1995 AES Annual Meeting Abstracts

Structure and histology of uterine trophonemata in the Atlantic stingray, Dasyatis sabina. 

The mode of reproduction in all rays is aplacental viviparity, also termed ovoviviparity. Embryos are nourished by egg yolk during the early phases of development, but during later phases the source of nutrition is shifted to a secretion produced by the maternal uterus. We analyzed aspects of embryonic nutrition in Dasyatis sabina throughout gestation. Early gestation through mid-gestation embryos had an external yolk sac that ranged in weight from 66 mg to 2 mg, respectively. By late July the external yolk was absorbed, no internal yolk sac was present, and the embryos were entirely dependent upon histotroph nutrition. The inner wall of the maternal uterus was lined with vascularized evaginations called trophonemata. In the non-gravid uterus, trophonemata averaged 2.6 mm long, maximum 3.2 mm, and uniformly 0.4 mm wide. By early gestation trophonemata maximum length reached 15.9 mm. After this rapid increase, average trophonemata length stayed relatively constant through mid- and late-gestation, although a few hypertrophied strands attained maximum length of 31.7 mm. Width continued to vary throughout gestation. After parturition the strands began to shrink and resembled pre-gestation trophonemata. The histological structure of trophonemata will be described. ; Keywords: Dasyatis, uterus, stingray, elasmobranch, embryo, nutrition

The kallikrein-kinin system in the Atlantic Stingray 

The renal kallikrein-kinin system in mammals participates in the regulation of urine volume. We have begun to characterize the components of this system in the stingray in order to investigate its possible role in the regulation of renal function in elasmobranch fish. When the euryhaline Atlantic Stingray Dasyatis sabina travels from seawater into estuarine waters, a compensatory increase in urine volume occurs, but the regulation of this process is not understood. We have identified a kallikrein-like activity (KLA) in various tissues of the stingray, and renal activity is increased 24 hrs after the animals are moved from seawater (910 mOsm/l) to dilute seawater (459 mOsm/l). Immunohistochemical studies show localization in extraglomerular cells of the mesangium. The kidney also contains a kinin-like substance detected by bradykinin (BK) RIA. When the mammalian peptide lysyl-BK is administered to the stingray, a 25% change in renal blood flow could be demonstrated with laser-doppler flowmetry. KLA in other osmoregulatory tissues also increased after dilution. The evidence suggests that a kallikrein-kinin system exists in the Atlantic Stingray, and that the system may be involved in osmoregulation. Supported by NIH HL44671. ; Keywords: stingray, kidney, osmoregulation, kinin, kallikrein

The effects of urea and trimethylamine oxide (TMAO) on membrane properties: The elasmobranch connection. 

The effects of the major organic solutes of marine elasmobranchs (urea and trimethylamine oxide (TMAO)) on membrane fluidity were determined in a model membrane system. Fluorescence polarizations of 1,6-diphenyl-1,3,5-hexatriene (DPH), trans-parinaric acid (tPNA) and cis-parinaric acid (cPNA) were used to study the effects of urea and TMAO on the fluidity of dipalmitoyl phosphatidylcholine (DPPC) liposomes. A further study was conducted to relate elasmobranch membrane composition to the effects of these organic solutes. A preliminary study (Glemet and Ballantyne, unpublished observations) found that although there were no differences in the phospholipid headgroups, liver mitochondrial membranes of an elasmobranch had phospholipids that were substantially more saturated than membranes of non-elasmobranch fish. Since the mitochondrial membrane does not contain cholesterol, adaptation of cholesterol-containing membranes to the presence of urea may employ other strategies. We have therefore, examined a cholesterol containing membrane (the plasma membrane of the red blood cell) from a urea-retaining elasmobranchRaja erinacea and an osmoregulating teleost Pleuronectes americanus.; Keywords: urea, TMAO, membrane properties, Raja erinacea, Pleuronectes americanus

Effect of a T-cell inhibitor on differential counts and immune organ histology in nurse sharks,Ginglymostoma cirratum.

Preliminary experiments have been conducted with the potent helper T-cell inhibitor cyclosporin A (Cyc A) (Sandoz) to determine if it would adversely affect the white cell population or the cellular structure/distribution in immune organs of the nurse shark. Nurse sharks were injected (IM) a total of three times at 48 hour intervals with either olive oil vehicle (control, N=2), 25 mg cyclosporin/kg body weight (N=4), or 50 mg cyclosporin/kg body weight (N=4). Prior to injections, and at frequent intervals thereafter, blood samples were withdrawn for differential counts and hematocrits. All animals at the high dose level became moribund and expired within 4 days after the final injection. Within two days following the 1st injection, animals at both dose levels demonstrated an inversion of the lymphocyte: granulocyte ratio which persisted for 72-96 hrs after final injection or until death in the high dose animals. Hematocrits were significantly lowered in either treatment group compared to control (P<.05), but in surviving animals, hematocrits returned to normal 3-5 days following the last injection of Cyc A. Histologically, there appeared to be a dose-dependent degeneration of tissue and cell integrity in the thymus, epigonal, and spleen of treatment animals with greater amounts of mitotic activity, cellular debris, and epithelial infiltration than in control animals. Keywords: Nurse shark, Cyclosporin A, T-cell inhibitor, Histology, Differential counts

Global trends and status of elasmobranch fisheries.

A brief synopsis of recent trends in elasmobranch exploitation and management on a worldwide basis is presented. The world elasmobranch catch reported in 1991 is 704,000 t and present trends indicate forecasts of 755,000-827,000 t by the year 2000. However, the present total annual catch inclusive of discarded and unreported catches is estimated at around 1.35 million tonnes. An index of relative production is developed and used to diagnose elasmobranch exploitation in each of 15 FAO’s Major Statistical Areas. Three of these Areas could probably support significant increases in elasmobranch exploitation while another five Areas are not likely to sustain further expansion in yields. The bulk of the world’s elasmobranch catch is taken by 26 countries: Japan, Indonesia, India, Taiwan and Pakistan have the highest average yields of elasmobranchs in the world. The estimated by-catches of elasmobranchs (mainly sharks) in high-seas fisheries of the world are 20,000-38,000 t/y in the recently banned driftnet fisheries, 232,425 t/y in the various longline fisheries for tunas and billfishes and 6,345 t/y in purse seine tuna fisheries. This is equivalent to an estimated total by-catch of 11.6-12.7 million sharks per annum. The discard of sharks in these fisheries is also very high, probably in the order of 230,000-240,000 t/y. Elasmobranch fisheries are poorly researched and managed worldwide: only Australia, New Zealand and USA are known to have specific management and research programmes for elasmobranch fisheries. The general problems found for appraising elasmobranch fisheries and the need for management are discussed.; Keywords: elasmobranch fisheries, catch trends, bycatches, worldwide.

