Current Research

Life History Database : Age and Growth : Age Validation Studies : Stable Isotope
Feeding Studies : Reproductive Studies : Habitat Associations : Demographic Analysis
Tracking & Tagging : Population Genetics : Continental Shelf & Pelagic Surveys
Shark Fisheries Database : Taxonomic Analysis

1. Chondrichthyan life history database. A life history data matrix is currently being compiled using all pertinent literature to analyze what is known and, more importantly, what is not known about the life histories, distributions, and population dynamics of chondrichthyans (sharks, skates, rays, and chimaeras) from the eastern North Pacific (ENP). The ENP as defined here includes the area ranging from the eastern Bering Sea to the southern tip of the Baja California peninsula. The data matrix will include approximately 108 species that are reported to occur in the region. The species-specific format will allow those interested to quickly access details including; diet, fecundity, genetic variance, growth rate, intrinsic rate of population increase, longevity, mortality estimates, movement patterns, nursery areas, parasites, size-at-birth, taxonomy, and the reproductive cycle. Aspects of the life history for which no information is available from the ENP will be clearly noted in the matrix and will help to guide the PSRC toward research projects that will fill those gaps in knowledge. The completed ENP Chondrichthyan Life History Data Matrix will be distributed to fisheries management agencies and be made available to the public through the PSRC's website. Once completed, information in the data matrix will be updated as new information becomes available. The format is similar to a life history data matrix researchers from Moss Landing Marine Laboratories' Ichthyology Lab produced in 2002 for 124 species of California nearshore marine fishes. (http://www.dfg.ca.gov/mrd/nfmp/index.html).

2. Age and growth studies. Age and growth studies of sharks and rays have been initiated to fill gaps that are discovered during the compilation of the life history data matrix. Estimates of growth rates and longevity in sharks and rays are typically obtained by microscopic examination of the banding pattern deposited within the vertebrae. Skates are one focus of PSRC age and growth studies. In recent years, skate landings have greatly increased in all Pacific states. In addition, they form a large part of fisheries' bycatch and discard in the region. The susceptibility of skates to commercial fishing pressure has been well documented in the North Atlantic, however very little is known of the biology of skates throughout the eastern North Pacific (ENP). Age and growth estimates are necessary to gain insight into the population structure and dynamics of a species. Appropriate techniques, using vertebrae, will be determined for clarifying growth zones in selected ENP skates, including the sandpaper (Bathyraja kincaidii), the roughtail (Bathyraja trachura), and California (Raja inornata) skates. Suitability of caudal thorns as an ageing structure will also be investigated, possibly providing another non-lethal ageing technique for this group. Age-at-size estimates based upon microscopic examination of vertebrae and other calcified structures will be fit to appropriate growth models to describe population and individual growth characteristics. These studies will provide estimates of age-at-maturity, longevity, and growth rates that are fundamental to stock assessment and sustainable fisheries management.

3. Feeding Studies. 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. Elasmobranchs have played important roles in marine ecosystems throughout their history, often occupying the highest trophic levels as apex predators. Despite the central importance of feeding relationships in understanding trophodynamics and community structure, little is known about the feeding ecology of elasmobranchs. 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 from shark and skate specimens collected from surveys conducted by the NMFS Southwest Fisheries Science Center Santa Cruz Lab. Species currently being examined are the sandpaper skate (Bathyraja kincaidii), California skate (R. inornata), longnose skate (R. rhina), brown catshark (Apristurus brunneus), and filetail catshark (Parmaturus xaniurus).

4. Reproductive Studies. Knowledge of the reproductive biology of most ENP sharks and rays is either unknown or extremely limited. Information on reproductive biology, including size-at-first-maturity and fecundity, is crucial for sound management decisions. The skates (Family: Arhynchobatidae and Rajidae) are very poorly known taxonomically and as a consequence, information on their reproductive biology is nearly non-existent. Of more than 20 species known to inhabit the waters of the ENP, limited information exists on only two, the big skate (Raja binoculata) and the longnose skate (Raja rhina). To increase our knowledge of the reproductive biology of ENP chondrichthyans, the PSRC in collaboration with the NMFS Alaska Fisheries Science Center, Northwest Fisheries Science Center, and Southwest Fisheries Science Center Santa Cruz Laboratory, are collecting and examining reproductive tracts of sharks and rays taken during research cruises in the Bering Sea and off the California, Oregon, and Washington coasts. Maturity status and reproductive condition are currently being assessed for several skate and catshark species in an effort to determine size-at-maturity, fecundity, and timing of reproductive events.

