Florida Museum of Natural History

Abstracts of AES Scientific Papers

American Elasmobranch Society 16th Annual Meeting
June 14-20,2000 La Paz, B.C.S., México, U.S.A.
ABSTRACTS - Part 2: Dávila Ortíz through Huff

Universidad Autónoma de Baja California Sur, Laboratorio de Elasmobranquios, Carretera al sur km. 5.5, La Paz, B.C.S., C.P. 23080, México

Gymnura marmorata (Cooper, 1863) and Gymnura crebripunctata (Peters, 1869), two species or sexual dimorphism?

The distribution of the butterfly ray Gymnura marmorata (Cooper, 1863), is from Punta Concepcion California to north of Perú and Gulf of California. Peters (1869) described  Gymnura crebripunctata as a new specie with a distribution from southwestern coast of Baja California to Ecuador and Gulf of California. Breder (1928), was the first in consider as an only specie. Castro Aguirre and Espinosa-Pérez (1996) considered G. crebripunctata as a valid specie. Observations in the fishery camp of Puerto Viejo in Bahía Almejas, western coast of Baja California Sur, México, reported since 1992, the presence of females of G. marmorarata and males of G. crebripunctata. We made morphometric measures to compare the growth, the form and the body structures including the rostrum length that McEachran and Notabartolo (1995) used for the species identification. The results indicated that the growth is similar for males and females (except rostrum length that has an alometric growth) and the males acquired their body form near reproductive size. We might say that G. marmorata enter to Bahía Almejas in spring-summer principally with reproductive intentions.

19/06/2000 - 08:00:00 AM - Salon Madre Perla


Estación Hidrobiológica de Puerto Quequén and Museo Argentino de Ciencias Naturales "Bernardino Rivadavia". Angel Gallardo Av. # 470, (1405) B.A. Argentina.

Seasonal variation on diet of the narrownose smooth hound, Mustelus schmitti, Springer, 1939 (Chondrichthyes: Triakidae) from Puerto Quequen, Argentina

The narrownose smooth hound is an important economic resource for the coastal fleet at Quequén harbor (38° 37´S, 58° 50´ W). The aim of this study is to analyze the seasonal variation on diet for this species in the Puerto Quequén area. We studied 84 stomachs obtained from specimens captured by the trawl coastal fleet, between October 1998 and November 1999. We compared the diet among seasons and between sexes by Spearman correlation index, taking into account the frequency of each prey item. Winter season was not correlated with summer (rsc 0.38; p > 0.2), autumn (rsc 0.015 ; p > 0.5) and spring (rsc 0.33; p > 0.2). Diet was not correlated between sexes neither in spring (rsc 0.62; p > 0.05) nor in winter (rsc 0.85 p > 0.1). The most common prey item were crabs (Fo = 78.57 %), polychaetes (Fo = 96.43 %), and during spring season, bony fishes (Fo = 76.92 %). Our results showed that, as in other areas of the species distribution, Mustelus schmitti (the narrownose smooth hound) has a fundamental benthonic and carcinophagous diet, particularly during autumn and winter. During spring their diet includes Clupeids (v.g. anchovy, Engraulis anchoita) which are pelagic and neritic species. These results might be showing an opportunistic predator behavior in this species.

19/06/2000 - 08:00:00 AM - Salon Madre Perla


(JDM) MLML, 8272 Moss Landing Road, CA 95039 USA; (SHG) BBFS, RSMAS, U. Miami, 4600 Rickenbacker Causeway, Miami, FL 33149 USA

Home range and diel movement patterns of the sub-adult lemon shark, Negaprion brevirostris, in Bimini, Bahamas

Knowledge of movement patterns is important for complete understanding of the natural history and ecology of a species. The lemon shark, Negaprion brevirostris, is a common shark of the shallow waters of Bimini Lagoon, Bahamas. Ultrasonic transmitters were surgically implanted in 29 sub-adult lemon sharks (144-198 cm in total length) to study spatial and temporal movements. During November 1992 to October 1995, 11817 position fixes were recorded. Sharks were tracked continuously for periods of 24 hours whenever possible and intermittently for up to 13 months. Using a modified minimum convex polygon method, mean home range estimates of sub-adults lemon sharks were an order of magnitude larger than those of juveniles (> 20 km+2). Juveniles and sub-adults used only a fraction of the available habitat. Home range overlapped and aggregations of up to 25 individuals occurred, suggesting that lemon sharks are not territorial. Sub-adult lemon sharks had distinct night and day centers of activity. Lemon sharks initially captured on the western side of the lagoon at night moved eastward at dawn and westward at dusk, whereas individuals captured in the eastern side of the lagoon appeared to have different diel patterns. These patterns may be related to feeding or refuging.

17/06/2000 - 04:45:00 PM - Salon Madre Perla


Universidad Autónoma de Baja California Sur Laboratorio de Elasmobranquios Carretera al Sur km. 5.5, La Paz, B.C.S., C.P. 23080, México

"El Niño"/Southern Oscillation effects on the shovelnose guitarfish, Rinobatos productus, and Pacific electric ray, Narcine entemedor, in Bahía Almejas, B.C.S., México

"El Niño" refers to a periodic warming of the sea surface along the coast of South America. "El Niño" also affected Baja California's species near the coast. Rhinobatos productus and Narcine entemedor are two viviparous species that conclude the reproductive cycle in Bahía Almejas. The shovelnose guitarfish and Pacific electric ray, have an annual reproductive cycle, with ovulation and fertilization occurring in late summer (July-August), followed by offshore movements and embryonic diapause. During 1998, the reproductive cycle was affected, the embryos development in part of the females started in late March or the first days of April, when normally they start the last days of April. The ova had the same reaction, the mature ova were ready in the same period. The uterus also were found with eggs with out embryos development, and all melted. Finally we could find only a few females in July and no one in August.

18/06/2000 - 10:15:00 AM - Salon Madre Perla


(DHCA)(VGCJ), Universidad Autónoma de Baja California Sur, Laboratorio de Elasmobranquios, Carretera al Sur Km. 5.5, La Paz, B.C.S., C.P. 23080, México. (FUR), CICIMAR-IPN, Departamento de Pesquerías, Carretera al Conchalito s/n, La Paz, B.C.S., C.P. 23090, México

Age and growth of the shovelnose guitarfish, Rhinobatos productus, in the western coast of Baja California Sur, México

The shovelnose guitarfish, Rhinobatos productus, has an annual reproductive cycle, with ovulation and fertilization occurring in early August followed by offshore movements and embryos diapause. Embryonic development started in May and completed by July or August (3 months). Males and females over 80 and 99 cm TL were mature. We describe the age and growth of the shovelnose guitarfish, on the western coast of Baja California Sur, Mexico. Samples were collected from artisanal fisheries in Bahía Almejas and Laguna San Ignacio from 1992 to 1998. The age was estimated from bands in the vertebral centra of 98 males and 321 females; the number of bands in females goes from one to 16 and in males from one to 11. The validation was attempted by using the marginal increment analysis; assuming an annual band formation. The length-weight relationship indicated an isometric growth for both sex (males = 2.92, females = 3.17). The Von Bertalanffy growth function parameters from the vertebral analysis were: L¥ = 100.5, K=0.24, to =-0.83 for males; L¥ = 136.69, K=0.16, to = -0.83 for females. The largest male and female were 106 and 142 cm TL.

