Effectiveness of the releases of hatchery-produced stock of Japanese flounder Paralichthys olivaceus in Kagoshima Bay, southern Japan

The Fish stock enhancement program of Japanese flounder Paralichthys olivaceus in Kagoshima Bay started in 1984 and in recent years about 300 thousand juveniles have been released per year. To clarify the effectiveness of the releases in Kagoshima Bay, a continuous survey on the commercial catch in Kagoshima Fish Market was conducted from 1989 to 2002 and revealed that the ratio of released fish in the landings amounted to 18.9-49.2% in number. Using the age-weight-key estimated by sex based on the samples collected from Kagoshima waters, the catches in number for weight classes in Kagoshima Fish Market from 1989 to 2002 were transformed to those for the age classes. Estimates of recapture rate during 7 years after the release ranged from 1.51 to 3.52% and economic efficiencies were estimated to be from 0.97 to 1.17. Cohort analyses showed the recent decrease in recruitment and spawning biomass. Further studies on the stock management of P. olivaceus in Kagoshima Bay are needed.