2006 AES Abstracts



(IEB, DJM) University of Florida, Department of Fisheries and Aquatic Sciences, 7922 NW 71st St., Gainesville, FL, 32653, USA; (JKC) NOAA Fisheries Service, 3500 Delwood Beach Rd., Panama City, FL, 32408, USA

Trophic dynamics of the Atlantic Angel Shark in the northern Gulf of Mexico

Atlantic angel sharks (Squatina dumerili) were collected for stomach content analysis from a trawl fishery in northeastern Florida on 11 February (n=50) and 29 April (n=59) 2005. Angel sharks consumed mostly teleost fishes (90% occurrence in stomachs containing food), with Atlantic croaker (Micropogonias undulatus) being the most common fish species in both diets. Other prey items that contributed to the diet but were less important than teleosts overall were squid (Loligo sp.) and crustaceans, occurring in 17% and 14% of non-empty stomachs, respectively. Cumulative prey curves were used to assess the sample sizes for both sampling trips and indicated that the diets were well described in both cases. To estimate the potential prey size and abundance available to angel sharks, portions of the trawl catch in which angels sharks were landed were sampled using a stratified random design during normal sorting operations. These samples were used to quantify prey availability based on total catch numbers recorded by the fishery. Prey items from stomach contents were roughly proportional to prey abundance, though squid, Atlantic croaker, and some eels (F. Ophidiidae) were preferred. Stomachs previously collected (n=442) will be used to assess prey size selection, and ontogenetic and seasonal shifts in diet.


(LAKB, DAE) Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA, 95039, USA; (DAD) Department of Biological Sciences, Millersville University, P.O. Box 1002, Millersville, PA, 17551, USA; (DJL) Department of Biology, St. Mary’s College, 1928 St. Mary’s Road, Moraga, CA, 94575, USA; Department of Ichthyology, California Academy of Sciences, 875 Howard Street, San Francisco, CA, 94103, USA

Deep-water submersible sampling for taxonomic research: Discovery of Hydrolagus from the Galápagos Islands (Chimaeriformes: Chimaeridae)

A new chimaeroid species, Hydrolagus sp. nov., is described from the Galápagos Islands. This species represents the second member of the family Chimaeridae known from the eastern equatorial Pacific and the first record of a chimaeroid from the Galápagos Archipelago. Discovery of chimaeras within the Galápagos archipelago is likely due to improvements in sampling technology (i.e. submersibles). The steep slopes and rough volcanic terrain characteristic of deep-water environments in the archipelago have impeded thorough investigation of fish communities with traditional trawling methods. In a joint expedition of the California Academy of Sciences, Smithsonian Institution, Discovery Channel and Imax, ltd., the submersible Johnson Sea-Link II sampled the Galápagos archipelago to depths of 1000 m. Nine Hydrolagus sp. nov. were observed at depths from 396–506 m along slope habitat composed of igneous boulders, cobbles and pebbles. A single specimen was collected with a suction hose, allowing the individual to retain fresh coloration and natural morphology for surface observation. Hydrolagus sp. nov. can be distinguished from congeners by a combination of the following characters: small head with short, blunt snout; dorsal spine, when fully depressed against the body, extending well beyond both the distal tip of the first dorsal fin and the origin of the second dorsal fin; preopercular and oral lateral line canals branching from the same node off the infraorbital canal and sharing a short common branch; dorsum medium brown with numerous narrow, sharply delineated circular and elongate white blotches; ventrum white to tan with extremely fine brown mottling. This study demonstrates the benefits of using submersibles as a method of taxonomic research, allowing identification of a new species from limited type material while yielding information on live body color, behavior, distribution and habitat associations with accuracy and precision that would be otherwise unavailable from deep waters.


(BM) CICIMAR-IPN, Av. IPN s/n, Colonia Palo Playa de Santa Rita, La Paz, Baja California Sur, C.P. 23096, Mexico; (RA, JA) Carrera 2 No. 11 – 68 Edificio Mundo Marino, El Rodadero, Santa Marta, Colombia

Observations of courtship and mating in the Nurse Shark (Ginglymostoma cirratum), in Cartagena, Colombia

The nurse shark courtship and mating behavior in the Rosario Islands Aquarium in Colombia is described on 10 days direct observations (7 daily hours) on the captivity sharks, during June 2002. A general ethogram was obtained, in where four courtship events were identified (precoupling, coupling, positioning and alignment), and also three mating events (insertion, copulation and postcopulation). Twenty-two sharks were observed (14 males and 8 females) with more than 50 mating attempts. Each mating event had a mean length of 2 minutes, although a 15 minutes length was registered. The short lengths of these courtships and mating events is because of the fact that captivity shows a safe environment, in where distractions are rare, so females don′t run away and there were few males competing for females. Most of mating events were successful, taking place mainly during early morning. The released semen into the water was detected at the end of copulation when the male′s clasper was extracted from the female′s cloaca. Behavior observations were made in the group of sharks, and as well as in other surveys, males competed for females or helped each other for copulation. Four births were registered after capsules were found empty in the sharks’ enclosure. Only a 270 mm long male was found associated to these births, maybe because the others went out trough the enclosure mesh. This survey extends the given information by other investigations on the species, since these are incomplete or short.


NOAA Fisheries, Southeast Fisheries Science Center, Panama City Laboratory, 3500 Delwood Beach Rd., Panama City Beach, FL, 32408, USA

Diet of the roundel skate Raja texana from the northern Gulf of Mexico

Skates are an important component of benthic marine ecosystems. Fishery management stresses the need for an ecosystem approach, but skates have often been ignored. To evaluate trophic role, the diet and feeding habits of the Roundel Skate Raja texana have been examined from offshore waters in the northern Gulf of Mexico. Diet was assessed by life-stage and quantified using six indices: percent by number, percent by weight, frequency of occurrence, the index of relative importance (IRI), IRI expressed on a percent basis (%IRI), and %IRI based on prey category (%IRIPC). Preliminary analysis of stomachs from 31 juveniles (25 non-empty; mean DW=23.5 cm) and 46 mature individuals (39 non-empty; mean DW=32.2 cm) indicate shrimp make up 95 %IRIPC of juvenile skate diet with Family Solenoceridae as the most important (22.1 %IRI). Osteichthyes (Micropogonias undulatus and Ophidium sp.) were also found in the diet of juvenile skates although in much smaller amounts (0.9 %IRI and 2.9 %IRI, respectively; 3.2 %IRIPC overall). Mature skate diet was also predominantly shrimp (58.6 %IRIPC). Crab and other crustaceans (e.g., Squilla sp.) were also found in the diet (2.3 and 17.4 %IRIPC, respectively). Osteichthyes (all unidentifiable) made up 21 %IRIPC of mature skate diets. Preliminary analysis does not indicate ontogenetic diet shifts; however, mature individuals consistently have larger and more than one prey item or type in their stomachs.


Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Rd., Moss Landing, CA, 95039, USA

Comparative feeding ecology of four sympatric skate species (Bathyraja and Raja spp.) off central California

The big (Raja binoculata), California (R. inornata), longnose (R. rhina), and sandpaper (Bathyraja kincaidii) skates are the most common batoids taken over soft-bottom regions of the central California continental shelf and upper slope. Based on the results of previously conducted species-specific diet studies, the feeding ecology of this assemblage was compared to evaluate the degree of trophic separation among species. Specimens were collected from 2002-2005 NMFS, Santa Cruz Laboratory trawl surveys conducted between 18-823 m. Using single (%W, %N) and compound (%IRI) index values, overall, ontogenetic, spatial, and temporal diet composition were compared with traditional (e.g., similarity indices) and multivariate (e.g., Principal Components Analysis, MANOVA) techniques. Raja binoculata consumed primarily demersal teleosts (e.g., Citharichthys spp., Porichtys notatus, Sebastes spp.), crustaceans (e.g., crangonid shrimps, Cancer gracilis, Mursia gaudichaudii), and cephalopods (e.g., Octopus rubescens, Loligo opalescens). Diet composition of R. inornata was similar, consisting mainly of crustaceans (e.g., M. gaudichaudii, C. gracilis, crangonid shrimps), demersal teleosts (e.g., Chilara taylori, Citharichthys spp., P. notatus), and cephalopods (e.g., L. opalescens). The diet of R. rhina was comprised largely of demersal teleosts (e.g., Sebastes spp., pleuronectiforms, Merluccius productus), shrimps (e.g., Neocrangon resima), euphausiids (e.g., Euphausiidae), and cephalopods (e.g., O. rubescens). Bathyraja kincaidii, the smallest of the studied species, ingested euphausiids (e.g., Euphausiidae), polychaetes (e.g., Onuphidae, Nephtyidae), cephalopods (e.g., Teuthida), shrimps, and teleosts (e.g., Myctophidae). The trophic ecology of this skate assemblage was further investigated to elucidate its role in benthic food webs off central California.


(MPB-P) Posgrado en Ciencias del Mar y Limnología, UNAM, Circuito exterior s/n, Ciudad Universitaria, México D.F., Mexico; (FG-M) Centro Interdisciplinario de Ciencias Marinas, CICIMAR-IPN, Av. Politécnico Nacional s/n, Col. Playa Palo de Santa Rita, La Paz, B.C.S. México, COFAA-IPN; (JFM-F) Centro Regional de Investigaciones Pesqueras, Mazatlán. Instituto Nacional de la Pesca, Calzada Sábalo-Cerritos, S/N CP 82010, Mazatlán, Sin., México

Trophic ecology of the Banded Guitarfish, Zapterix exasperata, in the central Gulf of California

The banded guitarfish, Zapterix exasperata is one of the most important ray caught in the Sonora artisanal fishery. Stomach contents of 475 banded guitarfish were analyzed. The rays were caught in the central portion of the Gulf of California close to Guaymas and Bahia de Kino from November 2004 to july 2005. Stomach content was found in 33% of the specimens examined. The main prey species found were the daisy midshipman, Porichthys margaritatus (54%), followed by the northern anchovy Engraulis mordax (6.84%) and striped cusk eel, Ophidion galeoides (6.35%). The trophic niche breadth (Levins Index) and diversity index (Shannon-Wiener) indicated that banded guitarfish is a specialist feeder, because predate mainly in one species (P. margaritatus). We found a trophic overlap (Morisita-Horn index= 0.75) between sexes, but no between juveniles and adults (Morisita-Horn= 0.23).


(MEB, GDG, ETJ, TJM, CGL) California State Univ. Long Beach, Dept. of Biological Sciences, CA, 90840, USA; (JBO) Monterey Bay Aquarium, Monterey, CA, 93940, USA

Occurrence of juvenile white sharks (Carcharodon carcharias) in fisheries throughout the Southern California Bight

Much of what is known about the distribution of white sharks (Carcharodon carcharias) off the coast of California has come from fishing data and field observations, with a majority of these observations focused on subadult and adult sharks. Adults are typically observed north of Point Conception, while juveniles are thought to be more common in the Southern California Bight (SCB). However, the degree to which white sharks are influenced by local fisheries in southern California is unknown. We analyzed fisheries data to describe juvenile white shark distribution throughout the SCB and examine the degree of fishery interaction. Sources examined included: (1) scientific observers and fisherman logbooks from the drift gillnet fishery in the SCB; (2) DFG and NMFS tagging research; (3) recreational landing and shark tournament records; and (4) sightings from fishers and lifeguards. The degree of fishery interaction varies widely by fishery and over time. Juvenile white sharks are caught by both recreational and commercial fisheries closer to shore. Based on data from southern California only, it is unclear whether historic changes in fishing methods have significantly decreased juvenile white shark catch and to what extent sharks may interact with fisheries off Baja, Mexico.


(RB) 351 E 4th St, 1D. New York, NY, 10009, USA; (CD) Department of Conservation, Auckland, New Zealand; (MF, MM) National Institute of Water and Atmospheric Research (NIWA), Wellington, New Zealand; (SO) 2415 Western Ave., Apt. 226, Seattle, WA, 98121, USA

Large-scales spatial dynamics of white sharks (Carcharodon carcharias) in the south Pacific Ocean using satellite tags: A case of foraging migrations?

Recent discoveries about white shark movements using satellite tags have helped scientists draw an increasingly detailed and complete picture of the behavioural patterns of space utilization of the most prominent marine apex predator. All previous information on long-range movements of white sharks using satellite technology has been gathered from only three geographical areas: the waters around Australia, off Southern Africa, and the northwest Pacific Ocean. Here we report on preliminary results from the first study in New Zealand using satellite tags to study sharks. The goals of our study are to unveil the meso- and macro-scale movements, habitat use, and migratory patterns of white sharks from New Zealand waters, as well as the interactions among Southern Hemisphere populations of white sharks. During two expeditions to the Chatham Islands east of mainland New Zealand (April 05 and March 06), an international team of scientists and institutions tagged white sharks using pop-up archival tags and real-time satellite tags. Pop-up archival tag results from the 2005 expedition show most of the tagged white sharks having long- distance northward movements of 1,000-3,000 km towards the open ocean as well as tropical areas in the South Pacific. Our preliminary results confirm recent findings of fast oceanic travel and extremely well oriented and directed navigation to specific sites apparently well-known and commonly visited by white sharks. Circumstantial information suggests that the visits of NZ white sharks to some of these sites might be regular foraging migrations. Further data from the 2006 tagging campaign will be reported in this presentation. The information gathered from our study will be used to support proposals for the conservation of white sharks in New Zealand and the South Pacific Ocean.


CSIRO Marine and Atmospheric Research, GPO Box 1538, Hobart, Tasmania, 7001, Australia

Coastal migrations, temporary residency and site fidelity of white sharks in Australian waters

Recent studies on white sharks have revealed diverse and extensive patterns of movement. The movement patterns of white sharks in Australian waters were investigated using pop-off archival transponding tags (PSATs), direct satellite tracking (SATs) and long-life acoustic transmitters (RCODEs) monitored by listening station arrays moored on the sea floor. Sharks were tagged at various locations around southern Australia and tracked for periods of up to two years. All three electronic tag types recorded extensive movements of individuals covering the species range in Australia from northwest Western Australia around the south coast to central Queensland. Sharks showed a combination of directed long-distance coastal movements, temporary residency at common hotspots and repeatedly returned to selected sites (site fidelity). Movements were generally confined to shelf waters; however, limited offshore excursions were recorded, coupled with dives to a maximum depth of 570 m. In one case a PSAT tag attached to a 3.0 m shark was consumed by what we deduced to be another white shark and disgorged after two weeks. These electronic data, combined with our previous conventional tag data, support the broad-scale mixing of white sharks in Australian coastal waters and across the Tasman Sea to New Zealand.


University of Zurich, Institute of Zoology, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland

Insight into bull shark, Carcharhinus leucas, behavior in the south Pacific

Shark Reef Marine Reserve in Fiji is one of the very few places where up to eight different shark species can be encountered together in a relatively small area. Among them are bull sharks, Carcharhinus leucas, which occur in reasonable numbers for most of the year. Since 2003, the different shark species as well as other vertebrate taxa are monitored on a regular basis. These data allow estimating the local population size by using natural marks and resightings information. I used a modified Petersen estimate to calculate the bull shark population size at Shark Reef at the end of each month in 2004. The total population size was estimated to be 57. The ecology and behaviour of bull sharks are still largely unknown. To address these questions, 11 bull sharks were equipped with pop-up archival satellite tags in 2004. All except one tag reported back and gave insight into the behaviour of the bull shark in the South Pacific. Nocturnal and diurnal depth distributions were not identical. Bull sharks spent more time in deeper water during the day and more time in the top 30 m of the water column during the night. Occasional deep dives were made to a maximum depth of 204.4 m. Ambient water temperatures encountered were between 21.37 and 28.57 C and most time was spent in water of 26-27 C. These data help to better define the ecological niche of this charismatic species.


(SEC) Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia, Canada B2Y 4A2; (MPF) National Institute of Water and Atmospheric Research Ltd, Private Bag 14901, Wellington, New Zealand; (CMJ) Center for Quantitative Fisheries Ecology, Old Dominion University, Norfolk, VA, 23508, USA

Is there a maximum age which can be determined from shark vertebrae?

The age composition of porbeagle sharks (Lamna nasus) in the Northwest Atlantic has been corroborated and validated using a broad range of rigorous techniques, making it one of the most reliably-aged shark species in the world. However, when vertebral sections from New Zealand porbeagles were examined microscopically and under X radiography, the presence of many fine increments near the margin of very old sharks raised concerns that band deposition may not have been annual. Bomb radiocarbon dating supported the ages assigned to New Zealand porbeagles up to about 20 years of age; however, for older sharks, the radiocarbon chronologies were delayed by periods of up to 34 years, suggesting substantial age underestimation. Alternative explanations for the observed radiocarbon patterns in vertebrae were implausible; surface marine radiocarbon in the vicinity of New Zealand was comparable to that found elsewhere in the world, and porbeagle feed on short-lived surface prey that reflect the radiocarbon of surface waters. These results imply that the older New Zealand porbeagles were under-aged from band counts by as much as 50%, and could reach an age of 75 years. Although it seems likely that vertebral band counts provide accurate age estimates under normal conditions, it may be that very slow growing old sharks push the method too far.


(ABC, GMC, DAE) Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA, 95039, USA; (RMS) Moss Landing Marine Laboratories, University of California Sea Grant Extension Program, 8272 Moss Landing Road, Moss Landing, CA, 95039, USA

Patterns of movement and habitat utilization of female leopard sharks in Elkhorn Slough, California

The leopard shark (Triakis semifasciata) is one of the most abundant nearshore sharks in California and is commonly found in bays and estuaries. Elkhorn Slough is a shallow tidal embayment at the edge of Monterey Bay that is extensively utilized by leopard sharks of all ages, for which it is believed to function as a nursery ground. Since much of the life history of leopard sharks occurs in the slough, understanding how sharks utilize this habitat is important. Patterns of movement and habitat use of female leopard sharks in Elkhorn Slough were examined using acoustic tags and a combination of manual tracking and passive monitoring techniques between May 2003 and February 2005. Ten leopard sharks (91-132 cm TL) were tagged and manually tracked for 20-71.5 hours. An additional 13 leopard sharks (78-140 cm TL) were tagged and monitored for 4-443 days using an array of acoustic receivers. Analyses done to date indicate that the Elkhorn Slough National Estuarine Research Reserve marsh restoration site (ESNERR) is important for leopard sharks and may serve as a nursery ground for them. Shark movements and habitat use were tidally influenced, and in terms of large-scale movements, they generally moved with the tides. In the ESNERR they moved up onto intertidal mudflats at higher tides and were restricted to deeper channels during low tides. While in the main channel of Elkhorn Slough they exhibited a highly periodic pattern of movement, during which they were in the upper slough during higher tidal levels and would move up and down the length of the slough during periods of large tidal change. There also was a seasonal pattern of general habitat use, where sharks spent most of their time in the ESNERR during the spring and summer, and more time in the main channel during the fall.


(JKC) National Marine Fisheries Service, Southeast Fisheries Science Center, 3500 Delwood Beach Road, Panama City, FL, 32408, USA; (JO) National Park Service, South Florida Natural Resource Center, 40001 State Road, Homestead, FL, 33034, USA; (TWS) National Park Service, South Florida Ecosystem Office, 950 North Krome Avenue, 3rd Floor, Homestead, FL, 33030, USA

Monitoring the recovery of Smalltooth Sawfish using standardized indices of relative abundance

The U.S. population of Smalltooth Sawfish, Pristis pectinata, is currently listed as endangered under the Endangered Species Act. An important component of monitoring the recovery of this species is establishing long-term baseline trends in abundance. In the absence of scientific survey data, assessing and monitoring the status of some marine species has required the utilization of fishery-dependent data. However, bias is associated with these data because fishers commonly change methods and consequently time series developed from these data require statistical modeling to correct for factors unrelated to abundance. The current center of abundance for smalltooth sawfish in the United States is in the Ten Thousand Islands and Florida Bay region of the Everglades National Park and detailed catch and effort data are available from this region from 1972-2004. The data are collected by Everglades National Park during voluntary dockside interviews of sport fishermen. Interviewers record effort, landings, and releases of all species caught. Using this data, a standardized index of abundance was created for smalltooth sawfish using the delta-lognormal method by combining two generalized linear models. Smalltooth sawfish were not reported until 1989. From 1989, the index shows a small increase in abundance at an average rate of about 3 to 5 percent per year. These results indicate that the population of smalltooth sawfish in the Everglades may have at least stabilized and may be slightly increasing. However, additional data and analyses from multiple sources are required before definitive conclusions on the recovery of smalltooth sawfish can be established.


(DPC, NW, SA, JBG) Scripps Institution of Oceanography, 9500 Gilman Dr., La Jolla, CA, 92093-0204, USA; (CS) Pfleger Institute of Environmental Research, 901-B Pier View Way, Oceanside, CA, 92054, USA; (AB) San Diego State University, Biology Department, San Diego, CA, 92182, USA

Acoustic telemetry studies of common thresher shark, Alopias vulpinus, in the Southern California Bight

The largest commercial shark fishery in California waters is for the common thresher shark, Alopias vulpinus. We used acoustic telemetry to study the fine-scale movement patterns and habitat preferences of the common thresher in the Southern California Bight. One juvenile (fork length, FL: 84 cm) and eight subadult or adult thresher (FL: 122 to 203 cm) sharks were tagged with temperature and depth sensing acoustic transmitters and tracked for up to 49 h. Temperature-depth profiles were made every 2-3 h to characterize the thermal structure of the water column. Position and depth data were plotted in GIS and analyzed in relation to oceanographic data and time of day. Larger threshers utilized areas offshore of the continental shelf, while the juvenile shark remained in shallow waters over the continental shelf. All sharks displayed highly directed movements over entire tracks or extended portions of tracks, although there was no consistent direction of travel among the different sharks. Horizontal rate of movement (ROM) of the eight subadult or adult sharks averaged 2.15 ± 0.46 km h-1 (mean ± SD), and was significantly higher than ROM of the juvenile shark (1.45 ± 0.31 km h-1). ROM peaked at dawn (2.61 ± 0.36 km h-1), and decreased until sunset, as did linearity of shark movements. Maximum ROM for all sharks was 4.42 km h-1. No relationship was found between ROM and FL for the larger sharks. Diurnal movements of several sharks were characterized by repeated vertical excursions below the thermocline into waters less than 10° C (maximum dive depth of 217 m). Nocturnally, local thermocline depth appears to have a strong limiting effect on the vertical distribution of common thresher sharks, and thus affects their susceptibility to the drift gillnet fishery.


University of South Florida, College of Marine Science, 140 7th Avenue South, St. Petersburg, FL, 33702, USA

The directional hearing abilities of elasmobranchs

The hearing abilities of elasmobranchs have long been postulated as being one of their more important and acute sensory modalities. This has recently been brought into question as laboratory experiments have produced results that are contrary to field attraction experiments. Recent data suggest that elasmobranchs can detect a relatively narrow, low frequency range with thresholds that are not as sensitive as many bony fishes. However, an important aspect of audition which has been generally ignored is directional hearing sensitivity. Previous experiments have focused primarily on behavioral responses with the fishes being trained to swim towards a sound source for a reward. We built a shaker system which can stimulate the sharks, auditory system from any direction in three dimensions. The sensitivity to linear acceleration which mimics acoustic particle acceleration was measured using auditory evoked potential measurements from the brain of the brown banded bamboo shark, Chiloscyllium punctatum. Thresholds of detection were obtained from several directions and multiple frequencies to create directional audiograms for determining if sharks primarily detect sound from a specific direction as has been proposed or if they detect sounds from all directions equally.


(RMC) Dalhousie University, Department of Biology, Halifax, NS, B3H 4J1, Canada; (SEC) Department of Fisheries and Oceans, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia, B2Y 4A2, Canada; (SM) Institute of Marine Research, P.O. Box 1870, Nordnes, N-5817 Bergen, Norway

Changes in baseline growth and maturation parameters of Northwest Atlantic porbeagle shark, Lamna nasus, following heavy exploitation

We tested for density-dependent changes in growth and maturation of northwest Atlantic porbeagle shark (Lamna nasus) after intense fishing pressure. Vertebral samples and reproductive data collected from the virgin (1961-1966) and heavily exploited (1993-2004) populations were analysed in order to test for differences in growth and age/size at maturity between the time periods. Porbeagle grew faster and matured earlier after the population had been reduced by 75-80% from fishing. Likelihood ratio tests detected significant differences in reparameterized von Bertalanffy growth models and all of its parameters between the sampling periods. Beyond an age of 7 years, mean length-at-age of recently captured sharks was greater than that of sharks captured during the 1960s. Between 1961-1963 and 1999-2001, size at maturity in males decreased from 179 to 174 cm FL, while size at maturity in females remained unchanged (216 cm FL). This, combined with increased growth rate, led to a decline in age at maturity from 8 to 7 years in males, and from 19 to 14 years in females, since the early 1960s. An analysis of porbeagle temperature associations indicated that sharks occupied similar temperature conditions during the 1960s and 1990s, thereby ruling out the possibility of temperature-induced changes in porbeagle growth. This is the first study to document changes in baseline life-history parameters in an elasmobranch population following exploitation. The observed increase in growth rate and decrease in age at maturity following exploitation support the hypothesis of a compensatory density-dependent growth response, although reductions in interspecific competition could not be dismissed as an alternative explanation.


Laboratorio de Ecología Pesquera, División de Oceanología, Centro de Investigación Científica y Estudios Superiores de Ensenada (CICESE), Km. 107, Carretera Tijuana- Ensenada, C.P. 22860, Ensenada, Baja California, México

Observations on the reproductive biology of Raja inornata (Jordan and Gilbert, 1881), R. velezi (Chirichigno, 1973), and R. rhina (Jordan and Gilbert, 1880) in northern Gulf of California

A total of 520 skates of three species (Raja inornata, R. velezi and R. rhina) were collected from the commercial bottom trawl fishery operating off Puerto Penasco in the Northern Gulf of California, between March 2003 and April 2004. R. inornata had a female:male ratio of 1.2:1 (n=376), where the largest male and female measured 585 and 613 mm in total length (TL), respectively. The relationship between total body mass and TL was significantly different between sexes. The size at which 50% of males were sexually mature was 443 mm TL (75.7% of the maximum size), whereas 50% of females were mature at 514 mm TL (83.8% of the maximum size). The presence of females carrying egg-cases in different stages of development through the year (n=37), suggested a continuous reproductive cycle. Also, male and females were caught in different maturity stages through the range of trawled depths (68-272 m) suggesting a lack of spatial segregation by size and sex in the area. R. velezi had a sex ratio of 1.15:1 (n=73), where the largest male and female measured 910 mm and 1000 mm TL, respectively. The smallest mature male examined had a TL of 650 mm, whereas the smallest mature female measured 790 mm TL. R. rhina presented a sex ratio of 1.09:1 (n=71), with largest male and female size of 800 mm and 950 mm TL, respectively. The smallest mature male examined had a TL of 690 mm, whereas the smallest mature female measured 790 mm. Females of R. velezi and R. rhina attained larger body size and weight than males. And in both species the relationship between total body mass and TL was not significantly different between sexes. The amount of reproductive data collected for these two last species did not allow the outline the reproductive cycle duration.


(PC-A) Programa de Pos-Graduacao em Ciencias Biologicas (Zoologia) and (RSR) Laboratorio de Ictiologia, Departamento de Sistematica e Ecologia, Centro de Ciencias Exatas e da Natureza, Universidade Federal da Paraiba, Joao Pessoa, PB, 58059-900, Brazil; (ASV) Centro de Ciencias Exatas e Naturais, Universidade Federal do Para, Belem, PA, 66075-110, Brazil; (MPA) Programa de Pos-Graduacao em Zoologia, Campus de Pesquisa, Museu Paraense Emilio Goeldi, Belem, PA, 66077-530, Brazil

Reproductive biology of the freshwater stingray Potamotrygon leopoldi (Chondrichthyes: Potamotrygonidae)

Potamotrygonids are completely adapted to live in freshwater and Potamotrygon leopoldi is restricted to the Xingu River basin. Freshwater stingrays present a reproductive mode known as matrotrophic viviparity with development of trophonemata or matrotrophic histotrophy. Specimens (n = 154) were collected in the mid Xingu River region in the years 2003 through 2005. Females (n = 77) and males (n = 77) were dissected and had their main reproductive characteristics studied in the field and laboratory. The following sequence of events was observed: gonadal maturation, copulation, pregnancy, birth and resting. Hepatosomatic index (HSI) values varied from 1.12 – 6.33 for males and 1.23 – 5.86 for females. Gonadosomatic index (GSI) values varied from 0.05 – 3.31 for males and 0.08 – 0.98 for females. HSI and GSI varied according to river level. Gonadal maturation lasts for about 4 months, pregnancy around 5 to 6 months, copulation takes place during the flood season and births begin as the water level goes down. Adult females presented an average ovarian fecundity of 9.7 and uterine fecundity of 4.8. Clasper size and number of embryos were positively correlated to disc width. Embryos (n = 200) were assigned to five different development stages. The results indicate that the reproductive cycle of P. leopoldi is closely related to the hydrologic cycle of the Xingu River and any changes in this system, such as damming, potentially will affect this species reproduction (partially supported by CAPES, WWF – Brazil and ACEPOAT / ACEPOP A).


(JHC, CAL) Instituto Nacional de Investigación y Desarrollo Pesquero, Proyecto Especies Demersales Costeras Evaluación Manejo y Desarrollo, Paseo Victoria Ocampo Número 1 Escollera Norte, Mar del PLata, 7600, Argentina; (MLG) Universidad Nacional de La Plata Facultad de Ciencias Naturales y Museo, Departamento Científico de Zoología Vertebrados, Paseo del Bosque S/N, La Plata, 1900, Argentina

Reproductive biology of Rioraja agassizi from coastal southwest Atlantic between northern Uruguay (34 ̊S) to northern Argentina (42 ̊S)

The Rio skate Rioraja agassizi is a common endemic skate from coastal Southwest Atlantic waters between southern Brazil to northern Argentina (42 ̊S). The objectives of this study were to analyze the size at maturity and the monthly variation in the reproductive condition. A total of 407 individuals (185 females and 222 males) were captured by bottom trawl in the Southwest Atlantic coastal ecosystem between 34 ̊ and 42 ̊S. The size of the smallest mature female was 495 mm and the largest immature female was 565 mm. Female size at 50% maturity (LT50) was 519.5 mm total length (78.01% of the maximum TL). The largest immature male measured 553 mm, and the smallest mature one 443 mm. The TL50 of males was 475.4 mm (76.6% of the maximum TL), which was significantly different of the TL50 of females. In males, significant differences throughout the year were founded in Hepatosomatic Index (HSI) but not in Gonadosomatic (GSI). The females had a partially defined annual reproductive cycle from July (winter) to March (summer) with peaks during November and December (late spring). This conclusion was based on the monthly variation of the GSI, oviducal gland width and largest ovarian follicles diameter. Egg- laying females were found between July and December and with atresic ovarian follicles in December and March. Egg-laying females were found between July and December and with atresic ovarian follicles in December and March.


