1998 AES Annual Meeting Abstracts

Steroid hormones and uterine gland formation in the Atlantic stingray, Dasyatis sabina.

Testosterone and 17-ß estradiol concentrations have been correlated with ovulation, embryonic nutrition and parturition in various elasmobranch species. In this study, we test the hypothesis that variations in serum concentrations of sex steroid hormones correlate with reproductive changes occurring during gestation in the Atlantic stingray, Dasyatis sabina. To test this hypothesis, blood and uterine samples were collected from rays during the non-reproductive and reproductive seasons. Histological analysis revealed that the uterus became glandular and highly vascular early in the reproductive season, when females were carrying uterine encapsulated eggs. During early gestation, serum estradiol concentrations were low, averaging 140 + 84 pg/ml. However, by mid-gestation, serum concentrations were significantly elevated to 8293 + 4840 pg/ml. High estrogen concentrations during mid- to late-gestation could be correlated with later gestational events, not with gland formation and the onset of histotroph production. Testosterone concentrations varied significantly through the cycle. Serum concentrations increased to 279 + 43 pg/ml during mid-gestation.

Reproductive strategy of a freshwater stingray Potamotrygon sp. from the mid-Rio Negro Basin, Amazonas, Brazil. 

An undescribed species of South American stingray, Potamotrygon, local name “cururu,” is endemic to the middle Rio Negro Basin. The reproductive biology, migration, and the impact of its fishery have been investigated. Potamotrygon sp. reach a maximum size of 300 mm disk width. It is a relatively small species for South American freshwater stingray. They live in shallow floodplain and river margin with sandy bottom and leaf litter. The water is usually warm, acidic and low in dissolved oxygen. The reproductive cycle follows the river pulse, flood and drought, of the basin. Beginning in July, when water level has peaked and started to descend, males and females are aggregated in different areas; spermatogenesis starts earlier than vitellogenesis. After copulation in August, ovulation may start three weeks later. The gestation period is about three months and new born start to appear in November. The embryos are nourished by yolk sac and trophonemata in the uterus. New born stay on top of female for 3-4 days before they assume an independent life. During the reproductive season of 1996-97, females had one gestation period. However, during the current El Niño year 1997-98, an earlier and prolonged drought has occurred in the region, females have a second gestation.

Electroreception: Mechanisms for detecting weak signals in noise

The elasmobranch electrosense is known for its extraordinary sensitivity which is necessary for detecting the feeble, behaviorally-relevant electric fields in the sea. But a cost of this sensitivity is vulnerability to electrical noise including that produced by the fish’s own behaviors. Behavioral, morphological and physiological specializations are all necessary for extracting the important weak signals from noise. Each of these types of specializations will be discussed and recent work on the physiological mechanisms for extracting weak signals from noise will be reviewed. Physiological adaptations include receptors that can operate over an extended voltage range without loss of sensitivity, simple subtractive circuits in the hindbrain and sophisticated adaptive filter mechanisms that involve the development of an expectation of the noise typically associated with each of the fish’s different behaviors. The end result of these mechanisms is that all traces of the noise can be eliminated in the hindbrain without any loss of sensitivity to the signals important for behavior.

History and management of the dogfish fishery of British Columbia, Canada.

The fishery for dogfish (Squalus acanthias) of British Columbia is one of the oldest shark fisheries in the world. This paper describes the main features in the long evolution of this fishery. It also analyses the current situation and the management system of the fishery. Presently, this is a small fishery characterized by strong market limitations. Although there is a reasonably modern management system for the fishery, the apparent success to keep the dogfish stocks at healthy levels for the major part of the 125+ years of the fishery is more a product of the lack of strong demand for dogfish which has offered a fortuitous protection to the stock. Some suggestions for improvements to the stock assessment and possible ways to develop the fishery are given. Keywords: Squalus acanthias, fisheries management, British Columbia.

Corneal pathology associated with the attachment of Ommatokoita elongata (Copepoda: Lernaepodidae) (Grant) to the cornea of Greenland sharks (Somniosus microcephalus).

Eyes from six Greenland sharks, Somniosus microcephalus (Bloch and Schneider), infected with the parasitic copepod Ommatokoita elongata (Grant) were collected Arctic waters of Victor Bay, Northwest Territories, for study. Transformed adult female copepods, one per eye, were firmly attached to the corneas by an anchoring structure (i.e., the bulla), and each bulla was associated with an opaque area on the cornea. In addition to opacities associated with copepods at the time of collection, there were several randomly distributed, small, round to irregular, full-thickness corneal opacities which were not associated with copepods. The sclera at the limbus of infected eyes was thickened at the radius corresponding to the feeding range of the copepod. Histologically, corneal epithelial ulceration and heterophilic keratitis, disruption, mineralization, and detachment of Bowman’s membrane, thinning, disorganization, mineralization, and fibrosis of the corneal substantia propria, and focal thinning of Descement’s membrane were observed. Mild heterophilic and mononuclear scleritis at the limbus that was continuous with anterior uveitis was also present. Based on our observations, we conclude that parasitism by O. elongata could lead to severe visual impairment in Greenland sharks. However, our current research is directed at understanding the physiology of the normal and altered visual apparatus in this species. We are examining retinal enzymes and analyzing the photopigment prosthetic group. In addition we are investigating alterations in the density and localization of glutamate and GABA transporters in the M=FCller cells. The results of this work could be used to objectively quantify the extent of visual impairment caused by O. elongata in Greenland sharks.

Odontological variations in the dentition of the manta ray (Manta birostris) 

The study of Neogene batoids requires an understanding of extant species. An in-depth understanding of the ondontological characteristics of the living fish is needed because fossil material is largely limited to teeth and dermal denticles. Although cursory descriptions of dentitions are often provided, these descriptions usually lack the detail required for paleontological purposes. I initiated a study of a Manta birostris dentition in an effort to identify manta-like teeth from the Miocene of North Carolina. These teeth, which are commonly referred to as “simple peg-like”, were more variable then anticipated and clearly reflect their mobulid origin.

A comparison of a stage-based model and a yield per recruit model of the sandbar shark (Carcharhinus plumbeus). 

A stage-based model of sandbar shark populations indicates that fishing mortality (F) needs to be reduced to 0.08 to ensure sustainability of the population. This model assumes the natural mortality (M) is 0.10. However, stage-based models do not consider the effect size limits may have on the fishery. We have used a yield per recruit (YPR) analysis to examine the effects of adopting different size limits in the fishery. We used various growth parameter estimates, an age of recruitment of 1, and M = 0.10. Based on estimates from Casey et. al (1985), peak YPR occurs at a combination of F = 0.40 and an age of first capture of 10 years or approximately 144 cm fork length (fl). When growth parameter estimates from Casey and Natanson (1992) are used, peak YPR occurs at a combination of F = 0.30 and an age of first capture of 10 years or approximately 99 cm fl. Maximum YPR for F = 0.08, predicted by the stage-based model, is approximately 80% of the peak YPRs found above, and occur at an age of first capture of approximately 6 years. With growth parameters estimated for 1991 to 1992 from Sminkey and Musick (1995), peak YPR occurs at an F = 0.45 and an age of first capture of 9 years or approximately 124 cm fl. In this case, maximum YPR for F = 0.08 is approximately 75% of the peak YPR estimated and occurs at an age of first capture of approximately 5 years. These results suggest that in order to have a stable population, YPR for each set of growth parameter estimates must be 20 to 25% smaller than the peak YPR.

Tooth replacement rate of the Great White Shark, Carcharodon carcharias (Linnaeus, 1758)

Analysis of 31 jaws of Carcharodon carcharias, from specimens ranging in total length from 143.5 to 460.9 cm, finds a range in tooth replacement rate of the Second Lateral tooth family of (Upper/Lower) 106.24/113.59 days for young individuals to 225.90/242.18 days for old individuals using the Strasburg Plot Method. The Second Lateral tooth family of the upper and lower jaws gives the best estimates of tooth replacement rate. Upper and lower jaws demonstrate fluctuating asymmetry within the number of tooth positions. The range in dental formulae of the upper/lower jaw for this sample is 11 to 15 – 0 – 12 to 14 / 11 to 16 – 0 – 11 to 15. One male (NOAA-NMFS Tag #610, TL 149.5 cm) taken off New Jersey in the Northwest Atlantic, has a very minute parasymphysial tooth in the upper right jaw. This is the first report of a parasymphysial tooth present in a white shark and is considered here as an atavistic character. Using the tooth replacement rate of 106.24 days/tooth, and previous reports of near term white shark embryos with 3 to 4 full tooth sets present in their alimentary canals, an estimate of when tooth replacement begins prior to parturition and therefore a minimum estimate of gestation period for the white shark can be calculated as 425 days. KEYWORDS: Carcharodon carcharias, tooth replacement rate, gestation period, fluctuating asymmetry, parasymphysial tooth, dental formulae

Tapeworms as indicators of elasmobranch feeding biology

Tapeworms are potentially valuable indicators of elasmobranch feeding biology because their life cycles require more than one host species and transmission between these host species is accomplished through predation. Thus, tapeworms enter their elasmobranch hosts when the intermediate hosts in which they reside as larvae are consumed by elasmobranchs. The lack of life cycle data and lack of information on degree of specificity for their final intermediate hosts currently limits the specific predictive value of tapeworms. However, some generalizations can be made from the complete tapeworm assemblage observed in a host. Inconsistencies in the tapeworm assemblages of related elasmobranch species can provide indirect evidence of differences in food habit. For example, the tapeworms of megamouth are fully consistent with this shark’s status as a filter feeder rather than an apex predator. Changes in the tapeworm fauna of a host species over time may reflect age related changes in diet. For example, the differences in the tapeworm fauna between small and large individuals of the Atlantic nurse shark may be indicative of a shift in food habit. Depending on their specificity for their intermediate hosts, tapeworms may act as indicators of specific prey species consumed by a host species or individuals.

