Connectivity of loggerhead sea turtle populations in Macaronesia: Genetic markers and stable isotopes

Abstract

Loggerhead sea turtle (Caretta caretta), globally threatened, is the most common sea turtle species in Macaronesia, where juveniles mix in oceanic foraging grounds around Azores, Madeira and the Canary Islands. Furthermore, the second largest nesting aggregation of this species in the Atlantic occurs in Cabo Verde Islands. This project aims to determine the spatio-temporal connectivity of loggerheads feeding in Macaronesian waters using genetic markers and stable isotopes. With this objective, mitochondrial DNA control region sequences and stable isotope ratios (d13C and d15N) in carapace scute layers of juvenile loggerheads stranded in the Canary Islands and adult females nesting in Cabo Verde were analysed and compared with published data from Azores. Foraging ground centric many-to-many mixed stock analysis revealed that, in the Canary Islands foraging ground, the juveniles come basically from the Northwestern Atlantic (Florida) and less than a 10% from Cabo Verde. Stable isotope ratios differentiated five isospaces: (1) Azores, (2) Oceanic Canary Islands, (3) Neritic Canary Islands, (4) Oceanic Cabo Verde and (5) Neritic Cabo Verde. The analysis of carapace scute layers of turtles of the Canary Islands revealed that 61% of the juveniles sampled presented only isotopic values of oceanic Canarian waters. The remaining 39% presented values of three other foraging grounds, including the following: oceanic Canary Islands and neritic Canary Islands (4%), Azores and oceanic Canary Islands (9%), oceanic Canary Islands and oceanic Cabo Verde (22%), oceanic Cabo Verde and neritic Canary Islands (4%). These results revealed that some individuals have changed their habitat or have been moving between habitats during their development, showing, for the first time, the fidelity, for several years (from 1.44 to 12.6 years ago) to certain foraging grounds of the Macaronesia.