Florida Museum of Natural History
Sharks
  HOME COLLECTION EDUCATION IMAGE GALLERY SOUTH FLORIDA ORGANIZATIONS MEETINGS STAFF
  SHARK FRESHWATER
RESEARCH
BIOLOGICAL
PROFILES
JUST FOR KIDS SITE LINKS FLMNH

Abstracts of AES Scientific Papers

American Elasmobranch Society 2001 Annual Meeting
State College, Pennsylvania
ABSTRACTS - Part 2: Gelsleichter through Luer
GELSLEICHTER, JIM

1600 Ken Thompson Parkway, Mote Marine Laboratory, Sarasota, FL 34236

The ultimobranchial gland and calcitonin production in the Atlantic stingray, Dasyatis sabina.

In elasmobranchs, the ultimobranchial gland (UBG) is a paired organ situated between the dorsal musculature of the pericardial cavity and the ventral pharyngeal epithelium. The UBG consists of small round follicles with cuboidal or columnar epithelial walls and central lumina. Parenchymal cells of the UBG produce calcitonin, a 32-amino acid peptide hormone that is best known for its role in protecting the mammalian skeleton from demineralization. In an effort to elucidate the role of this phylogenetically ancient hormone in elasmobranchs, the present study investigated changes in tissue architecture and calcitonin production in the UBG of the Atlantic stingray, Dasyatis sabina, associated with sex, season, reproductive status, and environmental salinity. In addition, data on immunoreactivity of calcitonin in tissues and secretions of D. Sabina are presented to clarify target organs of calcitonin action. (Session 20, Sunday, July 8, Penn Stater, Room 207, 2:30)

 


GIBBON, GEORGE J.

Private Bag 3, University of the Witwatersrand, Johannesburg, Gauteng 2050 South Africa

The Reaction between Underwater Electrical Equipment and Elasmobranchii.

The increase in the quantity and types of electrically powered underwater apparatus and instrumentation is exposing marine life to increasing electromagnetic (EM) radiation. This equipment is used by both recreational and commercial users of the marine habitat. The Elasmobranchii (sharks, rays and skates) have sensory organs which detect weak electric fields for hunting and possibly navigational purposes. This presentation describes the initial results of a research program to investigate the electric fields produced by underwater electrical equipment and to relate these to the Elasmobranchii's sensitivity. Underwater observations, with two video clips, indicating both distress and interest by sharks to underwater EM radiation are discussed together with measurements of electric fields from electrical apparatus. The initial findings indicate that underwater electrical apparatus do adversely influence the Elasmobranchii. Further research should be conducted to quantify this influence and determine methods to shield the apparatus in order to prevent the radiation of EM fields and the resultant possible decline in marine resources and tourist potential. (Session 16, Sunday, July 8, Penn Stater, Room 207, 9:15)

 


*GOLDMAN, KENNETH J., ANDERSON, SCOT D., MUSICK, JOHN A.

(KJG, JAM) P.O. Box 1346, Virginia Institute of Marine Science, Gloucester Point, VA 23062; (SDA) P.O. Box 390, Oceanic Society, Inverness, CA 94937

Regulation of body temperature in the salmon shark, Lamna ditropis.

The salmon shark, Lamna ditropis, occurs in the boreal and cool temperate coastal and oceanic waters of the North Pacific Ocean. As with all other members of the Family Lamnidae, they are known to be endothermic based on their possession of vascular countercurrent heat exchangers (retia mirabilia). Previous body temperatures obtained from moribund and recently killed specimens showed elevations ranging from eight to 15.6o C over sea surface temperature. We present results from over 50 hours of temperature telemetry data obtained from four free-swimming salmon sharks. This species displayed a very high thermoregulatory ability, maintaining an average body temperature of 25.3o C in ambient water temperatures ranging from just over five to 16o C. Depth distribution ranged from the surface to over 140 m. (Session 20, Sunday, July 8, Penn Stater, Room 207, 11:45)

 


*GOLDMAN, KENNETH J., MUSICK, JOHN A.

P.O. Box 1346, Virginia Institute of Marine Science, Gloucester Point, VA 23062

Growth dynamics of female salmon sharks in the eastern and western North Pacific: a spatially structured population?