Multiple foraging strategies to maximize energy return in the Atlantic stingray, Dasyatis sabina.

The diet of the Atlantic stingray, Dasyatis sabina, is temporally variable but it is unknown whether this feeding pattern reflects seasonal prey abundance or active preferences for prey with high energy return. Caloric content was determined for the six major prey types: in rank order amphipods, isopods, ophiuroids, mysids, polychaetes, and bivalves. Maximum caloric density occurs in the mysids Bowmaniella spp. (5.98 mg/AFDW) and the minimum in the isopod Cymadusa faxoni (4.73 mg/AFDW). Caloric density among species varies within these taxonomic orders from 2.1% in isopods to 14.9 % in amphipods. Despite the perennial occurrence of ophiuroids at the study site, they are taken only in the summer when caloric content is 16.5% higher than in winter. The prey of D. sabina are divided into two functional groups: 1) small prey that require negligible handling time, and 2) large prey that require post-capture processing. It is proposed that energetic returns from small crustaceans are maximized by selection of dense patches whereas returns from large prey are constrained by post-capture processing.; Keywords: bivalves, caloric content, crustaceans, Dasyatis sabina, energetics, foraging, handling time, ophiuroids, predation, stingray

Gastric evacuation in juvenile scalloped hammerhead sharks, Sphyrna lewini

Gastric evacuation was studied in juvenile scalloped hammerhead sharks (Sphyrna lewini) in Kaneohe bay, Oahu, Hawaii. Sharks were caught using handlines and kept in individual enclosures. Experimental meals consist of goldspot herring (Herklotsichthys qaudrimaculatus) equal to 1.2% of the sharks weight. Stomach contents were recovered by gastric eversion, and dried to constant weight. Fifty-six percent of the meal was digested in ten hours, and 73% in twenty hours. Water temperatures during the experiment ranged from 22.0 to 24.5 C.; Keywords: gastric evacuation, Sphyrna lewini

Phylogenetic relationships of the Upper Jurassic shark Protospinax Woodward, 1919 (Chondrichthyes, Elasmobranchii). 

The phylogenetic relationships of Protospinax annectans, an Upper Jurassic shark from Solnhofen (Germany), has been subjected to much debate by numerous previous authors, with varying conclusions. Based on two additional specimens, the anatomy of this enigmatic fossil was further studied. Using recent cladistic analyses, the phylogenetic position of Protospinax is now corroborated to a greater extent. Protospinax is resolved as a very derived member of the Squalea, and is the sister-group to the Hypnosqualea (a group comprising squatinoids, pristiophoroids and batoids). 10 characters support this contention. Although our analyses varied with respect to included/excluded characters and weighting, Protospinax still remained the most basal hypnosqualean.; Key words: Protospinax, Squalea, Hypnosqualea, systematics.

The biology of the blacktip shark, Carcharhinus limbatus, off the southeastern United States.

The blacktip shark is a cosmopolitan species found throughout tropical and subtropical waters. It is common along the southeast coast of the United States, where it migrates northward to Georgia and the Carolinas in summer and southward to Florida in winter. The blacktip shark feeds on small bony fishes, primarily menhaden, and small elasmobranchs. Males mature between 1425 and 1450 mm TL, and all males over 1450 mm TL are mature. Females mature at about 1560 mm TL. The reproductive cycle lasts two years and includes biennial ovulation with a one year gestation period. Mating and ovulation occur in Bulls Bay, South Carolina, from mid-May to early June. Parturition occurs the following year from early May to early June in the shallow coastal waters of the Carolinas. The blacktip shark is a viviparous, placental species. Implantation usually occurs during the 10th and 11th weeks of gestation when the embryos measure 178-194 mm TL. The young are born at about 550-600 mm TL during May and early June in the shallow water, coastal nurseries of Georgia and the Carolinas. The neonate stage lasts about a month. The young remain in the shallow water nurseries until fall.; Keywords: sharks, life history, reproduction, migrations, Carcharhinus limbatus.

Age and growth of the blue stingray Dasyatis chrysonota chrysonota from the southeastern Cape coast of South Africa

The age and growth of Dasyatis chrysonota chrysonota from the southeast coast of South Africa was investigated by examination of bands on the vertebral centra. The annual nature of band deposition was verified by centrum edge characteristics and supported by gowth of known-age individuals kept in captivity. The derived von Bertalanffy parameters from age and length data were La= 532 mm DW, K = 0.175 and to = -3.65 for males and La= 913 mm DW, K = 0.070 and to = -4.48 for females. Growth of captive specimens showed distinct seasonal differences, with a mean monthly growth rate of 7.3 mm/month during the summer and 3.8 mm/month during the winter. The mean rate of growth in captivity for the first year after birth, calculated at 66.7 mm/year, is similar to the value obtained from back calculations (64.6 mm/year) but lower than the calculated value of 45.1 mm/year. The estimated age at first maturity is five years for males and seven years for females.; Keywords: Elasmobranch age and growth, growth in captivity validation, Dasyatis sp.

