1994 AES Annual Meeting Abstracts

SPINE REPLACEMENT IN A FRESHWATER POPULATION OF THE ATLANTIC STING-RAY, DASYATIS SABINA

Dasyatis sabina is broadly euryhaline and individuals often stray into fresh water. The only well-known population to reside permanently in fresh water occurs in the St. John’s River, FL. We studied the pattern of caudal spine replacement in this population to see if it differed from marine populations. Monthly samples totaling 181 adults were taken from November, 1990 to May, 1992. Spine replacement began in May with the appearance of a primordial bud. A calcified replacement spine was present in 45 percent of June specimens and in 95 percent of July and August specimens. Replacement spines were present in only 20 percent of specimens taken in September and October, indicating that replacement was completed in most individuals by late summer or fall. Replacement spines grew rapidly from an average length of 6 mm in June to 28 mm in August. The primary spine exfoliated when the replacement spine reached about 50-60 percent of its definitive length. The replacement spine reached its definitive length, averaging 60-65 mm, by the early winter. Definitive spine length was strongly correlated with body size. In all cases the replacement spine originated posterior to the primary spine. Spine replacement and growth patterns in this population were similar to those in the population from the eastern Gulf of Mexico. ; Keywords: Dasyatis, spine, barb, Florida, stingray, venom apparatus, replacement, freshwater, elasmobranch

OBSERVATIONS ON SHARK EMBRYOS AND JUVENILES CAUGHT BY SANTOS LONGLINERS OFF SOUTH AND SOUTHEAST BRAZIL

Samples were collected during 1988-93, from Santos longliners operating off South/Southeast Brazil (18°-33° S and 35°-51° W). The Average Lengths (AL) of 269Sphyrna lewini embryos, were: May=24.4; June=29.7; July=32.9; Sept.=42.0; Oct.=46.5; and Nov.=47.4 cm. The birth size is 45.0 to 55.0 cm*. The birth probably occurs in Nov-Dec. The length/weight relationship (L/W) was W=4.07×10-3 L3.01. The AL of 98 Carcharhinus maou embryos were: Sept.=18.1; Feb.=40.5; Mar.=56.5; Apr.=57.1; May=58.1; June=52.8; July=63.1; Aug.=58.8; Oct.=69.2; Nov.=69.7 cm. Four juveniles were hooked in Oct. (80 and 84) and Feb. (86.5 and 101.5 cm). Probably this species has the gestation period longer than one year, and the birth occurs at least in Sept.- Nov. (birth size is 60.0 to 65.0 cm *). The L/W was W=5.20×10-3 L3.03. The AL of 159 Carcharhinus signatus embryos were: Apr.=25.5; June=43.0; Aug.=47.4; Oct.=49.7; Nov.=54.4, Dec.=56.4 and Feb.=54.1 cm. Two juveniles were found in Nov. with 73.0 and 82.0 cm. Probably the birth occurs in Nov.-Feb. (birth size is about 60 cm *). The L/W W=7.56×10-3 L2.86. The AL of 14 embryos from 7 females of Alopias superciliosus were: Aug.=91.7; Oct.=79.2; Nov.=75.4; Dec.=97.1 and Mar.=103.0 cm. The birth probably occurs in Dec.-Mar. (birth size is about 100 cm *). The sex ratio of these four species was about 1:1. (* = information from literature).; Keywords: Brazil, shark embryos, shark juveniles

ARE ELECTRIC RAYS (TORPEDO SPP.) A HEALTH HAZARD TO DIVERS?

Electric rays of the genus Torpedo are known to produce powerful electric discharges used to kill fish prey and deter predators. Pacific electric rays (Torpedo californica) are found in shallow water along the Pacific coast, where they are frequently encountered by scuba divers. There have been over 40 unexplained scuba diving fatalities off Los Angeles County attributed to “accidental drowning”; electric rays have never been considered as the primary cause of death.; The discharges produced by electric rays, measured in situ by Lowe et al. (in press), and Bray et al. (in prep.), resemble the discharge pattern known to reliably induce ventricular fibrillation in large mammals. Until more is known about the discharges produced by electric rays and the electrical characteristics of divers in seawater, we urge that divers be cautious of electric rays. These rays may pose the greatest hazard at night, during which they appear to be actively hunting prey. ; Keywords: Torpedo, electric organ discharge, ventricular fibrillation, scuba divers

PARASITES OF THE ORECTILOBIFORM SHARKS: WHAT HAPPENED TOPEDIBOTHRIUM?

The discovery of multiple species of Pedibothrium in Ginglymostoma cirratum prompted a survey of the tapeworms of Orectilobiform sharks to determine the generality of this phenomenon. A 15,000 mile road trip throughout Australia resulted in the collection of tapeworms from 5 to 30 individuals of each of 9 species representing the 5 families of orectilobiform sharks. All tapeworms were removed from spiral intestines and examined with light and electron microscopy. Multiple species of Pedibothrium were found inNebrius ferrugineus and Stegostoma fasciatum, but there was no overlap ofPedibothrium species among these host species. Cladistic analysis suggests that multiple congeners within each of the 3 rhinodontid species examined are not each other’s closest relatives, instead each is more closely related to a species in one of the other 2 rhinodontid species. Pedibothrium was not found outside of the Rhinodontidae. At least 1 species in each of the other 4 families of orectilobiform sharks hosted Acanthobothrium, a genus widespread among the Heterodontiformes and the batoids. Generally, shark species within a family hosted similar parasites, but there were no similarities between the parasites ofHemiscyllium ocellatum and Chiloscyllium punctatum. In general, few tapeworm groups were shared among the 5 orectilobiform families. ; Keywords: parasites, tapeworms, Orectilobiformes

LARGE SHARKS AND PLASTIC DEBRIS IN NATAL, SOUTH AFRICA

Approximately 1,440 large sharks, comprising 14 species, are caught annually in the nets which protect users of the tourist beaches of Natal against shark attack. Between 1978 and 1993 13,371 of these sharks (60% of the catch) were examined in the laboratory. The presence of plastic debris either in the stomach or entangled around the shark’s body was recorded. Fishing line was excluded to avoid confusion between discarded debris and material from directed fishing activities.; Of the 12,737 sharks with recorded stomach contents, 51 (0.40%) had ingested plastic items. Of the 411 tiger sharks Galeocerdo cuvier examined, 8.3% had ingested plastics. The frequency of occurrence of plastics in the stomachs of each of seven other species was less than 1% and no plastics were found in six species. There was no evidence of any increase in the ingestion of plastics with time. All the sharks appeared to be healthy and unaffected by the ingestion of the items. ; Twenty three sharks (0.17% of those examined) were encircled in the gill region with a single polypropylene band such as is used to secure cartons. No entangled sharks were reported between 1978 and 1982. There was no evidence of an increasing trend in the incidence of entanglement from 1983 to 1993. The injuries in some cases were considerable but there was also some tissue regeneration.; Keywords: feeding, sharks, plastic debris, entangling, Natal, shark nets, injuries.

