National Shark Research Consortium
Pacific Shark Research Center - Moss Landing Marine Laboratories
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NSRC-supported Initiatives
Eastern North Pacific chondrichthyan life history data matrix
The objectives of this project are to refine and update pertinent life history information that was compiled during 2002-03 for at least 109 species of sharks, rays, and chimaeras by the Pacific Shark Research Center (PSRC). We will create a queryable web-based version of the data matrix that will provide expanded access to interested biologists, students, and the general public. The matrix will contain comprehensive information on individual species (including longevity, fecundity, gestation period, growth, age and size at maturity, size at birth, mortality, feeding habits, distribution, movement patterns, habitat use, maximum recorded size, and population structure) and clearly indicate which aspects of their life history and distribution remain unknown. A review of the matrix, therefore, allows NSRC personnel, fisheries biologists, and students to quickly assess the gaps in biological knowledge for an individual species and better develop studies that address this lack of critical information. The resulting updated life history data matrix will be distributed to state and federal fisheries management agencies and provided for broad, general access on the PSRC web site being developed.
Age, growth, and demographic studies
Staff and students associated with the PSRC will initiate studies on the age and growth of rays and skates that are common direct or indirect components of eastern North Pacific fisheries. Estimates of growth rates and longevity in sharks and rays are typically obtained by microscopic examination of the banding pattern deposited within vertebrae. We will determine if vertebrae, or other structures such as caudal thorns, serve as reliable ageing structures for the roughtail, Bathyraja trachura, and California, Raja inornata, skates. The population dynamics of commercially exploited rays will be further examined using age-based demographic models. Net reproductive rates, intrinsic rates of increase, generation times, stable age distribution, and elasticity analyses will be calculated for the diamond stingray, Dasyatis dipterura. A demographic comparison of myliobatoid (stingrays) and rajoid (skates) rays will be initiated.
Age validation studies
The interpretation of vertebral growth bands to estimate growth and life history parameters is a subjective process that requires validation to determine the temporal nature of growth zone formation. The accuracy of age estimates often remains unconfirmed and may lead to inappropriate management decisions. The PSRC will continue to advance a novel technique for age validation through the analysis of radiocarbon isotopes from vertebral centra. Testing of nuclear bombs in the 1950's and 1960's released large amounts of radiocarbon (Δ14C) into the atmosphere. As a consequence, radiocarbon entered the ocean through gas exchange of carbon dioxide, and spread throughout the water column. It was then readily incorporated into animals that were growing during this time. Since the original rapid increase introduced by bomb testing, there has been a constant decrease of radiocarbon in the atmosphere and marine environment that is readily detectable in carbonate structures such as vertebrae. The level of radiocarbon recorded from a shark's vertebral centrum may therefore be used to confirm the age of a specimen. The objectives of this study are to provide validated growth rates for the white shark, Carcharodon carcharias, and shortfin mako, Isurus oxyrinchus. The PSRC will also collaborate with Dr. Lisa J. Natanson (NMFS, Rhode Island), George Burgess, and Dr. Frank Snelson (University of Florida) on radiocarbon age validation of several other east coast species, including the sandbar (Carcharhinus plumbeus) and dusky (C. obscurus) sharks.
Stable isotope analysis
PSRC staff will expand the original research initiated during 2002-03 of the variation in stable isotope signatures recorded in the vertebral centra of Pacific sharks. Stable isotopes have proven to be powerful markers in other ecological studies, but have not yet been used to discern movement patterns in elasmobranchs. We will examine the composition of carbon (Δ13C) and nitrogen (Δ15N) in vertebrae and white muscle tissue of the blue shark, Prionace glauca. Questions to be addressed through the course of this research are: 1) How does isotopic composition of adult and juvenile blue sharks vary within vertebral centra? and 2) Does variation in the composition of stable carbon, nitrogen, and oxygen isotopes within banding of vertebral centra support on-shore-off-shore movement patterns indicated by tag-return studies?
Habitat associations and nursery grounds
The PSRC will build upon pilot studies initiated during 2002-03 that will help to determine which marine and estuarine habitats might serve as Essential Fish Habitat for Pacific sharks. With increased knowledge of movement patterns and spatial utilization gained from this study, proper steps can be taken to identify critical habitat types and lead to the identification of Essential Fish Habitat for these species. A mixture of both active and passive tracking techniques will allow PSRC researchers to collect data on short- and long-term movements and habitat use by transient and resident sharks.
In cooperation with the Monterey Bay Aquarium Research Institute and Moss Landing Marine Laboratories Center for Habitat Studies, archived video footage recorded from remotely-operated and manned submersible dives in Monterey Bay will begin to be reviewed to determine possible nursery locations for oviparous chondrichthyans including skates, catsharks, and ratfishes. We will examine which habitat features skate and catshark egg cases are associated with and the depth and habitat associations of the dominant skate species within Monterey Bay, CA.