The salmon shark, Lamna ditropis, occurs in the boreal and cool temperate coastal and oceanic waters of the North Pacific Ocean. In the eastern North Pacific, we found adults of this species typically ranged in size from 200-260 cm TL and weighed upwards of 220 kg. To date, our study shows that maximum age is 20 for females with a growth coefficient (k) of 0.187. Our results show that female salmon sharks in the eastern North Pacific possess a faster growth rate, reach sexual maturity earlier, have greater longevity, and attain greater length and weight than those living in the western North Pacific. The variability in these life history parameters may be due to ecological differences between the eastern and western North Pacific or due to population structure. North-south migrations are fairly well documented in salmon sharks, while cross-Pacific migrations are suspected. (Session 3, Friday, July 6, Penn Stater, Room 207, 2:30)

 


GOTTFRIED, MICHAEL D.

MSU Museum, Michigan State University, East Lansing, MI 48824

The Megatooth Shark: Myth, History, and Science

The public's fascination with the fossil megatooth shark Carcharodon megalodon approaches that seen for dinosaurs. Much of this revolves around its tremendous size: the megatooth reached a length of ca. 16 meters (52 feet), making it the most spectacularly large Mio/Pliocene marine predator. C. megalodon is primarily known only from teeth (and occasional vertebral centra). Renaissance accounts held that its large, triangular teeth were the petrified tongues, or glossopetrae, of dragons and snakes, an interpretation corrected in the 1600s by the great early naturalist Steno, who recognized them as ancient shark teeth (and famously produced a rather grotesque depiction of a shark's head bearing such teeth). Since Steno's time, many attempts---some fanciful, others more realistic---have been made to reconstruct the megatooth. Modern reconstructions have generally used the extant Great White Shark C. carcharias as a starting point, recognizing that the two forms are related (although some have questioned just how closely). One stubborn bit of megatooth folklore is that it is still living, lurking like the coelacanth in cryptic deep-sea environments---this persists despite the lack of any physical evidence, and the improbability of a 50-foot-long shark, which consumes large coastal prey, somehow remaining undetected. (Session 26, Monday, July 9, Penn Stater, Room 207, 1:30)

 


GRANT, ALAN T.

University Avenue, University of Glasgow, Glasgow, Scotland G12 8QQ U.K.

Preliminary trophic model of a lemon shark (Negaprion brevirostris) nursery at Bimini, Bahamas

The North Sound, Bimini, Bahamas, is a highly enclosed, mangrove-fringed, sub-tropical lagoon which functions as a nursery for approximately 75 juvenile lemon sharks Negaprion brevirostris. Despite low species diversity and reduced water quality due to restriction of tidal flow, the nursery appears to be a stable and adequate environment for the early development of lemon sharks. A preliminary trophic model using the Ecopath 3.0 software is presented. Estimates are calculated of guild trophic position, ecotrophic efficiency, omnivory index, flow to detritus, respiration, niche overlap, electivity and trophic impacts. Whole ecosystem parameters estimated include total and guild energy throughput, trophic level transfer efficiency, Finn's recycling index, ascendancy, system overhead and system capacity. Additionally, all trophic pathways are tabulated. Knowledge of guild and ecosystem parameters will reveal how the nursery functions to support the lemon sharks, identify vulnerable components, and indicate the level of system stability and maturity. An energy flow model will also be elaborated to assess the capacity of the North Sound with respect to the production of lemon sharks. This in turn will provide an estimate for the recruitment of sub-adults into the general population, and indicate levels of sustainability within the nursery. Funded by the Florida State Department of Education. (Session 7, Saturday, July 7, Penn Stater, Room 207, 8:45)

 


*HAMMOND, TIM, ELLIS, JIM

Pakefield Rd., The Centre for Environment Fisheries and Aquaculture Science (CEFAS), Lowestoft, Suffolk NR33 0HT UK

