Florida Museum of Natural History

Abstracts of AES Scientific Papers

American Elasmobranch Society 1999 Annual Meeting
State College, Pennsylvania
ABSTRACTS - Part 4: Rasmussen through Yano
*Rasmussen, L.E.L., Luer, Carl A., Manire, Charles A.

(LR) Dept of Biochemistry & Molecular Biology, Oregon Graduate Institute, Beaverton, OR 97006; (CAL, CAM) Mote Marine Laboratory, Sarasota, FL 34236

Elasmobranch pheromones:hints from the clearnose skate,  Raja eglanteria 

The identified sex pheromones of vertebrates include a somewhat random variety of chemical compounds; lampreys utilize bile salts, while some teleost fishes employ steroid derivatives, especially progestins, and prostaglandins. Snakes, salamanders, hamsters, pigs and elephants utilize methyl ketones, a protein, a dimethyl disulfide protein complex, a steroid and an acetate, respectively. Among the various compounds employed by marine invertebrates,  Aplysia  utilizes a novel peptide. Identification of elasmobranch pheromones has potential to provide chemical, functional and evolutionary insight. Over a five-year period bioassays were conducted with isolated male skates during their active reproductive period. Three types of female-derived material (urine, ovarian extracts and serum extracts from actively mating females) and selected steroidal hormone derivatives were investigated. Significantly elevated male response was observed to urine from ?hot" females, extracts of serum from females with elevated testosterone and estradiol levels, and dichloromethane extracts of ovaries. The results from assays of nine substituted estradiols and five progestins were generally negative. There was some response observed to estradiol 17-sulfate and less to estradiol 3-sulfate. Continued research will include a placental viviparous species, the bonnethead shark, Sphyrna tiburo, and will focus on the assay of protein extracts from female urine.

*Rechisky, Erin L., Wetherbee, Bradley M.

(ELR) Fisheries, Animal and Veterinary Science, University of Rhode Island, Kingston, RI 02881; (BMW) NOAA/NMFS/NEFSC, Narragansett, RI 02882

Short-term movements of juvenile sandbar sharks, Carcharhinus plumbeus, in Delaware Bay using acoustic telemetry

Acoustic telemetry was used to investigate short-term movements of neonate and juvenile sandbar sharks,  Carcharhinus plumbeus, on the shark nursery grounds in Delaware Bay during the summer of 1998. A total of 12 sharks was tracked continuously for between 6-70 hours. The majority of the sharks caught and tracked in the southern region of the bay remained in this area for the entire duration of the tracks. These sharks predominantly limited their movements to within 3 km of shore and to water that was approximately 2-5 m deep. Two sharks made longer offshore movements, one into the deepest section of the bay (37 m), and the other crossed the bay from Lewes, DE to Cape May, NJ. Tidal flow appears to affect the fine-scale movements of these small sharks, however no diel patterns were observed for distance from shore, rate of movement or depth. The results of this study indicate that young sandbar sharks concentrate their movements within a restricted portion of the bay, and therefore, area closures during the summer months might prove to be an effective management technique for this species.

*Ritter, Erich K., Godknecht, Alexander J.

(EKR) Green Marine Institute, Miami, FL 33173; (AJG) Winterthurerstr, University of Zurich, Zurich 8057 Switzerland

Agonistic display in sharks with special reference to the blacktip shark,  Carcharhinus limbatus 

Some carcharhinid show aggressive behavior patterns starting with forms of agonistic display. This display has been described in detail for the gray reef shark,  Carcharhinus amblyrhynchos . Modified or less extensive forms of this display have been described for other carcharhinid species as well. We will describe the agonistic display observed in the blacktip shark,  Carcharhinus limbatus, and discuss possible origins of these patterns. 

*Ritter, Erich K., Godknecht, Alexander J.

