. For the little skate, Leucoraja erinacea, we found that head shape among juveniles did not differ significantly between the sexes, whereas adults exhibited highly significant differences. In addition, significant ontogenetic changes in head shape were apparent for both sexes. Rostral cartilage length was significantly greater for females than males; a reversal of the pattern seen in S. tiburo. In contrast, rostral cartilage length did not differ significantly between the sexes in the California ray, Raja inornata. Thus, sexually dimorphic head shape may be widespread within the class Chondrichthyes and close examination of the rostral cartilages of other elasmobranch species may reveal previously overlooked differences.
(BEW) Department of Zoology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria; (IRT) Centre for Marine Studies, University of Queensland, St Lucia QLD 4072, Australia
Electroreception of rhinobatids
Electroreception is a phylogenetically old sensory modality found amongst fishes, amphibians and mammals. Elasmobranchs use their electroreceptive structures, the ampullae of Lorenzini (each consisting of a canal connecting an ampulla with a somatic pore), during foraging, social interactions and orientation in the earth’s magnetic field. In this study, I comprehensively described the electrosensory system of Rhinobatos typus andAptychotrema rostrata, two rhinobatids commonly found on sandy bottoms in shallow coastal habitats of South East Queensland, Australia. The electrosensory system of both species was mapped and ampulla were processed for light and transmission electron microscopy. I found basic pore patterns to be similar for both species, with 85.7% of pores located on the ventral side of the disk in Rhinobatos typus and 80.4% in Aptychotrema rostrata. The highest densities of pores were found ventrally along the rostrum, around the mouth and in the area surrounded by gills, mouth and abdominal lateral line canal. Ampullae of the ventral side of the rostrum possess short canals (7.3 ± 2.8 mm in R. typus and 8.9 ± 3.4 mm in A. rostrata) compared to long canals leading to pores on the pectorals (22.5 ± 7.5 mm in R. typus and 23.4 ± 9.6 mm in A. rostrata). Behavioural studies to identify the intensity of electric fields used in detection of prey are ongoing. Further study of these complex systems is warranted and would help to increase our knowledge of the food sensing abilities of elasmobranchs in general
(JTW, YI) Aichi Medical University, Laboratory of Biology, Nagakute, Aichi, 480-1195, Japan; (MM) Hekinan Seaside Aquarium, 2-3 Hamamachi, Hekinan, Aichi, 447-0853, Japan; (JS) Aichi Medical University, First Department of Physiology, Nagakute, Aichi, 480-1195, Japan
Transient anatomical features of Scyliorhinus torazame embryos
Fertile Scyliorhinus torazame ova require 210 days to complete embryonic development at 14-16 °C. During this time the embryo and egg case continually adapt to each other. Embryos possess transient structures specialized for development within the egg case. In common with other oviparous elasmobranchs, gill filaments and the external yolk sac surface provide surface area for oxygen transfer. Both remain prominent features of embryos until buccal respiration commences. The egg case respiratory slits are opened by the action of the hatching gland 101 days after oviposition. Next, specialized primary scales found in two rows at the dorsal and ventral margin of both sides of the caudal fin erupt. The tip of the caudal fin is an extension of the notochord and forms a concave scoop for water transfer through the egg case by active pumping of the tail. Embryos have been observed to project this tail extension through the hatching terminus of the egg case in the months preceding hatching. The cup-like extension and caudal scales can be observed in embryos after eclosion but are gradually resorbed during the following months. The final specialized embryonic structure to develop are primary scales found in 2 dorsolateral rows along the trunk. These scales erupt before hatching and may be used to aid in escape from the egg case during ecolsion. Ordinary placoid scales do not erupt until after hatching.
