Differences in size and reproductive output of loggerhead turtles Caretta caretta nesting in the eastern Mediterranean Sea are linked to foraging site

Abstract

Foraging success affects reproductive output in sea turtles, and is therefore an impor- tant factor to measure in order to understand population dynamics. During 2010 and 2011, we used satellite telemetry to track the at-sea behavior of 20 post-nesting loggerhead turtles Caretta caretta from Rethymno, Crete, Greece. Nineteen transmitters provided location and dive data throughout the turtles' migration towards their foraging grounds and the transition into foraging behavior. We identified 3 foraging regions: (1) 9 turtles migrated southwest towards the North African coast, with 8 concentrated in the region of the Gulf of Gabes, Tunisia; (2) 6 turtles migrated north towards the Aegean Sea; and (3) 4 turtles did not take long-distance migrations, instead remaining resident within the waters of Crete. Two fitness proxies were associated with differ- ences in post-nesting strategies. Turtles foraging in northern waters had significantly larger curved and straight carapace lengths and clutch sizes than turtles foraging near Crete or Africa. Those differences reflect the disparity in benthic prey abundances among the 3 regions. The Aegean had a higher abundance of macrobenthic fauna than the other 2 regions, and the Gulf of Gabes had an increased level of eutrophication. Deterioration of the aquatic resources in the Gulf of Gabes region may be a contributing factor in the observed steady decline in clutch size and total nests per season in 2 critical nesting beaches for loggerheads in Greece.