Foraging ecology of loggerhead sea turtles Caretta caretta in the central Mediterranean Sea: evidence for a relaxed life history model

Abstract

In the central Mediterranean Sea, gut contents and feces of 95 turtles captured by bottom trawlers and pelagic longliners fishing in neritic and oceanic areas, respectively, were examined. Ben- thic prey were more abundant than pelagic, a probable bias due to the higher digestibility of the latter. Animal and plant taxa belonging to 12 Phyla and 20 Classes were observed, with 63 new records of prey species, and Malacostraca, Gastropoda, and Echinoidea were the most commonly occurring animal classes. Results showed a highly opportunistic foraging behavior by the turtles on both live and dead ma- terial in the epipelagic zone as well as on all types of seafloor. Benthic taxa were found in turtles as small as 26 cm curved carapace length (CCL), indicating an early use of benthic resources, and also among turtles over a wide size range caught by pelagic longliners. The lack of evidence of a strict oceanic/ pelagic stage and of a clear habitat shift in the observed size range (25 to 80.3 cm CCL), when consid- ered together with other recent findings, challenges the current ontogenetic model of life history for the species. A relaxed model is proposed, with an early short obligate epipelagic stage due to limited div- ing capacity, followed by the main opportunistic amphi-habitat stage, with a tendency to prefer benthic prey as turtles grow and their benthic foraging efficiency improves. Under this model, temporary or per- manent association or fidelity to specific oceanic or neritic zones would vary among individuals or pop- ulations according to food availability and oceanographic features in the foraging or migratory areas.