Identifying the foraging grounds of the new loggerhead turtle nesters in the western Mediterranean

Abstract

The western Mediterranean Sea has traditionally served as a primary foraging ground for juvenile loggerhead turtles from three distinct regional management units: the North-western Atlantic, the Mediterranean and Cape Verde. Nesting activities were sporadic. Recently, nesting activity on the beaches of eastern Spain has increased, due to warmer sand and water temperatures during the summer months. The study has integrated stable isotope analysis of carbon (C), nitrogen (N) and sulphur (S) with satellite telemetry to identify the foraging grounds of these new colonizers nesting on Spanish beaches. Results indicate that the majority of these adult females forage oceanically in the Algerian Basin, with a few exhibiting distinct stable isotope signals, tentatively associated with foraging in shallow coastal areas in the central Mediterranean Sea. The dominance of oceanic foragers in this new population is noteworthy, given the Algerian Basin's oligotrophic nature. This contrasts with the prevalence of neritic foraging in adult females nesting in the central and eastern Mediterranean Sea. The use of the Algerian Basin as a foraging ground for adult loggerhead turtles exposes them to bycatch from drifting longlines. The authorities should refrain from increasing bluefin quotas imposed on longliners in the Algerian Basin unless the fishery avoids using squid as bait and agrees to deploy hooks deeper than 25 m to reduce loggerhead turtle bycatch.