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Assessment of Sea-Turtle Status and Trends: Integrating Demography and Abundance
the South Atlantic Bight provided a rough estimate of a 20% probability of reaching shore for a wind- and current-driven carcass, with strong seasonal and spatial variability (Hart et al., 2006); similar studies need to be conducted in the Gulf of Mexico and the northeast United States, with an emphasis on establishing the likelihood of detection and statistical discrimination among spatial scales (Wiens, 1989).
The level of environmental monitoring needed to identify relationships between oceanography and strandings may be substantial, given the complexity and variability of nearshore ocean processes. It is possible that environmental variance will nullify strandings as a source of trend and distribution information for nesting populations, but large strandings events are still valuable indicators of local conditions (e.g., harmful algal blooms, intense fishing mortality), and samples from dead animals can provide important information through diet evaluation about local population structure, growth rates, maturation rates, and habitat use.
Every recovered carcass can be a valuable source of information for assessment if recovery efforts are standardized; proper measurements are taken; and samples are collected, processed, and archived according to established protocols. To improve the value of strandings data for assessment, each state program needs to be reviewed and evaluated for consistency in recovery effort, volunteer training, and protocols. Areas that have low or inconsistent sampling effort could be identified to improve extrapolation methods. Programs for evaluating size distributions and growth rates from turtle hard parts need to be supported and enhanced to maximize the amount of information obtained from each stranded animal. Flipper collection could become standard protocol for STSSN volunteers in the southeastern and Gulf states, but a considerable investment in time and resources will be needed to process and evaluate those samples.
Researchers should give high priority to generating estimates for the following parameters: survival of immature turtles and nesting females, age at sexual maturity, breeding rates, and clutch frequency.
Because demographic rates can vary over time and space, researchers should collect data over both dimensions so that population trends can be detected and evaluated adequately.
Researchers should be aware that evaluation of point estimates of demographic parameters is not sufficient for population assessment; characterizing uncertainty and variance is also necessary.
Researchers should strive to understand the mechanisms regulating variation in demographic rates; this is essential for diagnosing changes in population abundance and mitigating population declines.