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Atlantic Loggerhead Turtle Recovery Team Stakeholder Meeting

April 8-9, 2003

Silver Spring, Maryland (NOAA Headquarters - Science Center)

DEVELOPMENT OF A QUANTITATIVE APPROACH TO THREATS ANALYSIS

FOR THE ATLANTIC LOGGERHEAD RECOVERY PLAN

Presented by Alan Bolten

The development of a quantitative and objective threats analysis is essential for developing and prioritizing recovery actions. The lack of a quantitative threats analysis in recovery plans has been recognized as a factor contributing to the failure of recovery plans to address threats with prioritized recovery actions (Clark et al. 2002, Lawler et al. 2002).

The loggerhead recovery team has identified the following process to develop a quantitative and objective threats analysis:

• Determine ages and life stages to be evaluated
• Determine habitats / ecosystems inhabited by each age / life stage
• Identify threats
• Quantify annual mortality for each threat by life stage / ecosystem
• Adjust annual mortality by reproductive value for each life stage
• Evaluate results; identify and prioritize recovery actions

Loggerhead sea turtles are slow growing and have complex life-histories that involve terrestrial, neritic (coastal waters), and oceanic (open ocean) habitats (see Bolten in press for a review of loggerhead life history). The team has identified the following life stages and corresponding ecosystems/habitats that will be evaluated in our threats analysis:

We have identified the following 8 categories of threats:

• Fisheries Bycatch (e.g., trawl, longline, gillnets, recreational hook and line, sargassum harvest)
• (e.g., direct and indirect take except bycatch, legal and illegal harvest; oil and gas platform removal; boat strikes; beach recreational use)
• Construction (e.g., beach nourishment; beach armoring and other shoreline stabilizations (sand fences, groins, and jetties); offshore breakwaters; ship channel dredging; water diversions (dams); storm water outflows; coastal construction)
• Alteration of Ecosystem Dynamics (e.g., trophic changes from overfishing; trophic changes from habitat alterations from trawl fisheries, sponge fisheries, live rock harvest; beach erosion)
• Pollution (e.g., toxins; marine debris ingestion; marine debris entanglement; oil; lighting; noise including low frequency sonar and seismic)
• Species Interactions (non exotic species) (e.g., predation; disease)
• Exotic Species Interactions (e.g., nest predation; habitat modification by plants, for example, shading, dune modification)
• Other Factors (e.g., climate change (temperature dependent sex determination and sea level rise); natural catastrophes (hurricanes); conservation/research activities (nest relocation); military exercises)

We combined the life stage / ecosystem grid (above) with the threats categories to create a series of spreadsheets that allowed us to quantify the annual mortality for each threat by life stage and ecosystem. The recovery team is now completing a draft of these spreadsheets and when the spreadsheets are completed, they will be posted on the Atlantic loggerhead recovery website for suggestions and comments:

http://www.fws.gov/northflorida/SeaTurtles/loggerhead-recovery/default-loggerhead.htm

Please send any comments and suggestions to: seaturtle@fws.gov

The annual mortality for each threat at each life stage must be adjusted by the “reproductive value” for each life stage. Some individuals in a population are more “valuable” than others in terms of the number of offspring they are expected to produce. An individual’s potential for contributing offspring to future generations is its reproductive value. To determine the stable age distribution for the population, we solved the age-based matrix model for a stable age distribution (right eigenvector). By transposing the matrix model, the model can be solved for the reproductive values for each age class (left eigenvector). See Caswell (2001) for discussion of matrix population models. We were also able to calculate a weighted mean reproductive value for each stage. Once we derived the reproductive values for each age and stage, we could then adjust the annual estimated mortality by the corresponding reproductive value relative to a nesting female for each age / life stage. The recovery team gratefully acknowledges the help of Melissa Snover for providing the matrix model and calculations for this aspect of the threats analysis.

The final step in the threats analysis process is to evaluate the results and identify trends (both within a threat category or column within the spreadsheets or within a life stage or row within the spreadsheets). Based on these analyses, we will then be able to identify and prioritize recovery activities and identify data gaps and research needs.

Literature Cited

Bolten, A.B. In press. Active Swimmers -- Passive Drifters: The Oceanic Juvenile Stage of Loggerheads in the Atlantic System. In Bolten, A.B. and B.E Witherington (editors) Loggerhead Sea Turtles. Smithsonian Institution Press, Washington, DC.

Caswell, H. 2001. Matrix Population Models, 2^nd Edition. Sinauer Associates, Sunderland, MA.

Clark, J.A., J.M. Hoekstra, P.D. Boersma, and P. Kareiva. 2002. Improving U.S. Endangered Species Act Recovery Plans: key findings and recommendations of the SCB Recovery Plan Project. Conservation Biology 16:1510-1519.

Lawler, J.J., S.P. Campbell, A.D. Guerry, M.B. Kolozsvary, R.J. O’Connor, and L.C.N. Seward. 2002. The scope and treatment of threats in endangered species recovery plans. Ecological Applications 12:663-667.

• Meeting Overview
• Agenda
• Participant List - PDF 152KB