2004 AES Annual Meeting Posters

Western blot immunodetection of heat shock protein 70 in the Bonnethead Shark, Sphyrna tiburo

Heat shock protein 70 (HSP70) is a stress response protein inducible through exposure to endocrine disrupting pollutants, such as organochlorine pesticides. We sought to detect the presence of HSP70 in hepatic tissue of the Bonnethead Shark, Sphyrna tiburo, to evaluate the use of this protein as a bioindicator of pollutant exposure in sharks and their relatives. Homogenized hepatic tissue from this small coastal shark was tested through Western blot immunodetection for the presence of HSP70. Liver samples from bonnethead sharks collected from four sites on Florida’s Gulf coast (Apalachicola Bay, Charlotte Harbor, Florida Bay, Tampa Bay) with varying levels of organochlorine contamination were examined. Tissues from laboratory animals exposed to 17 b-estradiol and the anti-estrogenic b-naphthoflavone were also examined. Weak reactions in most samples yield no evidence that HSP70 is induced with exposure to estrogenic or antiestrogenic signals. Variability in HSP70 expression among wild specimens taken from the same regions was observed. We conclude that through our methodology, HSP70 in Sphyrna tiburo is not a reliable biomarker for environmental endocrine disruptors.

Observations on the reproductive biology and fishery for Rhinoptera steindachneri in the Gulf of California and Baha Almejas, Mexico

The Pacific Cow-nose Ray, Rhinoptera steindachneri, is a common nearshore stingray ranging from the Pacific coast of Baja California Sur to the Galapagos Islands, yet little is known about its basic biology. From 1998-2000, surveys of artisanal fishing camps throughout the Gulf of California (GOC) and in Bahía Almejas identified and characterized elasmobranch fisheries and sampled landings. Fishery-derived R. steindachneri were enumerated, sexed, measured, weighed, and examined for reproductive condition. This species was the sixth most abundant of 44 elasmobranch species observed in northern GOC, comprising 6.92% (n=11,142) of overall landings and 11.45% (n=4,079) of summer landings. In the Bahía Almejas summer batoid fishery, it was the fifth most abundant of twenty-one elasmobranch species (2.13%, n=113). Rhinoptera steindachneri is typically landed with bottomset gillnets in mixed species fisheries for batoids, small coastal sharks, and demersal teleosts. The mean size of females captured in the GOC was 64.4 + 11.8 cm disc width (DW) (mean and SD, n=505) whereas males averaged 64.2 + 14.0 cm DW (n=586). Landed specimens measured from 39 to 98 cm DW, with only females occupying the largest size classes (>89 cm DW). Maximum size records for both males (96 cm DW) and females (104 cm DW) were noted among Bahía Almejas landings. Median DW at 50% maturity was similar between sexes (males=69.9 cm, females=70.0 cm). Fecundity was only one embryo per female in all gravid specimens examined (n=149). The largest embryo was 43 cm, slightly smaller than the largest free-living specimen (39 cm DW). Gravid females were recorded during all seasons, with most observed in spring (59.7%, n=89) and fewest in summer (2.7%, n=4). The mean DW of GOC embryos increased from April (x=26.3 cm, n=16) to May (x=30.4 cm, n=63), to June (x=38.8, n=2). In all months, larger females carried larger embryos.

Delineation of Bull Shark, Carcharhinus leucas, nursery habitat in Louisiana waters

