1988 AES Annual Meeting Abstracts

Virginia Institute of Marine Science, Gloucester Point, Virginia 23062 USA

Tidally-oriented movement of cownose rays, Rhinoptera bonasus, determined from biotelemetry

Ultrasonic and radio frequency transmitters were employed to follow the movements of adult cownose rays for periods ranging from six to sixteen hours. Ultrasonic transmitters allowed location of the ray when submerged while radio transmissions were received when the ray was near the surface, thus providing information on the amount of time the ray remained near the surface. The amount of time spent near the surface was small compared to time spent below (less than 5% of the total tracking time). All of the rays moved in directions significantly different from random (Rayliegh test, P < 0.05). Furthermore, the mean direction of movement was not significantly different from the direction of the tidal flow (P < 0.05). The adaptive significance of tidally-oriented swimming may be twofold. First, by taking advantage of the current a ray may achieve significant energy savings. Second, during flood tide a greater abundance of prey (infaunal benthic mollusca) is available than at low tide. Analysis of video tapes of captive cownose rays indicated that transmitter attachment had no significant short-term effect on swimming behavior (P < 0.05).

Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, Texas 77843 USA

The status of Raja fuliginea and Raja bigelowi: ecophenotypes or species?

In their original description Bigelow and Schroeder (1954) noted Raja fuliginea most closely resembled R. bathyphila, and could be distinguished by only a few characteristics. Subsequently, Stehmann (1978) recognized a third species, R. bigelowi, which had apparently long been confused with R. bathyphila. He noted that R. fuliginea differed fromR. bigelowi in having a much shorter snout and heavier spination pattern. At first glance, the densely prickled R. fuliginea appears to be distinct from R. bigelowi. However, our recent investigations of both species indicate that there is considerable overlap in morphometric and skeletal characteristics, suggesting that R. fuliginea of the Gulf of Mexico and R. bigelowi of the northwestern Atlantic may -actually represent distinct phenotypes of a single species.

Department of Biology, Albion College, Albion, Michigan 49224 USA and Hawaii Institute of Geophysics, 2525 Correa Road, Honolulu, Hawaii 96822 USA

Preliminary evaluation of age and growth in juvenile nurse sharks (Ginglymostoma cirratum) using visual and electron microprobe assessment of tetracycline-labelled vertebral centra

Vertebral samples from recaptured, tetracycline-injected nurse sharks up to 200cm (TL) were visually evaluated for opaque growth bands, and electron microprobe analysis was undertaken in several samples to verify annual periodicity of band formation. Length/age relationships were examined, and annual growth rate estimates were predicted from recapture measurements and from extrapolation of length/age relationships. Both techniques support an average rate of approximately 9.9 +/- 4.7 cm/yr and 2.8 +/- 0.9 kg/yr.

CASTRO, J. I.,* and J. P. WOURMS
Department of Biological Sciences, Clemson University, Clemson, South Carolina 29631 USA<

Insemination by spermozeugma in the finetooth shark, Carcharhinus isodon

A pair of finetooth sharks were caught together. in a bottom gill net apparently just after mating. The male, 1400 mm TL, was sexually active, while the 1585 mm TL female had fresh, still bleeding mating bite marks. There were ten mature eggs 29 mm in diameter in the ovary. A yellowish white, oval, gelatinous mass about 50 x 20 mm, the spermozeugma, was found midway in each uterus. Phase microscopy of sperm smear revealed non-motile sperm; upon dilution with elasmobranch saline, sperm became motile. When stored undiluted at 4 ° C, sperm motility persisted for 72-96 hours in vitro. SCM of spermozeugma revealed sperm, spherical cells, and cellular debris embedded in a fibrous extra-cellular matrix. Histological examination of testis revealed sperm, cellular debris, spherical cells, and extra-cellular matrix (ECM) in the lumen of the ducts. ECM is derived from secretory cells in the ducts, while spherical cells and cellular debris appear to be shed Sertoli cells.