Estimates of daily ration and a bioenergetic model for the blacknose shark, Carcharhinus acronotus. 

Daily ration estimates and bioenergetic models for blacknose sharks, Carcharhinus acronotus, were developed from laboratory experiments on metabolism and growth at 28″2.0°C. Size-specific metabolic rates were determined by closed-system respirometry and growth estimated through sharks held in captivity. Daily ration was estimated for sharks 0.5-0.8 kg, 1.5 kg, and 3.5 kg using the equation of Winberg (1956). Daily ration (%body weight/day) decreased with body size and was estimated as 1.56 for smallest sharks and 0.87 for largest sharks based on a diet of menhaden, Brevoortia spp. General energy budgets were constructed for each size class. No estimation of reproductive investment was made because all individuals were determined to be immature. Routine metabolism generally accounted for the largest percentage of the energy budget but differed among size classes. Metabolism increased with body size from 60% of the energy budget in small sharks (0.5-0.8 kg) to 71% for the largest sharks. In contrast, growth of somatic tissue was highest in small sharks (mean=9.9%) but was 1.5% for the larger sharks.

Mating, Gestation, and Birth in Nurse Sharks (Ginglymostoma cirratum): The Complete Story. 

Shark mating activities were filmed in the wild and females recorded as participants in the June mating events were subsequently captured. Each shark was examined in the field using ultrasonography to determine the extent of the presence of eggs, and two animals were selected from the reproductively active population and transferred to holding facilities at Sea World of Florida (Orlando). Serial blood samples were taken from both animals during the captive period. One animal was examined monthly using ultrasound and, in August and October, by intrauterine endoscopy to assess the progress of the presumed pregnancy. The endoscopic procedures verified the presence of numerous eggs and revealed the appearance of young that had emerged from egg cases. Ultrasonic imagery was used to further confirm the presence of hatchlings. Both animals eventually carried young to term. The first births occurred after 3.5 months, and these earliest births occurred with remnants of the yolk sac in place. The longest surviving offspring was born at the end of October, approximately 4.5 months following observations of mating in the field. This time frame differs from previous estimates of six months that were based solely on observations from necropsy. A total of 15 offspring were born, five from one animal and ten from the second animal. Only one newborn survived. Both of the females and the surviving offspring were tagged for return to the site of capture. The value and restrictions of the evaluation methodology and the limitations of the capture and captive elements are discussed.

Seasonal Habitat Use of the Flower Garden Banks National Marine Sanctuary by Pelagic Elasmobranchs 

The Flower Garden Banks National Marine Sanctuary consists of three topographic highs in the northwestern Gulf of Mexico, that support the northernmost coral reefs on the North American continental shelf. These banks are seasonally inhabitated by a variety of pelagic elasmobranchs, which often occur in considerable numbers. To date, 20 elasmobranch species have been reported or recorded in the Sanctuary. Seasonal occurrence, size, and social organization will be presented for several of the pelagic elasmobranchs known to frequent the Sanctuary.

EXPERIMENTAL HOMING IN JUVENILE LEMON SHARKS, Negaprion brevirostris, AT BIMINI, BAHAMAS 

This study represents the first experimental trials on an elasmobranch’s ability to return home from an unfamiliar area. Ten juvenile lemon sharks (66.0 to 96.0 cm total lengths) were tagged with ultrasonic transmitters and their home ranges determined over a minimum of 3 days of tracking. Thereafter they were recaptured and experimentally displaced 4 km off shore, south of the island. From late October 1997 to February 1998, seven displacements during daylight and three displacements at night were performed. Sharks were tracked for between 2 and 14 hours, and in all ten cases successfully returned to their home ranges. The behavioral pattern of the sharks at the time of release was characterized by circling and vertical migrations suggesting that they were attempting to orient to sensory cues in a way similar to homing pigeons. Further, sharks released at night appeared to change course to a more direct route home at sunrise, suggesting that visual cues may play an important role in the final stages of homing. Therefore, we are testing the hypothesis that sharks are able to use the position of the sun as a cue for orientation. Finally, we are carefully documenting the behavior of sharks at the time of release to give insight into possible mechanisms of orientation. Supported by the Florida State Department of Education with a grant to SHG.

Standardized diet compositions and trophic levels of sharks. 

Sharks are marine consumers believed to occupy top positions in marine food webs. But surprisingly few quantitative estimates of trophic levels (TL) exist for this group. With the hope to better define the ecological role of sharks in marine communities, this paper presents standardized diet compositions and trophic levels for a suite of species. Dietary compositions were calculated from published quantitative studies using a weighted average index. TL values of the eleven food types used to characterize the diet were obtained from published accounts and used to calculate fractional trophic levels for 151 species representing seven orders and 21 families. Sharks as a group are tertiary consumers (TL>4), and significant differences were found among six orders compared, attributable mainly to differences between orectolobiformes and all other orders. Among four families of carcharhiniform sharks, carcharhinids had significantly higher TL than triakids and scyliorhinids, but not sphyrnids. When compared to TL for other top predators of marine communities obtained from the literature, mean TL for sharks was significantly higher than for seabirds, but not for marine mammals. Trophic level and body size were positively correlated, with the fit increasing when the three predominantly planktivorous species were omitted and when considering carcharhinids only.

Sharks associated with the gulf menhaden Brevoortia patronus fishery and their relavance to shark populations of the Atlantic and Gulf of Mexico 

We describe the shark bycatch in the U.S. gulf menhaden fishery their species composition, fates, distribution and estimate the annual number of sharks caught by the fishery. Ten species of sharks were identified, with blacktip sharks Carcharhinus limbatus accounting for 50% of those observed. Approximately 75% of the sharks encountered died, 12% were released disoriented and 8% were released healthy. Using loglinear and logit models we determined spatial and temporal patterns in the shark bycatch. Contrasts revealed the odds of observing a fishing set with shark bycatch was significantly greater in June-August than September-October. The odds of observing shark bycatch during April-May was also significantly different from September-October. However, these differences were only apparent east of 93 degrees W (central Louisiana). For the 1994 and 1995 fishing seasons we estimated an annual take of approximately 30,000 sharks. Stomach analyses on sharks indicated that the menhaden schools were functioning as a foraging base for those sharks captured. While detailed age and growth information were not collected, comparisons to length distributions in the literature indicated that the fishery appears to be impacting the summer nursery grounds of sharks in the northern Gulf of Mexico.

Dietary changes associated with life history and sex for the sevengill shark: implications for intraspecific competition and resource partitioning.

Dietary changes associated with life history stage and sex for the sevengill shark are analysized and discussed. Data collected over a 15 year period were used to analyze the sevengill shark’s dietary habits. The size categories were grouped so as to approximate this shark’s life history stage; juvenile, adolescent, and adult. In addition, the diet of male and female sharks of each life history stage was compared to note any differences between the sexes. Dietary changes associated with an elasmobranchs life history and sexual stage of development may explain how food resources within a given territory are partitioned such that competiton between conspecifics at different stages of life may be reduced. A reduction in competition between conspecifics may have evolved to ensure that resource partitioning and cannibalism would be reduced between conspecifics at different stages of life. Thus increasing survivorship for the species during the critical early stages of life. The implications of dietary changes as related to life history and sexual stage of development may be complex and far reaching, yet may play a critical role in the success of elasmobranchs as a group.

The feeding ecology of elasmobranch fishes from the British Isles. 

