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Comparing Sea Turtle Distributions and Fisheries Interactions in the Atlantic and Pacific

Progress Reports (PDF): FY 2008, FY 2007, FY 2006, FY 2005

Project Overview
Project researchers propose to run quantitative and qualitative analyses of existing data on the ecology, distribution and fishery interactions of leatherback and loggerhead sea turtles in both the North Pacific and North Atlantic oceans. The primary goal is to use a comparative approach to determine why populations of sea turtles in the Atlantic, where fisheries interactions are common, appear to be stable or increasing, while populations of the same species in the Pacific are declining. Because of great concerns for their survival, and their protected status under the Endangered Species Act, sea turtle take in pelagic fisheries has resulted in complete closures (e.g., Hawaii, Grand Banks) or major restrictions on effort and area for the US fleet (e.g., NE Distant Sector, Atlantic). Scientific understanding of the extent and nature of worldwide take patterns in pelagic fisheries, and impacts on stock rebuilding, is incomplete, at best.

Researchers will conduct comparative and statistically rigorous analyses to eliminate alternative hypotheses for the causes of sea turtle population declines in the Pacific. Researchers will follow the assessment approach (not previously applied for sea turtles) adopted by a recent National Research Council Panel to evaluate Steller sea lion and fisheries interactions in Alaska (NRC 2003). The proposed research fits within PFRP Program target objectives of developing integrated statistical models of protected species population dynamics and collaborative assembly of stock-wide data bases for other marine turtle populations. This focus on the Pacific ocean will be viewed against data analyses from the Atlantic, for a more complete understanding of information available for both sea turtle species.

Nesting beach surveys indicate dramatic population declines for both leatherback and loggerhead sea turtles in the North and Central Pacific. It is clear that these populations are in trouble, but the causes of, and means of slowing or preventing these declines are not obvious. Egg harvest is believed to be a major cause of sharp reductions in numbers of leatherback nests in Central America and Malaysia (Chan and Liew. 1996, Spotila et al. 1996), but has not been a problem on Japan nesting beaches for some time (Kamezaki et al. 2003). On the other hand, direct and delayed incidental mortality through fisheries interactions has been identified as a major contributing factor for sea turtle population declines worldwide, and bycatch in pelagic fisheries has been implicated in observed Pacific trends (Lutcavage et al., 1996; Eckert and Sarti, 1997; Eckert, 1997; Spotila et al. 2000, Crowder 2000, Chaloupka 2003). In contrast, leatherback and loggerhead sea turtles on the Atlantic and Gulf coasts of the U.S. are stable or increasing, and some Caribbean nesting beaches also show this trend (Eckert 1995; Dutton et al., Boulon et al. 1996, Pritchard 1996, TEWG 2000, NOAA 2002). How can there be such large differences in recruitment success between the Atlantic and Pacific? Can fishing effort and associated incidental take account for the disparity? Pelagic fisheries operate in all major oceans, and alternative hypotheses that could account for differences in recruitment success between the Pacific and Atlantic stocks have not been examined. Like other pelagic species, sea turtle populations are affected by anthropogenic factors (e.g., interactions with fishing gear, nesting habitat alteration, egg harvesting) and environmental factors (e.g., ocean productivity, current regime shifts, climate change). Researchers have addressed some of these components, but these elements have not been linked, nor compared for different ocean basins.

Because sea turtles are rarely encountered at sea and are difficult to age, there are insufficient data to run formal statistical stock assessments for either leatherbacks or loggerheads. Nevertheless, a substantial amount of data on migration, fishery interactions, life history, and population trends have been gathered for both species in the Atlantic and Pacific. Through combined expertise and collaboration with sea turtle researchers in both ocean basins, project researchers hope to accumulate and integrate these data. A collaborative approach is strongly advocated, to put all the available data "on the table" to determine the role of pelagic fisheries in sea turtle declines. The data do not exist to run this assessment for any one population - there are too many unknowns, which allows biased interpretations of trends to compete without validation. Project researchers believe that a comparative analysis of data for two species in two ocean basins, both incidentally taken by longline fisheries but at different life history stages and levels of interactions, holds the key to this management puzzle.

1. Compile published and unpublished data on the life history, at-sea distribution, pelagic and coastal fisheries interactions, and history of direct exploitation for loggerhead and leatherback sea turtle populations in the North Pacific and North Atlantic oceans.

2. Identify and evaluate alternative hypotheses for population change for each species in each ocean basin, by postulating the changes in abundance, distribution, genetic composition or size distributions that would be anticipated from these hypotheses.

