1997 AES Annual Meeting Abstracts

Unique evolution of neurohypophysial hormones in cartilaginous fishes: Possible implications in the urea-based osmoregulation.

Most bony vertebrate species display a great evolutionary stability of their two neurohypophysial hormones so that two molecular lineages, isotocinmesotocin-oxytocin and vasotocin-vasopressin lineages, have been traced from bony fishes to mammals. Chondrichthyes, in contrast, show on the one hand a striking diversity of their oxytocin-like hormones, on the other hand an important decrease in vasotocin stored in the neurohypophysis when compared to nonmammalian bony vertebrates. In the rays, glumitocin ([Ser⁴, Gin⁸]-oxytocin) has been identified. In the spiny dogfish, aspargtocin ([Asn⁴]-oxytocin} and valitocin ([Val⁸]-oxytocin) has been characterized whereas in the spotted dogfish, asvatocin ([Asn⁴, Val⁸]-oxytocin) and phasvotocin ([Phe³, Asn⁴, Val⁸]-oxytocin) have been found. Finally, in the holocephalan Pacific ratfish, oxytocin, the typical peptide of placental mammals, has been discovered. Cartilaginous fishes have developed an original urea-based osmoregulation involving a glutamine-dependent urea synthesis and a blood urea retention through renal urea transporters. Furthermore, marine species use a rectal salt gland for sodium chloride excretion. Whereas vasopressin in mammals and vasotocin in nonmammalian tetrapods are clearly implied in water and salt homeostasis, the hormones involved in the he blood osmotic pressure regulation in elasmobranchs are still largely unknown. It is suggested that the particular great diversity of oxytocin-like hormones expresses a relieve of the evolutionary receptor binding constraint, so that amino acid substitutions are relevant to neutral evolution. In contrast, the preservation of vasotocin suggests a selective pressure and may be related to the regulation of the renal urea transporter mechanism as it has been shown for vasopressin in mammals.

Fishery and trade of whale shark (Rhincodon typus) in the Philippines

Fishery and trade for whale sharks (Rhincodon typus) in the central Visayas and northern Mindanao were investigated from 1993 t0 1996, as an offshoot of the National Marine Mammal Conservation Project. At least six villages (Sawang-Sawang and Embatuhan, on Camiguin; Selinog Island and Talisayan, in Mindanao; and Pamilacan Island, Bohol) have active annual hunts. Catches at the first three are modest amounting to no more than a few in any given year. At Pamilacan and Talisayan, hunters have taken an estimated 30 sharks per year in recent years. Lucrative markets exist for shark fins, skin and meat. Data are presented on fishing operation, catches per unit effort and length/sex composition of the catches at Pamilican. since there is no local or national protection for whale sharks, concern has been growing regarding the sustainability of such an activity and the exstirpation of the species. To date, data on volume and trade of whale sharks and manta ray is being done by Silliman University and Kabang Kalikasan ng Pilipinas for the 1997 hunting season. Parallel to this, consulation with local government officials, non-government organizations, and villagers is being conducted to come up with a plan to better manage the resources and ensure conservation of the species.

Photographic identification of white sharks, Carcharodon carcharias, at the South Farallon Islands, central California.

Photo identification methods have been used effectively with whales and dolphins. Photographs of distinctive fins and markings on individuals allow them to be reidentified at a later date. This method has also been effective with white sharks at the South Farallon Islands (SFI), central California. White shark’s first dorsal and caudal fins often break the surface during feeding, enabling them to be photographed. The trailing edges of their dorsal fins have distinctive arrangements of notches that are unique to each individual. There is also variation in the shape of dorsal fins (rounded vs. pointed). Our observations show that the notches and shape remain unchanged for long periods of time. Dorsal and caudal fins of white sharks have been photographed at SFI since 1988 and more than 20 known individuals have been resighted in two or more years. This suggests that photographic identification of white sharks is reliable over for long periods of time. Photographs may be more reliable for large species than tagging since tags can be shed and require retrieval either by physical removal or capture of the shark for identification.

Degradation of shark cartilage in an in vitro enzyme reactor.

Cartilage was obtained from sandbar sharks and stored at -20 C. The cartilage was freed of extraneous material and rough-ground using a stainless steel grinder. The cartilage was vacuum-dried and reground to pass a 5 mm screen. It was suspended in pH 2 HCl and incubated with 0.5 units pepsin per mg of cartilage for 2.5 hr at 37 C in a shaking water bath. The suspension was centrifuged at 3000 X g and 1 C. The supernatant was aspirated and separated into < 1OK daltons and > 1OK daltons fractions by centrifugal ultrafiltration. The residue was washed and then suspended in bicarbonate buffer, pH 8.0 containing 1mM Ca⁺², and 1.0 units trypsin. 0.1 units chymotrypsin, and 0.1 units elastase per mg cartilage. The suspension was incubated for 3 hr at 37 C. After incubation the suspension was treated as above. In five replicates pepsin treatment effected < 10% digestion of shark cartilage. The subsequent mixed enzyme digestion resulted in > 60% digestion of the pepsin-pretreated cartilage. Very little > 1OK protein was detected in the pepsin digest as assayed by HPLC gel filtration. The mixed enzyme digest contained small amounts of > 400K protein and much higher amounts of 15-25 K proteins/polypeptides.

The application of a stage-based model to the sandbar shark (Carcharhinus plumbeus): Implications for management.

We modeled the population dynamics of the sandbar shark (Carcharhinus plumbeus) using a stage-based matrix model that segregated the life-cycle of the sandbar shark into five stages: neonate, juvenile, sub-adult, pregnant adult, non-pregnant adult to follow female abundances. The model was used to examine the effects of variability in vital rates on the dynamics of the population and to assess different management strategies. We explored the implications of two schedules of age and growth, and a range of estimates of fishing and natural morality. The management strategies assessed were minimum size, time/area closures, and quota reductions. Analyses indicated that with a life expectancy of 30 years, an age of maturity of 15 years, and a natural mortality of 0.10 for all life stages, fishing mortalities (F) greater than 0.08 yield produce declining populations. The model was most sensitive to vital rates for juveniles and sub-adults while parameters for neonates and non-pregnant females had the lowest sensitivities. This suggests management strategies should focus on conserving juveniles and sub-adults. Moreover, at current F levels, a nursery closure scheme that ensures the survival of every neonate and removes pregnant females from fishing mortality pressures, still would not result in an increasing population.

Tooth Replacement rate of a Northwestern Atlantic population of Squalus acanthiasLinnaeus, 1758.

Analysis of 30 lower mandibular arches taken from Squalus acanthias (TL 60.325 to 104.14 cm) collected in 1974 (7 males, 12 females) and 1971 (11 females, and including 11 first dorsal spurs) from near Martha’s Vineyard, Massachusetts finds a tooth replacement rate of 0.955 years. The lower jaws demonstrate directional antisymmetry within the number of tooth positions. The distribution of difference in number of tooth positions (left – right rows) for the 30 specimens is: 21 fish having a higher number of tooth rows on the right side of the lower jaw (L-R<0), 2 showing perfect symmetry (L-R=0), and 7 having a higher number on the left side (L-R>0). The amount of kurtosis for this sample (-0.119007) is not statistically significant. The range in dental formulae for this sample from the western North Atlantic was lower jaw: 11 to 15 -0 (or 1) -10 to 15. This is the first report of any individual S. acanthias from the Northwest Atlantic having a symmetrical symphysial tooth. This sample is compared to a similar sample of 34 specimens of S. acanthias from the Eastern Pacific.

Diet, gastric evacuation, and daily ration of juvenile scalloped hammerhead sharks,Sphyrna lewini.

Gastric evacuation, diet, and daily ration of juvenile scalloped hammerhead sharks,Sphyrna lewini, were studied in Kane’ohe Bay, O’ahu, Hawai’i. Stomach contents were collected from the 251 sharks that were caught in gill nets, and gastric evacuation data was obtained from 63 sharks held in field enclosures. Stomach contents were recovered by gastric eversion in all cases. For the 194 (87.3%) sharks whose stomachs contained food, crustaceans made up 53.7% of the diet (IRI), teleosts accounted for 13.5% of the diet, and unidentifiable material 32.6%. an alpheid shrimp. Alpheus mackayi, was the most important prey item, accounting for 38.4% of the total diet. The average amount of food in the stomachs was 0.35 g (+/-) 0.3 g) dry weight. Gastric evacuation of teleost prey proceeded in a curvilinear manner, and was 90% complete in 19.7 hours at 27.l C, and in 28.6 hours at 24.0 C. Daily ration estimates were based on stomach contents of wild sharks and digestion rates of captive individuals, and were low compared to estimates made for other species of sharks.

Studies of nurse shark reproduction: bridging the gap between field investigations and captive research.

An ongoing, long-term study of nurse shark mating behaviors in the Florida Keys has demonstrated the need to develop a process for extended monitoring of females that have been involved in mating events using techniques that cannot be used in free-living animals. To more completely monitor physiological correlates of gestation, tagged females that have been documented participants in mating events have been captured and transported to the facilities of Sea World of Florida where they have been held for periods as long as 15 months. Methods for identification and selection of study animals and the methods for capture, transport, maintenance, and eventual release of study animals are described.

