Genetic composition, origin and conservation of loggerhead sea turtles (Caretta caretta) frequenting the French Mediterranean coasts

This study aims to characterise the genetic structure and composition of 245 individuals of loggerhead sea turtles collected from stranding and bycatch events along the French Mediterranean coasts (Gulf of Lion, Provence and Corsica). We obtained sequences of the mitochondrial control region for two fragments (683 bp and 241 bp for 170 and 51 individuals, respectively). The analysis of the long fragment revealed that 163 samples (95.9%) are attributed to the haplogroup II (mainly Mediterranean) whereas only seven individuals are included in haplogroup IB (Atlantic Ocean). The mixed stock analysis performed on the same dataset indicated that the biggest rookeries from the eastern Mediterranean mainly contributed to the French stock, with major contributions being from Greece (36% and 56% for adults and juveniles, respectively), Crete (12% and 18%) and Western Turkey (14% and 4%). The thirteen microsatellite nuclear markers that have been analysed for 81 specimens did not reveal much genetic structure within sampled individuals, thus suggesting that the studied individuals could belong to the same genetic group. The microsatellite analyses revealed however that the nine individuals issuing from two nests sampled in Gulf of Lion and Provence are clearly differentiated from the remaining samples, thus suggesting a long-distance colonisation of the western Mediterranean. Our results allowed addressing the question of loggerhead turtle conservation in the western Mediterranean basin that until now is not considered as a Management Unit despite high densities of juveniles and recent nesting observed on French, Italian and Spanish coasts.