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The American Elasmobranch Society


Abstracts of AES Scientific Papers
American Elasmobranch Society 1990 Annual Meeting
Charleston, South Carolina
ABSTRACTS - Part 1: Able through Eitner
(Presenting author's name in BOLDFACE
ABLE, K.W., R.A. ROUNDTREE, T. AZAROVITZ, AND B. O'GORMAN

MOVEMENTS OF MUSTELUS CANIS IN THE MID-ATLANTIC BIGHT AND NEW JERSEY ESTUARIES.

The occurrence of Mustelus canis in New Jersey estuaries is closely related to seasonal movements in the Mid-Atlantic Bight. During the winter the adults are found off Virginia and North Carolina. In April and May they move north along the coast as far as Cape Cod. The pups are born in New Jersey estuaries in June and can be found through September. They exhibit pronounced nocturnal movements into subtidal march creeks to feed on crustaceans (Crangon septemspinosa, Palaemonetes vulgaris, Callinectes sapidus, Libinia spp.). Growth is fast, averaging 1.6-2.2 mm/day with no apparent differences between the sexes. By the time the pups leave the estuary in the fall most are 40-50 cm. The juveniles and adults then migrate south for the winter. The fast growth rates achieved in the estuary are indicative of the importance of estuaries as nursery areas for this species.

BRANSTETTER, S., J.A. MUSICK, AND C.A. COLVOCORESSES

ANALYSIS OF TRENDS IN LONGLINE CATCHES OF JUVENILE SANDBAR SHARKS, CARCHARHINUS PLUMBEUS, FOR THE CHESAPEAKE BAY REGION.

The Chesapeake Bay area is a major nursery ground for sandbar sharks along the eastern U.S. Atlantic coast. From 1973 to present VIMS personnel have sampled the shark population of this area using longlines. Although effort has varied by year, this collection provides an historical indication of utilization of the Chesapeake region. Given the recent rapid expansion of fishing effort for C. plumbeus, fluctuations in population structure may be reflected in these records. The data are analyzed for catch-per-unit-effort (CPUE) by size class on a spatial and temporal basis to determine the extent of any such fluctuations.

CALLARD, I.P., C. SCHWABE, AND L.A. SORBERA

HORMONAL REGULATION OF THE REPRODUCTIVE TRACT IN SQUALUS ACANTHIAS.

Although the identity of the major ovarian steroids of a number of elasmobranchs, including S. acanthias, has been known for some 25 years, little is known of their effects on the reproductive tract. Our laboratory has been concerned for some time with the role of gonadal steroids in the regulation of myometrial activity and its response to peptide hormones in elasmobranchs. Of particular interest is the potential for modulation of myometrial activity associated with viviparity and the retention of developing young. In this paper we will present the results of recent studies in which we demonstrate that homologous Squalus relaxin produces a marked slowing of the spontaneous rhythmic contraction of the oviduct accompanied by a marked lengthening of the interval between contractions. In estrogen treated animals, these effects of relaxin are accentuated. In contrast, if progesterone is administered along with estradiol the effects of relaxin are not seen. These results are discussed in the context of the overall control to the myometrium of the dogfish. Supported by NSF Grant DCB 86-06344 to IPC.

CAPAPE, C.

NEW DATA ON THE BIOLOGY OF THE THORNY STINGRAY, DASYATIS CENTROURA (MITCHILL, 1815), FROM OFF THE TUNISIAN COASTS.

The study of the thorny stingray Dasyatis centroura (Mitchill, 1815) caught from off the Tunisian coasts, mainly from off the Gulf of Tunis and Gabes allows to describe some aspects about the biology of this non-placental viviparous Selachian. The size at first sexual maturity of males is reached between 15 cm and 80 cm of disc width (DW). Females keep juvenile genital apparatus until they reach 65 cm DW, thereafter maturation proceeds between 66 cm and 100 cm DW. The first adult females are 100 cm DW. Females are larger than males. Gestation spreads about 4 to 5 months at a minimum, but it is impossible to know the number of reproductive cycles per year, vitellogenesis completes at the end of the gestation. Parturition and ovulation occur in June. Fecundity (s.1.) reaches from 2 to 8 individuals per litter.