Studies of nurse shark reproduction: uses of endoscopy, ultrasound, and serial blood chemistry in the evaluation and monitoring of presumed pregnancy in captive nurse sharks.

Free-living nurse sharks that have been documented as participants in mating events in the wild have been captured, held, and systematically studied in facilities at Sea World of Florida. Serial blood sampling was used to evaluate changes in serum steroids. DNA profiles were developed in an effort to characterize both the wild population and the eventual offspring with the intent of determining paternity. Ultrasound and endoscopy were used to evaluate changes in the uteri and their contents throughout the captive period. Preliminary results suggest answers for problems encountered in the study and future directions for expanded studies.

Mating behaviors of male nurse sharks: use of ultrasonic telemetry for tracking animals between mating events.

Observations of mating behaviors of nurse sharks have demonstrated that females seek refuge in shallow waters and are periodically discovered and mated by males that then quickly leave the area. Tracking studies using ultrasonic telemetry and GPS positioning are presented that describe movements of males between mating events. Results suggest that the tracks of males tagged in this fashion can be used to reveal patterns of daily movements and mating excursions, and to identify additional locations of reproductively active animals.

The reproductive biology of the nurse shark, Ginglymostoma cirratum.

Although the nurse shark is very abundant in Florida and the Caribbean Sea, its reproductive biology is very poorly known. Here I present preliminary observations on the mode of reproduction of the species. The nurse shark is a viviparous, aplacental species, with a gestation period of about five months and biennial reproduction. Females carry from 32 to 62 large oocytes in the spring. Mating and ovulation take place in June. Oocytes reach 60 mm in diameter at ovulation and are enclosed in thin, horny egg cases after ovulation. Embryos are lecithotrophic throughout development. Egg case slits open when the embryos are about 60 mm TL. Embryos emerge from the egg cases at about 220 mm TL. Embryos are found in different stages of development. In late October, some embryos in a given female may still be inside the egg cases while later embryos have already absorbed their yolk sac and appear ready for birth. Embryos are born at about 280 mm TL in November and December. After parturition, females enter a resting stage and do not mate the next summer. These females will mate again the following summer or eighteen months after parturition. The reproductive cycle, from one ovulation, or parturition, to the next is two years (biennial).

A report on the status of shark species prepared for FAO.

In 1994, the Convention on International Trade in Endangered Species (CITES) passed a resolution requesting international organizations to create programs to collect and assemble biological and trade data on sharks. In July, 1996, the Food and Agriculture Organization of the United Nations (FAO), asked us to develop a database which would indicate the species of sharks that may be threatened by overexploitation or trade, in response to the CITES request. It was stipulated that the work had to be completed in six months. We produced short biological and fishery profiles for each shark species and assigned a status category to each, based on reproductive potential, on historical fishery trends, and on the current impact of fisheries on the species. These categories are: non-exploited species, data deficient, lower risk, vulnerable, highly vulnerable, and endangered. This database is severely limited due to the lack of biological or fishery data. Its main purpose is to indicate how a given species will help fishery managers to understand the limitations of shark fisheries and thus prevent the unregulated development and overcapitalization of these fisheries.

Correlation of movement patterns of subadult lemon sharks (Negaprion brevirostris) in Bimini Lagoon, Bahamas, with the local hydrodynamics.

Between 1994 and 1995 seventeen subadult lemon sharks were tracked in Bimini Lagoon. An hydrodynamic bidimensional model using a semi-implicit (ADI) method was used to provide several scenarios of depth in the Lagoon using different tidal amplitudes. The model was validated by comparison of movements from floaters tracked in the field against movements of simulated lagrangean particles. The results showed that exceptional low tide conditions are associated with total exposure in the central area of Bimini Lagoon. When such conditions occur during sunrise or sunset the sharks do not cross the Lagoon east nor westwards, despite the fact that there is a canal with enough water that permits crossing the Lagoon even at low-tide. These observations lead to the conclusion that the shark movements are positively correlated with the hydrodynamic pattern in Bimini Lagoon and were showing path-habits.

Estimation of natural mortality in sharks through life history methods.

Natural mortality is one of the most difficult parameters to estimate in fisheries science, yet is essential in most mathematical models attempting to describe the dynamics of a fish stock or population. Current methods to estimate the instantaneous rate of natural mortality (M) can be divided into two general categories: those analyzing catch data, and those seeking correlations between M and other life history parameters. The objective of the present study was to generate estimates of M for sharks through four methods that utilize empirical formulas to describe the relationship between M and life history parameters in fishes: (1) Hoenig’s (1983) equation relating longevity to total instantaneous mortality rate; (2) Pauly’s (1980) equation relating M to von Bertalanffy growth (VBG) parameters and water temperature; (3) Chen and Peterson and Wroblewski (1984) that relates M to body weight. Estimates from the four methods yielded a mean discrepancy of 18% (95% CL: 13%-24%) in predicting M and a correlation matrix between the four methods indicated that only predictions from the weight-based method were not significantly correlated with those from methods (1) and (2). Overall, results indicate that the use of these predictive equations holds promise in studies of shark population dynamics.

Thyroid hyperplasia in captive sharks: Relationship of water chemistry to serum thyroid hormones.

Two goitred whitetip reef sharks, Triaenodon obesus, from an open system saltwater well facility, and two non-goitred T. obesus at a natural seawater lagoon were compared for environmental origin of goitre. The water chemistry (temperature, salinity, pH, 0₂, iodine, nitrogen, and phosphorus species) of the two facilities was analyzed. The size of the thyroid gland was determined by ultrasound, and serum thyroid hormones (T₃, T₄ were measured by radioimmunoassay. After the initial monitoring, the goitred sharks were moved to the natural seawater lagoon with the two non-goitred sharks. The goitres were initially 11.4 cm and 14.6 cm in depth, and after 3 months decreased to 4.7 cm and 5.7 cm. Sera T₃concentrations were initially 0.22 ng/ml and 0.33 ng/ml, and increased to 184 ng/ml after being placed in natural seawater. Sera T₄ were initially 0.93 ng/ml and 0.99 ng/ml and increased dramatically to 17 ng/ml and 56, ng/ml. Two sharks already in the natural lagoon had sera T₃ concentrations of 0.89 to 1.1 ng/ml and sera T₄ concentrations that ranged from 3.1 to 7.9 ng/ml over six months. The hypothyroid state in the goitred sharks is related to water chemistry containing low iodide (<0.005 uM) and high nitrate (111 uM).

Serum T3 and serum T4 concentrations in immature whitetip reef sharks, Triaenodon obesus.

Serum T3 (3,5,3; triiodothyronine) and serum T4 (thyroxine) concentrations were assayed by radioimmunoassay over a four-year period in tow male and two female immature whitetip reef sharks, Triaenodon obesus. These sharks were maintained at the Waikiki Aquarium in an open system holding pool receiving 568 liters per minute of well water with a 1.73 µM concentration if iodide. No significant male – female difference was observed for either serum T3 or serum T4. No seasonal pattern was detected in serum T3. Serum T3 in male ranged from 0.48 to 0.83 ng/ml (mean – 0.67 ng/ml, SEM ± 0.01, n = 32). Serum T3 in females ranged from 0.52 to 0.83 ng/ml, SEM ± 0.01, n = 43). A significant seasonal difference was observed for serum T4 in both male and female sharks. Winter (Oct to Jan) serum T4 concentrations was higher for males (mean – 0.67 ng/ml, SEM ± 0.58, n = 11) and females (mean – 6.44 ng/ml, SEM ± 0.44, n = 13) than in the summer (May to Aug.) for males (mean = 3.54 ng/ml, SEM ± 0.27, n = 13) and females (mean – 3.77 ng/ml, SEM ± 0.25, n = 20). It appears that serum T4 has a strong seasonal rhythm that is expressed even in immature sharks.

Population structure and dynamics of the lemon shark, Negaprion brevirostris, on a local scale: microsatellite and mitochondrial DNA analysis.

Very little is known about the mating system of sharks. Using both microsatellite and mitochondrial DNA (mtDNA) analysis, we will determine the genetic mating system of a population of lemon sharks, Negaprion brevirosttis, in Bimini, Bahamas. A genomic library for lemon sharks has been screened, and ten primer pairs have been developed for polymerase chain reaction (PCR) amplification. Over 400 fin samples from both juvenile and adult lemon sharks have been collected over the past four years from Bimini lagoon. PCR-amplification of microsatellite loci and mtDNA haplotyping will be used to genotype every sample. We propose to address the following questions: 1) How many adult females use the Bimini lagoon as a nursery? 2) What is the reproductive cycle of those females returning to Bimini? 3) What is the mating system of this population? Do single males sire an entire litter or does multiple paternity occur? Is there skewed male mating success? Is there inbreeding in the population?

An assessment of fisheries impacting juvenile sandbar sharks (Carcharhinus plumbeus) in Delaware Bay: Implications for managing shark nursery habitat.