(CLC) Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, P.O. Box 117800, Gainesville, FL, 32611, USA; (JAM) Virginia Institute of Marine Science, College of William and Mary, P.O. Box 1346, Gloucester Point, VA, 23062, USA

Tracking juvenile sandbar sharks, Carcharhinus plumbeus, in the coastal bays and lagoons of the Eastern Shore of Virginia using a passive acoustic system

Previous manual tracking studies of neonate and juvenile sandbar sharks in the western North Atlantic Ocean have contributed valuable knowledge about the activity space and movements of these animals within their summer nursery areas. The use of a passive telemetry system within the coastal bays and lagoons of the Eastern Shore of Virginia has given us the ability to study longer time scale space use patterns of juvenile sandbar sharks. In addition the use of a passive telemetry system in combination with long battery life transmitters has allowed for the examination of annual survivorship and philopatry of juvenile sandbar sharks within this Virginia nursery area. An array of 15 passive acoustic receivers was deployed in 2003 in an approximately 7.5 km expanse of Millstone Creek in Wachapreague Inlet. This array was expanded to 21 receivers in 2004, and 19 receivers were deployed in 2005. During the summers of 2003 and 2004 transmitters were implanted in 64 juvenile sandbar sharks. The effect of environmental parameters on use of space by juvenile sandbar sharks at varying distances from the inlet and periodicity in the short-term movements of these animals was examined. In addition the attachment of juvenile sharks to the array area was studied using both acoustic data and tag return data. Minimum estimates of annual survivorship and philopatry of juvenile sandbar sharks to the array area were estimated using known fates of sharks in subsequent summers. At least 65% of the sharks tagged with transmitters in 2003 and 2004 survived to the subsequent summer. In addition a high degree of philopatry was demonstrated with 37% of the sharks transmittered in 2003 and 65% of the sharks transmittered in 2004 returning to the array area, one summer after tagging.


(EC) NOAA Fisheries Service, Panama City Laboratory, 3500 Delwood Beach Rd., Panama City, FL, 32408, USA; (EB, CAB) NOAA Fisheries Service, SEFSC, 75 Virginia Beach Dr., Miami, FL, 33149, USA; (PA) CEFAS, Lowestoft Laboratory, Pakefield Rd., Lowestoft, Suffork, NR33 0HT, United Kingdom

Stock assessment of dusky sharks (Carcharhinus obscurus) in the U.S. Atlantic and Gulf of Mexico

Dusky sharks off the U.S. East Coast were classified as a prohibited species in the 1999 NMFS FMP, but were never individually assessed. In 1997, they were designated by NMFS as a candidate species for listing under the ESA and are presently listed by the IUCN Red List of Threatened Species as vulnerable in the Northwest Atlantic and Gulf of Mexico. Despite uncertainty in the magnitude of the catches, all landings/catches showed declines since the early to mid 1990s. Decreasing average size trends suggest that the stock of dusky sharks off the U.S Atlantic and Gulf of Mexico is heavily exploited. All data sources also indicated that the majority of animals caught were immature. Analysis of CPUE series standardized through GLM techniques also yielded decreasing trends. Analysis of biological information in a stochastic demographic framework resulted in very low values of population growth rate as would be expected from a species with very late age at first reproduction (20 years), high longevity (>40 years), and very limited reproductive potential. Accordingly, generation times were also very protracted (30 years) and the juvenile stage identified as the main contributor to population growth according to elasticity analysis. Multiple stock assessment methods were used to assess the status of dusky shark stocks. In the baseline analyses, three forms of surplus production models used predicted current depletions of over 80% of virgin biomass, whereas depletions obtained with a catch-free model were 92% or more of virgin biomass. The age-structured model generally provided the least pessimistic results, but the majority of scenarios still estimated depletions of 62-80% with respect to virgin levels. In all, despite some recent signs of recovery, the various stock assessment methodologies used to estimate present (for 2003) stock status were all consistent in showing large depletions with respect to virgin levels.


Russian Federal Research Institute of Fisheries and Oceanography (VNIRO), 17, V. Krasnoselskaya, Moscow, 107140, Russia, Virginia Institute of Marine Science, Department of Fisheries Science, P.O. Box 1346, Gloucester Point, VA 23062, USA, Moerforsking Aalesund, P.O. Box 5075, Gangstoevika, 6021 Aalesund, Norway, Moerforsking Aalesund, P.O. Box 5075, Gangstoevika, 6021 Aalesund, Norway

New data on two deepwater skates Bathyraja richardsoni and Rajella kukujevi from the North East Atlantic

The deepwater skate fauna of the North Atlantic Ocean has been insufficiently studied. Many deepwater species have been discovered rather recently. Most of these are known from only a few records. Richardson′s skate, Bathyraja richardsoni (Garrick), was described in 1961 from waters around New Zealand. Since the original description, only 66 Richardson′s skates have reportedly been captured. Of these, morphometric data were recorded for 21 adults and 4 advanced embryos. The Mid- Atlantic skate, Rajella kukujevi (Dolganov) was described more recently, in 1985, near the Mid-Atlantic Ridge. Since then only a single additional record appears from the literature, though no morphological data were provided with this record. Several specimens of B. richardsoni and R. kukujevi were caught in the summer of 2004 while sampling aboard the Norwegian trawler R/V G.O. Sars and the Norwegian longliner M/S Loran. Bottom trawls reached depths up to 3500 meters and bottom longlines were set in depths up to 4200 meters along the Mid-Atlantic Ridge from the Azores to Charlie Gibbs Fracture Zone and also in the Hatton Bank area. Additional specimens of R. kukujevi and B. richardsoni were examined at the Museum National d′Histoire Naturelle in Paris, France. Additional data on capture locations of R. kukujevi and B. richardsoni were obtained from the FishBase website (http://www.fishbase.org) and also through personal communications with numerous European fisheries scientists. Prior to our 2004 sampling, Richardson′s skate was unknown from the Mid-Atlantic Ridge. However, our study indicates that this species is common in this area. The 151 specimens captured by the R/V G.O. Sars and the M/S Loran allowed us to obtain new data on external morphology, spatial distribution, size composition, sex ratio, maturation and sexual dimorphism of this species. New data on range, depth, size and external morphological characters of R. kukujevi are presented as well.


Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, Gainesville, FL, 32611, USA

Daily movements and habitat use of immature bull sharks, Carcharhinus leucas, in the Indian River Lagoon System, Florida

Bull sharks (Carcharhinus leucas) are a component of the large coastal shark fishery, and are regularly captured by commercial longline fishermen off the southeastern United States. Effective management of this species requires accurate delineation and description of its critical nursery habitats. Though several coastal bull shark nursery areas have been identified, little is known of their daily activity patterns and habitat use within these areas. We acoustically tracked five young-of-the-year (60-71 cm FL) and five juvenile (79-94 cm FL) bull sharks in the Indian River Lagoon, a shark nursery along the Florida Atlantic coast. Active tracks were 2-24 hours in duration, yielding a combined total of approximately 144 hours of short-term movement and habitat use data. The daily activity spaces of these bull sharks were relatively small (< 5 km2), as compared to the reported activity spaces of other carcharhinids on their nursery grounds. Most of the sharks demonstrated some degree of site attachment to either freshwater creeks or power plant outfalls. During their tracks the sharks swam in depths of 0.2-3.6 m, temperatures of 18.5-34.2° C, salinities of 1.2-31.9 ppt, in dissolved oxygen concentrations of 1.8-8.2 mg/L, and in water clarity levels as low as 0.7 m. The most common activity pattern was swimming parallel to the shoreline, repeatedly patrolling the edges of shallow seagrass beds or deeper dropoffs. There was little evidence of diel changes in activity. This information will help us to better define the habitats that are essential to the growth and development of these immature sharks in this region.


(TDE) University of Hawaii at Manoa, Deptartment of Zoology, 2538 McCarthy Mall, Edmondson 152, Honolulu, HI, 96822, USA; (RDG) Department of Fisheries Science, Virginia Institute of Marine Science, P.O. Box 1346, Gloucester Point, VA, 23062, USA; (BWB, RJT) Hawaii Institute of Marine Biology, P.O. Box 1346, Kaneohe, HI, 96744, USA

Frequency of multiple paternity in an unfished tropical population of sandbar sharks (Carcharhinus plumbeus)

The mating systems of elasmobranchs have received growing attention in the past few years due to worldwide overexploitation and vulnerability of shark populations. The sandbar shark (Carcharhinus plumbeus) is heavily harvested around the world, and constitutes 70% of the largest directed shark fishery in the United States. Although the degree of depletion in most areas is unknown, the population in the Northwest Atlantic was reduced by 80% during the 1980s. As a result of management, this population is currently recovering but remains at approximately 50% of its pre-exploitation levels. Hawaii hosts one of the few populations of sandbar sharks protected from commercial exploitation because of a ban on longline fishing in coastal waters. Strong cultural taboos against killing sharks and the lack of artisanal fisheries make Hawaii one of the only known unfished populations of sandbar sharks in the world. We examined the frequency of multiple paternity in this population through direct sampling of gravid females outside Kaneohe Bay on the Windward coast of Oahu. We genotyped 130 individuals (20 mothers with 3-8 pups each per litter) using 6 polymorphic microsatellite loci and found 12 of the 20 litters were sired by a single male. This sample closely matched the expected population level of multiple mating based on a Bayesian approach which estimates the frequency of multiple mating to be 43.8%, with a 95% confidence interval of 23-63%. Because of difficulty in sampling, few studies to date have examined mating systems in sharks. The Hawaiian population of sandbar sharks represents an important opportunity to gather data on the reproductive biology of a vulnerable shark species without the confounding effects of obvious sources of anthropogenic mortality.


(CDD) Moss Landing Marine Laboratories, Ichthyology laboratory, 8272 Moss Landing Road, Moss Landing, CA, 95039-9647,USA (GMC, DAE) Professor, Moss Landing Marine Laboratories, Ichthyology Laboratory, and Program Director, Pacific Shark Research Center, 8272 Moss Landing Road, Moss Landing, CA, 95039-9647, USA

Age and growth of the roughtail skate, Bathyraja trachura, (Gilbert, 1892) from the eastern North Pacific

To investigate the age and growth of B. trachura, specimens were obtained along the continental slope of the contiguous western United States from the Northwest Fisheries Science Center groundfish survey cruises and commercial fishing vessels. Samples were collected between June 2003 and May 2005. Vertebrae (r2 = 0.94) and caudal thorns (r2 = 0.67) grew proportionately with total length, suggesting that they are appropriate ageing structures for B. trachura. Age was estimated for 237 individuals using band counts of vertebral thin sections and for 100 individuals using band counts of caudal thorns. Bias and precision calculations (vertebrae, APE = 12%, CV = 16%, D = 11; caudal thorns APE = 11% CV = 21%, D = 15) for both structures were similar. When band counts were compared between structures, there was a significant difference in age estimates (t = 3.00, p < 0.01). The maximum ages estimated from vertebrae (18 yrs, females; 20 yrs, males) were older than those estimated from caudal thorns (9 yrs, females; 9 yrs, males). Vertebral growth provided a better fit to total length; therefore vertebral age estimates were selected for growth analysis. Multiple growth functions were fitted to age at length and age at weight data. The 2-parameter Von Bertalanffy Growth function using age at length data provided the best fit (female, r2 = 0.92, SEE = 5.22; males, r2 = 0.89, SEE = 6.61). There is no statistical difference between the growth of males (Linf = 95.95 cm, k = 0.10 y-1) and growth of females (Linf = 103.29 cm, k = 0.08 y-1).


(CLD) Moss Landing Marine Laboratories, 8272 Moss Landing Rd., Moss Landing, CA, 95039, USA; (RMS) University of California Sea Grant Extension Program, 8272 Moss Landing Rd., Moss Landing, CA, 95039, USA

Movements and habitat utilization of the Prickly Shark, Echinorhinus cookei, in the Monterey Submarine Canyon

Spatial utilization and movement patterns are fundamental to understanding the life history of a species. The prickly shark, Echinorhinus cookei, is a poorly known large predator that commonly occurs at the head of the Monterey Submarine Canyon (MSC). It has a distribution throughout the Pacific Ocean and is characterized in the literature as a deep-water species (100 – 650 m). Several observations and catches have been made at the head of the MSC in water less than 60 m deep. These observations are in contrast with the generally accepted depth distribution of prickly sharks and lead to questions about their depth range and movement patterns. We used acoustic telemetry to determine the movements, habitat utilization patterns, and seasonal abundance of prickly sharks in the MSC. Acoustic transmitters were implanted in 10 female and 5 male prickly sharks from March – August 2005. Tagged sharks ranged in size from 1.7 – 2.5 m. Acoustic signals from tags were collected by a combination of active tracking from the surface and passive tracking via moored receivers. Male and female prickly sharks exhibited a pronounced diel movement pattern. The pattern included an offshore movement along the axis of the canyon during the day and an onshore movement at night. To date, tagged sharks have had sustained residency at the head of the MSC in depths less 60 m, which is much shallower than the depth range reported in the literature. A 95 % kernel utilization distribution was calculated to determine home range size for each prickly shark.


(MRC) Departamento de Biologia-FFCLRP, Universidade de São Paulo,
Av. Bandeirantes 3900, Ribeirão Preto, SP, CEP 14040-901, Brazil; (ULG) Departamento de Zoologia, Universidade do Estado do Rio de Janeiro, Instituto de Biologia, Rua São Francisco Xavier 524, Rio de Janeiro, RJ, CEP 20559-900, Brazil

A systematic overview of the Brazilian skate fauna (Chondrichthyes: Rajidae)

We present here an updated review of the systematics of skates occurring in the western South Atlantic off the coast of Brazil, based in part on newly collected material. The skates from this region represent just over 40% of its batoid fauna, and has grown considerably in recent years due to a Federal sampling program carried out on the Brazilian continental slope. We report 26 to 31 rajid species placed in 12 to 15 genera from this region, namely: Cruriraja rugosa, Dipturus flavirostris, Dipturus teevani, Dipturus garricki, Dipturus leptocauda, Dipturus mennii, Dipturus sp. 1, Dipturus sp. 2, Rajella sadowskii, Rajella purpuriventralis, Rajella fuliginea, Breviraja spinosa, Malacoraja obscura, Gurgesiella atlantica, Gurgesiella dorsalifera, Atlantoraja cyclophora, Atlantoraja castelnaui, Atlantoraja platana, Rioraja agassizi, Bathyraja schroederi, Psammobatis bergi, Psammobatis extenta, Psammobatis lentiginosa, Psammobatis rutrum, Sympterygia acuta, Sympterygia bonapartii, and three unidentified species which are still unassigned to genus. Additionally, a Dactylobatus and another Dipturus species have been reported locally in Brazil (material not examined by us). Some of the species and genera are reported here for the first time from this region, but a few of these were originally described from the western North Atlantic, Gulf of Mexico and Caribbean Sea. The species range vertically from shallow coastal waters to the lower continental slope. Taxonomic and biogeographic aspects of this skate fauna are also treated.


(JDD, APH) McGill University, Redpath Museum and Department of Biology, 859 Sherbrooke St. W., Montréal, QC, H3A 2K6, Canada; (KAF) The Field Museum, Pritzker Laboratory for Molecular Systematics and Evolution, 1400 South Lake Shore Drive, Chicago, IL, 60605, USA; (SHG) Rosenstiel School of Marine and Atmospheric Science, Division of Marine Biology and Fisheries, 4600 Rickenbacker Causeway, Miami, FL, 33149, USA

When bigger is not better: Selection against large size, high condition, and fast growth in juvenile lemon sharks

A lemon shark nursery site at Bimini, Bahamas, was exhaustively sampled from 1995 to 2000. Morphological measures were obtained from approximately 200 individually-tagged juvenile sharks per year and their survival was recorded in subsequent years. To test the bigger is better and faster is better hypotheses of life- history theory, we determined whether body size, condition factor, or growth rate were related to survival. The mark-recapture program, MARK 5.1, was also used to validate our study site and population as one suitable for estimating the strength of selection. In young of the year sharks, selection on all measured traits was weak, but consistently suggested selection against large size, high condition, and fast growth. The pattern was similar but much stronger for age-1 juveniles. These results suggest that selective pressures at Bimini may be constraining the size and growth of juvenile sharks. These conclusions fit well with the observed low growth rate at this site.


(AD, WAB) The University of West Florida, Department of Biology, 11000 University Parkway, Pensacola, FL, 32514, USA; (SHG) The University of Miami, Rosensteil School of Marine and Atmospheric Sciences, 4600 Rickenbacker Causeway, Miami, FL, 33149, USA

Thermal ecology and activity patterns of juvenile lemon sharks, Negaprion brevirostris, in a shallow water nursery

Ten juvenile lemon sharks (Negaprion brevirostris) captured between July of 2004 and April of 2005 were fitted with iButton temperature loggers and internal acoustic telemetry tags to simultaneously monitor diel movements and body temperatures. Temperature loggers were also used to record daily environmental temperatures within the home range of each individual shark. Regression analysis of a small pilot study examining the relationship between internal body and external water temperature showed a highly significant relationship (R = 0.995; p<0.001) and suggested that juvenile lemon sharks have a relatively small thermal inertia. Consequently, body temperature data show that juvenile sharks did not attempt, and perhaps were precluded from, behaviorally maintaining a constant internal eccritic temperature. Rather the sharks appeared to behaviorally exploit home range thermal heterogeneity in a way that allowed the body temperature of the juveniles to approach the upper end of the temperatures available. The heat loading phenomenon was observed at all times but was most pronounced in the hours between mid- afternoon and dusk (p < 0.001). It is possible that by maximizing heat loading lemon sharks prolong the efficiency of activities such as feeding or digestion well into the cooler periods of the night. Large fluctuations in body temperature may also have negative bioenergetic impacts that may explain the slower growth rates of juveniles in Bimini compared to other known lemon shark nurseries. Laboratory work relating to the temperature preference of lemon sharks and temperature mediated respirometry would shed more light into the importance of these findings and allow a better understanding of the physiological implications of thermal habitat selection in this group.


Pfleger Institute of Environmental Research, 901-B Pier View Way, Oceanside, CA, 92054, USA

Description of a white shark aggregation in the eastern Pacific (Guadalupe Island, Mexico) using photographic methods

White sharks, Carcharodon carcharias, aggregate annually around Guadalupe Island, Mexico. A method of photo-identification (photo-ID) was developed and used to document individual white sharks present at the island from 2001 through 2005. The most reliable features for repeat identification across multiple years were the pigment patterns on the gill flaps, pelvic fins, and caudal fins. Pigment patterns in all three regions were asymmetrical on the right and left sides making it necessary to photograph both sides to catalogue each individual. However, once catalogued, an individual could be identified using less than the full complement of observations from both sides. The present study, based upon this photo-ID method, addressed the following questions: (1) Do individual sharks identified at Guadalupe Island demonstrate annual site fidelity?, (2) What is the sex ratio of the Guadalupe Island white sharks? and (3) how many white sharks frequent Guadalupe Island? This study identified over 60 individual sharks around Guadalupe Island, many of which have been sighted on several occasions over multiple years. This project has identified Guadalupe Island as an important aggregation site for white sharks and in the future may be used to complement studies on long-range movements, population dynamics, and recruitment of white sharks in the Pacific.


Pfleger Institute of Environmental Research, 901-B Pier View Way, Oceanside, CA, 92054, USA

Large scale movement patterns of Guadalupe Island, Mexico, white sharks (Carcharodon carcharias) described from archival tag data

Published satellite tagging data from the Farallon Islands, California (USA) and the coast of South Africa have proven white sharks (Carcharodon carcharias) to be capable of lengthy basin-scale migrations. A satellite tagging program targetting an annual aggregation of white sharks found off Guadalupe Island, Mexico, was initiated in 2000. Seventy-two popup tags were deployed on white sharks resulting in tracks of up to 386 days. Seven of the tags were physically recovered allowing us to study high-resolution tag data from several individuals; three of these were recovered from sharks upon their return to the island. White sharks were found to remain near Guadalupe Island between the months of August and April, with a large degree of variability between individuals with respect to the actual time spent at the island. When sharks left Guadalupe, movement was always westerly, with one individual going as far as the Hawaiian Islands. The offshore region occupied by these sharks is large and diffuse; this region appears to be the same as that described by researchers studying white sharks off the central California coast, indicating some degree of connectivity between these aggregations.


Marine Conservation Unit, Department of Conservation, Private Bag 68908, Newton, Auckland 1, New Zealand

Distribution and biology of the white shark (Carcharodon carcharias) in New Zealand waters

The US Atlantic seaboard, South Africa, North Pacific, and southern Australia have long been recognised as centres of abundance for the white shark. Historically the occurrence of white sharks from New Zealand waters was generally considered to be exceptional by the New Zealand public and scientific community. Locally recognised hotspots for white sharks were all located around southern New Zealand and included the Chatham Islands, Otago, Stewart Island and Fiordland. Popular belief was that white sharks straggled to New Zealand from warm Australian waters. Marine scientists gave scientific credibility to this belief by suggesting that oceanic circulation around New Zealand produces a thermal cul-de-sac that trapped white sharks off the east coast of South Island and at Chatham Islands. The distribution of captures, sightings and predation events in New Zealand waters documented by the author since 1991 contrast dramatically with this popular view of white shark distribution and ecology. White sharks are widely distributed within the New Zealand exclusive economic zone, occurring in coastal and oceanic waters from about 33oS to 52.5oS (Campbell Island). Information on distribution, nursery areas, size at maturity, diet and potential threats obtained from more than 460 records of white sharks from New Zealand is presented. This information provides the biological context to the collaborative satellite tagging studies currently being undertaken at the Chatham Islands and around mainland New Zealand, and will be used along with information from these and other tagging studies to inform the conservation and management of the species in the southwest Pacific.


Pacific Shark Research Center/Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA, 95039, USA

Standardized diet composition and trophic levels of skates

Skates (Rajiformes: Rajodei), although fairly conservative morphologically, are the most diverse elasmobranch group with approximately 275 recognized species. They are common components of benthic communities in temperate and boreal regions, where they serve important trophic roles. Most skate species are benthic or infaunal predators on unconsolidated substrates. Although somewhat restricted in habitat, skates exhibit considerable dietary diversity, consuming a variety of prey taxa, including: polychaetes, molluscs, crustaceans, and fishes. Trophic estimates for these benthic predators, however, are virtually non-existent. Therefore, to better understand the ecological role of skates in demersal marine communities, we present standardized diet compositions and trophic levels calculated from published quantitative studies. Trophic level values were estimated for all available species and compared among taxa, size classes, and regions. Given the diversity and abundance of skates in many regions, results of this study could prove useful for elucidating benthic food web dynamics and for effective ecosystem-based management.


Centre for Environment, Fisheries and Aquaculture Science (Cefas), Pakefield Road, Lowestoft, Suffolk, NR33 0HT, United Kingdom

The biology of smalleyed ray Raja microocellata in the Bristol Channel

Smalleyed ray Raja microocellata has a restricted distribution in north-western Europe, though is locally abundant in sandy bays. The Bristol Channel is an area where it is relatively abundant, and it is the second most important rajid in this area, accounting for 34.9% (by numbers) and 37.8% (by biomass) of the rajid assemblage. Juvenile fish ranging from 160-320 mm length are abundant in intertidal areas and, during the summer, grow at a rate of 0.91mm.d-1 (0.98g.d-1). Larger fish occur further from shore and the overall sex ratio in this area is 1:1. Data on the morphology, dentition, distribution and reproductive biology are provided. The diet is composed primarily of Crangon crangon, mysids, teleosts and amphipods.


Husbandry Division, Monterey Bay Aquarium. 886 Cannery Row, Monterey, CA, 93940, USA

Captive feeding and growth of a juvenile white shark, Carcharodon carcharias, at the Monterey Bay Aquarium

The Monterey Bay Aquarium conducted a three year program with the support of colleagues from the Hopkins Marine Station of Stanford University, the Shark Lab at California State University at Long Beach and the Southern California Marine Institute to display a live white shark, Carcharodon carcharias. This program culminated in the display of a juvenile white shark in the 1.2 million gallon Outer Bay exhibit for 198 days, during which time attendance at the aquarium increased 34%. The Outer Bay exhibit displays a variety pelagic fishes such as yellowfin tuna, Thunnus albacares, Pacific bluefin tuna, Thunnus orientalis, and scalloped hammerhead sharks, Sphyrna lewini. This exhibit is 27.5 m long, 16.0 m wide, 10.7 m deep and maintained at 20 degrees C. During this time the white shark was fed mostly king salmon, Onchorhynchus tshawytscha, and Pacific mackerel, Scomber japonica, at a mean daily ration of 747 grams + 558 (S.D.) or 1.6 % body mass per day + 1.4 (S.D.). The initial mass of the white shark on September 14, 2004 was 28.0 kg and total length was 151 cm (over the curve); the final mass on March 31, 2005 was 73.4 kg and total length was 194 cm. The captive white shark gained a total of 45.4 kg for a gross conversion of 30.9 % and grew at an annual rate of 79.3 cm/yr, which is over two times faster than the estimated growth in the wild.


(VVF) Iowa State University, Dept. of Ecology, Evolution, and Organismal Biology, Ames, IA, 50011, USA; (MTM) University of Virginia, School of Law, Charlottesville, VA, 22903- 1738, USA

Taxonomy review of the Sawfish (Chondrichthyes, Pristidae)

Sawfishes are among the most endangered elasmobranch species. But conservation measures have been hampered due to the unsettled situation of the taxonomy of this group. The goals of this study were to answer the three primary and urgent questions about sawfish taxonomy. Question 1: How many species (real entities) exist? To answer this question we examined external morphology (morphometric and meristic characters) of specimens deposited in 14 public museums located in the USA, Brazil and five European countries. In addition, molecular evidence was investigated by sequencing a partial mitochondrial gene from representative museum specimens and four mitochondrial and three nuclear genes from specimens directly sampled in the field. Question 2: What is the distribution range of each one of these entities? Information was gathered from identification of museum specimens, review of museum and literature records, archaeological remains and anthropological artifacts. Question 3: What are the most appropriate names (available nominal species) to be assigned to each one of these entities? In order to answer this question we reviewed original descriptions and examined historical specimens deposited in collections. The obtained results will be discussed in the context of a formal proposal about valid sawfish species.


(ME, FDE, SLB, DAJM) Universidad Nacional de Mar del Plata, Facultad de Ciencias Exactas y Naturales, Departamento de Ciencias Marinas, Laboratorio de Ictiología, Funes 3350, 7600, Mar del Plata, Argentina; (DAJM, CJH, MAM) Instituto Nacional de Investigación y Desarrollo Pesquero, Paseo Victoria Ocampo s/n, 7600, Mar del Plata, Argentina; (ME) Museo del Mar, Colón 1114, 7600, Mar del Plata, Argentina; (DAJM, SLB, CJH) Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina

Chondrichthyan egg cases from the southwestern Atlantic

Egg cases of 16 species of oviparous chondrichthyans from the southwestern Atlantic were described and compared. Samples (n= 130) were obtained from females containing egg cases in their uteri and egg cases found in benthic samples, collected during research cruises carried out by the Instituto Nacional de Investigación y Desarrollo Pesquero on the Argentinean continental shelf (34 °-55 ° S) and from captivity specimens in Museo del Mar. Eight morphometric characteristics were measured following traditional methodology and two more were added, keel thickness (KT) and straight distance from anterior apron margin to curvature of anterior horn. The speciose genus Psammobatis, whose ECL (egg case length without horns) ranged 25-53 mm, presented a great variety of egg cases features and showed the smallest ECL. Those of the endemic genus Sympterygia (ECL range: 51-68 mm) presented the highest KT and the longest posterior horns. Egg cases of Rioraja agassizi (EC range: 61-68 mm) had relative straight sides. Egg cases of the genus Bathyraja (ECL range: 75-98 mm) were characterized by a conservative morphology, rough surface case and curved horns. Atlantoraja castelnaui presented a large egg case with a wide lateral keel (ECL range: 97-104 mm). The genus Dipturus (ECL range: 115-230 mm) showed the largest ECL and very developed posterior apron. The unique oviparous shark that occurs in Argentinean waters, Schroederichthys bivius , had a cigar-shaped egg case with curled tendrils on posterior tip. Egg cases of the elephant fish, Callorhynchus callorhynchus , were spindle-shaped with anterior and posterior tubular extensions. Chondricthyans egg cases can be a useful tool for identifying individual species and egg laying areas, therefore a provisional key to the southwestern Atlantic chondricthyans egg cases was constructed. Some results presented in this abstract are part of an ongoing study about ecology, biology and biodiversity of species of Bathyraja on the Argentinean continental shelf.


Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, P.O. Box 117800, Gainesville, FL 32611, USA; National Marine Fisheries Service, Southeast Fisheries Science Center, Mississippi Laboratories, P.O. Drawer 1207, Pascagoula, MS 39568, USA; National Marine Fisheries Service, Southeast Fisheries Science Center, Panama City Laboratory, 3500 Delwood Beach Road, Panama City, FL 32408, USA

Reproductive cycle of the blacknose shark, Carcharhinus acronotus, in the Gulf of Mexico

The reproductive periodicity of blacknose sharks, Carcharhinus acronotus, in the northern Gulf of Mexico was determined by examining reproductive tissues from specimens collected monthly from 2002 through 2005. Monthly changes in shell gland weight, right ovary weight and ovarian follicle diameter were assessed for 74 mature females. Temporal changes in testes weight, testes width and percent of mature spermatocysts were examined for 64 mature males. Trends in female reproductive tissues suggested an annual peak in reproductive activity during June and July, while trends in male parameters suggested an annual reproductive peak during May and June. Although male and female reproductive activity peaked in different months, a strong synchronicity existed between the percent of mature spermatocysts and the diameter of the largest ovarian follicle. Based on these results, the mating season of blacknose sharks lasts from mid May to July in the Gulf of Mexico. Maximum embryo sizes were observed in May which suggested that partition occurs during late May or early June. Results indicate that blacknose sharks have a clearly defined annual cycle in the Gulf of Mexico. This conclusion is further supported by the complete absence of gravid females without vitellogenic ovarian follicles among all mature females examined.