17/06/2000 - 03:45:00 PM - Salon Madre Perla


Departamento de Oceanografia e Pescas da Universidade Dos Açores (DOP/UAÇ) Cais Sta. Cruz, 9901-862 Horta Azores - Portugal

Age and growth of juvenile tope shark, Galeorhinus galeus (Linnaeus, 1758), in the Azores

The age and growth of tope shark, Galeorhinus galeus, juvenile population segment in the Azores is presented. Vertebral centra were sampled between 1995-1997, during groundfish survey cruises aboard R/V "Arquipélago" within the Azorean EEZ. A modification of the cobalt nitrate technique provided highest reproducibility of age estimates and was therefore used in vertebral staining. Age estimates were based on calcified band counts. No significant differences in mean length-at-age data were found between males and females, hence von Bertalanffy juvenile growth parameters were estimated for sexes combined(L¥=207.34 cm, K=0.067, t0=-2.56). Empirical growth curve indicated that tope shark grows steadily at an average rate of 10 cm/year, in its first six years of life in the Azores. Periodicity of band deposition was assumed annual, according to previous research on the species. This assumption was not confirmed fully by independent length-frequency analysis (Bhattacharya method), however non-linear back-calculation (Monastirsky potencial equation) allowed verification of age readings. Comparison between these estimates and available published literature revealed significant differences on tope shark juvenile growth between the Azores and elsewhere. The possible causes and implications of the results are discussed, under the assumption of a single tope shark stock in the North-Eastern Atlantic.

17/06/2000 - 01:45:00 PM - Salon Madre Perla


(ND) Biological Sciences, University of East Anglia, Norwich, Norfolk, Nr47tj, UK; (JM) Centre For Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory, Lowestoft, Suffolk, Nr33 Oht, UK,

Movements of thornback rays Raja clavata in the Irish Sea: A comparison of conventional and archival tagging methods

Conventional tagging methods are a cheap and widely used method for estimating patterns and rates of movement. However, the behaviour and distribution of fishers determine the quality and quantity of information. To independently evaluate the utility of conventional tagging we marked 1810 individuals with Petersen discs at six sites in 1995. In 1996 we tagged 96 adults with electronic data storage tags (DSTs) which logged depth (pressure) every 10-min. and temperature every 24hrs. For comparison we tagged 120 adults with Petersen discs. Most of the Petersen tagged individuals (79%) were recaptured within 60-km of the release site. There was no evidence for directional or seasonal migration. Five of the 17 recaptured DSTs recorded data for >50 days. The tidal components of the pressure data allowed geolocation with a resolution of 12-km. The spatial patterns of movement were small-scale similar to that detected by Petersen tags, an average of 62.4-km on an N-S axis and 64.8-km on an E-W axis. The DSTs indicated marked heterogeneity in vertical movement patterns anging from extended periods on the bottom to extended excursions into mid-water, occasionally for days. Both tagging methods indicate that that this species does not undertake extensive movements or seasonal migrations.

17/06/2000 - 09:15:00 AM - Salon Madre Perla


(SAE) Hubbs Sea World Research Institute, 2595 Ingraham St., San Diego, CA 92109; (MLLD) Silliman University, 6363 Lakewood St., San Diego, CA 92122 , USA; (GLK) Scholander Hall, Scripps Institution of Oceanography, University of California San Diego, CA; (WFP) Southwest Fisheries Science Center, U.S. National Marine Fisheries Service, P.O. Box 271, La Jolla, CA. ; (RAR) Head, Borneo Marine Research Unit, Jalan Tuaran, Campus, Universiti Malaysia, Sabah, Locked Bag 2073, 88999 Kota Kinabalu, Sabah, East Malaysia.

Are the whale sharks (Rhincodon typus) of Southeast Asia resident or migratory?

Movements of individual whale sharks (Rhincodon typus), are almost unknown. Recent studies from the Sea of Cortez, indicates that whale sharks are highly mobile and may range for thousands of kilometers. However, most information on distribution is related to seasonal occurrences based on anecdotal reports of occasional sightings. This lack of information on basic biology, especially movement and migration patterns is a problem for resource managers, as the species is increasingly utilized for ecotourism and commercial harvest. The latter use had become particularly intense in the Philippines, where an unregulated harvest burgeoned in response to a dramatic increase in the market for whale shark meat and fins in Taiwan. Catches had fallen steeply despite increasing fishing effort and rising prices. In January 1998 we initiated an international cooperative research program with the Borneo Marine Research Unit of the Univ. of Malaysia, Sabah, the Marine Laboratory of Silliman University, Dumaguete, Philippines; and the World Wildlife Fund-Philippines to determine if the whale sharks observed in the greater Sulu Sea region are resident or migratory. Using satellite telemetry we monitored the movements of whale sharks from the greater Sulu Sea region for up to 4 months. Results of this study will be presented.

15/06/2000 - 02:00:00 PM - Salon Madre Perla

*FAHY, D. P., and SPIELER, R. E.

Nova Southeastern University Oceanographic Center (NSUOC) and Guy Harvey Research Institute (GHRI) 8000 North Ocean Drive, Dania Beach, FL 33004, USA

Ultrasonic tracking of the yellow stingray, Urolophus jamaicensis

In order to initiate a study on the diel and seasonal movements of yellow stingrays in South Florida, we completed preliminary tracking utilizing ultrasonic telemetry. A 75-kHz tag (Sonotronics, Tucson, AZ) was sutured to the medial epaxial musculature of a 35-cm female stingray immediately after capture and anesthesia (MS-222). The stingray was returned to the capture site within 11 min of capture and tracked from a 9-m boat with a handheld directional hydrophone. The animal was tracked continuously for 28 h and locations were recorded at 30 - 45 min intervals. There was an increase in activity after sunset with peak activity between 0100 and 0700 hours. During photophase, the stingray apparently remained in a fixed location (at least within the 5-m circular error of our methodology as determined by previous accuracy tests). Direct observations during photophase showed the stingray to be buried in the sediment with only the transmitter uncovered. Laboratory testing for effects of transmitter placement on captive behavior demonstrated no apparent influence on swimming or feeding. Our study indicates that ultrasonic telemetry is a suitable methodology for studying the movements of yellow stingrays.

