内湾および干潟における物質循環と生物生産 【65】瀬戸内海漁獲量の減少要因6.底層魚類の漁獲変動

摘要

It is supposed that demersal fishes in the Seto Inland Sea are shark, flatfish, drum fish, conger eel, 50%hairtail, ray, red sea bream, black sea bream, mullet, conger eel and 50% residual fish. It is assumed that the 50%hairtail is demersal fish and another 50% one is epipelagic fish. It is similar in the case of 50% residual fish. The demersal fish catch in the Seto Inland Sea is about 2.8 ten thousand ton at 1952,increased to about 6.1 ten thousand ton at 1978,decreased little by little to about 5.2 ten thousand ton at 1993 and decreased rapidly to about 2.1 ten thousand ton at 2014. The process of the fish catches of 50% hairtail and conger eel is similar to that of total demersal fish. It is estimated that these two fishes were decreased by the depletion of total demersal fish since these two fishes are fish-eating and prey on the demersal fishes. The catch of flatfish was about one ten thousand ton at 1996, then decreased three thousand ton at 2014. Oxygen-deficient water is estimated as the factor of the decrease of the flatfish catch.