1Graduate School of Fisheries, National Taiwan College of Marine Science and Technology; 2NMFS, SW Fisheries Center, La Jolla, California 92037 USA

Age and Growth of Scalloped Hammerhead, Sphyrna lewini, in Northeastern Taiwan Waters

Age and growth of 325 scalloped hammerhead, Sphyrna lewini, caught in northeastern Taiwan waters from December 1984 to November 1985 were determined following analyses of vertebral centra annuli. Linear regressions expressed the relationships between centrum radius (cm, R) and total length (cm, L): females L = 16.25 + 152.33 R and males L = 22.19 + 154.81 R. Translucent and opaque zones on vertebral centra were formed twice a year, the latter were a semi-annual annuli formed in June and December. Von Bertalanffy parameters obtained by nonlinear regression methods were: L=365.01 cm TL, K=0.156, t= -1.053 for females; and L=303.82 cm TL, K=0.240, to = -1.076 for males. Age at sexual maturity was 4.4 yr (210 cm TL) for females and 3.3 yr (198 cm TL) for males. Holden’s method was also used to obtain comparative growth parameter estimates. Estimates for K are 0.175 for females and 0.194 for males, both approximated those recorded by Holden’s (1974) value (0.1-0.2). The growth rate for Taiwanese hammerheads was double that of hammerheads from the Gulf of Mexico and North Carolina.

The Living Seas, P, 0. Box 10,000, Lake Buena Vista, Florida 32830-1000 USA

Rostra1 tooth regeneration of smalltooth sawfish (Pristis pectinata)

Three smalltooth sawfish (Pristis pectinata) were observed over a twelve month period at.EPCOT Center’s Living Seas pavilion. Monthly sketches and photographs were used to document the regeneration of broken or damaged rostra1 teeth.

Observations confirmed that the fibrous rostra1 teeth grow continually. Regeneration of a broken tooth began with the formation of an enamel-like tip. The tip elongated from the cortex area of the tooth, along with growth at the socket base. Regenerative growth was faster than normal growth with minor repairs taking less than one month. Tip formation was delayed if the tooth base or socket was damaged.

Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, Virginia 23062 USA

Comparative food habits of subtropical sharks in the Chesapeake Bight

Stomach contents of 1,056 sharks taken during a longline survey conducted in Chesapeake Bight coastal and shelf waters during 1980-81 and in subsequent incidental collections were quantitatively examined. Seven of the 20 species collected, Carcharhinus plumbeusC. obscurusRhizoprionodon terraenovaeMustelus canisOdontaspis taurus,Galeocerdo cuvieri and C. limbatus were taken in sufficient numbers for adequate dietary characterization.

Approximately 60% of stomachs examined contained food, but this varied with species, ranging from 50% (for C. plumbeus and C. obscurus) to 100% (M. canis). 0. taurus andC. limbatus were almost exclusively piscivorous; C. plumbeusC. obscurus and G. cuvieri strongly so. C. plumbeus, particularly juveniles, also fed on decapod crustaceans.R. terraenovae diets were almost equally balanced between teleosts and decapods, while invertebrates (primarily decapods with some bivalve molluscs) constituted almost the entire diet of M. canis. Some ontogenetic shifts in diet were evident, but these were much less pronounced than those observed in many teleost fishes. Those species which fed on decapod crustaceans exhibited a much higher proportion of recently molted (softshell) individuals than was observed in concurrent trawl collections.

COOK, S. F.*1, R. KREUZER2, and F. A. DE BOER3, 
1Arqus-Mariner Consulting Scientists, 801 NW 27th #2, Corvallis, Oregon 97330 USA; 2Food and Agriculture Organization of the United Nations, 28 Via Odoardo Beccari, Rome 00154, Italy; and 3Food and Agriculture Organization of the United Nations, B.P. 13225 (DELMAS), Port au Prince, Haiti.

The development of commercial shark fisheries: a perspective

Although man has undoubtedly caught sharks for as long as he has fished the oceans, the practice of directing commercial fishing ventures toward them is a phemonenon of the Twentieth Century. This has been primarily the result of three driving forces: 1) improved technology which has allowed for solving problems of capture, handling, and extraction of useful products; 2) interest in sharks as a recruitable natural resource; and 3) the declining of other fish resources in an increasingly hungry world. For the majority of this century, even in time of global war, shark fisheries have existed at various places in the world. To be certain commercial shark ventures have, historically, been more difficult to develop and sustain than fisheries for other types of marine living resources. This paper will examine some of the problems inherent to shark fisheries and their successful operation, i.e., fishing methods, over-exploitation of stocks, quality.control of products, and marketing problems as they relate to consumer education and acceptance of shark.