A meta-assessment for elasmobranchs based on dietary data and Bayesian networks

Meta-assessments are models enhanced by the incorporation of other stock assessment results. We used this idea to estimate historic biomass trends for demersal elasmobranchs of the Irish Sea. Bayesian networks, constructed from published dietary data and resembling food webs, allowed us to incorporate into our estimates the results from virtual population analysis (VPA) for Irish Sea cod, sole, plaice and whiting. To assess accuracy, we used cross-validation, estimating historic biomass trends in each individual VPA species from trends in the other three plus trends in fishing effort. We compared predicted annual trends to those derived from VPA and found 66% accuracy. We also compared biomass trends estimated from annual trawl surveys to corresponding network predictions, recovering survey trends correctly 61% of the time for elasmobranchs, 78% of the time for gurnards (Triglidae) and 89% for bib and pout (Trisopterus spp.). Results suggest that of the 11 elasmobranchs examined, the angel shark (Squatina squatina) suffered the most from 1987 to 1997, a view consistent with survey results. Our approach also suggested a marked decline in common skate (Dipturus batis) over the period 1965-1978, during which time the skate was extirpated from the Irish Sea. We conclude that meta-assessment can serve as a useful tool for the preliminary identification of threatened stocks. (Session 3, Friday, July 6, Penn Stater, Room 207, 3:30)

 


*HARRIE, ANN C., MITCHUM, GREGORY, SCOTT, DR. GEOFF

(ACH) Health Sciences Building, University of South Carolina, Columbia, SC 29208; (GM, GS) 219 Fort Johnson Road, Center for Coastal Environmental Health and Biomolecular Research/NOAA/NOS, Charleston, SC 29412

Contaminants in Sharks of the South Atlantic Bighty: An Assessment of Pesticides and PCBs in Shark Livers as an Environmental Risk

Charleston, South Carolina is surrounded by abundant marshes and estuaries that serve as potential sinks for contaminants, but are also nursery grounds for abundant species of fish, including sharks. Top level predators such as sharks may be used as bioindicators of coastal environmental health since they are known to accumulate persistent chemical contaminants. This research involved analyzing the livers of sharks [Atlantic Sharpnose (Rhizoprionodon terraenovae), Blacknose (Carcharhinus acronotus), and the Bonnethead (Sphyrna tiburo)] caught in near-shore coastal waters in Charleston, SC, and documenting the levels of lipophilic contaminants, including polychlorinated biphenyl's (PCB's) and chlorinated pesticides. Sharks were collected by longline, measured for total and fork length, and sexed on board. Sharks within each species fell into three size classes: pup, juvenile and adult. The whole liver was removed, iced, and brought to the laboratory, where 1-gram sub-samples were taken. Each liver sample was extracted using Accelerated Solvent Extraction, and the lipid was removed from the analytes of interest by size exclusion chromatography. The analyte levels were determined using gas chromatography/mass spectroscopy and reported as ng/g lipid. Results indicated the presence of PCB's and persistent organochlorine pesticides in each species of shark studied. Size, life stage and species differences will be discussed. (Session P-14, Saturday, July 7, Penn Stater, Deans Hall)

 


*HEITHAUS, MICHAEL R., DILL, LAWRENCE M., MARSHALL, GREG J.

(MRH) 1600 Ken Thompson Pkwy, Mote Marine Laboratory, Sarasota, FL 34236; (LMD) 8888 University Dr, Simon Fraser University, Burnaby, British Columbia V5A 1S6 Canada; (GJM) 1145 17th St. NW, National Geographic Special Projects, Washington DC, DC 20036

The behavior and ecology of tiger sharks in a subtropical seagrass ecosystem

Tiger sharks (Galeocerdo cuvier) are apex predators in a variety of nearshore ecosystems throughout the world, but relatively little is known about how they function in these systems. From 1997-2000, we conducted studies of the behavioral ecology of tiger sharks and their prey in Shark Bay, Western Australia. Tiger sharks were the most commonly caught species of large shark in the bay, but were not present in all seasons. Tiger shark catch rates were highly correlated with water temperature, but were also correlated with the seasonal occurrence of their main prey. The importance of seagrass grazers (turtles and dugongs) in the diet of tiger sharks suggests the possibility that these sharks may influence community structure through trophic interactions. Tiger sharks may also be important in this community because of their influence on habitat use decisions by their prey species. Our studies of habitat use by tiger sharks and their prey suggest that habitat use decisions by these species may result in indirect behavioral effects, and that tiger sharks may mediate these effects. Ongoing studies in Shark Bay will continue to elucidate the role of tiger sharks in seagrass ecosystems. (Session 7, Saturday, July 7, Penn Stater, Room 207, 9:00)

 


*HEITHAUS, MICHAEL R., HAMILTON, IAN M.