Data obtained from 3 fisheries databases and one gill net survey were used to assess the sources of fishing mortality on juvenile sandbar sharks in Delaware Bay, a primary nursery ground for this commercially important shark species. Recent commercial landings data (1990-1994) were used to identify the commercial fisheries likely impacting the population of juvenile sandbar sharks in Delaware Bay. The landings associated with the gear types used by the commercial fisheries operating in the region, and the overlap of these fisheries with the sandbar shark’s nursery season (May through October) were used as the basis for this assessment. Recreational sandbar shark catch estimates for Delaware Bay (1990-1995) were used to assess sources of recreational mortality on this species. Additionally, tag and recapture data provided information regarding where recreational anglers have caught sandbar sharks from this region in recent years, and the size ranges that these anglers are catching. Finally, information from the aforementioned data sets was used to evaluate two management measures based upon their ability to reduce sources of recreational and commercial fishing mortality on sandbar sharks in Delaware Bay.

Feeding kinematics of newborn swellsharks, Cephaloscyllium ventriosum(Scyliorhinidae): the importance of predator size vs. predatory experience.

Survival past the newborn life-history stage depends on energy acquisition. Energy acquisition is determined by an organism’s morphology and its use of that morphology, or behavior. Unfortunately, previous studies of newborn feeding behavior have been unable to separate changes in behavior caused by additional feeding experience from changes caused by morphological transitions (i.e., the larvae-juvenile transition). Swellsharks,Cephaloscyllium ventriosum, lack such morphological transitions and were thus chosen to investigate the importance of predatory experience in determining feeding behaviors. First-feeding sharks were filmed using high-speed video, and the resulting kinematic variables (used to describe and quantify behavior) contrasted with predatorily experienced one-year olds. Newborn prey captures were high-velocity, ram-dominated attacks while one-year-old prey captures had a suction component. Significant kinematic differences, however, do not appear responsible for shifting prey-capture mode. Timing differences between ages were not detected. a scaling analysis confirmed that swellsharks grow isometrically, thus changes in feeding behavior could not be attributed to ontogenetic morphological changes. This is further supported by a flow model which indicated that isometric increases in buccal volume do not require changes in prey-capture timing to negate a potential size effect; flow rates through the buccal cavity of sharks of both sizes are similar.

The metabolic rate of two species of benthic elasmobranchs, nurse sharks and southern stingrays.

The metabolism of two benthic elasmobranchs was determined using a tunnel respirometer. At 20 C, the standard metabolic rate of the nurse shark, Ginglymostoma cirratum, was found to be 79.08 ± 16.7 mgO₂/kg/hr and is the lowest value of oxygen consumption obtained for any shark to date. Its sedentary lifestyle continued even in the respirometer. The southern stingray, Dasyatis americana, was more active in the respirometer. Therefore, routine, rather than standard metabolism was determined to be 164.3 ± 8.9.0 mgO₂/kg/hr at 20 C. This value is comparable to results from previous studies of batoids.

Morphology and histology of the reproductive tract of a hermaphroditic spiny dogfish,Squalus acanthias.

We report on the recent collection of a hermaphroditic spiny dogfish, Squalus acanthias.Externally, this individual appeared male and possessed well-developed siphon sacs and calcified claspers complete with accessory spurs. Internally, the animal possessed ovarian tissue containing pale ova of variable sizes. There was no evidence of nidamental glands, yet the anterior portions of the reproductive tract resembled oviducts in structure. These ducts led to enlarged, fluid-filled sacs which emptied into the urogenital papillae. Fluid obtained from both sacs was clear and did not appear to contain sperm. Additional observations on the histology of the reproductive organs are discussed. In addition, sexual differentiation and intersexuality in elasmobranchs are reviewed.

Hormonal regulation of proteoglycan synthesis in vertebral cartilage of the clearnose skate,Raja eganteria.

The role of insulin-like growth factor-I (IGF-I) in elasmobranch vertebral cartilage physiology was examined in vitro. Incorporation of ³⁵S-sulfate into cultured vertebral cartilage from the clearnose skate, Raja eglanteria, was used to examine the hormonal regulation of vertebral proteoglycan synthesis. Addition of human recombinant IGF-I to the culture system significantly stimulated ³⁵S-sulfate incorporation into vertebral cartilage, thus indicating enhanced synthesis of calcifiable proteoglycan growth and vertebral cartilage development which may be mediated through IGF-I. Furthermore, this study suggests a link between seasonal variations in somatic growth and vertebral calcification.

Fish and cetacean mutilation by cookiecutter shark Isistius brasiliensis (Squaliformes: Squalidae) in São Paulo coast, southeastern Brazil.

Mutilation of fish and cetacean by cookiecutter shark, Isistius brasiliensis(Chondrichthyes, Squaliformes), was studied at the São Paulo coast, southeastern Brazil.Makaira nigricans andTetrapturus albidus (Istiophoridae), Thunnus thynnus(Scombridae), Epinephelus niveatus (Serranidae), Prionace glauca (Carcharhinidae),Megaptera novaeangliae (Balaenopteridae) were, in decreasing order, the fish mutilated with higher frequency. Shark attacks on fishes and cetaceans were directed mainly to the lateral region of prey 92’s body. Although a secondary food item in the cookiecutter diet, fish and cetacean parts obtained by mutilation may be an important animal protein source to this shark. This sharks feeds crustaceans, gonostomatids, and other invertebrates. One of the possible consequences of the loss of body parts, were bacterial infection or invertebrate parasites.

An associated specimen of Carcharodon angustidens (Chondrichthyes, Lamnidae) from the Oligocene of New Zealand.

Cenozoic sharks are represented in the fossil record by relatively abundant isolated teeth and occasional vertebral centra, but only very rarely by associated specimens. The giant lamnid sharks of the genus Carcharodon are no exception — while a few associated tooth sets of fossil Carcharodon species have been collected, typically only single teeth are found. Recently an associated specimen of C. angustidens was recovered from the Late Oligocene of New Zealand’s South Island. The specimen includes ca. 160 teeth associated with 34 anterior vertebral centra, all clearly from one individual. The full range of dental variation is preserved, including uppers and lowers and anterior through posterior tooth positions. These allow for an accurate reconstruction of the dentition in C. angustidenswhich is poorly known relative to the Mio-Pliocene species C. megalodon . Extrapolating from a regression relating tooth size to body length (TL) in living white sharks (C. carcharias, the specimen of C. angustidens had a TL of ca. 9m, significantly larger than living white sharks but well below the 16m maximum TL estimated for C. megalodon.

Preliminary results of pilot studies to assess the distribution and abundance of coastal sharks in the U.S. gold of Mexico and western North Atlantic (1995 and 1996).

During 1995 and 1996, the National Marine Fisheries Service, Mississippi Laboratories, Southeast Fisheries Science Center, conducted pilot studies to develop survey methodology and a sampling strategy for assessment of coastal shark populations in the Gulf of Mexico and western North Atlantic. Longline gear similar to that used in the commercial shark fishery was deployed at randomly selected stations within 3 depth strata per 60 nautical mile grid from Browsnville, TX to Cape Ann, MA. The survey methodology and gear design used in these surveys proved effective for capturing many of the small and large coastal sharks regulated under the auspices of the 1993 Fisheries Management Plan for Sharks of the atlantic Ocean (NOAA 1993). Shark catch rates, species composition, and relative abundance documented in these pilot surveys were similar to those reported from observer programs monitoring commercial shark longlining activities (Branstetter 1996). During 78 survey days, 278 longline sets were completed with 879 sharks captured. Based upon the preliminary analyses, an index of relative abundance for shark management species can be obtained through fishery independent longline surveys.

Description of the Chimaerid Jaw.

The definition of a chimaerid palatoquadrate has been extensively debated as it relateds to evolutionary analyses of jaw suspensoria and the interrelationships of Selachi, Holocephiali and particular Paleozoic fossil fishes. Embryological and adult analyses of the chimaerid cranium and jaw structure have been combined with comparative morphological studies of modern shark and select euchondrocephalan (autodiastylic paraselachian) crania. The dimensions of the palatoquadrate in modern chimaerids and related Paleozoic fishes are described. The caranial basitrabecular cartilage is described as a critical element in the plesiomorphous autodiastylic suspensorium and a structure which persists in chimerids today. Analyses of the extant and fossil data permit us to conclude that the primordial chondrichthyan palatoquadrate did not extend posteriorly to include an otic process. Rather, the posteriormost extent of this element is primitively found within or at the limits of the orbit; a region consistent with the basal connection and anterior limit of the common vertebrate basitrabecular element.

Abundance and Age Composition of Juvenile Carcharhinus plumbeus in Chesapeake Bay and the Effects of a Directed Fishery.