GUT RECIPES: RECOMMENDED METHODS FOR STUDY OF FOOD, FEEDING HABITS AND CONSUMPTION IN SHARKS BASED ON ANALYSIS OF STOMACH CONTENTS

Methods used in food studies of fishes and sharks are briefly reviewed, and methodological recommendations for food studies are presented and illustrated using stomach contents data for several species of sharks. Calculating frequency of occurrence (%O) and the index of relative importance (IRI) by taxonomic level, and expressing IRI as a percentage (%IRI), are recommended. A three-dimensional graphical presentation of %O, percent number (%N), and percent weight (%W) of prey items allowing easy interpretation of relative prey importance and degree of homogeneity of the diet is proposed. Use of contingency table analysis to detect dietary differences among predators, or seasonality and size-related variations in the diet for a given predator, as proposed by Crow (1981), is recommended. Application of the most widely used measures of diet overlap and diet breadth along with the statistical treatment of stomach contents data is discussed. The limitations of ANOVA and ANCOVA in detecting diel feeding discontinuity are presented and the applicability to elasmobranchs of the main approaches used for estimating diurnal food consumption and daily ration in other fishes is reviewed. Use of jackknife and bootstrap techniques is recommended to obtain estimates of daily ration with standard errors and confidence intervals. ; Keywords: shark diet, food habits, diel feeding chronology, daily ration, IRI

DIET, FEEDING HABITS AND DIEL FEEDING CHRONOLOGY OF THE BONNETHEAD SHARK, SPHYRNA TIBURO, IN SOUTHWEST FLORIDA

The diet, feeding habits, and diel feeding chronology of the bonnethead shark Sphyrna tiburo in Tampa Bay and Charlotte Harbor, two estuaries of southwest Florida, were investigated through analysis of stomach contents. The diet was very homogeneous and was dominated by crustaceans, consisting mostly of blue crabs, followed by seagrasses and traces of mollusks, teleosts, and other material. Contingency table analysis and measures of dietary overlap were used to detect seasonal, sex, size, locality, and habitat-related quantitative differences in stomach contents. Overall, results suggested that bonnethead sharks are specialists that undergo dietary shifts depending on season and habitat. Values of dietary breadth were also calculated and found to be low, attesting to the specialized feeding habits of this species. A significant prey/predator length relationship was found for blue crabs and bonnethead sharks. Bonnethead sharks do not consume larger, commercially harvestable blue crabs in the area. Discontinuity of feeding was investigated using two different statistical techniques. Results varied according to the method used, revealing the shortcomings of the most commonly used approach and the limited value of considering only stomach contents weight to draw conclusions on diel feeding chronology.; Keywords: shark diet, feeding habits, diel feeding chronology, bonnethead shark

COMPARATIVE DEMOGRAPHY OF THE BONNETHEAD SHARK, SPHYRNA TIBURO, IN SOUTHWEST FLORIDA

Demographic analyses of the bonnethead shark, Sphyrna tiburo, in Tampa Bay and Florida Bay, Florida, are presented. Input parameters to the models included age at maturity and maximum age, age-specific litter size, periodicity of parturition, sex ratios at birth, and age-specific total instantaneous mortality rate (z). Z was estimated through four methods for bonnethead sharks from Tampa Bay and through two methods for sharks from Florida Bay. The life-history tables constructed for bonnethead sharks in Tampa Bay yielded net reproductive rates (Ro) ranging from 1.18 to 5.22, generation lengths (G) varying from 3.8 to 5.0 years, and corrected instantaneous rates of population increase (r) ranging from 0.043 to 0.390. For the Florida Bay population, Ro ranged from 1.57 to 5.48, G from 3.9 to 5.0 years, and r from 0.119 to 0.404. Mean expectation of further life at age (ex) and theoretical population doubling time were also calculated in each simulation. Sensitivity analysis was used to assess the influence of changing natality and mortality rates on computed demographic parameters. Overall, population growth in Tampa Bay appears to be faster than in Florida Bay and r values for bonnethead sharks are considerably larger than those computed for other species of sharks.; Keywords: demography, bonnethead shark, Sphyrna tiburo, mortality, catch curve, sensitivity analysis

ANALYSIS OF MAKO SHARKS, ISURUS OXYRINCHUS, FROM SANTOS LONGLINERS OFF SOUTH AND SOUTHEAST BRAZIL

The fisheries of mako shark caught by Santos (Sao Paulo, Brazil) longliners in the area 18°-33° S/35°-51° W, from 1971 to 1990 were studied in this paper. The annual yield fluctuated from 13.3 t in 1975 (N=267) to 138.3 t in 1990 (N=3,241). The average weight ranged from 41 kg in 1984 to 51 kg in 1977. The fishing effort has increased from 4.3×105 (l972) to 3×106 (l990). The CPUE (N° /thousand hooks) ranged from 0.6 in 1982 to 1.8 in l988. Usually the lowest catch occurred in February and the highest in November. The condition factor (k) from length/weight relationship was: W=0.1×10-3 L2.86. From April to November the catches in weight and number were higher, but the average weight decreased. It probably happened due to recruitment period and also the high condition factor index. Ten out of 13 embryos (TL=645 to 720 mm), had teeth in their stomachs. This fact suggests uterine cannibalism because the teeth were held in plaques, eliminating the possibility of the fishes having swallowed their own teeth.; Keywords: Brazil, mako shark, longliner fishery

GROSS BRAIN DEVELOPMENT IN THE WHITE SHARK: A DISAPPOINTMENT?

Based on estimates of brain to body size ratios and the relative development of brain areas from a specimen of an 11’9” male, the brain of the adult Carcharodon carcharias is only moderately developed, fairly generalized and similar to other lamniods i.e. makos and basking sharks. The pallium of the telencephalon is not exceptional as it is in hammerheads and certain carcharhinids where enlargement of the area seems to be correlated with acquisition of elaborate social and territorial behaviors which may require learning of environmental landmarks and individual recognition. Thus, such behaviors may not be typical of white sharks. With regard to the major sensory systems controlling prey detection in sharks (hearing, mechano and electroreceptive lateral-line and vision), only vision may be well-developed from a comparative standpoint. A brain-eye heater (orbital rete) is present which may function to stabilize the thermal environment of the brain and retina in situations where convectional heat loss might otherwise impair neural processing (see Block and Carey, J. Comp. Physiol. B, 156: 229-236). ; Keywords: brain weight, olfaction, vision, behavior, sense organs, elasmobranch.

REPRODUCTIVE BIOLOGY OF THE SHOVELNOSE GUITARFISH,RHINOBATOS PRODUCTUS, IN BAHIA ALMEJAS, B.C.S., MEXICO

The commercial catch of the shovelnose guitarfish, Rhinobatos productus, was used to study the reproductive biology in Bahía Almejas, western coast of the Baja California Peninsula, with a monthly sampling from January to December of 1992. Females were abundant during May-August. The total length (TL) average in males was 68.77 and in females 113.66 cm. Females arrive to the bay by mid May, starting the embryonic development (gestation) and the ovocyte growth, and reaching it’s maximum development in early August. Birth occurs during mid August, around 20 cm TL. Mature males with semen enter to the bay in July. Females ovulate and mate before both leave the area. From August through April females have eggs in the oviducts, without embryonic development. In adults, females outnumbered males, but in embryos, sex ratio was 1.04:1. Fecundity was variable between 4-18 embryos per female, and it seems to be size dependent. AES Samuel Gruber Award Competitor; Keywords: shovelnose guitarfish, Rhinobatos productus, reproductive biology, Pacific, Bahía Almejas

ASSESSMENT OF THE POPULATION STRUCTURE OF ALOPIAS VULPINUSFROM WATERS ADJACENT TO THE WESTERN COAST OF NORTH AMERICA 

Allozymes of 146 individuals of Alopias vulpinus captured from the eastern Pacific were used to assess population structure. Of 13 presumptive loci surveyed, four were polyallelic. Samples collected from waters adjacent to Baja California, southern California, and central California were monoallelic for all four of these loci. These results failed to disprove the null hypothesis that this “southern group” of samples came from a single, panmictic subpopulation. Replicate samples collected from waters adjacent to northern Oregon and Washington were all polyallelic for two or more loci, and statistically different from the “southern group” of samples. Furthermore, statistically significant differences were found among some of the samples from Oregon-Washington, suggesting that individuals representing at least two different subpopulations were captured from this region. The hypothesis that a single, panmictic subpopulation of A. vulpinus exists along the western coast of North America was not supported. AES Samuel Gruber Award Competitor, ASIH Stoye Award Competitor – Genetics, Development, and Morphology; Keywords: allozymes, Alopias vulpinus, eastern Pacific, population structure

REPRODUCTIVE BIOLOGY OF SCYLIORHINUS CANICULA (L.)