(EKR) Green Marine Institute, Miami, FL 33173; (AJG) Winterthurerstr, University of Zurich, Zurich 8057 Switzerland

Subordinate hierarchy between two closely related shark species, Caribbean reef shark ( Carcharhinus perezi ) and blacktip shark ( C. limbatus )

Anecdotal evidence suggests that different shark species exhibit interspecific subordinate hierarchies while feeding. Such events have never been statistically examined. This paper describes subordinate associations between two closely related carcharhinid species of similar size, the Caribbean reef shark,  Carcharhinus perezi, and the blacktip shark,  Carcharhinus limbatus, during a controlled setup. A subordinate event was identified when a shark initiated a bite at the food source but then first hit, bit or pushed another approaching shark away, before taking the actual bite. After analyzing 610 biting acts, 35 interspecific subordinate events were recorded between specimens of the two species. 

Robinson, Michael P.

Department of Biology, University of Miami, Coral Gables, FL 33124

The relationship between home range and body size in several sharks.

The home range of an animal is an important facet of its biology and can give insight into other aspects of its lifestyle. Home range size is correlated with the energetic requirements of terrestrial organisms. The home range areas of several shark species as reported in the literature are discussed here and their relationship to shark size is examined. The home ranges of several shark species (i.e.  Heterodontus fransisci,  Sphyrna lewini,  Carcharhinus amblyrhynchos ) did not regress significantly against animal size. Only the home range of the lemon shark,  Negaprion brevirostris  showed a significant, positive increase with the size of the individual. This increase was similar to that of the increase in metabolic requirements with mass; the home range increased at a greater rate than that predicted by both mammalian and elasmobranch data. It is proposed that the lemon shark has a high metabolic rate for elasmobranchs and thus requires a relatively larger area per mass from which to acquire energy. 

*Rojas, José Rodrigo, Camhi, Merry D.

(JRR) ProAmbiente, San Jose, Costa Rica; (MDC) Living Oceans Program, National Audubon Society, Islip, NY 11751

Status of sharks and their fisheries in Central America

Shark fisheries in Central America represent an important source of labor for artisanal fishers as well as protein for local populations. The demand for shark products, especially fins and cartilage, has led to an expansion in fisheries and trade throughout the region. Limited data on landings suggest that shark populations have been declining over the past 10 years. Increased fishing effort, scant data on biological reference points, and lack of management are key factors that negatively impact this fishery. A project currently under way aims to gather basic information on population status, nursery and fishery grounds, socioeconomics of the fishery, and needed conservation measures. Twenty four commercially valuable species have been identified including  Carcharhinus falciformes  and  Nasolamia velox  (Guatemala),  C. falciformis  (Nicaragua, Costa Rica),  C. obscurus  (El Salvador), and  C. limbatus  (Panama). Commercial products include the meat, fin, oil, cartilage, and skin. Shark fins are the most valuable product (e.g., dried caudal fins sell for to $US 150 - 400 per kg in Costa Rica), which are exported to Hong Kong, Taiwan, Japan, and the United States. Recommended management measures to improve the long-term viability of these sharks and the sustainability of their fisheries are discussed. 

Rosenberger, Lisa J.

Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637

The Evolution of Batoid Locomotion

The recent integration of functional morphology with phylogenetic data is creating a renaissance in our view of functional evolution. A phylogenetic context provides the ability to distinguish between patterns that arise from similar selective pressures or constraints independently and patterns that only reflect a common ancestry. Comparative methods using current higher level phylogenies for batoids (skates, stingrays, etc.) will reveal the evolutionary patterns of locomotion within this unique and diverse group of fishes by tracing morphology and kinematic behavior. Batoids exhibit three locomotor modes related to their lifestyles including axial-based locomotion (shark-like), undulation of the pectoral fins (waves propagated down the fins), and oscillation of the pectoral fins (bird-like flapping). Some species use a combination of at least two of these, like guitarfish in the family Rhinobatidae which use both axial and pectoral fin undulation. Others, such as the dasyatids, are able to modify their locomotor style from undulation to oscillation at high velocities. The assumed evolutionary trend for these locomotor types is axial (sawfish, electric rays, guitarfish) to undulation (skates and stingrays) to oscillation (eagle and manta rays), however undulation and oscillation may have independently evolved multiple times in these fishes. 