(MRH) 1600 Ken Thompson Pkwy, Mote Marine Laboratory, sarasota, FL 34236; (IMH) 8888 University Dr, Simon Fraser University, Burnaby, British Columbia V5A 1S6 Canada

Randomization techniques for analyzing habitat preferences from tracking data Acoustic tracking has been widely used in studies of elasmobranch movements and habitat use.

However, it is often difficult to determine how often individuals should use a particular habitat in the absence of a preference. This results in difficulties conducting appropriate statistical tests of habitat use to determine whether there is a significant habitat preference. Many difficulties can be overcome by employing a variety of randomization techniques to data analysis. We will present three different randomization techniques: correlated random walk, within track randomization, and randomization of a sample of tracks. Each of these techniques has a unique set of underlying assumptions and can be used to answer different questions. The differences among techniques will be illustrated with analyses of both computer-generated tracks with known habitat preferences and movement biases and empirical tracking data from tiger sharks (Galeocerdo cuvier). In general, the sample randomization is ideal for looking at the overall preference of a sample or differences in habitat use among subsamples (e.g. sex-classes). However, the correlated random walk and within track randomization allow analysis of individual habitat preferences, and may be more appropriate for some research questions. (Session 10, Saturday, July 7, Penn Stater, Room 207, 10:30)

 


*HEUPEL, MICHELLE R., SIMPFENDORFER, COLIN A., HUETER, ROBERT E.

1600 Ken Thompson Pkwy, Mote Marine Laboratory, Sarasota, FL 34236

Comparison of home range estimates by passive monitoring and active tracking techniques

An array of 24 data-logging acoustic hydrophones was deployed in a known shark nursery area on the central Gulf coast of Florida to monitor the movements of juvenile blacktip sharks, Carcharhinus limbatus. During the summer of 2000, 33 C. limbatus were monitored via the automated array. An additional four sharks were actively tracked for periods of 24-hours each to define their short-term movement patterns. Results from the array allowed home range estimates to be determined for all individuals monitored. Sharks were monitored for periods of 2 - 167 days. Weekly, monthly and cumulative home range areas were estimated for seven sharks using minimum convex polygon and fixed Kernel home range estimators. Daily home ranges were also calculated for actively tracked animals using minimum convex polygon and fixed Kernel home range estimators. For purposes of comparison, a daily home range estimate was calculated for five sharks monitored by the array on the same day of each of the manual tracks. An extrapolated randomization of manual tracks was also completed to allow weekly and cumulative home range estimates to be calculated based on active tracking data. The results of all home range estimates and the comparison of results among techniques will be discussed. (Session 10, Saturday, July 7, Penn Stater, Room 207, 11:45)

 


*HOFFMAYER, ERIC R., HORTON, JEFF L., PARSONS, GLENN R.

(ERH) Gulf Coast Research Laboratory, The University of Mississippi, Ocean Springs, MS 39564; (JLH) 123 Shoemaker Hall, The University of Mississippi, University, MS 38677; (GRP) 123 Shoemaker Hall, The University of Mississippi, University, MS 38677

Are Inshore, Shallow Water Nursery Areas Energetically Demanding for the Atlantic Sharpnose Shark, Rhizoprionodon terraenovae in the Northern Gulf of Mexico?

The inshore waters surrounding the extensive barrier island system off the coast of Mississippi have been identified as an important nursery ground for several shark species including the Atlantic sharpnose shark. Annually, sharpnose sharks migrate into these waters in the early spring and in the fall migrate to offshore warmer waters. Seasonal changes in environmental parameters in the inshore habitat, specifically temperature, may affect the energy budget in this species. The objective of this study was to determine if the energetic condition of the sharpnose shark changes seasonally while they inhabit the inshore nursery area. Two indicators of energetic condition were used in this study, condition factor and hepatosomatic index, as well as a direct measurement of total energy content by the use of bomb calorimetry. A significant seasonal change in the energetic condition was found to occur in the sharpnose shark while they inhabited these nursery areas. The energetic condition of these sharks was high when they moved inshore in the spring, decreased during the summer months and increased to higher levels in the fall. Inshore, shallow water nursery areas in the northern Gulf of Mexico appear to be energetically demanding for the Atlantic sharpnose shark during the summer. (Session 20, Sunday, July 8, Penn Stater, Room 207, 11:15)

 


*HOFFMAYER, ERIC R., PARSONS, GLENN R.