19/06/2000 - 08:00:00 AM - Salon Madre Perla


(KAF; MVA) Bimini Biological Field Station/University of Illinois at Chicago, Department of Biological Sciences, Chicago, Il 60607-7060; (SHG) Bimini Biological Field Station/University of Miami, Division of Marine Biology and Fisheries, Miami, FL 33194;

Genetic variability of Western Atlantic lemon sharks, Negaprion brevirostris, based on microsatellite DNA analysis

The application of microsatellite DNA analysis in elasmobranch biology is becoming a powerful tool in determining genetic relationships within and between populations. We have developed several microsatellite markers for lemon sharks Negaprion brevirostris to assess within population variability and large-scale stock structure of this species. Screening approximately 15,000 colonies yielded 95 positive clones, of which 45 have been sequenced. Four loci, LS11, LS15, LS22 and LS 30, have been used to genotype several hundred individuals from four populations: Gullivan Bay, Florida (N=24), Marquesas Key, Florida (N=100), Bimini, Bahamas (N=400), and Atol das Rocas, Brazil (N=30). High levels of heterozygosity (.69-.90) and numerous alleles (18-41) were observed at all four loci. Analyses of the data suggest very little structure in Western Atlantic populations. Although Rho values between populations and Weir and Cockerham's F were significant, all values were small (rho ranged from -.008 to .045; F=.019). Significance is likely attributable to our large sample size and high resolution of the markers and may not reflect biological differences. These low levels of differentiation and few observed private alleles suggest that the Western Atlantic populations may comprise one breeding stock.

18/06/2000 - 04:00:00 PM - Salon Madre Perla


Centro Interdisciplinario de Ciencias Marinas-IPN; IPN s/n, La Paz, B.C.S. C.P.2300 México

Trophic role of sharks in the ecosystem and its response to exploitation

Characteristics like low reproductive potentials, slow growth rates, delayed sexual maturation, as well as newborn recruitment to artisanal fisheries, they point out sharks as highly vulnerable. The objective of this study is to obtain interpretations on the role of sharks in the ecosystem, and to evaluate its answer to the exploitation, using the dynamic simulation model ECOSIM. Starting from representative solutions of 11 ECOPATH ecosystem models, ECOSIM was used to simulate increments in exploitation rate of the sharks group, evaluating the answers through changes in biomass and stability properties of the ecosystem. The groups of sharks subjected habitually to fishing, showed a higher capacity to resist increments in the exploitation rate, their responses were bigger as the fishing effort increases and finally their recovery time was low. On the other hand, strong and fast responses were presented in sharks groups originally with smaller fish rate levels, the responses didn't change significantly with the increment of the exploitation rate and their recovery was slow. Contrary to the rest, in reef ecosystems the impact is important and its recovery critical, although there were not bigger changes in the ecosystem.

19/06/2000 - 08:00:00 AM - Salon Madre Perla


University of California, Santa Cruz 922 Ponselle Lane #2; Capitola, CA, USA

Chondrichthyans using evans blue dye techniques

Evans blue dye techniques were employed to estimate the plasma and blood volumes of two species of chondrichthyans: the gray smoothhound, Mustelus californicus (n = 10) and the leopard shark, Triakis semifasciata (n = 20). The dye was administered intravenously (0.5-0.6 mg/kg) and blood samples were collected at 10, 20, and 30 minutes after injection. Optical density of plasma samples was measured at 620nm using a spectrometer and compared against standard curves to find the concentration of the dye in the plasma. The concentration of dye in the blood at the time of injection was mathematically extrapolated and then used to calculate plasma and blood volumes. Mean plasma volumes were estimated to be 30.82 +/- 2.45ml/kg and 39.15 +/- 4.48ml/kg, for M. californicus and T. semifasciata, respectively. Likewise, after correction with simultaneously measured hematocrit values, mean blood volumes found were 45.49 +/- 2.99ml/kg and 54.16 +/- 5.96ml/kg. These values appear to fit into both the evolutionary trend previously proposed for fishes and the notion that within a phylogenetic group, blood volume increases with activity level (Thorson 1961; Smith 1982).

16/06/2000 - 08:00:00 AM - PingPong Area


Department of Marine Science University of South Florida 140 7th Ave. SO. ST. Petersburg, FL USA

A comparative assessment of biochemical measures of nutritional condition in two Antarctic fishes

Electrona antarctica and Bathylagus antarcticus, dominant components of the Southern Ocean pelagic ecosystem with disparate life histories, were utilized for a comparative study of 21 indices of nutritional condition. Indices were compared by observing spatial and temporal changes associated with the marginal ice zone bloom in the Northwestern Weddell Sea. Variability between indices and species were observed. Nutritional condition of Electrona increased in 11 of 21 indices in response to the bloom. In contrast, only 3 indices changed in Bathylagus. Earlier work, which suggested that deeper living, non-migrating species would not be affected by the bloom until after shallower living, migratory species, was supported. Of the assays tested, RNA:DNA appeared to be the most sensitive; lipid analysis was also effective. The combined assessment of many measures, including biochemical, compositional, dietary, and age estimates from single specimens is possible if the samples are treated with sufficient care. The reliance upon a single measure to help interpret the ecology of a species, especially in nekton sized species, is not as effective as techniques used in combination.

16/06/2000 - 08:00:00 AM - PingPong Area


Mote Marine Laboratory, Sarasota FL 342356

Preliminary investigations on the effects of exposure to the endocrine-disrupting compound 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) on clearnose skate Raja eglanteria development

Studies conducted on teleosts, amphibians, reptiles, birds, and mammals have established that exposure to endocrine-disrupting compounds during the critical period of embryogenesis can drastically impair normal developmental processes. However, little or no information is available on the effects of xenobiotic chemicals on development in elasmobranchs, animals that possess limited reproductive capacities and often tend to bioaccumulate environmental contaminants. In response to this need, the goal of this preliminary study was to investigate the effects of the putative endocrine disruptor 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) on sexual differentiation and immunological development of captive bred clearnose skate Raja eglanteria embryos. Skate embryos were exposed to one of two environmentally-relevant levels of DDT or vehicle via immersion during weeks 3-7 of the 12-week developmental period. Following chemical exposures, animals were sacrificed and patterns of sexual differentiation were investigated through histologic and immunocytochemical observations on primary and secondary sex characters. Development of the immune system was examined through peripheral white blood cell counts. Impairment of ovarian but not testicular development was observed in some skate embryos at both levels of chemical exposure. Disturbances in the development of secondary sex characters (gonaducts, claspers) were not observed in either sex. Significant reductions in peripheral white blood cell counts were associated with both levels of chemical exposure and may be associated with endocrine-related processes. Though preliminary, this study represents one of few investigations on the effects of endocrine disruption in this phylogenetically ancient and ecologically important vertebrate group. In addition, it introduces a sophisticated animal model for assessing chemically-mediated disturbances in embryonic development.