GROGAN, E. D.,* and R. LUND
Adelphi University, Biology Department, Garden City, New York 11530 USA

The elasmobranch immune system: preliminary observations and methods of analysis

Hematological studies have been undertaken to define the immunologic capacity of elasmobranchs. Periphera1 blood cells isolated from the blood of non-captive animals were analyzed using a number of histological and immunochemical techniques. These studies were facilitated by the development of an in vitro system which allows the maintenance and proliferation of isolated cells. The cellular composition of blood and anatomical compartmentalization of immunocytes are noted in addition to response to temperature, serum, and mitogenic lectins. This research has permitted interpretations to be drawn in relation to phylogenetic and ontogenetic development as well as physiology.

University of Miami, 4600 Rickenbacker Causeway, Miami, Florida 33149 USA

Annual production of juvenile lemon sharks (Negaprion brevirostris) in a tropical lagoon

Annual production of a population of juvenile lemon sharks (Negaprion brevirostris) in the North Sound, Bimini, Bahamas was estimated by the instantaneous growth-rate method. The number of sharks estimated from tag-recapture data was 74 and the instantaneous rate of total mortality was 0.74. The average biomass was 0.03 g m-2 from May 1985 to November 1985, and production on an annual basis was estimated to be 0.06 g m-2 yr-1 a value much lower than that reported for many teleost species. The P/B ratio was 0.72. This is the first estimate of natural production for a shark species. Supported by NSF-OCE 8743949.

Mote Marine Laboratory, 1600 City Island Park, Sarasota, Florida 34236 USA

Retinotectal projection, retinal topography, and implications for the visual ecology of the juvenile lemon shark (Negaprion brevirostris)

To understand the organization of spatial vision and its role in the visual ecology of sharks, the retinotectal projection pattern, retinal cone distribution, and retinal ganglion cell distribution were mapped in the juvenile lemon shark. The retinotectal projection reveals an orderly point-to-point pattern as in other vertebrates, confirming the mesencephalic tectum as the primary center for spatial visual input in elasmobranchs. All three maps reveal a prominent “visual streak,” a horizontal band of proportionately greater retinal cell density and retinotectal magnification, located within about l5° above and l5° below the horizontal meridian in the visual field. Three times more tectum is devoted to vision in the streak than to peripheral vision, and ganglion cell and cone densities increase by factors of 3 and 13, respectively, from peripheral retina to inside the streak. This conforms with the “terrain theory,” which states that the visual streak enhances spatial vision along the horizon in animals whose habitats are dominated by a two-dimensional horizontal terrain. Constant patrolling over the benthos may also add to the adaptive value of the visual streak in the juvenile lemon shark.

Bodega Marine Laboratory, University of California, Davis, P. 0. Box 247, Bodega Bay, California 94923 USA and Graduate Department(A-008), Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093 USA

Homing of a shark to a seamount and relationship to local geomagnetic features

Theoretical mechanisms used by a scalloped hammerhead shark (Sphyrna lewini) to home to a seamount are evaluated by comparison of a shark’s movements to those local features with directional information. Position-to-position vectors and telemetered swimming directions of the shark were highly directional to a distance of 19.4 km from the seamount, indicating a guiding environmental feature of this spatial scale. The return path of the shark also coincided with its outward path, and those direction changes along that path were antiparallel to changes along the outward path. This “retracing of steps” despite the presence of strong crosswise currents indicated that the shark oriented to a fixed feature associated with the sea floor. The shark’s track was compared to the spatial distribution of the following environmental features: 1) sea surface temperature, 2) bottom topography, 3) the earth’s main dipole geomagnetic field, 4) local total fields, and 5) local anomaly fields. The track coincided most closely with a negative anomaly gradient’s upper boundary which may be the polarity transition zone to a geomagnetic reversal lineation.

LAST, Peter R.*
CSIRO Marine Laboratories, GPO Box 1538, Hobart, Tasmania, 7001, Australia

The batoid fauna of Australia–Composition and eoogeographic patterns

In 1940, Whitley, in a review of the chondrichthyan fauna, listed 55 batoids from the Australian region. Since, as a byproduct of recent exploratory fishing surveys to all parts of the Australian Fishing Zone, our knowledge of the fauna of Australia has grown significantly. Compared to other regions of similar size, the fauna is diverse and the checklist presently contains more than a hundred species from 15 families (sensu McEachran, 1982). Only members of the families Platyrhinidae, Pseudorajidae, Narkidae and Potamotrygonidae have not been recorded from this area. The largest families are the Rajidae (36 species), Urolophidae (24 species) and Dasyatididae (17 species). More than three-quarters of the species are endemic to the region and many of these appear to be undescribed. Although endemism is most pronounced in the southern component, only the families Torpedinidae and the monotypic, endemic Hypnidae are confined to temperate parts of the region. Members of the families Rhynchobatidae, Dasyatididae and Mobulidae are mostly widely distributed throughout the Indo-Pacific. Three families, Rajidae, Urolophidae and Narcinidae are represented throughout the region but their members are generally endemic with narrow distributional ranges.

