Demographic scenario inferred from genetic data in leatherback turtles nesting in French Guiana and Suriname Original Research Article

Nesting beaches around the Maroni estuary, at the border between French Guiana and Suriname (South America), currently host about 40% of the world’s population of breeding female leatherback turtles. Although the population size has been variable but always large since the 1980s, observations of leatherbacks in the region before 1950 were sporadic or absent and the number of nesting females was extremely low. These observations motivated us to use molecular markers to investigate whether the appearance of leatherbacks in this region was the result of natural long-term population cycles or of immigration. Analysis of 12 microsatellite loci failed to detect the signature of a recent demographic perturbation in the Maroni population of leatherbacks. This result suggests that the marked increase in population size can neither be explained by natural long-term cycles, nor by a founder effect. We conclude that the current population of the Maroni region likely resulted from extensive migrations of animals from elsewhere. Consequently, the Maroni population probably belongs to a metapopulation whose limits remain currently unknown. This metapopulation dynamic suggested by our results is a major feature that should be taken into account in future conservation strategies. We also estimate the effective population size at 90–220 individuals, which is lower than the target effective population size for conservation purposes. This relatively low effective population size indicates vulnerability, despite the large number of nesting turtles currently observed annually.