Study of Remaining and Migration of Skipjack Tuna in Waters Around Yonaguni Island, Okinawa, Japan

Abstract

We conducted an investigation for remaining period and behavioral ecology of skipjack tuna (Katsuwonus pelamis) around the fish aggregating devices (FADs) in the sea near Yonaguni Island, Okinawa, Japan. Skipjack is known that it is altitude migratory fish and stays around an island and artificial fishing reefs [1]. The knowledge concerning skipjack ecology and behavior are still poor and the reasons for staying around FADs are unknown. Investigation of migratory fish has a wide movement range and it is difficult to track continuously long-term. For this reason, a method of attaching a data logger directly to a fish body and measuring behavior are mainstream. However, since this method requires recapture of fish for the data collection, the data collection rate is extremely low. In this study, we tried long-term research and improvement of data recovery rate using ultrasonic biotelemetry system and FADs dotted in the sea near Yonaguni Island, Okinawa, Japan. As a result of the investigation, it was possible to confirm received signals of 71 individuals out of the 181 individuals released. And it became clear that many of the received skipjacks stayed more than 10 days and stayed in the sea near Yonaguni Island. Furthermore, we were able to obtain about the migration between FADs and the diurnal behavior around the FADs.