SCIENTIFIC COMMITTEE EIGHTH REGULAR SESSION 7-15 August 2012 Busan, Republic of Korea Association of Early Juvenile Yellowfin Tuna Thunnus albacares with a Network of Payaos in the Philippines

To understand how early juvenile yellowfin tuna use the habitat and environment provided by fish aggregating devices (FADs), fish (19–31 cm FL) implanted with ultrasonic transmitters into their abdominal cavities were released in a network of payaos in Panay Gulf, the Philippines. Self-recording receivers were attached to the anchor ropes of the payaos to detect the presence of the fish. Some aspects of the behavior of juveniles were similar to those reported in adults. One juvenile showed a diurnal vertical swimming pattern, swam within a limited shallow range during the nighttime, and dived to deeper waters during the daytime. Two juveniles performed deep dives over 100 m during payao-to-payao excursion. Three juveniles showed a diurnal horizontal swimming pattern that was synchronized. In contrast, juveniles stayed \6 days in the network, shorter than adults. No juveniles returned to the same payao after an interruption of over 24 h. It is suggested that juveniles in this area are just starting to migrate and are temporarily staying around a payao for a few days to forage before continuing their migration.