The reproductive biology of the tiger shark Galeocerdo cuvier in Hawaii: A compilation of historical and contemporary data 

The reproductive biology of the tiger shark Galeocerdo cuvier has never been fully documented. Reproductive data were gathered from 111 females and 106 males from the 1959-1960 and 1967-1969 shark control programs in Hawaii. Additional data from 11 females and 4 males were obtained from 1993-1994. Based on oviducal width, the smallest mature female was 282 cm TL and the largest immature was 303 cm TL. The smallest mature male was 292 cm TL and the largest immature was 323 cm TL, based on calcification of the claspers. Tiger sharks are aplacental and have a compartmentalized uterus with presumed matrotrophy. Based on mating scars, free flowing male “sperm”, and a copulatory plug, copulation occurs primarily in January and February. Oviducal “sperm” storage occurs until ovulation in May-July. Embryonic uterine development starts almost immediately and gestation lasts 15-16 months. Pups are typically born at 80-90 cm TL in September and October. Excluding very near term females, tiger sharks in Hawaii average 41 pups (n=13). Based on “sperm” storage and the long gestation period, the females are thought to have a triennial reproductive cycle. The male reproductive cycle is unknown but may be annual. Keywords: Tiger shark, Galeocerdo cuvier, Reproductive cycle, Maturity

Development of gonadotropin hormone releasing (GnRH)- immunoreactive systems in the terminal nerve and brain of the clearnosed skate, Raja eglanteria, with preliminary observations on terminal nerve regeneration. 

Skates (7-32 weeks & adult) were obtained from Mote Marine Laboratory. The terminal nerve (TN) has bundles of GnRH- immunoreactive (ir) fibers that arise from ir-ganglia located on the olfactory bulb (OB) and distribute peripherally to the olfactory epithelium and OB and centrally into the ventral medial telencephalon. TN GnRH-ir was similar in all stages with the exception that diffuse fibers in the telencephalon, thought to be of TN origin, were scarce in younger stages. Numerous scattered GnRH-ir cells are located in the basal forebrain. In all stages, the largest group of GnRH-ir cells is in the midbrain near the midline below the ventricle. From 10 weeks, ir-fibers, most likely from TN and basal forebrain cells, extend throughout the forebrain with heavy projections into the septopreoptic area, basal hypothalamus and pituitary and ir-fibers, most likely from midbrain cells, project to most areas of the brainstem and spinal cord. Thus, while GnRH-ir cell groups are present at 7 & 8 weeks, it appears that fiber growth does not approach the adult condition until 10 to 16 weeks. In the younger stages, cutting the TN just proximal to its ganglia can result in axonal sprouting and reinnervation of the OB.; Keywords: reproduction, elasmobranch, batoid, nervous system

Feeding ecology of Scyliorhinus canicula in the Bristol Channel

The stomach contents of 731 specimens of Scyliorhinus canicula were examined and the diet assessed by the frequency of occurrence, by numbers and by the points method. Seasonal, geographical, sexual and sized -based differences in the diet were determined. The most common prey species were Pagurus bernhardus, Cancer pagurus, Carcinus maenas, Buccinum undatum, Ensis spp. and Ascidiella sp.. The most important factors in determining the diet appeared to be the geographical location, season and size. ; Keywords: Scyliorhinus canicula, Scyliorhinidae, diet, Bristol Channel

Diversity of Elasmobranchs in Mexico

There are over 150 species of sharks and rays in Mexico, this is more than 18% of the world’s elasmobranchs, of which only less than 2% are endemic to Mexican waters. This fauna is an important resource in the country, as over 20 species are economically useful. Patterns of distribution, diversity and efforts for conservation are summarized hereine. ; Key words: Elasmobranchs, Mexico, Diversity.

Review of senescence in fishes with application to elasmobranch demography 

A comprehensive literature review on senescence in fishes reveals it may be an important life history feature in many species. Many fishes are valuable for senescence research because they can be easily manipulated in captivity, are generally short lived, and produce many young per litter. Evidence of senescence has been found mainly in these short-lived fishes, including changes in immune and endocrine systems, intracellular composition and decay rates, reproductive rate and output, and genetic predisposition. Major regulating factors of growth and longevity are temperature and food availability. Two main theories attempt to explain the occurrence of senescence: 1) the disposable soma theory (combining theories of mutation accumulation, cellular damage, and decay); and 2) the anatagonistic pleiotopy theory. Although many mechanisms have been suggested, few have included such factors in modeling life histories of populations. Senescence may play a role in the life histories of many elasmobranch species, and its impact must be considered. We have used the latest life history information for the North Pacific population of spiny dogfish, Squalus acanthias, and refined its demography to evaluate the effect of senescence (i.e. changes in age-specific natality) on its predicted population dynamics. ; Keywords: demography, elasmobranchs, life history, longevity, reproduction, senescence

How does the heterocercal tail function in leopard shark locomotion? 

Two different hypotheses exist to explain the function of the heterocercal tail in shark locomotion. The classic model proposes that the tail creates a dorsally directed thrust that is countered by the shark’s pectoral fins, while Thomson’s (1976) model suggests that the tail generates thrust directed ventrally through the shark’s center of gravity. In this study, we test these hypotheses by examining the kinematics of the heterocercal tail in the leopard shark,Triakis semifasciata. Using two high speed video cameras filming simultaneously at 250 fps, lateral and posterior views of the tail were examined from four individuals swimming in a flow tank at 1.2 BL/s. Eight marked points on the tail were followed in three dimensions and used to divide the tail into six triangular elements. Three-dimensional coordinate data were used to calculate planar angles of intersection with three reference planes (frontal, sagittal, and transverse), and to estimate thrust production by each of the elements. Results indicate that different portions of the tail travel through substantially different excursions in the transverse plane, and that the triangular segments of the tail vary in both magnitude of force and direction of thrust throughout the tail beat cycle.; keywords: Leopard sharks, Triakis semifasciata, locomotion, heterocercal tail

Cartilage canals and chondrocyte nutrition in the vertebral cartilage of the sandbar shark,Carcharhinus plumbeus

Vascular furrows, known as cartilage canals, have been described from the cartilage of mammals, birds, amphibians, reptiles, and recently, elasmobranchs. Despite their widespread occurrence, however, little is known about the function of these canals. In this study, the potential role of cartilage canals in chondrocyte nutrition was studied in the sandbar shark, Carcharhinus plumbeus. The objective of this study was to determine if the nutritional requirements of vertebral cartilage, as measured by chondrocyte density, is related to the density and surface area of cartilage canals. Chondrocyte density was determined from histological vertebral sections. The density and surface area of cartilage canals was determined through morphological examination of whole vertebral centra. The relationship between canal surface area and chondrocyte density was examined for significance using ANOVA. The role of cartilage canals in elasmobranch cartilage is discussed in relation to nutrition and calcium metabolism. ; Keywords: Carcharhinus plumbeus, cartilage, cartilage canals, vertebrae.