*Ryburn, Julie A., Naylor, Gavin, Fedrigo, Olivier, Lopez, Andres

Zoology and Genetics, Iowa State University, Ames, IA 50011

The phylogenetic relationships of carcharhinid shark: An inference based on both nuclear and mitochondrial genes.

The Carcharhinidae is one of the most diverse families of sharks, as well as one of the most commercially important. Our current understanding of carcharhinid phylogeny is based on the comparative morphological studies by Compagno (1988) and allozyme studies by Lavery (1992) and Naylor (1992). In the present study we present phylogenetic inferences based on 6kb of sequence data comprising 3 mitochondrial genes and one nuclear gene for 45 carcharhinid taxa. 

*Sasko, Desirée, Motta, Philip

University of South Florida, Tampa, FL 33569

The prey capture behavior and kinematics of the Atlantic cownose ray,   Rhinoptera bonasus .

This study explores the feeding behavior and mechanics of the myliobatid Atlantic cownose ray,   Rhinoptera bonasus . This species possesses a euhyostylic jaw suspension permitting extensive ventral protrusion of the jaws. Inertial suction prey capture during the preparatory phase is characterized by depression of the subrostral lobes. The expansive phase begins with the closure of the spiracle, followed by depression of the mandible and protrusion of the palatoquadrate and nasal cartilages. Throughout the feeding sequence, the subrostral lobes are fully depressed, forming a laterally enclosed chamber trapping the food. During the compressive phase, the mandible is elevated toward the palatoquadrate and nasal cartilages grasping the food. In the recovery phase, the jaws are brought back to the resting position and the spiracle is reopened. Manipulation involves repeated jaw open and closing movements such that the hard parts of the food are winnowed from the edible portions and ejected from the mouth. Total prey-capture duration is 240 ms. When excavating food from the sand, the ray repeatedly opens and closes its mouth to fluidize the sand, and suspend the food, before using suction to capture the food. 

*Saville, Kenneth J., Lindley, Andrea M., Maries, Eleonora G., Carrier, Jeffrey C.

Biology Department, Albion College, Albion, MI 49224

The use of PCR-RFLP and DNA sequence analysis of major histocompatibility class II alpha genes for paternity testing in the nurse shark,  Ginglymostoma cirratum .

We have developed a DNA-based paternity test with which to further our understanding of the mating behavior and reproductive biology of the nurse shark. It is hoped that this paternity test will allow us to determine if matings of female nurse sharks with multiple males can lead to multiple paternity in a single brood of offspring. We have focused our analysis on the major histocompatibility class II alpha (MHC II A) locus. Others have shown that this locus is duplicated, and that each of the duplicated loci is highly polymorphic(Kasahara et al.,1992, Eur. J. Immunol. 23: 2160-2165). We have used a PCR-RFLP strategy to determine the MHC class II A genotypes of DNA amplified from frozen shark tissue of one small family consisting of one mother and seven offspring. We were able to assign genotypes to each member of this family, but there was no evidence for multiple paternity. However, the sample size was too small to rule out this possibility. The analysis of a second family consisting of one mother and 33 offspring is underway, and the results of this analysis will be reported. 

*Schulze, Margo, Lent, Rebecca , Brewster-Geisz, Karyl, Meyers, Stephen

Highly Migratory Species Division, F/SF1, National Marine Fisheries Service, Silver Spring, MD 20910

The Highly Migratory Species Fishery Management Plan

On October 21, 1998, the Highly Migratory Species (HMS) Management Division of the National Marine Fisheries Service (NMFS) announced the availability of the draft Fishery Management Plan (FMP) for Atlantic highly migratory species, including Atlantic tunas, swordfish, and sharks. The draft FMP addresses rebuilding of overfished stocks (western Atlantic bluefin tuna, Atlantic bigeye tuna, Atlantic swordfish, and large coastal sharks), managing healthy stocks at optimum yield levels, limited access, essential fish habitat, economic and social impacts, safety at sea, scientific data and research needs, and permitting and reporting requirements. NMFS released the proposed rule to implement the provisions contained in the draft HMS FMP on January 20, 1999, and is conducting numerous public hearings throughout the Atlantic, Gulf of Mexico, and Caribbean coasts. 

