Stock enhancement and management of Japanese flounder Paralichthys olivaceus in Sagami Bay of Kanagawa prefecture [Japan]

Japanese flounder (Paralichthys olivaceus) is an important coastal fishery resource in Sagami Bay of Kanagawa prefecture. The catch started to decline in the early 1970's and fell into a fourth of that of the 1960's in the end of the 1980's. However, the catch recovered during the 1990's. In recent years, the catch was stable at the level of the end of the 1990's. In Sagami Bay, a flatfish-gillnet is used to catch Japanese flounder; therefore, the 1- and 2-years-old fish are fished mainly. High fishing mortality coefficients were estimated for the fish older than 1 year by virtual population analysis. The stock enhancement program of Japanese flounder has been carried out in Kanagawa prefecture since 1987, and the stock management plan was launched in 1998. A total of 95-325 thousand hatchery-product juveniles (60 mm in mean total length) were released every year from 1 992 to 2003. The catch of hatchery-product juveniles accounted for 13-29% of all individuals in number. The recapture rates of each brood-year were estimated to be 1.9-8.8% (4.4% on average). The stock management was developed toward Kanagawa prefecture wide area resource management (Japanese flounder). The principal management aims to protect smaller fish (30-35 cm in total length). The stock enhancement and management were evaluated by the catch and number of adult stock (age 3+) simulations. According to the simulations, if all actions are accomplished in 2006 and later, the catch is expected to be 9% higher and adult stock in number is expected to be 17% higher than those expected in the case that the present action continued until 2010. On the contrary, if all action are stopped in 2006, the catch is expected to be 15% lower and the adult stock in number is expected to be 19% lower than those expected in the case that the present action continued until 2010. Both of the actions would be required to sustain the stock in Sagami Bay.