Louisiana has the largest area of estuarine habitat in the United States, however little is known about the shark species that occur there. Several studies have documented the presence of bull sharks, Carcharhinus leucas, in both the inland waters and coastal estuaries of Louisiana. However, no systematic review or analyses have been produced to define bull shark nursery habitat following the Bass (1978) definition for the state as a whole. In order to synthesize the current information on bull sharks in Louisiana waters, we gathered and analyzed data sets from a variety of previously published and unpublished sources. This included information from state agencies, other universities, and from research conducted at Louisiana State University. Six separate data sets representing six geographic regions were used in this synthesis. Descriptive statistics were calculated for biological and environmental parameters for all data sets. Primary and secondary nursery areas were delineated with convex polygons constructed within the geographic information system (GIS) environment by connecting the inner and outermost sampling locations of each study site and smoothing the lines connecting each point. All six geographic locations were delineated as containing both primary and secondary habitat. This study confirms the occurrence of young bull sharks in several of the low salinity and freshwater systems in Louisiana and provides substantial evidence that such occurrences are not random. The regular occurrence and high abundance of young bull sharks in Louisiana inland waters indicate that low salinity and freshwater environments serve as both primary and secondary nursery habitat and should therefore be considered essential fish habitat for bull sharks.

At-vessel mortality of large and small coastal sharks in the U.S. Atlantic shark bottom longline fishery

The Commercial Shark Fishery Observer Program has placed observers on commercial shark fishing vessels since 1994 to collect biological information on the sharks caught in the fishery. Knowledge of at-vessel mortality (sharks caught that arrive at the vessel dead) is important for management of the various species taken. Some species are more susceptible to hooking mortality than others and therefore may need to be managed differently. We compared the at-vessel mortality rates of nine commonly captured large and small coastal sharks, Carcharhinus plumbeus (N=14,890), C. limbatus (N=2896), C. acronotus (N=1560), C. obscurus (N=1221), C. leucas (N=447), Rhizoprionodon terraenovae (N=10,726), Galeocerdo cuvier (N=4955), Sphyrna lewini (N=733), and S. mokarran (N=282), with reference to soak time, water depth, water temperature, and the shark’s fork length. Analyses showed that hammerhead sharks (Sphyrna spp.) were the most susceptible to hooking mortality while bull (C. leucas) and tiger (G. cuvier) sharks were the least susceptible. Across species, at-vessel mortality generally decreased as shark length increased whereas increases in soak time, depth and temperature generally increased mortality. This indicates that regulation of multi-species management groups may not adequately account for differences between species and their vulnerability to mortality on longlines.

Brick by brick: Propagation of tissue mineralization in elasmobranchs

Unlike mammalian articular cartilage, the skeletal cartilage of elasmobranchs (sharks, skates, and rays) possesses surface mineralization comprised of a mosaic of small calcified blocks called tesserae. In some species this calcification is sparse in young animals and grows to cover skeletal elements with age. In others, the calcification is present over the entire element at birth. To accommodate growth and continue to cover skeletal elements, tesserae must change in quantity and/or size. Various forms of tesseral propagation may determine calcification patterns. We surveyed tesseral size and coverage patterns in ontogenetic series from several species to determine the pattern of tesseral growth and/or multiplication. Tesserae were counted and measured over a 5mm square area on the pectoral girdle of Myliobatis californica, Urobatis halleri, Gymnura marmorata, and Rhinobatos productus. A comparision of the pattern of tesseral growth with the number of tesserae on the pectoral girdle showed significant variation between species. Because generation of tesserae takes place beneath the fibrous perichondrium and in the absence of vascular perfusion, we expect that the pattern of growth and generation of the tesserae will reveal clues to the mechanism and signaling responsible for mineralization.

A life history data matrix for chondrichthyan fishes of the eastern North Pacific Ocean

One the primary objectives of the newly-formed Pacific Shark Research Center (PSRC) at Moss Landing Marine Laboratories (MLML) was the creation of a comprehensive life history data matrix covering the entire body of literature on all chondrichthyans (sharks, rays, and chimaeras) of the eastern North Pacific, from the eastern Bering Sea to the southern tip of Baja California. We, along with 11 additional contributors at PSRC/MLML, have completed this literature review and produced a data matrix designed after a previous version, completed in 2001, on the life histories of 124 common nearshore fish species of California for the California Department of Fish and Game (dfg.ca.gov), under Pacific States Marine Fisheries Commission support. The new chondricththyan data matrix covers 21 families and 63 species of sharks, 11 families and 42 species of rays, and 2 families and 4 species of chimaeras. It includes information on taxonomy, geographic range, age and growth, longevity, reproduction, demography, trophic interactions, habitat utilization, genetics, recruitment, mortality, and behavior of these 109 species. PSRC scientists and graduate students are now working on research projects to fill data gaps uncovered by this extensive literature search. We will discuss the format of the data matrix and present the life history information on selected, exemplary chondrichthyan species. It will soon be available on the MLML and PSRC/NSRC web pages (www.mlml.calstate.edu and www.flmnh.ufl.edu/fish/Sharks/nsrc/NSRC.htm) and we invite constructive suggestions on it.