(ERH) Gulf Coast Research Laboratory, The University of Mississippi, Ocean Springs, MS 39564; (GRP) 123 Shoemaker Hall, The University of Mississippi, University, MS 38677

Identification and Characterization of Shark Nursery Grounds of the Northern Gulf of Mexico.

From October 1997 until September 2000 we conducted a survey of shark nursery grounds along the Mississippi and Alabama coasts. Our objectives were (1) to identify shark nursery/pupping areas in the northern Gulf of Mexico, (2) to compare abundance and diversity of sharks between sites, seasons and years, and (3) to characterize the nursery areas in terms of environmental parameters. Sampling was conducted using gill nets fished from 1500 to 2200 hours from March to October each year of the study. At each sampling station environmental data was recorded. All sharks collected were identified to species, sexed, measured (total length), and, when possible, tagged and released. In 1998, 1999 and 2000 we collected 522, 517 and 1650, while tagging 300, 300, and 700 sharks, respectively. The most abundant species were found to be Rhizoprionodon terraenovae, Carcharhinus limbatus, and Carcharhinus isodon. Other species collected were Carcharhinus leucas, Sphyrna tiburo, Carcharhinus acronotus, Sphyrna lewini, Carcharhinus brevipinna and Carcharhinus plumbeus. Nursery grounds were identified in a number of areas along the coasts of Mississippi and Alabama. Most notably, the Mississippi Sound and the waters surrounding the barrier islands serve as important habitat for neonates and juveniles of all of the above species. (Session 3, Friday, July 6, Penn Stater, Room 207, 1:30)

 


*HUETER, ROBERT, CHILDS, JEFF

(RH) 1600 Ken Thompson Parkway, Mote Marine Laboratory, Sarasota, FL 34236; (JC) 6300 Ocean Drive, Texas A&M University, Corpus Christi, TX 78412

Sharks and rays attracted to offshore oil and gas platforms in the Gulf of Mexico.

Offshore oil and gas platforms can function as fish attracting devices (FADs) for a variety of marine fishes, including elasmobranchs. Sharks and rays may use these structures as refuges, as core areas for daily activities, or as areas to feed on natural prey or anthropogenic food (bait, offal). In the shallows surrounding platforms in the Gulf of Mexico, sharks such as the silky shark (Carcharhinus falciformis), scalloped hammerhead (Sphyrna lewini) and whale shark (Rhincodon typus) and rays such as the spotted eagle ray (Aetobatus narinari) and the Atlantic manta (Manta birostris) have been frequently observed, photographed and videotaped. Some pelagic elasmobranchs such as the silky shark appear to use these structures as core areas for juvenile stages. In the deep waters (>300 m) surrounding the structures, elasmobranchs such as sixgill sharks (Hexanchus spp.), gulper sharks (Centrophorus spp.) and skates (Raja spp.) have been recorded by ROV-mounted video cameras deployed from the structures. Shallow and deepwater video of these various elasmobranch species around Gulf of Mexico platforms will be shown. The potential impacts of the offshore oil and gas structures on elasmobranch populations will be discussed in relation to the emerging trend of deeper structures being deployed in the oceans. (Session 16, Sunday, July 8, Penn Stater, Room 207, 9:00)

 


HUETER, ROBERT E.

1600 Ken Thompson Parkway, Mote Marine Laboratory, Sarasota, FL 34236

Shark Feeding Dives: Are They All Bad?

Shark feeding dives have come under attack as being detrimental to the health and ecology of sharks and the marine environment, a threat to diver safety, and a source of user conflicts. Wildlife conservationists caution that feeding wild animals always has negative consequences, and resource managers have been receptive to banning shark feeding dives altogether on general principle. What has been missing in the discussion are any real scientific data on the effects of these dives, which in some areas have been operating consistently for 15-20 years. Effects on the behavior, health, ecology and life history of fed sharks can be classified as certain, probable, or possible, and these will be discussed in light of the minimal scientific information that exists. Possible effects on the marine environment also will be examined with what little data exist. Diver safety will be addressed using records of the Bahamas Diving Association compiled since 1973, indicating the dives have been relatively safe for customers but have carried higher risks in recent years for staff. These various effects will be weighed against the positive benefits of the dives, which under certain circumstances have included advances in public education, scientific research, and conservation measures on sharks. (Session 16, Sunday, July 8, Penn Stater, Room 207, 10:30)

 


*HUNTER, GREGORY A., HARPER, JAY W., LANGER, ROBERT S., MOSES, MARSHA A., LUER, CARL A.