Over 700 specimens of Scyliorhinus canicula have been examined during a study of the reproductive biology of the species. Maturity was assessed by visual inspection of gonads and, quantitively, by gonad weight and clasper length/nidamental gland width. 50% maturity was attained at a length of 52cm (males) and 55cm (females). Seasonal cycles in the gonadosomatic index (GSI) were found in both sexes with the peak GSI of females and males occurring in May and August respectively. The egg laying season was determined from the percentage of female fish carrying eggs and was found to peak in June. Fecundity was found to increase with length.; Keywords: Scyliorhinus canicula, reproductive biology

PREDATORY BEHAVIOR OF THE PACIFIC ANGEL SHARK, SQUATINA CALIFORNICA: VISUALLY-MEDIATED ATTACKS AND AMBUSH SITE CHARACTERISTICS

Pacific angel sharks ambush diurnal and crepuscular-migratory demersal fishes. They enhance their crypsis by partially burying themselves in soft-substrata; an imprint remains in the sediment after an ambush site has been recently abandoned. I tested angelsharks for: 1)in situ preference of a prey’s direction of approach and 2) habituation to my experimental methods. I also recorded spatiotemporal characteristics of their ambush sites at Big Fisherman’s Cove, Santa Catalina Island, southern California, from July through December 1993. Individuals were identifiable based on the pigment patterns on their first dorsal fins. I placed an acrylic partition above each resting shark and passed a fish-model immediately above the partition’s transparent surface, along the shark’s mid-line. Visually-mediated attacks occurred during both anterior- and posterior-approach trials (trial = up to ten sequential passes of model); however, attacks on the first pass of the model only occurred during anterior-approach trials. Three sharks habituated to the experiment; all had attacked on two occasions prior to evidence of habituation. Resting sharks and vacated imprints were usually oriented upslope and were usually adjacent to natural or artificial reefs. Two sharks returned to the proximities (<2 m) of previous ambush sites. AES Samuel Gruber Award Competitor; Keywords: Pacific angel shark, Squatina californica, ambush, predation

ORGANIC MATRICES FROM ELASMOBRANCH VERTEBRAL CARTILAGE: IMPLICATIONS FOR BIOMINERALIZATION

The importance of non-collagenous organic matrices from the vertebrae of the clearnose skate, Raja eglanteria, was examined in regards to biomineralization. Organic matrices were removed from vertebral samples by EDTA – mediated decalcification. The possible inhibition of calcium phosphate formation by matrix extract was examined in vitro. In addition, the calcium binding capacity of matrix extract was measured with the use of a calcium electrode. The role of matrix in vertebral formation is discussed with particular emphasis on the formation of alternating mineral-rich and mineral-poor sublayers, currently used in ageing studies. AES Samuel Gruber Award Competitor; Keywords: cartilage, biomineralization, Raja eglanteria, organic matrices, age and growth

THERMOREGULATION AND POSSIBLE ENDOTHERMY IN THE WHITE SHARK (CARCHARODON CARCHARIAS)

Stomach temperature of three adult male white sharks (Carcharodon carcharias ) were intermittently recorded by acoustic telemetry over eight, seventeen, and ten day periods respectively, at the South Farallon Islands, central California. Temperature profiles of the water column were also obtained. The observed elevated stomach temperatures were maintained within a narrow range regardless of ambient water temperature. These data demonstrate thermoregulation in this species, and in combination with previous work on “warm-bodied” sharks may allow for the classification of the white shark as an endotherm.AES Samuel Gruber Award Competitor; Keywords: Carcharodon carcharias, South Farallon Islands, acoustic telemetry, stomach tempertature, thermoregulation, endothermy, elasmobranch physiology

A REDESCRIPTION OF THE SUSPENSORIUM OF HETEROPETALUS ELEGANTULUS AND ITS IMPLICATIONS FOR THE PRIMITIVE CONDITION WITHIN THE CHONDRICHTHYAN BASAL COMPLEX

COSMOPOLITAN POPULATION GENETICS OF THE SHORTFIN MAKO

The shortfin mako (Isurus oxyrinchus) is an active lamnid shark that supports commercial and recreational fisheries throughout the temperate, subtropical, and tropical oceans. Although tagging data indicate movements of great distances within the North Atlantic, it is not known if exchanges between ocean basins occur. Because of its great vagility and migratory potential, it is possible that a single cosmopolitan genetic stock occurs. Restriction fragment length polymorphism analysis of mitochondrial DNA is used to demonstrate that significant partitioning of genetic variability in shortfin mako occurs between ocean basins, and hence multiple genetic stocks are present. Comparisons are made with genetic studies of other large pelagic fishes (tunas and billfishes). Estimates of exchange rates between ocean basins are provided. AES Samuel Gruber Award Competitor; Keywords: shortfin mako, shark, population genetics, mtDNA

SHARK NURSERIES OF THE EASTERN GULF OF MEXICO: BIOLOGY AND FISHERIES-RELATED MORTALITY OF JUVENILE SHARKS IN TAMPA BAY AND CHARLOTTE HARBOR, FLORIDA

A two-year study of Tampa Bay and Charlotte Harbor, Florida, has revealed these areas to be nurseries for 11 shark species, with at least four, and possibly as many as nine, of these giving birth within the region. Of 1,862 sharks of 13 species collected in commercial-type fishing gear and documented by scientific personnel, 1,275 were tagged and released. An additional 1,477 sharks were documented and released by anglers in the 1992 and 1993 Gulf Coast Shark Census. Predominant species were bonnethead, blacktip, and blacknose, with lesser numbers of bull, Atlantic sharpnose, great hammerhead, nurse, lemon, scalloped hammerhead, Florida smoothhound, spinner, finetooth, and sandbar sharks. Juveniles of all species except Florida smoothhound and sandbar, and neonates of four species (blacktip, bull, lemon, and blacknose), were found, with neonates from an additional five species (bonnethead, great and scalloped hammerheads, nurse, and spinner) suspected of occurring in the area. Regional distribution patterns, migration, feeding, and reproduction of these various shark species will be discussed. Observed shark bycatch in regional commercial fisheries was low, but an estimated 54.8% of all small sharks caught by nets in the nurseries do not survive a singular fishing event. [Supported by FDEP Grant 7237/7849 and NMFS/MARFIN Grant NA17FF0378-01 to REH]; Keywords: shark, nursery, reproduction, Tampa Bay, Charlotte Harbor, tagging, migration, mortality

DYNAMIC REFRACTIVE STATE AND ACCOMMODATION IN THE EYES OF FREE-SWIMMING VS. RESTRAINED LEMON SHARKS (NEGAPRION BREVIROSTRIS)