19/06/2000 - 08:00:00 AM - Salon Madre Perla


Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota FL 34236

Life and death in the oviducal gland: apoptosis during sperm storage in female bonnethead sharks, Sphyrna tiburo

Sperm storage is a complex mechanism that permits successful reproduction to occur despite temporal separation between between mating and ovulation. Although sperm storage has evolved independently in every vertebrate class except Agnatha, certain elasmobranchs are the only placental vertebrates other than some bat species that are known to store sperm for long periods of time (>2 weeks). Observations on sperm storage in elasmobranchs have largely been confined to reports on its presence or absence in selected species and little information is available on the actual maintenance of sperm viability in the oviducal gland, the organ responsible for sperm storage in female elasmobranchs. The present study examined apoptosis (programmed cell death) of spermatozoa in the oviducal gland of preovulatory female bonnethead sharks, Sphyrna tiburo, as part of a larger investigation on environmentally-mediated differences in reproductive success. Sperm apoptosis was detected in the oviducal gland through enzymatic in situ labeling of apoptosis-induced DNA strand breaks using the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) technique. Apoptotic sperm were detected in all oviducal preparations examined at varying levels of cellular density. However, no apparent differences in sperm viability were observed between females collected from two study sites. Thus, differences observed in the reproductive success of these groups cannot be attributed to differences in cell survival during oviducal sperm storage. Despite these observations, the present study describes a useful method for defining the physiological mechanisms that regulate sperm storage in elasmobranchs.

18/06/2000 - 08:45:00 AM - Salon Madre Perla


(JG; CAM) Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway; Sarasota, FL 34236.; (BGS) New York University School of Medicine, Nelson Institute of Environmental Medicine; (KA) Biology Department, New College, University of South Florida 5700 North Tamiami Trail; Sarasota, FL 34243

Relaxin n' reproducin' in the male bonnethead shark Sphyrna tiburo

Relaxin is a 6-kDa polypeptide that is best known for its role in regulating the extensibility of the reproductive tract of female mammals during pregnancy and parturition. Relaxin is also roduced in certain male vertebrates (i.e., elasmobranchs, birds, mammals) by the testes or accessory sex organs and appears to play some, albeit unclear, role in regulating sperm kinematics. The present study investigated changes in serum relaxin concentrations of immature and mature bonnethead sharks Sphyrna tiburo, in an effort to clarify its role in this gender. Serum relaxin concentrations in two groups of mature S. tiburo and one group of immature S. tiburo were measured by radioimmunoassay. In mature male S. tiburo, serum relaxin concentrations followed a pattern associated with the reproductive cycle in which peak levels occurred during late spermatogenesis and mating. No temporal pattern in serum relaxin concentrations was observed for immature male S. tiburo, also supporting the hypothesis that relaxin functions in sperm transport. Preliminary observations on the immunohistochemical localization of relaxin in the male reproductive tract will be presented to better define its specific role during reproductive events.

18/06/2000 - 09:30:00 AM - Salon Madre Perla

*GOLDMAN, K. J., and MUSICK, J. A.

Virginia Institute of Marine Science P.O. Box 1346 Gloucester Point, Virginia, 23062 U.S.A.

Distribution, segregation, and the potential for variable growth rates in salmon shark, Lamna ditropis, in the western and eastern North Pacific

The salmon shark, Lamna ditropis, is widespread in the boreal North Pacific, ranging between 35oN-65oN in the western Pacific and 30oN-65oN in the eastern Pacific. They are the largest apex fish predator in the upper pelagic zone there. Maximum size has been reported at 305cm TL, but average size range seems to be between 200-250cm TL. Like many other elasmobranchs they appear to exhibit a life history strategy characterized by slow growth, late maturity, low fecundity and, therefore, extremely low intrinsic rates of population increase. Their seasonal distribution is difficult to assess at this point, however there appears to be some north-south movement during the year in both the eastern and western Pacific. Additionally, there appears to be movement across the Pacific basin which may create mating aggregations in the Gulf of Alaska and Prince William Sound during late summer. Current research is focusing on age, growth, demographics and thermal biology of salmon sharks in Gulf of Alaska and Bering Sea waters, with the goal of fostering responsible long-term management. The potential variability existing between growth rates of salmon sharks in the western and eastern North Pacific, strong sexual and size segregation, and unknown amounts of bycatch all complicate management issues for this species.

17/06/2000 - 05:30:00 PM - Salon Madre Perla


Universidad Autónoma de Baja California Sur Departamento de Geología Marina Carretera al sur Km. 5.5, La Paz, B.C.S., C.P. 23080, México

Cenozoic Chondrichthyans assemblages from Baja California Peninsula

This study is part of my Master´s Thesis. Until now, it is the most complete record of sharks, batoids and chimaeroids in the Baja California Peninsula. At least nine time periods with records of these fossils are recognized. The first record is the Sepultura Formation (east-southeast of El Rosario, Baja California) with a small fossil fauna of sharks and rays corresponding to a Danian age (in correlation to the Tethys age reference) or Early Paleocene. It is dominated mainly by small specimens from Odontaspididae and Myliobatoidea. The second record is from the Tepetate Formation (arroyo El Conejo, west of La Paz). The fauna contains an increased number of 13 species of Thanetian age (Late Paleocene), including Paleocarcharodon orientalis (Sinzow 1899). This is probably the only seventh global record for this specie, including Russia, Congo, Marroco, Germany, Maryland and South Carolina. The third record is found in the Tepetate Formation (from the arroyo El Aguajito to the rancho La Fortuna, northwest of La Paz) and in the Bateque Formation (Mesas San Ramón and Todos Santos, east of the San Ignacio Lagoon, and Arroyo El Mezquital west-northwest of La Purísima) with a record of at least 30 species of sharks and batoids corresponding to a Lutetian - Bartonian age (Middle Eocene). The faunas are mainly dominated by Isurus praecursor (Leriche 1904), Carcharocles sokolowi (Jaekel 1895), Rhinobatus sp. and Coupatezia sp. The fourth record belongs to the basal bed of the San Gregorio Formation (rancho San Ramón, arroyo San Gregorio and rancho El Malbar, arroyo El Mezquital) and El Cien Formation.