*Sedoruk, Sarah, Hopkins, Todd

(SS) Southampton College, Southampton College of Long Island University, Southampton, NY 11968; (TH) Rookery Bay National Research Resreve, Naples, FL 34113

Flushing Behavior of the Bluntnose Stingray ( Dasyatis sayii )From the Southwest Gulf Coast of Florida

This study was carried out to determine whether method of approach influenced the flushing distance of bluntnose stingrays. Juvenile bluntnose stingrays were captured, tagged with a small float, and released at the site of capture. One hour after release each ray was approached by a researcher and the flushing distance was recorded. Flushing distance was a measure of the distance between the investigator and the ray at the moment the ray "spooked". During the first part of the study each ray was approached once by a researcher walking normally and once by a researcher doing the "stingray shuffle". During the second part of this study each ray was approached once by a barefoot researcher and once by a researcher wearing booties. Statistical analysis showed that neither the "stingray shuffle" nor booties influenced flushing distances. Short flushing distances were observed in response to all methods of approach. While the "stingray shuffle" did not increase the flushing distances observed, it did have the benefit of reducing one's chances of stepping directly on top of the ray and therefore one's chances of getting stung. The results did show a significant difference in the flushing distances recorded between the beginning and end of the study period.

*Shivji, Mahmood S., Rogers, Scott O., Stanhope, Michael J.

(MSS) Oceanographic Center, Nova Southeastern University, Dania, FL 33004; (SOR) College of Environmental Science and Forestry, State University of New York, Syracuse, NY 13210; (MJS) Biology and Biochemistry, The Queen's University, Belfast, Northern Ireland BT9 7BL UK

Species-specific markers for PCR-based identification of sharks

Since individual species of sharks respond differently to exploitation, management of the shark fishery on a species-specific basis is considered imperative for effective conservation and sustainable harvesting of this resource. The morphological similarities of many of the commercially harvested species, coupled with on-board processing methods have made it very difficult to collect accurate, species-specific catch data. As a result, many of the sharks landed are either incorrectly identified or classified as "unidentified sharks" in fishery records. Moreover, the widespread practice of shark finning in many parts of the world, and a potentially expanded list of prohibited shark fishery species in US waters will require the ability to identify sharks accurately from dried fins and other body parts for legal forensic purposes. To this end we are exploring the development of DNA sequence-based differences in sharks as markers for reliable species identification. In the quest to develop a streamlined process, we investigating the utility of multiplex PCR-based protocols for rapid identification of tissues using nucleotide differences in the ribosomal internal transcribed spacer regions. We report here on our progress to date in this endeavor.

Simpfendorfer, Colin A.

Mote Marine Laboratory, Center for Shark Research, Sarasota, FL 34236

Demography of western Atlantic sawfishes: Implications for conservation

Sawfish are a group of elasmobranchs that have been heavily impacted by humans due to targeted fishing, entanglement in fishing gear, and habitat modification. Four species are currently listed on the World Conservation Unions Red List of Threatened Animals, two as critically endangered. Two species occur in the western Atlantic: the small tooth sawfish ( Pristis pectinata ) and the large tooth sawfish ( P. perotteti ). There are limited biological and population data available. However, sufficient exists to construct preliminary demographic models for both western Atlantic species. A series of models were constructed to examine the sensitivity of demographic results to uncertainties in the biological and population data. The results of these models indicate that  P. perotteti  has an intrinsic rates of population increase of between 0.04 and 0.07, while  P. pectinata  has a rate between 0.08 and 0.13. These intrinsic rates of increase result in estimates of population doubling time of 10 - 17 years for  P. perotteti  and 5 -9 years for  P. pectinata . The implications of these results for conservation of sawfish populations are discussed. 