The diets of inshore elasmobranchs from the waters of the British Isles are reviewed from historical and contemporary data. The feeding habits of ten of these species (Scyliorhinus canicula, Scyliorhinus stellaris, Mustelus asterias, Galeorhinus galeus, Squatina squatina, Raja brachyura, R.clavata, R.microocellata, R.montagui and R.naevus) are discussed in relation to their comparative feeding ecology, their distributions in the Irish Sea and English Channel, the demersal faunal assemblages to which they belong and their dentition.

Characterization of blue shark (P. glauca) mitochondrial genome control region sequences for population genetic studies. 

Blue sharks are highly vagile elasmobranchs with a circumglobal temperate and tropical distribution. This species displays complex reproductive and migratory behavior, making it difficult to realize a clear picture of genetic stock structure. We report here our examination of the utility of mitochondrial (mt) DNA control region sequences for assessing blue shark genetic structure on a global scale. Complete control region (1069 bp in size) sequences were obtained from 16 blue shark individuals collected from 5 globally distributed sites. Contrary to the case in most vertebrates, this locus is remarkably conserved in blue sharks. The 11 haplotypes observed differed from each other by 5 or less single nucleotide substitutions or indels over the entire control region. Most of the genetic variation (8 of 12 variable sites) was restricted to the 350 bp region adjacent to the tRNA-proline gene, with no variation observed in the central 400 bp section of this locus. Phylogenetic analysis revealed no indication of geographic population structuring. We infer from these data that either the blue shark mt control region may be too conserved to be useful for population genetic studies, or that dispersal over a global scale is occurring, or has occurred in the recent past. KEY WORDS: Blue shark, Prionace glauca, genetic variation, mitochondrial DNA, control region.

Modulation of the feeding behavior of the horn shark, Heterodontus francisci

Many fishes are capable of modulating prey capture behavior according to prey size or elusivity. The physical attributes of the prey appear to affect attack behavior, but factors such as position or location of prey may also be important. This study tests the hypothesis that capture behavior can be modulated according to prey accessibility. Using a high-speed video kinematic analysis, prey capture events are examined for the horn shark,Heterodontus francisci. Each individual encounters three feeding situations: (1) squid pieces resting freely on a platform; (2) attached to a platform; and (3) fitted snugly in a tube. Using suction behavior, H. francisci successfully captures prey in each feeding situation with a common series of kinematic events. However, repeated bites with palatoquadrate protrusion occur during attached feedings, and the labial cartilages extend to form a seal around the tube opening during tube feedings. Average bite duration for three individuals is approximately 124 ms, although significant inter-individual variation is observed. Preliminary analyses show that H. francisci is capable of modulating the duration of some kinematic events during capture, such as mandible elevation and palatoquadrate protrusion/retraction, according to the accessibility of the prey.

Mechanics and modulation of prey capture in generalists vs. specialist predators: a kinematic comparison using two carcharhiniform sharks. 

Recent work on teleosts suggests that attack kinematics (= behaviors) may be modified by a predator based on specific attributes of the prey item Sharks are generally presumed to be highly visual predators and, thus, it is reasonable to expect that they are also capable of such modulation. Work on swellsharks, Cephaloscyllium ventriosum, however, indicated that prey size did not induce modulation. To determine the generality of this finding, I investigated the effect of both prey size and elusivity on prey capture kinematics in a species with a more generalized diet, the leopard shark, Triakis semifasciata. Sharks were filmed using high speed video feeding on two sizes of the same prey (shrimp pieces) and two more elusive prey (earthworms and live mud shrimp). In leopard sharks, size effects were noted for kinematic parameters related to buccal cavity expansion. Elusivity effects were not detected for any parameters, but a performance consequence was also not detected with increasingly elusive prey. These studies cumulatively suggest that rather than possessing a single attack behavior, generalists are capable of kinematic modulation. They also suggest that the phrase “master of none” that is typically used to describe a “jack of all trades” generalist may not apply.

Mechanics of ventilation in the swellshark, Cephaloscyllium ventriosum (Scyliorhinidae). 

Most fishes are faced with one of two options for gill ventilation: physically moving their gills through the medium (“ram” ventilation), or actively pumping the medium over their gills via “buccal pumping”. The basic pattern of mechanical movements during buccal pumping was studied over 40 years ago. However, unique patterns of water flow through the head of the swellshark during feeding suggested that the generation of respiratory currents might not be as simple as once thought. Using pressure transducers implanted into the buccal and gill cavities of actively respiring swellsharks, it was discovered that pressure traces vary within and among individuals. These data, combined with both video and electrical impedance data for the displacement of the lower jaw and gill septum, suggest that although the classic pattern of pressure generation regularly occurs, at least one novel pattern of pressure generation exists. During this novel pattern, pressure reversals exist over a much longer duration than previously thought possible, and at much larger magnitudes. It is questionable whether the classic alternating “suction” and “pressure” pumps are always used for moving water over the gills unidirectionally, and whether continuous water flow over the gills exists for large intervals of time in this species.

Distribution, evolution, and functional significance of gonadotropin-releasing hormone in the elasmobranch brain.

The basic structure of gonadotropin-releasing hormone (GnRH) includes at least nine different forms found across the vertebrates. Some forms are believed to serve extrapituitary functions, as indicated by their wide distribution throughout the brain. Chicken II GnRH (cII) is considered the most evolutionarily conserved variant because it is generally found to coexist with at least one other form in all the jawed vertebrate classes, while dogfish GnRH (df) is found exclusively in elasmobranch fishes. This study examined the distribution of df and cII GnRH-immunoreactive (ir) cell bodies and fibers in the brain of the Atlantic stingray, Dasyatis sabina, by immunocytochemical methods as a first step to correlate anatomical distribution with possible functionality of the different forms in an elasmobranch. Dogfish GnRH-ir cells and fibers were localized in the ganglia of the terminal nerve and throughout the ventro-caudal telencephalon and preoptic area, while a large, discrete cII GnRH-ir cell nucleus was found in the midbrain tegmentum with main projections to the diencephalon and hindbrain. This is the first study to show differential distribution of cII and df GnRH in the elasmobranch brain, and supports the hypothesis of divergent function of GnRH variants such as gonadotropin control and neuromodulation of sensory function. Keywords: stingray, brain, endocrinology, sensory biology

Hormonal regulation of growth in vertebral cartilage of the clearnose skate, Raja eglanteria. 

In most elasmobranchs, growth of vertebral cartilage proceeds incrementally and forms periodic marks that are extensively used in age and growth studies. Such research is essential for the management of these fishes, yet is often limited by poor understanding of the physiological processes that regulate vertebral growth. Since skeletal growth in most vertebrates is under strict control of the endocrine system, the goal of this study was to investigate the hormonal regulation of vertebral growth in the clearnose skate, Raja eglanteria. Synthesis of cartilage matrix glycosaminoglycans (GAG) was used as a marker for vertebral growth using an in vitro culture system. The effects of growth hormone (GH), insulin-like growth factor-I (IGF-I), tri-iodo-L-thyronine (T3), and corticosteroids on GAG synthesis were assessed, due to their well-documented roles in cartilage growth. The effect of calcitonin (CT) on vertebral growth was also investigated, due to its involvement in the skeletal physiology and mineral homeostasis of terrestrial vertebrates. Finally, the effect of parathyroid hormone-related protein (PTHrp) on GAG synthesis was examined, because of its critical role in mammalian skeletogenesis. PTHrp has recently been detected in the perichondrium of elasmobranch vertebral cartilage, thus it may play a role in chondrocyte proliferation and differentiation. The present study is the first investigation on the hormonal regulation of elasmobranch skeletal physiology.

SENSORY BIOLOGY OF VISION IN THE ELASMOBRANCHS. 

The visual system of elasmobranchs is reviewed with respect to structure, function and behavior. As a general review, the visual systems of elasmobranchs and teleosts are compared and contrasted. Similar visual structures and functions of phylogenetically unrelated elasmobranchs are shown to occur in species occupying similar habitats and often displaying comparable behaviors. For example, the vertical slit pupil is found in active, pelagic and epibenthic elasmobranchs as widely divergent as carcharhinid sharks and myliobatid rays. Likewise, a strong correlation is found between depth of occurrence and position of the peak spectral absorption of the visual pigment, regardless of systematic affiliation. Performance testing of the visual system also reveals features adaptive to behavior and environment. Since the majority of information on visual performance has been gleaned from the lemon shark (Negaprion brevirostris), that visual system is reviewed. Correlates between visual structure, function and behavior show that the lemon shark has an ecologically broad period of activity and is able to carry out its normal behavior throughout the entire diel period. The review ends with an unexpected finding relating the lemon shark’s visual pigments to habitat changes with aging. The final conclusion is that an understanding of how elasmobranch visual structure and function are correlated with behavior and ecology is barely at a beginning stage, and the field of elasmobranch vision, even after extensive study in recent decades, remains wide open. Supported by a grant from the Florida Department of Education to SHG and NOAA/NMFS grants to REH.

