Post-nesting habitat selection by female loggerhead turtles in Japan

The number of loggerhead turtle ( Caretta caretta ) nests in Japan has been declining since the mid-2010s, highlighting the need for conservation efforts. As most sea turtle species spend the majority of their lives in foraging areas, understanding their habitat preferences and the factors influencing their distribution is crucial for effective conservation measures. During the 2018 and 2019 nesting seasons, we attached satellite transmitters to 23 nesting females on Tanegashima Island, one of the largest nesting rookeries in Japan, and tracked their post-nesting migrations. Most individuals inhabited the East China Sea (ECS) and the Tsushima Strait (TS), using 3 core areas during the warm season and 2 during the cold season. Seasonal migration occurred around November, when sea surface temperature averaged 22.4°C. We constructed distribution models for each core area to examine environmental factors influencing overall distribution patterns and assessed how body size may influence individual distributions. Slope, salinity, and sea surface currents affected distributions in some core areas; however, there were no consistent factors influencing distribution among the areas, suggesting that individuals flexibly adapt to local environmental conditions. Although body size did not differ significantly among the core areas, individuals utilizing the TS tended to be larger, indicating that body size may influence habitat selection. These findings contribute to informing effective conservation measures for this population.