Maintenance of nurse shark in captivity

In Brazil there is not a study of sharks kept in captivity. In reason to this a job about G. cirratum was developed during four years. The fish (two males and two females) were captured in Cananeia Sea, Sao Paulo South Coastal. During the acclimatization period, three specimens showed bacterial infection on their fins, which was quickly controlled adding antibiotic to the water. During the first year, one of the females died due to cestode infection. Along the second year, another death. This time one of the males. Its death was probably due to lack of folic acid. The growth was followed monthly through measuring and weighing. The sharks obtained a growth of 13,3 cm and a gain of 2100 g weight/year. Several behaviors were carefully watched in captivity, and one of the most important is related to temperature. If it is below 20oC, the sharks did not feed themselves and kept motionless. If the temperature is above 30C, they also did not feed themselves, but showed an aggressive behavior, comprising biting each other.; Keywords: Brazil, maintenance, captivity, nurse shark, behavior

Intraspecific mtDNA variation in three sharks with different species distributions.

Restriction fragment length polymorphism analysis of mitochondrial DNA (mtDNA) was used to investigate the distribution of mtDNA haplotypes and sequence diversity across the ranges of three sharks with different species distributions. The Atlantic sharpnose shark (Rhizoprionodon terraenovae) has a continuous distribution along the Atlantic coast of North America, the sandbar shark (Carcharhinus plumbeus) has numerous allopatric populations along temperate and subtropical coastlines, and the shortfin mako (Isurus oxyrinchus) is a pelagic species with a cosmopolitan distribution. Intrapopulation variation in mtDNA was lowest in the sandbar shark (mean percent nucleotide sequence diversity (NSD) = 0.04), however there were fixed genetic differences between isolated populations. The Atlantic sharpnose shark exhibited a slightly higher degree of intrapopulation mtDNA diversity (NSD = 0.12), with an apparently homogeneous distribution of mtDNA haplotypes throughout the range of the species. Of the three species in this study, the shortfin mako had the highest degree of sequence diversity (NSD = 0.76). However samples from distant locations differed only in the frequencies of haplotypes, there were no fixed genetic differences between regions.; Keywords: Carcharhinus, Isurus, Rhizoprionodon, mitochondrial DNA, population genetics.

Biology of the spiny butterfly ray, Gymnura altavela, in a captive environment

Gymnurid rays have not been previoulsy survived long-term (> one year) in captivity. Two specimens of the spiny butterfly ray, Gymnura altavela, have been maintained in captivity for 19 months at the National Aquarium in Baltimore. An aggressive husbandry protocol of force feeding maintained energy levels until the rays began to eat on their own. The rays used their pectoral fins to strike at food items, a behavior which they may use in the wild to stun and capture prey. The first estimates of growth in captivity for any species of gymnurid ray were determined. In addition, the first estimates of conversion efficiency (K1) for any species of batoid using direct methods were determined. These results suggest that growth and conversion efficiency in the spiny butterfly ray is on par with other active elasmobranchs.; Keywords: batoid, growth, efficiency, Gymnura altavela

Inferred mating activity from the temporal distribution and abundance of mating scars in the Atlantic stingray, Dasyatis sabina.

This study demonstrates that dermal scars on elasmobranch fishes may be used to deduce their mating period and quantify reproductive activity. The morphology, distribution and abundance of fresh body scars inflicted by male dentition was determined for male and female Atlantic stingrays, Dasyatis sabina, sampled over a consecutive one year period. Scars were categorized into five distinct classes: single scrape from lower jaw, parallel scrape from upper jaw, bite, margin abrasion and fin excision. The frequency of total scars on females ranged from near null in August to a maximum mean of >20 scars/female in April. Scar counts on males covaried with those of females but were less abundant. Scar categories occurred in equal abundance among sexes except for pectoral margin abrasions which were more prevalent on females and reflect male grasping of the pectoral fin during copulation. From these data we conclude that mating activity occurs in this population from October through June with a peak in April. This is in distinct contrast to gonadal index data that show maximum testes size occurs in November and places in question the value of the GSI as an indicator of elasmobranch reproductive activity.; Keywords: bite, dentition, elasmobranch, mating scars, reproduction, stingray

Reproduction of captive rays from temperate waters

Dolfinarium Harderwijk is an attraction park specializing in marine animals. In the “Rayreef” East Atlantic elasmobranchs are kept in captivity. Reproduction of three species of rays (Raja clavata, R. montagui and R. microocellata), collected in the English Channel, was investigated over a period of two years (`93/’94). Data on numbers of eggs laid and hatched, periods of spawning and hatching, incubation time and mortality of young rays are presented.; Keywords: Raja sp., reproduction, East Atlantic, captive fish

The taxonomy of Indo-Pacific stingrays (F. Dasyatididae) – Did Bleeker get it wrong?

Despite their imposing size, high human interest value and commercial importance in some regions, stingrays remain amongst the most poorly researched groups of inshore fishes in the Indo-Pacific. Most of the plethora of names contributed by early ichthyologists are now regarded as junior synonyms. Of the 19th century ichthyologists, Pieter Bleeker’s activities in the Indonesian Archipelago are perhaps the most dynamic and are arguably the most noteworthy. The value of his research on dasyatidid fishes is assessed in the light of new information. Features of the Indo-Pacific stingray fauna are discussed and future research directions proposed.; Keywords: Indo-Pacific fishes, Bleeker, Dasyatididae, stingrays.