National Institute of Water and Atmospheric Research, Private Bag 14901, Wellington, New Zealand

Habitat, movements and life history of the deepwater Antarctic starry skate,

Amblyraja georgiana

Antarctic toothfish (Dissostichus spp.) are targeted by a longline fishery in 600-1500 m depth in the Ross Sea, Antarctica. Skates, mainly Antarctic starry skate Amblyraja georgiana, are an important bycatch of the fishery, comprising around 10% of the catch. In recent years, most skates have been released from the longlines at the surface on hauling, and many of these have been tagged. Recapture rates are low, but there have been some between-season recaptures, and moderate movements, showing that some skates survive capture and tagging from depths greater than 1000 m. The spatial and depth range of the starry skate are summarised using commercial and observer data. Starry skates mature at about 64 cm pelvic length (PL) for males and 66-69 cm PL for females. Length-frequency data indicate that a large proportion of the catch is immature. Vertebrae and caudal thorns were examined for their utility as ageing structures, and the latter were used to age specimens and generate growth curves. Although the age estimates are unvalidated, they suggest that starry skates grow rapidly, reaching sexual maturity at 6-7 years for males and 8-11 years for females. The oldest skate was 14 years, but this probably underestimates longevity.


(MPF, MJM) National Institute of Water and Atmospheric Research, Private Bag 14901, Wellington, New Zealand; (RB) 351 E 4th St, 1D, New York, NY, 10009, USA; (CD) Marine Conservation Unit, Department of Conservation, Auckland, New Zealand; (SO’B) 2415 Western Ave, Apt 226, Seattle, WA, 98121, USA

Surface cruising and deep diving during ocean crossings by white sharks (Carcharodon carcharias)

Until the advent of data-recording electronic tags, accurate information on the depth distribution of large marine animals was nearly impossible to obtain. This technology has opened an exciting new window into the vertical behaviour of white sharks. Through an international research collaboration, pop-up archival tags were attached to white sharks at the Chatham Islands, east of mainland New Zealand, in April 2005 and March 2006. Preliminary results indicate that the sharks spend nearly all of their time shallower than 100 m depth while patrolling near a seal colony over a period of 2-5 months. During trans-oceanic migrations of up to 3,000 km, their behaviour changes dramatically, with most of their time being spent in water shallower than 10 m (including a high proportion in the top 1 m), punctuated by periodic deep dives. This produces a strongly bimodal depth distribution, which is consistent with the behaviour shown by the two other migrating white sharks reported in the literature

to date. In some sharks, we observed diurnal variability in the diving behaviour. This vertical movement pattern, in combination with a migration from cool temperate waters to the tropics, results in the sharks experiencing a very wide range of ambient water temperatures. We present several hypotheses that might explain the observed patterns.


(BRF, JRS) Drexel University, Dept. of Biosciences, Philadelphia, PA, 19105, USA; (SHG) University of Miami, Rosenstiel School of Marine and Atmospheric Sciences, Miami, FL, 33176, USA and Bimini Biological Field Station, Bimini, Bahamas

Behavioral strategies of space use by young lemon sharks (Negaprion brevirostris) in their primary nursery areas

We studied a population of neonate and juvenile lemon sharks within two primary nursery areas at Bimini, Bahamas using both active and passive telemetry to answer questions about movement patterns and habitat selection. Between July 2002 and December 2005 we implanted transmitters in 66 neonate and juvenile lemon sharks; actively tracking 50 individuals and monitoring 16 using bottom mounted acoustic receivers. Ten individuals were tracked for longer than one year and one individual was monitored for the entire 3-year study. Research questions being investigated include: Do lemon sharks exhibit habitat selection within the primary nursery areas; do environmental factors affect the movements of juvenile sharks; are movements within the nursery correlated with areas of low predation risk and/or high prey availability; does time of day, season, age of shark, or site affect either activity patterns or habitat preference; is the shift from primary to secondary nursery area gradual or rapid? Answers to these questions will help define the role of nursery grounds as essential fish habitat (EFH) and provide information on the early life history and evolution of lemon sharks. Initial results suggest that juvenile lemon sharks have clearly defined home ranges which remain relatively restricted during the first 3 years of life. Preliminary analysis shows that sharks increase home range during the wet season and spend more time in rather low productivity nursery areas where predation risk is lower. As individuals approach 1 meter in length, space use begins to increase and sharks utilize previously unknown areas which may be facilitated because predation risk decreases as size increases to a critical length. Habitat selection in the primary nursery is apparently correlated with water depth, temperature, prey availability, and predation risk. These interrelated factors are the driving influence in habitat choice for neonate and juvenile lemon sharks.


University of Washington, School of Aquatic and Fishery Sciences and Quantitative Ecology and Resource Management, Box 355020, Seattle, WA, 98195, US

Use of reproductive value in the conservation and management of exploited shark populations

Certain life history traits of sharks make juveniles particularly vulnurable to exploitation. Reproductive value and reproductive potential are used to quantify the impacts of age specific removals via the harvest (directed or incidental). The Leslie matrix and a harvest matrix are used to compare the harvests of a long lived and short lived species. A new theorem in demographic analysis is presented. The theorem allows the estimation of population removals as a function of the fraction of reproductive potential removed by a harvest, instead by the instanteous rate of fishing mortality, F. Stochastic projections also associate risk of depletion with the fraction of reproductive potential removed. The bottom line: Conservation efforts should be focused upon preservation of reproductive potential.


(LVC, MA) Universidad Jorge Tadeo Lozano. Facultad Biologia Marina. Carrera 4 # 22-61 Bogota, Colombia; (GMF) Centro Interdiscipliinario de Ciencias Marinas. A.P. 592 La Paz, Baja California Sur, Mexico.COFAA-IPN; (RMR) Universidad Nacional Autonoma de Mexico. Facultad de Medicina Veterinaria y Zootecnia. C.P. 04510. Mexico. D.F.

Mercury bioaccumulation in sharks from Baja California Sur, Mexico

The bioaccumulation of mercury in muscle tissue was determined for four shark species: Carcharhinus falciformis (2.64 ± 0.28 ppm Hg), Isurus oxyrinchus (1.50 ± 0.20 ppm Hg), Sphyrna zygaena (1.33 ± 0.22 ppm Hg) and Prionace glauca (0.82 ± 0.34 ppm Hg), caught off the western coast of Baja California Sur and in the Gulf of California. We obtained significant differences in mercury concentration by shark size, except for P. glauca, which did not present a significant correlation (r=0.09837 p=0.7610). We found no significant difference in mercury concentration between sexes (p=0.4438) among the shark species analyzed. Mercury was also measured in the main prey consumed by the sharks, including jumbo squid (Dosidicus gigas 0.1158 ± 0.0527 ppm Hg), mackerel (Scomber japonicus 0.570 ± 0.0202 ppm Hg), red crab (Pleuroncodes planipes 0.1303 ± 0.0090 ppm Hg), and myctophid fish (Symbolophorus evermanni 0.3396 ± 0.1324 ppm Hg). The prey species that biomagnificate the most mercury to sharks was the squid, with more than 1 ppm Hg. We concluded that all sharks, with the exception of P. glauca, have levels of mercury that are above the established limit for human consumption (> 1 ppm Hg).


Resource Ecology and Fisheries Management Division, Alaska Fisheries Science Center, Seattle, WA, 98115, USA

Age and growth of the big skate (Raja binoculata) and the longnose skate (Raja rhina) being targeted in the Gulf of Alaska

An on-going skate fishery targeting the big skate (Raja binoculata) and the longnose skate (Raja rhina) in the Gulf of Alaska has created a need for age data. Stock assessment requires age estimates to properly manage and conserve marine fishes. Elasmobranches, notably skates and rays (Rajidae), have been identified as a particularly vulnerable group to exploitation due to their large body size, late maturation, and low fecundity when compared to teleosts. In this study we generated age and growth estimates from big and longnose skate thoracic vertebrae. The total length (TL) of both species ranged from 30 to 190 cm. Vertebral thin sections appeared to provide the most reliable ageing preparation. Vertebral bands for the big skate were clearer than those for the longnose skate. Samples from sub-adults (< 60 cm TL) were limited for both species; therefore, back-calculation was performed using image analysis. The maximum estimated age for the female big skate was 13 years (180 cm TL). For the female longnose skate, the maximum estimated age was 17 years (160 cm TL).


(JG, CAM, JPT, HC, EV, EK) Elasmobranch Physiology and Environmental Biology Program, Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL, 34236, USA; (LELR) Department of Biochemistry and Molecular Biology, OGI School of Science and Engineering, Oregon Health and Science University, 20000 NW Walker Rd., Beaverton, OR, 97006, USA; (NJS) Analytical Toxicology Core Laboratory, University of Florida, Box 110885, Gainesville, FL, 32611, USA; (EC, JC) NOAA Fisheries Service, Southeast Fisheries Science Center, 3500 Delwood Beach Road, Panama City, FL, 32408, USA

Variations in breeding success and reproductive endocrinology of bonnethead sharks (Sphyrna tiburo) from four Florida estuaries

Previous studies on reproduction of the bonnethead shark (Sphyrna tiburo) have reported high rates of infertility in populations of this species residing in pollutant- impacted regions on Florida’s Gulf coast. The objectives of this study were to determine the physiological factors that lead to the production of non-fertile ova in S. tiburo and investigate whether these abnormalities were associated with exposure to endocrine-disrupting pollutants, in particular, estrogen-mimicking organochlorine pesticides (OCPs). Reproductive endpoints and serum gonadal steroid concentrations were examined and compared in bonnethead sharks from four Florida estuaries experiencing differing levels of OCP contamination: Apalachicola Bay (high), Tampa Bay (high), Charlotte Harbor (intermediate), and Florida Bay (low). Infertility rate was lower in Florida Bay S. tiburo (1.5%) than in sharks from all other sites (7-10%). The higher rate of infertility in Tampa Bay and Charlotte Harbor sharks, in particular, may be associated with less efficient sperm storage in females from these estuaries, based on differences in the vitality of spermatozoa obtained from the female sperm storage organ. Variations in egg quality may also contribute to infertility, based on lower serum concentrations of 17-estradiol in vitellogenic females from sites exhibiting high rates of developmental failure. Despite endocrine-related differences between populations, the absence of the xenoestrogen biomarker vitellogenin in male S. tiburo from all study sites does not support the hypothesis that sharks from populations with high infertility rates are physiologically altered by OCP exposure. Therefore, the link between infertility and OCP contaminants is tenuous at best. Future studies will investigate other factors, both natural and anthropogenic, that may contribute to the reproductive complications observed in this species.


(RLJ, MNB) Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa; (EG) Department of Animal and Human Biology, University of Rome, Rome; (MAM, WHO) Branch Marine and Coastal Management, Department of Environmental Affairs and Tourism, Private Bag X2, Roggebaai, South Africa

Acoustic telemetry offers new insight into the hunting behaviour of white sharks at a Seal Island

Between June 2001 and December 2005 we attached 98 RCODE acoustic transmitters to white sharks at Mossel Bay, South Africa. During this period we monitored their presence and absence at Seal Island by means of two underwater VR2 listening stations. During 2005, a further three sharks were fitted with continuous acoustic pingers and manually tracked for 605 hours in and around Mossel Bay. Information on spatial and temporal trends in predatory activity was garnished by photographic surveys of shark bitten seals residing at Seal Island and direct observation of attacks. Multiple day tracks of patrolling sharks offer new insights into the feeding periodicity, patrolling behaviour, and behavioural plasticity of individual white sharks at Seal Island. Inter and intra annual patterns of habitat use reveal that the white shark is a seasonal hunter of Cape fur seals that concentrate their hunting activity in the winter period. The seasonal reduction in hunting activity results from change in pinniped availability and accessibility during the mating and pupping season. Diel patterns of hunting confirm that activity is essentially crepuscular with hunting effort concentrated in the early morning and late afternoon and evening. However, speculation that white sharks are obligatory diurnal hunters of pinnpeds is incorrect, as a night time attacks was documented. At this location, high behavioural flexibility by white sharks appears paramount to successfully exploit a pinniped resource whose accessibility can vary dramatically in relation to time, space and anti- predatory stratigies.


(SPG, CDW) University of Rhode Island, Dept. Biological Sciences, 100 Flagg Rd, Kingston, RI, 02881, USA; (MND) University of California Irvine, Ecology & Evolutionary Biology, 321 Steinhaus Hall, Irvine, CA, 92697, USA

Bilateral jaw muscle activity in spiny dogfish

Asynchronous activation of bilateral jaw muscles permits a higher degree of motor control during feeding and food processing. Most previous studies of motor activity in elasmobranchs and bony fishes have implanted electrodes unilaterally to determine basic feeding patterns. Detailed studies of basal bony fish show synchrony during the initial strike at the prey and asynchrony during prey manipulation. Spiny dogfish modulate their behavior dependent on prey type. We predict that dogfish will use synchronous activity during suction or biting, but asynchronous muscle activity during head-shaking. We investigated bilateral muscle activity during feeding on multiple prey items. Electrodes were implanted bilaterally in the dorsal and ventral quadratomandibularis, preorbitalis (jaw adductors), epaxialis (head elevator) and unilaterally in the coracomandibularis (mouth opener) to determine the timing of muscle activation during prey capture. The dorsal and ventral quadratomandibularis, preorbitalis and epaxialis were bilaterally and synchronously active during suction feeding and biting on small pieces of herring, supporting our hypothesis. All muscles were active asynchronously during prey processing. Therefore, dogfish are able to modulate jaw muscle activity based on prey type. Additionally, this implies that independent neural control over the jaw muscles may be an ancestral trait in vertebrates since it is exhibited by a shark, the most basal vertebrate, and a basal bony fish.


NOAA National Marine Fisheries Service, Northeast Fisheries Observer Program, 166 Water Street, Woods Hole, MA, 02543, USA

Incidental catch of sharks from gillnet and otter trawl fisheries from North Carolina to Maine as seen by the Northeast Fisheries Observer Program

Many shark species are caught incidentally in both the otter trawl and gillnet fisheries from North Carolina to Maine. Data collected by the Northeast Fisheries Observer Program were used to examine the numbers of sharks caught incidentally in otter trawl and gillnet fisheries as documented by onboard observers. Twenty- eight species were documented as incidental catch (n=9,074) from 1993 to 2005. The thresher shark, Alopias vulpinus, porbeagle, Lamna nasus, sandbar shark, Carcharhinus plumbeus, dusky shark, Carcharhinus obscurus, blacktip shark, Carcharhinus limbatus, Atlantic angel shark, Squatina dumerili, and Atlantic sharpnose shark, Rhizoprionodon terranovae comprised over 78.9% of the incidental shark catch of observed trips based on numbers of individuals. C. plumbeus, was the most prevalent at 34.5% of the incidental shark catch. S. dumerili made up the largest percentage of incidentally caught sharks in the observed otter trawl fishery, while C. plumbeus made up the highest percentage in the observed gillnet fishery. Of all the sharks caught, 50.8% were alive when initially brought up in the gear, 38.9% were dead and 10.3% were of unknown status. Of the fish brought up alive, 20.5% were kept for market, 73.4% were released alive, 2.9% were discarded dead, and 3.2% were discarded with an unknown status. 55.7% of the fish brought onboard dead were kept for market and 44.3% were discarded. Of the fish with unknown status 89.4% were discarded, 10.4% were kept and 0.2% were unknown. The majority of the individuals in the incidental catch from observed trips were immature based on their size distributions. Further analyses should be conducted to determine the accuracy and precision of these estimates and to examine what effect these levels of incidental catch may have on shark populations in the Northwest Atlantic.


(KJG) Alaska Department of Fish and Game, 3298 Douglas Place, Homer, AK, 99603, USA; (JAM) College of William & Mary, School of Marine Science, Virginia Institute of Marine Science, Route 1208, Greate Road, Gloucester Point, VA, 23062, USA

Demographic analysis of salmon sharks in the North Pacific; testing the intrinsic rebound potential model

The majority of demographic analyses on elasmobranch fishes have used deterministic life-tables (or Leslie matrix models) to calculate intrinsic rates of population increase and other vital rate parameters. While density-dependent compensation is a standard concept in ecology and fisheries biology, incorporating the effect of uncertainty in vital rates into demographic analyses of elasmobranches is a relatively new and extremely useful approach to demographic modeling. We used life-table models incorporating uncertainty by establishing probability distributions for maximum age, age at first reproduction, fecundity and survivorship at age for salmon sharks in the eastern and western North Pacific. Monte Carlo simulations were then used to generate population growth rates, generation times, net reproductive rates, mean life expectancies, population doubling or halving times, and fertility, juvenile and adult elasticities. In order to utilize life-table models for analyses where fishing mortality was included, density-compensation values generated from the Intrinsic Rebound Potential model (of Au and Smith) were incorporated into the life-table models. The goals of this research are to provide the first estimates of demographic parameters for salmon sharks in the eastern and western North Pacific, and observe whether the Intrinsic Rebound Potential model adequately predicts the necessary degree of compensatory survival in sub-adult age classes to keep population growth rates and other demographic parameter estimates stable under various levels of fishing mortality.


NOAA/NMFS/SEFSC, Mississippi Laboratories, P.O. Drawer 1207, Pascagoula, MS, 39568-1207, USA

Utilizing fisheries independent bottom longline catch data to determine optimum sampling levels for coastal sharks

Since 1995 the National Marine Fisheries Service Mississippi Laboratories (MSLABS) has conducted annual bottom longline surveys in U.S. territorial waters of the Gulf of Mexico. Using standardized survey gear and a consistent survey design has facilitated development of a fisheries independent data set useful for assessing species-specific interannual variability in catch per unit effort. Based on MSLABS time series data, species-specific optimum sampling levels, with varying levels of precision, hae been established. Customizing a species-specific survey design within acceptable precision levels is possible for both geographically broad or discrete areas.


Virginia Institute of Marine Science, Department of Fisheries Science, Gloucester Point, VA, 23062, USA

Long-term population stability of large coastal sharks in the main Hawaiian Islands

Worldwide populations of large coastal sharks have been heavily exploited over the past three decades. While many nearshore resources in the main Hawaiian Islands have been heavily exploited, the region supports one of the few relatively unexploited populations of large coastal sharks. The only significant source of fishing mortality in the population was through a number shark control programs conducted by the State of Hawaii beginning in the late 1950’s in response to concerns over public safety following fatal shark attacks. From 1959 to 1976, these programs caught 2,849 sharks in state waters comprising 17 species. More than 50% of the sharks caught were sandbar sharks (Carcharhinus plumbeus). Tiger sharks (Galeocerdo cuvier) were the next most common species (19%). The only significant commercial exploitation of coastal sharks in the region occurred when about 50 metric tons per year (dressed) were harvested by a single bottom longline vessel in 1997 and 1998. Longlining was subsequently banned in nearshore waters. In 2002, a fishery- independent longline survey began to monitor seasonal and inter-annual changes in abundance of large coastal sharks along the windward coast of Oahu in the Main Hawaiian Islands. Approximately 46% of the sharks caught in the historical shark control programs were also caught around the island of Oahu. Analyses of data collected from 2002-2005 were compared to historical data from the shark control programs of the late 1950’s and late 1960’s to examine long-term changes in inter- annual and inter-seasonal abundance of coastal sharks. Comparisons of length frequency data and sex ratios were also examined between the two time periods for sandbar sharks. In addition, stomach contents were collected from approximately 200 sandbar sharks during the current survey. These data were compared to published historical data to examine changes in diet that may be a function of exploitation of prey taxa.


(LFH, CGL) Department of Biological Sciences, California State University Long Beach, 1250 Bellflower Blvd., Long Beach, CA, 90840, USA; (LFH) NOAA Fisheries Service, Southeast Fisheries Science Center, 3500 Delwood Beach Rd., Panama City, FL, 32408, USA; (JD, AZM) Institute for Integrated Research in Materials, Environments and Society, California State University Long Beach, 1250 Bellflower Blvd., Long Beach, CA, 90840, USA

Elemental signatures in the vertebral cartilage of the round stingray, Urobatis halleri, from Seal Beach, California

Although numerous studies have utilized elemental analysis techniques for age determination in bony fishes, little work has been conducted utilizing these procedures to verify age assessments or temporal periodicity of growth band formation in elasmobranchs. The goal of this study was to determine the potential of laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) to provide information on the seasonal deposition of elements in the vertebrae of the Round Stingray collected from Seal Beach, California. Spatially resolved time scans for elements across the Round Stingray vertebrae showed peaks in calcium intensity that aligned with and corresponded to the number of seasonal growth bands identified using standard light microscopy. Higher signals of calcium were associated with the wide opaque bands while lower signals of calcium corresponded to the narrow translucent bands. While a close alignment between the numbers of calcium peaks and annual growth bands was observed in round stingray samples aged five years or younger, this relationship was less well defined in vertebral samples from round stingrays over 11 years old. To the best of our knowledge, this is the first study of its kind to utilize ICP-MS to verify age assessments and seasonal band formation in an elasmobranch. The results from this preliminary study indicate that LA-ICP-MS elemental analysis of the vertebral cartilage of the round stingray may have potential to independently verify optically derived age assessments and seasonal banding patterns in elasmobranch vertebrae.


(RAM) Fish Museum, Zoology Department, University of British Columbia, Vancouver, British Columbia, V7X 1A3, Canada; (DKR) Department of Criminal Justice, Texas State University-San Marcos, San Marcos, TX, 78666, USA; (NH) Pew Institute for Ocean Science, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, 33149, USA

Geographic profiling of white shark (Carcharodon carcharias) predation

Stalking predators must balance minimum strike distance against the need to maintain crypsis. White sharks (Carcharodon carcharias) aggregate seasonally off Seal Island, South Africa, where they stalk and attack Cape fur seals (CFS, Arctocephalus pusillus pusillus). White sharks typically attack CFS at the surface via a sudden vertical strike, a strategy which maximises their ability to spot prey silhouetted in Snell’s window and minimises strike distance and duration while limiting preys’ ability to detect, assess, and escape attack. White shark attacks on CFS at Seal Island are concentrated at the seals’ primary entry-exit point, but it is not known whether sharks search randomly or limit their search to areas adjacent to prey entry-exit points. Direct observation of white sharks near Seal Island is difficult, due to water turbidity and low crepuscular light levels, when predatory activity is greatest. Geographic profiling, originally developed as a law enforcement tool that prioritises suspect searches to the probable area of a serial criminal’s residence or base, was used to show that white sharks hunting CFS at Seal Island do not search randomly around the island or at the primary entry-exit point, where prey concentration is highest. Instead, white sharks appear to concentrate hunting effort to an area seaward of the entry-exit point along the travel path seals follow to and from the island. Our results suggest that hunting strategy of stalking predators and serial criminals are optimal behaviours, shaped by common tactical constraints. We propose six constraints shared by both human and non-human predators.


(ADH, BRW) National Aquarium in Baltimore, Biological Programs Department, Pier 3, 501 E. Pratt Street, Baltimore, MD, 21202, USA; (LELR) Oregon Graduate Institute, Department of Biochemistry and Molecular Biology, 20,000 NW Walker Road, Beaverton, OR, 97006, USA; (FLM) Kerzner International Limited, 1000 South Pine Island Road, Suite 800,Plantation, FL, 33324, USA: (GV) SeaWorld Orlando,7007 Sea World Dr.,Orlando, FL, 32821, USA

Serum levels of steroid hormones in captive adult male sand tiger sharks, Carcharias taurus, and their relation to sexual conflicts

Levels of the reproductively-related steroid hormones 17-estradiol (E2), progesterone (P4), testosterone (T), and 5- dihydrotestosterone (DHT) were determined via standard radioimmunoassay from sera obtained from captive male adult sand tiger sharks, Carcharias taurus. Results were obtained from samples collected twice yearly from 1988 to 2000 from male sharks at the National Aquarium in Baltimore (NAIB) and SeaWorld Orlando (SWO). These samples provided a reasonable comparison between a reproductively active (NAIB) and a reproductively inactive (SWO) captive population, especially during periods of overlap in sampling times, April, September, and November. Significant elevations were found in SWO males for T and DHT in November and in NAIB males for P4 in April. Serial samples, collected from three male sharks at NAIB for 17 months in 2001-2002, yielded monthly variation in steroid levels as well as individual variation between male sharks involved in sexual conflicts within the dominance hierarchy. Mean levels of T peaked in November at 19353.3 ± 8399.7 (SE) pg/ml declining to 930.0 ±317.9 (SE) pg/ml in May, and DHT followed this pattern peaking in October at 803.3 ± 328.4 (SE) pg/ml and reaching its lowest level in June at 10.0 ± 0.0 (SE) pg/ml. Mean levels of P4 peaked in January at 1343.0 ± 637.6 (SE) pg/ml, and declined to undetectable levels in August. Mean levels of E2 peaked in January at 6136.5 ± 4197.3 (SE) pg/ml and declined to its lowest levels in June to 20.0 ± 5.5 (SE) pg/ml. Hormone concentrations at the individual shark level reflected both its place in the dominance hierarchy and specific behavioral characteristics associated with the sexual conflicts.


(EMS, MMH) SharkDefense Chemical Repellents and Research, PO Box 2593, Oak Ridge, NJ, 07438, USA; (SHG) Bimini Biological Field Station and University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, FL, 33149, USA

Evaluation of neodymium-iron-boride magnets on demersal longlines

The U.S. Atlantic pelagic longline fishery primarily targets Swordfish (Xiphias gladius), Yellowfin Tuna (Thunnus albacares), and Bigeye tuna (Thunnus obesus) in various areas and seasons. Secondary target species include Dolphin (Coryphaena hippurus), Albacore Tuna (Thunnus alalunga), as well as several species of pelagic sharks and several species of large coastal sharks. Although some sharks such as the Shortfin Mako (Isurus oxyrinchus) are a commercially valuable secondary species, many non-commercially valuable sharks are captured as bycatch during pelagic longline fishing. Such bycatch has several negative impacts including but not limited to: (1) removal of ecologically important species with no little commercial value, (2) reduction of fishing efficiency aimed at target species by reducing the number of hooks available to target species while occupying hooks, (3) reduction of fishing profits associated with commercial fishing through increased gear costs associated with lost hooks gear resulting damage by sharks. In an experiment to reduce these impacts, neodymium-iron-boride magnets were deployed on demersal longlines at South Bimini, Bahamas. The magnets used in this evaluation did not produce aversive behavior in captive Yellowfin Tuna and Cobia (Rachycentron canadum). The localized magnetic field permits a single demersal line to have both controls and treatments. This line consisted of fifteen gangions with 16/0 steel circle hooks and hook event timers. Seven gangions on this line were fitted with magnets. All hooks received the same type of bait, were rebaited at the same time of day, and were monitored at 4 hour intervals for shark catch. During two sets, we report fewer sharks were caught on magnetic treatment gangions when compared to control gangions. In a separate observation, we report that two tiger sharks (Galeocerdo cuvier) were captured within the same three hour period when undersized magnetics were used. A third tiger shark was also captured on a control gangion within the same period.


(MRH, CAS) Mote Marine Laboratory, Center for Shark Research, Sarasota, FL, 34236, USA (PD) South Florida Water Management District, West Palm Beach, FL, 33416-4680, USA

A river runs: Examination of habitat use and response to freshwater flow by bull sharks

To examine the use of river areas by large, mobile predators we examined the residency and movement patterns of juvenile bull sharks within the lower reaches of the Caloosahatchee River. A series of 23 acoustic receivers was deployed within the Caloosahatchee River to define how much of this section of the river bull sharks used

and how use of the river changed through time. Sharks captured within the river were fitted with acoustic transmitters to allow their movement patterns to be tracked. Movement data were compared to environmental conditions within the river including water temperature, salinity and flow rate. A collaborative effort between the South Florida Water Management District and Mote Marine Laboratory scientists has provided a unique opportunity to examine the movements of mobile animals in response to freshwater releases into the river. Bull sharks are capable of tolerating full freshwater conditions and are physically able to swim the length of the river and/or leave the river system. Data collected from monitored sharks revealed that sharks stay within the river for extended periods of time and tend not to move into adjacent estuaries. Sharks have been monitored within the river for periods of 5 to 389 days. Sharks tended to use a small portion of the river during the course of a day with typically less than 5 km of the river used during a single day. Differences in the amount of the river used through time suggest small changes in habitat use, with sharks typically not moving larger distances from one day to the next. Examination of salinity within the river suggests that shark movements are correlated to river salinity level. Data from 2003 (a high freshwater flow year) and 2004 (a lower freshwater flow year) were compared to examine differences in river usage. Current data suggest that freshwater flow in the river has a direct effect on how bull sharks use the river and how much of the river they traverse.


(MH, FG) Centro Interdisciplinario de Ciencias Marinas, Av. Instituto Politécnico Nacional s/n., Col. Playa Palo de Santa Rita, C.P. 23096, Baja California Sur, México*COFAA- IPN;(CR, PB) Universidad Nacional Autónoma de México, Instituto de Ciencias del Mar y Limnología, Unidad Académica Mazatlán, Av. Joel Montes Camarena S/N Apartado Postal 811 C.P. 82040, Mazatlán, Sin. México; (PK) University of California, Davis, Department of Wildlife, Fish, & Conservation Biology. One Shields Avenue. Davis, CA 95616, USA; (MD) Pfleger Institute of Environmental Research.901-B Pier View Way.Oceanside, CA 92054. USA

Preliminary studies of the biology of white sharks at Guadalupe Island, Mexico Guadalupe Island is home to a large population of great white sharks (Carcharodon carcharias). The few Mexican notes on the biology of white sharks are based on dead specimens, and therefore provide little insight into the behavior and ecology of these sharks. We have initiated a collaborative research program on the white sharks at Guadalupe Island, providing information that will be essential in the development of future management and conservation plans for this species in Mexico. To date we have tracked four white sharks carrying ultrasonic transmitters. Preliminary results from this study suggest that these sharks: 1) spend a considerable amount of time in the waters adjacent to northern elephant seals and Guadalupe fur seal colonies, 2) swim with yo–yo–like vertical oscillations from the surface to almost 90 m, 3) maintain a stomach temperature 7 °C higher than the surrounding water (25–26 °C). Additionally we have collected tissue samples from white sharks for both genetic and stable isotope analyses, and from their prey species for stable isotope analyses.