18/06/2000 - 01:45:00 PM - Salon Madre Perla


Instituto de Ecología, A. C. Km 2.5 Antigua Carretera a Coatepec, Xalapa, Veracruz, México

Phylogenetic relationships among hammerhead sharks

Hammerhead sharks are considered to be closely related to the carcharhinid sharks based on the large number of shared morphological and molecular characteres. However, studes of the phylogenetic relationships within the family Carcharhinidae have yielded conflicting results. The family Carcharhinidae is not monophyletic unless the hammerheads are included within that family. Then, despite its many unique features, the Sphyrnidae is not a valid family? The resent family Sphyrnidae is currently divided into two genera: Eusphyra and Sphyrna. This study attempts to understand the interspecificic relationships among the hammerhead sharks based on chondrocranium morphology, tooth arregement and external morphology data. Morphological features were contrasted for eight species of Sphyrnids, and two species of Carcharhinids sharks as outgroups for character polarization and for rooting. Maximum parsimony analyses were employed using quantitative and qualitative characters in the program PAUP 3.1.1.

18/06/2000 - 04:15:00 PM - Salon Madre Perla


Instituto de Ecología, A. C. Km 2.5 Antigua Carretera a Coatepec, Xalapa, Veracruz, México

Allometry and skull design in sphyrnids sharks

The hammerhead sharks, as all vertebrates, increases in size during development. This study shows the consequences of the changes of size for morphological shape and function of the skull in the sharks of the Family Sphyrnidae. Additionally, it represents an effort to elucidate evolutionary aspects about ontogeny, embriology and morphology of the group. Multivariate comparisons of head shape among species indicate that mensural attributes are highly correlated with head size, thus displaying strong evolutionary allometry. The ratio head length/total length considered diagnostic to Sphyrna blochii is as strongly dependent on body size as untransformed measurements and not reflect multivariate pattern of shape variation and, thus not can be useful in descriptive taxonomic studies. Size-independendent variation in form seems to be continuous among species with no apparent morphological gaps with which to distinguish natural species groups. Changes in morphology in these fishes are highly corservative and result from subtle, allometric and heterochronic changes in relative growth rates among skull structures.

19/06/2000 - 08:00:00 AM - Salon Madre Perla


(WH) 62 Front Street, Punta Gorda, Belize, (BK) Department of Geological Sciences and Marine Science Program, University of South Carolina, Columbia, SC 29208, USA.

Population size estimates of whale sharks, Rhincodon typus, off the Belize Barrier Reef

At least 6 sites where whale sharks aggregate predictably are recorded for the Indo-Pacific and Pacific Oceans, whereas the literature reports none, save occasional sightings, for the Atlantic Ocean. Following an investigation of local fishermen's reports, we document here a new aggregation site and possible centre of distribution of whale sharks Rhincodon typus in the Caribbean, on the Belize Barrier Reef. Gladden Spit, a promontory on the barrier reef harbours a dense and predictable aggregation of whale sharks that feed on the freshly released gametes of large spawning aggregations of 2 Lutjanid species during the full moon periods from April to June. A preliminary survey of the population in 1998 based on individual markings and scars yielded an estimated population of 25 individuals. A tagging programme undertaken in 1999 identified 15 sharks. Combined with a mark release recapture study undertaken in 1999, that also accounted for sighted but untagged sharks, the population is estimated at a minimum of 23 individuals. Mean tail length (TL) of tagged whale sharks was 5.05 m. Although the sex ratio could not be determined with confidence, only one shark possessed the TL to qualify it as sexually mature. Tagged individuals from the May full moon were re-sighted feeding during the June full moon indicating tag retention and site fidelity at Gladden Spit during the snapper spawning-season. Following this period, tagged whale sharks were re-sighted north, south, and east of the aggregation site outside the barrier reef in deep water, associated with schools of bonito, blackfin, bigeye, and skipjack.

15/06/2000 - 03:00:00 PM - Salon Madre Perla

*GRUBBS, R. D., and MUSICK, J. A.

Department of Fisheries Science Virginia Institute of Marine Science School of Marine Science College of William & Mary

Movements of juvenile Carcharhinus plumbeus in Chesapeake Bay, Virginia USA using sonic telemetry and mark-recapture methods

Ultrasonic telemetry was used to investigate short-tem movements of juvenile Carcharhinus plumbeus (sandbar sharks) in Chesapeake Bay. During the summers of 1997, 1998, and 1999 a total of ten juvenile (44-62 cm PCL) C. plumbeus were fitted with transmitters containing depth sensors and tracked continuously for 10-50 hours. CTD casts were made from surface to bottom hourly. Minimum convex polygon activity space estimates (N=7; tracks>24hrs) ranged from 39.5 to 249.5 km2. Bottom depth was one to forty meters and mean swimming depth ranged from 6.6 to 15.5 meters. Twenty to fifty percent of depth fixes were within two meters of the bottom and subjects frequently made rapid ascents to surface waters, even when bottom depth was >35 meters. Swimming depth was significantly deeper during daylight hours for three tracks. Movement patterns were analyzed with environmental data and tidal current models and compared with nursery delineation models using GIS. From 1995 to 1999, 1603 juvenile (<100cm PCL) C. plumbeus were tagged in Chesapeake Bay and Virginia coastal waters. Data from 39 recaptures (mean=230 days; range 4-918) were used to investigate longer-term movements within the summer nursery and during migrations to wintering areas and to investigate summer nursery fidelity in subsequent years.

17/06/2000 - 10:45:00 AM - Salon Madre Perla

*GRUBBS, R. D., and MUSICK, J. A.

Department of Fisheries Science Virginia Institute of Marine Science School of Marine Science College of William & Mary

Temporal and spatial nursery delineation for Carcharhinus plumbeus in the lower Chesapeake Bay, Virginia USA

The lower Chesapeake Bay represents a primary nursery for Carcharhinus plumbeus, sandbar sharks. The VIMS Longline Survey was expanded from 1993 to 1999 to include ancillary stations throughout the Virginia Chesapeake Bay to spatially delineate the nursery. Catch and environmental data from 120 stations were used to characterize nursery habitat using categorical analysis regression tree (CART) modeling and Spearman's rank correlation. Distance from Bay mouth and salinity were the most influential parameters in these models. These data were used to construct GIS maps delineating areas of Chesapeake Bay meeting the environmental criteria thereby identifying essential nursery habitat for this species in Chesapeake Bay. The VIMS survey has included standard stations the lower Chesapeake Bay since 1980. CPUE and environmental data from two stations sampled consistently in summer months from 1990 to 1999 were used to temporally delineate utilization of this nursery. Immigration was highly correlated with surface temperature while emigration was highly correlated with length of day. From 1995-1999, 1603 juvenile C. plumbeus were tagged in Chesapeake Bay and Virginia coastal waters. Data from 39 reported recaptures support the temporal nursery dynamics described from the CPUE data as well as elucidate migration atterns and winter nursery areas.