Optical measurements of the refractive state of the eyes of various shark species typically have depicted sharks as hyperopic (far-sighted) with little evidence of accommodation (ability to change focus for visualizing objects at different distances from the eye). Such estimates have been obtained using retinoscopy or direct ophthalmoscopy on restrained animals. In this study, we used infrared video retinoscopy to measure refractive state in juvenile lemon sharks (Negaprion brevirostris). This technique allows dynamic measurement of refractive state in free-swimming animals as they pass by an aquarium window. We found that unrestrained lemon sharks are emmetropic for the lateral visual field, but when restrained either right-side up or upside-down (the latter in tonic immobility) the sharks become hyperopic, an artifact of handling previously found in some birds and other vertebrates. In addition, unrestrained lemon sharks could accommodate around emmetropia by several diopters while swimming, whereas restrained sharks ceased accommodating after becoming hyperopic. The lemon shark, therefore, is emmetropic with the eye at rest and can accommodate in the natural, free-swimming state, but becomes statically hyperopic when restrained. Refractive state measurements on restrained sharks in general, then, may not reflect the natural state of the shark eye.; Keywords: shark, Negaprion brevirostris, eye, vision, optics, refractive state, accommodation, retinoscopy

VARIATION IN THE ELECTRIC ORGANS AND ELECTROCYTES OF THE SKATE GENUS BREVIRAJA (ELASMOBRANCHII: RAJOIDEI)

The electric organ and electrocyte variation of the six nominal species of the skate genusBreviraja and selected taxa from the subgenus Raja (Leucoraja) [including the four subspecies of R. (L.) garmani, R. (L.) erinacea, and R. (L.) ocellata] are investigated to estimate variation of electric organ and electrocyte development in a genus of skates. Relative to the outgroup, B. marklei, putatively the most basal member of the genus, possesses unmodified cup-shape electrocytes that resemble a juvenile ontogenetic condition. In general, the electric organs of the remaining taxa within the genus are composed of modified cup-shape and intermediate-shape electrocytes, characterized a gradual widening and shortening of their electrocytes. Electrocyte variation within Brevirajais hypermorphic. These findings also support the recent discovery that B. marklei is the junior synonym of Raja (Rajella) fyllae, and suggest that R. (Rajella) rather than R. (Leucoraja) is the sister group of Breviraja. AES Samuel Gruber Award Competitor; Keywords: western North Atlantic, skates, Breviraja spp., electric organs, electrocytes, heterochrony

SEASONAL DYNAMICS OF DENTAL SEXUAL DIMORPHISM IN THE ATLANTIC STINGRAY, DASYATIS SABINA

In many batoids, males possess sharp teeth and females relatively rounded but there are no known differences in diet to account for this phenomenon. Dental sexual dimorphism supports the hypothesis that male tooth shape has evolved to increase reproductive success by providing them with a firm grip on the females during mating. Because mating in batoids is strictly seasonal it was predicted that male teeth should be sharpest during the reproductive period. Dentition of the Atlantic stingray, Dasyatis sabina, was examined over a 24 month period. Teeth sampled from males during the mating season are characterized by a pointed cusp while female teeth are molariform. During the non-mating season male dentition resembles female teeth which do not vary in shape with season. Pre-emergent teeth are similar in shape to teeth in active use and tooth replacement rate does not differ between the sexes which indicates that molariform teeth are not a result of differential wear. This work is the first demonstration of seasonal changes in tooth morphology that coincide with reproductive activity. Thus the dynamics of tooth shape in male batoids is driven by selection for mating rather than feeding efficiency. ; Keywords: elasmobranch, stingray, Dasyatis sabina, sexual dimorphism, mating, molariform, dental morphology

DO WHITE SHARKS (CARCHARODON CARCHARIAS) SELECT PREY BASED UPON HIGH FAT CONTENT? 

Adult white sharks feed on seals, sea lions, and whale carcasses, but release birds, sea otters, and humans at times without removing tissue after swimming briefly with them in the mouth. Marine mammals differ from the latter species by the possession of thick external layers of fatty tissue that prevent heat loss from the body. The energy content of fat exceeds that of protein from which the muscles of birds, sea otters, and humans are largely composed (8.0 kcal/gram versus 3.9-4.5 kcal/g). Could the white shark assess the fat content of items during transport and reject lean ones? White sharks were observed to seize and release skinless sheep carcasses nine times, but to consume fatty tissues from pinniped carcasses three times. A consequence of this energy rich diet may be the rapid rate of white shark growth when feeding upon marine mammals, averaging 4.8% of a shark’s total length per year from 11 to 15 years of age. In contrast, a cold water but piscivorous species from the same family, the porbeagle shark (Lamna nasus), grows over the same period at half the mean rate, 2.4% TL per year, and males and females of a piscivorous, tropical species from the lamnid family, the shortfin mako (Isurus oxyrhinchus), grow at only 1.0% and 1.5% TL per year, respectively.; Keywords: Carcharodon, predation, optimal foraging

CHASING THE DEEP SCATTERING LAYER 

To come.—— homocercal tail, with its externally symmetrical dorsal and ventral lobes, characterizes many teleost fishes and has been presumed to function symmetrically during locomotion. In contrast, previous work on heterocercal tails has shown that the asymmetrical morphology of the tail is correlated with asymmetrical function. In this study, the kinematics of the homocercal tail in a teleost, the bluegill sunfish Lepomis macrochirus, were examined in four individuals swimming in a flow tank at two steady speeds (1.2 and 2.2 TL/sec) and during unsteady burst-and-glide swimming. Both lateral and posterior views were obtained, allowing the position of four marked points on the caudal rays to be followed in three dimensions. Results show (1) that tail beat amplitude increases with swimming speed, (2) that the dorsal lobe of the tail undergoes greater lateral excursions than the ventral lobe, and (3) that the caudal fin is not vertically oriented through the tail beat cycle. Thus, the dorsal and ventral lobes of the homocercal caudal fin may function asymmetrically even during steady forward locomotion. Asymmetrical function may generate lift forces in a manner similar to heterocercal tails, and may be due to the action of the hypochordal longitudinalis, an intrinsic tail muscle.; Keywords:

SYSTEMATICS AND HISTORICAL BIOGEOGRAPHY OF NEOTROPICAL FRESHWATER STINGRAYS (POTAMOTRYGONIDAE)

The neotropical freshwater ichthyofauna includes representatives of some 15 primarily marine groups. However, a lack of phylogenetic and biogeographic data leaves the historical origins of these taxa unresolved – are they the result of multiple independent riverine invasions, or was a single vicariance event responsible? To begin to answer these questions, the evolutionary history of neotropical freshwater stingrays was investigated. A phylogenetic analysis of 17 stingray taxa was undertaken using 38 morphological characters. The resultant tree indicates that amphi-American Himantura represents the sister group to potamotrygonids, based on synapomorphies of the ventral mandibular musculature and the hyomandibular/mandibular articulation. Such a topology suggests that potamotrygonids are derived from a freshwater-invading ancestor distributed along the northern coast of South America prior to the emergence of the isthmus of Panama. NIA Award Competitor; Keywords: Potamotrygonidae, Himantura, stingrays, South America, systematics, biogeography