Identifying cryptic carcharhiniform shark species: tapeworms as diagnostic tools

Tetraphyllidean tapeworms are restricted to elasmobranch hosts and can be highly host specific; in fact, some species parasitize single species of elasmobranchs and thus may assist in identifying elasmobranch species. Spiral intestines of Prionace glauca, Galeocerdo cuvier, Eusphyra blochii, 4 Sphyrna species, 2 Negaprion species, 3 Rhizoprionodonspecies, and 19 Carcharhinus species from locations including the western North Atlantic Ocean, Gulf of California, and Timor Sea off of northern Australia were examined for tetraphyllideans in the family Onchobothriidae. Species of the genera Dicranobothrium, Phoreiobothrium, and Platybothrium were found to be restricted in distribution to carcharhiniform sharks and were found in most of the species examined. Many of the onchobothriids found are new to science and currently undescribed. Our results suggest that the host species examined are parasitized by at least 1 strictly host specific onchobothriid species. In some cases, more than 1 host specific onchobothriid species was found in a single host species. For example, Negaprion acutidens hosted 3 new species of Phoreiobothrium that were not found in the other 30 species of carcharhiniform sharks examined. These results suggest that each carcharhiniform species may possess a unique parasite fauna that could be used as a diagnostic tool for species identification.

The identity of the spotted eagle ray, Aetobatus narinari – a parasitological perspective

Spiral intestines of rays identified as Aetobatus narinari, from the Gulf of California, the Gulf of Thailand and the Timor Sea were examined for tapeworms. Light and electron microscopy of these worms revealed faunal differences among individuals from these localities. Rays from México hosted several different species in the order Tetraphyllidea. Rays from Thailand and Australia hosted species belonging to the order Lecanicephalidea, but, the species of lecanicephalideans differed between the two localities. Although these differences may simply reflect differences in intermediate host availability, it is possible that these data are indicative of differences in the specific identities of the rays. Host morphology seems to support the latter explanation. Although rays from all three localities exhibited dark dorsal surfaces with white spots, size and distribution of these spots differed substantially. Additional differences were seen in the angle of the anterior margin of the pectoral fins and in snout length. Combined these data lead us to suspect that the of spotted eagle ray found in the Eastern Pacific might not be conspecific with those found in the two localities in the Indian Ocean. In addition, based on our data, the conspecific identity of the spotted eagle rays from Thailand and Australia is questionable.

Electroreception in neonatal bonnethead sharks, Sphyrna tiburo.  

Digital video analysis was used to quantify behavioural response of neonatal bonnethead sharks, Sphyrna tiburo, to pre-simulating electric fields.  Sharks less than twelve hours post-parturition failed to demonstrate a positive feeding response to the electrodes, however, vigorous biting at the electrodes was observed in sharks greater than 24 hours post-parturition.  Orientation behaviours were classified as one of four types straight approach, single turn, looping return and spiral tracking where the shark appears to follow the voltage equipotential to the centre of the dipole.  Most orientations to the dipole were from a distance of less than 10 cm with a maximum orientation distance of 22 cm. The mean threshold for initiation of orientation was 0.14 µV.cm-1 with a minimum of less than 0.001 µV.cm-1.  The mean value is almost double that obtained for juvenile scalloped hammerhead sharks, S. lewini, which require a mean stimulus of only 0.08 µV.cm-1 to initiate an attack.  The greater sensitivity of S. lewini may be attributed to their larger size and consequent longer ampullary canals.

Egg capsules of the viviparous matrotroph, Sphyrna tiburo, restrict the passage of molecules greater than 2 kDa

A semi-permeable egg capsule surrounds each embryo of most viviparous sharks throughout gestation. Though the presence of this acellular matrix as an embryonic investment in viviparous species has long been thought to moderate physiological exchange, there is little information concerning its structural, biochemical, or permeability characteristics. We used a variety of histological and physiochemical approaches to investigate both the form and function of this membrane in the placental viviparous shark,Sphyrna tiburo, to better understand the capsule’s role as a moderator of maternal-embryonic relationships, and why this structure persists in many matrotrophic sharks. Scanning electron and light microscopy reveal that the capsule consisits of multiple fibrillar layers of an extracellular matrix. The capsule is significantly thinner (~1 um) than those of viviparous and oviparous species examined thus far. Capillary electrophoresis, combined with SDS/PAGE and spectrophotometry were used to measure the passage of different molecular weight markers across the egg capsule. We have found that materials less than 900 Da are capable of diffusing across the egg capsule, while those greater than 2 kDa are not.

Conventional Tagging Methods as Applied to Sharks: Past, Present, and Future 

Tagging programs provide valuable means to increase our biological understanding of sharks and to obtain information for rational resource management. Shark tagging programs throughout the world have been directed toward several objectives, including collecting data on movements and migration, abundance, stock identity, age and growth, mortality, and behavior. Results of these studies include recaptures from tagged Australian school sharks over a 40 year period, recaptures from sandbar sharks and spiny dogfish after 19 years, and recaptures of Greenland sharks after 16 years. An extensive shark tagging program has been conducted by the National Marine Fisheries Service in the North Atlantic. This continuing study, covering 36 years, currently involves over 6,500 volunteer fishermen and scientists along the North American and European coasts. Under this program, 142,384 sharks representing 51 species were tagged between 1962 and 1997. In the same period, 7,276 sharks of 33 species were recaptured by fishermen. Results of the US program include: movements of blue sharks between North America and Europe, Africa and South America (maximum distance — 3740 nmi.), transatlantic movements of tiger sharks between North America and Africa, and a recapture of a sandbar shark after 28 years. A review of tagging methods and summary of results of the major tagging programs on large sharks are provided. Keywords: tagging, shark, migration, recapture

A preliminary demographic analysis of the bigeye thresher shark, Alopias superciliosus

Population growth and exploitation of Alopias superciliosus were estimated by demographic analyses using best known life history parameters. Life history tables were constructed by using both estimates of natural mortality (M) of 0.1316 and age-specific natural mortality for maximum ages of 30. Fecundity was 1 and age at maturity was at age 12. With age-specific mortality, the population increase rate was 1.2%/year, and the generation time was about 16.45 years without exploitation. Sensitivity analyses indicated that the mortality of juvenile stage was the most sensitive factor in input parameters and net reproductive value was the most sensitive factor in computed parameters. The net reproductive value, generation time and intrinsic population growth rate decreased with the increase of fishing mortality. At F=0.1 and fishing started at age 12, the population increase rate was 0.3%/year, and the generation time was 17.0 years with age-specific natural mortality. The bigeye thresher population would decline when F=0.1 and fishing started at age 10.

Using bioenergetics models to estimate food consumption in elasmobranchs 

Measuring food consumption in elasmobranch fishes has proven to be a challenge, and has resulted in the use of a variety of methods. In recent years, bioenergetics models have increased in popularity and complexity. These models take into account energetic costs of living (metabolism, wastes, and growth) in order to estimate consumption requirements. Bioenergetics models have been used to estimate consumption rates for a number of different species including lemon, sandbar, greyreef, galapagos, tiger, bull, spiny dogfish, scalloped hammerhead sharks, and spiny butterfly ray. Like all models, output is reliant on the quality of input data, thus direct measurements of the costs of living and how costs vary with environmental variables and body size are needed. A complete model has been assembled for the lemon shark, which through laboratory and field research has shown good cross-validation. However, accuracy of some models may be questionable due to inclusion of data from other species or by using laboratory data alone. Recent advances in telemetry techniques and captive husbandry may offer new opportunities for estimating energetic parameters in both the field and laboratory. Bioenergetics models may also be useful in quantifying the ecological association of elasmobranchs on habitats and prey populations.

Physiological telemetry of elasmobranchs: taking the laboratory to the field 

Physiological telemetry is a powerful tool in studying elasmobranchs in the laboratory and field. Controlled laboratory studies of the physiology of elasmobranchs has increased our understanding of the behavior, life history, and ecology of many species. However, extrapolating results from laboratory studies alone may misrepresent these biological aspects of animals in the field. Additionally, some elasmobranchs are too large, logistically difficult to maintain, or have low survivorship in captivity making them extremely hard to study in the laboratory. Physiological telemetry offers a bridge between the laboratory and the field providing an opportunity to elucidate similarities and differences. Previous studies have coupled a variety of sensors to acoustic transmitters to remotely relay information on swimming speed, tailbeat frequency, muscle contraction rate, heart rate, muscle, cranial and stomach temperature, and neural activity. These techniques have been used on elasmobranchs ranging from stingrays to white sharks, but have been restricted by the size of the electronic components, attachment methods, or logistical difficulties in conducting long-term tracks. Recent developments in sensor technology and miniaturization of electronics have increased the diversity and applications of physiological telemetry. Acoustic modem and satellite telemetry may offer a means of downloading archived data collected from animals in the field.