(GAH, CAL) 1600 Ken Thompson Parkway, Mote Marine Laboratory, Sarasota, FL 34236; (JWH, MAM) 320 Longwood Avenue, Harvard Medical School, Children's Hospital, Boston, MA 02115; (RSL) 77 Massachusetts Avenue, Massachusetts Institute of Technology, Cambridge, MA 02139

Isolation and preliminary characterization of a collagenase/gelatinase inhibitor from shark cartilage

Angiogenesis, the process of new blood vessel formation, is essential for the uncontrolled growth of solid tumors, and facilitates the metastasis of transformed cells. Inhibitors of angiogenesis hold great promise in the search for improved cancer therapies. During angiogenesis, the successful migration of endothelial cells from the vasculature to a focus of developing tumor cells depends upon the proteolytic activity of matrix metalloproteases (MMPs) to degrade the basement membrane of the parent vessel and the extracellular matrix. Inhibitors of these enzymes have been shown to inhibit angiogenesis. We show that high salt extracts of cartilage from several shark species, including bull Carcharhinus leucas, lemon Negaprion brevirostris, and nurse Ginglymostoma cirratum, contain collagenase/gelatinase inhibitory activity. From such extracts, a protein that inhibits gelatin degradation by the mixture of MMPs secreted by A2058 human malignant melanoma tumor cell line has been isolated. The partially purified inhibitor is heat stable in the absence of a reducing agent, and has an approximate molecular weight of 20 kD, as determined by both size exclusion chromatography and SDS polyacrylamide gel electrophoresis. Isoelectric focusing indicates the inhibitor is a basic protein, with a pI of approximately 9.0. The potential anti-angiogenic activity of the inhibitor is currently being investigated. (Session 20, Sunday, July 8, Penn Stater, Room 207, 1:30)

 


*JENSEN, CHRISTOPHER F., NATANSON, LISA J., PRATT, JR., HAROLD L., KOHLER, NANCY E., CAMPANA, STEVEN E.

(CFJ, LJN, HLP, NEK) 28 Tarzwell Dr., NOAA/NMFS, Narragansett, RI 02882; (SEC) P.O. Box 1006, Bedford Institute of Oceanography, Nova Scotia, Nova Scotia B2Y 4A2 Canada

The reproductive biology of the porbeagle shark, Lamna nasus, in the western north Atlantic ocean

Reproductive organs from 393 male and 382 female porbeagles, Lamna nasus, caught in the western North Atlantic Ocean, were examined to determine size at maturity and reproductive cycle. Males ranged in size from 86 to 246 cm fork length (FL) and females ranged from 94 to 288 cm FL. Maturity in males was best described by an inflection in the relationship of clasper to fork length when combined with clasper calcification. Males matured between 162 and 185 cm FL with 50% mature at 174 cm FL. In females, all internal organ measurements related to body length showed a strong inflection around the size of maturity. Females matured between 209 and 231 cm FL with 50% mature at 218 cm FL. After a protracted fall mating period (September - November), females give birth to an average of 3.9 young in the spring (March - June). As in other lamnids, young are nourished through oophagy. Evidence from this study indicates a one year reproductive cycle with gestation lasting 8-9 months. (Session 10, Saturday, July 7, Penn Stater, Room 207, 2:15)

 


KAJIURA, STEPHEN M.