Shark wounds in the seals of Guadalupe Island, Mexico

In six expeditions to study pinnipeds at Isla de Guadalupe in the Mexican Pacific, that took place during the winters and summers of 1992 and 1993, we observed different wounds caused by sharks on the three pinnipeds that inhabit at the island. The species affected by these sharks were Arctocephalus townsendi, Mirounga angustirostris and Zalophus californianus. We were able to identify the wounds caused by three species of sharks Isistius brasiliensis, Carcharhinus limbatus and Carcharodon carcharias, although the majority of wounds were caused by cookiecutter sharks I. brasiliensis, in 72% of the individuals followed by 24% of individuals showing wounds of C. carcharias. The majority (86%) of observed pinnipeds presenting wounds were adults and the species more affected was M. angustirostris. There are several records of wounds caused by cookiecutter sharks on Isla de Guadalupe affecting A. townsendi and M. angustirostris, nevertheless there was no report of this shark species affecting Z. californianus. During winter we observed a major incidence of individuals with wounds and a large percentage of these were in adults of M. angustirostris. Wounds caused by C. limbatus only were observed during summer.

Comparative material and biochemical properties of elasmobranch cartilage

In spite of swimming the oceans for 450 million years, little is known of the cartilaginous skeleton of elasmobranchs. Cartilaginous skeletons are perceived to be less stiff and strong than bone, but there is no empirical evidence to support this supposition. These animals function at functional extremes – they grow big, swim fast, and eat hard prey. This leads us to believe they must structurally support their skeletons. We have found that elasmobranch vertebral cartilage has similar stiffness, strength, and mineral fraction compared to mammalian trabecular bone. Elasmobranch vertebral cartilage and mammalian articular cartilage have similar proteoglycan and collagen content. Here we compared the material and biochemical properties of both vertebral and jaw cartilages in sharks, skates, and rays. Collagen concentrations in the jaw are similar to those in the vertebrae. Proteoglycan in the vertebrae is generally two times that found in the jaw cartilage. Maximum strength is the same in both jaw and vertebral cartilage, although there are differences between species. Vertebral cartilage is an order of magnitude stiffer than jaw cartilage. Percent strain for the jaw cartilage ranges from 35-60% while the vertebral cartilage ranges from 6-20%. Many of these differences may be due to mineralization found in vertebral cartilage. Just over half the dry weight of vertebrae can be mineral while the jaw cartilage has very little mineralization. The arrangement of the vertebral mineralization is also an important contributor to the differences in structural properties.

Phylogeography of thresher sharks, Alopias spp., based upon mitochondrial DNA control region sequences: Preliminary results

The global population structure of thresher sharks (Alopias pelagicus, A. superciliosus, and A. vulpinus) is virtually unknown. Thresher sharks are taken worldwide both by directed commercial fisheries and as bycatch in tuna and billfish fisheries. Recent analysis of logbook data for the U.S. pelagic longline fleets targeting swordfish and tunas in the Northwest Atlantic indicates that catches of thresher sharks have declined by 80% since 1986, a trend that may reflect their global status. Effective conservation and management strategies for pelagic sharks require a fundamental understanding of their life histories, including population structure. If thresher shark populations are genetically distinct, management guidelines aimed at large geographic areas could be inappropriate, perhaps leading to the permanent loss of regional populations and decreasing their genetic diversity and evolutionary potential. Tissue samples of A. pelagicus, A. superciliosus, and A. vulpinus have been collected from the Northeast Pacific (N = 13,0,32), Central Pacific (N = 0,16,0), Northwest Pacific (N = 3,3,0), Southeast Pacific (N = 21,19,0), Southwest Pacific (N = 0,0,5), Northwest Atlantic (N = 0,15,15), Northeast Atlantic (N = 0,0,6), and Indian (N = 0,1,0) Oceans. We are using mitochondrial DNA control region sequences to quantify the degree of genetic relatedness among geographically disjunct populations of thresher sharks. In addition, DNA sequences from the cytochrome b gene are being used to confirm species identifications of the samples collected. Results will be presented in the context of thresher shark conservation and management.