Effects of splenectomy on the immune system of the nurse shark, Ginglymostoma cirratum, assessed by changes in peripheral blood leukocyte populations and histology of lymphomyeloid tissues. 

In the absence of bone marrow and lymph nodes, elasmobranch fish must rely on alternative lymphomyeloid tissues for production of immune cells. Principle tissues include spleen, thymus, epigonal organ, and, in some species, Leydig organ. To investigate the role of spleen in immune cell production, spleens were removed surgically from juvenile nurse sharks, Ginglymostoma cirratum, (n=8). Sham operated (n=5) and non-operated (n=5) juveniles served as controls. Peripheral blood, from which hematocrits and differential white cell counts were obtained, was sampled at varying intervals during the first week after surgery, then at weekly intervals for five weeks. Animals were sacrificed at various times for histological examination of lymphomyeloid tissues. Hematocrits did not vary significantly during the study. Circulating levels of lymphocytes decreased during the first three days, after which levels gradually returned to normal ranges within two to three weeks. Granulocyte levels increased initially and recovered after approximately three weeks. Preliminary assessment of tissue imprints indicates an increase in immature lymphocytes and granulocytes in epigonal organs of splenectomized animals compared with controls, suggesting that epigonal organ may increase its production of lymphocytes in the absence of spleen, but not at the expense of its role in granulocyte production.

The elasmobranch mechanosensory lateral line system: form and function?

The biological function of the mechanosensory lateral line in relation to ecology and behavior is essentially unknown in elasmobranch fishes. One function of the teleost lateral line is to facilitate prey detection, but does the elasmobranch mechanosensory system possess the morphology and organization to support a role in prey localization and capture? General organization of the ventral lateral line system was examined in several representative batoid species (Dasyatis sabina, Raja eglanteria, Narcine brasiliensis, Gymnura micrura) in relation to their food habits and feeding behavior. Batoid ventral lateral line systems consist of pored and non-pored canals, and vesicles of Savi. The relative distribution of these mechanosensory structures differs between species and may be related to function. It is proposed that the ventral lateral line system in most benthic feeding batoids functions in the localization of invertebrate prey via a novel mechanotactile mechanism mediated by the non-pored canals and vesicles of Savi around the rostrum and mouth. This presentation will summarize current knowledge of elasmobranch lateral line anatomy, physiology and behavior; discuss relationships between batoid ventral mechanosensory systems and feeding ecology; and propose future research on lateral line form and function in elasmobranch fishes.

Length-at-birth of the sandbar shark, (Carcharhinus plumbeus), in Delaware Bay

As part of ongoing research on the ecology of shark nursery grounds, we investigated the distribution of length-at-birth of sandbar sharks pupped in Delaware Bay. A neonate (newborn) sandbar shark is identified by an unhealed umbilical scar. Young-of-the-year sandbar sharks grow in length before their umbilical scars are healed. This study takes that into account by separating umbilical scar healing stages and produces a more accurate length-at-birth than studies which report the lengths of sandbar sharks with open umbilical scars. We examined 798 sandbar sharks captured by gill net or longline in Delaware Bay between 1995 and 1997. Six distinct umbilical scar healing stages were termed cord-remains, open-fresh, partly-healed, mostly-healed, well-healed and none. Sharks with the three earliest umbilical healing stages did not differ in length, thus represented the length-at-birth. The mean length-at-birth is 49.3 cm “0.3 cm fork length (95% confidence interval, n=238) with a range of 40 to 55 cm fork length in Delaware Bay. Our results are comparable to published reports of sandbar length-at-birth along the US east coast and therefore do not support the hypothesis that sandbar sharks are born “somewhat” smaller in the northern pupping range

Captive feeding biology of elasmobranchs

We observed large food consumption of 7.1 (s.e. 0.7, n = 17) percent body-mass per day for a captive juvenile pelagic stingray, Dasyatis violace (disc width 44.4 cm, PIT tag # AVID 017-085-067), in a holding pool kept at 20^oC. This confirmed earlier results in the 4600 m³ Outer Bay Water Exhibit of the Monterey Bay Aquarium when 3 juvenile pelagic stingrays were displayed for three months. It suggests possible large differences in food consumption and corresponding growth rates between captive and wild pelagic stingrays. Food consumption and growth rates of juvenile elasmobranchs in captivity are compared with those in the wild. The dietary requirements of captive temperate water sharks in a semi-open sea water system and pelagic stingrays in a nearly closed system are compared with results for elasmobranchs in other aquaria.

Sensory Mechanisms Underpinning Feeding Behavior in Elasmobranchs 

Elasmobranchs have some sophisticated feeding strategies, ranging from tail clipping bill-fishes, to locating concentrations of patchily distributed prey. These strategies are underpinned by an equally sophisticated array of sensory systems. To take one example, many rays feed on buried bivalves, and dig where the prey densities are high (Hine et al. 1997). Behavioral studies (Montgomery and Skipworth, 1997) illustrate the potential importance of mechanosensory systems in this feeding behavior. Both mechanosensory and electrosensory systems share a high level of sensitivity, to the extent that behaviorally relevant inputs could be swamped by self-generated noise. One interesting aspect of the sensory biology of elasmobranchs is that hindbrain signal processing effectively resolves this problem (Montgomery and Bodnzick, 1994).Hine AH, Whitlatch RB, Thrush SF, Hewitt JE, Cummings VJ, Dayton PK, Legendre P (1997) Nonlinear foraging response of a large marine predator to benthic prey: eagle ray pits and bivalves in a New Zealand sandflat. J Exp Mar Biol Ecol 216: 191-210Montgomery JC, Bodznick D (1994) An adaptive filter cancels self-induced noise in the electrosensory and lateral line mechanosensory systems of fish. Neurosci Lett 174: 145-148; Montgomery JC, Skipworth E (1997) Detection of weak water jets by the short-tailed stingray Dasyatis brevicaudatus (Pisces: dasyatididae). Copeia 1997: 881-883.

Orientation and Navigation in Elasmobranchs: Which Way Forward? 

Elasmobranchs possess a multiplicity of mechanisms controlling posture and short distance orientation. Vestibular contributions to posture and locomotion are well documented. So too, are the contributions of vision, olfaction and the octavolateralis senses to short distance orientation, particularly orientation to specific environmental stimuli such as those generated by prey. Less well understood are the mechanisms guiding orientation over longer distances. Anecdotal and systematic observations of behavior show tidal, daily, repeat long distance, and even seasonal movement patterns. True bi-coordinate navigation has not been demonstrated in elasmobranchs. The mechanisms underlying the above movement patterns are largely speculative, however, they are likely to include responses water currents, physical parameters such as temperature and pressure, and the geomagnetic field. Of particular interest in elasmobranchs is that geomagnetic orientation could be mediated directly via a magnetite based sensory system, or indirectly via the electrosensory system. Systematic studies of movement patterns, and experimental studies of the underlying mechanisms of orientation are required to gain an understanding of orientation and navigation in this intriguing group.

Suction feeding in sharks: a kinematic analysis of feeding in the nurse shark,Ginglymostoma cirratum. 

Despite relatively simple feeding mechanisms, sharks exhibit a variety of feeding types. Ancestral cladodont sharks presumably grasped and possibly swallowed their prey whole. Modern sharks have radiated to include biting, gouging and biting, ram-feeding, suction-feeding, filter-feeding, and crushing types. Convergence and specialization for suction feeding have arisen in a variety of divergent extant taxa. The orectolobiform nurse shark,Ginglymostoma cirratum, is a specialized and apparently obligate suction feeder. Kinematic analysis from high speed video of five sharks reveals a conservative feeding sequence involving mandible depression and labial cartilage protrusion, followed by mandible elevation and labial cartilage retraction. The expansive and compressive phases are very rapid, with a mean duration of 92 ms. Similar to other elasmobranchs, there is significant variability among sharks in nine kinematic variables. Within sharks, bite durations are very constant as the sharks become satiated. The suction feeding nurse shark differs from ram feeding carcharhinid sharks by its short and relatively constant durations of mouth expansion, minimal contribution of palatoquadrate protrusion and cranial elevation, reduced dentition, formation of a laterally enclosed and anteriorly directed mouth, and hypertrophied abductor muscles. Continuing studies seek functional and evolutionary patterns in shark feeding.