They can tan their own hides!!!: evidence for suntanning in juvenile hammerhead sharks

Skin color in juvenile scalloped hammerhead sharks, Sphyrna lewini, darkened when placed in a shallow tidal pond and exposed to ultraviolet (UV) and visible light (PAR) levels higher than those in their natural habitat. Melanin was extracted from small patches of skin (6 mm diameter) using standard techniques and analyzed spectrophotometerically. Spectral characteristics indicated a two-fold increase in melanin between tanned and untanned sharks. In addition, the difference in melanin concentration between tanned and untanned sharks was greatest in the UV-A (320-400 nm) region. Reflectance measurements of tanned and untanned shark skins revealed similar spectral absorbance characteristics, however, tanned shark skins absorbed twice as much light. This color change does not appear to be a cryptic response, but may instead serve as a protective mechanism against damaging increases in solar radiation. This inducible color change phenomenon in these sharks appears to resemble suntanning, which has only been previously described in humans. ; Keywords: Sphyrna lewini, suntanning, solar radiation, melanin

In vitro reactivity of sperm from the clearnose skate, Raja eglanteria, in response to autologous alkaline gland fluid and clasper gland secretion, natural seawater, and elasmobranch-modified semen extender.

In efforts to improve artificial insemination techniques initiated previously in our laboratory using the clearnose skate, Raja eglanteria, functional roles of several fluids potentially involved in the natural fertilization process were investigated. Natural seawater and autologous alkaline gland fluid and clasper gland secretion were evaluated for their relative effects on skate sperm motility and viability. These reactivities were compared to responses achieved by exposure to elasmobranch- modified semen extender, a synthetic medium which, when combined with skate seminal fluid has resulted in successful insemination. Skate fluids and secretions were obtained from an anesthetized mature male by direct aspiration from seminal vesicles, alkaline glands, and clasper glands. Wet mount preparations of semen mixed with equal volumes of the various fluids, added separately or in combination, were observed with light microscopy. Maximum motility, assessed by relative movement of sperm tails, was observed whenever alkaline gland fluid was included in the mixture. Sperm viability, determined using a fluorescent assay which identified viable sperm with carboxyfluorescein diacetate and non-viable sperm with ethidium bromide, was high in all preparations. Preliminary biochemical analyses of seminal plasma, alkaline gland fluid, and clasper gland secretion included steroid hormone profiles and protein, fatty acid, and carbohydrate composition. ; Keywords: Raja eglanteria, seminal fluid, alkaline gland, clasper gland, sperm motility, sperm viability

Rod-cone ratios and cone characteristics of various chondrichthyan species. 

The retinas of four chondrichthyan species have been examined so far for their rod and cone content. Two of the four species have been found to have cones present. The Black-tip reef shark (Carcharhinus melanopterus) and ratfish (Hydrolagus colliei) have been found to be pure rod. The Sand Tiger Shark (Eugomphodus taurus) is reported at 24:1 and the dogfish (Squalus acanthias) is tentatively reported at 20:1. ; key words; retina, rod, cone

Reproductive Biology of the Diamond Stingray, Dasyatis brevis, in the Western Pacific, Mexico.

The reproductive biology of the diamond stingray, Dasyatis brevis, was studied in the fish camp of Puerto Viejo, Almejas Bay, western coast of the Peninsula of Baja California, from 1990 to 1994. This ray is the most important in the fishery. The disk width (DW) average was 47.26 cm in males and 50.96 in females with a maximum size when 25-30 mm in diameter, suggesting that females mature at 66 cm DW. The sexual activity in males is during spring and summer. On the other hand, the embryos start there development in June and reaching it’s maximum size the last days of August, the neonates are born at 19 cm DW. The fecundity is from two to four embryos per female. The females ovulate after the copulation during the last day of August, from September through June the females have eggs in the oviducts without embryonic development, starting the stage of diapause in June.; Key words: Dasyatis brevis, Diamond stingray, Reproductive biology, Western Pacific, Mexico

Is the Von Bertalanffy growth function adequate to describe the growth of sevengill sharks,Notorynchus cepedianus?

Growth data from 10 captive, juvenile sevengill sharks were collected for 9 years from 1985 to 1994. Three methods used to calculate Von Bertalanffy growth function (VBGF) parameters produced high k and unreasonably low Woo (or TLoo) values. In addition, k was not constant and larger for pups. The VBGF for juvenile sevengill sharks and the interpretation of k in general are reviewed. The VBGF has been successfully used as an empirical equation to describe shark growth. One of the parameters (k) was mistakenly considered to be a growth constant, when in fact the parameter kappa = 3k (with units of time-1) was introduced by Von Bertalanffy to characterize the catabolic (= break-down) term. A large k produces a mature adult shark of low mass which is reached in a short time. This was mistaken as fast or large growth, however the corresponding growth rates (with units of kg/yr or m/yr) are small if k is large.; Keywords: Von Bertalanffy growth function (VBGF), sevengill shark, Notorynchus cepedianus, growth constant, anabolic, catabolic

A summary of ten years of shark taxonomy 

Forty-two species of sharks have been described in the past decade (including 18 scyliorhinids and 15 squalids). Therefore, 390 species of sharks are known (if one includes seven formerly invalid species). The most speciose genera are Apristurus and Carcharhinus. The largest families are Scyliorhinidae and Squalidae. Other important events of the past decade include the publication by the ICZN of a) the third edition of the International Code of Zoological Nomenclature and b) several opinion papers, both of which affect the nomenclature of many common species of sharks. Most noteworthy are a) Opinion 1278 conserving Rhincodon, b) Opinion 1459 conserving Carcharias, and c) Article 31a of the 1985 Code. This article states that a) nouns in the genitive case are to be formed in accordance with the rules of Latin grammar (e.g., perezi rather than perezii) and b) use of nouns in apposition is permitted, although discouraged (e.g., cuvier rather than cuvieri). Last, a great deal of alpha-level taxonomy still needs to be done. At least 45 unidentified species are known (35 of which are scyliorhinids and squalids) and several genera (e.g., Apristurus, Centrophorus, and Squalus) are in need of a global revision.; Keywords: elasmobranch, systematics

Morphometrics and preliminary feeding and growth data for the pelagic stingray, Dasyatis violacea