University of South Florida, Dept. of Biology, 4202 E. Fowler Ave., SCA 110, Tampa, FL, 33620, USA

Mechanical factors involved in the evolution of chondrichthyan jaw suspension mechanisms

The elegant interplay between musculoskeletal elements in vertebrate feeding mechanisms has long been studied because of the wealth of information these systems possess regarding organismal evolution and ecology. Aquatic feeding mechanisms are particularly known for their extensive kinesis, the anatomical basis and functional consequences of which have been established by innumerable empirical studies. Despite decades of research dedicated to understanding form- function relationships in aquatic feeding mechanisms, the evolutionary processes by which the forms that afford substantial cranial kinesis (jaw suspension) came to be have largely been ignored. Jaw suspension, the manner in which the jaws articulate with the cranium, varies greatly among gnathostomes, perhaps nowhere so much as in the chondrichthyan fishes. Chondrichthyan jaw suspension mechanisms range from complete fusion of the upper jaw to the cranium (autostyly) to indirect articulation between the jaws and the cranium via a pair of mobile hyomandibular cartilages (euhyostyly). Through biomechanical modeling of the feeding mechanisms of chondrichthyan fishes with divergent feeding mechanisms we have begun to understand the role that cranial force distributions associated with prey capture have had on the evolution of chondrichthyan jaw suspensions. Evidence from several species suggests that changes in jaw suspensions associated with enhanced upper jaw kinesis (protrusion) involved a reduction in anterior palato-cranial loading and a transition from tensile to compressive posterior palato-cranial loading. These findings have provided a glimpse of the mechanics of evolutionary change, with a more complete story yet to come.


(CH, RH) Graduate School of the Environment, Macquarie University, Sydney, NSW, 2109, Australia; (NO) Department of Primary Industries, Port Stephens Fisheries Centre, Taylors Beach Road, Taylors Beach, NSW, 2316, Australia

Reproductive characteristics of the Ornate Wobbegong Shark (Orectolobus ornatus) for population assessment

Three species of wobbegongs can be found in temperate eastern Australia (New South Wales, NSW). Two are already described (Orectolobus ornatus, O. maculatus) and a new species previously thought to be a subspecies of O. ornatus has recently been described. All three species are targeted by commercial fishers. Their catch rates have declined dramatically, circa 50%, over the last decade. This reduction has lead to wobbegongs being listed as vulnerable in NSW on the IUCN Red List of Threatened Species. We are investigating the reproduction of the O. ornatus which reaches sexual maturity at total lengths of 796-875 mm and 799-889 mm for males and females, respectively. The decline of male gonadosomatic index (July-August) prior to female ovulation (November-December) potentially suggests mating 2-3 months before ovulation and possible sperm storage by the females. Parturition occurs between September and October after a gestation period of approximately 12 months. Litter size is 4-16 (8.8 ± 0.46, n = 28). Ovulation occurs when follicles are at 43.3 ± 1.36 mm diameter (n = 24). Size at birth is 21.7 ± 0.07 mm (n = 57). Sex ratio at birth does not differ from unity (Chi-square1df, P > 0.05). The reproductive cycle is most likely to be triennial. This reproductive information is crucial for fisheries assessments in order to determine the resilience of each species to fishing pressure and to make recommendations for the future management of the fishery.


(DEJ, ALR) Roehampton University, School of Human and Life Sciences, Whitelands College, Holybourne Avenue, London, SW15 4JD, United Kingdom; (SHG) University of Miami, Rosentiel School of Marine and Atmospheric Sciences, 4600 Rickenbecker Causeway, Miami, FL, 33149-1098, USA; (STK) Cardiff University, School of Earth, Ocean and Planetary Sciences, Main Building, Park Place, Cardiff, CF10 3EY, UK; (BRF) Drexel University, Department of Biosciences and Biotechnology, 3141 Chestnut Street, Philadelphia, PA, 19104, USA

Anthropogenic effects of large-scale resort development on juvenile lemon shark (Negaprion brevirostris) populations of Bimini

The shallow waters around the islands of Bimini (25°43.70′N, 79°18.00′W) provide an ideal nursery location for the lemon shark (Negaprion brevirostris), but this habitat is under threat from a large tourist development known as the Bimini Bay Resort, which has been carrying out dredging operations and removing mangroves in and around the North Sound lagoon. The effects of the development so far were investigated by studying the growth rates of juvenile lemon sharks in the North Sound, Sharkland and South Bimini nursery areas using before-after, control-impact analysis; the first-year survival rates of neonate lemon sharks in the North Sound and Sharkland between 1995-2005; and a comparison of habitat structures in the North Sound and off South Bimini in 2003 and 2005. The results from this study found no statistically significant interaction term between the growth rates of juvenile lemon sharks in the three nursery areas before and after March 2001, which was when the largest dredging operation to date was initiated. Statistical significance in the first- year survival rates of neonate lemon sharks in the North Sound (F = 9.058, p<0.05), and the North Sound and Sharkland combined (F = 8.358, p<0.05) before and after March 2001 was found however. Some significant differences were also found between the habitat structure of the North Sound in 2003 and 2005, the most obvious being a reduction in the mean percentage cover of the seagrass Thalassia testudinum by 17.68 percent since 2003, and in the location closest to the dredging it had been reduced by 46.5 percent. The results obtained suggest that the development so far has had a negative effect on both the first-year survival rates of neonate lemon sharks and the habitat of the North Sound, and to avoid further damage the extent of the development should be reduced.


(RLJ, MNB) Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, 0002, (MAM, WHO, SS, DK) Branch Marine and Coastal Management, Department of Environmental Affairs and Tourism, Private Bag X2, Roggebaai, South Africa

Using acoustic telemetry to monitor and track the behaviour of white sharks (Carcharodon carcharias) at Mosselbaai, South Africa

Between June 2001 and December 2005 an underwater array of 10 VR2 acoustic listening stations was in continuous operation at Mosselbaai, South Africa. Receiver placement covered coastal swimming beaches, the near shore seal island, coastal reefs, river mouths, offshore areas, and commercial dive spots. Whilst the array was in operation 98 white sharks (Carcharodon carcharias) were fitted with RCODE acoustic transmitters at Mosselbaai. Spatial and temporal trends in site fidelity, habitat use were monitored. In addition, during 2005 a further three sharks were fitted with continuous acoustic pingers which enabled manual tracking possible. These three sharks were tracked for a total of 605 hours, including a 103 hour continuous track. This data was used to investigate fine scale movements of white sharks within and around the bay. Acoustic telemetry produced further insight into the white sharks degree of sociality, hunting behaviour, rate of movement, and response to chumming vessels. The high degree of residency and newly demonstrated patterns of habitat use offers new insight into the white sharks life history. Results give management the opportunity to effectively mitigate the impact of consumptive (incidental fishing) and non-consumptive (cage diving activities) exploitation of white sharks in South Africa, as well as offering new means for humans to avoid shark attacks.


University of California, Los Angeles, Department of Ecology and Evolutionary Biology, Los Angeles, CA, 90095, USA

Stingray mechanosensory and electrosensory ecomorphology: implications for near field prey detection (Elasmobranchii: Batoidea)

Elasmobranch fishes (sharks, skates, and rays) demonstrate remarkable sensory capabilities which are used for a variety of purposes including locating and capturing prey. This study compares the sensory anatomy of the mechanosensory lateral line system and the electrosensory system in benthic, benthopelagic, and pelagic rays. These systems allow elasmobranchs to locate prey through detecting water movements and electric fields respectively. Morphometric measurements and detailed maps of the sensory anatomy were constructed and analyzed using high resolution images for each species. Striking differences exist in distributions and densities of both lateral line and electrosensory pores. Urobatis halleri is a benthic ray feeding primarily on small epifaunal benthic invertebrate prey. The lateral line of this species shows a high proportion of non-pored ventral canals while the electrosensory pores are concentrated ventrally around the mouth. Myliobatis californica is a benthopelagic ray, capable of utilizing both the benthic and pelagic environment, and feeds primarily on deeply buried infaunal benthic invertebrates as well as some more mobile invertebrates and fishes. The lateral line system is highly branched with a large number of pores per branch which may help it locate water jets from the siphons of buried prey. The electrosensory system shows the highest pore number of these three species and is highly concentrated anteriorly. Dasyatis or Pteroplatytrygon violacea is a pelagic ray typically caught in the upper 100m in coastal waters. D. violacea feeds on highly mobile fishes and invertebrates, primarily squid. The lateral line branching and ratio of pored to non-pored canals is intermediate in this species while the electrosensory pore number is greatly reduced. Relationships between the ecology of these species, sensory morphology, and potential differences in detection capabilities are explored.


(SJJ, KW, AMB, BAB) Tuna Research and Conservation Center, Hopkins Marine Station of Stanford University and Monterey Bay Aquarium, 120 Oceanview Boulevard, Pacific Grove, CA, 93950, USA; (SA, AB) Point Reyes Bird Observatory, 4990 Shoreline Hwy, Stinson Beach, CA, 94970, USA; (SVS, SL, CF) Pelagic Shark Research Foundation, 750 Bay Avenue, Unit 216, Capitola, CA, 95010, USA; (SL) California Department of Fish and Game, 20 Lower Ragsdale, Suite 100, Monterey, CA, 93940, USA; (PP) Institute for Bird Populations, P.O. Box 1346, Point Reyes Station, CA, 94956-1346, USA; (TC, APK) Department of Wildlife, Fish, & Conservation Biology, 1334 Academic Surge, University of California Davis, CA, 95616, USA

The white shark cafe: Seasonal offshore migration of adult white sharks to the central northeast Pacific

The white shark Carcharodon carcharias, an important apex predator, is a species of conservation concern yet their ecology remains poorly understood. We identified an offshore region of the subtropical eastern Pacific consistently utilized by adult white sharks migrating from the coast of central California. We tagged 58 adults with pop- up satellite archival tags in coastal waters of northern California, and have retrieved 20 records to date. 28 tags remain on white sharks and are due to pop up in 2006. Adult white sharks resided near pinniped colonies and were observed feeding during fall and early winter. Movements offshore occurred over a long time period, some sharks left the coast by the end of November while others did not leave until late February. Over the five years of the study, most sharks moved to the same oligotrophic region of the central north Pacific gyre and remained there throughout the spring and summer. Sharks appeared to make directed movements between the coastal and offshore regions. Some hypotheses about the nature of these migrations are discussed.


(SMK, TLM) Biological Sciences, Florida Atlantic University, 777 Glades Road, Boca Raton, FL, 33431, USA; (TCT) Dept. of Zoology and Hawaii Institute of Marine Biology, University of Hawaii at Manoa, 2538 McCarthy Mall, Honolulu, HI, 96822, USA

Olfactory responses and crypsis of natural prey metabolites to juvenile hammerhead sharks

Hammerhead sharks have a unique neurocranium morphology formed by lateral expansion of the olfactory capsules. Their correspondingly widely separated, enlarged and elongated olfactory organs are hypothesized to confer enhanced sensitivity, detection and localization of prey. Whereas a few studies have examined the response to amino acid stimuli in elasmobranchs, none have empirically tested the ability to detect the metabolites from their natural prey. This study employed an electro-olfactogram technique to quantify the response of juvenile scalloped hammerhead sharks, Sphyrna lewini, to the six most common prey items in their diet: three teleost and three crustacean species. Metabolites from all prey items evoked responses from the shark olfactory epithelium, but those from teleosts generally elicited a greater response than did those from crustaceans. Commensal shrimp/goby pairs live in a shared burrow excavated by the shrimp and are the primary prey items in the diet of juvenile sharks in Kaneohe Bay, Oahu. Whereas the response of the shark to the burrowing shrimp did not differ significantly from the other crustaceans, the commensal goby elicited the greatest magnitude response of all species. However, when the metabolites from the burrowing shrimp were combined with its commensal goby, the response was of lower magnitude than that to metabolites of the goby alone. Additionally, water from shrimp/goby burrows did not elicit a response that differed from adjacent seawater indicating that the chemical inhibition of the metabolites from the two species was effective at masking the odor signature of the burrow inhabitants. This represents the first report of differential olfactory sensitivity to natural prey in a shark, and the first example of possible olfactory crypsis between commensal prey species.


(STK) Bimini Biological Field Station, Shark Lab, South Bimini, Bahamas; (SHG) University of Miami, Rosentiel School of Marine and Atmospheric Sciences, 4600 Rickenbacker Causeway, Miami, FL, 33149-1098, USA; (RGP) Cardiff University, School of Earth, Ocean and Planetary Sciences, Main Building, Park Place, Cardiff, CF10 3EY, United Kingdom

Seasonality in shark long-line catches at Bimini, Bahamas

A bi-monthly long-line regime conducted at Bimini, Bahamas (25°44N, 79°16W) since July 2003 was designed to sample the resident and nomadic shark populations for structure, growth, movements and seasonality. Every 24hr-fishing period, five bottom lines, each approximately 400m in length with 15 baited gangions interspersed by surface floats, are set and checked every three-five hours. Captured specimens are secured to the boat, measured (pre-caudal, fork and total length) and individuals over 140cm fitted with a NOAA/NMFS M-type dart tag. All lemon sharks (Negaprion brevirostris) receive a PIT tag and a DNA sample is taken. Catch per unit effort (CPUE) shows little seasonal variation other than a drop in February and March to 0.1, but recovers to the highest rate in April at 0.37. Carcharhinus acronotus catches are too infrequent and sparsely distributed to conclude anything on seasonality. C.leucas catches are also infrequent but CPUE is highest in April (0.04) and present from June to August, which is contrary to the period of most local sightings in the winter months. Rhizoprionodon porosus catches are again infrequent and seasonal with highest CPUE in April (0.08) and May (0.03). C.limbatus CPUE peaks at 0.1 in the summer months (August/September), with fresh mating scars observed at this time. This species is absent from the catches during the month of February when they are likely birthing over the flats. Ginglymostoma cirratum CPUE also peaks in the summer months at 0.15 and drops off to absent in the February and March. Galeocerdo cuvier is the only species represented by catches year round, with neonates caught throughout, suggesting the absence of a defined pupping season. N.brevirostris CPUE peaks at 0.07 in the early summer (April/May/ June), which coincides with their know parturition period at Bimini. This species is completely absent from catches in February and March.

*KIM, S.; KERR, L.; SUK, S.; KOCH, P.

(SK, PK) University of California, Santa Cruz, Department of Earth Sciences, 1156 High St., Santa Cruz, CA, 95060, USA; (LK) Chesapeake Biological Laboratory, P.O. Box 38 / One Williams Street, Solomons, MD, 20688, USA; (SS) NOAA Southwest Fisheries Science Center, 8604 La Jolla Shores Dr., La Jolla, CA, 92037, USA

Isotopic evidence for dietary shift in historical and modern white sharks off the coast of California

White sharks (Carcharodon carcharias) are top-level opportunistic predators that have been observed to prey on marine mammals off the coast of California. However, California pinniped populations were in decline until 1970s. Populations began to rebound after enactment of the Marine Mammal Protection Act in 1972. We used stable isotope analysis to determine feeding patterns of white sharks from 1955 through present as marine mammal populations fluctuated off California. Stable isotope ratios of carbon (13C/12C) and nitrogen (15N/14N) can be utilized as tracers for ecological studies. Carbon isotopes vary at the base of the food web with primary productivity, onshore versus offshore location, and latitude. Nitrogen isotopes are strongly sorted by trophic level, with greater 15N-enricment at higher trophic levels. The life history of a white shark may be recorded in its concentrically accreted vertebrae, assuming subsequent turnover does not overprint earlier events. To track the diet of a shark through its lifetime, we determined the 13C and 15N values of organic matter extracted from individual vertebral growth rings. Our preliminary results indicate that white sharks fed at a high trophic level in the 1950 and 1960s, when pinniped populations off California were not high. Isotopic data suggest that white shark diets consisted of pinnipeds from higher latitude or migratory populations and perhaps baleen whales. In addition, ontogenetic dietary shifts are discernable within vertebral centra. A controlled feeding study is needed to verify diet-to-tissue fractionation factors and remodeling dynamics of vertebral centra. Additional samples from historic and archaeological sites will also help define the trends of white shark feeding habits through time.


(JK, DEF, PCWT) University of New Hampshire, Department of Animal and Nutritional Sciences, Durham, NH, USA; (JAS) Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, Gainesville, FL, USA

Endocrinological evidence for differences in the annual reproductive cycles of two sympatric skate species from the Gulf of Maine

The smooth skate, Malacoraja senta, and thorny skate, Amblyraja radiata, are two sympatric batoids whose stocks are at or below threshold levels within the Gulf of Maine. During the past five years, a large life history study was conducted in an attempt to accurately describe important biological life history parameters previously lacking for these species. As part of that project, the goal of the current study was to gain insight into the reproductive biology of these species. Plasma samples were obtained from mature smooth and thorny skates of both sexes captured all months of the year, and the Estradiol (E2), Testosterone (T), and Progesterone (P4) concentrations were determined using radioimmunoassay (RIA). The respective steroid hormone concentrations were averaged, compared to morphological reproductive parameters, and plotted to examine any monthly trends. Based on morphological parameters, each species exhibited an annual reproductive pattern. Furthermore, preliminary analysis indicated that E2 concentrations in females may be different between the two skate species over the course of their reproductive cycles. Analyses of the other steroid hormones in female and male smooth and thorny skates are currently underway so that we can compare the respective plasma profiles during their reproductive cycles.


(AK, LJVC) Shark Research Centre, Iziko South Africa Museum, P.O. Box 61, Cape Town, South Africa; (KL) Biological Sciences Department, Simon Fraser University, Burnaby, BC, Canada, V5A 2S1; (CG, AK) Department of Zoology, University of the Cape Town, Private Bag, Rondebosch 7701, South Africa; (HO) Marine and Coastal Management Branch, Department of Environmental Affairs and Tourism, Private Bag X2, Roggebaai, South Africa

Seasonal occurrence, residency patterns and habitat use of white sharks at Seal Island, South Africa

South Africa is a centre of white shark (Carcharodon carcharias) abundance and the first country to protect this apex predator. White sharks are listed as Vulnerable on the IUCN’s Red List of Threatened Species and on CITES Appendix II, but vital information required on this species’ ecology, including occurrence, residency patterns, site–fidelity, identification of critical habitats and habitat utilisation, are still limited. This information is crucial when trying to ensure that protection and management measures are adequate. As a result, a telemetry study aimed at addressing these ecological issues was initiated in May 2004 at Seal Island, False Bay, the largest island Cape fur seal (Arctocephalus pusillus pusillus) breeding colony in South Africa and one of the areas along the South African coast where shark tourism activities (shark cage diving and viewing) are a regular occurrence. Vemco VR2 acoustic listening stations (2 – 6) have been deployed on the seafloor around the island, and 40 white sharks of both sexes, ranging in size from 200 – 500 cm, have been tagged with a combination of Vemco V16 and V16P acoustic transmitters. White sharks are seasonally present at Seal Island during the southern hemisphere’s winter months, actively preying on young of the year Cape fur seals. Residency times are highly variable among individuals and range from a few days to up to 6 months, having important ecological consequences. Spatial and temporal activity patterns are correlated to seal availability. We discuss these preliminary results, their ecological implications and future research objectives.


Marine Fish Species at Risk, Aquatic Resources Division, Science Branch, Fisheries and Oceans, Northwest Atlantic Fisheries Centre, St. Johns, Newfoundland & Labrador A1C 5X1

Biogeography, growth and maturity of the skate complex on the Grand Banks, northeast Newfoundland and Labrador Shelf

There is a paucity of information on species of skate that occur on the Grand Banks and Labrador Shelf of Atlantic Canada. Data collected during Department of Fisheries and Oceans Canada (DFO) research surveys during 1971-2005 were used to describe the biogeography of about 14 species occurring there. Distribution and abundance changes are mapped and variation in distribution in relation to depth/ temperature examined. Relative importance of each of the species within the ecosystem is discussed. Growth rates and size at maturity of selected species is compared over a gradient of about 20 degrees of latitude. External characteristics of onset of maturity for all skate species, specifically an abrupt increase in male clasper lengths and female ovicucal (shell) gland widths is compared to condition of the gonads over a range of sizes. Vertebrae and spines will be examined to determine best approach to aging for each of the species.


(RKL, LMD) Behavioural Ecology Research Group, Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada, V5A 1S6; (AAK) Shark Research Centre, South African Museum, P.O.Box 61, Cape Town 8001, South Africa; (AAK) Department of Zoology, University of Cape Town, Private Bag, Rondebosch 7701, South Africa; (WHO) Marine and Coastal Management Branch, Department of Environmental Affairs and Tourism, Private Bag X2, Roggebaai 8012, South Africa

Effects of provisioning ecotourism activity on the behavior of white sharks,

Carcharodon carcharias

Ecotourism operations which provide food to large predators have the potential to impact negatively on their target species, by conditioning them to associate humans with food, or by generally altering their behavioural patterns at the individual or population level. This latter effect could potentially have detrimental consequences for the predator′s ecosystem, as any behavioural changes could impact on the species with which they interact. Here we present the results of a study examining the effects of provisioning ecotourism operation on the behaviour of white sharks around a small island seal colony in South Africa. Although ecotourism activity had an effect on the behaviour of some sharks (without which this ecotourism industry would not be viable), this was relatively mild, and the majority of sharks showed very little interest in the food rewards being presented. It is unlikely that conditioning would occur from the amount of ecotourism activity tested, as even those identified sharks which supplied most of the data presented here (which may possess a stronger predisposition towards conditioning, as their persistence around the boat is what allowed them to be identified) showed a nearly ubiquitous trend of decreasing response with time. Further, those sharks which succeeded in acquiring food rewards more than others demonstrated a clear ability to ignore ecotourism offerings, and typically stopped responding after several interactions. Consequently, moderate levels of ecotourism probably have only a minor impact on the behaviour of white sharks, and therefore are unlikely to create behavioural effects at the ecosystem level.


CSIRO Marine and Atmospheric Research, Hobart 7001, Australia
The Maugean Skate (Zearaja sp.) — a micro-endemic, Gondwanan relict from

Tasmanian estuaries

A new species of rajin skate is described on the basis of specimens from two estuaries in remote southwestern Tasmania. The species, known locally as the Maugean Skate, has a conservation status of Endangered based on its rarity and very narrow geographic range. It is also one of the few skates worldwide occurring mainly in brackish water. The Maugean Skate belongs to a group of anatomically conservative, Dipturus-like skates conforming to the currently unrecognized genus Zearaja (Whitley). This ancient group, with a Gondwanan lineage possibly dating back to the Cretaceous, contains at least two other species: Z. nasuta from New Zealand and Z. chilensis from South America. The skeletal morphologies of the Zearaja species are compared with typical Dipturus skates and their phylogenetic position discussed.


(LEL, SPC, KAF) Vision, Touch and Hearing Research Center, School of Biomedical Science, University of Queensland, Brisbane, 4072, Australia; (MB) Anatomy and Developmental Biology, School of Biomedical Science, University of Queensland, Brisbane, 4072, Australia; (JDS) CSIRO Marine Research Hobart, Tasmania, 7000 Australia

Visual ecology of the sandbar shark, Carcharhinus plumbeus

Elasmobranchs rely heavily on a rich diversity of sensory input to identify prey, navigate, reproduce and interact within their environment. The role vision plays in these behaviours remains unknown for many species. This study examines the visual ecology of the sandbar shark, Carcharhinus plumbeus, a species which inhabits a diversity of visual environments, ranging from clear water fringing reef habitats to turbid water estuarine habitats. Here the visual ecology of the sandbar shark is assessed throughout ontogenetic development to identify visual strategies of this species in different visual environments. Using anatomical and electrophysiological techniques, key capabilities such as sensitivity to light, spatial and temporal resolution, as well as spatial and temporal summation are assessed. Topographic distributions of photoreceptor and retinal ganglion cells revealed a region of higher cell density in the centro-temporal retina, slightly ventral of the horizontal meridian. This specialisation would afford improved visual resolution in the lateral and frontal visual field with a peak spatial resolution of 5-6 cycles per degree recorded in the adult sandbar shark. Electroretinograms are used to record sensitivity to light and temporal resolution, determined by the flicker fusion frequency (FFF), at different intensities and frequencies of light stimulus. Peak light sensitivity was recorded at relatively low light intensities, indicating a high sensitivity to dim light as compared to a tuna, for instance. Peak FFF values recorded ranged between 35 to 40 Hz. Variations in temporal resolution between habitats will be discussed. This study provides insights into the visual physiology of sharks and identifies thresholds of the sandbar shark′s visual sense. This knowledge could aid our understanding of the underlying mechanisms of diurnal and nocturnal activity patterns, reproductive behaviour and predator–prey interactions in this species.


AtlantNIRO, Laboratory of the fish demography and stock assessment, Dmitry Donskoy Str., 5, Kaliningrad, Russia

Distribution, abundance and feeding of skates in western African waters and adjacent submarine mounts

The skates of North African (22°N-36°N) and central African (7°N-11°N) shelf and slope and adjacent submarine mounts were analyzed with respect to diet composition, standard depths occurrence and distribution patterns. There were used data from 1225 trawl hauls and 371 stomachs in total. There were observed 18 skate species in northern zone and 22 in the central one. The most abundant northern species was Raja montagui, it dominated between all the elasmobranchs, sharks included, on the depths 25-200 m. It consumed 47 food items in total, the most important were cephalopods, then crustaceans and fish. Another relatively abundant species were T. marmorata, R. miraletus, R. straeleni, R. clavata, D. pastinaca. The relative importance of R. maderensis, R. asterias, Leucoraja circularis and L. fullonica was much higher on the submarine mount Conception comparing continental shelf and slope. On the submarine banks southward Azores were observed R. clavata, T. nobiliana and R. madarensis. The most abundant elasmobranch species in the central zone were Dasyatis margarita (at 10 and 25 m) and Raja miraletus (at 75 and 100 m). R. miraletus fed mainly on bottom crustaceans (15 items), fish (7 items), and cephalopods being less important (1 item). In the northern zone bottom crustaceans were also very important for this species (13 items), crustaceans and fish being of the minor significance (two items for each). As a whole, skates of both zones fed mainly on crustaceans and fish, cephalopods were not important, but abundant R. montagui, which preferred cephalopods. The preys were bottom, near-bottom and pelagic species. There was the pronounced correlation between the body disc shape and share of pelagic items in the food composition of Raja spp. Dasyatis pastinaca in northern zone and D. hastata in central zone demonstrated high percentage of polychaets in food comparing other skates. There were revealed some distribution patterns in both zones: R. montagui have not ever been observed northward 34°N, as some other shark species; Z. schoenleinii was quite rare southward 8°N, Rh. rhinobatos was found there in May-April only. Such gaps inside species ranges are suggested to be boundaries between stock units.


(CAL, CJW) Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL, 34236, USA; (JTW, ABB) Department of Animal and Veterinary Sciences, Clemson University, Clemson, SC, 29634, USA

Reproductive biology of the clearnose skate, Raja eglanteria, in captivity

Clearnose skates (Raja eglanteria) are a common species of skate found seasonally along the Atlantic coast of North America from Cape Cod to mid-Florida and in the Gulf of Mexico from mid-Florida to eastern Texas. Clearnose skates inhabit the west central coast of Florida during winter months, when Gulf temperatures are conducive to mating and egg-laying (approximately 16-22 °C). Specimens collected during this time will breed in captivity and, if maintained at 20 °C, mated females will store sperm and continue to lay fertile eggs for up to six months. Following copulation, sperm move up the female’s paired uterine horns and are stored in the shell glands (also known as oviducal or nidamental glands) located between the uteri and oviducts. Ova are released from the ovaries in pairs, enter a common ostium and travel through the oviducts to the shell glands, where fertilization and encapsulation of eggs take place. Experiments resulting in the first artificial insemination for any elasmobranch fish have provided evidence for functional roles of the alkaline gland, whose secretions stimulate sperm motility and may enhance migration of sperm to the shell glands, and the clasper gland, whose secretions may provide nutrition during storage of viable sperm in the shell gland. Females will lay 30-35 pairs of eggs per season with a 3-5 day interval between laying of successive egg pairs. Developmental landmarks include formation of primitive streak (day 4), closure of neural tube (day 6), early stages of sensory organs, CNS, and gill arches (days 10-14), rostral migration of pectoral fins (weeks 3-5), proliferation and resorption of external gill filaments (weeks 3-8), and appearance of dermal pigmentation (weeks 8-9). If eggs are maintained at 20 °C, embryos will develop and offspring will hatch after a period of approximately 12 weeks (84±6 days).


Florida Atlantic Univeristy, Dept. of Biological Sciences, Boca Raton, FL, 33431, USA

Behavioral function of the electric organs of Bancroft′s numbfish, Narcine bancroftii

All elasmobranchs have the ability to detect electricity, however only skates (Rajiformes) and electric rays (Torpediniformes) are capable of bioelectrogenesis. Within these orders, skates emit weak electric organ discharges (EODs) involved in communication, whereas electric rays emit strong EODs during prey-capture. Of the Narcinids, Bancroft′s numbfish, N. bancroftii, produces both strong and weak EODs from large main electric organs and small accessory organs respectively; however, the function of these discharges remains unknown. Prior to investigating the behavioral function of the EODs, morphometrics were studied to examine possible sexual dimorphisms and ontogenetic changes in the electric organs. The number of electroplaques and the surface area of the main electric organ correlate positively with size morphometrics. The mean electro-somatic indices (ESIs) for the main and accessory electric organs were 13.69± 0.63% SE (n=15) and 0.10 ± 0.01% SE (n=15), respectively. Moreover, the ESI for the accessory electric organ demonstrates positive allometry, whereas, for the main electric organ, it is negatively allometric. None of the morphometric characters were sexually dimorphic. Electrophysiological experiments reveal a logarithmic relationship between the main EOD amplitude and disc width; disc widths ranged from 6cm (9V) to 23cm (56V). Main EODs were often in trains fewer than 10, however, trains of more than 100 were also observed. Fundamental frequencies for the main EODs ranged from 78-215Hz. Results of behavioral experiments indicate that the main EOD functions primarily in defense, and not in predation. Preliminary results from behavioral experiments of accessory EODs suggest their use in intraspecific communication.