(JTW, YI) Aichi Medical University, Laboratory of Biology, Nagakute, Aichi 480-1195, Japan; (MM) Hekinan Seaside Aquarium, 2-3 Hamamachi, Hekinan, Aichi, 447-0853, Japan
Developmental abnormalities in Scyliorhinus torazame
Scyliorhinus torazame is an oviparous elasmobranch found year-round in the western Pacific continental shelf. It is easily maintained in captivity and readily reproduces. A single pair of eggs is laid every 20-30 days and development to hatching requires 210 days at 14-16 °C. Beginning in May, 2004, eggs from 3 females at Hekinan Seaside Aquarium, Aichi, Japan, were collected for an analysis of embryonic development. The percentage of fertile eggs was 75%, 83% and 23% for females 1, 2 and 3 respectively. Fertile ova were monitored daily for developmental progress. Each female had ova that experienced terminal abnormalities during their development. All abnormal embryos except one successfully completed gastrulation. Failure to complete epiboly was a common occurrence and resulted in a ruptured ovum with a contracted blastoderm surrounding the embryo. Most abnormalities were seen in the developing tail and occurred concurrent with vascularization of the yolk sac. One remarkable embryo survived more than 3 months with no blood cells circulating within its blood vascular system despite the presence of a beating heart. The percentage of abnormal embryos observed was 17%, 10% and 33% for females 1, 2 and 3 respectively. The reasons for the observed developmental abnormalities are unknown but several factors may contribute including age of female, interval of last mating, water quality, sperm quality and interbreeding.
Coastal Carolina University, Coastal Marine and Wetland Studies Graduate Program, Conway, SC, 29526, USA
Habitat utilization by multiple coastal shark species in a salt marsh nursery
Southeastern coastal shark species utilize shallow, highly productive nearshore waters, estuaries, and inlets as nursery grounds from early spring to fall. This study examined the temporal and spatial partitioning of multiple shark species within one salt marsh nursery ground in South Carolina and further investigated the effect of creek size and tide on shark occurrence. A total of 74 sharks were caught on 256 demersal longlines from April through October of 2004 in North Inlet Estuary. Seven species were represented: Rhizoprionodon terraenovae, Carcharhinus limbatus, Sphyrna tiburo, Negaprion brevirostris, C. plumbeus, C. acronotus and C. isodon. Longline effort was equal for both high and low tide and large and small creeks (mean width ± SE: 106.7 ± 23.3 m and 35.3 ± 2.3 m, respectively). We observed staggered peaks of abundance for species throughout the sampling season, indicating that shark species in this system exhibit temporal partitioning. The abundance of neonate R. terraenovae in June suggests North Inlet serves as a primary nursery ground for this species. Hierarchical loglinear analysis found the interaction of creek size and tide significantly affected shark occurrence. Further research on factors influencing shark habitat selection is necessary to understand their habitat requirements at all life stages and to apply effective management strategies.
(BGY, MRH) Mote Marine Laboratory, Center for Shark Research, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA; (JKC) National Marine Fisheries Service, Southeast Fisheries Science Center, 3500 Delwood Beach Road, Panama City, FL 32408, USA
Examination of winter grounds for blacktip sharks, Carcharhinus limbatus, in Florida
Nursery areas for neonate and juvenile blacktip sharks (Carcharhinus limbatus) have been well studied along the Gulf coast of Florida, but the location of wintering grounds for this species has yet to be identified. Recapture data from sharks tagged along the central Gulf coast suggest that young blacktip sharks migrate south to or through Florida Bay and the Florida Keys. Similar data from northwest Florida also suggests movement to the south (up to 205 nautical miles) by juvenile sharks during winter months. However, this data is limited and the location of winter grounds in the northern Gulf of Mexico is unknown. To fill these gaps in our knowledge a research project was developed to target young blacktip sharks during winter months to identify potential winter grounds. This project incorporated the aid of local charter fishermen along the panhandle and in Florida Bay and the Florida Keys. Charter fishermen were trained to tag sharks as cooperative partners in the project. From December 2004 through March 2005 blacktip sharks were captured and tagged with conventional tags. In addition, pop-off archival satellite tags were deployed on two larger individuals to determine if they would move into the central or northern Gulf of Mexico during summer months. Winter habitat preference, tag recaptures, and satellite tag results will be presented.