The NOAA vessel David Starr Jordan 94-08 cruise dates were July 11-24, 1994. Twenty-two (22) longline sets for pelagic sharks were conducted within the southern California bight. 114 pelagic rays, Dasyatis violacea were caught as by-catch and 14 females were transported to the Monterey Bay Aquarium. The rays were maintained in a 3.2 m x 1.5 m tank at 17.7 oC. On March 1, 1995, these rays were injected with PIT tags, weighed, three length measurements were taken ventrally over the curve on live animals, and a five months feeding and growth study was initiated. The weight (W, in kg) – diskwidth (DW, in m) relation was W = 49.5 DW 3.607 (back-transformed, ordinary power regression, n = 15 (14 + 1), s.e.e = 0.144, r2 = 0.927, W-range 2.35 – 14.55 kg). We will present additional morphometrics and preliminary feeding and growth data. ; Keywords: Pelagic stingray, Dasyatis violacea, NOAA vessel David Starr Jordan, incidental-catch, morphometrics, feeding, growth

On the geometry and mechanics of tooth position in the white shark, Carcharodon carcharias

The teeth of captured specimens, prepared museum specimens and high-speed videotape images of the white shark, Carcharodon carcharias, were compared with respect to 1) deviation of each tooth from the animal’s midline and 2) the crown angle of the functional teeth along the jaw margin. Tooth positions were measured either directly using a meter stick apparatus, or derived from tracings of the video footage. Tooth positions were not statistically unique in any region of the upper or lower jaw, but demonstrated less variability in crown angle within 30o of the midline (71.48o±10o). Videotape analysis of feeding sharks indicated an 8.7o increase in crown angle of the center-most teeth during bites where the jaws were closed through an angle of 20o to 35o, and a 15.7o reduction in this same parameter during jaw adduction through 35o or more. Such changes in tooth orientation (relative to the rear of the buccal cavity) are ascribed to flexure of the cartilaginous jaws and cranium by the cranial musculature, and possibly also to sliding of the tooth bed over the jaw. Outward rotation of the teeth describes a ‘plucking’ action during feeding or prey sampling, while larger bites rotate the front-most teeth inward towards the gullet. Functionally, this may make the teeth more effective at grasping small prey items or gouging chunks from larger prey. However, testing of the load required to remove teeth showed no significant increase in tensile resistance with reduced crown angle.; Keywords: Carcharodon, dentition, feeding dynamics, biomechanics

Parkway, Philadelphia, Pennsylvania 19103 USA

A new look at Hydrolagus media (Garman, 1911): Is this species really just anotherHydrolagus colliei (Lay and Bennett, 1839)? There are presently 34 recognized species of living chimaeroid fishes. The genus Hydrolagus is the most speciose group of chimaeroids with 17 described species and as many as 6 undescribed species. In order to discover and define characters that distinguish species of Hydrolagus we examined variation among 12 species (149 specimens). There are only two known specimens of Hydrolagus media and the locality for these is unknown. Hydrolagus media is identical to Hydrolagus colliei in coloration and patterning, body proportions, fin shapes, tooth plate morphology, lateral line canal patterns, head pore numbers, and secondary sexual characteristics. In addition, these forms share a characteristic sexual dimorphism in pelvic fin shape which has not been described for any other chimaeroid. H. media was compared with 52 specimens of H. colliei, represented by a range of ontogenetic stages and near equal number of males and females. Our redescription of H. colliei and H. media is based on comparison of body proportions, coloration, dentition, lateral line canals, secondary sexual characteristics, and fin shapes. Based on these data we suggest H. media is a synonym of H. colliei. ; keywords: Holocephali, Chimaeroidei, Hydrolagus, taxonomy

The southern Western Australian shark fishery – management and stock assessment in a multispecies shark fishery.

The shark fishery off southern Western Australia exploits three main species of sharks (dusky whaler, gummy and whiskery), as well as a variety of minor shark species (eg. sandbar, hammerhead, wobbegong and school) and scalefish. The fishery is managed by input controls on gillnets and longlines. The management of the fishery is described. Problems encountered during the implementation of management, and their implication, are also outlined. Annual assessment of the stock is currently undertaken using catch and effort information provided by fishers. To facilitate the management decision making process projections of future stock levels are also made using age structured population models for the main species. The stock assessment and modelling are described and their relationship to the management process discussed.; Keywords: commercial fishery, fisheries management, stock assessment; Carcharhinus obscurus, Mustelus antarcticus, Furgaleus macki

Biology of the Australian sharpnose shark, Rhizoprionodon taylori.

The biology of the Australian sharpnose shark, Rhizoprionodon taylori, was studied in the waters around, Townsville, northern Queensland. Specimens were collected using gillnets (5 and 10 cm stretched mesh), longlines, handlines and otter trawls. Size selectivity of the gillnets resulted in mostly adult specimens being captured. Maximum size recorded for males was 691 mmTL and females 784 mmTL. Ageing using annuli in sections of vertebrae gave a maximum age of 6 years for males and 7 years for females. Von Bertalanffy growth parameters estimated from vertebral ageing data for males were t0=0.41 yr, K=1.34, L¥=652 mm, and for females t0=0.46 yr, K=1.01 and L¥=732 mm. Males and females mature after one year at 550 mm. Mating occurs in mid-summer. Females reproduce each year, producing litters of between 1 and 10 (mean 4.5). After fertilisation the embryos enter a seven month period of diapause during which little or no development occurs. The young are born shortly before the mating season, after an 11.5 month gestation period. The young are born at 220-260 mm. Adults feed mostly on small demersal teleosts, as well as some prawns, crabs and squid. ; Keywords: Rhizoprionodon taylori, Australia, reproduction, growth, embryonic diapause, growth, feeding

Biology and status of the dusky whaler (Carcharhinus obscurus) in the waters off Western Australia.

The dusky whaler is major component of the shark fishery in southern Western Australia, where it is exploited mostly as 0+ pups. To provide biological information on the dusky whaler for management purposes the Fisheries Department of Western Australia commenced a research project on this species in 1993. This research is targeted at the juveniles that are exploited by the fishery, and includes a tagging project, biological sampling onboard commercial vessels and a research fishing survey for adults. Preliminary results from the research are discussed, including information on movement, growth, feeding, and reproduction. The results of stock assessment and population modelling are also outlined.; Keywords: Carcharhinus obscurus, tagging, movement, growth, commercial fishery, stock assessment, feeding

Growth of sandbar sharks, Carcharhinus plumbeus, before and after population depletion.