Hearing in elasmobranchs: a review

A brief history is provided of the studies which established that elasmobranchs not only detect underwater sounds, but respond to them in ways that suggested a rapid ability to locate specific sound-sources. The latter included acoustical features that mimicked sounds produced by struggling prey as well as providing a point-source to observe the behavioral activities of such predators. The rapid speed in locating sound-sources by free-ranging sharks created controversy, however. An important theory, at the time, precluded fishes, and particularly sharks, from directional hearing in the acoustical far-field (distances beyond one wavelength of a sound). Repeated confirmation that sharks could accomplish such a feat during the late ’60s – mid ’70s resulted in several new theories that could account for rapid directional hearing by these animals. These theories will also be briefly reviewed as will be the findings that resulted from a renewed interest in the neural mechanisms of elasmobranch hearing in the ’80s. The report will end with ideas concerning future directions of hearing research in elasmobranchs.

Aspects of the life history of the Pacific electric ray, Torpedo californica (Ayres), in central and southern California

Pacific electric rays were collected from central and southern California from July 1994 through January 1996 for an age and growth, reproduction and demography study. Vertebral centra were used for ageing. The maximum age estimate from vertebral centra was 16 years. The von Bertalanffy growth model provided the best fit to the size at age estimate data, predicting an asymptotic total length (TL) of 1372 mm for females and 921 mm for males. Estimated size (and age) at sexual maturity is 600 mm TL (6 years) for males and 840 mm TL (11 years) in females. Pacific electric rays have a low fecundity of approximately 17 young per litter. Time of partuition could not be determined. Instantaneous mortality estimates (z) ranged from 0.048 to 0.277, depending on the longevity estimates used. Best demographic estimates indicate that the Pacific electric ray population is at or slightly exceeding a stable equilibrium with a generation time of 12.7 to 14.7 years.

Comparative Anatomy of the Elasmobranch Cerebellum: Theme and Variations of a Sensorimotor Interface 

The cerebellum of elasmobranch fishes demonstrates a wide range of variation in size and complexity across taxa. Previous studies have demonstrated that the cerebellum of squaliform sharks is relatively simple, with a single smooth corpus, whereas that of galeomorph sharks is relatively much larger and multilobate, with numerous sulci in each lobe. The majority of previous studies have focussed on those taxa possessing smaller and simpler cerebelli. The purpose of this paper is to examine in detail the anatomy of the cerebellum of carcharhiniform sharks, particularly Carcharhinus limbatus and Spyrna lewini and compare the structure and cytoarchitecture with those previously described in elasmobranchs with smaller and simpler cerebellar structures. Models of cerebellar function and sensorimotor integration in other vertebrates will be compared with what is known of the physiology and role of the cerebellum in elasmobranchs to generate hypotheses explaining the wide variety of cerebellar morphologies in elasmobranchs.

The Reproductive Behavior of Elasmobranchs. 

The study of elasmobranch reproductive behavior, a relatively new endeavor, has emerged from four overlapping areas: inferences from fresh caught animals, captive observations, underwater and field observations of live animals, and laboratory studies of reproductive structure and function. Several common behaviors have been described from various species which include: sexual segregation, courtship behavior and copulation. Sexual segregation is the seasonal aggregating behavior common to many elasmobranch species such as: Squalus acanthias, Sphyrna lewini, and Prionace glauca. Courtship behavior has been inferred for: Carcharhinus plumbeus, C. limbatus, P. glauca, Odontaspis taurus, Dasyatis centroura, D. sabina, and others through the appearance of tooth cuts on the female’s body and noted in more detail with underwater observations on C. melanopterus, Trianodon obesus, Ginglymostoma cirratum, among others. Copulation has been directly observed in captive settings in: Scyliorhinus canicula, S. torazame, T. obesus, Aetobatus narinari, Rhinoptera javanica, Raja eglanteria, and Heterodontus francisci, and in the wild for three species of urolophids, and for T. obesus, and G. cirratum. Ongoing studies in G. cirratum are continuing with research into paternity, sperm competition and social structure by characterizing members of the population through diver identified tagging, acoustic telemetry, and DNA fingerprinting of wild animals. Two wild, freshly-mated females are captured annually for laboratory observations on gestation and associated changes in reproductive steroid hormones.

The effects of scale on the feeding kinematics of the nurse shark, Ginglymostoma cirratum.

Successful inertial suction feeding depends, in part, on the speed of the feeding sequence. One variable potentially important to the speed of this behavior is the size of the animal. The effects of scale on the muscular dynamics of aquatic vertebrates are still uncertain. We present data on the scaling of the prey capture kinematics of the nurse shark,Ginglymostoma cirratum, an inertial suction feeder. Morphometrics of the head and feeding apparatus were analyzed in twelve specimens ranging from 71 to 244 cm TL. These data indicated isometric growth of the feeding apparatus. The kinematics of prey capture in another twelve specimens (33 to 268 cm) were recorded with high speed video and subsequently analyzed. The maximal excursions of angular variables remained constant through ontogeny, while the maxima of the linear excursions increased. The time required to reach the maximum excursion of the kinematic variables also increased with increasing animal size. The slopes of the log-transformed data were not significantly different from 0.333, thus these data are consistent with a model of muscular scaling initially proposed for largemouth bass by Richard and Wainwright (1995). This pattern of scaling does not appear to apply to sharks in general.

Kinematics of shark pectoral fin movements and their implications for lift-production.

Elasmobranchs, negatively buoyant animals, must produce dynamic lift to avoid sinking. Current models of shark locomotion assume that lift is produced posteriorly by the heterocercal caudal fin and anteriorly by the pectoral fins and head. These two components of lift produce torques at the center of mass that negate one another. All models have assumed that the pectoral fins are static during swimming. Using a dual video camera system I recorded spiny dogfish, {i/Squalus acanthias}, swimming in a large flume. Marks placed on the fins divided them into separate segments. Three-dimensional kinematic analyses of these individual segments of the fins and head of the shark demonstrated manipulation of the pectoral fins by the sharks during swimming. The angle of the pectoral fin was modified during steady swimming and was correlated with the position of the caudal fin during its beat. An index of lift was calculated for each fraction of the pectoral fin and head. The head appears to produce significantly more lift during steady swimming and while the animal is ascending in the water column. The negative lift produced by the pectoral fins appears to be important in angling the animal down when it begins a descent.

Atlantic shark management update: developing a combined fishery management plan for Atlantic sharks, tunas, and swordfish 

The Highly Migratory Species (HMS) Management Division of the National Marine Fisheries Service (NMFS) is responsible for management of Atlantic tunas, swordfish, billfish and sharks. Thirty-nine species of Atlantic sharks are grouped into 4 management units – large coastal sharks, pelagic sharks, small coastal sharks, and prohibited species. In the “Report to Congress: Status of the Fisheries of the United States” (September, 1997), NMFS identified all large coastal sharks and prohibited species as overfished, and pelagic and small coastal sharks as fully fished. The Magnuson-Stevens Fishery Conservation and Management Act of 1996, as amended, requires that all species designated as overfished must have fishery management plans (FMPs) or FMP amendments that include rebuilding plans submitted for Secretarial review within one year (September, 1998) and that NMFS establish an advisory panel for each FMP or amendment. The HMS Management Division is developing a combined HMS plan, with assistance from an HMS Advisory Panel, which will build on the existing plans for sharks and swordfish and will add a new management framework for tunas. An FMP amendment for Atlantic billfish will be prepared separately. An update on the status of the HMS plan will be provided.

A first glance at pelagic shark catches in the Azores. 

This paper reports a first attempt to estimate pelagic shark catches in the northeastern Atlantic Ocean around the Azores. Blue shark (Prionace glauca) and shortfin mako (Isurus oxyrinchus) commercial catches reported for the Azorean archipelago as well as non-reported fishing data from logbooks of swordfish longliners operating in the area are presented for the period 1993-1996. Three major fleet components catching pelagic sharks are identified according to vessel characteristics and fishing regime: open deck wooden boats, small covered deck boats (gross tonnage less than 100 tons) and large covered deck boats (GRT exceeding 100 tons). The latter vessel class lands most of the catches in Portuguese and Spanish mainland ports, accounting for 86-89% and 71-85% of the total estimated blue shark and mako catches taken in the Azores during the study period. Catch rates for blue shark and swordfish exhibit a pronounced seasonal and asynchronic nature. While the highest catch levels for the former species are obtained in the Spring (averaging 807 Kg/1000 hooks), the fishing season for the latter targeted species is from August to February. The implications of this pattern for future management are discussed. Blue shark bycatch represents a major proportion of the total catches taken by the Azorean swordfish longline fishery, reaching a minimum and a maximum of 39% and 91% respectively during October and June. Blue shark catches have been gradually increasing over the period 1993-1996, peaking at an estimated maximum of 2,433 mt in 1996. Shortfin mako catch levels have increased to an estimated maximum of 76 mt in 1995, followed by a decline to 54 mt in 1996. An observed increase of pelagic shark catch rates over the study period is probably due to a shift of fishing effort towards pelagic sharks during times of low abundance of swordfish.