18/06/2000 - 10:45:00 AM - Salon Madre Perla


Department of Fisheries & Allied Aquacultures Auburn University 8300 State Highway 104 Fairhope, AL 36532 USA.

Short-term survival and movements of small carcharhinid sharks after catch-and-release angling in the northeast Gulf of Mexico

Ultrasonic telemetry was used to assess short-term survival and movements of small hooked sharks (Carcharhinidae) after release in a coastal nursery area in the northeast Gulf of Mexico. Sharks were caught with standardized rod and reel gear during June-October 1999. Ten Atlantic sharpnose Rhizoprionodon terraenovae, three finetooth Carcharhinus isodon, two spinner C. brevipinna, and two blacktip sharks C. limbatus were measured (<108 cm TL) and continuously tracked for a mean duration of 2.5 1.8 SD h (0.5-5.9 h). Activity and movement suggested short-term survival was at least 94%. The estimated rate of movement averaged 1.4 1.1 SD km/h, (0.5-5.2 km/h). The mean rate of movement of C. limbatus (3.6 km/h) was significantly faster than the other species (F=36.58, p<0.05). Differences in movements did not differ among hooking locations or fishing sites. Rate of movement was significantly correlated with playing time (r=0.671, p<0.05). The mean direction of net movement was 208° 77 SD or south-southwest. These findings suggest that anglers should be encouraged to reduce handling time of recreational bycatch in shark nursery grounds. High short-term survival of small hooked sharks suggests catch and release may reduce bycatch mortality and may be used in management of recreational shark fisheries.

17/06/2000 - 09:30:00 AM - Salon Madre Perla


Universidade Federal Rural de Pernambuco, Departamento de Pesca, Laboratório de Oceanografia, Av. Dom Manuel de Medeiros. s/n, Dois Irmáos, Recife - Pe, Brazil, Cep:52.171-900,

Reproductive biology of the scalloped hammerhead shark, Sphyrna lewini, in the southwestern equatorial Atlantic Ocean

The scalloped hammerhead shark, Sphyrna lewini, is globally distributed throughout tropical and temperate oceans. While aspects of their reproductive biology have been quantified in fishery-dependant studies at various locations, there is a paucity of relevant data from adult females and particularly gravid individuals throughout their distributions. Further, there is an absence of information describing life history in the southwestern equatorial Atlantic. In an attempt to address these issues, we examined ninety two specimens ranging in size from 121 to 321 cm total length (TL), collected from surface gillnetters operating off northeastern Brazil between January and December 1996. A common regression for TL and eviscerated weight (EW) was calculated as, logEW = -11.786+ 2.889 logTL. Females and males were categorised into reproductive stages (4 and 2, respectively) according to morphological changes in their gonads. Size at sexual maturity for females was estimated to be 240 cm TL, while males appeared to mature at between 180 and 200 cm TL. Gravid females had between 2 and 21 pups, varying in TL from 3 to 38 cm. Copulation and parturition occur outside the sampled area and possibly closer to the coast. Vitellogenisis and gestation each appear to take about 10 months with ovulation and parturition occurring during autumn and summer, respectively. With the exception of slightly lower uterine and ovarian fecundities, the results support the few existing data on the reproductive cycle of S. lewni in other areas.

18/06/2000 - 09:15:00 AM - Salon Madre Perla


Universidade Federal Rural de Pernambuco,Departamento de Pesca, Laboratório de Oceanografia Pesqueira, Av. Dom Manuel de Medeiros, s/n, Dois Irmáos, Recife - PE, Brazil, CEP: 52.171-900

Reproductive cycle of the blacknose shark, Carcharhinus acronotus, off northeastern Brazil

The blacknose shark, Carcharhinus acronotus, is a relatively small carcharhinid, typically occurring across continental shelf areas in the Atlantic Ocean, from North Carolina in the USA to southeastern Brazil. Its abundance and accessibility in nearshore areas off northeastern Brazil means that it often comprises a large proportion of elasmobranch catches from artisanal fishing operations. Despite its commercial importance, very little information is available with respect to life history traits and particularly reproductive biology off Brazil. To address this issue, we examined 129 specimens (81 females and 48 males), ranging in size from 49 to 131 cm total length (TL), caught by artisanal fishers using gillnets and research vessels using bottom longlines off the coast of Pernambuco, Brazil. Size at sexual maturity for males was estimated at between 93 and 104 cm TL, while females matured at between 101 and 106 cm TL. All gravid females (22 examined) contained 4 pups, varying in TL from 25.5 to 48.5 cm TL. Gestation appears to take between 8 and 9 months, with copulation and parturition occurring within the sampled area and mainly during April and December, respectively. The results provide evidence to suggest an annual reproductive cycle.

18/06/2000 - 08:30:00 AM - Salon Madre Perla


(HEJ) Southern Illinois University, Carbondale, IL; (GJR), Texas A&M University, College Station, TX. Southern Illinois University Fisheries and Illinois Aquaculture Center;

DNA microsatellites in blacktip shark (Carcharhinus limbatus): variation, population structure, and cross-species amplification

The blacktip shark (Carcharhinus limbatus) occurs in coastal waters of warm-temperate and subtropical oceans. To test the hypothesis that blacktip sharks in the US Atlantic and Gulfof Mexico comprise a single genetic stock a suite of polymorphic DNA microsatellite loci were developed and scored in blacktip sharks collected from Virginia, USA to Tamaulipas, Mexico. The power of individual loci to discern population structure was examined by scoring additional blacktip sharks from Baja California, Mexico. Cross-species amplification and the utility of microsatellite loci in carcharhinid sharks was evaluated by amplifying blacktip sharks DNA with primers developed in other species, and by amplifying DNAs from other species with primers developed in blacktip shark. The relationship between heterozygosity and the number of repeat units per microsatellite motif, and the relationship between number of alleles and statistical power for detecting stock structure will be discussed. Conclusions of genetic studies are compared to tagging data.