Chesapeake Bay is a major western Atlantic nursery for Carcharhinus plumbeus, sandbar sharks. The primary nursery is located in the higher salinity, lower eastern portion of the bay. Recruitment of pregnant females and returning juveniles occurs in mid-May through June and the young remain in the bay until mid-September or early October. Virginia Institute of Marine Science (VIMS) longline data indicated that the abundance of juveniles in Chesapeake Bay increased substantially from 1990-1992 while the abundance of large coastal sharks in Virginia waters was the lowest since the survey began in 1974. Increased survivorship of younger age classes may explain the increased nursery abundance and is supported by a juvenescence trend in this population. Abundance in the nursery decreased in 1993 and 1994 but leveled off in 1995 concomitant with the reversal in juvenescence. In 1995 and 1996, a directed commercial gillnet fishery developed in Chesapeake Bay. More than 43,000 pounds of juvenile C. plumbeus were landed in 1996 in the primary nursery. The VIMS abundance index was the lowest ever and extreme juvenescence was observed. A large proportion of the nursery population likely was caught in 1996 stressing the need for protection of vital nursery areas for proper management of large coastal sharks.

Comparative morphology of the appendiculae, umbilical stalks, and placentae of sphyrnid sharks: Functional correlates.

Light and scanning electron microscopy of the placentae and yolk stalks of Sphyrna mokarran, Sphyrna lewini, and Sphyrna tiburo embryos reveals species-specific variations in structure. S. mokarran has an umbilical stalk devoid of appendiculae. Gestation appears to last 11-12 months. Term embryos measure 50-70 cm. Litters contain 13-42 pups. S. lewini has an umbilical stalk with many short branched, spatulate appendiculae. Gestation is postulated at 10-12 months. Term embryos measure 42-55cm. Litters contain 15-31 pups. S. tiburo has an umbilical stalk with many, elongate appendiculae. Gestation lasts 6-8 months. Term embryos measure 35-40 cm. Litters contain 4-16 pups. Several factors affect litter and embryo size, and length of gestation. There appears to be an inverse relationship between the size of term embryos and complexity of the umbilical stalk. There are also species-specific differences in placental size and morphology. Size of term embryos appears related to maternal size and length of gestation. Litter size within a species is usually a function of maternal size, whereas differences in litter size between species may reflect different reproductive strategies and allocation of resources. Length of gestation appears directly related to appendicular number and complexity, as well as other factors

Growth rates of juvenile scalloped hammerhead sharks Sphyrna lewini.

A tag and recapture study was conducted on juvenile scalloped hammerhead sharks in Kaneohe Bay, Hawaii. 503 sharks were caught using hook and line. All sharks were weighed, measured, sexed and tagged with nylon dart tags over a ten week period from 18 July to 21 August 1996 to determine neonatal growth rates. 63 sharks were recaptured during that period and subsequent months. CPUE over the tagging period was 0.05 sharks hook^-1 hr^-1. Time at liberty ranged from a few minutes to 145 days. Average growth was -0.03 cmd^-1 and -2.50 gd^-1. A measurement error test was conducted to determine measurement variability. Simultaneously, 10 shark pups were kept in a seawater pond. One group was fed once a day, while another group was fed once every 7 d. Pups fed every day grew faster over a 15-day period than those fed once every 7 d and those at liberty in the field over the same time period. Tagging seemed to have minimal effect on growth in the captive population. These results suggest that hammerhead shark pups in Kaneohe Bay grow slower than hammerhead shark populations in other locations.

The role of the renin angiotensin system in elasmobranch fish.

Until the first elasmobranch angiotensin was isolated (Takei et al, 1993, J. Endocr., 138, 284-285) it was generally believed that the renin angiotensin system (RAS) evolved in primitive bony fish. Angiotensins (AI and AII) are highly conserved throughout vertebrates with amino acid substitutions in AII occurring at position 1 and 5. Elasmobranch angiotensins possess asparagine at position !, isoleucine at position 5 but usually have a proline residue at position 3 (Takei et al, 1993). To date most studies regarding the physiological role of RAS have been carried out in mammals where it plays a role in cardiovascular, renal and adrenocortical function as well as salt and water balance. Radioligand binding techniques have demonstrated specific receptor sits in gill cells, interrenal tissue and the unique elasmobranch salt secreting gland, the rectal gland. Using a blood pressure bioassay both dogfish AI and AII (0.001 -0.3nmol/kg) caused a dose dependent pressor response and captopril blocked the response to AI but not AII. Dogfish AII also stimulated corticosteroid release from the isolated dogfish interrenal gland and decreased secretion in an isolated perfused rectal gland preparation. These studies indicate a physiological role for dogfish AII in cardiovascular responses and fluid and electrolyte balance in elasmobranchs.

Observations of the reproductive biology of captive southern stingrays, Dasyatis americana.

Data were collected from 33 litters of captive born southern stingrays, Dasyatis americana, from five females between March, 1993 and January, 1997 at the National Aquarium in Baltimore (NAIB). Information from 124 pups (55 males, 69 females) was analyzed to yield results on sex ratios and size and weight at birth. Results will also be given on the gestation time in the captive population of southern stingrays at the NAB as well as the relation of maternal size versus litter size. In addition, qualitative observations were made on mating behavior following parturition.

Analysis of tissue responses to dart and roto tagging in four shark species.

Samples of dermal and epidermal tissues of sharks were examined histologically to assess damage caused by tagging. Tissues from dart tag and roto tag sites were removed at intervals of between 100 min-284 days and 5-553 days post-tagging respectively. Samples showed acute and chronic responses to tagging. Acute responses in dart tag sites consisted of localised tissue breakdown and haemorrhaging which occurred soon after tagging. The intermediate response was apparent 10 hours post-tagging and was characterised by further haemorrhage and white blood cell movement into the area. Chronic responses observed in 10-284 day dart tagged samples showed fibrous tissue formation around the tag. This provided a continuous barrier between the internal and external milieu. Similar responses were observed in fin tagged specimens, but proceeded more slowly with an acute tissue response present at 5 days and intermediate response present at 20 days post-tagging. Chronic tissue response began at 301 days and was complete at 553 days post-tagging. No secondary infections of tag sites were observed. Tagging generally produced minor localised tissue disruption, but 2.0% of dart tagged specimens showed a more severe external response and fin tag reactions ranged from scale loss and sores to tissue overgrowth of the tag.

A study on collection, transportation and breeding of a Scalloped hammerhead Sphyrna lewini.

Marine World Umino-nakamichi celebrated our grand opening in April, 1995. Since then Marine World has been maintaining collection activities of various species of sharks and rays. Those species of hammerhead have peculiar flat-shaped heads, which are extended horizontally, are very attractive to spectators. In the sea off Japan, three species of hammerhead are seen. They are Scalloped hammerhead, Great hammerhead and Smooth hammerhead. Marine World ever performed two series of collection work in Kasasa Town, Kagoshima. Prefecture in April through June, 1995 and July through October, 1996 respectively. Scalloped hammerhead are generally strong in swimming and very sensitive to lack of oxygen. Their eyeballs, which are located at the both edges of hammer-shaped head, are easily damaged by various external factors. Marine World, therefore, has been keeping our full attention to those conditions. The display of Scalloped hammerheads to the public commenced with our large water tank (1400 ton) in November, 1996 and its condition has been well maintained as of now. We will report this time on the transportation and breeding of Scalloped hammerhead in Kasasa Town, Kagoshima, southern-most prefecture in Japan in July through October, 1996.

Movement patterns of tiger sharks in Hawaiian waters.

Acoustic telemetry and traditional tag-and-capture methods were used to elucidate both the short and long-term movement patterns of tiger sharks (Galeocerdo cuvier) around the southern shoreline of Oahu, Hawaii. Acoustic telemetry consisted of both active tracking and the use of anchored data loggers to record the return of telemetered animals to the location where they were initially caught, tagged and released. Transmitters were either attached to the dorsal musculature with a small arrowhead barb or placed intraperitoneally. Eighty tiger sharks have been tagged at a recapture rate of 23%. Eight of the 15 sharks carrying long life transmitters have been electronically detected by stationary data loggers. Three sharks have been electronically detected in excess of one year from transmitter implantation. Tag-and-recapture and data logger information suggests that tiger sharks along the south shore of Oahu show long term site fidelity. In addition, active tracking indicates tiger sharks are capable of long distance movements over short time periods and that home ranges appear to be very large.

Philopatry, natal homing and localized stock depletion in sharks: strictly a hypothesis

Although philopatry, defined by Ernst Mayr (1963) as an animal’s drive or tendency to return to its home area, birthplace or another adopted locality, is common among many groups of vertebrates and even invertebrates, it is not widely recognized in marine fishes, especially actively swimming species including sharks. Philopatry of sharks for their natal pupping areas wouId lead successive generations of a population to reproduce at the same geographic location, as opposed to selecting a set of environmental conditions that are not always in the same place, the latter strategy tending towards dispersal (Cury, 1994). Without complete life-cycle tagging data, sharks have been assumed to primarily follow the second strategy. For philopatry for natal areas to exist in sharks, a natal homing mechanism(s) must be at work, which is plausible given sharks’ elaborate sensory systems. Natal homing or philopatry for other range components, such as juvenile habitats, seasonal feeding areas or mating areas, would make sharks vulnerable to localized stock depletion either through local overexploitation or habitat destruction. Historical examples of such localized stock depletions, tag-recapture data and population genetic data are all needed to test this hypothesis. Evidence from the first two data categories is accumulating; the slow mutation rate of elasmobranchs has been problematic in the search for genetic evidence.