Selective foraging behaviour of basking sharks on zooplankton in tidal fronts

Individual and grouped basking sharks (Cetorhinus maximus) filter-feeding on zooplankton at the water’s surface were tracked visually together with zooplankton sampling from their feeding paths. Along tidal slicks they exhibited area-restricted searching behaviour and actively selected areas containing high densities of large zooplankton above a threshold level. Basking sharks remained in the most profitable patches transported by tidal currents for up to 27h and moved between patches over 24-48h periods. Between years, the location of shark foraging areas changed according to the effects of prevailing weather conditions on frontal boundary sharpness and the maintenance of frontal upwellings. Our results show that basking sharks are selective filter-feeders on specific zooplankton assemblages and therefore useful as biological indicators of abundance trends in zooplankton species influenced by climatic fluctuations of the North Atlantic Oscillation (NAO)

What is the current status of chemical shark repellents?

Efforts by the US Navy to develop a chemical shark repellent during the post W.W.II years were unsuccessful and later abandoned. Interest in chemical shark repellents was renewed by the discovery of pardaxin, a natural shark repellent secreted by the Moses sole (Pardachirus marmoratus). The surfactant-like nature of pardaxin led researchers to test the shark repellency of various surfactants. The most effective surfactant tested to date is the alkyl sulfate surfactant sodium dodecyl sulfate (SDS). Swim-through repellency tests were conducted in a roundabout test tank using swell sharks, Cephaloscyllium ventriosum, to determine if repellent efficacy of alkyl sulfate surfactants was affected by carbon chain length, ethylene oxide (EO) groups, and counterions. Results indicate repellency increases as alkyl chain length increases from octyl to dodecyl, decreases with the addition of EO groups, and is not affected by counterions. SDS is the most effective known chemical repellent, but it does not meet the Navy’s potency requirement for a classic surrounding-cloud type repellent of 100 parts per billion. Thus, SDS is only practical as a directional repellent such as in a squirt application. Recent work on semiochemicals may offer a new prospective direction for the search of a more effective chemical shark repellent.

A review of South African feeding studies of elasmobranch fishes: Perspectives and future directions.

A review of the South African literature over the last decade shows that more than 20 papers have been published dealing with elasmobranch feeding, although many were part of general studies of their biology. They describe the feeding of more than 50 elasmobranch species based on identification of recently ingested prey. Accurate prey identification was possible in many studies using digestion-resistant prey hard parts such as cephalopod beaks and fish otoliths, which allowed more precise understanding of the impact of each species. The relationship between predator size and prey choice is crucial but was often not described. Although such studies provide insights into prey taken, on their own they are poor reflections of the complex interactions between predator and prey over time. Studies of predator/prey interactions in the wild have been initiated and such studies are vital to clearer understanding of predation. The large size of most chondrichthyans limits their suitability in laboratory based experimental studies, but the rapid advances in the technology of electronic tracking devices is facilitating remote data collection in the wild, thereby > augmenting direct observations. This promising area of research has the potential to clarify details of behaviour and feeding ecology that otherwise would be unobtainable. Keywords: elasmobranchs, feeding, ecology, predation, review

Archival tagging of school sharks in southern Australia 

School sharks, Galeorhinus galeus, are an important commercial species in the Australian Southern Shark Fishery. A current project is using archival tags to try and answer certain questions on vertical distribution, ‘onshelf’ and ‘offshelf’ movement components, Tasman Sea distribution, pupping migrations and pupping areas. A ‘dummy’ tagging experiment was carried out to evaluate the suitability of internal versus externally located tags and between unstreamlined and hydrodynamically shaped external tags. The overall recapture rate after three years was 15% and although unstreamlined external tags were returned at a lower rate (11%) than streamlined externals (16%) and internal tags (19%) these differences were not statistically significant. In November 1997, 30 archival tags were deployed on school sharks in waters off South Australia; these tags were mounted externally on the first dorsal fin and were semi-streamlined. One tag was returned after 7 days and another after 23 days. No further returns have been made to date. Both recaptures showed an interesting diurnal vertical migration between as deep as 500 m during the day to near the surface at night. Geo-positioning from the light data are discussed. Immediate plans are to release a further batch of fish with internal tags.

Elasmobranch behavioral ecology: oxymoron or opportunity?

Behaviorally and ecologically, sharks and their allies exhibit remarkable diversity. Over the past several decades, Don Nelson and his contemporaries made enormous progress in the understanding of shark behavior. The vexing task of relating this behavior to species and community ecology now stands in plain view. The study of behavioral ecology can, in the broad sense, be construed to include almost anything the animal does within the context of its environment. As a discipline, however, behavioral ecology has specific stated goals, principally to understand the evolution of animal behaviors. Sharks in general are not well suited to these goals. As a result, empirical work is often limited to descriptions of life history, distribution and abundance and basic investigations of morphological and behavioral adaptations. Critically assessing how the latter affect survivorship and fitness is a formidable task, one that largely remains in the domain of those who study teleosts, birds, etc. Nonetheless, elasmobranchs possess a number of unique traits. And given their long-held positions as apex predators of the world ocean, much work remains to be done in the area of predation. Understanding sharks’ roles in the ecosystems they inhabit is central to species management and, ultimately, to the “holy grail” of successful, system-wide management.

Trabecular prismatic cartilage: a novel solution to strengthening the jaws of a cartilaginous fish 

A synapomorphy of the cartilaginous fishes (Chondrichthyes) is that some, or all, of the skeleton is composed of calcified cartilage known as prismatic cartilage. The surface of prismatic cartilage is a mosaic of plates of calcium apatite crystals called tesserae. These tesserae surround a core of hyaline cartilage much as the rind surrounds the pulpy fruit of an orange and serve to stiffen the skeletal element. In both jaw cartilage of the cownose ray, Rhinoptera bonasus, struts of calcification run through the hyaline cartilage core. Cownose rays feed on mollusks, ophiuroids and other hard prey. Tooth plates of adults show distinct wear patterns where the prey is usually crushed. A sagittal section through this ‘trabecular cartilage’ shows that the struts are positioned so as to prevent buckling in this area. The common ancestor of cartilaginous and bony fishes is thought to have had a bony endoskeleton. The lamellar bone of the tesserae and vertebrae of chondrichthians is evidence that the skeleton has not lost osteogenic potential entirely. The data presented here indicate that a novel developmental and biochemical process is also at work in the cartilage. Data from neonate individuals indicates that teh process of trabeculation is not epigenetic, but rather is part of a fixed developmental pattern. Bone is typically strengthened through endosteal deposition and trabeculation. In a remarkable example of convergence, multiple layers of tesserae and strut formation serve the same purpose in cartilage.

Local occurrence of basking sharks (Cetorhinus maximus Gunnerus) in relation to spatio-temporal patterns of zooplankton abundance

The distribution of basking sharks (Cetorhinus maximus) around the Isle of Arran in the Clyde sea area on the west coast of Scotland, UK was investigated during July 1997. A network of shore based volunteers conducted visual searches between 06-00 and 22-00 from seven vantage points for a total of 1538 hours over 20 days between July 6 and 28. 29 sightings were recorded. A plankton sampling programmewas carried out in the same area and over the same time period. Themajority of shark sightings occurred in the afternoon and evening corresponding to an increase in zooplankton abundance during this period. Three peaks in shark sightings occurred over the study period which followed peaks in zooplankton abundance with a lag of one to three days. The spatial distribution of shark sightings was also associated with the distribution of zooplankton in the area. Increases in the number of sharks occurred when zooplankton dry weights were at the maximum normally found in the area. This study, has shown, therefore, that fine-scale spatio-temporal variability in the distribution of basking sharks can be explained in terms of patchiness in the distribution and abundance of zooplankton.

The structure of basking shark Cetorhinus maximus populations in the North-East Atlantic – development of genetic markers.

Basking shark populations have been subject to exploitation for many years and are currently considered to be endangered in European waters. However, little is known of their population structure. In the recent past population structure assessments have been made on the basis of capture-mark-recapture studies or differentiation of meristic and morphological characteristics of different stocks. However, for a species such as the basking shark which are not easy to tag in large numbers and which little is known about their ecology a new approach is required. Molecular genetic methods are increasingly being used with success in determining the stock structure of commercially important fish species in both marine and freshwater environments.In particular, the use of microsatellite DNA sequences is finding increasing use in fisheries stock assessment. This poster presents reports on work to develop microsatellite DNA markers for use in assessing the population structure and migratory behaviour of basking sharks in the north-east Atlantic.

