Residence in cold overwintering habitats shapes seasonal space-use plasticity of loggerhead sea turtles in their largest Mediterranean neritic foraging area

Abstract Adriatic Sea represents the largest neritic foraging ground for loggerhead sea turtles ( Caretta caretta ) within the Mediterranean Sea. As ectothermic organisms, loggerhead sea turtles in Adriatic Sea inhabit seasonally dynamic thermal environment with winter sea temperatures as low as 7 °C. Despite the ecological and conservation significance, the space use strategies employed as a response to thermal variation remain poorly understood. We tracked 21 loggerhead sea turtles, of which 10 were small juveniles with < 45 cm curved carapace length. We quantified individual movement patterns and seasonal space use relative to sea surface temperature. Two space use strategies were identified: some turtles remained resident year-round in northern foraging and overwintering areas, while others undertook long-distance southward migrations, with overwintering concentrated within a thermal range of 11–15 °C for both groups. The persistence of loggerhead sea turtles in such conditions suggests greater plasticity in thermal tolerance and winter habitat use than previously assumed. Individuals occupied small areas in the coldest period (January–February) during overwintering and in the warmest period (July–October) during foraging, while the most extensive space use was observed in the transitional period from cold to warm (March–April). Our study provides first insights into the spatial ecology of small juveniles in the Mediterranean Sea and expands the limited body of knowledge on the wintering biology of the species.