Mass production affects the conservation and management of Pacific bluefin tuna

The construction of a land facility aiming to mass production of Pacific bluefin tuna is in the final stage in Nagasaki, Japan. This facility run by the National Research Agency of Japan will begin operation in the middle of this year for producing 100,000 juvenile bluefin annually, through complete aquaculture, to be used for tuna farming.
The complete aquaculture means that the complete life cycle from egg to adult is successfully repeated for several generations under artificial conditions, like domestic animals.
In my view, there are multiple objectives for the construction. First, stable provision of the seedling in large amount to tuna farmers in Japan. In fact, the tuna farmers have been suffering from big fluctuation of availability of wild seedling. Second, this facility provides invaluable opportunities to conduct scientific experiments to improve knowledge of various key aquaculture aspects including finding better strains. Third, reduction of fishing pressure to juveniles among the wild bluefin population. Four, stabilization and restocking of the stock when it becomes necessary.

The third and fourth objectives have important implications for the management of the Pacific bluefin tuna. Recent stock assessment of the Pacific bluefin indicates that the adult fish population is in the lowest level in the last 60 years but reduction of taking juveniles toward appropriate level would rebuild the adult stock to a healthy level. Presently, out of the total 650,000 seed juveniles used for tuna aquaculture (3-4months old), around a 25% (150,000 fish) is produced by the complete aquaculture and the rest are taken from the wild stock. Further, the level of mass production of seedling by this facility would contribute much to recover the stock (The stock assessment of the west Atlantic bluefin tuna indicates that the level of recruitment of age one fish is about the same or less than 150,000 fish.)