5. Age validation studies. Validation of the periodicity of growth zone deposition patterns observed within vertebrae or other calcified structures is essential to determine the accuracy of age estimates. Although banding patterns may be evident within an ageing structure such as vertebra, the patterns may not be deposited in an annual or predictable manner. The PSRC will advance the analysis of radiocarbon isotopes (¹⁴C) as a novel method of age validation for chondrichthyan fishes. Testing of nuclear bombs in the 1950's and 1960's released large amounts of radiocarbon into the atmosphere. As a consequence, radiocarbon has entered the ocean through gas exchange of carbon dioxide, spread through the water column, and has been 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 ¹⁴C within a calcified structure can serve as a chemical tag, allowing the age of a specimen to be confirmed from a vertebral core or other structure. This method is well suited for long-lived species, such as many sharks and rays. Samples are currently being obtained from pre- and post-bomb era specimens. Primary species under investigation are the shortfin mako (Isurus oxyrinchus) and white shark (Carcharodon carcharias); the first of which is commercially important while the second, already protected, is an apex predator about which little is known. Successful completion of this research will provide definitive growth characteristics for these commercially important species and promote more effective fisheries management.

6. Stable isotope analyses. Natural stable isotopic signatures are found in a variety of animals and plants. Differences in the composition of these isotopes are derived from the environment and diet. Stable isotopes have proven to be powerful markers for ecological studies. Environmental and foodweb isotopic signatures can vary spatially based on a variety of biogeochemical processes. Organisms moving between isotopically distinct foodwebs or regions may incorporate these distinguishable signatures into their tissues. Trophic level, temperature, depth, and latitude are some factors known to influence the enrichment or depletion of atomically 'heavier' isotopes (fractionation) in tissues. Organisms moving between isotopically distinct foodwebs or regions may incorporate these distinguishable signatures into their tissues. The feasibility of stable isotope analysis is being tested to track size- and age-specific movement patterns of the blue shark (Prionace glauca). Blue sharks have been found to sexually segregate during the year and have been shown to exhibit large migrations. Analysis of stable composition deposited within vertebrae will be used to identify changes in environmental regimes and will be related to geographic areas inhabited during movement. Analyses will be performed on stable carbon, nitrogen, and oxygen isotopes using the mass spectrometer at the Earth Sciences Laboratory, University of California at Santa Cruz. Currently, vertebral and muscle tissue samples are being collected from specimens throughout the Pacific Ocean.

7. Habitat associations. The PSRC has initiated several projects intended to determine which marine and estuarine habitats might serve as Essential Fish Habitat for several species of central California elasmobranchs. This research will include an evaluation of the bays, estuaries, and deep-water habitats along the Pacific coast to examine their role as nursery grounds. We are currently examining the spatial and temporal patterns in habitat utilization and movements of leopard sharks inside Elkhorn Slough, CA using acoustic telemetry techniques. A mixture of both active and passive tracking techniques will allow us to collect data on short- and long-term movements and habitat use by transient and resident sharks. With increased knowledge of spatial utilization, proper steps can be taken to protect critical areas of the slough that will lead to more effective management of the species.

   Archived video footage of elasmobranchs taken from remotely-operated vehicles and manned submarine dives in Monterey Bay is being reviewed and related to existing habitat maps of the region to estimate distribution, abundance, species composition, habitat associations, and potential nursery grounds and for deep-water sharks. Three elasmobranch species, the filetail catshark (Parmaturus xaniurus), California skate (Raja inornata), and longnose skate (R. rhina) are commonly observed during manned submersible dives and their habitat associations are currently under investigation. Similar studies are being initiated using data obtained from fishery-independent trawl and longline surveys conducted by the NMFS Santa Cruz Lab.

8. Demographic analyses. Using the information resulting from PSRC life history studies, we will begin to examine the population dynamics of commercially exploited elasmobranchs from the ENP. We will model demographic parameters, including net reproductive rate, generation times, intrinsic rates of increase, and stable age distributions of Pacific sharks using life history table analysis and age-based Leslie matrices. We will also conduct sensitivity and elasticity analyses to determine the most sensitive life stages of select species of Pacific sharks. Deterministic and stochastic demographic models will be developed in an effort to best predict the population status and future trends of Pacific sharks. These approaches are ideally suited to sharks and rays due to the lack of or uncertainty in life history information that is generally available for most species. Demographic analyses are being coordinated with and methodologies are being further developed by PSRC colleague, Dr. Henry Mollet. Species currently being assessed include the diamond stingray (Dasyatis dipterura), pelagic stingray (D. violacea), and shortfin mako (Isurus oxyrinchus).

9. Tagging and tracking studies. The PSRC will work closely with and support the Monterey Bay Aquarium, National Marine Fisheries Service (NMFS), and Tagging of Pacific Pelagics (TOPP) programs to tag, release, track, and recapture sharks in central and southern California. We will work with NMFS Southwest Fisheries Science Center colleagues during summer tagging and tracking cruises and in cooperation with NMFS Santa Cruz Laboratory staff during their nearshore coastal long-line and trawl surveys to further develop tag and release procedures. The PSRC will coordinate with MLML graduate student research actively tracking prickly sharks (Echinorhinus cookei) and leopard sharks (Triakis semifasciata) in the Monterey Bay region. Using an array of receivers placed throughout Elkhorn Slough, passive tracking techniques will also be implemented to monitor longer term movement patterns and habitat use. These studies will serve to provide an improved understanding of movement patterns, habitat use, and age validation of Pacific sharks.

