耳石Sr/Ca比による広島県芦田川水系における陸封アユの確認

広島県芦田川中流・上流域で捕獲したアユ成魚10個体の耳石Sr/Ca比を調べ由来判別を行った。その結果, 9個体の耳石Sr/Ca比に変動がなく, 終始低レベルに推移したため, それらは仔稚魚期に海洋生活を送らなかった陸封アユと判断された。これら陸封アユは, 芦田川に建設された八田原ダムや三川ダムによって形成された人造湖(芦田湖, 神農湖)で再生産したものと考えられた。

Ayu Plecoglossus altivelis is one of the most important freshwater fishes in Japan and usually amphidromous. Stock identification was conducted using otolith Sr/Ca analysis for ayu from the Ashida River, Hiroshima Prefecture. In nine of 10 adults sampled from the upper and middle-reaches in August-October 2006, the ratio did not fluctuate and remained at a low level, indicating that these ayu were landlocked fish without staying as larvae and juveniles in coastal marine waters. The landlocked ayu likely reproduce in two artificial lakes (Lake Ashida and Lake Jin-no formed by Hattabara Dam and Mikawa Dam, respectirely) in the Ashida River.