CASTRO, J.I

THE SHARK NURSERIES OF THE EAST COAST OF THE UNITED STATES.

The females of many species of sharks travel to specific, geographically discrete, nursery areas to lay their eggs or to give birth to their young. These nurseries are usually in shallow, coastal waters in highly productive zones, where the young find abundant prey and where they are free from predation by larger sharks. The newborn young remain in the nurseries for a few months in temperate latitudes or for a few years in tropical waters. Criterion for a nursery area is the presence of both gravid females carrying term pups and free swimming, newborn young in the area. The following species of sharks have nurseries along the east coast: Atlantic sharpnose, blacknose, blacktip, bull, dusky, finetooth, lemon, sandbar, sandtiger, scalloped hammerhead, and spinner,

COX. D.L. and T.J. Koob

PREDATION ON ELASMOBRANCH EGGS.

Predation on large, energy-rich eggs occurs commonly in terrestrial and freshwater communities, with amphibians, reptiles, and birds figuring as prominent targets. We might predict that predation on large eggs would be widespread in marine communities, however there is little information for testing this prediction. For example, few instances of predation on elasmobranch eggs have been reported. We present evidence for the occurrence based on SCUBA observation, long-term incubations of caged egg capsules held in museum collections. The principle egg predators appear to be gastropods, though vertebrates contribute in some measure to mortality of embryonic elasmobranchs. As yet we can only speculate about the consequences of egg predation for populations of oviparous elasmobranchs, or about the impact their energy-rich eggs may have on marine communities.

DEMSKI, L.S., L. Qin, and D.E. Wright

GONADOTROPIN HORMONE-RELEASING HORMONE (GnRH) PATHWAYS AND REPRODUCTIVE CONTROL IN ELASMOBRANCHS.

Immunocytochemical studies have localized GnRH in neurons of the terminal nerve (TN), preoptic area (a few cells only) and midbrain tegmentum. The paucity of preoptic immunoreactive (ir) cells may relate to an unusual feature of the elasmobranch pituitary, i.e. a lack of portal control of the gonadotropin producing cells. TN and midbrain GnRH-ir neurons may be major sources of GnRH used to modulate or otherwise control both pituitary and brain cells via delivery through the systemic circulation. These ir-nuclei also appear to directly innervate CNS regions (the preoptic area, habenula and clasper control area of the spinal cord) involved in sexual functions. Important regulatory mechanisms, represented by interactions between GnRH pathways and sex-steroid concentrating neurons, are likely to occur in the preoptic area, habenula and midbrain tegmentum.

EBERT, D.A.

REPRODUCTIVE STRATEGIES IN TWO SPECIES OF HEXANCHOID SHARKS.

The sixgill shark (Hexanchus griseus) and the sevengill shark (Notorynchus cepedianus), both members of the family Hexanchidae, employ similar reproductive strategies to enhance survivorship of their young. Both species give birth during the spring months and appear to be site specific as to where they pup. Sixgill and sevengill sharks give birth in areas of high primary productivity. Energetically, this is advantageous for the newborns to be placed in an area with an abundant food source. The rapid growth rates of sixgill and sevengill sharks over the first year would enhance their survivorship since neither species has many predators.

EITNER, B.L.

ENZYME EXPRESSION IN THE BLUE SHARK PRIONACE GLAUCA.

Patterns of enzyme expression, including number of presumptive loci and tissue specificity of expression (tissues surveyed included brain, heart, muscle, and liver) were determined for a number of enzyme systems in Prionace glauca using starch gel electrophoresis. Patterns of enzyme expression in the blue shark are compared to those reported in other vertebrate taxa.