Electroreception in juvenile scalloped hammerhead sharks

Electroreception has been hypothesized to be a possible mechanism driving selection for the laterally expanded cephalofoll of sphyrnid sharks. However, experimental tests of hammerhead electroreceptive capabilities are lacking. Response to prey-simulating dipole electric fields was quantified for juvenile scalloped hammerhead sharks, Sphyrna lewini.Sharks were able to precisely localize a buried dipole within 0.5 seconds of initial orientation and would bite the dipole repeatedly before losing interest. The sharks responded from a maximum distance of 28.5 cm, detecting a voltage gradient of 5.4 nvoltscm^-1l^-1. However, most responses were initiated from within 10 cm of the dipole and in the plane parallel to the dipole axis. Response distance was inversely proportional to electric current in the range from 6.0 to 8.5 µAmps and sharks were initially attracted to but would not bite at dipoles with currents greater than 12 uAmps. Future experiments will examine the electrosensory response of other species of sharks to determine if the hammerhead morphology provides an increased sensitivity to bioelectric fields.

Early observations on elasmobranchs in captivity: the first fifty years (1870-1920).

During the latter half of the nineteenth century and first part of the twentieth century, public aquariums sprang up around the world, especially after Loyd’s pioneering design and implementation of a contained sea water system. By 1920, over 45 aquariums were drawing crowds numbering nearly ten million a year. Not well appreciated is the fact that most of these aquariums from the start successfully maintained sharks and skates for years in captivity for public display and education. Particularly successful in this regard were aquariums in Brighton, Plymouth, Berlin, Frankfurt, Hamburg, Rovigno, Naples and New York. This achievement, coupled with watchful attendants and interested scientists, allowed novel observations on elasmobranch biology , observations that otherwise would have been impossible at the time, including mating, egg laying behavior, incubation times, hatching, neonatal growth rates, diurnal activity and feeding behavior. In addition, experimental work on shark senses, some involving surgical intervention, was first accomplished on captive animals maintained in research aquariums just after the turn of the century. Maintaining elasmobranchs in captivity for both public amusement and education, as well as biological research, has been a traditional activity of the marine aquarium for over one hundred and thirty years.

Reproductive endocrinology of the little skate Raja erinacea and spiny dogfish Squalus acanthias.

The diversity of reproductive modes among extant female elasmobranchs suggests that the endocrine system adapted novel cycles for regulating steroidogenesis, vitellogenesis, egg encapsulation, uterine accommodation, gestation and oviposition/parturition. We have shown that the follicular compartments, theca and granulosa, and corpora lutea are responsible for biosynthesis of estradiol, testosterone and progesterone during ovulatory cycles, egg laying and pregnancy. However, the complex assemblage of different sized developing follicles together with corpora lutea, all functioning concurrently in one ovary, both in oviparous species during egglaying periods and viviparous species during pregnancy, presents special problems for regulating circulating titers of these steroids. Based on in vitro studies, segregation of steroidogenic potential may account for the relative amounts and timing of steroid secretion in order to effect cycles in circulating titers. Additional complexity derives from processes temporally separated in other vertebrates occur simultaneously in elasmobranchs, e.g. follicular development/vitellogenesis coincident with egg laying or gestation. This pattern suggests that ovarian derived steroids have tissue specificity or functions unique to elasmobranchs and that reproductive tract mechanisms are regulated in original ways.

Evaluation of thyroid hormone economy in wild dogfish.

When held in captivity, elasmobranch fishes are prone to the development of thyroid lesions, usually simple goiters. Attempts to assess the thyroid status of captive fishes ave relied on measurements of plasma thyroid hormone concentrations; however, since there are few data of thyroid parameters in wild elasmobranch fishes, the interpretation of the values found in captive animals is questionable. Of particular interest in the assessment of thyroid hormone economy of vertebrates is the measurement of the enzymatic conversion (by 5′-monodieodinase [5′-MDA]) of the pro-hormone, L-thyroxine (T4), to the biologically active hormone, triiodo-L-thyronine (T3) by peripheral organ systems, such as the liver. In this report, freshly collected dogfish, Squalus acanthias, were used as a source of liver for the development of enzyme assay methods for measurement of 5′-MDA in adult and yolksac embryos. The study evaluates the roles of organic osmolytes on enzyme activity, and measures the changes in 5′-MDA activity associated with fasting of adult dogfish.

Effects of surgically-implanted dummy transmitters on captive, juvenile sandbar sharks,Carcharhinus plumbeus (Nardo 1827).

A laboratory study was undertaken to determine the behavioral and physiological effects of surgical implatnation of dummy acoustrictransmitters into the peritoneal cavities of juvenile sandbarsharks, Carcharhinus plumbeus (Nardo 1827). Intraperitoneal implantation lacked significant effect on red (hematocrit) and white blood cell count, growth rate, and condition factor. Recovery from the surgical implantation was neither rapid nor total; feeding behavior was delayed, and mortality rate of experimental sharks was greater than those of control sharks. Two sharks ruptured sutures at the incision site, resulting in eventual mortality. In addition to general appearance, identification of a moribund shark was possible through the monitoring of compromised parameters such as red and white blood cell counts. With refined surgical procedure and carefully assessed experimental protocol, intraperitoneal implantation appears to provide a suitable technique for attaching transmitters to sharks, and may be preferable to existing methods for many other fishes.

Development and utility of an acoustic tailbeat-sensing transmitter for sharks and fishes.

An acoustic tailbeat-sensing transmitter was developed to accurately determining activity rates, swimming speeds, and metabolic rates of free-swimming fishes and sharks. This device operates on a simple CMOS circuit and is triggered by the lateral movement of the animal’s caudal fin. The transmitter can be attached quickly using dissolvable sutures or surgical staples and weighs 25 g in air and less than 2 g in seawater. Activity and metabolic rates of free-swimming instrumented sharks and fishes in the field can be predicted using laboratory measurements of swimming speed and oxygen consumption as a function of tailbeat frequency. Preliminary tracks of juvenile scalloped hammerhead sharks (Sphyrna lewini) carrying tailbeat-sensing transmitters indicate that their activity rates differ between day and night, with peaks of activity occurring during crepuscular periods. Shark pups exhibit an average diel swimming speed of 1.9 ± 4 kcal d^-1. The development of this minimally intrusive, activity-sensing transmitter provides a cost efficient, accurate method for determining energy consumption of active sharks and fishes in the field.

Identification of potential B-lymphocytes and T-lymphocytes from the clearnose skate,Raja eglanteria, using RNA probes.

Before the functional roles of elasmobranch lymphocytes can be characterized, methods to differentiate B-cells from T-cells must be developed. Recently, two constant region heavy chain genes from immunoglobulin M (IgM) and immunoglobulin X (IgX), two variable region light chain immunoglobulin genes (LCI and LCII), and from T-cell receptor (TCR) genes (, ß, , and ) have been identified four the clearnose skate. Digoxigenin-labeled RNA probes prepared from these eight genes were utilized in RNA in situ hybridization studies with 6-8 micron frozen sections of various skate tissues (spleen, thymus, liver, epigonal organ, Leydig organ, kidney, spiral intestine, and rectal gland). Enzymatic detection of hybridized probes resulted in the identification of lymphocytes expressing mRNA for the Ig or TCR genes. IgM and IgX heavy chain mRNAs were expressed in all tissues examined except liver and kidney. Patterns of expression were generally similar, although IgM was always greater in abundance and intensity than IgX. RNA expression of heavy chain genes did not colocalize with either LCI or LCII in any tissues examined. Hybridization of TCR probes was most intense in the thymus, with /ß being stronger than /. TCR mRNA was also expressed to lesser and varying degrees in spleen, epigonal, Leydig and spiral intestine.

Evolution of the holocephalan tenaculum and pelvis.

The prepelvic tenaculum of chimaeras and related fishes is unique among the vertebrates and the modern chimaeroid pelvic girdle is a highly derived chondrichthyan structure. Understanding their structure and derivation provides a rich character complex which is critically necessary to unravel the evolutionary relationships of the Holocephali. The plesiomorphous chondrichthyan pelvic girdle is a low triangular paired plate; no extended basipterygium is present and all but the terminal radials articulate with the girdle. The plesiomorphous euchondrocephalan condition entails the development of an extended basipterygium and the shift of most radials onto this element. The prepelvic tenaculum is a specialization of the first pelvic radial. The separation of the teilaculum from the fin and subsequent specializations originated not within the Chimaeriformes but among the cochliodonts. The origin of a pelvic girdle with a high dorsal and extended ventral process correlates with a more compressed body form and a fundamental change in ecomorphology.

Serum 11-ketotestosterone, 11-ketoandrostenedione and dihydroprogesterone concentrations in the bonnethead shark, Sphyrna tiburo.