*Simpfendorfer, Colin A., Hall, Norman

WA Marine Research Labs, Fisheries Western Australia, North Beach, Western Australia 6020 Australia

Stock assessment and risk analysis for the whiskery shark ( Furgaleus macki ) in south-western Australia

The status of the whiskery shark population in south-western Australia was assessed using an age and sex structured model. The results from the best estimates of the model indicate that fishing prior to 1975 had a limited impact on the population, with total biomass estimated to be 97% of virgin and mature female biomass estimated to be 95% of virgin. The best estimate of total biomass in 1998 was 38.8% of virgin (95% confidence interval (CI) 22.7% to 47.2%) indicating that heavy commercial fishing had resulted in a significant decrease in the population. The best estimate of mature female biomass in 1998 was 23.0% of virgin (95% CI 13.4% to 36.4%), demonstrating that the impact of the fishery has been biased towards mature animals. Sensitivity tests indicated that uncertainty in the catch and effort data, or the way it was corrected, had the greatest effect on the biomass estimates. Uncertainty in biological and gear parameters resulted in only small changes in the biomass estimates. Risk analysis indicated that to have a greater than 60% probability of achieving biomass targets set by the management body would require annual catches to be reduced to less than 160 tonnes. 

*Skjaeraasen , Jon Egil, Bergstad, Odd Aksel

(JS) Norwegian University of Science and Technology (NTNU), Trondheim, 7035 Norway; (OB) Flødevigen Marine Research, Institute of Marine Research, His, N-4817 His Norway

Distribution and feeding of rays in the northeastern North Sea and on the Norwegian Sea Slope

Spatial distribution and diet composition of five ray species were analysed based on data from several research vessel cruises in the period 1984-1996.

Three species were characteristic members of the demersal fish communities of the northeastern North Sea and Skagerrak and the warm upper continental slope waters of the eastern Norwegian Sea, i.e. Raja radiata, R. lintea, and R. fyllae. Within the North Sea, the southern slope of the Norwegian Deeps at the entrance to the Skagerrak had a particularly high density of rays.

In the Norwegian Sea, two species, Raja hyperborea and Bathyraja spinicauda, occurred near the slope front between the Atlantic Watermass and the cold Norwegian Sea Deep-water. R. hyperborea was the only ray inhabiting sub-zero temperature water beneath the front.

The gut contents of Raja hyperborea and Bathyraja spinicauda were dominated by fish, also epipelagic species, suggesting extensive scavenging. Also R. lintea had mainly consumed fish prey, but also deep-water shrimps. R. fyllae was the more typical benthivore, feeding mainly on polychaetes and benthic crustaceans. The diet of Raja radiata differed between the slope and North Sea-Skagerrak areas. Along the slope euphausids were the prominent prey, whereas in the North Sea, shrimp, polychaetes and, in the bigger specimens, fish were significant. 

*Smith, Mark, Correia, Joáó P.

Esplanada D. Carlos I, Oceanário de Lisboa, Lisboa, 1998 Portugal

An update on elasmobranch landings in Portugal: 1986-1998

Elasmobranch Portuguese landings from 1986 until 1998 were analysed. Landings were discriminated by species, port, year, month and selling cost. All species totalled 77651 metric tonnes, where Squaliformes and Hexanchiformes accounted for 46% of the total, Charcharhiniformes and Lamniformes for 16% and Squatiniformes for 38%. A total of 36 species (some only identified by genus) were officially landed during that period of time. The most landed species were  Raja spp.  (36% of the total landed between 1986 and 1998),  Centrophorus granulosus  (11%),  Centroscymnus coelolepis  (10%),  Scyliorhinus spp.  (10%),  Centrophorus squamosus  (8%),  Prionace glauca  (7%),  Dalatias licha  (6%) and  Mustelus spp.  (4%). Because landings are only available for a period of 13 years, it is hard to determine accurately whether there is an increasing or decreasing trend. However, when looking at monthly values it is possible to observe that some species show high and low variations within each year. All species that showed landings greater than 250 metric tonnes and ports with landings greater than 500 metric tonnes were analysed with detail. Some species show a clear boom-and-crash pattern parallelled by an increase in value. 

