Florida Museum of Natural History

Abstracts of AES Scientific Papers

American Elasmobranch Society 2005 Annual Meeting
Tampa, Florida
AES Presentation Abstracts
(*=presenter; G=Gruber, C=Carrier)

(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 with trophonemata. 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).

(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.

(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.

(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.

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.

(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 aiereba corresponds 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. and Oxyrinchus 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.

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.

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.

(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 of Centrophorus 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.

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.

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.

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.

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

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.

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.

(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. sabina exhibited 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.

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.

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.

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.

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 (rhueter@mote.org or 941-388-4441) at the Center for Shark Research, Mote Marine Laboratory to submit a research proposal.

(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.

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.

(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).

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.

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.

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).

(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.

(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.

(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. whitleyi and 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) and D.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.

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.

(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 and Aptychotrema 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

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.