LUER, C. A.*, P. C. BLUM, and P. W. GILBERT
Mote Marine Laboratory, 1600 City Island Park, Sarasota, FLorida 34236 USA

Rates of tooth replacement in the nurse shark, Ginglymostoma cirratum

It is well known that jaws of sharks possess several rows of teeth, the outer row being continually replaced by new teeth as older ones become worn or broken. No long-term investigations have been performed with any shark species, however, to determine rates at which teeth move forward during the replacement process. Three juvenile nurse sharks were examined weekly for three years to document rates at which teeth, marked by clipping the cusps of newly exposed teeth, moved from the innermost to the outermost row and were eventually shed. Following the shedding of marked teeth, additional sets of newly exposed teeth were clipped and monitored throughout the study period. Order in which teeth were shed from the outer row did not follow a consistent pattern; tooth loss may initiate near the articulation, at or near the symphysis, or at varying sites in between. Rates of tooth replacement varied during the year depending upon water temperature. Fastest rates occurred in summer months (water temperature 27-29 ° C) when a row was shed every 2-3 weeks. Winter water temperatures (19-22 ° C) produced the slowest rates, ranging from 7-10 weeks per row. (Supported in part by R.C. Dorion Fund.)

Department of Biology, Bucknell University, Lewisburg, Pennsylvania 17837 USA

The peripheral innervation and histology of the ampullary electroreceptors in the freshwater ray, Potamotrygon

As a consequence of their freshwater habitat, the electroreceptive system of Potamotrygon differs from that of marine elasmobranchs in gross structure and arrangement . However, the functional significance of these differences has remained undiscussed. The present study quantifies ampullary complexity in Potamotrygon through counts of receptor cells. Ampullae from 8 areas of the body innervated by the major afferents of the anterior lateral line nerve were serially sectioned and examined through a series of light micrographs. A greater number of ampullae were found on the ventral surface, particularly around the mouth. Furthermore, whereas a general similarity in the numbers of receptor cells from most areas was observed, those ampullae from the mandibular area typically exhibited more receptor cells. This suggests that electroreceptive input to specific areas is enhanced by both an increase in the number of ampullae as well as an increase in receptor cells. These findings corroborate previous results on marine batoids, implying that electro-reception is an important accessory cue in feeding for the dorsoventrally flattened stingray.

Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, Texas, 77843 USA

Historical Biology of Skates (Chondrichthyes, Rajoidei)

Skates comprise the largest putative monophyletic subordinal level taxon of chondrichthyans. Currently there are about 220 nominal species and as many as 20 undescribed species in collections around the world. Thus skates represent about 30 percent of the elasmobranchs. The relatively high diversity of skates is an enigma because they are morphologically and ecologically conservative. To better understand the evolutionary processes which led to the relatively high diversity of skates a phylogenetic hypothesis is generated from anatomical comparisons of the majority of the nominal species. The subgeneric and generic level clades of this phylogenetic hypothesis are then compared as to 1) their phylogenetic position, 2) their species richness, 3) extent of the horizontal and vertical ranges of their species and 4) their distinctive morphological character states. Finally skates are compared with other elasmobranch taxa, i.e. squalids, squatinids and scyliorhinids with respect to 1) species richness, 2) extent of species ranges, 3) morphological and chromatic diversity, 4) diversity of prey types and reproductive biology.

Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon 97331 USA and National Museum of Chile

Sharks of the Chilean Continental Slope

Two cruises on the continental slope (500 to 1050 m) off Chile between Isla Mocha (38 ° 30′ S) and Arica (18 ° 19′ S) produced 11 species of sharks. Seven were squaliforms and four were carcharhiniforms. Southeastern Pacific endemics are Aculeola piara,Centroscyllium nigrum, Apristurus nasutus and Halaelurus canescens. Two predominantly Patagonian species are reported for the first time in the Pacific basin: Etmopterus granulosus and Centroscyllium granulatum. Two species are eastern Pacific endemics:Apristurus brunneus and Cephalurus cephalus and one, Echinorhinus cookei, is widespread in the North and South Pacific. Finally, Centroscymnus crepidater andDeania calcea are world wide in distribution. Support of Grant 5057/86 (National Council Science & Technology Chile) is acknowledged.