(MM) National Institute of Water and Atmospheric Research (NIWA), 301 Evans Bay Parade, Kilbirnie, Wellington, New Zealand; (SH, MS) National Institute of Water and Atmospheric Research (NIWA), 217 Akersten Street, Port Nelson, Nelson, New Zealand

Species at Risk or Cockroach of the Sea? Abundance of Spiny Dogfish (Squalus acanthias) in the New Zealand Exclusive Economic Zone

Spiny dogfish (Squalus acanthias) is a small- to moderate-sized benthopelagic squaloid shark distributed globally in temperate marine waters. It has been commercially exploited on an industrial scale over much of its range for more than a century, but recently concerns have been raised about the status of the stocks in certain areas, notably in the North Atlantic. At this time, the Northwest and Northeast Atlantic stocks are thought to be severely depleted, with the reproductive biomass of each stock thought to be about 25% and 5% (respectively) of average unfished biomass. Indeed, the stocks were assessed as ‘vulnerable’ and ‘endangered’ (respectively) by the IUCN in 2003. However, below the equator, the status of stocks in the New Zealand Exclusive Economic Zone (EEZ) appears much less perilous. At this time, stocks in the New Zealand EEZ support four major commercial fisheries with a total catch that has averaged over 8000 t per year over the past ten years (1995–2004). In this paper, we summarise the results of recent studies on the abundance of the New Zealand stocks. We briefly describe their known biology, major fisheries, available abundance indices, and ongoing management measures, comparing and contrasting the New Zealand experience to date with that in the North Atlantic—of the four major New Zealand fisheries, in only one does stock abundance appear to be declining; in the remaining three, abundance appears to be static or increasing. Finally, we speculate on what effect current fisheries and management practises in New Zealand might have on the future abundance of the New Zealand stocks.


(JFMF) Centro Regional de Investigación Pesquera de Mazatlán, Instituto Nacional de la Pesca. SAGARPA. Calzada Sábalo-Cerritos S/N, CP. 82010, Mazatlán, Sinaloa, México; (AR, MACM) 2 World Wildlife Foundation. Blvd. Beltrones Rivera 264, Local 3 Edificio Hacienda Plaza San Carlos, Sonora, México

Investigation of the movement and depth-temperature preferences of the white shark (Carcharodon carcharias) from the Gulf of California, Mexico

Commercial fishermen have reported the occurrence of the white shark (Carcharodon carcharias) throughout the Gulf of California (GOC) for many years. It has been hypothesized that the location of pinniped colonies, among other factors, may play an important role in determining its presence in the region, but little is actually known of the distribution, seasonality, movement patterns, or residence time of C. carcharias in this region. Given the extent and importance of commercial fisheries in the GOC, identification of movement patterns may provide essential details for reducing fishery interactions and improve the management and conservation of this species. Satellite tagging efforts were therefore conducted to better understand the behavior and ecological preferences of C. carcharias. A satellite PAT-Tag was attached to a 280 m total length (estimated, sex no available) white shark in the vicinity of San Pedro Nolasco Island (eastern central GOC) in November 7, 2004 and the tag successfully released April 30, 2005 166 km to the south. Maximum recorded depths by month were Nov 232 m, Dec 92 m, Jan 104 m, Feb 180 m and March 244 m. The monthly temperature ranges logged by the tag were Nov 13.2 -26.4°C, Dec 18.2- 22.7 °C, Jan 16.2-21.3 °C, Feb 13.9 -20.2°C and 13.2-22.3°C during March. Preliminary tracking results indicate movements of the white shark into the upper GOC.


The University of Queensland, School of Biomedical Sciences, St Lucia, QLD 4072, Australia

Reproductive ecology of Manta birostris

Manta rays, Manta birostris, are common in southern Mozambican waters. Research since 2003 has identified 350 individual rays, using their unique dorsal and ventral markings, on a single reef. The study site supports three major cleaning stations, where mantas spend a significant amount of time allowing several species of fish to remove parasites and necrotic tissue. The reef is utilized year-round, with multiple individuals generally present. This population is sexually segregated, with 22% male and 78% female. The high re-sighting rate (32%) infers a semi-resident local population, which has allowed the reproductive condition of known individuals to be regularly assessed. The smallest mature male observed was approximately 3.5 m disk width, while the smallest pregnant female recorded was 3.8 m DW. Pregnancy has been observed in over 60 individuals. Courtship and mating behavior occurs in November/December, while pregnancy becomes externally evident around August. Parturition occurs in the summer months, from late November to early February. One, or rarely two, pups are born per litter. The smallest free-swimming individuals measured 1.2-1.4 m DW, while a 1.3 m DW pup was extracted in early October from a pregnant female killed by local spear fisherman. Preliminary data suggests that the gestation period in this population is 12 months with an overall two-year reproductive cycle.


Fish Museum, Zoology Department, University of British Columbia, 6270 University Boulevard, Vancouver, BC, V6T 1Z4, Canada

Behavioral ecology of white sharks in False Bay, South Africa, with recommendations for local management and conservation

The white shark (Carcharodon carcharias) is a nomadic apex macropredator exploiting a broad range of habitat types and prey. False Bay, South Africa, is a rich coastal temperate ecosystem inhabited year-round by a small resident population of white sharks and visited seasonally by large numbers of individuals during late autumn and winter. Since 1997, the author and his co-workers have studied selected aspects of the synecology of white sharks in False Bay. The physical environment of False Bay is briefly reviewed and seasonal patterns in white shark distribution within the bay are described. Seal Island, at the foot of False Bay, is a seasonal aggregation site for white sharks; site fidelity and residence times of individuals are described. Seasonal differences in the diet of False Bay white sharks are described and trophic relationships are modeled. Predatory behaviour of white sharks at Seal Island, along with social and environmental factors affecting predatory success, are reviewed and compared with published data on this species at the Farallon Islands, California. Size and sex distribution and growth rate of known individual white sharks is summarised and compared with published estimates. Intraspecific associations and social interactions among white sharks observed at Seal Island are described, including agonistic displays that facilitate establishment and stability of social rank. The uneasy relationship between humans and white sharks within False Bay is reviewed, including attacks on people and boats, sport angling for white sharks, and white shark ecotourism. Recommendations for local management and conservation of white sharks are offered.


(BM) University of Washington, School of Fishery and Aquatic Sciences, 1122 NE Boat St., Seattle, WA, 98105, USA; Alaska Fisheries Science Center, NOAA Fisheries, 7600 Sand Point Way NE, Seattle, WA, 98115, USA; (DG) University of Washington, School of Fishery and Aquatic Sciences, 1122 NE Boat St., Seattle, WA 98105, USA

Age and growth of the Alaska skate, Bathyraja parmifera

The Alaska skate (Bathyraja parmifera) is the most abundant species of skate on the Bering Sea shelf, accounting for over 90% of total skate biomass. However, little is known regarding the life history of this species despite its common occurrence in the bycatch of Bering Sea cod longline and flatfish trawl fisheries. Studies focusing on age, growth, and reproductive biology are essential to stock assessment and management of this species. Since 2003, over 600 specimens have been collected in the summer during groundfish surveys conducted by the National Marine Fisheries Service (NMFS) and seasonally by the NMFS Observer Program. Banding patterns in thin sections of vertebrae and in whole caudal thorns, a non-lethal aging method, were compared for age determination. Periodicity of annulus formation was verified by marginal increment analysis. Results presented will include maximum age, age at maturity, and von Bertalanffy growth parameters. Life history parameters obtained from this study will be considered in the development of a stock assessment for B. parmifera and will serve as a model for other skate species in the Bering Sea for which life history parameters have not yet been described.


(JDM) Texas A&M University, Dept. Wildlife and Fisheries Sciences, College Station, TX 77843-2258, USA; (MRC) Universidade de Sao Paulo, Departamento de Biologia (FFCLRP), Av. dos Bandeirantes, 3900, Ribeirao Preto, SP, Brasil 14040-901

Evolutionary biology of skates (Chondrichthyes: Rajidae)

Skates (Rajidae) are a highly corroborated monophyletic group and interrelationships within the taxon are fairly well resolved. However, a number of polytomies remain within the subfamily Rajinae, and two generic level taxa are unnamed and poorly defined. A new analysis of the interrelationships of rajids largely corroborates an earlier study but further resolves some of the polytomies and provides additional support for recognition of the unnamed generic level taxa. The family consists of two subfamilial-level taxa: Rajinae and Arhynchobatinae. The two subfamilies have similar numbers of genera and species but are largely complementary in their distributional patterns. Rajinae dominate, in both generic level taxa and species richness, in the North Atlantic, eastern Central and South Atlantic, western South Indian Ocean, western Central Pacific, and eastern Central Pacific. Arhynchobatinae dominate, in both generic level taxa and species richness, in the North Pacific, eastern South Pacific, Antarctic waters, and western South Atlantic. In ocean basins where the subfamilies overlap, Rajinae are more diverse at lower latitudes and lesser depths and Arhynchobatinae are more diverse at higher latitudes and greater depths. The distributional patterns suggest that most of the evolution of Rajinae occurred in the Atlantic while most of the evolution of Arhynchobatinae occurred in the Pacific. Despite the fact that Rajidae is the most species rich family within Chondrichthyes, most of the evolution appears to be the result of vicariance events rather than adaptive radiations. Skates remain ecological generalists that occur on terrigenous substrates over a wide depth range.

(WDM) Department of Fisheries, Animal and Veterinary Science, University of Rhode Island, 20A Woodward Hall, 9 East Alumni Ave, Kingston, RI, 02881, USA; (CTM, NEK) Apex Predator Investigations, Narragansett Laboratory, NOAA/NMFS, 28 Tarzwell Dr., Narragansett, RI, 02882, USA

Diet and ontogenetic change of juvenile sandbar sharks, Carcharhinus plumbeus, in the Delaware Bay nursery

The sandbar shark (Carcharhinus plumbeus) is a common coastal shark species along the U.S. Atlantic coast, and it is one of the most heavily exploited species by both commercial and recreational fisheries. This species uses coastal estuaries as nursery areas, and Delaware Bay is one of the largest nursery areas along the U.S. east coast. This portion of a larger feeding ecology study characterizes the diet of the sandbar shark in Delaware Bay. Sharks were caught using bottom longlines and gillnets at locations throughout the bay. Stomachs were everted and contents were collected using non-lethal techniques. Stomach contents were identified to the lowest taxon possible, and the diet characterized using several indices. A total of 654 of 1,173 sandbar sharks sampled contained food in their stomach. The diet was predominantly composed of teleosts (82% by IRI), with crustaceans (16%) and elasmobranchs (1%) as the other major prey categories. Important teleost prey species included B. tyrannus, A. mitchilli, T. maculatus, O. marginatum, and several species of sciaenid. L. emarginata, C. sapidus, O. ocellatus, and some Pagurid crabs composed the majority of the crustacean prey. Neonates and smaller juveniles fed to a greater extent on crustaceans, benthic, and smaller fish species. Larger juveniles preyed upon a greater diversity of species, and elasmobranchs, larger bodied, and faster swimming species were increasingly found in the diet.


Dept. of Fisheries and Oceans, Pacific Biological Station, 3190 Hammond Bay Road, Nanaimo, BC, Canada, V9T6N7

Migration patterns of Big Skate (Raja binoculata) in British Columbia waters

Since 1996, catches of Big Skate have increased dramatically in British Columbia waters as a response to increased market demand. Two major fisheries occur: in Queen Charlotte Sound and; Dixon Entrance in Northern Hecate Strait. Concern regarding exploitation of this elasmobranch species led to questions regarding the stock structure of big skate populations in Northern waters. Since 2003, approximately 12,000 big skate have been tagged and released in these two areas combined. This program is the most extensive tagging study conducted on a skate species and offers a rare opportunity to examine migration patterns big skate. As of May 2005, 549 tagged skate have been recaptured with reliable recovery location information. Generally, big skate were recaptured close to their release site, within 20 km. Approximately 18% of the recapture big skate had moved between 20-100 km from their release location. Some big skate (5 % of those recaptured) moved between the two main fishing areas (i.e. >100 km). Most surprising are the five extensive migrations (>1000 km) that have been observed. One big skate released in March 2003 in Dixon Entrance, was recaptured in the Bering Sea, just north of the Aleutian Chain, in November 2004. Two big skate released in August 2003 in Queen Charlotte Sound, were recaptured in April 2004 in Prince William Sound. An additional 2 big skate released in August 2003 in Queen Charlotte Sound, were recaptured in April and May 2005 in Prince William Sound and near Kodiak Island, respectively. Although 76% of recaptured big skate were recovered very close to their release location, the movement of the remaining 24% illustrates that big skate migration may be more complex than previously thought.


(BM, DB, AF) Warnell School of Forest Resources, University of Georgia, Athens, GA, 30602-2152, USA; (WB) Alaska Department of Fish and Game, 1255 West 8th Street, P.O. Box 115525, Juneau, AK 99811-5525, USA

Essential and non-essential element concentrations in polar sharks

Certain elements/metals, which are often toxic and known to biomagnify (e.g., mercury, cadmium), have raised increasing concern in the Arctic, and for large predatory fish. Past studies on element concentrations in the Arctic have focused on marine mammals and seabirds, but element concentrations for the only two shark species known to regularly inhabit Arctic waters have never been reported. Twenty- five essential and non-essential elements were analyzed in liver tissue of Greenland sharks (Somniousus microcephalus), collected about Cumberland Sound in the Canadian Arctic, and Pacific sleeper sharks (Somniosus pacificus), collected about Prince William Sound in Alaska, to asses the influence of Arctic region on element concentration. Univariate and multivariate statistics were used to asses both absolute concentrations and patterns of elements. The two shark species were assumed to have similar physiologies, and were combined in the analysis to help elucidate geographical exposure differences. Zn had the highest absolute concentrations of all samples, followed by As, Cd, Cu, Se, and Rb. Mean concentrations of hepatic Hg and Cd were higher in the polar sharks than for other previously reported Arctic fishes, but were lower than concentrations in other shark species that inhabit more southern latitudes. Of the non-essential elements, As, Ag, Cd, Hg, and Rb were significantly different between locations, and all but Rb were higher in Cumberland Sound than Prince William Sound, which could suggest geographical exposure differences, but could also be related to species differences (e.g., diet). Concerning the essential elements, Mo and Se did not significantly differ between locations, but Co, Cu, Mn, Zn did vary between locations, which may indicate different physiological requirements between the Greenland and Pacific sleeper sharks. Essential elements are likely regulated to maintain necessary concentrations, and could therefore be useful in drawing conclusions about an organism′s physiology.


Bedford Institute of Oceanography, Population Ecology Division, 1 Challenger Dr., P.O. Box 1006, Dartmouth, NS, B2Y 4A2, Canada

Age and growth estimates of four species of northwest Atlantic skate (Family Rajidae) on the eastern Scotian Shelf

Little is known about the life histories of the most common species of skate (Family Rajidae) inhabiting waters off the coast of Atlantic Canada. Recent declines in numbers of all species, and a subsequent consideration of the winter skate (Leucoraja ocellata) on the eastern Scotian Shelf (ESS) for listing under Canada′s Species at Risk Act, have heightened the need for validated age and growth estimates in this region. Winter skate, little skate (Leucoraja erinacea), thorny skate (Amblyraja radiata), and smooth skate (Malacoraja senta) were collected seasonally from the eastern Scotian Shelf on research vessel surveys and aboard commercial vessels from July of 2004 to March of 2006. Vertebral band counts taken from digitally photographed vertebral sections of 100 skate of each species, ranging in size from embryonic to mature, were used to estimate length-at-age, growth, and longevity. Mark-recapture of chemically- tagged wild skates, captive rearing of skates within the laboratory, and a marginal increment analysis were undertaken to validate the age interpretations. Age-bias plots and the coefficient of variation indicated that band counts represent a reproducible method for estimating age in all four species, particularly in winter and thorny skate. Relative growth rate was found to be inversely related to species′ longevity. Growth increment deposition in other structures with calcium phosphate deposits, such as caudal and dorsal thorns, was also examined using both recaptured and laboratory-reared fish. Results indicate that skates on the ESS exhibit age and growth characteristics known to increase species′ susceptibility to extirpation, with certain species (such as the smooth and little skate) exhibiting greater resiliencies to exploitation based on life history theory.


(AM, GHB) Florida Program for Shark Research, Florida Museum of Natural History, Dickinson Hall, Museum Road, Gainesville, FL 32611, USA; (JC) National Marine Fisheries Service, Southeast Fisheries Science Center, Panama City Laboratory, 3500 Delwood Beach Road, Panama City, FL, 32408, USA

The capture depth, time and hooked survival rate for bottom longline caught sharks

Over the past year, the Florida Program for Shark Research (FPSR) has been working cooperatively with commercial shark fishers in conducting fishery independent monitoring in the Gulf of Mexico and Atlantic Ocean off the southeastern United States. Bottom longline gear, hook timers and time depth recorders were used to collect data pertaining to the relationship between soak time and capture depth on fishing mortality and catch per unit effort (CPUE) of individual shark species and shark species aggregates. Primary species represented in the catch included the Atlantic sharpnose (Rhizoprionodon terraenovae), 36.8% of total catch), nurse (Ginglymostoma cirratum, 19.2%), blacknose (Carcharhinus acronotus, 16.1%), tiger (Galeocerdo cuvier, 10.4%) and blacktip (Carcharhinus limbatus, 10.4%) sharks. We report preliminary results related to the length of time the fishing gear was in the water prior to a shark biting and being hooked, and the length of time individual shark species remained alive after being hooked. Initial analyses demonstrate that the majority of sharks bit the hook within the first four hours the hooks were in the water. Sixty percent of the sharks were caught during the first two hours in sets with soak times lasting 0-4 hours or > 8 hours, and 68% of sharks were caught during the first four hours in sets with soak times ranging between 4-8 hours. Tiger and nurse sharks were retrieved alive 100% of the time, while blacknose and blacktip sharks suffered 100% mortality on sets over four hours in length. The latter two species suffered 20% and 0% mortality, respectively, on sets of less than four hours. The Atlantic sharpnose shark also suffered a 100% mortality rate during sets longer than eight hours and 88.9% during sets lasting 4-8 hours, while only a 20% mortality rate occurred on sets of less than four hours.


Hofstra University, Dept. Biology, 114 Hofstra University, Hempstead, NY, 11549, USA Morphological variation in the electric organ of Leucoraja erinacea and its

possible role in courtship

Skates are among a small grouping of fish families that have electric organs. Of that limited number of families, skates are one of only ten families that have electric organ discharges (EODs) too weak to be used for defense or predation, and skates may be alone in that grouping in that they do not discharge the organ continuously for electrolocation. Much research, physiological, morphological, and behavioral, has been done on the weakly electric teleosts (e.g., mormyrids and gymnotiforms) that has led to the conclusion that their electric organs serve a communicative purpose during courtship. It follows that skates may have evolved a similar device for a similar function. This research aims to support the notion that the electric organ in skates may play a role in interspecific communications, particularly during courtship. To do so, it is important for us to determine if any sexual or ontogenetic variations exist in their electric organs. Therefore, male (n=30; 20.2 − 50 cm TL) and female (n=45; 25 − 50 cm TL) electric organs of the little skate, Leucoraja erinacea, were removed and examined using light-level microscopy and common histological procedures. Mean organ weight, organ length, organ height, electrocyte width, number of electrocytes, number of electrocyte rows, height of electroplate layer, and electrocyte height were correlated with skate mean total length, mass, width, clasper length (in males), and oviducal gland width (in females). This research will determine whether or not the electric organ varies sexually or ontogenetically in the little skate. Such variation, if detected, will support our hypothesis that the electric organ of skates may play a role in communication during courtship.


Department of Biology, California State University Long Beach, 1250 Bellflower Blvd. Long Beach, CA, 90840, USA

Plasma testosterone concentrations and GSI as predictors of mating periodicity in male round stingrays (Urobatis halleri)

Round stingrays breed annually during the late spring- early summer, with parturition occurring in autumn. While breeding behavior, gonadosomatic index (GSI), and hormone levels correlate in some species, this is not true of all elasmobranchs. We hypothesized that the annual cycle of testosterone in a wild population of male round stingrays was correlated with seasonal gonad development and spermatogenesis. Round rays were collected monthly for 12 months in Seal Beach, CA. Gonadal tissue and blood samples were collected for each ray, and processed for histological examination and analyses by radioimmunoassay, respectively. Seasonal changes in testes structure were categorized into three phases: inactive (May-July), recrudescent (August-October), and degenerative (November- April). During the inactive phase testes were composed primarily of stage I spermatocysts and both GSI and testosterone were reduced as compared to other stages (p<0.05). The recrudescent phase was characterized by increases in both GSI and testosterone compared with all other groups (p<0.001). While testosterone levels were not significantly different between the inactive and recrudescent stages, plasma levels did increase 4.75 fold when the testes returned to their active state. Maturation of spermatocysts and sperm from early stage I and II spermatocysts to later stages (III-V) was noted during the recrudescent stage. Finally, the degeneration phase was characterized by a decrease in GSI, following the peak in October, (p<0.001) and a final maturation of sperm and degeneration of spermatocysts (stage VI and VII). Testosterone levels continued to rise throughout the degeneration phase and remained elevated until mating occurs (p<0.01). Interestingly, GSI peaked in October, 5 months before the established mating season, and peak sperm production occurred in December, two months after peak GSI and 3 months prior to mating. These results suggest that plasma testosterone is a more reliable indicator of seasonal maturation of testes in round stingrays than GSI.


Clemson University, Dept. of Biological Sciences, Clemson, SC, 29630, USA

Population genetics of the scalloped hammerhead shark, Sphyrna lewini, in the Gulf of California

The scalloped hammerhead shark, Sphyrna lewini, is a circumtropical species that uses shallow bays and estuaries for reproductive purposes. While Mexico’s Gulf of California (GOC) is the only large inland sea along the eastern Pacific and therefore may be vital to the reproductive success of the eastern Pacific stock, populations of S. lewini have declined there in recent years and require protection from over- exploitation. Genetic markers are widely used to study such threatened species, and can be useful in the design of marine reserves. To effectively protect a species, genetic connectivity must be maintained among populations throughout the species’ range. Connectivity is a measure of gene flow among populations and can be determined by studying the genetic variation, or genetic structure, within those populations. Knowledge of population structure is necessary for managers to determine the effect that fishing in one part of a species’ range will have on other populations elsewhere. I have used microsatellites to determine the genetic structure of S. lewini populations in the GOC spatially and temporally. Two microsatellites were used in previous studies on blacktip sharks, and a third was designed for the bonnethead shark. While I am in the process of designing more loci for S. lewini, a difference among frequencies of these genetic sequences resistant to selection indicates that populations within La Paz Bay were significantly different in January 2001 and January 2004. This temporal structure suggests that S. lewini populations do not practice natal homing by returning to the same pupping grounds in La Paz Bay for reproductive purposes. However, these results are tentative. More microsatellite loci, as well as analyses of tissue samples from La Paz Bay, Mazatlan, and Chiapas in 2006 are requisite before definitive conclusions can be made regarding the population structure of S. lewini.


(LJN) NMFS, 28 Tarzwell Dr., Narragansett, RI, 02879, USA (JK) University of New Hampshire, Zoology Department; Spaulding Hall, 46 College Road, Durham, NH, 03824, USA; (PCWT) University of New Hampshire, Department of Animal and Nutritional Sciences, Kendall Hall, 129 Main St, Durham, NH, 03824, USA; (JAS) Florida Program for Shark Research, Florida Museum of Natural History, University of Florida P O Box 117800 Gainesville, FL, 32611, USA

Age and growth of the smooth skate, Malacoraja senta, from the western Gulf of Maine

The smooth skate, Malacoraja senta, is a small rajid species endemic to the offshore waters of the Northwest Atlantic. While not directly targeted, precipitous declines, as a consequence of bycatch in the groundfish fishery, have consistently placed the stock status of this species at or below threshold levels in the Gulf of Maine, USA. Although the smooth skate has a relatively broad geographic distribution, ranging from Newfoundland, Canada to New Jersey in the United States, no direct biological data exists for this species. The present study intends to use counts from vertebral centra to age this species. To date, vertebrae from 495 skates ranging in size from 230 mm to 680 mm have been processed. Contingency tables and coefficient of variation will be used to test for bias and precision in our age assessment. Marginal increment and edge analyses will be used to verify annual band formation. Growth will be assessed using the original von Bertalanffy (VBGM) with size at birth (Lo) as a parameter. Additional methods including a set Lo and the to form of the VBGM equation will also be evaluated in order to produce the best representation of the data. The resulting information will represent an important life history parameter needed for the proper management of this overfished species.


(JAN, EC) NOAA Fisheries, 3500 Delwood Beach Road, Panama City, FL, 32408, USA; (KAR) Coastal Fisheries Institute, Louisiana State University, Baton Rouge, LA, 70803, USA

Simulating the effects of temperature on individual and population growth of the cownose ray, Rhinoptera bonasus: A coupled bioenergetics-matrix modeling approach

The cownose ray, Rhinoptera bonasus, is a commonly observed elasmobranch throughout the Gulf of Mexico and appears to be sensitive to water temperature. We performed laboratory experiments and collected field data to obtain basic life history and metabolic information, and used the information to configure an individual- based bioenergetics model. The bioenergetics model was coupled to a matrix projection model, and the coupled models were used to predict how warmer and cooler water temperatures would affect the growth and population dynamics of the cownose rays. The bioenergetics model predicted that rays would have a slower growth rate and reach smaller average weights at age (9.6-16.8% smaller) if they inhabited 2oC warmer water than baseline (current) conditions, while individuals would grow faster and attain heavier weights at age (13.4-17.2% heavier) under a 2oC cooler scenario. Changes in growth rates under the warmer and cooler conditions also lead to changes in age-specific survivorship, maturity, and pup production, which we used as inputs to a matrix projection model. Faster growth of individuals under the cooler scenarios translated into an increased population growth rate (4.4- 4.7%/year versus 2.7%/year under baseline), shorter generation time, and higher net reproductive rates, while slower growth under the warmer scenarios translated into slower population growth rate (0.05-1.2%/year), longer generation times, and lower net reproductive rates. Elasticity analysis indicated that population growth rate was most sensitive to adult survival. Reproductive values by age were highest for intermediate ages. The combination of coordinated laboratory experiments, field data collection, and coupled individual-based bioenergetics and matrix projection models provides a powerful approach for relating physiology to demographic responses.


(SPN, RDH) School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, United Kingdom; (SPN, SHG) Bimini Biological Field Station, Bimini, Bahamas; (SHG) Rosensteil School of Marine and Atmospheric Sciences, University of Miami, Miami, FL, USA

Ontogenetic variation in diet and prey preference of juvenile lemon sharks,

Negaprion brevirostris

Stomach contents were collected from 396 lemon sharks (Negaprion brevirostris) at Bimini, Bahamas, between March 2000 and March 2003, and analysed to examine ontogenetic variation in diet and feeding habits. Lemon sharks were predominantly piscivorous and diet was homogenous with shark size (2 = 64.36, 12 df, P = 0.057), with mojarra (Gerreidae) the major prey of all shark sizes. High levels of dietary overlap (simplified Morisita and Horn′s index > 0.88, Spearman rank P < 0.001) between all shark sizes suggested no resource partitioning. However, a significant ontogenetic decrease in the number of dietary items (Kruskal-Wallis test, P = 0.006) and a significant increase in stomach content weight (Kruskal-Wallis test, P = 0.017) suggested larger sharks consumed fewer but larger prey. Prey sizes were measured where possible or calculated using bone-length regression equations, and sharks over 60.0 cm precaudal length were found to consume significantly larger prey than smaller sharks (ANOVA, P < 0.001). Diet breadth decreased with increasing shark precaudal length, suggesting more opportunistic feeding by neonates that are typically associated with rapid growth and a large appetite. However, proportions of prey families in the environment were significantly different to those found in the diet of all sizes of lemon shark (2, P < 0.0001). Barracuda (Sphyraenidae), mojarra, toadfish (Batrachoididae) and parrotfish were highly selected, and silversides (Atherinidae) negatively selected by lemon sharks of all sizes. Larger sharks exhibited a switch in prey preference from slow benthic fish and invertebrates to faster moving snappers and grunts. These data suggest that lack of hunting experience, reduced swimming ability and a restricted home range may force smaller sharks to forage more opportunistically on small, easier to catch prey, while larger and faster swimming sharks may be more efficient foragers in nurseries with patchy prey distributions.


(JWO, DES, GRH) NOAA, National Marine Fisheries Service, Alaska Fisheries Science Center, Resource Assessment and Conservation Engineering Division, 7600 Sand Point Way NE, Seattle, WA, 98115, USA; (JDM) Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX, 77843, USA

Recent progress in the taxonomy and systematics of the skates (Rajidae) of Alaska and the North Pacific

The skates of Alaska are represented by 15 species in three genera: Bathyraja, Raja, and Amblyraja. Among the species of Bathyraja, we recently described B. mariposa from the Aleutian Islands, where it appears to be endemic. The description of another species, also apparently endemic to the Aleutian Islands and related to B. parmifera, is underway as part of a review of the subgenus Arctoraja and its three nominal species. We are progressing on an examination of the B. interrupta complex of northern waters, a complex that may be composed of three species, including two that are presently undescribed. Morphological variation among other species of Bathyraja will be examined in future research to clarify, in particular, the status of Aleutian populations as compared with Bering Sea populations. In conjunction with this morphological work, molecular analyses are also being conducted. Preliminary results from the analysis of cytochrome oxidase subunit 1 sequence data produced markers to separate all species known from Alaska, including the new species from the Aleutian Islands. The relationships and zoogeography of the skates of Alaska will be discussed in light of our results to date.


(AP, JS, GB) Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, Gainesville, FL, 32611, USA; (JC, AM) NOAA/National Marine Fisheries Service, Southeast Fisheries Science Center, Panama City, FL. 32408, USA

The age and growth of Sphyrna lewini and S. mokarran in southeastern U.S. waters

We examined the age and growth of the scalloped hammerhead (Sphryna lewini) and great hammerhead (S. mokarran) off the southeast United States and in the eastern Gulf of Mexico. Our growth estimates for the scalloped hammerhead shark suggest slower growth than populations in the Pacific Ocean but faster growth than previously reported in the Gulf of Mexico. Our growth estimates for the great hammerhead are the first reported for this species. These results show that growth rates differ between these two species. The life history characteristics obtained as a result of this study suggest that the scalloped hammerhead and great hammerhead sharks are highly susceptible to exploitation by commercial fishing.


