Florida Museum of Natural History

Abstracts of AES Scientific Papers

American Elasmobranch Society 1998 Annual Meeting
Guelph, Ontario, Canada
Editor's Note: The pages which follow list most of the papers presented at the 1998 meetings. Some abstracts were communicated after the initial deadline and have not yet been added to this list. Certain special characters transmitted electronically are not faithfully retained, and those corrections are being made. All corrections should be in place by the end of September. Constructive critique is welcomed. (JCC)
ABSTRACTS - Part 2: Healy through Myrberg
Healy, Claire J. and Caira, J. N.

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 Rhizoprionodon species, 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.

Jensen, K. and Caira, J. N.

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 Mxico 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.

Kajiura, S.M.

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 V.cm-1 with a minimum of less than 0.001 V.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 V.cm-1 to initiate an attack.  The greater sensitivity of S. lewini may be attributed to their larger size and consequent longer ampullary canals.

King, Tisha C., Thomas Koob, Charles Manire, and Julian Lombardi

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.

Kohler, Nancy E. and Turner, Patricia A.

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

Liu, Kwang-Ming and Chen, Che-Tsung

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.

Lowe, C.G.

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.

Lowe, C.G. and K.J. Goldman

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.

Luer, C.A., C. J. Walsh, A. B. Bodine and J. T. Wyffels

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.

Maruska, Karen P.

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.

Merson, Rebeka Rand and Pratt, Harold L. Jr.,

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

Mollet, H. F.

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 20oC. 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.

Montgomery, J.C. and C. Thornburn

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.

Montgomery, J.C. and M.M. Walker

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.

Motta, P.J.

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.

Myrberg, Jr., Arthur A.

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.