Occurrence of loggerhead sea turtles in the offshore areas of the central-southern Tyrrhenian Sea (western Mediterranean): results of the first five years of surveys using passenger ferries as observation platforms

Abstract

The spatial behavior of Mediterranean loggerhead sea turtles (Caretta caretta, Linnaeus, 1758) in offshore areas, particularly in the Tyrrhenian Sea, remains poorly understood. This study presents preliminary results from a five-year visual data collection (2019-2023) on loggerheads conducted within the FLT Med Net and LIFE Conceptu Maris Projects, using passenger ferries as observation platforms. Over 32 surveys covering about 6000 km along the Salerno-Palermo and Naples-Palermo routes, 176 specimens were sighted. Spatial analyses revealed a stable presence of turtles, with a mean SPUE index of 0.03 and a significant hotspot centered ~60 km northeast of Palermo, as indicated by Kernel Density Estimation and Getis-Ord Gi* statistics. Consistent with satellite-tagging studies, turtles dispersed widely in spring-summer, concentrating in smaller areas during autumn-winter. Notably, in spring, turtles seemed to favor areas near seamounts, which are known to attract pelagic predators. These findings emphasize the ecological importance of the Tyrrhenian basin for loggerheads.