Recent studies have shown that by 1991 the sandbar shark (Carcharhinus plumbeus) population along the Atlantic coast of the U.S. had declined in abundance to ca. 20% of its level in the late 1970’s. The hypothesis that compensatory growth occurred after severe population reduction was tested. Growth of sandbar sharks was investigated by counting annuli and back-calculating lengths at previous ages from vertebral samples collected in 1980 – 1981 and 1991 – 1992. The collections included 188 sharks from 1980 – 1981 and 412 sharks from 1990 – 1991 ranging in length from 51 – 172 cm precaudal length (PCL). All sharks were mature at lengths > 136 cm PCL. Minimum and maximum ages were 0 and 24 years. Age at maturity was 15 – 16 years for both sample periods and both sexes. For sexes combined, the von Bertalanffy growth parameters were LI=199 cm PCL, K=0.057, to=-4.9 years for the 1980 – 1981 sample and LI=164 cm PCL, K=0.089, to=-3.8 years for the 1991 – 1992 sample. Statistical tests found significant differences between the two growth models. Significant differences in size at age and annual incremental growth of juveniles suggest a small increase in juvenile sandbar shark growth rate between the two sampling periods. However, age at maturity was unchanged between samples suggesting that any biological significance of a growth rate increase has not been realized.; Keywords: sandbar shark, growth, Carcharhinus plumbeus

Observations on manta rays in Yap, Micronesia

A large and persistent population of medium-sized manta rays (Manta birostris) occurs around the main island complex in the state of Yap, Federated States of Micronesia. This population has gained notoriety among recreational divers and is a significant source of ecotourism in Yap. I made observations on the population for 10 days in late 1994 and early 1995, and some video records are available for the population dating back to 1991. Many, perhaps most, individuals are recognizable on the basis of natural tags and color pattern, especially dark markings on the venter. Video documentation shows that some individuals have been a persistent part of the population over several years, suggesting that at least a core group of animals is resident. Mantas appear to use the channels around Yap for courtship, cleaning, and limited feeding. These and other elements of manta biology and ecology in Yap will be discussed. ; Key Words: manta, ray, Micronesia, Yap, cleaning, courtship, behavior

Phylogenetic relationships among myelin basic proteins from Chondrichthyes.

Myelin basic proteins (MBPs) are a family of alternatively-spliced proteins present in most vertebrate myelin sheaths. They are believed to function in the compaction of the cytoplasmic leaflets within the myelin sheath during development, and to stabilize the myelin sheaths of adults. As a key antigen in experimental allergic encephalitis, a model for multiple sclerosis, MBPs were purified and sequenced from many mammals in the 1970s. More recently, MBPs from rat, mouse, human chicken and several cartilaginous fish have been cloned. Oligonucleotide primers, designed to the N- and C-terminal regions of horn shark MBP amplify, via RT-PCR, MBP cDNAs for all Chondrichthyes. Primers matching highly conserved sequences in exons 1 and 3 amplify roughly 240 bp of MBP from all vertebrate classes. The entire coding region from seven cartilaginous fish, and exons 1 and 3 from fourteen others, have been sequenced-exon 2 has not been found outside of mammals. Among all Chondrichthyes, the amino acid sequence of exon 1 is 64% identical, whereas, the exon 3 sequence is only 31% identical. Ratfish sequence is the most divergent. Phylogenetic trees constructed using the program MacClade 3.0 were found to nearly match the known phylogenetic relationships among Chondrichthyes.; Key words: cartilaginous fishes, evolution, myelin basic protein, phylogenetic tree, RT-PCR

Presence of an incipient swim bladder in the stomach of sand tiger sharks, Carcharias taurus

Anti-evolutionists frequently argue that natural selection cannot account for inviable transitional stages during evolution of a characteristic. This shallow criticism can be dismissed if one assumes that developmental redundancy provides organismal flexibility during the evolutionary process. Sand tiger sharks, Carcharias taurus, are the only elasmobranch known to gulp air to increase their buoyancy. The dorsal and ventral linings of the fundic stomach were studied with light and electron microscopy, and revealed major differences between the dorsal and ventral surfaces of the stomach. The thin, tough dorsal surface of the lining accounts for approximately 60% of the exposed surface, whereas the remaining 40% is occupied by the ventral portion of the stomach. The dorsal wall is approximately 1/3 the thickness of the ventral lining, and has fewer cells with zymogen-like granules, and fewer vesiculations (probable homologues to mammalian chief and parietal cells). These data suggest a decrease in the capacity for acid and enzymatic secretion of the dorsal surface of the stomach. The observations are consistent with the interpretation that a hydrostatic organ is evolving from the stomach of the sand tiger shark.; Keywords: Carcharias taurus, elasmobranch, stomach, histology, swim bladder

Observations on the short-term movements and behaviour of whale sharks at Ningaloo Reef, Western Australia

Whale sharks Rhincodon typus aggregate in large numbers at Ningaloo Reef on the north west coast of Western Australia each year from March to late April. The aggregations appear to be linked to coral spawning events which cause a localised increase in productivity. The movement and behaviour of whale sharks during this period is reported from data collected by acoustic telemetry and archival tags. The methods of attaching these devices to large, free-swimming animals is described. In recent years, an ecotourist industry has developed around snorkelling with these sharks at Ningaloo. ; Keywords: Whale sharks, Ningaloo Reef, Tracking

Is there really bilateral asynchrony in muscle activation patterns in batoids?

Typically, electromyograms (EMGs) of cranial muscles during feeding are assumed to be bilaterally synchronous. That is, the left and right adductor mandibulae are activated at the same time. This has simplified the process of modelling muscle function in teleost fishes and in elasmobranchs. However, in many skates and rays morphological features of the feeding apparatus indicate that the left and right sides of the mouth operate independently. This could be important in prey processing. In this experiment several of the cranial muscles important in prey processing were found to be activated asynchronously. EMGs of four muscles in six individual Raja erinacea were recorded while the subjects consumed unshelled and shelled shrimp. There were more asynchronous events in feeding bouts that required extensive processing. One Dasyatis sayi was video radiographed while feeding to determine if this asynchrony in activation is accompanied by asymmetry in movements of cranial elements. It appears that there is some asymmetrical movement of the jaws. These results indicate that feeding in skates and rays is a more complex process than in other elasmobranchs and most bony fishes. Keywords: batoid, Dasyatis sayi, Raja erinacea, feeding, prey processing

Refutation of identification of a lamnoid shark embryo by Sanzo (1912) as Carcharodon carcharias.