*Smith, Wade D., Bizzarro, Joseph J., Jones, Erin M., Neer, Julie A., Tyminski, John, Márquez-Farias, J. Fernando, Cailliet, Gregor M., Hueter, Robert E.

(WDS, JJB, EMJ, JAN, GMC) Moss Landing Marine Laboratories, Moss Landing, CA 95039; (JT, REHMote Marine Laboratory, Sarasota, FL 34236; (JM) Instituto Nacional de la Pesca, Sonora, Mexico

A preliminary assessment of the elasmobranch fishery in the northern Gulf of California, Mexico

Mexican elasmobranch fisheries have expanded to become the largest in the Americas (~30,000 MT/year), with much of the yield taken from the Gulf of California (GOC). To improve the understanding, conservation, and management of shark and ray resources in the GOC, a 2-year, multi-institutional project involving Mexican and US scientists was initiated. The extent and activity of fishing camps within the northern GOC and catch information from these camps, including species composition, sex, weight, size, and other pertinent biological information were determined during 1998 field surveys. A total of 31 elasmobranch species were encountered. Fishing effort was highly variable among seasons in both Baja California Norte (BCN) and Sonora. Landings were highest in summer and fall. Batoids numerically dominated BCN catches and were important constituents of the Sonoran fishery. Large sharks (esp.  Alopias pelagicus,  Carcharhinus falciformis, and  C. limbatus )comprised a greater component of the catch in BCN than Sonora. Small sharks, juveniles of larger species, and batoids dominated landings in both locations. Females dominated the fall catch composition of  Mustelus  sp. and  Gymnura marmorata . These primary data represent an important step toward documenting fishing trends that are critical for sustainable fisheries management of elasmobranchs in the GOC. 

*Tyminski, John P., Cortés, Enric, Manire, Charles A., Hueter, Robert E.

(JPT, CAM, REH) Center for Shark Research, Mote Marine Laboratory, Sarasota, FL 34236; (EC) Southeast Fisheries Science Center, National Marine Fisheries Service, Panama City, FL 32408

Gastric Evacuation and Estimates of Daily Ration in the Bonnethead Shark  Sphyrna tiburo 

The rate of gastric evacuation is an integral component in estimating daily ration in fishes caught in the wild. The gastric evacuation curve for the bonnethead shark was established in a laboratory study by force feeding a pre-weighed meal of the iridescent swim crab,  Portunus gibbesii . Stomach contents were removed by everting the stomachs at selected times after feeding. These data were best fit by both the exponential and Gompertz nonlinear models. Analysis of these contents was used to develop a discrete stage-of-digestion scale that then was applied to prey items from bonnethead stomach contents obtained in the wild. This allowed reconstruction of meal size which, together with feeding frequency, was used to estimate daily ration. As an alternative approach, stomach contents were collected from bonnethead sharks in the field over a 24-hr period at 3-hr intervals. Stomach content weight and stage of digestion were used to determine daily ration with this method. Daily ration also was estimated through the balanced energy equation. These and other methods of estimating daily ration will be compared for their suitability given the assumptions implicit in each method. 

*Villavicencio-Garayzar, Carlos, Cailliet, Gregor M.