18/06/2000 - 03:45:00 PM - Salon Madre Perla


Department of Biological Sciences, Simon Fraser University, Burnaby, BC, V5a 1s6 Canada, Behavioural Ecology Research Group,

Tiger shark (Galeocerdo cuvier) habitat use and behavior in Shark Bay, Western Australia

Understanding the spatial distribution of animals, and the factors influencing these distributions, is one of the primary goals of ecologists. We used both acoustic telemetry and animal-borne video cameras ("Crittercams") to study tiger shark (Galeocerdo cuvier) predatory behavior and determine the influence of prey availability on shark habitat use. Crittercams provided depth and video data, which allowed us to collect behavioral data and accurate estimates of shark habitat use. Tiger sharks were found to move regularly between surface waters and the bottom. This diving behavior may be energetically more efficient than constant-depth swimming and may aid in prey detection and capture. Despite multiple encounters with potential prey, sharks rarely engaged in high-speed chases, and did not attack potential prey items that were vigilant. The abundance of tiger sharks' potential prey was significantly higher over shallow, seagrass habitats. Tiger sharks preferred these habitats, which is consistent with the hypothesis that shark distribution is at least partially determined by prey availability. Comparison of data collected simultaneously with Crittercams and acoustic telemetry showed no significant difference in average habitat use by tiger sharks, although, estimated habitat use of some individuals differed greatly between these methods.

17/06/2000 - 11:15:00 AM - Salon Madre Perla


Biological Programs. National Aquarium in Baltimore and University of Maryland and Center of Marine Biotechnology. University of Maryland Biotechnology Institute

The short term in vitro response of stingray trophonemata to exogenous agents

Myliobatoid rays reproduce via aplacental viviparity. Following absorption of the yolk, embryos consume organically rich uterine fluid (histotroph) produced by the uterine villi (trophonemata) for the remainder of gestation. Previous studues have suggested that endocrine changes during the reproductive cycle in female rays trigger the synthesis and release of histotroph. To examine the effects of several hormonal factors, a series of short term in vitro experiments (24 and 48 h duration) were conducted on trophonemata from adult female Atlantic stingrays, Dasyatis sabina, from the pre-ovulatory to post-ovulatory stage. A variety of peptide and steroidal hormones and activators of signal transduction pathways were evaluated for their ability to directly induce histotroph secretion in vitro. The preliminary results using estradiol, progesterone, ovine prolactin, bovine insulin, bovine growth hormone, forskolin, and a phorbol ester with trophonemata of non-gravid females failed to show a change in the rate of protein accumulation in the culture media.

18/06/2000 - 05:15:00 PM - Salon Madre Perla


(DAH; JMH)Virginia Institute of Marine Science Gloucester Point, VA 23062 USA; (REH; CAM) Mote Marine Laboratory Sarasota, FL 34236 USA

Assessing post-release mortality of coastal sharks using a logistic model of relative survival

Assessing the survival of fish released from fishing operations (either sport or commercial) is an important but difficult step in managing a fishery to have acceptable mortality. We developed a logistic model of relative survival of live releases and applied it to data on two species of coastal sharks, the blacktip (Carcharhinus limbatus) and the bonnethead (Sphyrna tiburo). Sharks caught in a gillnet were tagged, released, and assigned to one of four condition categories based on their behavior on release. Condition 1 was assigned to sharks that swam away vigorously with no signs of stress; at the other extreme, sharks exhibiting signs of severe stress were assigned to category 4. If sharks in two condition categories have the same survival rate the ratio of catches, and presumably tag recaptures, of the two groups should remain constant over time. The relative survival rate of the two groups can be estimated from the way that the ratio changes over time. If it is assumed that all animals in category 1 survived the initial capture, then the absolute survival rate of animals in categories 2, 3, and 4 can be determined and, hence, the total number of released sharks that died can be determined. This method can be applied to estimates of discard mortality in fisheries as well as post-release mortality in tagging operations.

16/06/2000 - 05:00:00 PM - Salon Madre Perla


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

Patterns of movement by neonate blacktip sharks, Carcharhinus limbatus, within a coastal nursery area

An array of 14 remote acoustic hydrophone stations was used to monitor the movements of neonate blacktip sharks, Carcharhinus limbatus, within a coastal nursery area. The telemetry system provided continuous tracking data for 18 sharks over a seven-month period before the sharks left the nursery area. Sharks were tracked for periods of 3 - 159 days. Five sharks were present within the study site for greater than five months, six sharks were present for two to four months and seven sharks remained for one month or less. Five sharks that had left the study site returned intermittently throughout the study period. The acoustic array collected a vast amount of data that was sorted and condensed for analysis by the Remote Acoustic Telemetry Searcher program (RATS). Processed data was analyzed to examine diurnal or tidally influenced movements. The amount of time sharks spent in various portions of the nursery area was compared to environmental data to define possible reasons for site attachment. The direction of movement away from a station and associations between sharks fitted with transmitters were examined. These results are summarized to examine the overall use and habitat preferences of neonate C. Limbatus within this nursery area.

17/06/2000 - 09:45:00 AM - Salon Madre Perla


(RMH; ACS) Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, Florida 34236

A random walk model for assessing the movements of neonate blacktip sharks

A Monte-Carlo simulation model of the movement of neonate blacktip sharks in a summer nursery area in Terra Ceia Bay, Florida, was developed and the results compared to data from remotely monitored individuals. The model contained 22 individual cells that replicated the shape of the bay. Fourteen cells corresponded to acoustic hydrophone stations that monitored the movements of tagged sharks. The model estimated the frequency of occurrence of individuals in each cell, and estimated the time it took to leave the study area. The model was used to test three hypotheses: (1) that sharks move randomly within the nursery area, (2) that sharks remain in the nursery area by directional movement to the north of the bay, and (3) that sharks remain in the nursery area by preferring to stay at the cell that they currently occupy rather than move to an adjacent cell. The results of the model indicated that early in the summer neonate blacktip sharks remain in the nursery area by being 3.5 times more likely to move north than other directions. Changes in the behavior of the blacktip sharks later in the summer failed to match any of those from the model.

19/06/2000 - 08:00:00 AM - Salon Madre Perla


(DWH) The Nature Conservancy, 62 Front Street, Punta Gorda, Belize; (RG) Environment Department, University of York, Box 170, Punta Gorda, Belize,; (BK) Department of Geological Sciences and Marine Science Program, University of South Carolina, Columbia, SC 29208, USA,

Whale sharks feed on gametes released from snapper spawning aggregations in Belize

Whale sharks (Rhincodon typus) are considered opportunistic planktivores, whose diet includes nektonic prey such as squid and small fry. They are commonly known to target dense patches of their prey. Here we report the first direct observations of whale sharks feeding on the freshly released gametes of reef fish in large spawning aggregations. This food source attracts the densest and most predictable aggregation of whale sharks ever reported with 25 individual whale sharks recorded in less than a 100m diameter area. Over 126 hours of underwater observations made during the April-June full moon periods in 1998 and 1999 indicate that whale sharks aggregate to feed at dusk on the spawn of two reef snappers, Lutjanus cyanopterus and L. jocu. Several additional species of finfish are also thought to spawn at Gladden Spit during this season, including mutton snappers (L. analis), and Carangids Caranx ruber and C. hippos. Scuba observations of these seasonally aggregating finfish in proximity to whale sharks, and gonadal analysis of captured fish, indicate that their spawn may also be targeted by feeding whale sharks. Whale shark feeding on spawning snapper has implications for traditional snapper fisheries, predictable whale shark visitations, and the burgeoning whale shark tourism at the site.