PO Box 1346, University of Hawaii, Kaneohe, HI 96744

Electroreception in carcharhinid and sphyrnid sharks

The unique head morphology of sphyrnid sharks might have evolved to enhance electrosensory capabilities. The enhanced electrosensory hypothesis is tested by comparing the behavioral responses of carcharhinid and sphyrnid sharks to prey-simulating electric stimuli. Juvenile scalloped hammerhead and sandbar sharks orient to dipole electric fields from approximately the same distance (25-30 cm) and thus demonstrate comparable threshold sensitivities (<5 nV/cm). Despite the similarity of response threshold, the orientation pathways and behaviors differ for the two species. Hammerheads typically demonstrate a pivot orientation in which the edge of the cephalofoil closest to the dipole remains stationary while the shark bends its trunk to orient to the center of the dipole. In contrast, sandbar sharks orient with a lateral head snap to bite at the dipole. The different orientation types are attributable to the hydrodynamic properties of the cephalofoil, which enable the hammerheads to execute sharp turns at high speed. The greater trunk width of the sandbar sharks prevents them from demonstrating the same degree of flexibility. Therefore, although the sphyrnid head morphology does not appear to confer a greater sensitivity to dipole electric fields, it does provide i) a greater lateral search area, which may increase the probability of prey encounter, and ii) enhanced maneuverability, which may aid in prey capture. (Session 7, Saturday, July 7, Penn Stater, Room 207, 9:30

 


*KEENEY, DEVON B., HEUPEL, MICHELLE, HUETER, ROBERT E., HEIST, EDWARD J.

(DBK, EJH) Fisheries and Illinois Aquaculture Center, Southern Illinois University Carbondale, Carbondale, IL 62901; (MH, REH) 1600 Ken Thompson Parkway, Mote Marine Laboratory, Sarasota, FL 34236

A genetic investigation of philopatry in blacktip sharks (Carcharhinus limbatus) utilizing continental nurseries along the U.S. Atlantic and Gulf of Mexico coasts: preliminary results using mitochondrial control region haplotypes.

Blacktip sharks (Carcharhinus limbatus) are a highly migratory elasmobranch species with large populations occurring along the U.S. south Atlantic coast and the Gulf coasts of the U.S. and Mexico. Tagging and tracking studies conducted by Mote Marine Laboratory have suggested philopatric behavior in C. limbatus populations located in coastal areas of the Gulf of Mexico. The present study investigated natal site fidelity, a form of philopatry, within blacktip populations based upon haplotype frequencies among five continental nursery areas. Haplotype frequencies were determined by manually sequencing the entire mitochondrial control region (approximately 1068 bp) of 30 neonates from each of three nursery areas on the central Gulf coast of Florida, 30 neonates from the western Gulf coast of Mexico and 8 neonates from the Atlantic coast of South Carolina. If female blacktip sharks in these regions are philopatric for their natal nursery areas, a significant difference in mtDNA haplotype frequencies should be present among nurseries as a result of genetic drift. (Session 3, Friday, July 6, Penn Stater, Room 207, 4:00)

 


*KOESTER, DAVID M., MEDINA, CYNTHIA L., LUER, CARL A.

(DMK, CLM) 11 Hills Beach Road, University of New England, College of Osteopathic Medicine, Biddeford, ME 04005; (CAL) 1600 Ken Thompson Parkway, Mote Marine Laboratory, Sarasota, FL 34236

Development of the electric organ of Raja eglanteria

The electric organ of Raja eglanteria consists of paired, longitudinal columns of disc-shaped electrocytes within the lateral musculature of the tail. Although it is known that electrocytes develop from embryonic hypaxial muscle fibers, little information exists on the stages of this differentiation process. Examination of H&E stained paraffin sections through the tail of skate embryos sampled at weekly intervals (hatching occurs around week 12) and at 3 months post-hatching reveals that each electrocyte develops from a single skeletal muscle fiber. Electroblasts, or immature electrocytes, are first identified during the 5th week of development and are distinguished from their skeletal muscle precursors by an increase in number of nuclei and a shortening of fiber length. As development proceeds (weeks 6-8) electroblasts continue to shorten as the rostral end expands to form a club-shaped cell. By the 10th week of development, a further expansion of the rostral end and regression and thinning of the caudal end results in the formation of a thick, transversely oriented disc-like cell which closely resembles a structurally mature disc-shaped electrocyte. Further development of electrocytes involves expansion and thinning of the disc in the transverse plane. Electrocytes are fully differentiated by 3 months post-hatching. (Session P-14, Saturday, July 7, Penn Stater, Deans Hall)

 


KOOB, THOMAS J.