(EKP) Pew Institute for Ocean Science, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 126 East 56th Street, New York, NY, 10022, USA; (DDC, MSS) Guy Harvey Research Institute/Nova Southeastern University Oceanographic Center, Dania Beach, FL 33004, USA; (EAB) Pew Institute for Ocean Science, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA

Shark movement and habitat use at Glovers Reef Marine Reserve, Belize

A six-year annual longline survey of the sharks and rays of Glover’s Reef Marine Reserve, Belize documents the use of this oceanic atoll by at least twelve elasmobranch species, including early life-stages of Caribbean reef Carcharhinus perezi, nurse Ginglymostoma cirratum and lemon Negaprion brevirostris sharks and southern stingrays Dasyatis americana. Catch rates from the longline study were used to compare the species and age-distribution of sharks in different habitat types (shallow lagoon, deep lagoon, ocean reef). Nurse sharks dominated both shallow and deep lagoon catches, with smaller individuals more prevalent in the shallow lagoon. Caribbean reef sharks of all size classes dominated the ocean reef catches, but small juveniles were also common in the deep lagoon. An array of acoustic monitors throughout Glover’s Reef was used to track the movements of tagged individuals of the two most common shark species, nurse and Caribbean reef sharks. Both nurse sharks and Caribbean reef sharks, although occasionally wide-ranging, exhibited site- fidelity to particular locations around the atoll. All sharks were most frequently detected at the site nearest their capture and visited up to 13 additional, usually neighboring, receiver sites less frequently. Although less than 6 % of the total area of Glover’s Reef was within the detection range of this non-overlapping receiver array, most sharks of both species were detected somewhere within the array on an almost daily basis from May to October 2004, with no evidence of seasonal emigration of these two species away from the atoll over this period. Both species also moved widely throughout the 10 by 30 km atoll. The findings suggest that effective no-take marine reserves need to be large (boundaries of at least tens of kilometers) and encompass not only diverse habitats (ocean reefs, seagrass flats, lagoons) but also the areas that connect them (i.e. major channels).


Moore Laboratory of Zoology, Occidental College, 1600 Campus Rd., Los Angeles, CA, 90041, USA

The fall and rise of nearshore sharks in the southern California bight

The southern California bight has not been an exception to the global fisheries declines. In our nearshore environment, top down fisheries decimated the nearshore shark fauna and other apex predators in this ecosystem. For coastal elasmobranches the most storied decline was for soupfin sharks (Galeorhynus galeus) due to their exploitation during WWII. Prior to this fisheries exploitation (1930-1938) a mean of 235 (SE = 22) mt were landed annually. This stock was allowed to be exploited again with less than 50% (range 66-103 mt) pre WWII landings reported until 1985 at which point catches started declining precipitously (F1,9 = 83.47, R = 0.950, p <0.001) through 1995. Leopard shark (Triakis semifasciata), landings also declined dramatically during this period (1983-1996; R = 0.906, F1,12 = 54.7, p < 0.0001). The exploitation of these sharks was a result of the crash of white seabass (Scianidae: Atractoscion nobilis) fishery and the exclusion of Californian fishers from Mexican waters, which increased pressure on our local stocks. Fortunately, gill nets and trammel nets were banned starting in 1994 in state waters. In spite of regional productivity problems associated with the warm phase of the Pacific Decadal Oscillation during the last three decades, all of the apex predators on our nearshore reefs have returned. Ten coastal fishery independent monitoring stations were sampled regularly by gill nets from 1995-2004. Soupfin sharks (F1,8 = 8.63, R = 0.720, p = 0.018) and adult leopard sharks (R = 0.870, F1,8 = 24.8, p < 0.0001) have increased linearly since this fishery closure. This recovery was so dramatic that these fishes now appear in diurnal scuba transect programs where they had been absent for the prior three decades. The same trend (F1,8 = 16.8, R = 0.823, p = 0.003) was also found for giant seabass (Polyprionidae: Stereolepis gigas). In fact, even the white seabass fishery has returned to its pre-crash California landings. Both fishery dependent and independent data sets indicate that nearshore elasmobranches in southern California are still susceptible to exploitation without proper management and the single most important management action in southern California has been the removal of gill nets from the nearshore arena.


(DSP, JAM, JAG) Virginia Institute of Marine Science, College of William and Mary, P.O. Box 1346, Gloucester Point, VA, 23062-1346, USA; (ANP, GHB) Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, P O Box 117800, Gainesville, FL, 32611, USA

Patterns of polyandry in the sandbar shark, Carcharhinus plumbeus, in the western North Atlantic

Five species-specific microsatellite markers were used to examine patterns of polyandry in the sandbar shark, Carcharhinus plumbeus, in the western North Atlantic. Genetic polyandry was found in the majority of litters examined. In multiply sired litters the number of sires estimated ranged from 2 to 5 with an average of 2.3 males per litter. Most litters were characterized by high levels of reproductive skew, with individual sires accounting for 60% or more of the offspring. Regression analyses showed no significant relationship between female fork length and fecundity or female fork length and sire number. Analyses of the strength of selection for females to acquire multiple mates and males to limit the number of additional sires were carried out following Bateman’s principles. Female fecundity had a weak relationship with the number of sires and both the standardized variance in reproductive success and mating success were low. This indicates that the acquisition of multiple mates may have little direct selective advantage to females. Male reproductive success showed a stronger, but inverse, relationship with the number of sires and the standardized variance in reproductive success was larger, indicating the ability to bias paternity may have significant selective advantage to males. These data, in light of past morphological and behavioral studies, suggest that intrasexual and intersexual conflict, as well as indirect female benefit, drive patterns of polyandry in elasmobranchs.


(HLP, TCP) Mote Marine Laboratory, 24244 Overseas Highway, Summerland Key, FL, 33042, USA; (JCC, ALH) Albion College, Department of Biology, Albion, MI, 49224, USA

Diel movements of adult nurse sharks, Ginglymostoma cirratum, in the Dry Tortugas, Florida reproductive refuge

Adult nurse sharks in Florida are often found mating in shallow (< 1 m) areas in June and July. Results from telemetry show that adults of both sexes display consistent diel movements spending more time in the shallows at night. Sharks typically leave the shallows just before dawn (0600) and return at various times throughout the afternoon and evening with a peak of abundance around 0100. Some females stay in the shallow refuge all day and are seen by observers to move at times to slightly deeper water, particularly during afternoon low tides. Some movements away from shore are clearly to avoid shoaling after retreating tides. Attempts to predict these larger movements by correlating them with changes in temperature, tide, dissolved oxygen and barometric pressure have shown little positive correlation. Female areal movements during times of reproductive activity are apparently driven more by individual reproductive states that have a stronger influences on activities than abiotic factors. Male diel movements apparently follow female activities during this time.


Universidad Autónoma de Baja California Sur, Departamento de Biología Marina, Carr. al sur km 5.5, La Paz, BCS, 23080, México

Bioeconomy of the shark fishery on the western coast of Baja California Sur, Mexico

In Mexico, the shark fishery is very heterogeneous since it is multispecific, a wide diversity of fishing gears, and artisanal and commercial fishermen are present. Thus, the fishery management is difficult. In the matter, Días-Uribe and Ramírez-Aguirre (2002) proposed the Importance Bioeconomic Index (IBI), which sort hierarchically the resources of a multiespecific fishery based on the catch, value and fishing season. In the present work, IBI was modified adding the concept of Vulnerability, which involves anthropologic pressure and species fragility, to locate the most important bioeconomic fishing areas of the shark fishery at the western coast of Baja California Sur, Mexico. Using logbooks from 1996 to 2001 and a geographic information system we located, by its high commercial value and vulnerability, the areas in front and to the north of Magdalena Bay (25 °-26 ° N and 113 °-114 ° W) as prior and we recommend management steps.


Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Rd., Moss Landing, CA, 95039, USA

Feeding habits of the sandpaper skate, Bathyraja kincaidii (Garman, 1908), from central California, U.S.A.

The sandpaper skate, Bathyraja kincaidii, is a small deep-sea batoid that most commonly occurs from depths of 200-500m from the Gulf of Alaska to Baja California. As with most eastern North Pacific skates, few studies have been done on the life history of this species. Examination of 130 sandpaper skate stomachs collected from central Californa by the Southwest Fisheries Science Center (SWFSC) Santa Cruz Lab (SCL) from 2002 to 2005 revealed that like most other skates, this species has a generalized diet, feeding on many different groups of prey. They fed predominantly on invertebrates such as euphausiids, small shrimps, cephalopods and polychaetes. In addition, myctophids, rockfishes, crabs and mysids were also in the diet. Multivariate analyses were used to test for differences in both proportional weight and number of major prey groups (shrimp-like crustaceans, polychaetes, teleosts, small benthic crustaceans, crabs and cephalopods) by sex, maturity status and oceanographic season (Upwelling, Oceanic and Davidson Current). Diets were significantly different among seasons, explaining the largest proportion of the variance in the diet. All major prey groups, except cephalopods, showed differences among seasons. Diets also differed between maturity stages, which accounted for the next greatest proportion of the variance. Higher proportions of polychaetes, small benthic crustaceans and crabs were consumed by immature skates, while mature skates preyed more on shrimp-like crustaceans and teleosts. Feeding habits differed significantly between sexes, but only for weight data, and was driven by the higher proportion of shrimp-like crustaceans, small benthic crustaceans and crabs in male diets.


Moss Landing Marine Laboratories, 8272 Moss Landing Rd., Moss Landing, CA, 95039, USA

Dietary analysis of the longnose skate, Raja rhina (Jordan and Gilbert, 1880), in California waters

The longnose skate, Raja rhina, is one of the most important incidental species landed in central and northern California demersal fisheries. However, life history information is extremely limited for this species and aspects of its diet and feeding habits are unknown. Feeding ecology studies can provide researchers with important insights towards understanding potential fishery impacts on marine systems. The primary objective of this study was to analyze the feeding ecology of R. rhina off the coast of central California. Specimens of R. rhina were collected between September 2002 and August 2003 from fisheries-independent trawl surveys conducted by the National Marine Fisheries Service, South West Fisheries Science Center (NMFS- SWFSC). Of 1,193 longnose skates caught, 527 were female and 666 were male. A total of 618 R. rhina stomach samples was processed, and all prey items were identified to lowest possible taxa. For every stomach, the percentage of each prey item by number (%N) and weight (%W) were calculated and averaged to obtain a mean value. These measures were combined with the overall percent frequency occurrence (%FO) to determine the Index of Relative Importance (IRI), represented as %IRI. Results indicate that the five most important prey items were unidentified teleosts (31.6% IRI), unidentified shrimps (19.6%IRI), unidentified euphausiids (10.9% IRI), Crangonidae (7.4% IRI), and Neocrangon resima (6.0% IRI). Raja rhina diet was further analyzed through comparison of the following intraspecific variables: gender (male/female), depth (shelf/slope), and size class (<600 mm/>600 mm), using Morisita’s Index of Overlap. This analysis indicates there is a high degree of overlap between gender (95.9%) and shallow depths (96.4%), while size classes overlapped very little (34.8%). Additional multivariate statistics, Principle Component Analysis and MANOVA, are currently being conducted to further assess potential differences in diet among intraspecific variables.


Virginia Institute of Marine Science, 1208 Greate Rd, Gloucester Point, VA, 23062, USA Compensatory growth in the sandbar shark, Carcharhinus plumbeus: Fact or


Numbers of sandbar sharks, Carcharhinus plumbeus, in the Northwest Atlantic have experienced drastic declines since the early 1980’s reaching their minima during the early 1990’s. Catch rates in the early 1990’s were a mere 25% of those during the 1980’s. Such drastic reductions in other fish stocks have often caused compensatory responses, most notably the cod stocks in the Northwest Atlantic. Compensatory responses in depressed populations may include decreased natural mortality, increased fecundity, or increased growth rates. Compensation for population fluctuations below carrying capacities have been recognized for many terrestrial and oceanic r -selected organisms, but few instances have been noted for K-selected species. Due to slow-growth and late maturity, compensatory responses in K-selected species such as the sandbar shark probably require generation-scale time periods to become evident. A previous age and growth study discovered slight increases in juvenile sandbar shark growth rates when vertebral centra samples obtained in 1980- 81 and 1990-1992 were compared. The Virginia Institute of Marine Science shark long-line survey reported the lowest abundance of sandbar sharks in 1992. Animals pupped during this time may display greater differences in growth rates due to drastically reduced population size. Samples obtained over the 2001-2004 time period were compared to the aforementioned time periods to investigate potential compensatory responses in the sandbar shark population in the Northwest Atlantic.


(BS, IFI, IFA, TM)INIAP-IPIMAR, Avenida de Brasília, 1449-006 Lisboa, Portugal; (PJ, AN, LSG) Instituto de Oceanografia & Departamento de Biologia Animal, Faculdade de Ciências, Bloco C2, Campo Grande, 1749-016 Lisboa, Portugal

Reproductive dynamics of Leucoraja naevus and the role of oviducal gland

Rays are single oviparous species in which the egg production is limited by the ovarian and uterine capacities. They present external embryonic development of encapsulated fertilized eggs. The capsules are produced by the oviducal gland which also plays other important roles such as the production of egg jelly and sperm storage. Although it is generally admitted that spawning in rays occurs throughout the year, the temporal pattern of the reproductive output from mature females along the year is still uncertain for most of the populations. This aspect needs to be clarified to improve the knowledge on the behaviour of different cohorts in the population. This study presents results from the Portuguese project on the reproductive dynamics of Leucoraja naevus (Müller & Henle, 1841), using data on ovarian fecundity and on oviducal gland degree of activity, by month. Females in different maturity stages were continuously sampled from Portuguese commercial landings. Histological sections of the oviducal gland were performed in different zones: the proximal club zone, the papillary zone, the baffle zone and the terminal zone. Oocyte size-frequency histograms by month, particularly the relative frequencies of large oocytes (diam > 2.0 cm), indicated that egg-laying is not a continuous process along the year. The activity of different gland zones varied according to the level of maturation. In mature females before ovulation, the baffle zone, which secretes the capsule material, presented a high accumulation of secretions in the lumen. In the first two uterine stages, during which the formation of the capsule takes place, the club and papillary zones, both responsible for the formation of the egg jelly, were more active. Just prior the extrusion of the egg, it was observed a decrease in activity of the baffle zone and an increase at the terminal zone which secretes fibres deposited on the capsule′s surface.


(MSS, JM, DC) Nova Southeastern University, Guy Harvey Research Institute, 8000 N. Ocean Drive, Dania Beach, FL, 33004, USA; (EP) University of Miami, Pew Institute for Ocean Science, 126 East 56th St., New York, NY, 10022, USA

Application of genetic forensic tools in shark fishery monitoring and law enforcement

Management of shark fisheries in the U.S. and some other countries includes national legislation aimed at preventing landings of species considered especially vulnerable to fishing. Additionally, trade in some of these species (basking, white and whale sharks) is also regulated on an international level due to recent CITES listings. Despite these well-meaning regulations, however, landings and trade of these protected species is suspected to occur due to continued strong market demand for fins, and difficulties in identifying detached body parts. To assist in law enforcement and general monitoring of shark fisheries, we have developed species-specific PCR primers and a rapid assay that currently identifies 28 shark species of regulatory and conservation interest. We will report on our current genetic forensic abilities and present case studies where these techniques have been used to assist law enforcement. Species landed and traded in U.S. fisheries include protected taxa such as dusky, night, sand tiger, bigeye thresher, white and basking sharks. These findings suggest that assessing the effectiveness of fishery regulations will benefit from broader scale monitoring of shark landings by species.


Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL, 34236, USA

Can habitat suitability models be used to help recover the smalltooth sawfish population?

The distribution of areas important to the conservation of the endangered smalltooth sawfish was examined using habitat suitability models that utilized data from public encounters and research surveys. Public encounter data indicated that there was a significant correlation between the occurrence of juvenile sawfish (<200 cm) and the presence of shallow depths (<90 cm), mangroves and shorelines, but not seagrasses. There were significant positive size relationships in the distances from mangroves, shallow depths and shorelines with the size of sawfish. Public encounter data and research surveys also indicated that juvenile sawfish less than 200 cm in length were most commonly associated with estuarine conditions. Habitat suitability models were constructed using the distances to mangrove shorelines, shallow depths, and presence of estuarine conditions. Models with all combinations of these three factors were constructed and assessed using cumulative frequency plots of distance between encounters and areas of high habitat suitability. The three-parameter model was found to best represent the data. The model provided the best fit to data in areas south of 28°N where mangroves most commonly occur. The implications of the results for conservation planning for this endangered species will be discussed.


(SON, PJJC, CGJL, RMC, MOA, MLI) Laboratorio de Ecología Pesquera, Oceanografía Biológica, CICESE, Km. 107 Carretera Tijuana-Ensenada, Ensenada, Baja California, C. P. 22860, Mexico; (OJ) Monterey Bay Aquarium, 886 Cannery Row, Monterey CA, 93940, USA

The occurrence of juvenile white sharks (Carcharodon carcharias) in the northwestern Mexico

White sharks (Carcharodon carcharias) have been recorded throughout the North Pacific, from cold temperate coastal to tropical waters. In the Gulf of California, Carcharodon carcharias has being reported only in the southern part, close to the mouth of the gulf. In this study we report the characteristics of five juveniles white sharks caught by fishing vessel in the Upper Gulf of California during the summers of 2002, 2003 and February 2005; as well as the stomach contents of three of these sharks. Juvenile shark sizes ranged between 212 and 236 cm in total length (TL). The principal food items were bony fishes and rays (Rhinopteridae). Additionally, five juvenile white shark jaws were collected at garbage dumps near a fishing village at the Pacific coast of the middle Baja California Peninsula. The calculated size of these juveniles ranged between 199 and 243 cm TL. The importance of the Gulf of California for this species will be discussed and some of the management issues in the region.


CSIRO Marine and Atmospheric Research, PO Box 1538, Hobart, Tasmania 7001, Australia

Satellite tagging of pelagic sharks off eastern Australia

The movements and behaviour of pelagic sharks were studied using direct satellite tracking tags and pop-off archival transponding tags (PSATs) deployed off the central east coast of Australia from commercial longline vessels. Eight blue sharks were tagged with direct satellite tags, mostly Wildlife Computers SPOT or SPLASH tags, and five blue sharks were tagged with PSATs. One each of shortfin mako, common thresher and bigeye thresher were tagged with PSATs. Tracks from SPOT tags were up to 137 days duration. One blue shark double tagged with a SPOT and PSAT died soon after release, and two others only transmitted for 6 and 11 days. The PSATs collected data for up to 180 days and there was evidence that some tags were bitten off, presumably by other sharks. Blue sharks remained in the general Australasian region for the duration of the tracks and those fitted with direct satellite tags transmitted nearly every day. Regions of high residency where the sharks were clearly not in transit were identified from the tracking data. The physical and biological characteristics of these areas were obtained from remote sensing data and we attempted to identify regions of local productivity that cause aggregation of blue sharks and to characterize their biotic and abiotic features. The PSAT data from blue sharks showed they usually spent 20-30% of their time in the 0-10 m depth strata, with about 5% of their time spent down to 600 m depth and with some dives deeper than 600 m. Most time was spent in the 17.5-20.0 degrees temperature range. The PSAT data from the other pelagic sharks also showed time spent at depth down to about 600 m but the thresher sharks, particularly the bigeye thresher spent less time at or near the surface.


(DES, JWO, GRH) NMFS, Alaska Fisheries Science Center, 7600 Sand Point Way NE, Seattle, WA 98115, USA; (JDM) Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX, 77843, USA

The skates of Alaska: Distribution, abundance, and taxonomic progress

Historically, skate populations in the eastern North Pacific and Bering Sea have been inadequately studied and inaccurately represented because of incomplete taxonomic knowledge and difficulties in obtaining accurate species identifications. As a result of collaborative efforts among many taxonomists and fisheries biologists, recent NMFS bottom trawl survey data reflect great improvements in the reliability of skate identifications, and have been instrumental in the description of new taxa. A data set compiled from the catch records of bottom trawl surveys from 1999-2005, including the Gulf of Alaska, Aleutian Islands, and eastern Bering Sea, gives a comprehensive overview of the skate fauna of Alaska. This data set includes a total of 14 recognized species of skates and at least one undescribed form, all of which are documented by photographs and represented by voucher specimens deposited at the University of Washington Fish Collection, as well as other collections around the country. With these reliable species-level identifications, the distinct species assemblages associated with each geographical and bathymetric region of Alaska have been identified, and patterns of overall skate diversity and abundance in the eastern North Pacific and Bering Sea are beginning to emerge. Moreover, catch data from NMFS bottom trawl surveys are being used to evaluate new sources of skate distribution data, including species-specific catch data now being collected by North Pacific groundfish observers.


(EMS, MMH) SharkDefense LLC, PO Box 2593, Oak Ridge, NJ, 07438, USA; (SHG) Bimini Biological Field Station and University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, FL, 33149, USA

Evaluation of Semiochemical Shark Repellents on Demersal Longlines

International concerns have been raised about apparent population declines of large pelagic fishes including predatory sharks that are ecologically and commercially important. A major contributor to the international population decline of large pelagic predatory sharks is commercial pelagic longline fishing targeting tuna and swordfish (Falterman & Graves 2002; Peel et. al. 2003; Uozumi 2003; Kerstetter 2004). Beerkircher et. al. (2002) suggests that Carcharhinid sharks comprise the largest portion of shark bycatch during U.S. commercial pelagic longline fishing with blue sharks, Prionace glauca, comprising the greatest biomass of any bycatch species. As a potential means to reduce this shark bycatch, we have evaluated semiochemical shark repellents at South Bimini, Bahamas using demersal longlines. The semiochemicals used in this evaluation study did not produce aversive behavior in captive Yellowfin tuna, (Thunnus albacares) and Cobia, (Rachycentron canadum). Five demersal lines were set, with three lines dedicated as controls. Each line consisted of fifteen gangions equipped with 16/0 steel circle hooks and hook event timers. Adequate spacing between control and treatment sets was allowed to reduce the effects of chemical plumes. All hooks received the same type of bait, were rebaited at the same time of day, and were monitored at four-hour intervals for shark catch. Results demonstrated significantly lower shark catches on treatment lines as compared to the control lines.


Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, P O Box 117800, Gainesville, FL, 32611, USA

From histology to hormones: Advances in the study of skate reproductive biology and the potential use in conservation management

Information regarding sexual maturity and reproductive cycles in skates has largely been based on gross morphological changes. For example, past studies have used structural endpoints, such as clasper length in males, ovary weight in females, or gonadosomatic index (GSI), to help assess reproductive status in these species. In contrast, few studies have used histological changes or circulating steroid hormone concentrations as endpoints to establish when skates become reproductively capable or to determine reproductive cyclicity. The present study summarizes our current knowledge of histological and hormonal analyses in skate reproduction. This study also offers information that analysis of circulating steroid hormone concentrations, as a conservation management tool, may provide a means to determine size at sexual maturity and to assess reproductive cycles without the need to sacrifice the animal.


School of Aquatic and Fishery Sciences (SAFS) and Quantitative Ecology and Resource Management (QERM), Box 355020, University of Washington, Seattle, WA, 98195-5020, USA

Integration of historic and recent data for population dynamics modeling of spiny dogfish in the Northeast Pacific

The spiny dogfish, Squalus acanthias, has a long history of exploitation in the Northeast Pacific. Landings rose to a peak of over 50,000 mt in 1944 but have remained below 10,000 mt since 1950. Fishery statistics, biological data, and dorsal spines for ageing were collected in the 1940s and a tagging study was conducted. Information for the recent decades includes the same data types with the addition of bycatch data from observer programs and abundance indices from surveys and fisheries in the US and Canada. This paper describes an age-structured metapopulation model which integrates the historical data with the more recent sources. The metapopulation framework allows the modeling of declining abundance indices in inside waters of the Puget Sound along with stable indices in coastal waters. Uncertainty in the estimate of current depletion is discussed, and the implications for conservation and management of this long-lived, late-maturing species are considered. The use of alternative measures of population status, including reproductive value, is proposed.


(MAT, LJBL) School of Ecology and Environment, Deakin University, PO Box 423, Warrnambool, Victoria, 3280, Australia; (MAT, JDS) CSIRO Marine Research, GPO Box 1538, Hobart, Tasmania, 7001, Australia

Dietary habits and overlap in the rajid species in southeastern Australian waters

Dietary information on skates (Rajidae) is vital in determining their ecological role and trophic relationships within their local environment and for creating ecosystem models. In southeastern Australia, seven skate species (Dipturus sp. A, D. sp.B, D. cerva, D. gudgeri, D. lemprieri, D. whitleyi and Pavoraja nitida) were collected from commercial and recreational fishermen between 2002 and 2004. The aim of this study was to determine dietary overlap between the species and to examine the ontogenetic shifts in diet. All stomachs from dissected skate species were excised, contents weighed and preserved. All prey items were then counted, weighed and identified to the lowest possible taxon. Each prey group was assigned an ecological group listing to identify whether a shift in diet from benthic to pelagic prey occurred with ontogeny, size and species. The Index of relative importance was used to characterise diet. Seasonal, sex, trophic levels and geographic variations were also examined. Ontogenetic changes in diet were evident, five species as juveniles fed primarily on caridea (shrimp: Leptochela sydniensis), as size and maturity increased the diet progressed to larger prey items of a wider variety of taxa. The smallest skate species P. nitida consumed caridea throughout ontogeny. Dipturus gudgeri and D. sp. B showed the highest percentage of empty stomachs, possibly due to the fishing method, bottom drop-lining. Caridea, brachyura (crabs), cephlapoda and osteichthyes (fish/eels) were of the most importance in the diet of D. sp. A and D. whitleyi at different stages of ontogeny. Dipturus lemprieri preyed primarily on crabs, and the diet of D. cerva and P. nitida consisted of substantial amounts of L. sydniensis. Dipturus sp. B fed primarily on crustaceans (spider crabs, goneplacid crabs and squat lobsters). Dipturus gudgeri ingested similar prey to D. sp. B, although osteichthyes were also a significant part of the diet.


(JPT, JG) Mote Marine Laboratory, Center for Shark Research, 1600 Ken Thompson Parkway, Sarasota, FL, 34236, USA; (PJM) University of South Florida, 4202 East Fowler Avenue, Tampa, FL, 33620, USA

Bonnethead shark (Sphyrna tiburo) androgen receptor: cDNA cloning and tissue specific expression through the male reproductive cycle

Steroid hormones are essential for proper reproductive development in all vertebrates. Androgens are sex steroids secreted by the gonads that regulate virilization, spermatogenesis, and sexual behavior. These physiological actions require the binding of androgen to a specific receptor protein. Androgen receptors (AR) are ligand-activated transcription factors that bind to a specific nucleotide sequence of DNA and positively or negatively regulate transcription. An understanding of the distribution and levels of expression of the elasmobranch ARs on the cellular and tissue level demonstrates the pattern of responsiveness to the androgenic hormones. In this study, a fragment of the AR gene was cloned and sequenced from the bonnethead shark, Sphyrna tiburo, an elasmobranch species with a well-defined annual reproductive cycle. Acquiring this gene sequence facilitated the construction of species-specific AR polymerase chain reaction (PCR) primers and bonnethead AR mRNA probes that were used to screen reproductive tissues for evidence of AR gene expression using reverse transcription (RT)-PCR and in situ hybridization (ISH), respectively. The RT-PCR screens demonstrated AR gene expression in the testes, seminal vesicles, and epididymides of male bonnethead sharks. ISH results localized the AR expression to the interstitial cells of the testes and mature spermatozoa within the seminal vesicles and the testes. Immunocytochemical methods used to detect the AR protein produced comparable results in the shark testes. These findings along with seasonal and ontogenetic differences in AR expression will be discussed. Knowledge of AR receptors in elasmobranch fishes, being the oldest living animals that possess an archetypical vertebrate pattern of reproductive endocrinology, may provide insight into the evolution of steroid receptors and nuclear receptors as a whole. Further, knowledge of steroid receptor function may enhance our understanding of the mechanisms behind endocrine disrupting chemicals in the environment.


Universidad Autonoma de Baja California Sur, Dept. Biologia Marina. Carr. al Sur Km 5.5, La Paz, BCS, 23060, Mexico

Actual status of NOM-029-PESC-2004

In 1997 initiated the workshops of the Technical Group to elaborate the NOM-029 project about the shark fishery regulation in Mexico. After several meetings, in January 12, 2000 this project was published for its public consultation. Nevertheless, due to diverse observations, the final version was not published. Subsequently, in July 12, 2002 was published practically the same version for its public consultation. The main objective of NOM-029 was regulate the shark fishery, but this version did not regulate the fishing areas, neither establish prohibitions, neither regulate the types of hooks and nets, neither establish limits to the incidental catches and neither limit the fishing effort. So, in base to a NOM-029 workshop called by three Commissions of the Senate, one of the Representatives Camera and the government of the state of Baja California Sur, the entrance in vigor of the NOM-029 was abrogated. From then a review process began by the Technical Group, there were carried out diverse workshops about the impact of the fishery on marine mammals and turtles, fishing gears, legislative aspects and shark population status. With the results of these workshops a new NOM-029 project was elaborated and sent to competent Mexican government instances. Nevertheless this project was rejected by pressure of the industrial fishery sector, since the project regulated the type and number of hooks and established prohibition areas for the big boats. It is urgent to regulate the shark fishery in Mexico, since their populations have diminished hardly affecting the fisheries in both oceans.