ONTOGENIC DIETARY SHIFT IN HAWAIIAN TIGER SHARKS

Stomach contents of tiger sharks caught during shark control programs in Hawaii were reanalyzed to examine ontogenic shifts in diet. Of 210 tiger sharks caught by longline along the main Hawaiian Islands between 1967 and 1969, 183 (87%) had food in their stomachs. Sharks were grouped into three size-classes (<200, 200-300, and >300cm TL) and the percent occurrence of prey in stomachs of sharks was examined. Smaller sharks consumed a higher percentage of teleosts, while larger sharks contained more elasmobranchs, turtles and mammals. Comparisons between the tiger sharks of the main Hawaiian islands, the Northwest Hawaiian Islands (NWHI), and Australia suggests that tiger sharks are opportunistic feeders and prey heavily on abundant, easy to capture prey in those areas. Tiger sharks examined from the NWHI had a higher percentage of sea birds, turtles and mammals in their diets than the other two regions and appear to be exploiting the seasonal influx of large prey. Elasmobranchs, turtles and mammals first occur in the diet of tiger sharks of approximately 250cm TL. This indicates the general size at which tiger sharks are large enough to feed on prey approximately the same size as humans and may represent the size of sharks that pose the greatest threat to humans.; Keywords: tiger shark, Galeocerdo cuvier, diet, ontogenic, stomach contents

ARTIFICIAL INSEMINATION IN THE CLEARNOSE SKATE, RAJAEGLANTERIA

Captive breeding of elasmobranchs has met with limited success. Since fertilization occurs internally, methods for the successful artificial insemination of females actively ovulating or producing mature ova would provide the opportunity to produce offspring without copulation as a prerequisite behavior. Attempts to inseminate three captively maintained female clearnose skates (Raja eglanteria), which had been isolated from mature males for nearly five months and which had been laying infertile eggs for at least three months, resulted in the successful fertilization of two of the three females. Semen was obtained by anesthetizing a mature male and aspirating the seminal fluid directly from the seminal vesicles. Semen was diluted with an equal volume of elasmobranch-modified semen extender and sperm counts were estimated using a hemocytometer. Sperm viability was assessed using a fluorescent assay which identified viable sperm with carboxyfluorescein diacetate and non- viable sperm with ethidium bromide. Approximately 125-140 x 106 sperm with greater than 95% viability were introduced into each of three anesthetized females. Semen was inserted into the cloaca or into either uterine horn using a syringe with a 28 gauge needle extended with PE 10 polyethylene tubing. Within 5-7 days, two of the three females were laying fertile eggs.; Keywords: Raja eglanteria, artificial insemination, fertilization, reproduction, semen, seminal fluid, sperm

PRELIMINARY BIOCHEMICAL ANALYSIS OF HISTOTROPH SECRETIONS FROM THE COWNOSE RAY RHINOPTERA BONASUS AND THE ATLANTIC STINGRAY DASYATIS SABINA, WITH OBSERVATIONS ON THE UTERINE VILLI FROM R. BONASUS

Uterine villi, termed trophonemata, are present in many aplacental viviparous rays, and secrete a uterine milk, or histotroph, which is ingested by their embryos. Histotroph was obtained aseptically from Rhinoptera bonasus and Dasyatis sabina and was analyzed for fatty acids, free amino acids, protein, and carbohydrate. Greater than 85% of the fatty acids in D. sabina histotroph consisted of hexadecenoic, hexadecanoic, and octadecenoic acids, while more than 80% of R. bonasus histotroph fatty acids included hexadecanoic, docosahexaenoic, octadecanoic, octadecenoic, eicosatetraenoic, and hexadecenoic acids. Free amino acid profiles were similar in composition except individual amino acid concentrations were generally 10- to 30-fold higher in R. bonasus histotroph. Isoelectric focusing revealed three and four protein bands for the two ray species, with pI’s ranging from 4 to 7.8. Greater than 85% of the histotroph carbohydrate consisted of two to three as yet unidentified sugars. In R. bonasus, trophonemata were 4 to 5 mm in length, extremely vascular and generally flattened. Histological sections revealed prominent arteries near the edges of one or both of the flattened margins with numerous smaller arteries branching medially to a large central vein. Interspersed among peripheral arterioles were U-shaped glandular regions around which tiny globules of histotroph were often visible.; Keywords: Rhinoptera bonasus, Dasyatis sabina, aplacental viviparity, uterine milk, histotroph, uterine villi, trophonemata

CONCENTRATIONS OF SERUM STEROID HORMONES DURING THE MATING AND GESTATION PERIODS IN FEMALE BONNETHEAD SHARKS,SPHYRNA TIBURO 

The bonnethead shark Sphyrna tiburo reproduces by placental viviparity with one of the shortest gestation periods known in sharks. In Tampa Bay and Charlotte Harbor/Pine Island Sound, Florida, the reproductive events in bonnetheads from fertilization to pupping occur in only 4.5 months. Using radioimmunoassay, we determined serum concentrations of reproductive steroid hormones (17-beta estradiol, progesterone, testosterone and dihydrotestosterone) during mating and gestation in this wild population. Estradiol, known to be a major reproductive hormone in all species of elasmobranchs studied, was found in significantly lower concentrations during early and mid-pregnancy than during late pregnancy. Prgesterone and testostrone levels increase significantly during early pregnancy prior to implantation, while serum testosterone levels decreased significantly during the post-partum period. At mating there were concomitant, significant elevations of both estradiol and testosterone. Our study is the first to demonstrate a sustained rise in progesterone during gestation in a placental shark, suggesting an essential role for this hormone during the pre-implantation period. The significance of these changes during mating and pregnancy in the female bonnethead is discussed in the context of the placental reproductive strategy of this shark. ; Keywords: bonnethead, shark, hormones, radioimmunoassay, reproduction, Sphyrna tiburo

DIEL MOVEMENT PATTERNS AND BEHAVIOR OF LEOPARD SHARKS,TRIAKIS SEMIFASCIATA, AT SANTA CATALINA ISLAND, CALIFORNIA 

Ten leopard sharks were acoustically tracked for intermittent periods ranging from 1 to 23 days. Home-ranging behavior and diel-phase differences were analyzed through tracking positions and by underwater observations. All ten sharks occupied a relatively confined daytime home-range in Big Fisherman Cove (BFC). Six of ten sharks exhibited wider ranging nocturnal movements, often leaving BFC completely. Five of these six sharks always returned to BFC by the next morning. Nocturnal rates of movement showed an increase, both for sharks which remained in BFC and sharks which left BFC. Data suggest that leopard sharks are home-ranging and more active at night, with periodic forays away from a smaller daytime core area. Although foraging appears to be primarily nocturnal, some sharks in BFC were observed feeding during the day. Expanding their nocturnal activity space may facilitate increased foraging opportuniies. In addition to te telemetry study, schooling behavior was observed. School structure and activity patterns (resting vs. swimming) were recorded. School composition was also investigated by cataloging individual sharks based on photographs of natural body markings. AES Samuel Gruber Award Competitor ; Keywords: acoustic tracking, Triakis semifasciata, diel behavior, home-range, schooling

SIZE COMPOSITION, SEX RATIO AND REPRODUCTIVE CONDITION OF THE DIAMOND STINGRAY, DASYATIS BREVIS, IN BAHIA ALMEJAS, B.C.S. MEXICO 

The commercial capture of the diamond stingray, Dasyatis brevis in Bahía Almejas, western coast of Baja California Peninsula, were monthly sampled from January to December of 1992. A total of 2739 organisms (1516 males and 1223 females) were obtained. The annual disk width (DW) average was 47.26 cm in males and 50.96 cm in females, with a maximum size of 72 and 79 cm DW respectively. Monthly variations in size composition were detected, with the biggest average for both sex in March and April. Males outnumbered females, except in March and April when the sex ratio were 1:2 and 1:5 respectively. The sexual maturity size in males begin at 45-50 cm, whereas in females is at 60-65 cm DW. In Bahía Almejas the diamond sting ray is the most important species in the commercial fishery; it can be found during all year inside the bay. ; Keywords: Dasyatis brevis, diamond stingray, Bahía Almejas, Pacific, size composition, reproduction

