内湾および干潟における物質循環と生物生産【63】瀬戸内海漁獲量の減少要因4. イワシ類と瀬戸内海固有種の漁獲変動

摘要

The species fluctuating largely in the Seto Inland Sea are sardine, anchovy and white bait. Sardine and whitebait are transported from open sea into the Seto Inland Sea. Some part of whitebait grows to anchovy in the Sea. The fluctuation of fish catches of sardine and whitebait in the open sea are similar to that in the Seto Inland Sea. Therefore, the growth of sardine and whitebait are estimated to be not largely affected by the environment of the Seto Inland Sea. The catch of anchovy in the Seto Inland Sea is partly similar to that in the open sea and increased from about 16 thousand to about 40 thousand ton at 2000 year and continued until 2014. So, it is unlikely that anchovy decreases by less nutrient condition. The fish catches of the indigenous species such as sand eel, flatfish, bastard halibut, black sea bream, red sea bream, Japanese seaperch and drumfish decreased from 53 thousand ton at 1982 to 42 thousand ton at 2005. Since the catches of the indigenous fishes except sand eel was around 25 thousand ton per year from 1976 to 2000, it is difficult to say that the indigenous fishes were decreased by low nutrient condition. It is necessary to review the hypothesis that the low nutrients invoke the decrease of the fish catch in the Seto Inland Sea.