3. Compare expected distributions of loggerhead and leatherback turtles in each ocean basin based on habitat preferences and oceanographic regimes.

4. Develop a modeling framework for assessment of population-level impacts of pelagic fisheries on sea turtle populations that are subject to multiple stressors.

Primary Phases:

  • I. Collaborator workshop to identify the scope of the problem, existing data and hypothesis formation
    The approach is that inductive reasoning from the experience of researchers and fishermen can be combined with deductive reasoning from ecological principles to develop alternative hypotheses for sea turtle population declines in the Pacific. By comparing two species in two locations, researchers hope to eliminate some competing hypotheses. For example, possible reasons for stark differences in apparent recruitment success between Atlantic and Pacific oceans include:
    1. recruitment failures due to recent or continued egg harvest.
    2. recruitment failures due to interception of juveniles (and adults) by inshore and artisanal fisheries.
    3. time lags in the response of nesting female counts to management measures, or other changes in productivity.
    4. recruitment failures due to changes or differences in juvenile dispersal patterns that result in higher mortality rates from predation or inadequate forage.
    5. population bottlenecks.

  • II. Synthesis and statistical comparisons of existing data
    For each species in each ocean basin, project researchers will work with collaborators to compile existing data on: population trends, life history, size distributions, stock structure, spatial distribution/overlap with pelagic and coastal fisheries, correlations with oceanographic features, location and history of conservation/mitigation methods, and large-scale environmental variability.
    Data synthesis is a critical element as it will integrate data across national boundaries and ocean basins into a comprehensive dataset.

  • III. Demographic and Assessment models
    An important element to understanding the current population status is to reconstruct the demographic history of these populations. A comparative analysis of the divergent demographic and fisheries data for the two species in both ocean basins will identify influential parameters that account for the differences in observed trends between species and basins. Furthermore, this approach synthesizes existing data, linking fishery dependent and independent data in an integrated analysis.

  • IV. Mapping distributions with oceanographic models
    In consultation with Dr. David Kirby (SPC, New Caledonia), Dr. Lutcavage's lab will collect and map oceanographic information from remote sensing databases that will be used to examine sea turtle dispersal patterns obtained in the preceding phases. The scope of these analyses will depend on the quantity and extent of spatial and temporal data concerning these species and their life history stage. Considering the rapid decline of leatherback and loggerhead populations in the Pacific Ocean, it is critical for management purposes that at least a basic understanding of what designates essential pelagic habitat is reached as soon as possible. Project researchers will tackle this aspect by exploring the link between sea turtle distribution and oceanographic features using information from satellite tracking projects in the Atlantic and Pacific.

    The following steps will be taken to examine the dispersal and habitat use patterns for each species and ocean basin:
    1. Plot known nesting beaches and model dispersal of post-hatchlings and juveniles through simulations of their trajectories against relevant ocean current systems. Establish where post-hatchlings and juveniles are likely to be. Verify model with known distributions of post-hatchling and juvenile loggerheads in the Atlantic.
    2. Examine resulting distributions in relation to oceanographic features and primary productivity.
    3. Examine known dispersal patterns and habitat preferences of adults.
    4. Examine modeling results for distribution of juveniles and adults in relation to primary productivity and forage base.
    5. Examine resulting distributions in relation to fishing effort (coastal and pelagic) and fishing mortality rates for size classes.

  • V. Review results, identify data needs and compare management scenarios
    To highlight analyses to date and serve as a means of linking findings across work phases. This review will also be used to identify the gaps in the current data sets available, and point to additional analyses for Year 2 of the project. Given the management imperative of reducing sea turtle bycatch, the goal is to place the Year 1 ecological data into a management context. Year 1 findings will also be used to evaluate and compare bycatch reduction management scenarios, which will be one topic for discussion in the workshop meeting in Year 2.

Anticipated Products:
1. A summary of the meeting of turtle experts and collaborators that includes a list of research recommendations to fill critical data gaps that will allow the elimination of remaining alternative hypotheses. (YEAR 1)
2. A table of hypotheses for the effects of pelagic fisheries and other human induced stressors on sea turtle populations, with expected impacts on population growth rates, time lags in measurable impacts, and shifts in size distributions for the 4 stocks. (YEAR 1)
3. A report on the qualitative evaluation of those alternative hypotheses for Atlantic and Pacific stocks of leatherback and loggerhead sea turtles, including details on model formulation and evaluation. (YEAR 1)
4. A report on the development of new assessment models and the quantitative evaluation of population dynamics and oceanic dispersal/distribution for Atlantic and Pacific stocks of leatherback and loggerhead sea turtles, including details on sensitivity analysis to investigate the role of uncertainty. (YEAR 2)
5. Manuscript on the demographic assessment, oceanographic distribution analysis, and deductive assessment process for a peer-reviewed publication. (YEAR 2)

Year 1 funding for this 2-year project to be awarded in fall 2004.