Several steroid hormones, such as 11-ketotestosterone (11KT), 11-ketoandrostenedione ( 11KA) and 17alpha-hydroxy-20beta-dihydroprogesterone (DHP) have been found to be important in teleosts and have yet to be studied in any detail in elasmobranchs. 11KT and 11KA are androgens that have been found in teleosts to perform the functions that testosterone performs in many other animal groups. DHP is a progestin that recently has been shown to be important in a number of teleosts and has been demonstrated in Squalus acanthias and Scyliorhinus canicula testes. Analysis of sperm from 72 wild bonnet head sharks, Sphyrna tiburo, from southwest Florida indicates the presence of all three steroids in both males and females, juveniles and adults. Mature males had significantly more 11KT (P<0.001) than immature females and all males. There were significant differences in 11KA concentrations, but pairwise multiple comparison procedures failed to isolate any group as different. Mature females had the highest 11KA levels and immature females had the lowest 11KA levels, with all males being intermediate between the two female groups. Concentrations of the two androgens in mature males did not cycle concurrently with testosterone or dihydrotestosterone (DHT) and concentrations of DHP in mature females did not cycle concurrently with serum levels of progesterone. The significance of these values will be discussed.

Northern extent of the pupping grounds of the sandbar shark, Carcharhinus plumbeus, on the US east coast.

Historically, the sandbar shark, Carcharhinus plumbeus, pupping grounds extended along the US east coast to Great South Bay, Long Island, NY. Gill net and hook and line surveys were conducted in July and August, 1996, in coastal bays of New Jersey and New York. No sandbar sharks were caught in Great South Bay, Shinnecock Bay or Peconic Bay, NY, or in Barnegat Bay, NJ. Neonate sandbars captured in Great Bay, NJ, ranged in size from 42 to 52 cm fork length (47 to 62 cm TL). Most sandbars had fresh, open umbilical scars and 35% carried umbilical remains, indicating very recent birth. Our data suggest that the northern boundary of sandbar shark pupping grounds has receded approximately 125 km south to Great Bay, NJ.

Preliminary demographic analysis of the shortfin mako shark, Isurus oxyrinchus .

We have evaluated existing and added new life history information on the shortfin mako shark, Isurus oxyrinchus, including size frequencies, marginal increment analysis, tag-recapture growth rates, reproduction (see Mollet et al. AES abstract), and catch curves for use in a demographic analysis. We assume that the female mako shark lives – 25 years, has an instantaneous natural mortality coefficient (M) between 0.175 and 0.265 year^-1, matures at 4-6 years old, and has a two year reproductive cycle, a gestation period of ~12 months, and fecundities which increase with female size. From adjusted catch curves for females off southeastern Australia and based on two different mass-length equations, total instantaneous mortality coefficients (Z=F+M) were estimated to be 0.30 (s.e. 0.02) and 0.34 (s.e. 0.02). Our preliminary demographic analysis provided estimates of net reproductive rate (R₀) between 1.08-1.61, generation time (G) of 9.7-9.9 years, and instantaneous rate of population increase (r) of 0.048-0.0084 year^-1. These suggest that the mako shark could be vulnerable to both directed fishing and by-catch from other fisheries despite its relatively fast growth.

Reproductive parameters of the shortfin mako, Isurus oxyrinchus.

Litter data from 28 pregnant females, reproductive data from 47 mature non-pregnant females and 38 immature female shortfin makos Isurus oxyrinchus with a worldwide distribution were available. A logistic model maximum likelihood fit (N = 102) estimated 10%, 50%, and 90% of females to be mature at total length (TL) 2.59, 2.70, and 2.82 m, respectively. The gonadosomatic indices were 0.009% (s.e. 0.001), 0.21% (s.e. 0.01), and 1.9% (s.e. 0.7) for immature makos (n = 9), mature makos with inactive ovary (n = 41), and mature makos with active ovary (n = 3 only), respectively. Fecundity increased with the size of the mother (F = 0.57 TL^2.66(m), n =18, p = 0.016) and agreed with a model calculation. A TL-embryo vs. date regression (n 22, r = 0.72) predicted a gestation period of 10 months (s.e. ca. 0.75) and confirmed Spring parturition in both hemispheres. A combined temporal analysis of embryo size and gonadosomatic index indicated that the reproductive cycle lasts at least 2 years. A one year gestation period followed by a one year resting period is most likely.

Preliminary captive biology of the pelagic stingray, Dasyatis (Pteroplatytrygon) violacea.

Growth and feeding rates of 19 pelagic stingrays, Dasyatis (Pteroplaytrygon) violaceawere measured during 3 phases in 1995 and 1996. 1. Fifteen females were fed 3 times/week (mean 1.24% bodymass/day) in quarantine (T = 17.8 C) from march 1 to Oct. 18, 1995. Growth rates (mean 10.2 cm/yr, 3.1 kg/yr) and conversion factors (mean 9.3%) were seasonal. 2. During a transition period, interactions between pelagic stingrays and sunfish Mola mola were studied in the Open Bay Water exhibit (4600 m{+3}, T = 20 C). Daily feeding was introduced to minimize rays biting molas. 3. Four females and 2 males were fed daily (mean 2.5% bodymass/day) in quarantine (T = 20 C) from March 19 to Dec. 10, 1996. Females had larger growth rates (mean 19.5 cm/yr, 11.1 kg/yr) than males (mean 12.0 cm/yr, 3.1 kg/yr) and one female reached record size (83 cm diskwidth, 23 kg). Feeding and growth rates were again seasonal. A stillborn litter, an aborted 5 cm diskwidth embryo, an eggcase with 7 infertile eggs, an empty eggcase suggested sperm storage for over 2 year and likely mating in captivity.

Maternal-Embryonic Transfer of IgM via Eggs in Gingymostoma cirratum.

Immunoglobulin M (Ig M) is the chief circulating antibody in adult elasmobranchs. Although its presence has also been established in neonates and unborn pups, its origin is not conclusively known. There are two possibilities: de novo synthesis and maternal transfer. Maternal embryonic transfer of passive immunity via Ig M occurs in oviparous and viviparous teleosts. In viviparous elasmobranchs, placental transfer of IgM is questionable because the intervening collagenous egg envelope acts as a macromolecular sieve. Transfer of IgM has not been studied in aplacental vivparous elasmobranchs, oviparous species, or the eggs of either. Since IgM transfer and storage occurs in avian eggs, we hypothesized that the macrolecithal egg of elasmobranchs is also a likely vehicle for IgM storage and transfer. Ovaries and individual eggs of Gingymostoma cirratum were collected and analyzed for IgM. Eggs were freed of investing membranes and the yolk was processed using a chloroform/PEG procedure to isolate immunoglobulins. Gel electrophoresis of the Ig fraction revealed a protein banding pattern consistent with the molecular weights of IgM heavy and light chains. ELISA and Western blot assays indicated a strong cross-reactivity with antibodies against stingray IgM. We conclude that unfertilized eggs contain IgM transferred from the maternal serum during oogenesis.

Jaws meets Star Trek: the use of relative warps analysis int he study of shape-variation in the teeth of the white shark, Carcharondon carcharias.

The study of variation in shape has long been restricted to the use of either descriptive language or the analysis of linear measurements through multivariate statistics. Geometric morphometrics is a new technique that can capture shape-variation more completely than either of the previous techniques. Relative warps analysis, a type of geometric morphometrics, was used to analyze shape-variation with a population of fossil and modern teeth from the adult white shark, Carcharodon carcharias. Relative warps analysis successfully separates the categories of modern teeth in the upper jaw, but does not separate the lower jaw categories from the upper jaw categories very well. No difference was found between the three-million-year-old (MY) fossil teeth and the modern teeth, but the teeth from five million years ago are distinctly different. All categories of 5 MY teeth are narrower and have large terminal serrations at the base of one or both margins. The intermediate tooth is reversed in the 5 MY set, indicating a possible change in the morphology of the upper jaw.

Osmoregulation of the Atlantic Stingray (Dasyatis sabina) in the freshwater Lake Jessup of the St. Johns River, FL.

Dasyatis sabina is one of the few euryhaline elasmobranchs that can live and reproduce in fresh water (FW). To date, no lab studies have investigated the osmoregulation of such an elasmobranch in FW. The goals of this study were to describe the osmoregulation of D. sabina in the FW Lake Jessup of the St. Johns River, FL, and determine their ability to acclimate to sea water (SW). Plasma samples were collected from FW D.sabina captured in Lake Jessup and individuals acclimated to 100% SW in the lab. Analyses indicated that FW D. sabina hyper-osmoregulate with mean plasma Na⁺, Cl^–, K⁺, Ca²⁺, and urea concentrations of 208.96, 205.91, 5.37, 4.10, and 186.26 mmol/l, respectively. D. sabinasurvived the transition to 100% SW; they hypo-osmoregulate with mean plasma Na⁺, Cl^–, K⁺, Ca²⁺, and urea concentrations of 325.56, 306.26, 5.27, 5.55, and 325.79 mmol/l, respectively. Mean total plasma osmotic concentration increased from 608.80 mOsm/kg in FW to 949.81 mOsm/kg in 100% SW. These data suggest that D. sabina of Lake Jessup have not lost their ability to retain urea and are truly euryhaline elasmobranchs.

Correlates of serum hormone concentrations and reproductive events throughout the year in captive and wild caught clearnose skates, Raja eglanteria.