Michael, S. W.*
University of Nebraska-Lincoln, Lincoln, Nebraska 68588 USA

The food habits of the draughtsboard shark (Cephaloscyllium isabellum) near Stewart Island, New Zealand with notes on other aspects of its Biology

In 1979 and 1987 the food habits of the draughtsboard shark were investigated near Stewart Island, New Zealand. The stomach contents of 132 specimens, collected by commercial fishermen, were examined; 88 of these contained recognizable food. C. isabellum is an opportunistic generalist feeding on a diversity of benthic organisms. crustaceans and teleosts were the most predominant components of.the diet, but tunicates, molluscs and elasmobranchs were also important prey. Forty-five percent of the, sharks collected in 1987 had eaten pagurid crabs, but only one stomach contained the gastropod shell,that these crabs inhabit. A hypothesis on the handling techniques C. isabellumemploys to ingest pagurids will be presented. Comments will also be made on the re-production, social organization and size of the draughtsboard shark.

Michael, Scott W.
University of Nebraska, Lincoln, Nebraska 68588 USA

Preliminary observations on courtship copulation and the mating system of the Round Stingray, Urolophus halleri.

Observations were carried out on the mating behavior of the round stingray in the Gulf of California. The study site is a shallow bay with eelgrass (Zostera sp.) covering most of the bottom and a narrow mud or sand margin on the shoreward side of the grass bed. Courtship activity was video taped in order to allow detailed analysis later and to maximize data recovery. Mating behavior was observed only during the morning (630-1139). At this time most females bury in the substrate in front of the grass beds and males attempt to locate and mate with them. Males apparently employ severa1 distinct strategies to acquire mates. After the breeding phase of the diel cycle females disperse into the surrounding grass beds to forage.

Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, Texas, 77863 USA

Phylogenetic Interrelationships of Batoid Fishes (Chondrichthyes, Batoidea)

Phylogenetic interrelationships of batoid fishes were examined based on comparative anatomical studies of all major groups of chondrichthyans. The data matrix and anatomical character states were analysed by Phylogenetie Analysis Using Parsimony. A single tree is generated, and four monophyletic subgroups were recognized: electric rays, sawfishes, guitarfishes and skates and stingrays. Electric rays form the sister group of the remaining subgroups. Sawfishes form the sister group of guitarfishes, skates and stingrays. Guitarfishes and skates form the sister group of stingrays. The analysis did not find any synapomorphies for guitarfishes. The character states for morphology will be discussed.

Hofstra University, Hempstead, New York 11550 USA

A functional analysis of shark jaws

The jaw and chondrocranium anatomy in two distantly related species of sharks, the spiny dogfish, Squalus acanthias, and the blue shark, Prionace gluaca, were analyzed in an effort to quantify the relative force of adduction produced with the jaw retracted and then protracted. Two muscle-cartilage lever systems were analyzed using force vector components to compare the re1ative force of adduction produced at the symphysis of the lower jaw. Two additional muscle-cartilage lever systems were analyzed to compare the relative force of jaw protraction. Seven angles of gape and three angles of hyomandibula position were analyzed to account for any changes in relative force due to changes in muscle fiber orientation. Relative force produced by a given muscle was approximated using a modified muscle mass value. Results suggest that P. glauca has a stronger bite thanS. acanthias, but only when the angle of gape is greater than 30°-45°. In addition, P. glauca is capable of a more powerful jaw protrusion than Squalus acanthiasPrionace glauca is capable of producing a greater adductive force with its palatoquadrate protracted, but only when the angle of gape is 45°-60°. Squalus acanthias is capable of producing a more forceful bite at all angles of gape with its jaw retracted. These results are interpreted in light of current data concerning the feeding behavior of these two species of sharks.

MUSICK, J. A.,* and C. TABIT
Virginia Institute of Marine Science, School of Marine Science, The College of William and Mary, Gloucester Point, Virginia 23062 USA

Body surface areas of galeoid sharks

Body surface areas were measured on six species of galeoid sharks comprising 33 specimens. The dorsal and ventral aspects of the body of each specimen were covered with polyethelene plastic sheeting and outlined by scalpel. The plastic body outlines were subsequently cleaned, dried, and weighed in the laboratory. Outline weights were converted to body surface area (SA) by multiplying weight X a factor derived from weighing subsamples of plastics of known area. Regressions of SA on standard length (L) were calculated for four species and subjected to analysis of covariance. Regressions differed among species because of differences in body shape as expected, Terete-shaped species had smaller surface areas than robust species of the same length. Body girth (G) relative to body length seemed to provide an intuitive measure of body shape. Therefore several equations were tested to determine which would give the best estimate of body surface area from girth and length data. The equation SA = 0.7 G x L fit well for all species studied.

Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, Florida 33143 USA

Aggressive mimicry by the oceanic whitetip shark, Carcharhinus longimanus: an answer to baffling questions

Numerous species of sharks, particularly carcharhinids, possess regions of pigmentation along the edges and the tips of fins that contrast strongly with pigmentation found elsewhere on the body. The common occurrence of such markings strongly suggest a communicative function. One such function, aggressive mimicry, involves a predator using coloration and/or a part of its body to deceptively lure unsuspecting prey sufficiently close such that the chance of capture is enhanced. Numerous observations of free-ranging oceanic whitetip sharks in the Tongue of the Ocean, Bahamas, have provided the reasonable speculation that the highly contrasting white-tipped fins of such sharks are indeed lures to attract unsuspecting prey sufficiently close to their owners that the chance of capture is enhanced. This result, due to confusion based on a visual effect and the whitespots “acting” themselves as a tight school of small prey, answers two baffling questions about oceanic whitetip sharks: how can such slow-moving creatures have as their prey some of the fastest moving oceanic fishes (e.g., tunas, various scombroids, dolphinfsh, etc.) and why are its fins (= paddles) so much larger than those of other sharks?

Laboratory of Marine Zoology, Faculty of Fisheries, Hokkaido University, Hakodate, Japan.

Phylogeny and systematic position of the Rhinobatoidei

External and internal (skeletal and myological) features were examined in eight of nine currently recognized rhinobatoid genera. Interrelationships of the Rhinobatoidei and its systematic position among Rajiformes (sensu Nelson, 1984) were determined by cladistic analysis.

The Rhinobatoidei can not be monophyletic unless Rhynchobatus and Rhina are excluded. New higher rajiform relationships indicates that the Pristoidei is the sister group of all the other taxa; Rhynchobatus + Rhina is next separated from the others; the Torpedinoidei is the sister group of the Rhinobatoidei (sensu this paper) + Rajoidei + Myliobatoidei; the Rhinobatoidei is in the sister relation with the Rajoidei + Myliobatoidei. Among the Rhinobatoidei, Rhinobatos is the most plesiomorphic sister group of the others;Aptychotrema is the next plesiomorphic sister group of the remaining genera which trichotomously divided into ZapteryxTrygonorhina, and Platyrhinoidis + Platyrhina. A new suborder Rhynchobatoidei is proposed for Rhynchobatus + Rhina.

PIKE, C. S.,* and S. H. Gruber
University of Miami, 4600 Rickenbacker Causeway, Miami, Florida 33149 USA

The use of tetracycline validated vertebral centra in the estimation of age and growth of captive, juvenile lemon sharks (Negaprion brevirostris)

Forty-one juvenile lemon sharks, Negaprion brevirostris, reared in captivity were examined to estimate age by analyzing growth rings (circuli) on histologically stained and tetracycline-treated vertebral centra. Results demonstrated a significant linear relationships between the size of the shark, the size of the centrum and the number of circuli deposited. However, there was no apparent predictable time interval related to circulus deposition. Therefore, it is suggested that circulus deposition frequency is controlled by an environmental factor(s) as yet unknown, present in the wild and absent under controlled conditions of captivity. Supported by NSF-OCE8743949

ROSA, R. S.*
Universidade Federal da Paraiba, Dept. Sistemática e Ecologia, 58000 João Pessoa PB, Brasil

Biogeography of freshwater stingrays (Myliobatiformes)

Two families of stingrays include freshwater species: Dasyatididae and Potamotrygonidae. The former is predominantly marine, with few representatives of the genera Dasyatis and Himantura endemic in rivers of southeast Asia and Africa. The latter family occurs exclusively in freshwaters of South America, repre-sented by three genera (PlesiotrygonParatrygonand Potamotrygon) and 20 species. No close phylogenetic relationship can be postulated between these two families, on the basis of an analysis of morphological characters and on physiological grounds. The distinct osmoregulatory strategies of the two groups represent acquisitions related to independent events of freshwater colonization by marine ancestors.