MOLECULAR SYSTEMATICS OF FRESHWATER AND MARINE STINGRAYS 

Here we report on the results from phylogenetic analysis of mitochondrial (cytochrome b) DNA sequences from freshwater stingrays of the family Potamotrygonidae and marine relatives of the order Myliobatiformes, including species of Dasyatis, Urolophus(=Urobatis), Taeinura, Myliobatis, Mobula, and Gymnura. The data provide the basis to test alternative hypotheses of relationships among taxa, to estimate the timing of colonization of Amazonia by marine taxa, and to infer the historical biogeography of South America. ; Keywords: stingrays, phylogenetics, Amazon, mitochondrial DNA, cytochrome b

SURVEY OF THE VARIATION IN ALAR THORNS IN SKATES: PHYLOGENETIC IMPLICATIONS (CHONDRICHTHYES: RAJOIDEI) 

Alar thorns are found on the lateral apices of the pectoral fins in adult male skates, and possession of these structures is thought to be a synapomorphy for the rajoids. However similar structures were found in squatinids, the second outgroup of the batoids. Scanning electron microscopy of alar thorns of 20 species of skates, representing the seven major clades of the rajoids, revealed phylogenetic informative variation in orientation and surface ornamentation of these structures. Phylogenetic implications of alar thorn structure is discussed. ; Keywords: phylogenetics, alar thorns, Chondrichthyes, Rajoidei

HETEROGENEITY IN MORPHOLOGICAL EVOLUTION IN SKATES (CHONDRICH-THYES: RAJOIDEI) 

Skates are morphologically similar and clearly distinct from the other batoid fishes. They share an impressive number of morphological synapomorphies, however, the seven major clades of skates share few derived characters among themselves and each retains a number of plesiomorphic characters. These characters are little changed from those in the sister taxa of rajoids, Rhinobatos, Aptychotrema, Trygonorhina and Zapteryx (Rhinobatoidei). Lack of synapomorphies among the subsets of the seven rajoid clades and retention of the primitive character states suggest that the seven clades are ancient and may go back near the origin rajoids in the Cretaceous. Interrelationships of one of the seven clades of rajoids (Amblyrajini) is elucidated by using the sister groups of rajoids as outgroups. Morphological character evolution and biogeography of Amblyrajini are discussed. ; Keywords: phylogenetics, heterogeneity of character evolution, Chondrichthyes, Rajoidei

LENGTH VALIDATION OF THE KANGAROO ISLAND AND MALTA WHITE SHARKS, CARCHARODON CARCHARIAS, WITH ESTIMATED TOTAL LENGTH OF 7 M 

The total length (TL) of two large white sharks, Carcharodon carcharias, were estimated from upper jaw perimeter, tooth enameloid height, and pectoral fin size. The Kangaroo Island white shark was determined to be 5.3 to 8.2 m long, consistent with the > 7 m TL estimate of Peter Riseley. The Malta white shark was estimated to be 4.6 to 7.0 m long, making the disputed TL measurement of 7 m by John Abela possible. None of the additional morphometrics nor the estimated weight of the Malta shark ruled out a length of 7 m. The total length of large white sharks has to be measured if a precision of better than 10% is required. The estimates from the 95% confidence band for a new observation of upper jaw perimeter, tooth enameloid height, fin morphometrics, or weight from sharks of known TL were 2 to 4 times as large. Better definitions for certain morphometrics in terms of how they can be consistently measured and a proper protocol for measuring large white sharks should be drawn up by a panel of experts on the white shark. ; Keywords: White shark, length validation, morphometrics, allometry, ratio-on-size regression, confidence band, coefficient of variation

FEEDING MECHANICS OF THE LEMON SHARK, NEGAPRION BREVIROSTRIS: A MORPHOLOGICAL, KINEMATIC, AND ELECTROMYOGRAPHIC ANALYSIS

Despite a number of studies on the diet and feeding behavior of sharks, none integrate morphological, kinematic, and electromyographic analyses. The lemon shark, Negaprionbrevirostris, a carcharhinid, exhibits a derived feeding mechanism including a kinetic and protrusible upper jaw. The jaw has an extensive ligamentous network that resists lateral translation of the moveable elements. Biting kinematics include initial cranial elevation, followed by lower jaw depression, upper jaw protrusion, lower jaw elevation, cranial depression and closure on the prey. The kinematic model proposed for these movements includes a mechanism for jaw protrusion actuated by the preorbitalis and levator palatoquadrati muscles. We also propose a novel passive mechanism for upper jaw retraction that involves an elastic ethmopalatine ligament. Motor patterns of prey capture for weak bites, strong bites, and head shaking show distinctly different muscle recruitment patterns. ; Keywords: lemon shark, Negaprion brevirostris, morphology, feeding, electromyography, protrusion, jaws, kinematics

A METHOD TO IDENTIFY ISOLATED SHARKS’ TEETH OF THE GENUSCARCHAR-HINUS TO SPECIES FOR TRACKING PHYLETIC CHANGE IN THE FOSSIL RECORD 

Most sharks can be identified to genus on the basis of a combination of their tooth-shapes and tooth-counts. Some sharks can even be identified to species by this means. The requiem sharks (genus Carcharhinus) are one such group. This group also has a dense and relatively continuous fossil record of isolated teeth extending from the Eocene to the present day. If a means could be developed to identify their isolated teeth to species, it would be possible to trace directly their evolutionary history through the fossil record. This would provide an unprecedented opportunity to investigate the tempo and mode of evolutionary change. We have determined the extent to which the isolated teeth of extant Carcharhinuscan be correctly assigned to species using discriminant function analysis of linear measurements. Our conclusions are based on measurements taken from more than 12,000 teeth representing variation due to 22 species, ontogeny, sexual dimorphism, jaw, and tooth position. We propose an objective and quantitative protocol for the interpretation of phyletic change in fossil Carcharhinus teeth based on these empirical results. ; Keywords: fossil record, sharks teeth, multivariate morphometrics

THE PHYLOGENETIC RELATIONSHIPS OF “ADVANCED” CARCHARHINIFORM SHARKS BASED ON MTDNA SEQUENCE 

The complete ND2 gene sequence was determined for 28 carcharhinid, 5 sphyrnid, one hemigalid and two triakid sharks. Sequences were aligned and subjected to phylogenetic analysis. Results support many of the phylogenetic hypotheses previously held based on morphological data. However, the data are at odds with the conventional wisdom in several areas; most notably in suggesting that the Carcharhinidae is paraphyletic with respect to the Sphyrnidae and that C. brevipinna is the sister taxon to C. brachyurus not to C. limbatus as is often supposed. Phylogenetic inferences based on mtDNA sequences lend support to Dr. Stewart Springer’s early suspicions that the presence or absence of an interdorsal ridge was a useful character for assessing phylogenetic relationships within the genus Carcharhinus. ; Keywords: molecular systematics, mitochondrial DNA, carcharinid sharks

