Abstracts of AES Scientific Papers
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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 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.
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
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.
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.
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