The absence of potamotrygonids from the oriental Gondwanic fragments and the restricted distribution of the hypothesized primitive genus Plesiotrygon in the upper Amazon suggest that the early evolution of the group occurred in western South America, in parallel with the uplift of the Andes and the formation of the Amazon basin.

Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 USA and University of Miami, Miami, Florida 33149 USA

Heart rate and metabolic rate in the lemon shark, Negaprion brevirostris

Heart rate, metabolic rate, and activity were simultaneously recorded from juvenile lemon sharks for 24 hour periods to determine whether heart rate might be a suitable indicator of metabolic rate for field studies. Heart rate was monitored by acoustic telemetry using a frequency modulated ECG transmitter. Metabolic rate was measured as oxygen consumption rate in a flow through respirometer. In 7 sharks, mean resting values for heart rate and oxygen consumption rate were 52.1 +/- 0.4(S.E.) beats min-1 and 161.7 +/- 2.O(S.E.) mg kg-1 hr-1, respectively. Both parameters increased significantly (p=.05) during swimming, to means of 55.4 +/- 0.2 beats min-1 and 231.1 +/- 2.2 mg kg-1 hr-1, at a mean swimming speed of .400 +/- .002 body 1engths s-1 . The observed elevation in heart rate from rest to spontaneous exercise accounts for 14% of the increase in oxygen uptake, leaving the remainder to be accounted for by increases in stroke volume and/or arteriovenous oxygen difference. The small contribution of heart rate to changes in the oxygen transport system limits its value as a measure of metabolic rate. Supported in part by NSF-OCE8743949.

Massachusetts Division of Marine Fisheries, Oak Bluffs, Massachusetts 02557 USA and NOAA/NMFS/NEFC, Narragansett Laboratory, Narragansett, Rhode Island 02882 USA

Age and growth of the blue shark, Prionace glauca, in the North Atlantic

Age and growth estimates for the blue shark, Prionace glauca, were independently derived from 1322 tag-recaptures, 5200 length frequency samples, and 325 vertebral centra. Size information, tag and recapture data, and vertebral samples were obtained from the eastern and western North Atlantic by scientists and fishermen aboard research, recreational, and commercial fishing vessels. The data consisted of sharks ranging in length from 40 to 295 cm. fork length, separated and analyzed by sex. Vertebrae from 139 tag-recaptured sharks including one marked with oxytetracycline provided partial age validation. Growth curve corroboration supports the conclusion that this species grows faster than previously reported.

SNELSON, F. F.*1, S. H. GRUBER2, F. MURRU3, and T. H. SCHMID3, 
1Department of Biological Sciences, University of Central Florida, Orlando, Florida 328161 USA, 2 /sup>Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida 331491 USA, and Sea World of Florida, Orlando, FLorida 32821. USA

Preliminary report on a colony of southern stingrays (Dasyatis americana) at Bimini, Bahamas

Southern stingrays are aggregated around a wreck in 5-6 meters of water on the Bahamas Bank about 11 km east of Bimini. The wreck is encircled by a zone of bare sand; the bottom beyond the sand zone supports seagrasses. During the day rays are inactive, buried in the soft sand bottom. They lie oriented into the current and show preference for the sand-seagrass ecotone. Preliminary evidence suggests that they become active and leave the wreck site at night to feed over the grass beds. Census data indicate that there are about 40 rays in the group, with females outnumbering males by 4 or 5 to 1. The sample of rays measured ranged from 44-99 cm disk width; several larger animals were observed. This size range suggests that most animals are either subadult or adult. Tagged animals stay on the site and can be anesthetized, measured, and manipulated in situ. — We plan long-term studies of this colony emphasizing movements, behavior, and population structure.

Department of Biology, California State University, Long Beach, California 90840 USA

Behavioral ecology of the horn shark, Heterodontus francisci: Patterns of space utilization

Twelve horn sharks were telemetered via surgically implanted transmitters at Santa Catalina Island, California. All-night trackings as well as bi-daily position fixes were obtained from a sample shark population on a very regular basis during July and August, 1986. The sharks were followed by rowing, thus reducing artifacts in the movements due to engene noise. Daytime activity spaces were usually very small, often represented by a single point. At dusk, adults generally moved onto the main reef from their deeper daytime sites and, with the approach of dawn, descended steadily to the previous refuge areas. These crepuscular moves appear highly directional while those for night-time are described as meandering. Fifteen typical trackings of adult sharks yielded a mean nighttime activity space of 9793 m2 and a high degree of home range stability. Juveniles refuged at shallower depths on the reef or near the island. Based on the telemetry and over 300 conventional taggings, the local horn shark population and factors affecting their movements are reviewed with particular emphasis placed upon the importance of the algal habitat.

Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, Florida 33149 USA

Absorption efficiency of the juvenile lemon shark, Negaprion brevirostris, at varying levels of energy intake.

The efficiency with which the lemon shark, Negaprion brevirostris, is able to absorb energy, organic matter and dry matter was measured at five levels of energy intake. An indirect method was used by incorporating Celite, an inert reference substance, into food. Absorption efficiencies for energy, organic matter and dry matter were 68.79%, 80.82% and 76.73% respectively. Absorption efficiency increased as energy intake increased and declined at the highest level of intake. Growth rate and production efficiencies (K1 and K2 ) increased with ration. Time required for a meal to be completely eliminated from the digestive tracts of sharks also increased as rate of intake increased. Feces were egested at a constant rate, and fecal composition varied little throughout the duration of voidance. Estimates of absorption efficiencies using a total collection method overestimated absorption at all levels of intake. This study represents the first measurement of absorption efficiency reported for any elasmobranch species, and demonstrates that the lemon shark is capable of absorbing energy as efficiently as most teleosts. Supported by NSF-OCE 8843425

Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02138 USA

The functional morphology of suction feeding in the horn shark (Heterodontiformes) and the whitespotted bambooshark (Orectolobiformes).

The Heterodontiformes and Orectolobiformes are two closely allied basal groups of galeomorph sharks. Suction feeding in the horn shark, Heterodontus francisci, and the whitespotted bambooshark,  Chiloscyllium plagiosum, was investigated with high speed video and electromyography. Analysis showed that these sharks produce suction by a combination of elevation of the chondrocranium, depression of the mandible, and rapid expansion of the oropharyngeal cavity. Suction is enhanced by protraction of the upper jaw and by extension of the labial cartilages to produce a more rounded mouth opening in a manner analagous to the premaxilla-maxilla mechanism of jaw protrusion in teleosts. This supports the suggestion that the highly protrusile upper jaw in the more derived orders of galeomotph sharks, i.e., the Lamniformes and the Carcharhiniformes, evolved from the functional requirements for suction feeding.

YEARSLEY, G. K.,* and P. R. LAST
CSIRO Division of Fisheries Research, G.P.O. Box 1538, Hobart, Tasmania, 7001, Australia

The systematic studies of Australian urolophids

Myliobatiform rays of the family Urolophidae are represented by three genera in the Australian region: UrolophusTrygonoptera and Urotrygon. The fauna consists of 17 described species (13 Urolophus and 4 Trygonoptera) and a further 5 species (2Urolophus, 2 Trygonoptera and 1 Urotrygon) are either undescribed or unrecorded from the region. Trygonoptera, originally applied to those members of the family with a dorsal fin but considered by most recent authors to be a junior synonym of Urolophus, is shown to be valid. Unlike Urolophus species, Trygonoptera possess cutaneous folds at the lateral borders of the nostrils, an additional dorsal foramen in the scapulocoracoid, and differs in the shape of the cranium. The postorbital process of the cranium is divided (entire and bearing a foramen in Urolophus) and the internasal width is much broader dorsally. Distributional patterns of Australian species, the validity of species complexes as supraspecific taxa, and the importance of dorsal fins, lateral cutaneous skin folds and oronasal structures as supraspecific characters are also discussed.

ZORZI, G. D.,* and L. J. V.
CAMPAGNO, California Academy of Sciences, San Francisco, California 94118 USA and J. L. B. Smith Institute of Ichthyology, Private Bag 1015, Grahamstown 6140, Republic of South Africa

Occurrences of dasyatid stingrays in rivers and freshwater lakes

The whiptail stingray family, Dasyatidae, includes about 63 species in six or perhaps seven genera. Most are marine, and are commonly found close inshore, in estuaries and off beaches and river mouths. While many are sufficiently euryhaline, and tolerate reduced salinities, to 10% or even less, only three omnihaline species, Dasyatis fluviorum, D. sabinaand Hypolophus sephen, are recorded from great distances up rivers and in freshwater lakes, Seven species, Dasyatis garouaensisD. laosensisD. ukpamD. sp., Himantura fluviatilisH. krempfi and H. signifer, are known only from fresh or brackish waters.