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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: Neer through Yano
Neer, Julie A. and Cailliet, Gregor M.

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.


New, J.G.

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.


Pratt, H.L. Jr. and J.C. Carrier

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.


Robinson, Michael P. and Motta, Philip J.

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.


Robinson, Michael P.

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.


Schulze, Margo B., Brewster-Geisz, Karyl, and Lent, Rebecca

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.


Silva, A.A., G. Menezes and J. J. Pereira

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.


SIMS, DAVID W., and QUAYLE, VICTORIA A.

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)


Sisneros, Joseph A.

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.


Smale, Malcolm J.

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


Stevens, J.

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.


Strong, Wesley R.

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.


Summers, A.P.

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.


Thom, Tim J., O'Connell, Mark J., Lucas, Martyn C., Joplin, Lynn, and Downie, Alexander.

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.


Thom, Tim J., Hoelzel, A. R., O'Connell, Mark J., and Lucas, Martyn C.

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.


Tricas, Timothy C.

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


Voegeli, Frederick

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.


Wetherbee, Bradley, M.

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


Wetherbee, Bradley, M.

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


Wilga, C.D. and P. J. Motta

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.


Wyffels, Jennifer T., Bodine, A. B., Wourms, J. P., Luer, Carl A., and Walsh, Cathy J.

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


Yaptinchay, Arnel Andrew S.P., Uy, Roel, and Alava, Moonyeen Nida R.

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.


Yano, Kazunari, Sato, Fumihiko, and Takahashi, Tomoko

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.