Diverse foraging habits of juvenile green turtles ( Chelonia mydas ) in a summer-restricted foraging habitat in the northwest Pacific Ocean

Green turtles in year-round neritic foraging habitats are widely considered to have small home ranges and to mainly feed on plant-based diets. In contrast, few studies have examined the summer-restricted habitats to which these turtles seasonally migrate. In this study, we investigated the foraging habits of green turtles migrating to the Sanriku Coast, a summer-restricted foraging habitat in a temperate area (38–39°N) of the northwest Pacific Ocean, using stable isotope analysis and biologging experiments from 2007 to 2015. Stable isotope analysis ( n = 40, straight carapace length (SCL): 36.8–90.9 cm) indicated that most of the turtles, especially all smaller turtles ( n = 35, SCL < 58 cm), relied on gelatinous prey before arriving at the Sanriku Coast. According to the biologging experiments (451.2 h of behavioral data and 43.2 h of video data, n = 6, SCL: 44.5–81.0 cm), the turtles shifted their main food to macro-algae (135 out of 148 feeding events) and consumed it at the sea bottom during their stay in the specific localized area of the Sanriku Coast. However, the turtles still consumed gelatinous prey in midwater during their movement to other locations along the Sanriku Coast and/or during their migration to southern overwintering habitats (13 events). These results indicated that green turtles migrating to the Sanriku Coast exhibit dietary diversity relative to year-round habitats, and the turtles in this area seem to consume gelatinous prey during the transit period in addition to feeding on macro-algae during the resident period.