(KEY, JCM) Leigh Marine Laboratory, University of Auckland, P.O. Box 349, Warkworth 1241, New Zealand; (KEY, JCM) University of Auckland, School of Biological Sciences, Private Bag 92019, Auckland, New Zealand
Comparative morphometrics of the elasmobranch brain: Mapping neuromorphology onto behavior and environment
There is widespread variation in both brain size and complexity across the elasmobranch phylogeny. The relative brain weight of a species is dependent upon the enlargement or regression of individual brain structures, some of which can be identified with different sensory modalities and behaviors. We hypothesize that the degree of development of these brain structures is related to the relative development of sensory modalities and behaviors, which can in turn be related to the environment the animal inhabits. A total of 28 species from 16 families were collected from 3 localities in Australasia. Each brain was sectioned and the cross sections scanned using Sigma Scan® digital analysis program to produce weights of the individual brain structures. In addition, an index (1-5) of structural complexity of the cerebellum was created based on length, number, and depth of folds. The data show large variations in relative brain weight and complexity between species that do not follow a simple phylogenetic pattern. Pelagic sharks that move in 3-D space and hunt agile prey, such as Isurus oxyrinchus and Prionace glauca, have a similar structural hypertrophy with large, foliated cerebella (index grade 4-5) and enhanced telencephalons. In comparison, benthic and bathayal sharks, such as Notorhynchus cepedianus and Cephaloscyllium isabella, operate more in a 2-D environment and have a small, smooth corpus (index grade 1-2) and enlarged centers for electroreception and lateral line. Benthopelagic sharks, such as Mustelus lenticulatus and Carcharhinus brachyurus, fall in the middle of these two extremes in neuroanatomical development. It appears that brain development reflects the dimensionality of the environment and/or agile prey capture rather than phylogeny. One focus of our interest in morphometrics is the cerebellum and the controversy surrounding its function. Though principally associated with motor control, the alternative hypothesized function is that of active sensory exploration and target tracking; our morphometric data is consistent with either view.
California State University Long Beach, Dept. Biological Sciences, Long Beach, CA 90840, USA
Behavioral thermoregulation of the leopard shark, Triakis semifaciata, in nearshore embayments of Catalina Island, California
The leopard shark, Triakis semifasciata, is one of the most abundant nearshore elasmobranchs ranging from Baja California, Mexico to Oregon, with particular abundance in the bays of California. Mature female leopard sharks have been observed aggregating in Big Fishermans Cove (BFC) Santa Catalina Island for over 100 years; however, it is unclear why females aggregate in these shallow areas. During July and August of 2003, the numbers of aggregating sharks were counted in different sections of the shallow embayment of BFC during the day (n = 36, mean = 21.52 ± 8.17). Water temperature was simultaneously monitored in each section of the embayment. Temperatures in the embayment ranged from 17.8C° to 25.8C° (mean=21.8C° ± 1.2). Sharks preferred the warmest sampling areas of the embayment (correlation r = 0.557, p=0.01) and moved to warmer locations over the course of the day. These results suggest that leopard sharks are utilizing the warm water of the embayment to behaviorally thermoregulate. Currently manual acoustic tracking, acoustic monitoring and archival transponder technology (Vemco Ltd., V13, V13-R256, VX32TP-Chat tags respectively) are being used to monitor body temperature, swimming depth, and movements of mature female leopard sharks at Catalina Island (n=16). Passive acoustic monitor data demonstrates that these sharks show increased fidelity to thermal refuges around the island during the day and increase movement away from these refuges at night (2, p=0.01). Preliminary results from the Chat tags suggest that shark body temperature is warmer when in shallow water (correlation r=0.43, p = 0.01), and that shark body temperature is warmer during the day than at night (2 , p=0.01). Behavioral thermoregulation, as suggested by these results, may augment metabolic and physiological functions such as digestion, foraging behavior, and possibly reproduction.