10. Population genetic studies. Effective conservation and management strategies of marine species require a fundamental understanding of their population structure. Molecular genetic data can be used to discern this information by quantifying the degree of relatedness between specimens from different locations. The PSRC has initiated genetic research into the population structure of the common thresher shark (Alopias vulpinus). These sharks are found throughout the world's warm and temperate oceans and are often targeted by commercial fisheries. Specimens and tissue will be collected throughout the Pacific Ocean, and perhaps other areas of the world. Through analysis of DNA sequences from microsatellites and the mitochondrial control region, we will assess the levels of genetic diversity among global populations of thresher sharks to determine if the species' potential for large-scale dispersal is translated into broad gene flow throughout its range. Successful completion of this research will clarify the extent of common thresher shark movements and may reveal population subdivisions that require special attention for sustainable fisheries management.

11. Shelf, slope and pelagic surveys. To support ongoing NMFS shelf, slope, and pelagic survey efforts and obtain samples necessary for the broad suite of life history, genetic, and taxonomic studies we are engaged in, the PSRC has developed agreements to work with NMFS scientists from the Alaska Fisheries Science Center (AFSC), Northwest Fisheries Science Center (NWFSC), and Southwest Fisheries Science Center Santa Cruz Laboratory (SCL). PSRC personnel in cooperation with the NMFS SCL have initiated a detailed biological study of central California elasmobranchs. Since September, 2002, entire catches of skates and catsharks have been retained from groundfish longline and trawl surveys in Monterey Bay, CA. Detailed measurements, wet weights, reproductive tracts, tissue samples, parasites, vertebrae for age and growth estimation, are collected for further analyses. The primary species being examined are the sandpaper skate (Bathyraja kincaidii), big skate (Raja binoculata), California skate (R. inornata), longnose skate (R. rhina), brown catshark (Apristurus brunneus), and filetail catshark (Parmaturus xaniurus).

    In cooperation with the NMFS Northwest Fisheries Science Center, PSRC researchers have assisted in their annual continental slope surveys conducted between Washington and southern California. During the 2002 and 2003 surveys, we obtained several uncommon species including the deepsea skate (B. abyssicola), Aleutian skate (B. aleutica), roughtail skate (B. trachura), brown catshark (A. brunneus), longnose catshark (A. kampae), and Pacific black dogfish (Centroscyllium nigrum) which were collected and shipped to the PSRC for further investigation. PSRC personnel also participated in a research cruise sponsored by NMFS AFSC along the eastern Bering Sea slope in June and July 2002. Biological data on 10 poorly known species of skates were collected. In addition, tissue samples were saved for future genetic analysis.

12. Shark Fisheries Database. A fisheries database is currently being assembled by PSRC personnel that incorporates commercial and recreational landings for all elasmobranchs identified in the waters of the western continental United States. The database is subdivided by state (AK, CA, OR and WA) and contains landing data, fishery regulations, gear types, and market information. Fisheries-dependent data are being compiled from federal and state fishery agencies. Fisheries-independent data are being gathered primarily from the Resource Assessment and Conservation Engineering (RACE) database, which incorporates data from NMFS surveys throughout the US Pacific. Information derived from published literature will also be included, especially with regard to distribution and abundance. Once these data are assembled, long-term fishing trends will be analyzed (where possible). Special attention will be given to determining the amount and extent of shark (including skate and chimaera) bycatch and discard.

13. Taxonomic studies. The systematics of eastern North Pacific (ENP) chondrichthyans is very poorly known. Many of the species were first described over 100 years ago and the original descriptions in many cases are quite poor. Some groups, such as the skates, exhibit strong variation between adult male and female forms, which further complicates identification. This is a serious concern since many of these species are taken in large numbers, but cannot be properly identified without adequate guides. To date, representatives of all six known Bathyraja species from CA, OR, and WA have been examined either from material obtained through NMFS research cruises conducted out of their SCL and NWFSC facilities or from museum collections at the California Academy of Sciences, Harvard Museum of Comparative Zoology, Los Angeles County Museum of Natural History, Smithsonian Natural History Museum, and Scripps Institute of Oceanography Vertebrate Museum. Detailed studies of these specimens will result in improved identification keys and a better understanding of the distribution and fisheries importance of skates in the ENP. PSRC personnel are consulting and collaborating on this project with leading experts at the Shark Research Center, Cape Town, South Africa and at Texas A&M University.

    An investigation of the taxonomic status of two butterfly rays, Gymnura crebripunctata and G. marmorata, is near completion. These butterfly rays have been reported from the tropical and warm temperate waters between southern California and Peru, and are an important component of small-scale fisheries throughout the region. The primary features used to distinguish the two species have been reported to be highly variable or sexually dimorphic among other butterfly rays. Researchers at the PSRC in conjunction with scientists from Nova University and Mexico's national fisheries agency, Instituto Nacional de la Pesca, initiated a study to resolve the taxonomic controversy using molecular genetic and morphometric analysis. Results indicate that the two species are not valid, but are male and female forms of the same species, G. marmorata.