(CV) Departamento de Biologia Marina, Universidad Autonoma de Baja California Sur, La Paz, B.C.S, 23080 Mexico; (GMC) San Jose State University, Moss Landing Marine Laboratories, Moss Landing, CA 95039

Age and Growth of the Pacific lesser electric ray, Narcine entemedor, from the west coast of Baja California Sur, Mexico

We describe the age and growth of the Pacific lesser electric ray, Narcine entemedor, from artisanal fisheries in two locations, Almejas Bay and San Ignacio Lagoon, along the western coast of Baja California Sur, Mexico. We removed, cleaned and sectioned vertebrae for growth zone analysis. We independently counted pairs of opaque and translucent bands and calculated the average percent error (APE) and percent error (D) and produced precision histograms that indicate precision of counts was relatively good, with among-reader APE and D values for females being 10.38 and 6.10%, while for males they were 8.25 and 4.71%, respectively. Most age estimates were within 2 years of each other. Marginal increment measurements for large females over 70 cm TL and males over 50 cm TL indicated seasonal changes, with an increase in the dimension of opaque bands during the summer months. We fit the von Bertalanffy growth (VBG) function to the data from 315 female and 79 male rays, producing growth curves that indicated that females grew faster (k = 0.313) and reached a larger size (Loo = 82.4 cm TL) than males (Loo = 79.4 cm TL; k = 0.094). The oldest female and male rays were estimated to be 15 and 11 years old, respectively. Growth characteristics, coupled with information on reproduction, indicate that this ray could be susceptible to heavy fishing pressure, especially in their nursery areas. 

*Walker, Nancy B., Shivji, Mahmood S., Stanhope, Michael J., Rogers, Scott O.

(NBW, SOR) College of Environmental Science and Forestry, State University of New York, Syracuse, NY 13210; (MSS) Oceanographic Center, Nova Southeastern University, Dania, FL 33004; (MJS) Biology and Biochemistry, The Queen's University, Belfast, Northern Ireland BT9 7BL UK

Characterization of group I intron-like insertion elements in shark ribosomal DNA spacers.

A set of insertion elements has been found in the ribosomal DNA (rDNA) internal transcribed spacers in four Orders of sharks (Carcharhiniformes, Hexanchiformes, Lamniformes, and Orectolobiformes). These elements are from 303 to 575 nucleotides in length, and show all the RNA folding characteristics of group I introns, with each element having nine to eleven pairing regions and a conserved core region. Each of these putative introns has been cloned into RNA expression vectors and  in vitro  splicing experiments are underway. If these elements are capable of  in vitro splicing, this will be the only group I intron within rDNA reported for any metazoan. Also, this would be the only report of a group I intron within a transcribed spacer region. If these elements are incapable of  in vitro  splicing, they may represent remnants of a very ancient insertional event by a group I intron ancestor. Aside from the biological and evolutionary importance of these elements, their sequences vary greatly and so have the potential for use as species-specific markers for shark identification.

*Walsh, Cathy J., Luer, Carl A., Wyffels, Jennifer T., Bodine, A. B.

(CJW, CAL) Mote Marine Laboratory, Mote Marine Laboratory, Sarasota, FL 34236; (JTW, ABB) Clemson University, Clemson, SC 29634

Dexamethasone-induced apoptosis (programmed cell death) in immune cells from peripheral circulation and lymphomyeloid tissues of juvenile clearnose skates ( Raja eglanteria ).

Programmed cell death (apoptosis) plays a critical role in shaping the immune repertoire in higher vertebrate thymi. Elasmobranchs represent the earliest phylogenetic appearance of a clearly defined thymus. Apoptosis was induced in juvenile clearnose skates by IM injections of dexamethasone-21-phosphate in areas adjacent to the thymus at levels of 50, 75, and 100 mg/kg body weight. After 24 h, skates were sacrificed, and Leydig organ, spleen, and thymus were removed and frozen in liquid nitrogen. Blood was drawn via cardiac puncture, and peripheral blood leukocytes (PBL) isolated. A method to detect DNA strand breaks (TUNEL reaction) was used to assess apoptotic activity in cryostat sections of tissue and cytospin preparations of PBL, and transmission electron microscopy was utilized to examine glutaraldehyde/paraformaldehyde fixed thymi. Results show that dexamethasone treatment resulted in increased apoptotic activity in immune tissues and PBL of juvenile clearnose skates. These studies demonstrate that immune cells of elasmobranchs have the capacity for glucocorticoid-driven apoptosis, and that mechanisms of programmed cell death appear to have been well conserved during evolution. Knowledge gained from studies of these processes in primitive vertebrates such as elasmobranchs should contribute to a better understanding of the significance of apoptosis in higher vertebrates. 