Literature cited:
• Boulon Jr., R.H., Dutton, P.H., and McDonald, D.L. 1996. Leatherbacks (Dermochelys coriacea) on St. Croix, U.S. Virgin Islands: Fifteen years of conservation. Chelonian Conservation and Biology 2(2):141-147.
• Chaloupka, M. 2003. Stochastic simulation modelling of loggerhead population dynamics given exposure to competing mortality risks in the Western South Pacific. Pages 274-294 in Loggerhead Sea Turtles, eds A.B. Bolten & B. Witherington, Smithsonian Institution Press, Washington, DC, USA.
• Chan, E.H. and Liew, H.C. 1996. Decline of the leatherback population in Terrengganu, Malaysia, 1956-1995. Chelonian Conservation and Biology 2(2):196-203.
• Committee on the Alaska Groundfish Fishery and Steller Sea Lions, Ocean Studies Board, Polar Research Board, Division on Earth and Life Studies, National Research Council of the National Academies. 2003. Decline of the Steller sea lion in Alaskan waters : untangling food webs and fishing nets. Washington, D.C. : National Academies Press.
• Crowder, L. Letter to the editor: Leatherback's survival will depend on an international effort. 2000. Nature 405:881.
• Eckert, K. L. 1995. Leatherback Sea Turtle, Dermochelys coriacea. p. 37-75. In P.T. Plotkin (editor), National Marine Fisheries Service and U.S. Fish and Wildlife Service Status Reviews for Sea Turtles Listed under the Endangered Species Act of 1973. National Marine Fisheries Service, Silver Spring, MD.
• Eckert, S., 1997. Distant Fisheries Implicated in the Loss of the World's Largest Leatherback Nesting Population. Marine Turtle Newsletter. 78:2-7.
• Kamezaki, N. and 28 co-authors. 2003. Loggerhead turtles nesting in Japan. Pages 210- 217 in Loggerhead Sea Turtles, eds A.B. Bolten & B. Witherington, Smithsonian Institution Press, Washington, DC, USA.
• Lutcavage, Molly E., P. Plotkin, B. Witherington, and P. Lutz. 1996. Human Impacts on Sea Turtle Survival. Pp. 388-404. In, Peter L. Lutz and John A. Musick (editors), The Biology of Sea Turtles, CRC Press, Boca Raton, FL.
• NOAA 2002 NMFS/SEFSC. 2001. Stock assessments of loggerhead and leatherback sea turtles and an assessment of the impact of the pelagic longline fishery on the loggerhead and leatherback sea turtles of the western North Atlantic. NOAA Technical Memorandum NMFS-SEFSC-455.
• Pritchard, P.C.H. 1996. Are leatherbacks really threatened with extinction? Chelonian Conservation and Biology. 2:2: 303-305.
• Sarti M., L., S. A. Eckert, N.T. Garcia, and A. R. Barragan. 1996. Decline of the world's largest nesting assemblage of leatherback turtles. Marine Turtle Newsletter 74:2-5.
• Spotila, J.R., A.E. Dunham, A.J. Leslie, A.C. Steyermark, P.T. Plotkin and F.V. Paladino. 1996. Worldwide population decline of Dermochelys coriacea: are leatherback turtles going extinct? Chelonian Conservation and Biology 2:209-222.
• Spotila, J.R., R.D. Reina, A.C. Steyermark, P.T. Plotkin and F.V. Paladino. 2000. Pacific leatherback turtles face extinction. Nature 405:529-530.
• Turtle Expert Working Group. 2000. Assessment update for the Kemp's ridley and loggerhead sea turtle populations in the western North Atlantic. NOAA Technical Memorandum, NMFS-SEFSC-444.

Principal Investigators:

Dr. Molly Lutcavage
University of New Hampshire
Dept. of Zoology

177A Spaulding Hall
Durham, NH 03824 USA
Phone (603) 862-2891
FAX (603) 862-2717
email: molly.lutcavage@unh.edu


Dr. Selina Heppell
Oregon State University
Dept. of Fisheries and Wildlife
104 Nash Hall
Corvallis, OR 97331
Phone (541) 737-9039
FAX (541) 737-3590
email: selina_heppell@oregonstate.edu
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This page updated August 7, 2008