ANATOMICAL INDICATORS OF SEXUAL MATURITY IN SHARKS 

More precision is needed in determining maturity. Studies of population dynamics require knowledge of which animals are capable of reproduction. Quantitative numbers such as the size and age at 50% maturity are desirable. However, to understand a species life history, it is also important to define subadults, mature virgins, post-partum females, seasonally resting and senescent sharks of both sexes. Some signs of sexual maturity are easily recognized in sharks. The presence of embryos in a female, or robust calcified claspers in a male, leave little doubt as to reproductive condition. Frequently, however, the largest part of a sample may be not clearly mature and work must be done to assess reproductive status. Anatomical condition, relative size of organs, and the presence of sex products may all be useful. Specifically, the size and contents of testes, and the upper and lower (ampulla) epididymis may be used in the male as well as the size, calcification and articulation of the clasper and it’s associated organs. Female sharks may possess a complete or partial vaginal membrane. The size of ovarian eggs, development of the oviduct and uterine condition are all useful in determining maturity and reproductive seasonality. ; Keywords: shark reproduction, sexual maturity, anatomy

ENVIRONMENTAL FACTORS AFFECTING THE OCCURRENCE AND BEHAVIOR OF WHITE SHARKS AT THE SOUTH FARALLON ISLANDS, CALIFORNIA 

Basing analyses on events recorded during standardized observation periods from the South Farallon Islands, we examined the daily effects of 13 weather, oceanographic, and lunar variables on the predatory and non-predatory behavior of white sharks (Carcharodon carcharias). Effects were assessed with multivariate analyses including the development of models to statistically isolate each effect relative to those of others considered in the analyses. Frequency of attacks on pinnipeds increased with swell height and coastal upwelling the day before observation, and decreased with water clarity. Non-predatory sightings (including surfacings and breaches) increased with cloud cover, sea-surface temperature, and upwelling the day before observation, and decreased with wind speed, upwelling the day of observation, and lunar stage. Spatial patterns of activity indicate that white sharks stalk prey “downstream” according to oceanic and tidal currents. White shark breaches showed a different seasonal pattern than attacks, suggesting that they may represent social signaling rather than failed predatory attempts. Based on a synthesis of our results we speculate that sea-surface temperature, upwelling, and lunar illumination affected shark behavior; swell height and water clarity affected prey behavior relative to predation; and wind speed and cloud cover affected our ability to detect shark activity. ; Keywords: white shark, Carcharodon carcharias, predation, weather, upwelling, water clarity, breaching

GASTRIC EVACUATION MEASUREMENTS IN DOGFISH, SCYLIORHINUSCANICULA (L.) USING X-RADIOGRAPHY 

The rate of gastric evacuation in adult dogfish at 15°C was quantitatively assessed by serial X-radiographs of fish fed a diet containing radiopaque glass microspheres. The dogfish voluntarily consumed one of two ration levels, 7% and 3.5% wet body weight (wbw) and rate of disappearance of beads from the cardiac stomach was monitored at 24 h intervals. At each ration level the evacuation of food from the stomach was best represented by exponential models. Evacuation rate coefficients of -0.010 and -0.024 for 7 and 3.5% wbw meals respectively, indicated small meals were evacuated at over twice the rate of larger meals. The time taken for 99% stomach evacuation of the 3.5% wbw ration level was 83 h and at the higher level, 201 h. Predicted gastric emptying rates obtained by microsphere disappearance from the stomach were not different (P>0.25) compared to observed rates measured from dry weight stomach contents of serially slaughtered fish. Uniform microsphere passage through the pyloric sphincter was not observed and so the method cannot be reliably applied to precisely determine rates of gastrointestinal evacuation. Accurate estimates of food intake and gastric digestion rate can be made using this method and may therefore be useful for future studies on the feeding strategies operating in sharks. ; Keywords: gastric evacuation, X-radiography, Scyliorhinus canicula, exponential models, meal sizes

MOLECULAR PHYLOGENY OF GNATHOSTOME FISHES 

Many aspects of the interrelationships of gnathostome fishes are considered to be well established although a few remain controversial. In an effort to resolve these controversies, as well as to compare the results of molecular analyses with morphologically-based phylogenies, 18S ribosomal RNA (rRNA) sequences were determined from 27 species of gnathostome fishes. These species include representatives of the Elasmobranchii, Holocephali, Actinistia, Dipnoi, Cladistia, Chondrostei, Ginglymodi, Halecomorphi, and Teleostei. Phylogenetic comparisons included a lamprey sequence as an outgroup and tetrapod sequences from the literature. Maximum parsimony analyses supported the monophyly of the fish groups listed above (where multiple sequences allowed such a test), as well as the generally accepted monophyly of the Actinopterygii, Chondrichthyes and Neopterygii. The Osteichthyes, Sarcopterygii, and Tetrapoda were not monophyletic in the most parsimonious trees, but the alternative groupings were not strongly supported. The analyses provided some support for a grouping of the Cladistia with the Chondrostei (contradicting the monophyly of the Actinopteri), but could not resolve relationships within the Neopterygii. In general, 18S rRNA analyses agreed with morphological analyses where lineages are likely to have been separated from all others by long periods of time, but were unable to resolve relatively rapid radiations. ; Keywords: 18S rRNA, molecular phylogeny, Actinistia, Dipnoi, Chondrichthyes, Cladistia, Chondrostei, Ginglymodi, Halecomorphi, Teleostei

HOMEWARD ORIENTATION IN DISPLACED JUVENILE LEMON SHARKS,NEGAPRION BREVIROSTRIS 

As part of a larger homing study, young-of-year lemon sharks Negaprion brevirostriswere captured in their natal home ranges within the central lagoon at Bimini Island, Bahamas. Individuals were then transported via indirect routes to test sites located 3 km away from the island where they were placed inside an octagonal plastic cage (3 m dia x 1 m high) fixed to the seafloor. Testing consisted of recording the time spent in each of four quadrants (N, S, E, and W) of the cage following a 15-30 min acclimation period. Data were recorded manually or remotely by video. Overall, the sharks spent more time in (and entered more frequently) homeward-facing quadrants than in the ones opposite home. Interpretation of the results is confounded, however, by effects of current velocity and, in a few cases, the individual’s physical condition. By subjectively disqualifying trials that appear affected by these factors, directional distributions become increasingly non-random with respect to home. In light currents with healthy subjects, orientation appears homeward and is independent of current direction. AES Samuel Gruber Award Competitor ; Keywords: Negaprion brevirostris, shark, orientation, navigation, homing, orientation cage

ELECTRICALLY-MEDIATED ELASMOBRANCH SOCIAL BEHAVIOR: SIREN SONG OF THE FEMALE STINGRAY 

Male round stingrays, Urolophus halleri, successfully locate, court, and mate with individual females buried in visually cryptic aggregations under the sand. Field experiments were performed to determine the importance of chemoreception and electroreception in mate localization. Reproductively active females were enclosed in two identical electrically transparent agar chambers and one associated with an additional chemical stimulus of female seawater perfusate. These two presentation chambers (bioelectric and bioelectric + chemical) were then buried under the sand in the stingray mating area. Both male and female rays readily oriented to the chambered females but showed no preference for the bioelectric stimulus associated with the female perfusate. Furthermore, female rays often buried near their chambered consexuals. Playback experiments of electric potentials recorded from female rays confirm that electroreception is used by rays to locate buried conspecifics, and extends the function of the elasmobranch electrosensory system to include intraspecific social behavior. Neurophysiological experiments show that the frequency response of the stingray electrosensory system matches that of the frequency spectra of the stingray electric field. It is proposed that electroreception mediates for male stingrays the localization of potential mates, and for mated unreceptive females the formation of unisexual aggregations that may decrease the probability of harassment by persistent males. ; Keywords: chemoreception, elasmobranch, electroreception, mating, neurophysiology, reproductive strategies, stingray, Urolophus halleri

