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The American Elasmobranch Society


Abstracts of AES Scientific Papers
American Elasmobranch Society 1991 Annual Meeting
New York, New York
ABSTRACTS - Part 3: Morrissey through Weatherbee
MORRISSEY, J.F.* AND S.H. GRUBER. Rosenstiel School of Marine and Atmospheric Science, MBF, 4600 Rickenbacker Causeway, Miami, FL 33149.

HOME RANGE, DIEL ACTIVITY RHYTHMS, AND HABITAT SELECTION OF JUVENILE LEMON SHARKS, NEGAPRION BREVIROSTRIS (POEY).

Ultrasonic transmitters were surgically implanted into the coeloms of 38 lemon sharks, yielding 2281 telemetry fixes. Activity space area averaged 0.88 km2 (range = 0.23-1.26 km2) and was positively correlated with shark size. Indices of site attachment and defense reveal that juvenile lemon sharks establish an undefended home range. Rates of movement (median= 0.21 body lengths per second, range = 0-1.46 bl/s) revealed orepuscular peaks in diel activity. Water depth, temperature and bottom type were used disproportionately to their availability. Specifically, juvenile lemon sharks selected shallow, warmer water with an underlying rocky or sandy substrate, perhaps as a means of predator avoidance.

MUSICK, J.A., S. BRANSTETTER*, AND J.A. COLVOCORESSES. Virginia Inst. of Marine Sciences, College of William & Mary, Gloucester Point, VA 23062.

ANALYSIS OF SHARK CATCHES FOR 1974-1990 FOR THE CHESAPEAKE BIGHT REGION OF THE U.S. MID-ATLANTIC COAST.

Recent assessments indicate that the shark stock of the Western North Atlantic is exploited at a rate twice the maximum-sustainable-yield. This finding is supported by data generated by the VIMS longline program for sharks of the Chesapeake Bay and adjacent coastal waters. Trends in catch-per-unit-effort since 1974 indicate as much as five fold reductions in population size for the common species. Declines include numbers of individuals for all species, all size classes within species, and in one case a strong decline in relative abundance. Results suggest that continued unregulated exploitation will cause a total stock collapse for which recovery will require decades. Such a biological disaster would also have negative socio-economic impacts on user groups associated with this marine resource.

NELSON, D.R.* (1), J.N. McKIBBEN (1), C.G. LOWE (1), W.R. STRONG (2), J.A. SISNEROS (1), D. SCHROEDER (2), AND R.J. LAVENBERG (3). 1. California State Univ., Long Beach. 2. Univ. California, Santa Barbara. 3. Natural History Museum, Los Angeles County, CA.

AN ACOUSTIC TRACKING OF A MEGAMOUTH SHARK, MEGACHASMA PELAGIOS.

A 4.9 m shark (the 5th known specimen) was captured Oct. 21, 1990 in a drift gill net, towed 13 km to Dana Pt. Harbor, and restrained by tail rope overnight. The next afternoon it was towed to sea and released with two attached ultrasonic transmitters (one with depth sensor). It was tracked for 50.5 hours, during which it made distinct vertical moves at each dawn and dusk transition, staying shallow at night (11-22 m depth range) and deeper during the days (120-166 m, well above the 700-850 m bottom). These moves appeared triggered by light changes. Horizontally, the shark moved slowly (0.95 km/h rate), on a relatively straight path, with no clear diel changes. Previously proposed feeding patterns are considered re: these findings.

O'SULLIVAN, J., Monterey Bay Aquarium, Monterey, CA 93940.

THE PRICKLY SHARK ECHINORHINUS COOKEI, COLLECTION, AND DISPLAY OF THIS RARE DEEP-WATER SHARK.

The prickly shark, Echinorhinus cookei, found at depths of up to 1,000 meters was collected by the staff of the Monterey Bay Aquarium at the head of the Monterey submarine canyon near Moss Landing. This bottom-dweller is recorded from the coast of Monterey south to Baja California, and in the waters adjacent to Peru, Hawaii, New Zealand, Taiwan and Japan. This sluggish animal feeds on fishes, other sharks, octopus, squid and crustaceans. Using S.C.U.B.A., divers collected a single specimen at 33 meters depth. This specimen was transported to M.B.A. and displayed for seven days. During this time problems arose that affected buoyancy. It is hypothesized that this may be due to the large liver of this species. After seven days the shark was returned to the ocean. Future research is being planned to understand the problems in displaying deep-water elasmobranchs.

RUSSELL, SANDRA J., Coastal Fisheries Institute, Center for Wetland Resources, Louisiana State University, Baton Rouge, LA 70803.

OBSERVATIONS ON THE DIRECTED AND BYCATCH LONGLINE FISHERIES FOR SHARKS IN THE NORTHERN GULF OF MEXICO.