*Wyffels, Jennifer, Bodine, A. B., Wourms, J. P., Luer, C. A., Walsh , C. J.

(JW, ABB) AVS Department, Clemson University, Clemson, SC 29634; (JPW) Biological Sciences Department, Clemson University, Clemson, SC 29634; (CAL, CJWMote Marine Laboratory, Sarasota, FL 34236

A series of developmental stages for the clearnose skate,  Raja eglanteria 

A series of developmental stages for the clearnose skate,  Raja eglanteria, based on external morphology has been prepared. Images were collected with macrophotography, epifluorescent microscopy, and scanning electron microscopy from more than 100 embryos. The skates were maintained at 21 C and fixed with aldehydes at regular intervals throughout their 12 week incubation period. Embryonic development was observed from early cleavage to 1 week post-hatching. The embryos were staged based on modifications of the staging systems of Ballard and Mellinger, 1993; Scammon, 1911; and Balfour, 1876. Newly laid eggs are in the blastoderm stage. The embryonic axis of the skate is established 3 days after oviposition. Fusion of the neural folds is complete 7 days after oviposition. Otic and optic vesicles are apparent 10 days after oviposition. The olfactory pit is invaginated in day 12 embryos. Thirteen days after oviposition all pharyngeal grooves are open and gill filaments protrude from the gill bars. Pectoral and pelvic fins attain their definitive shape 17 days after oviposition. The stages established for the clearnose skate will be useful for comparative and evolutionary studies of vertebrate development. 

*Yano, Kazunari, Ito, Takashi, Sato, Fumihiko, Takahashi, Tomoko, Shimizu, Hirofumi

(KY) Ishigaki Tropical Station, Seikai National Fisheries Research Institute, Okinawa, 907-0451 Japan; (TI), Marine Service Ito, Okinawa, 907-1221 Japan; (FS) Byobudani, Chichijima, Ogasawara, Ogasawara Marine Center, Tokyo, 100-2101 Japan; (TT) Miyanohama-michi, Chichijima, Ogasawara, Sea-Tac Co., Tokyo, 100-2101 Japan; (HS) Seikai National Fisheries Research Institute, Seikai National Fisheries Research Institute, Ishigaki, Okinawa, 907-0451 Japan

Photo-identification of individual manta rays,  Manta birostris, at the Yaeyama Islands, the Miyako Islands, and the Ogasawara Islands, Japan

The manta ray,  Manta birostris  (family Mobulidae), is the largest ray and one of the largest living fishes, reaching a disc width of at least 6.7 m and a weight of more than 1360 kg. The manta ray occurs worldwide in tropical and subtropical regions, and occasionally migrates into temperate waters. Individual mantas are recognizable on the basis of natural marks and color patterns, especially dark markings on their abdomen. In this study mantas were recorded by photographs and video tape recording around several Japanese islands. We identified 180 individuals at the Yaeyama Islands, Okinawa, from 1978 to 1998, 48 individuals at the Miyako Islands, Okinawa, from 1996 to 1998, and 42 individuals at the Ogasawara Islands, Tokyo, from 1995 to 1998. We observed that manta rays migrated between the Yaeyama Islands and the Miyako Islands. The color patterns of manta rays differed between the Yaeyama Islands/Miyako Islands populations and the Ogasawara Islands population. Seasonal abundance, migration, and swimming behavior of manta rays are reported.