Evaluation of stocking effectiveness of the Japanese Spanish mackerel in the eastern Seto Inland Sea, Japan

This study evaluated the stocking effectiveness of two release groups of Japanese Spanish mackerel, Scomberomorus niphonius, in the eastern Seto Inland Sea, Japan. Juveniles of about 40 mm in total length (TL) that were directly harvested from seed production tanks and 100 mm TL that were reared in nursery facilities were released from early June to early July. The otoliths of released juveniles were marked with alizarin complexone. In 2002, 51,000 40-mm and 82,929 100-mm juveniles and, in 2003, 94,000 40-mm and 77,193 100-mm juveniles were released. A total of 2,761 individuals were sampled at the 14 main fish landing markets between 2002 and 2004, from September in the release year to June the next year. Recapture rates, yields from the released juveniles, contribution rates to the commercial landings, and the economic efficiency were estimated with standard errors. The variance estimators were derived by assuming simple random sampling of the commercial landings. All estimates for evaluating stocking effectiveness showed significantly higher values in the 100-mm release group than in the 40-mm release group. Consequently, releasing 100-mm juveniles reared in nursery facilities was more efficient than direct release of 40 mm juveniles.