A market for shark products developed concurrently with the development of a domestic tuna fishery in the Gulf of Mexico, so a directed, as well as a bycatch, longline fishery for sharks became established around 1986. Shark landings soared from 1.9 mil lb in 1986 to 12.4 mil lb in 1989. Observers recorded catch composition and effort data from 53 shark sets and 190 tuna sets between 10/89 and 9/90. The shark sets produced 1,180 shark which were retained for sale and 268 sharks which were discarded (21 alive). Predominant species were blacktip sharks, smooth dogfish, and Atlantic sharpnose sharks. Catch rate for shark sets was 8.3 sharks/100 hooks. Shark bycatch from the tuna sets consisted of 75 sharks retained for sale and 281 discarded (195 alive). Predominant species were spinner, blacktip, dusky, sandbar, and scalloped hammerhead sharks. Catch rate on tuna sets was 0.4 sharks/100 hooks. Sex ratios and total lengths were also recorded.

SCHMID, THOMAS H.* AND FRANK L. MURRU. Sea World of Florida, Orlando, FL 32821.

OBSERVATIONS ON THE REPRODUCTIVE BIOLOGY OF BAMBOO SHARKS (HEMISCYLLIDAE) MAINTAINED IN CAPTIVITY.

In 1985, Sea World of Florida initiated a captive breeding program consisting of three species of orectolobiform sharks: epaulette shark, Hemiscyllium ocellatum; brownbanded bambooshark, Chiloscyllium punctatum; and whitespotted bamboo shark, C. plagiosum. Mating behaviors have been observed in all three species. Two species, Hemiscyllium ocellatum and Chiloscyllium punctatum have produced numerous offspring. Gestation period at 24°C was 138da for H. ocellatum, and 160da for C. punctatum. Size at birth of H. ocellatum was 133mm TL, size at birth for C. punctatum was 158mm TL. Temperature affects gestation time; a temperature increase of 3°C decreases gestation period by 14% in H. ocellatum, and by 27% in C. punctatum. After 12 to 16 mo, mean TL for H. ocellatum was 418mm, mean TL for C. punctatum was 450mm.

SOTELO, FERNANDO MACIAS. Instituto de Geologia, UNAM Grupo Cipactl Circuito Exterior C.U. Delegacion de Coyocan, 045150 Mexico D.F.

A POLITICAL PROSPECTIVE OF SHARK CONSERVATION IN MEXICO.

Legally shark fishing in Mexico is controlled by the government which in many cases consists of persons that have little knowledge of sharks or shark fishing. Statistically sharks are not treated as separate species but divided into two categories: tiburones, those sharks over 1 meter, and cazones, or sharks around a meter or less. Often the same species is treated in this manner. There have been few sustained shark fisheries in Mexico. The oldest is that of Mazatlan for many years and also near Alvarado Veracruz. Recent failures have occurred in Baja California Sur, Tecouluta Veracruz and in Chiapas. A fishery exists in Quintana Roo that has shown with varying amounts of success. Usually much of the shark resource is wasted in that only the meat is used, or at other times, just the fins or the skin. We know of only one instance where an attempt was made to utilize the whole shark. In 1976 a group concerned with studying Mexican sharks was formed at the University of Mexico. This group has taken the name Cipactli which is the nahuatl name for sharks. Their work resulted in the publication of a Mexican book on sharks called Tiburones Mexicanos.

VAN DYKHUIZEN, GILBERT* AND H.F. MOLLET. Monterey Bay Aquarium, Monterey, CA 93940.

GROWTH RATES AND AGE ESTIMATION OF SEVENGILL SHARKS, NOTORYNCHUS CEPEDIANUS AT THE MONTEREY BAY AQUARIUM.

Growth was measured on 5 juvenile sevengills and von Bertalanffy growth curves were fitted to the data using Fabens' method. The von Bertalanffy growth model was inadequate in fitting the whole range. Therefore, an alternative method of growth analysis based on the von Bertalanffy model was used for the upper end of the range. Age of the five juvenile sevengills was estimated from calculations based on the von Bertalanffy model using the growth curve for each individual shark. The results confirmed the original age estimates that 2 of the sharks were approximately 5 months old when collected and 3 of the juveniles were 18 months old when collected. Length/age data were then used in an exponential regression based on the von Bertalanffy model. Age at sexual maturity for males and females was estimated to be 4 to 5 yr and 16 to 24, respectively.

WETHERBEE, B.M. Zoology Department, University of Hawaii, Honolulu, HI 96822.

BUOYANCY OF DEEP-SEA SHARKS.

Buoyancy of 7 species of deep-water squalids and 1 scyliorhinid shark collected in New Zealand waters was determined by measuring their weights in air, weight in water, and volume. Liver density and the area of surfaces capable of providing hydrodynamic lift were also measured. All species of deep-water sharks were neutrally buoyant or nearly so; weights in sea water were -3.5 to +2.0% of their body weights in air. There was considerable variation between species, but buoyancy was relatively constant for different size individuals within species. Size of fins and tail were not correlated with buoyancy, and these hydrodynamic features appear to be relatively unimportant for buoyancy. Liver size was fairly constant within species, accounting for about 20% of body weight. Buoyancy characteristics of the scyliorhinid shark were similar to those of shallow-water sharks, and differed from those of the deep-water squalid sharks. Despite minor variations in features that contribute to increased buoyancy, deep-water sharks of different species and sizes all maintained densities similar to the surrounding water.