This study examined epibionts on three species of sea turtles (loggerhead, green and hawksbill) obtained in Japanese waters as bycatch, strandings, or landings for breeding. Species diversity of barnacle epibionts on sea turtles appears to be affected by the behaviour and foraging habitat of the turtles. Green and hawksbill turtles are found in neritic areas all year round, while loggerhead turtles are found in inshore areas only during the breeding season in Japan. The turtle barnacle Cylindrolepas sinica is found on green and hawksbill turtles frequently, but occurrence on the loggerhead turtle is quite rare (1/190: a new host record). The present study recorded a single individual of loggerhead turtle (a large male) with C. sinica attached. This turtle was captured in August and December at the site of tagging on Okinawa. The recaptured records indicate that the loggerhead turtle wintered around Okinawa rather than migrating to the open sea as most Japanese loggerheads do and resulted in the attachment of C. sinica. Satellite tracking has been an important tool in investigating the sea turtles’ life histories; however, this method is costly and can elucidate migration routes only after the attachment of a transmitter. In contrast, studying the diversity of the epibionts can provide information on the foraging habitat (infection site) and behaviour of the turtles. Such a method can have benefits in getting large sample sizes at nesting beaches, from fishery bycatch and strandings.