This long term investigation of serum steroid reproductive hormones in the clearnose skate,Raja eglanteria, demonstrates interesting correlations between changing hormonal concentrations and reproductive events. Animals were sampled both individually (78 females and 20 males) and serially (15 females). Serum estradiol was detected throughout the year with significant elevations occurring during October and November when the ovarian follicles begin to develop and January and February when maximum mating occurs and egg laying begins. During this latter period similar, even more pronounced elevations occurred in serum testosterone and dihydrotestosterone concentrations. Subdividing the egg laying process into 5 stages defined by the position of palpable eggs revealed that 17 Beta estradiol levels were highest when the eggs were in the nidamental gland (stage 2) or uterus (stage 3), and testosterone and dihydrotestosterone concentrations were maximal when eggs were in the uterus or cloaca (stage 4). Conversely, progesterone levels were significantly elevated immediately after the egg laying (stage 5). These results strongly implicate hormonal control over the egg laying process, including observed periodic synchronies between estrogens and androgens. Initial studies to assess relative hormone concentrations and syntheses along the reproductive tract of females and within reproductively-related secretions of males have begun to provide information on sites of hormone production for this species.

Group I introns (“spintrons”) are present in shark nuclear ribosomal DNA internal transcribed spacers.

Group I introns are a family of sequence elements that interrupt genes, and are characterized by conserved secondary structure and short sequence regions essential for splicing. Although common in some lower eukaryotes, group I introns have thus far been conspicuously absent in metazoans. We report here the first observation of group I introns from animal nuclear genomes. These introns are present in diverse shark lineages, and are novel also because they interrupt a non-genic region (the ribosomal DNA internal transcribed spacer 2), rather than a genic region as in other organisms. In light of this unusual location, we refer to these elements as “spintrons” (for spacer introns) to reflect a previously undocumented spacer insertion. The presence of spintrons in the ITS2 likely has major implications for currently known mechanisms of precursor ribosomal RNA transcript processing. The spintrons in the nine shark species (representing four orders) examined here share a common insertion site in the ITS2. This observation, together with results from phylogenetic analyses of the spintron and ITS2 spacer sequences, suggests that a spintron was present in the common ancestor of sharks, and has likely been inherited vertically over at least 400 million years of shark evolution.

Some results on the blue shark (Prionae glauca) in Azorean waters from a research cruise by the R/V Arquipélago.

This paper summarizes some results on the blue shark based on data from a large pelagics cruise survey carried out with the R/V Arquipélago in Azorean waters during the Autumn of 1993 and the Spring of 1994. Blue shark CPUE data for the Azores, by geographical area and season, and length frequency distributions are presented. CPUE ranged from 0.2 to 36.2 blue sharks/100 hooks, with the highest values recorded for the oceanic area during the spring season. A strong increase in CPUE was detected from the autumn to the spring season. Length frequency samples collected during the autumn and spring seasons revealed a complex seasonal segregation pattern for the blue shark in Azorean waters. While the autumn sample showed a high incidence of juveniles and sub-adults, in approximately equal proportions, and an equal sex-ratio, the spring sample was clearly dominated by the juvenile segment and by females. This information suggests that the area around the Azores represents an important nursery ground for blue sharks in the Atlantic during the spring season. The implications of such a nursery area is discussed within the global Atlantic context.

Results of a tagging study on juvenile dusky sharks (Carcharhinus obscurus) in south-western Australia.

Juvenile dusky sharks, Carcharhinus obscurus, are an important component of the shark fishery in south-western Australia. to investigate the dynamics of juvenile C. obscurus in relation to the fishery, a tagging study was undertaken. 2199 juvenile C. obscurus, mostly 0+ individuals, were tagged with Jumbo Rototags from commercial gillnet vessels between March 1994 and June 1996. 517 of these animals were double tagged with metal headed dart tags. At the 1st of March 1997, 391 recaptures had been reported, most by commercial gillnet fishers, but also commercial line fishers and recreational fishers. Release and recapture locations show that juvenile C. obscurus can move long distances, with 23 individuals moving over 500 km. The majority of recaptures, however, were within 100 km of the release point. Movement patterns of juvenile C. obscurus are discussed. Estimates of growth rates of juvenile C. obscurus, based on the size at release and recapture, were 8.9 cm year^-1. Analysis of the return of double tagged individuals indicated that the tag shedding rate of Jumbo Rototags was 0.0385 year^-1 and for metal headed dart tags 0.346 year^-1. Tag recapture rates by commercial gillnet fishers, corrected for tag log and non-reporting, indicated that they catch between 20 and 28% of C. obscurus born each year.

Husbandry observations and treatment of fungal infection in tiger shark, Galeocerdo cuvier.

Tiger sharks, Galeocerdo cuvier, are rarely displayed in public aquariums, and little is known about their behavior and health in the captive environment. Omaha’s Henry Doorly Zoo displayed this species from March 15, 1995 to August 24, 1996. The tiger shark arrived at an estimated 35 kg body weight, and was about 152 cm TL. The initial diet averaged 3.4 kg per week. The body weight increased steadily, and at death the shark was estimated at 100 kg and measured 241 cm TL. At the peak of its appetite the shark was eating 7.6 kg and her total weight was probably much higher. Behaviorally the shark swam the perimeter of the exhibit, which led to skin abrasion problems. Most of the abrasions were successfully treated with enrofloxacin, but a secondary fungal infection was diagnosed and treated with ketaconazol. The ketaconazol treatment appeared to improve the fungal infection externally. At the time of the shark’s decline a possible Vibrio infection was suspected due to equilibrium problems and was treated with Florfenicol. Necropsy results showed sever multifocal ulcerative gastritis and large numbers of fungal hyphae. The purpose of this presentation is to exchange ideas, and share information about the captive care of Galeocerdo cuvier.

A summary of the freezing, thawing, preservation, and display methodology on a large Megamouth shark, Megachasma petagios

Freezing, thawing, preservation, and display methodology of a large megamouth shark,Megachasma palagios, are summarized. The specimen was frozen (-30 C) from the evening of 29 November 1994 to 1 February 1995. Thawing required nine days, from 1 to 9 February 1995. Half-strength sea-water, with its temperature was held at 3 C by circulating water, was used during the thawing process. After dissection on 9 February 1995, the abdominal cavity was stuffed with blankets and stitched closed to restore the shark’s original profile. The specimen was fixed for 45 days in a tank that contained formalin at a concentration of 20%. The size of the acrylic display tank is 500cm X 150 cm X 135 cm. The liquid preservative within the acrylic display tank darkened slightly after about three months.

Molecular aspects of elasmobranch steroid synthesis.

Steroid hormones control a number of physiological processes including osmotic regulation, metabolism, growth, immunity and reproduction. The adrenal and gonadal steroids produced by elasmobranchs were identified many years ago. However, the processes that control steroidogenesis only recently have been examined at the molecular level. The cDNAs encoding steroidogenic enzymes (cytochrome P450 17-hydoxylase, cholesterol side chain cleavage, and 3 beta-hydroxysteroid dehydrogenase [HSD]) have been isolated from two sharks and a stingray Squalus acanthias, Carcharhinus libatus, and Dasyatis americanus). The 17-hydroxylase from the testis of the spiny dogfish shark has been functionally expressed yeast. The enzymology characteristics of cytochrome P450 21-hydroxylase and 3 beta-HSD have been described in the adrenal of the blacktip shark, C. limbatus. The hormonal control of tereoidogenesis in the adrenal of D. sabina has also been examined. Our studies have demonstrated that steroidogenic enzymes isolated from elasmobranch adrenal or gonadal tissue share a relatively high degree of sequence homology and functional characteristics with other vertebrates in spite of their evolutionary distance.

Localization of parathyroid hormone-related protein (PTHrP) in bony and cartilaginous fish.

PTHrP is an onco-fetal hormone in mammals and acts on bone and kidney to elevate plasma calcium levels. Normal human kidney and skin contain PTHrP, indicating it probably has paracrine roles. Antibodies to human PTHrP were used to detect PTHrP in circulation and tissues in sea bream Sparrus aurata (Danks et al., 1993) and in dogfish Scyliorhinus canicula (Ingleton et al., 1995). These studies suggest that PTHrP might be a “classical” hormone in fish. In the present study tissues from a range of fish were examined for PTHrP distribution to elucidate possible roles in this group of animals. Samples from marine elasmobranchs through to freshwater bony fish were investigated using antibodies to human PTHrP in immunohistochemistry and a riboprobe to a conserved region of the mammalian gene for in situ hybridization. In all fish examined PTHrP protein and mRNA were found in skin and kidney, similar to higher vertebrates. In elasmobranchs, PTHrP was localized to rectal gland, gills, vertebrae and brain. A similar pattern was observed in rainbow trout. The results indicated that the PTHrP is widespread in lower vertebrates and that there is homology between the PTHrP molecules found in man and fish.

Ratfish romance at the Monterey Bay Aquarium

Mating observations of the Pacific ratfish, Hydrolagus collieri, were recorded on two separate occasions. The positioning of the male ratfish in relation to the female ratfish and the use of the cephalic and pelvic claspers were videotaped and photographed. Records indicate egg capsules are deposited throughout the year but viability of egg capsules appears to vary.

Reproductive biology of the horn shark, Heterodontus francisci, in Mexican waters.