15/06/2000 - 03:15:00 PM - Salon Madre Perla


(JMH) VIMS P.O. Box 1346, Gloucester Point, VA 23062-1346, USA. (JDM) MLML, Moss Landing Rd, Moss Landing, CA 95309, USA. (SHG) BBFS, RSMAS, 4600 Rickenbacker CWY, Miami, FL-33149

Survival of juvenile lemon sharks at Bimini, Bahamas, estimated by mark-depletion experiments

The survival rate of juvenile lemon sharks in North Sound, Bimini, Bahamas, was estimated by marking a cohort of small sharks (< 53 cm precaudal length) each spring from 1995 to 1999 and estimating the number of survivors one year later by using a depletion method on the marked population. Annual survival rate over the five seasons varied between 38 and 65% which was somewhat higher than the 39% steady-state survival predicted from a life cycle (Leslie matrix) model. This is the first direct estimate of survival rate of a juvenile elasmobranch and the results support modeling efforts that have been used in determining limits to sustainable exploitation of elasmobranchs. Estimates of survival rates in the present study were negatively correlated with estimated initial abundance and are consistent with strong density-dependent recruitment. Supported by the OCE/BO Division of the National Science Foundation.

17/06/2000 - 04:30:00 PM - Salon Madre Perla


(EMHP) U.N.A.M,Unidad Barrio de San Tiago, Sección Ii, Grupo 8, Edif-c, Dep.301 Colonia: Reforma Iztaccihuatl. C.P. 08800; (JLCG) Instituto Naconal de la Pesca Pitágoras # 130,4º Piso. Col. Santa Cruz Atoyac. C.P. 03310, México, D.F.

A review of the principal shark nurseries of the Gulf of México and Caribbean Sea

Several Carcharhiniforms species use coastal areas, lagoons, bays and estuaries as nursery areas in the Gulf of México and the Caribbean Sea. The shallow, open coastal waters of Tamaulipas, Veracruz and the Campeche Bank are considered unprotected nursery areas for Rhizoprionodon terraenovae; Carcharhinus signatus, Carcharhinus falciformis and Sphyrna tiburo respectively. Protected shark nurseries in waters of the Gulf of México are mainly coastal lagoons. Madre Lagoon, Tamiahua Lagoon, Alvarado Lagoon, Términos Lagoon, Yalahau Lagoon, Asención Bay, Espíritu Santo Bay and Chetumal Bay, localized from the north to the southeast of the Gulf of México respectively, are of prime importance as shark nursery grounds for several species of sharks from the families Carcharhinidae and Sphyrnidae. Most of the tropical shark nursery areas identified in waters of the Gulf of México are also important fishing grounds for local communities. The protection of nursery areas is a key aspect of fishery management. The delineation of the number and kind of the shark nursery grounds, besides the species of sharks that use them in this area must be known if we are to have effective management of mexican shark resources.

19/06/2000 - 08:00:00 AM - Salon Madre Perla


(HRE) Center for Shark Research, Mote Marine Laboratory, Sarasota FL 34236 USA; (CG) Moss Landing Marine Laboratories, Ca 95039 USA (MFJF), Crip/Instituto Nacional de la Pesca/SEMARNAP, Guaymas, Sonora CP 85400 México; (CGJL), Instituto Nacional de la Pesca/SEMARNAP, D. F. CP 03310 México; (VGCJ), Universidad Autónoma de Baja California Sur, La Paz, BCS CP 23080 México

Artisanal fisheries for elasmobranchs in the Gulf of California: a multi-institutional project

Mexican fisheries rely heavily on sharks and rays and more elasmobranch tonnage is landed in the Gulf of California than in any other Mexican region. To assess the status of sharks and rays in artisanal fisheries of the Gulf of California, two U.S. institutions (Mote Marine Laboratory and Moss Landing Marine Laboratories) and two Mexican institutions (Instituto Nacional de la Pesca and Universidad Autonoma de Baja California Sur) collaborated on a two-year project in 1998-99. Seasonal surveys of the four states bordering the Gulf were conducted to characterize target species, catch, fishing effort, and other parameters. A total of 171 fishing camps with over 5,300 active boats (pangas) were found, most of which targeted elasmobranchs to one degree or another. Over the two years, 394 sampling days resulted in direct observation of 165,513 elasmobranchs of 55 species in the artisanal catch, of which 14,142 specimens (9%) were measured by researchers. Total effort, catch and CPUE Gulf-wide by season is being estimated with survey data. Results will help identify elasmobranch populations at risk and be used to formulate management strategies for conservation of sharks and rays in the Gulf of California.

16/06/2000 - 08:15:00 AM - Salon Madre Perla


Huff, Chris.

Texas A & M University1008 Minturn Lane Austin, TX USA 78748

Tooth loss rate from one captive sandtiger shark (Carcharias taurus)

In 1942, C. M. Breder rejected F.G. Cawston's (1940) argument against tooth succession in sharks. Breder believed shed sand tiger (Carcharias taurus Rafinesque, 1810) teeth on the bottom of an aquarium tank indicated continuous tooth replacement. His study resulted in an estimated C. taurus tooth replacement rate of one tooth approximately every two days. He suggested a more definitive answer regarding tooth replacement rates could be obtained by confining one animal in a clean tank and collecting all shed teeth over a given period of time (Breder 1942). A 1988 study by Neal Overstrom confirmed Breder's findings, but Overstrom added the conditions of his study did not account for potential differences due to age and growth rates. In 1995, Joao P. Correia gathered C. taurus teeth from the bottom of a small tank in which water temperature varied during the course of the study, resulting in a potential correlation between increases in temperature, metabolic rates and tooth loss. The research progression of multiple sharks in a tank with a concrete bottom (Breder), to multiple sharks in a constant-temperature, substrate bottom tank (Overstrom), to multiple sharks in a variable-temperature, substrate bottom tank (Correia) has led to this project. The Texas State Aquarium maintains a single sand tiger in a large,constant-temperature, concrete bottom tank. This study will apply Breder's original suggestion to C. taurus tooth replacement rates as well attempt to compare constant-temperature tooth loss rates with variable-temperature tooth loss rates in C. taurus. Preliminary findings will be presented. {revised abstract}

16/06/2000 - 04:00:00 PM - Salon Madre Perla