Signal detection and range of acoustic receivers used to monitor stingrays off Seal Beach, California

The use of automated acoustic receiver arrays has become a popular method for studying the longer-term movements of marine fishes; however, quantifying the effective detection range of these arrays poses challenges and may be important for interpretation of fish movements. We are currently using one such array to monitor the movements of round stingrays in the nearshore waters off Seal Beach, California. The environmental conditions in this area (i.e. shallow water and wave exposure) can greatly attenuate acoustic transmissions and negatively affect the performance of this receiver array. To quantify the detection abilities of this array, we towed a transmitter (pulsing randomly every 60 to 180 sec) throughout the array during high and low tides to simulate fish movements. Over varying tidal heights, 68 ± 9 % (MEAN ± SD) of transmitter pulses were detected within 275 ± 86 m of all automated receivers. An estimated activity space based on receiver detections was 78 % of the size of the activity space determined based on the actual positions of the transmitter taken during simulated tracks. In addition, each receiver had a different effective detection range depending on its specific depth. Because round stingrays show relatively slow and aperiodic movements at Seal Beach, the shallow and wave exposed nature of this area does not appear to significantly influence the detection of tagged stingrays and provides adequate coverage needed to ascertain the longer-term movement patterns of rays at Seal Beach.

A preliminary analysis of the role of selachian tooth serrations during cutting events

Most studies concerning the functional morphology of feeding in elasmobranchs have focused on muscle function and the movement of cranial components, largely ignoring the role of teeth. The few studies that have addressed teeth are qualitative or theoretical in nature. This study quantitatively describes the role of serrations during cutting events via performance testing. Serrated and non-serrated teeth from a variety of lamniforms, carcharhiniforms and squaliforms were tested during puncture and unidirectional draw. Teeth were individually mounted on steel rods and driven through prey items at a rate of 400 mm/s using a MTS 858 MiniBionix II universal testing system. Prey items (squid and fish) were attached to a 5 kN load cell. Force and pressure at initial penetration (for puncture only), maximum force, Young’s modulus, and work to fracture were analyzed using a 3-way MANOVA. Results are presented, highlighting future directions for shark tooth functional morphology. In addition, a preliminary test on a novel artificial prey composite, designed to maintain consistency among samples of the same prey type, is discussed.

Group courtship, mating behaviour, and siphon sac function in the Whitetip Reef Shark, Triaenodon obesus.

Three mating events involving a total of nine whitetip reef sharks were filmed in Cocos Islands, Costa Rica and analyzed by the authors. Here we describe several behaviours for the first time in this species, as well as four new behaviours that have never been seen in any elasmobranch. This work also presents the first hypothesis of siphon sac function to be based on observations of mating sharks. The siphon sacs are poorly understood organs of the male reproductive system, and we introduce terminology for three separate siphon sac structural components that are externally visible during courtship and mating in this species. Based on our analyses of these new observations, as well as evidence from past mating studies, we believe that the siphon sacs in whitetip reef sharks are used as mechanisms of sperm propulsion, not for flushing the female’s reproductive tract of sperm from previous males. The implications of ‘group courtship’, ‘siphon isthmus constriction’, ‘reverse thrusting’, ‘post-release gaping’, and ‘non-copulatory ejaculation’ are discussed.