Neuroecology of elasmobranch fishes: Relating the brain to the real world.

Ethological studies on elasmobranch fishes have attempted to explain the adaptive value of specific behaviors. For example, laboratory studies have characterized the taxis responses during orientation to acoustic, olfactory, electric and visual stimuli. These studies complement field research that describes the motor patterns involved in natural behaviors such as reproductive interactions and feeding. Although lab and field studies have provided good descriptions of behavioral motor patterns, relatively little information is obtained on how sensory and central processing systems initiate and form these often complex behaviors. The ampullary electrosense of the elasmobranch is presented as a model system in which the peripheral morphology, neural response properties and central neuroanatomy can be interpreted in relation to the ecological factors that shape their behavior. Vector analysis of the peripheral organization of the ampullary canal system and neural response properties provide useful tools for predicting different ecological functions for the ampullary clusters. Chronic recording of electrosensory neurons in the alert swimming animal permit integration of neural activity with motor behavior. The mechanisms by which sensory input and central processing shape elasmobranch behavior can be better understood when interpreted in relation to the natural ecology of each species. KEYWORDS: ampullae of Lorenzini, behavior, electroreception, ethology, sensory biology

Ultrasonic telemetry, tracking and automated monitoring technology.

The tools for remote monitoring of marine animal behaviour have grown significantly in the last few years. The availability of micro-controllers in smaller low power packages has enabled the development of more sophisticated ultrasonic transmitters and battery powered automated monitoring sites. A brief historical perspective is presented leading to description of new systems that combine archived sensor data with ultrasonic data download. These systems provide multiple years of data gathering with the ability to gather the data and reprogram the device without recapture of the animal.

Buoyancy in deep-sea sharks from the Chatham Rise, New Zealand

Although deep-sea sharks approach neutral buoyancy through a large oily liver that contains low-density lipids such as squalene, there have been few comparisons of buoyancy within and among species of sharks. Buoyancy and chemical composition of the liver oil of sharks collected in deep-water trawls from the Chatham Rise, New Zealand were compared. Although there appears to be strong selection for neutral buoyancy in these sharks, buoyancy characteristics of sharks varied with species, size, sex and reproductive state. Livers of smaller sharks contain more squalene and are less dense than livers of larger sharks. However, livers of larger sharks contain a greater proportion of oil than livers of smaller sharks, and the whole body of sharks is nearly uniformly neutrally buoyant regardless of size of shark. Livers of mature male sharks contain more squalene and are less dense than those of mature females, but the non-liver tissue in females is less dense than that of males, and the whole bodies of both sexes are equally neutrally buoyant. Regulation of buoyancy of species of sharks found in shallow water differs considerably from that of deeper species, and appears to rely more on hydrodynamic lift provided by lifting surfaces such as fins.

Key words: sharks, buoyancy, liver lipids, deep-sea

Review of rate of consumption, food transit and digestive efficiency in sharks.

Sharks are important apex consumers in the marine environment and quantification of energy flow through sharks is important for understanding their impact in marine ecosystems. However, there have been relatively few studies on rates of consumption (daily ration) in sharks and it is difficult to generalize about the role of sharks in the flow of energy in an ecosystem. Estimates of the daily ration of sharks generally either incorporate data on the duration and rate of food emptying from the stomach and field observations on prey items ingested, or involve bioenergetic models based on a balanced energy budget. Several factors that may influence rates of consumption are poorly understood in elasmobranchs. There have been few studies on the efficiency of food digestion, absorption and conversion to growth, and the passage of food through the digestive tract, despite the importance of these factors on energy flow through the trophic level occupied by sharks. This study reviews the current state of knowledge on rates of consumption, rates of food transit through the stomach and entire digestive tract, and the efficiency with which ingested food is converted to energy stored as growth in sharks. Key words: consumption, rate of food passage, digestive efficiency, sharks

EVOLUTIONARY INNOVATIONS IN THE FEEDING MECHANISM OF ELASMOBRANCHS 

A major conclusion from comparative studies of feeding mechanisms in lower vertebrates is that some of the biomechanical couplings involved in mouth opening have been retained throughout evolution. However, recent studies of the jaw mechanism indicate that elasmobranchs differ from other lower vertebrates in that the geniohyoideus coupling is the primary mechanism for lower jaw depression rather than the rectus cervicus coupling. In addition, previous studies of the feeding mechanism in lower vertebrates indicate that structural differences among taxa may arise by the addition of a novel structure or as a result of modification of the existing musculoskeletal apparatus. Accompanying such changes, the ancestral motor pattern may be retained or the timing of motor activity may be altered. Evolutionary innovations in the musculoskeletal apparatus mediating upper jaw protrusion in elasmobranchs has involved both the addition of a novel feature, the dorsal preorbitalis coupling, and by the modification of an existing structure, the levator palatoquadrati coupling, while retaining the ancestral system, the ventral preorbitalis coupling. These changes in the musculoskeletal apparatus have involved conservation of the motor pattern in the ancestral mechanism and alteration of the motor pattern in the modified mechanism.

Ultrastructure of early oogenesis in juvenile Clearnose skates, Raja eglanteria

The ultrastructure of the pre-vitellogenic stages of oogenesis in juvenile Raja eglanteria are described. Stage 1 comprises a single follicle cell and oocyte. In stage 2, two follicle cells surround an oocyte that has a thin cytoplasmic shell and a large germinal vesicle with condensed chromosomes. In stage 3, 6-8 follicle cells adhere via tight junctions to the oocyte. Both cells lack microvilli. The ooplasm is weakly eosinophilic and contains occasional lipid droplets, mitochondria, glycogen rosettes and ribosomes. In stage 4, a monolayer of squamous follicle cells extend flattened processes that interdigitate and encapsulate the oocyte. Microvilli extend from these processes and the oocyte into the intercellular space. The cytoplasm contains spherical lipid droplets surrounded by mitochondria. The germinal vesicle has dispersed chromatin and a single nucleolus. A monolayer of follicle cells that contain many mitochondria and well developed golgi complexes invest stage 5 oocytes. The intercellular space is wider and contains amorphous material. Microvilli, clathrin coated, and non-coated pits occur on the oocyte surface. The cytoplasm is homogeneous, contains ribosomes, small electron dense particles, non-membrane bound lipid droplets, and peripheral clusters of mitochondria. Yolk platelets are absent. The large germinal vesicle contains chromosomes in the lampbrush configuration. KEYWORDS: ultrastructure, histology, oogenesis, clearnose skate

Catch and Effort Data of Whale Sharks in the Philippines

Abstract: Catch volume and trade of the whale shark fishery for the 1997-1998 season was monitored by WWF-Philippines and Silliman University. Methods of data collection include site-visits to coastal villages involved in whale shark and manta fishery, market surveys, fishers’ interviews and daily landing-site enumeration. Eight fishery sites were identified in the 1997 season, tha major landiong sites of which were in Pamilacan, Bohol and Talisayan, Misamis Oriental. A fishery site in Sorsogon, Luzon is recently operational for the 1998 season. Fishery profiles and changes in activity patterns related to whale shark fishery in these sites are presented. Increasing fishing effort, due to increasing demand, and decreasing catch per unit effort characterized the fishery. Management strategies employing Integrated Conservation and Development projects protecting both whale sharks and the fishing population dependent on them was recommended in the previous year. This recommendation is being evaluated against a government directive on total ban on whale shark fishery and trade.

Observation of the mating behavior of the manta ray, Manta birostris, at the Ogasawara Islands, Japan.

On 11 July 1997, the mating behavior of wild manta rays, Manta birostris, was observed while skin diving in Chichijima, the Ogasawara Islands, Japan, and was recorded with 49 underwater photographs and about 20 minutes of video tape. The female manta ray involved was estimated to be approximately 5-5.5 m in disc width (DW). The two males involved were slightly smaller than the female, and were estimated to be 4-4.5 m DW. Copulating behaviors of the two different males were observed in the present study and their behaviors were almost the same. The males chased behind the tail of the female for 20-30 minutes. The manta rays swam fast during this chasing phase of their mating behavior. The males nipped the tip of the left pectoral fin of the female during each copulation event, both of which occurred within one meter of the surface. The mating behavior of the manta rays is divided into the following five steps. Male chases behind the tail of the female, and attacks her several times while chasing her (chasing behavior, step 1). Male nips the tip of the pectoral fin of the female and then the male moves to the ventral surface of the female (nipping behavior, step 2). Male inserts a clasper into the cloaca of the female (copulating behavior, step 3). Male removes the clasper from the cloaca of the female, but maintains his oral hold of her pectoral fin (post-copulating behavior, step 4). Male releases the pectoral fin of the female, setting her free (separating behavior, step 5). The copulation of Manta birostris is of the abdomen-to-abdomen type.