In 1903 a 500 kg alleged white shark Carcharodon carcharias (pesce cane) was caught in the Strait of Messina, Italy. One of the 25-30 embryos of similar development with large yolk stomachs was brought to the local Marine Institute. The identification of this 0.361 m TL lamnoid embryo as a white shark by Sanzo (1912) was based on morphometrical arguments. Tortonese (1950) questioned the morphometrical reasoning but suggested that a fecundity of 25-30 was more likely for a white shark than a shortfin mako, Isurus oxyrinchus in view of the known low litter size (2 to 4) of the porbeagle Lamna nasus. An analysis using morphometric data for the white shark and shortfin mako indicated that the four morphometric criteria used by Sanzo (1912) were not adequate to distinguish between the two species. The embryo was located in 1994 in Florence, Italy and tissue samples were taken for a DNA sequence analysis. The preliminary analysis of dentition photographs and the precaudal vertebrae count suggested that it was a shortfin mako. We will present the results of dentition microscopy and histology, X-rays, dissection, and DNA sequence results. ; Keywords: Lamnoid embryo, morphometrics, dentition, X-ray, dissection, DNA sequence

First record of the bramble shark, Echinorhinus brucus, from the Gulf of Mexico with comments on life history and morphological variation

We report the capture of a large female bramble shark, Echinorhinus brucus, from the northcentral Gulf of Mexico at the edge of the Mississippi Canyon about 72 km S of Grand Isle, LA at 28o 37’N 90o 01’W. The 2,614 mm TL specimen was captured by bottom long-line at 110 fathom depth. It was reported to be olive-green in color while alive, but faded quickly to brown-black after death. Body proportions were similar to the 2,159 mm TL female reported by Musick and McEachran (1969), but our specimen was not nearly as robust as the 2,808 mm TL female reported by Schwartz (1993) from North Carolina, his being 200 kg vs 78.2 kg Musick and McEachran and 81.4 kg (ours). Teeth on our specimen were more multi-cusped compared to previous reports. Brambles on the dorsal track varied from 3.2 to 21.1 mm ( 12.6 mm) becoming more minute on the extremities of body and fins. Our specimen contained well developed oocytes, but no embryos, similar to other females reported for the western Atlantic. Twenty-three large oocytes were present, the largest being 24-25 mm diameter from ovaries measuring 335 x 89 mm (L) and 283 x 81 mm (R). One atretic oocyte (~50-60 mm) was present. This is the sixth record of the bramble shark from the western Atlantic and the first from the Gulf of Mexico.; Keywords: bramble shark, Gulf of Mexico, life history

Two populations of the Angel Shark, Squatina californica Ayres, in the North Pacific. 

Specimens of the angel shark, Squatina californica, were collected in the halibut fishery in San Ignacio lagoon, western coast of Baja California Sur and in the angel shark fishery form the eastern coast of Baja California Sur. The fishing season begins January until early May. The females and males mature in the Gulf of California at total length of 85 and 78 cm, respectively, while in the western coast are mature to 112 and 103 cm. The northern population of the angel shark have at least two subpulations distributed form Alaska to the southern Baja California and the second in the Gulf of California. Key words: Squatina californica, Pacific, Gulf of California, reproduction,populations.

Preparation and specificity of monoclonal antibodies against IgM of the Atlantic nurse shark, Ginglymostoma cirratum.

Two monoclonal antibodies were developed against serum immunoglobulins of the Atlantic nurse shark. The serum immunoglobulins were isolated by precipitation with 50% ammonium sulfate, and the immunoglobulin fraction was exhaustively dialyzed against elasmobranch phosphate buffered saline (960 mOsM) and filter sterilized. A Balb/C mouse received 3 injections of the immunoglobulin preparation at fourteen day intervals. Three days after the final immunization, the mouse was sacrificed and its spleen excised. A single cell suspension of splenic lymphocytes was fused with Sp2/O-Ag14 myeloma cells using polyethylene glycol. Hybridoma growth was favored by culturing in media containing hypoxanthine, aminopterin, and thymidine. Primary hybridomas were screened by ELISA with Immulon-4 plates coated with nurse shark immunoglobulin at 1.0-1.5 ug/well. Positive primary hybridomas were cloned by limiting dilution. Two monoclonals were isolated and isotyped to be of the IgM class. These monoclonals were tested for cross-reactivity against serum preparations of more than twenty elasmobranch species using a sandwich ELISA. The sera exhibiting a positive reaction with the monoclonals were analyzed using SDS-PAGE, IEF and Western blotting.; Keywords: Monclonal antibody, IgM, Ginglymostoma cirratum

Aspects of the biology of two deep-sea lantern sharks, Etmopterus granulosus and E. unicolor, collected from the waters around New Zealand 

The objective of the present study was to increase knowledge of the biology and life history of the deep-sea lanternshark Etmopterus granulosus(=E. baxteri) and E. unicolor by analyzing data on morphometric characters, distribution, reproductive habits, and stomach contents. One hundred ninety-three E. granulosus and 144 E. unicolor were caught with bottom longlines from the banks and seamounts around New Zealand and adjacent regions.Etmopterus granulosus and E. unicolor are distinguished by the shape of the dermal denticles, vertebral number, and number of turns of the spiral valve. Both species were collected mainly from depths greater than 900 m. No depth segregation among the species was found. Size at maturity for E. granulosus was about 550 mm TL in males and 650 mm TL in females, and for E. unicolor was about 530 mm TL in males and 600 mm TL in females. Litter size was 6-15 for E. granulosus and 11-23 for E. unicolor. Embryonic development of relies on yolk dependence in these aplacentally viviparous species. Stomachs of both species contained decapods, squids, and teleosts.; Keywords: New Zealand, Lanternsharks, E. granulosus, E. unicolor, Distribution, Reproduction