National Research Institute of Far Seas Fisheries, Fisheries Research Agency
Pacific bluefin tuna (PBT) is a worldwide fishing resource targeted mainly by Japan, Korea, Taiwan, the U.S. and Mexico. Japan, as the biggest fishing and consuming country of the PBT resource, should lead its sustainable use and adequate resource management in the international community.
More than 95% of the PBT catch consist of 0 to 3 years old young fish and juveniles. On the view of sustainable use of the resource, the current situation of the resource should be recognized precisely for appropriate fishing strategy. The Japan Fisheries Agency is stepping up research activities on PBT resources to promote management strategies. The National Research Institute of Far Seas Fisheries (NRIFSF) conducts several researches for collection and accumulation of young PBT ecology data; when, where and in what kind of environment they inhabit. Recently, archival tagging techniques have been developed as one of the strategies for gathering direct data for highly mobile fish. An archival tag attached to a target fish collects data of environmental water temperature, diving depth, location, and estimated migration route.
PBT juveniles, hatched in the area around the Nansei islands, migrated to Kochi and Nagasaki coastal areas 2 to 3 months after being hatched, and were targeted by troll fishing. During this period, the juveniles were still small (about 20cm in FL) and so weak that even direct touch to the fish can cause fatal damage. Their vulnerability makes it difficult to attach archival tags and collect vital data in the natural environment.
Thus, we at NRIFSF developed an operational stand for smooth and quick attachment of tags. Fish was kept in the water even during the operation and we achieved shorten the operation time to 30-60 seconds. Thanks to this technical progress, the survival rate of the tagged fish significantly increased. Also, the mechanical progress contributed to the survival rate; the tags became smaller dramatically (from 45g to 2.3g; weight in the water 1.2g). These innovations made it possible to attach archival tags to the smallest 0-year-old PBF (23-33 cm in FL) in the world. Now we can obtain the migration information of very young PBT under the natural environment.
Until today, the migration routes of young PBT had been estimated from fisheries data. With the new tagging strategies, we now can track actual routes by attaching archival tags to juveniles. Thus, migration and habitat changes between fishing seasons and exchange routes and proportions between the Pacific Ocean and the Japan Sea will be revealed soon. With this method, more practical data for the PBT resource management such as juvenile protection schemes will be provided in the future.
For further information, please contact fuji88@affrc.go.jp