The horn shark, Heterodontus francisci is an abundant species in the Pacific coast of Baja California Peninsula, which have no commercial value. A study on its biology was carried out at the San Ignacio Lagoon between August 1992 and June 1994. The sharks were caught with gill nets. The months with the largest abundances were April to June, in this period males dominated the sex ratio near 2:1. From August to February, only immature organisms were caught, but in late spring and early summer, mature were more abundant. The maximum size found in both males and females were 78 cm TL. In males the maturiy began at 50 cm TL, and is reached at 55-60 cm; in April and May, all males carried semen. Based on oocyte diameter, nidamental gland and egg case in uterus, the maturity size for females is at 63 cm TL. The maximum number of oocytes seen in females were 10 to 12. In conclusion, tile horn shark is an oviparous species that enters San Ignacio Lagoon in April, for mating and egg case formation, and stays until June or July, when males and females migrate out. Details on its embryonic development remain still largely unknown.

Regulation of elasmobranch color change.

An evaluation of the current state-of-the-art of pigment cell receptors and mechanisms of cell signaling in the elasmobranch fish will be presented. The studies regarding regulaton of pigment cell function in elasmobranchs are very scarce. So far, the following aspects have been investigated: 1) a variety of neural and hormonal agents (MCH, catecholamines and melatonin) failed to induce pigment granule translocations; 2) Both acetylated and desacetylated forms of alpha-MSH seem to be secreted by pars intermedia, but the former not only prevails, but is also more potent in in vitro and in vivo skin bioassays, suggesting that it is the physiological factor regulating elasmobranch color changes; 3) Immunoreactivity to MSH and MCH has been found in various hypothalmic regions and thalamic and mesencephalic fibers of 3 species, suggesting that they may also play a role as central neuromodulators or neurotransmitters; 4) the U light is an important mitogenic and melanogenic agent for mammalian melanocytes, and its physiological role has also been determined in the juveniles of the elasmobranch Sphyrna lewini, which shows an increase in the skin melanin content in response to increase in solar radiation.

Thyroid function and reproductive cycle in the Atlantic stingray, Dasyatis sabina.

This study carried out to examine the role of the thyroid gland in the control of reproduction in the viviparous Atlantic stingray, Dasyatis sabina. Thyroid activity of individuals in different reproductive states was assessed both by histological and ultrastructural examination of the gland, and by analysis of circulating levels of thyroid hormones. Stingray follicular cells possess characteristic features such as a single apical cilium, and a well-developed endoplasmic reticulum. They vary in size and shape, according to the activity of the gland. The average levels of serum thyroid hormones are 1.6 µg/100ml for total thyroxine (T4), and 2 ng/ml for total triiodothyronine (T3). Immature individuals have resting glands and low levels of circulating thyroid hormones. Females undergoing oogenesis have low serum hormone levels and moderately active glands. High thyroid gland activity, and high levels of circulating thyroid hormones is seen in females, from ovulation until mid-gestation. Hormonal levels and gland activity decline during the second half of gestation and in post-partum females. The decline in activity of the maternal gland may correspond to the beginning of autonomous function of the fetal thyroid gland, i.e. the time at which the maternal supply of thyroid hormones is no longer needed by the embryo.

Preliminary investigation of cell proliferation and programmed cell death in elasmobranch thymus.

Elasmobranchs represent the earliest phylogenetic appearance of a clearly defined thymus. Cell proliferation and programmed cell death, or apoptosis, are critical steps in shaping the immune repertoire in higher vertebrate thymi. Using the DNA analog, bromodeoxyuridine, cells undergoing DNA synthesis were found throughout the thymus of two species of elasmobranch fish, the clearnose skate (Raja eglanteria ) and the nurse shark (Ginglymostoma cirratum). The majority of proliferative activity was found in thymic cortex, as it is in higher vertebrates. Similarly, using a method to detect DNA strand breaks, apoptosis was observed throughout the thymus, but appeared to be more prevalent in the thymic cortex. Additionally, both proliferating and apoptotic cells were found associated with cells which appear to be phylogenetic counterparts of specialized cells called thymic nurse cells (TNC) recently described in higher vertebrate thymi. TNC may be involved with removal of apoptotic cells from the thymus, as well as with proliferation and maturation of thymocytes. Understanding the function and significance of the thymus and TNC in a phylogenetically primitive vertebrate contributes to understanding the evolution of lymphocytes and lymphocyte maturation processes in higher vertebrate immune systems. Supported in part by a grant to CJW by the National Science Foundation (MCB95-09105).

Lipid Composition of deep-sea sharks from the Chatham Rise, New Zealand

Deep-sea sharks approach neutral buoyancy by means of a large, oily liver that contains large amounts of low-density lipids, primarily squalene and diacyl glycerol ether (DAGE). As an animal increases in size and matures sexually, many biochemical changes take place within that animal. It was hypothesized that maintenance of neutral buoyancy in deep-sea sharks involves fine-scale adjustments in the chemical composition of liver oil as individuals grow and develop. To test this hypothesis the lipid composition of liver oil of individuals of different sizes and sex for several species of deep-sea sharks collected from the Chatham Rise, New Zealand were compared. The composition of liver oil varied within, and among species. Several species contained large amounts of squalene and DAGE, whereas only traces of these lipids were present in other species. There was an inverse relationship between the amount of squalene and DAGE in liver oil, and squalene content tended to decrease as sharks increased in size. The species with liver lipid characteristics most desirable for commercial exploitation were not abundant on the Chatham Rise. Maintenance of neutral buoyancy in deep-sea sharks is a dynamic process that involves changes in the composition of low-delisity liver lipids as the sharks increase in size.

Feeding Mechanics in the Bonnethead Shark, Sphyrna tiburo.

This kinematics and motor activity during feeding in the bonnethead shark Sphyrna tiburois quantified using anatomy, video and electromyography. Sphyrna tiburo exhibits tropotactic behavior while searching for potential prey. Prey capture is by ram feeding, supported by a ram-suction index of 0.38, in which the mouth is opened wide and the prey is grasped by the lower jaw. Hypotheses relating cranial movements to muscle activity are supported: the coracomandibuaris muscle is active concomitant with lower jaw depression; the epaxialis muscle is active concurrent with cranial elevation; the quadratomandibularis dorsal muscle is active concurrent with lower jaw elevation; the preorbitalis ventral and levator palatoquqadrati muscles are active concombitant with upper jaw protrusion; and the levantor hyomandibularis muscle is active concurrent with jaw retraction. The basic feeding mechanism in S. tiburo is conserved in diverse shark taxa. A relative slowing of movements with increasing body size occurred in some jaw movements, but the relative pattern remained the same. Molariform teeth in S. tiburo may be an adaptation for crushing hard shelled prey. Transport of the prey from the jaw to the esophagus is by suction. The basic feeding sequence in conserved in sharks, rays, bony fishes, aquatic salamanders, and aquatic turtles.

Development of the lymphomyeloid system in the Clearnose skate, Raja eglanteria.

Clearnose skate embryos were fixed in 10% formalin in elasmobranch-ringers at regular intervals during their 12 week developmental period. Preserved skates were processed by routine histological methods, embedded in either paraffin wax or methacrylate resin, sectioned at 2-6 microns, and stained with hematoxylin and eosin. Organogenesis was examined for the major components of the immune system, viz., spleen, thymus, leydig, and epigonal. The skate thymus is bilaterally paired, dorsomedial to the gills. Each lobe is comprised of 4 primordia formed from epithelia] evaginations from each of the bronchial pouches 2-5. The thymus is the first lymphoid organ to appear and is nearly contiguous at 4 weeks. Cortical and medullary zones as well as lobuies are pronounced after 6 weeks. The spleen is present as a swelling in the dorsal mesogastrium adjacent to the stomach by week 4. The spleen continues to enlarge with little or no distinction between red and white pulp until after hatching. The leydig is found in the dorsal and ventral submucosa of the esophagus by week 6. The epigonal is the last immune organ to develop. Granulocytes appear within the genital ridge by week 8.

Behavioral response of sharks to electric stimulation

The behavioral responses of four species of sharks, Carcharhinus falcifortnis (60 cm TL), Triaenodon obesus (119 cm TL), Galeocerdo cuvier (218 cm TL), andStegostoma fasciatum (220 cm TL), to electric stimulation were studied. The captive sharks swam in a tank (7 m in diameter). The source unit consisted of a signal generator and a power amplifier. The signal generator produced the wave form, frequency, and voltage. Electrodes were 5-cm x 10-cm copper plates, separated by a distance of 3.5 m. A 60-Hz sine wave and DC pulse electric fields were chosen. The 60-Hz sine wave was 10 V (r.m.s) and the DC pulse period was either 1 sec or 5 sec (duty ratio is 10%). All sharks swam close to the sides of the tank when the signal generator was off. When the 60-Hz sine wave and DC pulse electric fields were being produced, two species, C. falciformis and T. obesus, immediately turned round. Many turns of the sharks were associated with the DC pulse electric fields. Conversely, G. cuvier and S. fasciatum did not change thier swimming patterns when the signal generator was on. Hence, the behavioral response patterns were different among the species.