Genetic studies of the Hawksbill turtle Eretmochelys imbricata: evidence for multiple stocks in Australian waters

The hawksbill turtle, Eretmochelys imbricata, is endangered and currently declining in many parts of its global distribution. Efforts to manage the species are hampered by the lack of knowledge of the appropriate geographic units of management and the relationship among breeding populations and feeding assemblages. The Australian populations are among the few remaining large assemblages in the world, but may be under threat from harvesting in neighbouring countries. We use patterns of mitochondrial DNA variation to determine the geographic scale of breeding populations and to compare the genetic composition of turtles in feeding populations to those nesting at nearby major rookeries. Four of the major Australian rookeries were sampled, two on the western coast and two in northeastern Australia, as were turtles at two foraging sites. Significant differences in the frequency of two divergent mitochondrial DNA types separated the turtles nesting at major rookeries sampled on the northeastern versus western coasts of Australia, demonstrating that these populations are not connected by significant amounts of gene flow and should be considered as separate entities for management. There was no significant difference between the turtles nesting at two western rookeries 100 km apart, nor between those using the two northeastern rookeries separated by 750 km. This indicates that the size of the interbreeding unit for the hawksbill turtle is likely to be a region consisting of a group of islands rather than an individual island. Feeding populations were screened with a gene amplification test that discriminates between the two major DNA types. In each case, there was a significant difference in allele frequency between feeding populations and the nearest major rookery. This, together with previous reports of long distance migrations from tag returns, suggests that individual foraging areas support hawksbill turtles from distant breeding populations.