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Assessment of Sea-Turtle Status and Trends: Integrating Demography and Abundance
Researchers should examine the finest scale of female homing in each species (already underway with green, leatherback, hawksbill, ridley, and loggerhead turtles) with mtDNA surveys of nesting beaches, preferably in conjunction with tagging studies. That is necessary to resolve management units defined by female homing behavior. It requires sampling coverage of continental coastline or adjacent islands where nesting is intermittent. Adequate sample size depends on the extent of genetic diversity but may begin at about 30 per nesting population. Note that to avoid resampling the same maternal lineage specimens must come from nesting females or a single progeny per female.
Researchers should develop a suite of at least 10–15 variable microsatellite loci for each species. That is necessary to accomplish the next three goals in population resolution and to develop individual-specific DNA fingerprints. It has been largely accomplished for sea turtles in U.S. waters with the possible exception of Kemp’s ridley.
Researchers should survey nesting populations with microsatellites to determine the extent of connectivity between local nesting populations. That is necessary to resolve the male-mediated connections between nesting populations and to resolve RMUs. Adequate sample size depends on the extent of genetic diversity (heterozygosity) but may begin at about 50–80 per location.
Researchers should survey regional feeding populations (juveniles and adults) with mtDNA sequences to determine the source of these individuals with mixed-stock models, assignment tests, and related methods. That is necessary to determine which populations are present (and possibly at risk) in coastal and oceanic habitats. Microsatellite studies may also be useful. Priorities may be established for the most affected feeding populations.
Researchers should survey males in breeding populations off nesting beaches with mtDNA and microsatellites to determine whether they are homing. That is necessary to resolve which populations are present (and possibly at risk) in coastal and oceanic habitats.
Researchers should conduct a sea-turtle genome project for the explicit purpose of developing additional nuclear markers, possibly the next generation of genetic markers for sea turtles (see Appendix A). That will also provide benefits in understanding the natural history and genetic resilience of sea turtles. It may be accomplished in the context of the Genome 10K Project already under development (Genome 10K Community of Scientists, 2009).
Researchers should develop sex-specific metapopulation models to evaluate genetic differences in dispersal. Males and females use habitat differently for feeding and reproduction, and this argues for sex-specific models for evaluating connectivity and survival. The models will increase understanding of management units and demography as outlined above.