SATELLITE SPAWNING BEHAVIOR IN AMERICAN BROOK LAMPREYS (LAMPETRA APPENDIX)

American brook lampreys, Lampetra appendix, were videotaped during spawning at Jambo Creek, Wisconsin, in May, 1993. Analysis of the videotape revealed several cases in which a mating pair was briefly encircled by a third lamprey during the spawning act. Similar behavior by the European brook lamprey, L. planeri, has been previously interpreted as the attempt by satellite males to “sneak” fertilizations of eggs, much as has been reported for several teleost fishes. Whether or not satellite behavior arose independently in the two nonparasitic Lampetra species may be revealed by analysis of spawning by their presumably more primitive parasitic counterparts. The occurrence of satellite spawning behavior in lampreys has implications for the study of speciation in this group and for the control of the sea lamprey (Petromyzon marinus) through application of the sterile male technique in Great Lakes tributaries. ; Keywords: Lampetra, Petromyzontidae, reproduction, spawning, behavior, alternative reproductive strategies, lampreys, satellite males

BIOLOGY OF DEEP-SEA SHARKS FROM THE CHATHAM RISE, NEW ZEALAND

Sharks make up a substantial portion of the by-catch in deep-sea trawl fisheries of New Zealand, but the biology of these sharks is poorly known. To increase understanding of the impacts of exploitation on these populations of deep-sea sharks, species captured from the Chatham Rise, New Zealand were examined, and information on their biology and distribution was recorded. The most abundant species by biomass was Deania calcea, followed by Centroscymnus crepidater, Etmopterus baxteri, and Centroscymnus owstoni. Highest catch rates for the most prevalent species were at depths between 800 and 1000 m, but fishing depths appeared to be near the deeper limits for several species. There was no strong evidence of segregation according to size or sex. Size at maturity for Deania calcea was approximately 75 cm total length for males and 100 cm for females.Centroscymnus crepidater males were mature at 65 cm and females at 85 cm.Etmopterus baxteri reached maturity at 55 cm for males and 63 cm for females. This information may be used in models aimed at assessing the susceptibility of these populations to overfishing. AES Samuel Gruber Award Competitor ; Keywords: deep-sea sharks, reproduction, distribution, Deania calcea, Etmopterus baxteri, Centroscymnus crepidater

REVIEW OF SHARK CONTROL IN HAWAII WITH RECOMMENDATIONS FOR FUTURE RESEARCH

In response to public fears, the state of Hawaii spent over $300,000 on shark control programs between 1959-1976. Six control programs resulted in the killing of 4,668 sharks ($182 per shark). The programs furnished information on diet, reproduction, and distribution of sharks, but research efforts of the programs had shortcomings. Estimates of shark populations based on catch data from the programs are unreliable because of sampling biases, and results of the programs are not readily available to the scientific community. Research was centered on sharks other than the tiger shark, Galeocerdocuvier, which is responsible for most attacks on humans in Hawaii. Success in reducing shark populations and removing large sharks from Hawaiian waters may have been overestimated, considering seasonal changes observed in shark abundance and the variable fishing effort. Shark control programs do not appear to have had measurable effects on the rate of shark attack in Hawaii. Implementation of large-scale control programs in Hawaii the future may not be appropriate. Acoustic telemetry, conventional tagging, and studies on population dynamics concentrating primarily on the tiger shark would provide information on activity patterns, distribution, and population parameters, that may prove useful for reducing the risk of shark attack in Hawaii and elsewhere. AES Samuel Gruber Award Competitor ; Keywords: Shark attack, shark control, Galeocerdo cuvier

RAM FEEDING IN THE BONNETHEAD SHARK SPHYRNA TIBURO

The kinematics of feeding in the bonnethead shark Sphyrna tiburo are analyzed using high speed video. Ram-Suction Indices (RSI) calculated for capture and transport events clearly segregate the captures to the ram end and the transports to the suction end of the continuum. The basic feeding sequence in S. tiburo is lower jaw depression, snout lift, lower jaw elevation and snout drop, and upper jaw protrusion. This differs from other studies on shark feeding in that snout lift usually occurs first and upper jaw protrusion may occur before or after lower jaw elevation. Compared to sharks of similar length the duration of lower jaw depression and lower jaw elevation in S. tiburo is three and two times longer respectively. This is probably attributable to the benthic ram-feeding mechanism. During prey capture the branchial region first adducts, gill slits close, and then branchial expansion begins before maximum gape, indicating that suction inflow occurs. After prey capture, lower jaw elevation begins, gill slits open and the branchial region contracts. Upper jaw protrusion does not begin until the gill slits open and is not instrumental in prey capture but in confining the prey to the buccal cavity.&bbsp;AES Samuel Gruber Award Competitor ; Keywords: sharks, bonnethead, Sphyrna tiburo, kinematics, feeding, ram-suction index, high speed video, morphology

COMPARATIVE HISTOLOGY AND CYTOCHEMISTRY OF THE SPLEEN AND THYMUS OF AVES, MAMMALS, AND ELASMOBRANCHS 

Histology of the spleen and thymus was compared among a mouse (Mus musculus), chicken (Gallus domesticus), and clearnose skate (Raja eglanteria). Seven micron paraffin, and one micron plastic sections were stained with hematoxylin and eosin and examined. Obvious cortical and medullary boundaries were observed in the thymus of all specimens. Murine, avian, and elasmobranch spleens had regions of red and white pulp, however, germinal centers were obvious only in the mouse. Cytochemical analysis for enzyme markers indicative of cell function and maturation, vis., alpha-napthyl butyrate esterase, acid phosphatase, and beta-glucuronidase, was conducted on tissue imprints and frozen sections of both tissues. Murine medullary thymocytes exhibited alpha-napthyl butyrate esterase, acid phosphatase, and beta-glucuronidase activity. Cortical thymocytes demonstrated the presence of acid phosphatase only. All three enzymes were found associated with murine splenic germinal centers. Enzyme activity of chicken thymus tissue imprints followed the distribution patterns of the mouse. Activity of all three enzymes was found in elasmobranch thymocytes, but the distribution of each differed. As a consequence of poorly defined splenic germinal centers in skates and chickens, enzyme activities were not readily observed. Binding profiles from a panel of 20 lectins revealed differences in cell marker distributions among the three species. AES Samuel Gruber Award Competitor ; Keywords: spleen, thymus, cytochemistry, histology, lectins

SYSTEMATICS AND ASPECTS OF BIOLOGY OF SOMNIOSUS(ELASMOBRANCHII: SQUALIDAE) 

Recent treatment of the genus Somniosus contains three recognized species: S. microcephalus, S. pacificus, and S. rostratus. In a systematic study based on morphometrics and meristics, I concluded that this genus is represented by four species, namely the three recognized species and S. longus occur from Japan. Reproductive organs and stomach contents of two species, S. microcephalus and S. pacificus, were examined. Thirty-six specimens (648-4800 mm TL) of S. microcephalus were collected from Greenland, and 22 specimens (1050-2680 mm TL) of S. pacificus were collected from eastern Aleutian Islands, Bering Sea, Gulf of Alaska, and Japan. All the specimens were immature. The ovaries of several large-sized females contained numerous small ova. Stomachs of both species contained such varied items as seals, skates and their egg cases, teleost fishes, gastropods, squids, octopi, decapods, jellyfish, brittle stars, and human garbage. ; Keywords: systematics, reproduction, stomach contents, Somniosus microcephalus, S. pacificus, S. rostratus, S. longus