(CAW) Dalhousie University, Dept. Earth Science, LSC, Halifax, NS, B3H 4J1, Canada; (RAM) Dalhousie University, Dept. Biology, LSC, Halifax, NS, B3H 4J1, Canada; (CP) REEF Pacific Office, 4726 38th Ave NE, Seattle, WA, 98105, USA

Decline in yellow stingray (Urobatus jamaicensis) in the Florida Keys National Marine Sanctuary, USA

The ‘common’ elasmobranch species Urobatus jamaicensis (yellow stingray) has undergone a steady decline in the Florida Keys National Marine Sanctuary (FKNMS), USA. The yellow stingray is one of the smallest and most common elasmobranch species in the Caribbean. It is considered a good tropical fish for personal/commercial aquariums and is often used for scientific experiments. Currently, no permit is required for extracting U. jamaicensis, and only sold extractions are reported. This study analyzed temporal trends and environmental preferences of the yellow stingray in the FKNMS as recorded by trained volunteer divers using the Roving Diver Technique. Data were obtained from Reef Environmental Education Foundation (REEF) Fish Survey Project. Experienced divers in the FKNMS were interviewed about their impression of the yellow stingray to determine if the decline was detected. Included in this study were 10 different habitat types, depths from 0-37 m, and surface temperatures from 15-35°C. A generalized linear model on presence-absence data with a binomial distribution and logit link was used to estimate the change in U. jamaicensis by year. Habitat type, depth, site, average temperature, and Julian date were included in the model to standardize the data. A total of 15639 surveys conducted at 388 sites throughout the FKNMS were used. U. jamaicensis was seen on 2502 dives in FKNMS (16%). The decline in sighting frequency has occurred in all habitat types, depths, sites, and regions of the FKNMS. U. jamaicensis sightings declined from 32.1% SF (425 sightings in 1326 surveys) in 1994 to 8.5% SF (93 sightings in 1093 surveys) in 2005, averaging 18% decline per year. Preliminary analysis indicates that the decline in yellow stingrays is consistent in other areas of the Caribbean. The decline has gone virtually unnoticed. This study highlights the importance and use of trained volunteer divers for monitoring elasmobranchs.


(KCW, BAB) Tuna Research and Conservation Center, Hopkins Marine Station of Stanford University and Monterey Bay Aquarium, 120 Oceanview Boulevard, Pacific Grove, CA 93950; (JOS) Monterey Bay Aquarium, 866 Cannery Row, Monterey, CA, 93940, USA; (CGL) California State University, Long Beach, Dept. of Biological Sciences, 1250 Bellflower Blvd., Long Beach, CA, 90840, USA; (CW) Southern California Marine Institute, 820 South Seaside Ave., Terminal Island, CA, 90731, USA; (HD) Tagging of Pacific Pelagics/ CoML, c/o Inter-American Tropical Tuna Commission, 8604 La Jolla Shores Drive, La Jolla, CA, 92037, USA

Movement, behavior and habitat of juvenile white sharks in the eastern Pacific

Six juvenile white sharks ranging in age-class from 1 to 3 years were tagged in the Southern California Bight using pop-up satellite archival tags. Young-of-the-year white sharks in the Eastern Pacific occupy a larger nursery area than suggested in previous studies, spanning California Current waters of Southern California and Baja California, Mexico. Young-of-the-year sharks preferred surface mixed layer waters of 16-20C but made frequent movements through the thermocline, and showed a strong diel pattern in behavior. Three-year-old sharks used a larger geographic, vertical and thermal habitat, making movements to greater depths and cooler temperatures, and one individual moving into cooler waters north of Point Conception. This ontogenetic thermal niche expansion suggests that young-of-the-year sharks are thermally limited in their habitat. Juvenile white sharks are captured as bycatch in both US and Mexican waters, suggesting that management of fishing mortality should be of increased concern.


(CDW, SN) University of Rhode Island, Dept. Biological Sciences, Kingston, RI, 02881, USA; (GVL) Museum of Comparative Zoology, Harvard University, 26 Oxford St. Cambridge, MA, 02138, USA; (CPS) Department of Biology, 114 Hofstra University, Hempstead, NY, 11549, USA.

Fluid dynamics of suction feeding in bamboo sharks

In suction feeding, a volume of water is drawn into the mouth of a predator. Previous models and experiments of suction feeding in fishes have shown that significant fluid velocities are confined to a region within one mouth width (MW) from the mouth. Therefore the predator must be relatively close to the prey to ensure capture success. Most of those studies were conducted on bony fishes that feed in the water column with relatively little attention given to benthic feeding fishes. White-spotted bamboo sharks, Chiloscyllium plagiosum, live in benthic environments around coral reefs and are strong suction feeders. We predict that the shape of the fluid velocity field will change when feeding on the substrate compared to that in the water column due to conservation of momentum. Height should decrease while width and length should increase when feeding on the substrate compared to that in the water column. Therefore, the boundary of the fluid field will lie further away from the mouth, thereby exceeding the theoretical prediction of a maximal one MW distant flow field. To test these predictions, high resolution DPIV was used to visualize the fluid field and analyze the fluid dynamics around the mouth of bamboo sharks while suction feeding on the substrate and in the water column. Prey captures, transports and missed strikes were recorded as bamboo sharks were fed squid at various heights from the substrate. DPIV analysis results show that the boundary length of the flow field can be increased up to 2.5 MW distances from the center of the mouth due to passive substrate effects during prey capture. This indicates that feeding near a substrate extends the distance that suction flow is effective and thus requires less accuracy than feeding in the water column using the same effort.


(JTW, YI) Aichi Medical University, Laboratory of Biology, Nagakute, Aichi 480-1195, Japan; (MM) Hekinan Seaside Aquarium, 2-3 Hamamachi, Hekinan, Aichi, 447-0853, Japan; (JS) Aichi Medical University, First Department of Physiology, Nagakute, Aichi 480-1195, Japan

Transient anatomical features of Scyliorhinus torazame embryos

Scyliorhinus torazame is an oviparous elasmobranch and its embryos require 214±26 days to complete development at 14-16°C. During this time the embryo and egg case continually adapt to each other. There are four respiratory slits in the egg case, two dorsal and two ventral. The respiratory slits are sealed with solid jelly until 103±6 days at 14-16°C after oviposition. In common with other oviparous elasmobranchs, the tail is used to move water through the egg case via the respiratory slits. The tail has transient anatomical features specialized for development within the egg case. Primary scales found in two rows at the dorsal and ventral margin of both sides of the caudal fin erupt and increase surface area for water movement. The tip of the caudal fin is an extension of the notochord and forms a scoop for water transfer through the egg case by active pumping of the tail. Embryos have been observed to project this tail extension through the hatching terminus of the egg case in the months preceding hatching. The cup-like extension and caudal scales can be observed in embryos after eclosion but are gradually resorbed during the following months. Another specialized embryonic structure to develop during incubation is primary scales found in 2 dorsolateral rows along the trunk. These scales erupt before hatching and may be used to aid in escape from the egg case during ecolsion. Ordinary placoid scales do not erupt until after hatching.


Nagasaki University, Faculty of Fisheries, Bunkyo, Nagasaki, 8528521, Japan

Repruductive biology of Longheaded Eagle Ray, Aetobatus flagellum, in Ariake

Bay, Kyushu, Japan

The Longheaded Eagle Ray, Aetobatus flagellum, has recently increased significantly in number abruptly in Ariake Bay. The eagle ray is a seasonal visitor to Ariake Bay, increasing in number from April, and peaking during the summer. It is assumed that the eagle ray feeds on bivalves and so, to prevent predation on bivalves by eagle rays, a predator control program aimed at reducing the ray population has been in place since 2001. When the program was started, there was no biological information about eagle ray, therefore we clarified to examine their occurrence, age, growth and food in Ariake Bay to obtain data on the ecology of the eagle ray and provide basic information on their potential impact on bivalve stocks. In this study we studied reproductive biology of eagle ray. The size at sexual maturity is 800 mm DW for males and 900 mm DW for females. The histological examination of testis and the seasonal variation of GSI showed the mating occurred during August and October. The fertilized eggs were found from August until next May, and in June the smallest embryos were found in their uterus. The fertilization and parturition were occurred in August because the largest embryos were found in August (average size: 350mm DW), therefore the gestation period was approximately 12 month but the growth of embryos was rapid for 3 month. The fecundity was relatively low that ranged from 1 to 6 embryos. Low fecundity and slower maturity suggested that the predator control program is possible to reduce ray population size. The estuaries are used for their reproduction and nursery ground. The existence of large estuaries is one of the reasons with the recent rising water temperature why they increased in Ariake Bay.


(KEY, JCM) Leigh Marine Laboratory, University of Auckland, P.O. Box 349, Warkworth 1241, New Zealand; (KEY, JCM) University of Auckland, School of Biological Sciences, Private Bag 92019, Auckland, New Zealand

Comparative brain morphology in elasmobranchs: From structure to function

There is widespread variation in both brain size and complexity across the elasmobranch phylogeny. The relative brain weight of a species is dependent upon the relative enlargement or regression of individual brain structures, some of which can be identified with different sensory modalities and behaviors. The hypothesis that there is an environmental correlation with structural hypertrophy (AES abstract, 2005) was further tested by adding 18 species to the data set. The total database of 46 species from 25 families strengthens the environmental correlations amongst several families of Chondrichthyans. The data show large variations in relative brain weight and complexity between species that do not follow a simple phylogenetic pattern, as the relative development of the five major brain areas are similar in species that occupy similar habitats. Agile, pelagic species, such as Prionace glauca and Sphyrna zygaena, have enlarged telencephalons and highly foliated cerebella. Reef-associated benthopelagics have enlarged telencephalons, similar to the pelagic species, but show average cerebellar foliation while bathyal and demersal benthopelagic sharks, such as Squalus acanthias and Dalatias licha, have enlarged mesencephalon and medulla. Benthic species, such as Orectolobus ornatus and Cephaloscyllium isabella, have small, smooth cerebella and small telencephalons, though the demersal benthics have enlarged mesencephalons while the reef-associated benthic species have recessed this structure. In batoids, the species that had the highest levels of cerebellar foliation had the most complex batoid wing skeletal structure, adding weight to the hypothesis that there is a cerebellar correlation with fin dexterity. More detailed data will be presented on the cerebellum and the cerebellar like structures and the structure- function relationship of these brain areas. Functional implications of a comparative analysis of these brain structures will be discussed.


(JY and GWB) Middle Tennessee State University, Biology Department, Murfreesboro, TN, 37130; (SHG) Bimini Biological Field Station, Bimini, Bahamas

Rapid colonization of neonate lemon sharks by monogeneans

Sharks are commonly infected by monogeneans (Monogenea); however, few data exist regarding how soon after birth neonates become infected. Fifty juvenile lemon sharks, Negaprion brevirostris, captured about Bimini, Bahamas were examined for the presence or absence of monogeneans. Thirty-two percent of the sharks were infected by Dermophthirius nigrelli. Twenty-five of these sharks were neonates estimated to be less than 8-10 weeks old and some of these were as young as 3-4 weeks old. Twenty four percent of the neonates were infected by D. nigrelli, with the youngest sharks estimated to be 3-4 weeks old. These results indicate that lemon sharks can be infected by D. nigrelli soon after birth. This may have important husbandry implications when neonate sharks are selectively acquired for aquarium operations with the assumption that they will not yet be infected by monogeneans. This study was partially supported by an Undergraduate Research, Scholarship and Creative Activity Scholar award to J. Young from Middle Tennessee State University.



(ZB) University of Queensland, Brisbane, Queensland, Australia; (MLGD) Universidade estadual do Amazonas, Brazil

Status of freshwater stingray ornamental trade: From Rio Negro to the world

The artisan techniques of capture to the commercial exploration of freshwater stingrays as ornamentals based at the Negro river basin includes transport from fishing grounds, reception at distributor, wellbeing (quarantine), and shipping to international markets. Information of post-capture mortality either from fishing grounds to distributor center is around 7 %, and this is species-dependent. However, mortality data from distributor (at Manaus) to external markets is not known yet. The objectives of this work are to provide information about the mortality rate of these species during transport, considering time of the year and import country facility. Also, work will show briefly how this market is structured and the social economic impact on the riverine people. The data was obtained from mortality reports sent by the customer to the ornamental fish industry based at Manaus, Amazonas state. The average mortality for stingrays shipped is average 10 %, some factors can alter this variable such as time of the year, handling, and government regulations. With the reduction of mortality rates the fishermen will receive more money, however, the fishing effort over the species will not be effected. In conclusion, the best practices of fishing, handling, and transporting are important to guarantee conservation of the species and to continue the employment of the fisherman at the Rio Negro basin.


(LAK, LC) Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA, 95039, USA; (JJB, DAE) Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA, 95039, USA

In situ observations of deep-living skates and rays in the central and eastern North Pacific

We studied more than 2,000 deep-living skates and rays using in situ video observations from the Monterey Bay Aquarium Research Institute’s (MBARI) Video Annotation and Reference System (VARS). This database includes annotations for more than 16,000 videotapes recorded with the remotely operated vehicles (ROVs) Ventana and Tiburon since 1988. Observations were at depths below 200 m and primarily from the Monterey submarine canyon. Records also include the Pacific Northwest, southern California basins, central California seamounts, northern California, Hawaii, and the Gulf of California. We reviewed each observation, identifying animals to the lowest possible taxon, and noting gender when appropriate. We also recorded parameters such as geographic location, temperature, salinity, and oxygen content of the water, micro- and macrohabitat characters, and specific behaviors. Twelve species were observed. These video records extend the depth range of Amblyraja badia to 3,167 m, making it the deepest known skate species.


California State University, Northridge, Northridge, CA, USA

Population genetics of the Tope (galeorhinus galeus) in response to California fishery pressure

The tope (Galeorhinus galeus) has been the subject of intense fishery pressure over the last 74 years (Ripley 1946, FAO.org). Millions of sharks were harvested during the 1940s primarily for their vitamin A rich livers (Ripley 1946, Leet et al. 2001). This intense exploitation collapsed breeding areas within the San Francisco and Tomales bays (Leet et al. 2001). Currently all sharks face a new global threat, shark finning. Unfortunately, only well-qualified estimations exist as to how many sharks inhabit the world′s oceans. Without exact population data, the impact of overfishing on shark species can only be assumed. Because empirical estimation of true population sizes of pelagic shark species is unrealistic, a method of determining shark population health is sorely needed. The tope provides an excellent model in that this species of shark was once historically overfished (Leet et al 2001). By analyzing and comparing the DNA of present day topes with the DNA of preserved specimens dating back to the early 1900′s, evidence of inbreeding and the possible existence of a population bottleneck may be established. This information would be invaluable for the establishment of new conservation measures aimed at easing the current fishing pressure on topes, as well as other species of shark around the world.


(PCA) Programa de Pos-Graduacao em Ciencias Biologicas (Zoologia) and (RSR) Laboratorio de Ictiologia, Departamento de Sistematica e Ecologia, Centro de Ciencias Exatas e da Natureza, Universidade Federal da Paraiba, Joao Pessoa, PB, 58059-900, Brazil; (AJAS) Programa de Iniciacao Cientifica and (MPA) Programa de Pos-Graduacao em Zoologia, Campus de Pesquisa, Museu Paraense Emilio Goeldi, Belem, PA, 66077-530, Brazil; (ASV) Centro de Ciencias Exatas e Naturais, Universidade Federal do Para, Belem, PA, 66075-110, Brazil

Polychromatism of the freshwater stingray Potamotrygon leopoldi (Chondrichthyes: Potamotrygonidae)

Freshwater stingray dorsal color patterns have been widely used as important criteria in species identification. The intra-specific dorsal color variability (polychromatism) that occurs within this family almost always results in misidentifications or in the use of different designations for a same species. P. leopoldi is an endemic species of the Xingu River basin that was described as dorsally dark black with yellow spots that become irregular at the disc center (half-moon or kidney shaped). Female and male specimens (n = 166) were collected in the mid Xingu River region in the years 2003 through 2005. All stingrays were photographed dorsally and ventrally immediately after capture. A dorsal color pattern characterization study was carried out considering the shape, distribution and presence / absence of defined figures. Ventral color variations were also registered. Different color patterns were observed among neonates, juveniles, sub-adults and adult specimens. Most color patterns had not been previously registered for this species. Neonate and juvenile specimens are easily misidentified as P. henlei and P. motoro, even by the ornamental fish trade. Some of the sub-adult and adult color patterns are similar to P. henlei, an endemic species of a neighboring river basin (Tocantins-Araguaia basin). Conclusively, this species presents a higher polychromatism than once thought. It is recommended that color characteristics should be used with care and not solely when identifying potamotrygonid freshwater stingrays.


University of Miami, Dept. Biology, Coral Gables, FL, 33124, USA

Increase in predatory efficiency of hatchling whitespotted bamboosharks,

Chiloscyllium plagiosum

Foraging presents a significant challenge for neonatal predators. Adequate predatory skills must initially be present or must quickly develop. Additionally, predatory efficiency may change over time. Physical maturation may cause changes in efficiency due to improved neuromuscular coordination, increased sensory abilities, or morphological changes. Experience may allow predators to increase efficiency by honing existing skills and developing new ones. Predatorily naive whitespotted bamboosharks, Chiloscyllium plagiosum, of two age groups (2 days old or 21 days old) were video-recorded foraging on live polychaete worms. The first fifteen prey captures of each shark were analysed for predatory efficiency – the duration of the predatory sequence from initiation of trial to complete ingestion of prey. Predatory efficiency was then subdivided into three measures: latency to attack the prey, duration of attack (between first contact with prey and initial ingestion) and duration of prey processing (between initial ingestion and final swallowing). The changes in these measures over time were compared between the two groups of sharks.


(CLC) Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, PO BOX 117800, Gainesville, FL, 32611, USA; (JAM) Virginia Institute of Marine Science, PO Box 1346, Gloucester Point, VA, 23062, USA

A delineation of the Eastern Shore of Virginia summer nursery habitat of juvenile sandbar sharks, Carcharhinus plumbeus

The identification and delineation of pupping and nursery areas of Atlantic sharks has been identified as an important information need for future management efforts. Recent studies have found the principal summer nursery areas of the western North Atlantic population of sandbar sharks occur in shallow coastal bays from New Jersey to South Carolina. The primary objective of this project was to spatially delineate the summer nursery for sandbar sharks that occurs in the coastal bays and lagoons of the Eastern Shore of Virginia. To accomplish this, twenty sites were chosen within an area that spanned approximately 700 km2 from Magothy Bay to the south and Wachapreague Inlet to the north for repetitive sampling using longline gear. These sampling locations were situated within four inlets from south to north: Sand Shoal Inlet, Great Machipongo Inlet, Quinby Inlet, and Wachapreague Inlet. The mean catch rate at each site during the peak nursery season varied from 5.6 to 22.2 sharks per 100 hooks. Despite the high catch rates throughout the study area, there was significantly higher abundance in Great Machipongo Inlet and there was a significant positive correlation between abundance and both distance from the inlet and bottom temperature. Neonates, small juveniles, and large juveniles were present throughout the sampling area, but there were significant differences in the relative abundance of each age class with inlet and with distance from the inlet. The catch rates of neonate and juvenile sandbar sharks within this area were comparable to those of the nearby Chesapeake Bay though a larger proportion of juveniles greater than 100 cm total length were caught within the Eastern Shore lagoons. This study indicates that the bays and lagoons of the Eastern Shore of Virginia function as important primary and secondary nursery grounds for this species and fit the criteria to be included in future management measures as a habitat area of particular concern (HAPC).


(MND, APS) University of California, Ecology & Evolutionary Biology, 321 Steinhaus Hall, University of California, Irvine, CA, 92697, USA; (SG) Max Planck Institut für Metalforschung, Department Arzt, Heisenbergstrasse 3,70569 Stuttgart, Germany (WAC) University of California, Materials Characterization Center, Irvine, CA, 92697, USA

Ontogeny of calcification of the tessellated skeleton

A key component of the high level of performance of the elasmobranch skeleton is its tessellation: in most elements, the soft hyaline cartilage core is tiled with an outer rind of calcification, comprised of abutting blocks called tesserae. However, not only are we ignorant of the calcification mechanism of shark cartilage, we do not know whether it is homologous in any respects to vertebrate mineralization pathways. We examined ultrastructural changes in calcification across ontogeny in the jaws of the round stingray, Urobatis halleri using electron microscopy and histological techniques. The uncalcified cartilage of early embryonic stages (35-65mm DW) is highly cellular, with hypertrophic chondrocytes occluding the matrix. Cell size and density shows a marked decrease in late embryos (< 65mm DW) when tesserae arise as thin plates (100 m wide, 50 m deep). At the calcification front, chondrocytes are flattened and arranged in series along their long axes; these strings of cells are engulfed by globular calcification and incorporated intact into forming tesserae, creating cell-rich laminae with small passages connecting adjacent entombed cells. Cell spaces (lacunae) at the margins of tesserae are apparently continuous with cells invested in the fibrous intertesseral joints connecting tiles. Chondrocyte size and density continue to decrease to the adult stage as tesserae widen and deepen by 2-3 and 3-5 times, respectively. These preliminary data reveal similarities and reinforce well-known differences between elasmobranch and mammalian calcification. As in endochondral ossification, elasmobranch chondrocyte size and density decrease with age, yet lack the end-stage hypertrophication and cell-death of the tetrapod pathway.


University of Rhode Island, Dept. Biological Sciences, Kingston, RI, 02881, USA

Gill slit morphologies among extant sharks

The number of gill slits that an elasmobranch species possesses is often counted for taxonomic classification; however, the length of each slit relative to total body length, the spacing among the slits, and position of the slits relative to the pectoral girdle and fin have not been measured or compared phylogenetically. In this study, these variables are analyzed among species within each family of extant sharks. While it was expected that the slit morphologies would be similar among species within each family, we found differences in length, spacing, and position by order, family, and even genera, thus showing diverse slit morphology among extant sharks. However, there are three predominant morphologies: 1) all slits of similar length, spaced evenly apart, and positioned in front of the pectoral girdle and fin, 2) all slits of similar length, spaced evenly apart, and positioned just adjacent to the pectoral fin, and 3) all slits of similar length, anterior four slits spaced evenly with the fourth and fifth slit spaced with about half the distance between them as compared to slits one through four, and with at least slits four and five positioned dorso-laterally to the pectoral girdle and fin. The diversity among extant sharks indicates that slit morphology may not be influenced phylogenetically as much as by specific habitat, ventilatory mode, or locomotor style.


Pacific Shark Research Center/Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA, 95039, USA

Age, growth, and reproduction of six Alaskan skates (Chondrichthyes: Rajiformes: Bathyraja and Raja)

In Alaska, skates are taken in large numbers as bycatch in groundfish fisheries, with an estimated 55 million pounds caught in 2002. Additionally, a directed fishery for skates has emerged in the Gulf of Alaska. Given the large available biomass of skates and the need for alternative fishery targets and better bycatch utilization, Alaskan skates are likely to be increasingly targeted. Because many elasmobranchs, including skates, have life history characteristics that make them especially vulnerable to fishing (e.g. slow growth, large size at maturity, low fecundity), it is extremely important to harvest these species with caution. A lack of life history information on Alaskan skates, however, severely limits the potential for effective management. To address this knowledge gap, the age, growth, and reproductive biology of two rajid and four common bathyrajid species are being determined. Field sampling is taking place in the Eastern Bering Sea and Gulf of Alaska. To date, approximately 176 Raja binoculata, 156 R. rhina, 701 Bathyraja aleutica, 382 B. interrupta, 268 B. minispinosa and 134 B. taranetzi have been sampled during survey cruises. Vertebral centra, caudal thorns and reproductive tracts have been collected from these specimens. Successful completion of this project will provide fishery scientists and resource managers with critical biological information for effective management of these four Alaskan skate species. Establishing species-specific regulations and/or quotas as fisheries are being developed is necessary to ensure sustainability of these potentially susceptible batoids.


(DEF, JK, PCWT) University of New Hampshire, Department of Animal and Nutritional Sciences, Durham, NH, USA; (JAS) Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, Gainesville, FL, USA

Is there a relationship between the steroid hormone progesterone and egg case production/dynamics in oviparous elasmobranchs?

In most mammalian vertebrates, progesterone (P4) is known as the hormone of pregnancy. Not only does it regulate reproductive cycles and fertility, but it also inhibits uterine contractions, thickens cervical mucus, and builds the endometrium. However, the role of this hormone in non-mammalian vertebrates is not well understood. In oviparous elasmobranch fishes, for example, past research suggested that this hormone may be involved with egg case formation and/or oviposition in the little skate and the winter skate. In the current study, we examined whether such a relationship between P4 and egg case production/dynamics exists in the smooth skate, Malacoraja senta, a small oviparous elasmobranch that inhabits the shores of the western north Atlantic. Gross morphology and reproductive status were noted for mature females. In addition, plasma samples were extracted before P4 concentrations were determined by radioimmunoassay. When the profile of plasma P4 was plotted over a 12-month period, a trend was observed whereby high concentrations of P4 were observed in the months that preceded sampling of females with egg cases. However, when P4 concentrations in females with egg cases were compared to those without egg cases, our preliminary analysis indicated that mature females without egg cases may have higher P4 concentrations than females with egg cases. Being incomplete, the present results await further analysis before we can determine whether P4 has a possible relationship to egg case production/dynamics during the reproductive cycle of the female smooth skate.


(MB, EM, LS, SAB, DEF, JMD, MBC) Universidad Nacional de Mar del Plata, Facultad de Ciencias Exactas y Naturales, Departamento de Ciencias Marinas, Laboratorio de Ictiología, Funes 3350, 7600, Mar del Plata, Argentina; (JMD) Instituto Nacional de Investigación y Desarrollo Pesquero, Paseo Victoria Ocampo s/n, 7600, Mar del Plata, Argentina; (ME) Museo del Mar, Colón 1114, 7600, Mar del Plata, Argentina; (JMD, LS) Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina

Food habits of Bathyraja brachyurops (Chondrichthyes, Rajidae) on the Argentinean continental shelf

The broadnose skate, Bathyraja brachyurops, inhabits southern South America waters. Food habits of this species were studied based on analysis of stomach contents of specimens collected from research cruises carried out by Instituto Nacional de Investigación y Desarrollo Pesquero during 2003-2005 on the Argentinenan continental shelf (35°S−52°S). Prey items were counted, weighted and identified to the lowest possible taxonomic level. Diet composition was assessed using the Index of Relative Importance expressed as percentage (%IRI). The degrees of dietary overlap between sexes and size classes were compared by Schöener Index (SI), using %IRI. Trophic level (TR) was calculated to determine the position of the broadnose skate within the food web. For this purpose prey items were assigned into five groups. A total of 265 stomachs was examined, of which 75,5% contained food. Twenty-nine prey taxa were identified in the stomach contents. B. brachyurops fed mostly on fish (75.4%) and crabs (14.7%) and to a lesser extent on isopods (8.2%) and squids (0.97%) suggesting that the broadnose skate is a tertiary consumer (Trophic level = 4.04). A high degree of dietary overlap between sexes (SI= 0.71) was found, although females showed higher %IRI of fish prey than males. However, size classes variation in diet was observed. Smaller skates consumed both fish (46.2%) and invertebrates (28.8% isopods and 23.6% crabs), whereas larger individuals fed almost exclusively on fish (86%). Dietary changes with the size of the predator were reported for several ichthyophagous skate species. These results presented are part of an ongoing study about ecology, biology and biodiversity of Bathyraja species on the Argentinean continental shelf.


(IG-V) Instituto Tecnologico del Mar. A. P. 757. Mazatlan, Sinaloa, Mexico;(FG-M) Centro Interdisciplinario de Ciencias Marinas. Apartado Postal 592. La Paz, Baja California Sur, Mexico COFAA-IPN

Longline hook selectivity in shark capture in the southern Gulf of California

Selectivity in the capture of sharks and large pelagic fish was determined in the form of hooks used on longlines. The research was done aboard shark ships off Mazatlan, Mexico for the benefit of shark fisheries management. Four different types of hook were used, all of the same size. The types were: straight hook, flat tuna hook, kirbed tuna hook, and circle hook. Sharks comprised 66% of the 567 pelagic fish that were caught: Prionace glauca, Alopias pelagicus, Carcharhinus obscurus, Isurus oxyrinchus and Sphyrna zygaena. The other 34% were associated species: Makaira nigricans, Coryphaena hippurus, Dasyatis violacea, Tetrapturus audax, Xiphias gladius, Thunnus albacares, and Chelonia agassizi. The average capture by set was 14.9 individuals. The circle hook had the highest capture efficiency (4.4 organisms/100 fishhooks). In the capture of shark- associated species, the flat tuna hook was less selective (72% sharks, 28% associate species. Size distribution was determined for two species: Prionace glauca, and Makaira nigricans, All four hook types were used for capturing these species, and there was high overlap among them, so there was little evidence to caught a determined predator size vs. hook type.


(MBG) Eckerd College, 4200 54th Ave S., St. Petersburg, FL, 33711, USA; (JG) Elasmobranch Physiology and Environmental Biology Program, Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL, 34236, USA

Thiamine concentrations in egg yolk of bonnethead sharks (Sphyrna tiburo) and their association with infertility

Thiamine (Vitamin B1) is essential for the development and survival of progeny of egg bearing vertebrates. A reduction in thiamine concentration in egg yolk has been linked to diseases that cause low offspring survival rates in both salmonid and American alligator populations. In this study, thiamine status of bonnethead shark (Sphyrna tiburo) egg yolk was examined to determine if a link can be established between thiamine deficiency and high rates of infertility in several coastal Florida populations of this species. Thiamine levels per gram of egg yolk were measured by means of a new rapid solid phase extraction method. The results indicated no difference among three different stages of reproduction: pre-ovulation, peri- and post-ovulation and early pregnancy. A significant difference was demonstrated among three costal Florida populations, with yolk from Apalachicola Bay sharks having the lowest thiamine concentrations, followed by samples from Florida Bay and Tampa Bay sharks, respectively. The thiamine concentrations in the Tampa Bay populations were higher than expected given the high infertility rate of this population. However, a significant difference was observed between the infertile and fertile ova from Tampa Bay sharks that justifies further investigation on the relationship between thiamine status and shark fertility.


Mote Marine Laboratory, Center for Shark Research, Sarasota, FL, 34236, USA

Shark tracker: An interactive aquarium display for public education

Using state-of-the-art technology to study marine species results in an ever changing knowledge base among scientists and managers that may or may not reach the public. Mote Marine Laboratory and Aquarium have attempted to address this issue by building an interactive aquarium exhibit for public display and informal education. The exhibit is based on research conducted to monitor the long-term movement patterns of juvenile sharks inside a coastal nursery area in Florida. To demonstrate this research a live animal aquarium exhibit is being constructed to mimic shark monitoring efforts. Interactive animations of shark movements from the actual study are integrated into the exhibit and available on the internet for use by the public and school groups. Incorporating this simple, intuitive and interactive display into an aquarium exhibit enables learners of all levels to comprehend how the project works and understand the results. This highly visual, interactive exhibit provides a unique and intuitive learning experience for school groups and adults who visit the Mote Marine Aquarium. The author encourages scientists to consider informal science education efforts via in house displays or on-line content to help educate the public on new advances in marine technology and to keep them interested in advances in coastal ecology and marine biology.