12502 North Pine Drive, Shriners Hospital for Children, Tampa, FL 33612

A history of elasmobranchs in public aquariums and their impact on public perception: from visual imagery to swimming visuals

Prior to the opening of public aquariums in the second half of the 19th century, inhabitants of temperate latitudes had little chance of encountering elasmobranchs beyond the fish market, and certainly very few were lucky enough to see one alive. The only means of visualizing an elasmobranch was through illustrations in the scientific literature, artistic renditions, or sensational reports in the popular press. These sources were not at all times entirely accurate. Even scientific illustrations perpetuated earlier misconceptions of elasmobranch morphology. The opening of public aquariums dispelled many of the myths surrounding these fish. Sharks, skates and rays were displayed in public aquariums at Berlin (1869), Frankfurt (1872), Brighton (1872), Naples (1874), Hamburg (1884), Plymouth (1888), Helgoland (1892), Rovigno (1892), New York (1896), and Monaco (1905). Species regularly displayed included Scyliorhinus canicula, Scyliorhinus catulus, Squatina angelus, Squalus acanthias, Galerohinus galeus, Pristiurus malanostomus Mustelus laevis, Trigon sp., Torpedo oculata, Torpedo marmorata, Raja spp. By 1920, over 45 aquariums were drawing 10 million visitors a year. The public perception of sharks, skates and rays slowly evolved during this period, not only because of direct exposure to live fish, but also because of novel observations on elasmobranch biology by watchful attendants. (Session 26, Monday, July 9, Penn Stater, Room 207, 2:00)

 


KOOB, THOMAS J., *SUMMERS, ADAM P.

(TJK) 12502 North Pine Drive, Shriners Hospital for Children, Tampa, FL 33612; (APS) 3060 VLSB, University of Califronia, Berkeley, Berkeley, CA 94720

The art of illustrating elasmobranchs

Sixteenth to nineteenth century expeditions to the subtropical and tropical new world and beyond returned to Europe with astounding discoveries of animal and plant species, many of which were either preserved or brought back alive. Transporting elasmobranchs alive was impossible and preserving them was impractical. Expedition naturalists had to sketch fresh specimens, thereby capturing their natural shape and colors, in order to lend credence to the existence of these exotic fish. Many of these illustrations were gross misconceptions and clearly not drawn from life, others were accurate and wonderful renderings. As scientific illustration became the necessary norm in the 19th century, morphological accuracy became more important than artful execution. Many scientists and emerging professional illustrators incorporated masterful techniques while at the same time maintaining precise portrayals. The transition from fanciful renditions to anatomically accurate and artistically satisfying illustrations of elasmobranchs eventually gave way to a workmanlike iconographic style in the 20th century. This is pedantic and abbreviated illustrative technique seems to be giving ground to a renaissance of the more pleasing styles of the late 1800's and early 1900's. An historical narrative on the artistic and not, accurate and erroneous, portrayals of elasmobranchs will be delivered. (Session 26, Monday, July 9, Penn Stater, Room 207, 12:00)

 


*LUER, CARL A., WALSH, CATHY J., NOYES, DAVID R.

1600 Ken Thompson Parkway, Mote Marine Laboratory, Sarasota, FL 34236

Preliminary studies of allograft rejection in juvenile clearnose skates Raja eglanteria

As part of our effort to characterize cell mediated immune function in elasmobranch fishes, studies to examine rejection responses to skin autografts and allografts using juvenile clearnose skates Raja eglanteria were initiated. Approximately 1 cm2 sections of skin were removed from the dorsal surface of donor animals and transplanted either to the same animal (autograft, n= 8) or to unrelated animals of the same species (allograft, n= 9). Skin grafts were photographed weekly for the first eight weeks, then biweekly for up to eighteen weeks. Visible responses were evaluated in terms of progressive infiltration by pigmented cells, relative inflammation, and general appearance of the graft. Grafts were biopsied weekly for eight weeks, and the presence of potential B- and T-lymphocytes were visualized by RNA in situ hybridization using riboprobes specific for immunoglobulin and T-cell receptor antigen genes. Autografts were accepted within three to four weeks while allografts were chronically accepted over times ranging from four to eight weeks. None of the allografts was rejected. These preliminary findings with R. eglanteria contradict results of three earlier reports demonstrating chronic (6-7 week) rejection of skin allografts using shovelnose guitarfish Rhinobatos productus, southern stingray Dasyatis americana, and horn shark Heterodontus francisci. (Session 20, Sunday, July 8, Penn Stater, Room 207, 1:45)