Reproductive biology
Knowledge of the reproductive biology of most eastern north Pacific skates and rays is either unknown or extremely sparse. Of the more than 15 skate species that are reported from the region, limited information exists on only two; the big skate, Raja binoculata, and the longnose skate, R. rhina. Members of the PSRC in collaboration with the NMFS Santa Cruz Laboratory, Northwest Fisheries Science Center, and the Alaska Fisheries Science Center will collect and examine reproductive tracts of rays and skates taken during research cruises in the Bering Sea and off the California and Oregon coasts. The PSRC will complete a detailed study of the reproductive cycle of the sandpaper, Bathyraja kincaidii, California, R. inornata, and longnose skates and determine maturity and reproductive patterns for these skates in relation to season, size, and depth of occurrence. In addition, we will examine and compare the reproductive biology of a suite deep-living skates, Bathyraja spp., from the eastern Bering Sea.
Feeding ecology
Studies on diet and feeding ecology are necessary to determine trophic links between organisms and to estimate energy transfer within ecosystems. In addition, changes in both community structure and physical conditions may be monitored through an evaluation of dietary changes. Although elasmobranchs have played important roles in marine ecosystems throughout their history, often occupying the highest trophic levels as apex predators, little is known about their feeding habits. To address this general lack of information, research projects involving commercially landed species have been developed by the PSRC.
Diet and feeding ecology are currently being investigated for shark and skate specimens collected from groundfish surveys conducted by the NMFS Southwest Fisheries Science Center, Santa Cruz Lab. Diets of the California skate (Raja inornata), longnose skate (R. rhina), brown catshark (Apristurus brunneus), and filetail catshark (Parmaturus xaniurus) will be examined in relation to depth, size, sex, habitat, and season to determine their trophic roles in the demersal fish assemblage. In addition, the diets, dietary overlap, and feeding ecomorphology are being examined for several commercially harvested rays from the southern Pacific Baja coast [shovelnose guitarfish (Rhinobatos productus), Cortez electric ray (Narcine entemedor), diamond stingray (Dasyatis dipterura), and California butterfly ray (Gymnura marmorata)].
Despite the central importance of feeding relationships in understanding trophodynamics and community structure, little is known about the feeding ecology of elasmobranchs. The feeding habits and dietary overlap of skates (Bathyraja and Raja spp.) and catsharks (Apristurus and Parmaturus spp.) will be examined in relation to depth, size, sex, habitat, and season to determine their trophic roles in the demersal fish assemblage. The dietary overlap and feeding habits of four co-occurring rays (Dasyatis dipterura, Gymnura marmorata, Narcine entemedor, and Rhinobatos productus) will also be examined.
Population genetic studies
The population structure and extent of movement of highly mobile, pelagic species has proven difficult to discern. However, recent advances in molecular genetic techniques have been successful in determining population structure of these species by quantifying the degree of genetic relatedness between geographically separate populations. The PSRC will continue investigations of the population structure of the common thresher shark, Alopias vulpinus. The results of this investigation will provide details on the genetic diversity among Pacific and Atlantic regions and aid in determining the degree of exchange between these groups. The objectives of this research are to determine: 1) if microsatellite loci will serve as appropriate, independent markers of gene flow for A. vulpinus and 2) the degree of genetic relatedness among A. vulpinus within the Pacific and between the Atlantic and Pacific oceans.
Shelf, slope and pelagic surveys
National Marine Fisheries Service (NMFS) scientists conduct regional annual and bi-annual surveys to assess fishery stock status, species size composition, species abundance, and geographic distribution. The Pacific Shark Research Center are providing NMFS scientists onboard support during these surveys and also collect samples necessary for the broad suite of proposed life history, genetic, and taxonomic studies we have initiated. The PSRC has developed agreements to work with NMFS scientists from the Alaska Fisheries Science Center, Northwest Fisheries Science Center, and Santa Cruz Laboratory. Detailed biological examination of the sharks, skates, rays, and ratfishes collected during NMFS surveys will maximize the information that can be obtained for this poorly known group from the survey regions.
Eastern Pacific shark fisheries analysis
PSRC personnel previously compiled available commercial and recreational catch statistics and developed a comprehensive database containing state- and species-specific landings information on elasmobranchs from Alaska, Washington, Oregon, and California. The PSRC will continue to maintain and update this centralized database for staff and collaborative researchers. Long-term fishing trends will be analyzed (where possible) from the details available for both direct and indirect chondrichthyan fisheries and fishery-independent surveys from the eastern Pacific. Our investigations will also be expanded to include analyses of historic records of recreational and commercial elasmobranch landings from California and Hawaii.
Taxonomic studies
Most eastern Pacific rays and are poorly described, resulting in an extremely limited understanding of the species composition that is directly impacted by fishing activities. Without adequate guides or keys, these species cannot be properly identified. PSRC research personnel will continue to review and revise the large, complex skate genus Bathyraja (Family: Arhynchobatidae) to provide improved keys to onboard fisheries observers and fisheries management agencies along the U.S. west coast. In addition to the review and revision of the skate genera Bathyraja, the taxonomic status and validity of the butterfly rays, Gymnura crebripunctata and G. marmorata is being assessed.
Page updated November 2003
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