Center for Fisheries Research and Development, Gulf Coast Research Laboratory, The University of Southern Mississippi, Ocean Springs, MS, 39564, USA

Preliminary assessment of short-term movement patterns of young bull sharks in Davis Bayou, Mississippi, and notes on their concentration in Mississippi bayous as a result of Hurricane Katrina

Young-of-the-year bull sharks, Carcharhinus leucas, are common inhabitants of the bay and bayou systems along the Mississippi coast and rarely venture into higher salinity waters (>15 ppt). Since little information is available on how these shark utilize this low salinity habitat, the objective of this study was to investigate the short-term movement patterns of young-of-the-year bull sharks within this habitat. Acoustic telemetry was used to manually track the movements of five bull sharks in Davis Bayou, Mississippi continuously for four to eight hour periods totaling 21.5 hours. Mean straight line swimming speed was 1.81 ± 0.17 km h-1, with a maximum observed swimming speed of 4.8 km h-1. Sharks spent 98 % of their time within the bayou, and the majority of their movements were within 5-10 m of the coastline. Two sharks utilized small sloughs, which were not previous thought of as available habitat for this species, and one shark was observed resting on the bottom for nearly two hours, which is not characteristic of this species. As a result of Hurricane Katrina (29 August 2005), young bull sharks concentrated in the bayou systems along the Mississippi coast during the months of September and October. This concentration may have been the result of Katrina-related low dissolved oxygen levels in coastal rivers, which possibly reduced the shark’s access to the rivers. By the end of October, dissolved oxygen levels increased in coastal river systems and bull shark concentration diminished in the bayou systems.


(JLI, TEL) Department of Biology and Marine Biology, and Center for Marine Science, University of North Carolina Wilmington, 601 South College Road, Wilmington, NC, 28403, USA; (SHG) Rosenstiel School of Marine and Atmospheric Science, Division of Marine Biology and Fisheries, S107 Grosvenor South, 4600 Rickenbacker Causeway, Miami, FL, 33149, USA

Foraging ecology of juvenile lemon sharks in Bimini, Bahamas: Utilizing ultrasonic accelerometry to monitor feeding

A new ultrasonic accelerometer transmitter will be used to telemeter foraging behavior of juvenile lemon sharks (Negaprion brevirostris) by signaling lunges at prey. The accelerometer transmitter emits a coded pulse to allow trackers to recognize the shark, and emits a fast alarm pulse whenever it detects a change in acceleration greater than or equal to 1.5 g (1g = 9.8 m/s2). The objectives of this study are to investigate the utility of this new technology for studying shark foraging, gain direct evidence of juvenile lemon shark foraging in the wild, determine the physical locations of foraging events within the Bimini nurseries, and examine diel patterns of foraging. In order to gain quantitative and qualitative information about the accelerations juvenile lemon sharks make, captive trials will be conducted. During these trials, the total number and time of acceleration events will be recorded. Visual observations as well as stomach content analysis will be used to determine whether accelerations were associated with successful versus unsuccessful feeding events or other non-foraging behaviors. In addition to both pre- and post-consumptive observations, individual sharks will undergo trials with live teleost prey. Since it is unlikely that a shark will be able to chase, capture and consume live prey without the transmitter producing acceleration alarms, the following hypothesis will be tested: the number of prey pursued, attacked and consumed by each shark will be positively correlated with the number of acceleration alarms. Preliminary observations show a positive transmitter response during prey capture and handling, but also show acceleration alarms when sharks make sharp turns. The transmitter sensitivity will be adjusted as needed to reduce non-foraging acceleration alarms. Results of captive trials, preliminary results of field tracks, and future research directions will be presented, including the potential utility of this technology for other elasmobranch foraging studies.


Nagasaki University, Faculty of Fisheries, Bunkyo, Nagasaki, 8528521, Japan

Age, growth and maturity of fanray Platyrhina sinensis in Ariake Bay, Japan

Fanray Platyrhina sinensis is distributed widely in Northwest Pacific, which is the most abundant species of any elasmobranches in Ariake Bay, Japan. As the top predator of the benthic ecosystem in Ariake Bay, P. sinensis could greatly affect the dynamics of any other sympatric species including many commercially important species in Ariake Bay fishery. Accordingly, it is important to understand the ecology of P. sinensis on the purpose of the proper fisheries management in Ariake Bay. In this study, age, growth and age at sexual maturity of P. sinensis in Ariake Bay were examined. From May 2002 to February 2006, a total of 285 specimens (male: 142, female: 143) were sampled by small trawl fisheries and gill nets in the middle part of Ariake Bay. Age determination was practiced by centrum analysis using soft x- radiography. Based on seasonal centrum edge analysis, the dark ring was formed right after the parturition and thereafter once a year. The dark ring was formed mostly in November, when is the most active spawning season. Age can be calculated by subtracting 1 from the number of the dark rings, because its formation completed at the spawning season. Great differences were observed between sexes in the growth pattern of this species. The von Bertalanffy growth equations were described as follows, male: Lt = 438(1-exp(-0.428(t + 1.08))), female: Lt = 697(1-exp(- 0.118(t + 3.03))), where Lt is total length in mm and t is age in years. The maximum age was 5 years old for males and 12 years old for females. The growth over 5 years females trend to growth larger than males. Age at sexual maturity was assumed to be 3 years for male and 5 years for female, based on the hardness of clasper and the occurrence of eggs in uterus, respectively.


Universidade de Lisboa, Faculdade de Ciências, Instituto de Oceanografia & Departamento de Biologia, Campo Grande, 1749-016 Lisboa, Portugal

Parasitic fauna of the digestive tract of Shortfin Mako, Isurus oxyrinchus, off Portugal, NE Atlantic

The shortfin mako, Isurus oxyrinchus, is caught in the eastern North Atlantic as a steady bycatch of the surface drift longline fishery, mainly directed to the swordfish (Xiphias gladius). Endoparasites were recovered from the stomach of 87 of the 112 shortfin mako individuals sampled. Nematoda and Cestoda were the most common endoparasites, being present in all shark life stages including young–of–the–year sharks. All Nematoda (mainly Anisakidae) were found as L3 larvae indicating that they use this species as an intermediary host, while some Cestoda were found as adults with completely developed and mature proglottids, as is the case of Nybelinia and Echeneibothrium species. Nybelinia lingualis and Echeneibothrium cf. dubium abyssarum had the highest prevalence, mean abundance and mean intensity values. Digenea and Acanthocephala were also present although with low prevalence. Results indicate that Cestoda and Nematoda are important parasites throughout the host′s life–cycle since they appear in a very early stage, when elasmobranchs start feeding. Parasitosis′ dynamics are thus discussed regarding the host′s life–cycle and feeding ecology off the Portuguese coast.


Instituto Nacional de la Pesca. Centro Regional de Investigación Pesquera de Mazatlán. Calzada Sabalo-Cerritos S/N, CP. 82010, Mazatlán, Sinaloa, Mexico

Size of maturity of (Raja velezi) taken in the Gulf of California, Mexico

The rasptail skate, Raja velezi, is a relatively deep-water member of the family Rajidae that occurs from the Gulf of California (GOC), Mexico to Peru where little is know of its life history. It is incidentally caught in artisanal ray fisheries of the GOC in low numbers. However, it may be taken in significant amounts by trawling vessels targeting fishes and deepwater shrimp in the GOC where bycatch of skates is known to be common. Previous studies of skates worldwide have demonstrated low resilience to sustained, often indirect fishing mortality. It is therefore imperative to investigate biological characteristics of exploited skate species to provide details necessary for sustainable management. For the present study, specimens examined from trawlers and landings of the artisanal ray fishery in Sonora were used to determine the size at maturity of R. velezi. Maturity of males was judged based upon the condition (calcification, rotation) and development of the claspers. Macroscopic observation indicated that males reach maturity from 61 cm disc width (DW) onwards. Histological analysis of the testes of specimens ranging from 55.5–63.4 cm DW (mean= 60.8; sd= 2.8; n= 8) indicated the presence of spermatozoa in different levels of development. Females 64 cm DW and greater were determined to be mature. Histological analysis of females ranging from 60.5–65.0 cm DW (mean= 63.8; sd= 2.25; n= 4).


The University of Queensland, School of Biological Sciences, St Lucia, QLD 4072, Australia Impacts of shark predation on Manta birostris

The impact of predation upon elasmobranch populations has rarely been considered. Manta birostris has traditionally been considered to have few natural predators. However, data gathered since 2003 in an ongoing study on manta rays in Mozambique suggests otherwise. Of 317 different individuals, 73% exhibit injuries (all of which include missing flesh or tails) inflicted by sharks. Many minor injuries were also recorded, including crescent-shaped tooth mark punctures, rake marks from upper or lower teeth, and discoloration to the dorsal and ventral surfaces. While some individuals have as many as 7 discrete bite wounds, the mean number of bites marks is 1.41. Ninety percent of bite marks and injuries occur along the trailing edge of the pectoral fins, while six percent of bites occur on the head or cephalic fins. Two percent of bites are fresh, while a further seven percent are recent. Shark attack is likely to be a major source of natural mortality, while the fitness of individuals is also detrimentally affected by non-fatal attacks. Many rays cannot be visually sexed because of extensive damage to the posterior half of their body. Several males are missing one or both claspers. Damage to cephalic fins will also affect feeding efficiency. The prevalence of injuries also has a major influence on cleaning behavior, impacting upon short-term movement patterns and habitat usage. Therefore, the number and severity of shark bites sustained within this population may have a significant effect on manta ecology.


(TLM, SMK) Department of Biological Sciences, Florida Atlantic University, Boca Raton, FL, 33431, USA; (CAL) Mote Marine Laboratory, Sarasota, FL, 34236, USA

Olfactory responses of the clearnose skate, Raja eglanteria

Elasmobranchs are reputed to possess extremely sensitive olfactory capabilities despite a relative paucity of empirical evidence. Olfaction has been demonstrated to play an important role for elasmobranchs in the localization of prey, and amino acids in particular are known to be effective odorants. Whereas the responses to amino acids have been examined for stingrays, carcharhinid and sphyrnid sharks, the olfactory capabilities of the most speciose elasmobranch order, Rajiformes, remain unexplored. We employed an electro-olfactogram (EOG) technique to assay a suite of twenty proteinogenic amino acids to determine which elicited the greatest magnitude responses from the clearnose skate, Raja eglanteria. The largest responses were elicited by, in decreasing order, cysteine, glutamic acid, lysine, and aspartic acid. These four amino acids were subsequently assayed at decreasing concentrations to determine the threshold sensitivity of the skate, which is between 10-4 and 10-6 M. A greater stimulant concentration is required to elicit a response from the skates compared to other elasmobranchs that demonstrate thresholds of approximately 10-7 to 10-8 M. The relatively poor performance of R. eglanteria may indicate that olfaction is not of premiere importance as a sensory modality for this species. An unusual phenomenon was observed in which sixteen of the twenty amino acids elicited a positive deflection in the EOG trace. This may be due to an influx of negatively charged ions across the olfactory epithelium resulting in a net accumulation of positively charged ions within the olfactory capsule. The only amino acids that generated the typical negative deflection in the EOG trace were cysteine, arginine, and lysine. This study provides the first electrophysiological examination of the olfactory capabilities of skates making R. eglanteria only the fourth elasmobranch species to be empirically tested.


(MRM) Eckerd College, Box 945, 4200 54th Ave. S., St. Petersburg, FL, 33711, USA; (JG) Elasmobranch Physiology and Environmental Biology Program, Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL, 34236, USA

Ethoxyresorufin-O-deethylase (EROD) activity in bonnethead sharks (Sphyrna tiburo) and their relationship with infertility

Exposure to some cytochrome P450A (CYP1A)-inducing pollutants, such as polycyclic aromatic hydrocarbons (PAHs) and compounds present in pulp mill effluent, has been associated with reductions in circulating estrogen concentrations and vitellogenin production in females of certain fish species during the period of follicular development. These effects may lead to reductions in yolk quality and fertility that, in turn, reduce population growth and stability. In this study, we explored whether exposure to CYP1A-inducing pollutants may be associated with high rates of infertility in certain Florida populations of the bonnethead shark (Sphyrna tiburo), which exhibit evidence of hormonal alterations in females during oocyte development. Exposure to CYP1A-inducing compounds was evaluated by measuring hepatic ethoxyresorufin-O-deethylase (EROD) activity in bonnethead sharks obtained from 2 Atlantic and 5 Gulf populations, including 1 population with low infertility rate (Florida Bay) and at least 3 sites that are known experience comparatively high rates of reproductive failure (Apalachicola Bay, Tampa Bay, Charlotte Harbor). Prior to this, EROD activity was measured in sharks exposed to a known CYP1A inducer, -napthoflavone (BNF), and compared with that in control animals to validate use of this procedure. Animals treated with BNF experienced nearly a 7-fold increase in hepatic EROD activity compared with control animals, supporting use of this technique. However, EROD activity was low in sharks from Florida estuaries, suggesting that exposure to CYP1A-inducing compounds may not be linked with infertility in this species. In general, hepatic EROD activity was substantially greater in Atlantic sharks in comparison with their Gulf counterparts. Therefore, these populations appear to experience greater risks from the physiological effects of CYP1A-inducing pollutants.


University of Maryland Eastern Shore, Living Marine Resources Cooperative Science Center, Department of Natural Sciences, Princess Anne, MD, 21853, USA

Niche overlap between spiny and smooth dogfish from inshore and offshore winter habitats

Tophic ecology of marine fishes is important information for ecosystem modeling used by fishery managers. Currently, there is intensive management of spiny dogfish ( Squalus acanthias ), which declined in the late 20th century possibly due to fewer prey resources (depleted from commercial fishing) or due to it being bycatch or harvested. Like many other shark species, it has a late age to maturity (15 – 20 years), low fecundity (< 10 offspring), and long gestation periods (approximately 2 years). These life history traits make it highly vulnerable to overfishing and resulted in it being declared ‘overfished’ in 1998. We were especially interested in understanding resource use by this species and its competition with other benthic fishes for those resources. The objective of our study was to provide information on niche overlap between two dominant, benthic elasmobranchs: spiny dogfish and Mustelus canis (smooth dogfish). We sampled nearshore and offshore habitats for dogfish along the northwestern Atlantic Ocean (January 2006). We supplemented these data with existing data from the National Marine Fisheries Service collected in February 2005. In January 2006, we collected 137 spiny dogfish (279 kg; 71 to 110 cm) and 52 smooth dogfish (123 kg; 74 to 98 cm) at nearshore and offshore sites. The major prey item was loligo squid (46 kg); additional prey items included molluscans, shrimp, crab, and polychaetes. Using the two data sets, we will determine the level of niche overlap between these species (for 2005 and 2006) and determine if niche overlap differs by depth or latitude.


Russian Federal Research Institute of Fisheries and Oceanography (VNIRO), 17, V. Krasnoselskaya, Moscow, 107140, Russia Kamchatka Branch of Pacific Institute of Geography, Far East Branch of Russian Academy of Science (KB PIG FEB RAS), 6, Partizanskaya St., Petropavlovsk-Kamchatsky, 683000, Russia

New data on the ecology and biology of mud skate Rhinoraja taranetzi Dolganov, 1985 in the northwestern Pacific with emphasis to food habits of the species

The mud skate Rhinoraja taranetzi was described rather recently. This species is distributed from Central Kuril Islands to Pribyloff Islands in the eastern Bering Sea and along the Commander and Aleutian Islands to the western Gulf of Alaska. It is one of most abundant skates inhabiting Russian waters though the data on its ecology and biology are scarce. Spatial and vertical distribution and their seasonal changes, bottom temperature preferences, species co-occurring in catches, size composition, length-weight relation, sex ratio, sexual dimorphism in size and food habits of mud skate in the Pacific off the northern Kuril Islands and southeastern Kamchatka and relation between total length and maturity of mud skate in the western Bering Sea are considered. The mud skate during the whole year is most abundant in central part of study area. Proportion of this species in bottom trawl catches in different seasons has changed slightly. Maximum catches occur in September-December. In April-May mud skates occupy shallower depths moving deeper in summer period. In December-March this skate occurs at lower bottom temperatures while in the rest of the year it inhabits warmer waters. During the whole year decreasing of body weight with depth is observed indicating that adult and juvenile mud skates inhabit different depths. Total length of mud skates in catches ranged 17 to 70 cm with mean 51.71 cm. Males were more abundant among small skates only, while females predominated among larger skates. Female mud skates were longer and heavier than males. Species considered is benthophage, consuming mostly amphipods, polychaets, and decapods. Fishery discards also play considerable role in the diet. Small skates fed mostly on amphipods; medium-sized ate amphipods, polychaets and decapods; largest individuals consumed fishery offal and less amphipods and polychaets. Preliminary data on maturation of species considered in the western Bering Sea are also presented.


(KTP, SPN, RDH) School of Biological Sciences, University of Plymouth, Plymouth, Devon, PL4 8AA, United Kingdom; (KTP, SPN, SHG) Bimini Biological Field Station, Bimini, Bahamas; (SHG) Rosensteil School of Marine and Atmospheric Sciences, University of Miami, Miami, FL, USA

Dietary exposure to trace metals in nursery-bound lemon sharks (Negaprion brevirostris) at Bimini, Bahamas

Arsenic, cadmium, lead, mercury, nickel, tin and uranium are non-essential trace metals (NTMs) and may be toxic to sharks at low concentrations, affecting growth and survival. Sharks are prone to NTM bioaccumulation due to their high positions in trophic food webs and long life spans. Increases in bioavailability and bioaccumulation of sediment associated NTMs into marine food webs have been reported following dredging and mangrove removal, activities which have been impacting a juvenile lemon shark (Negaprion brevirostris) nursery at Bimini, Bahamas, since 1999. Subsequently, in 2004 we investigated 16 metal concentrations in sediments (n = 29), prey (n = 153) and lemon shark muscle tissue (n = 12) from the impacted nursery and an unimpacted control nursery, in order to elucidate and compare baseline metal contamination levels at Bimini. All NTM concentrations were higher in impacted nursery sediments, with significantly greater arsenic and mercury levels (Kolmogorov-Smirnov tests, P < 0.01). However, prey NTM concentrations were similar in both nurseries, with some of the highest levels recorded in mojarras (Gerreidae), probably as a result of their benthic feeding habits. Transfer of metals into the food web may be delayed due to sequestration of metals in sediments and limited tidal flushing in the impacted nursery. Muscle tissue concentrations of cadmium and tin were greater in sharks from the impacted nursery, and mean lead concentrations in lemon sharks (7.60 ± 1.77 mg kg-1 dry wt) were higher than previously reported for sharks. As the dominant prey of juvenile lemon sharks, mojarras may be the principal contributors of NTM exposure in these sharks. Consequently, early life dietary NTM exposure in Bimini lemon sharks was calculated using daily ration estimates. These data suggest NTMs may contribute to reduced growth rates reported in lemon sharks from the impacted nursery, although further work is required.


 (AP) Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, Gainesville, FL, 32611, USA; (AS) Physiological Ecology and Bioenergetics Laboratory, University of Central Florida, Orlando, FL, 32816, USA

Evaluation of fatty acid signatures in diet analysis of elasmobranch fishes: A test using the Atlantic Stingray

To test the hypothesis that the fatty acid signature of a predatory elasmobranch could be used to reconstruct its diet, we examined the effect of two different diets on the fatty acid composition of the Atlantic stingray, Dasyatis sabina. Captive stingrays were fed diets of fish or shrimp for a one-month period. At the conclusion of the feeding trials, the stingrays were sacrificed and liver and muscle tissues were analyzed for fatty acid composition. Muscle had much lower lipid content than liver and the two tissues were significantly different in fatty acid composition. However, there was no significant difference in fatty acid composition between fish-fed and shrimp-fed stingray liver or muscle samples. Both fish-fed and shrimp-fed stingray tissues were significantly different than corresponding diet samples in fatty acid composition. Statistical analysis did not group stingray muscle tissues with the corresponding diets. These data suggest that fatty acid analysis may not be suitable for elasmobranch diet reconstruction.


University of Rhode Island, Dept. Biological Sciences, Kingston, RI, 02881, USA

Anatomy and functional morphology of the feeding apparatus of white- spotted bamboo sharks, Chiloscyllium plagiosum

Anatomical investigation of the feeding apparatus in white-spotted bamboo sharks, Chiloscyllium plagiosum reveals many characters associated with inertial suction feeding such as labial cartilages to occlude the lateral portions of the gape and hypertrophied hypobranchial musculature to power hyoid depression against high negative pressures generated in the buccal cavity during suction feeding. Manual manipulation of the hyoid arch in these sharks identifies the medial hyoidiomandibular ligament as a possible biomechanical link convergent with the mandibulohyoid ligament in bony fishes and aquatic feeding salamanders that couples lower jaw depression with hyoid depression. Together, the medial hyoidiomandibular ligaments and ceratohyals form force amplifying second order levers that—during initial hyoid depression—may assist in lower jaw depression by harnessing force generated by the coracohyoideus and coracoarcualis and transferring it to the lower jaw where it will assist the coracomandibularis in generating posteroventral rotation. Later in hyoid depression the ligaments and ceratohyals form force amplifying first order levers that rotate the proximal ends of the ceratohyals and transfer force to the hyomandibula resulting in ventromedial compression of the distal ends of the hyomandibula. This action also causes medial compression of the jaw halves and anteroventral movement of the jaws in a manner that differs from that reported in Orectolobus maculatus. The mechanics of the hyoid arch mentioned above may be beneficial to suction feeding by amplifying the force generated by the coracohyoideus and coracoarcualis and transferring it to skeletal elements of the buccal cavity that experience the most displacement during the expansive phase. This may allow C. plagiosum to rapidly depress the lower jaw and expand the buccal cavity against negative pressures that may be as high as 100kPa.


(SLA, CSD, GCP) Universidad Jorge Tadeo Lozano. Facultad Biologia Marina. Carrera 4 # 22-61 Bogota, Colombia; (GMF) Centro Interdiscipliinario de Ciencias Marinas; COFAA- IPN A.P. 592 La Paz, Baja California Sur, Mexico

Feeding habits of the hammerhead sharks Sphyrna zygaena and Sphyrna lewini in Ecuador

Feeding habits in Ecuadorian waters of 156 specimens of smooth hammerhead shark Sphyrna zygaena (Linnaeus, 1758) and 91 specimens of scalloped hammerhead shark Sphyrna lewini (Griffith & Smith, 1834) were studied. The specimens were obtained from Ecuadorian small-scale fishing during 2003 at Manta, Ecuador. Of the smooth hammerhead stomachs examined, 143 contained food (92.3%), and 13 were empty (7.7%). This species fed on cephalopods, crustaceans, and fish, and using the index of relative importance (IRI), it was shown that S. zygaena has a preference for cephalopods such as: Dosidicus gigas (84.6%), Sthenoteuthis oualaniensis (6.7%), and Ancistrocheirus lesueurii (5.1%). Males and females of S. zygaena had similar diet and trophic overlap. Diet variation by size in this shark was not significant. The trophic niche width was narrow, so Sphyrna zygaena is a specialist predator, whereas of the scalloped hammerhead specimens, 82 (90.1%) had food or partially digested remains in their stomachs, and 9 (9.9%) had empty stomachs. Of the prey species found, 39 were identified. The IRI index showed the most important prey were cephalopods: Dosidicus gigas (43%), Mastigoteuthsi dentata (11.9%), and Ancistrocheirus lesueurii (11%). S. lewini is a specialist predator that fed mainly during the night in the oceanic area. We found differences in diet between males and females, and variations in diet by size.


University of California, Environmental Studies Dept. and the Center for Stock Assessment Research, Applied Mathematics and Statistics Department, Santa Cruz, CA, 95064, USA

Testing methods for estimating natural mortality in fish populations: A simulation study

Natural mortality, M, is a life history parameter in most stock assessment models. Very often it is treated as a constant, but there are a multitude of methods available to estimate the parameter. We review the methods available since the review by E. Vetter in 1988, and test each method using a simulated population. Our simulation is based on parameters of blue shark (Prionace glauca) with three aspects to their natural mortality: density independent, size dependent, and age dependent components. We find that methods based on life history invariants perform poorly in comparison to methods based on size or age. We recommend a new assessment of the methods and combination of age- and length-based estimation techniques.


(MH, CS) Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL, 34236, USA; (JC) National Marine Fisheries Service, Southeast Fisheries Science Center, Panama City Laboratory, 3500 Delwood Beach Road, Panama City, FL, 32408, USA

Shark nursery areas: Concepts, definition, characterization and assumptions

The implications of defining critical habitat for fishes are becoming more widespread as coastal resources are increasingly impacted. Proper definition of these areas is critical to fostering a common understanding of what is meant by an ecological term. The term nursery area is one of the more ambiguous terms in fish habitat studies and has been the subject of several recent papers regarding the definition of these regions for teleost fishes. Often cited literature concerning shark nursery areas involve descriptions by authors such as Springer and Bass which may have not been intended to provide the definitive description of these regions. We examined the historical literature, current literature and potential definitions of nursery area currently published for elasmobranches and teleosts. Based on this information we address some of the assumptions about the function of nursery areas and suggest criteria for assessing whether a region acts as a nursery. The importance of definition of shark nursery areas has increased in the last decade with the implementation of concepts such as Essential Fish Habitat. This trend is likely to continue, so providing a unified definition of what constitutes an elasmobranch nursery area will be critical for proper management and understanding of coastal species.


(MAT, LJBL) School of Ecology and Environment, Deakin University, PO Box 423, Warrnambool, Victoria, 3280, Australia; (MAT, JDS) CSIRO Marine Research, GPO Box 1538, Hobart, Tasmania, 7001, Australia

Age and growth of four skates commonly caught as by-catch in the southeast Australian fisheries

In Australia, skates (Rajidae) are a common by-catch/by product of both State and Commonwealth trawl and non-trawl fisheries. Three continental shelf species (Dipturus sp. A, D. cerva and D. whitleyi) and one continental slope species (D. gudgeri) were examined for annulus deposition in the vertebral centra and caudal thorns. The two largest bodied skates D. gudgeri (n=300) and D.whitleyi (n=73) showed the most promising band formations in both structures using two different methods: whole and sectioned vertebrae and whole and sectioned caudal thorns. Both Dipturus sp. A (n=437) and D. cerva (n=180) showed relatively clear annuli in vertebral sections. These were viewed with transmitted light using a dissecting microscope fitted with a ColourView digital camera by Soft Imaging System and processed with AnalySIS software. The periodicity of growth band deposition for D. gudgeri was verified using marginal increment analysis and the caudal thorns were used for comparative measures in both D. gudgeri and D. whitleyi. Estimates for male and female longevity of D. gudgeri are 20 and 21 years, respectively. Longevity estimates for male and female D. whitleyi are 13 and 18 years, respectively. The two smaller inshore skates have lower longevities. Dipturus cerva male and female longevity is estimated at 8 and 9 years, respectively. von Bertalanffy growth model (VBGM) parameters for D. cerva males were estimated as K = 0.20 and L inf = 73.35 cm and females K = 0.31 and L inf = 73.35 cm. Male and female longevity for Dipturus sp. A is estimated at 11 and 12 years, respectively. The Francis reparameterised VBGM equation was also used for comparison.


(LBW, PJM) University of South Florida, Dept. of Biology, Tampa, FL, 33620, USA; (DCS) University of South Florida, Dept. of Civil and Environmental Engineering, Tampa, FL, 33620, USA

Biology meets engineering: biomechanics and two-dimensional finite element analysis of carcharhinid teeth

Applying engineering techniques to biological studies can reveal functional insights into evolution undiscovered by traditional methods. The goal of this study was therefore to explore the evolution of selachian teeth in a biomechanical context. To determine the loads experienced by shark teeth during puncture and unidirectional draw, teeth from nine carcharhinid species were tested with a MTS MiniBionix II universal testing system. Puncture forces were determined by driving teeth into three teleosts of varying scale thickness at 400 mm/s. For unidirectional draw, teeth were embedded in the prey item and drawn in parallel at 400 mm/s. Force and pressure at initial penetration and maximum force and pressure were determined from both sets of experiments. Stress and strain distributions in the teeth were then computed via two-dimensional finite element (FE) analysis, using the measured maximum forces and mechanical properties of mammalian teeth. FE models of various carcharhinid tooth morphologies were created from the coordinates of tooth outlines from digital images. Tooth models were fixed at the base and point loaded at the tip for puncture and on the lateral cutting edges for unidirectional draw. Initial results indicate minimal strain in the teeth under either loading. During puncture, stress is concentrated primarily at the tooth tip for all morphologies. However, teeth with narrow triangular cusps, like those of Carcharhinus limbatus, have smaller regions of stress concentration overall than those with broad, curved cusps like C. leucas, in which a region of high stress extends along the lateral cutting edge. A stress concentration often occurs at a corner of the tooth base during unidirectional draw. High stress occurs along the cusp-base interface for narrow triangular cusps, and where the lateral cutting edge meets the base for broad, curved cusps. Overlapping bases and flexible attachment of teeth may alleviate these stresses in live sharks.


Dept. of Biological Sciences, Calif. State Univ. Long Beach, 1250 Bellflower Blvd., Long Beach, CA, 90840, USA

Temperature sensitivity of the round stingray, Urobatis halleri

The round stingray, Urobatis halleri, is a common nearshore elasmobranch found in bays and estuaries ranging from southern California to Panama. Round stingrays have been observed to aggregate in great numbers in shallow areas where sea floor water temperatures range from 11° to 21° C within a single tidal cycle. Because rays do not leave these areas during these periods of tidally-induced thermal change, they must be physiologically tolerant to these temperatures. The temperature sensitivity (Q10) of round stingrays was measured using static respirometry. Oxygen consumption rates were measured of rays exposed to two water temperatures of 16° and 21° C over 6 hr periods and their mass specific metabolic rates were determined at each temperature. Rays were found to have a Q10 of 2.4, indicating that they are comparatively tolerant to changes in water temperature within their thermal preferenda. This high thermal tolerance enables rays to occupy shallow areas where water temperature fluctuates considerably over the course of a day without significant metabolic consequences.