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6～8月にかけて主に沼田川中流域で採集したアユ30尾の耳石Sr/Ca比を調べ，由来判別を行った。その結果，30尾中12尾が天然遡上アユであることが判明した。また，支流の椋梨ダム湖（白竜湖）より上流の椋梨川で採集した13尾は，全ての個体で耳石Sr/Ca比の変動が認められなかったことから，これらはダム湖で再生産した陸封アユと考えられた。, Ayu, Plecoglossus altivelis altivelis, is a commercially important species of amphidromous fish. Thus it is being targeted for stock replenishment to sustain harvest numbers. Stock identification between amphidromous and hatchery fish was conducted using the otolith Sr/Ca concentration ratio on fish taken from the Nuta River in Hiroshima Prefecture, where 170,000 hatchery ayu had been previously released. Of 30 fish sampled from the middle-reaches, 12 were identified as an amphidromous form. Of the 13 fish sampled from the Mukunashi River, a branch of the Nuta River, all were identified as landlocked fish that would have completed their life cycle between the Mukunashi River and the artificial lakes formed by the Mukunashi Dam., 本研究は平成19年度広島大学地域貢献研究において，東広島市沼田川漁業協同組合より課題提案された「東広島市沼田川におけるアユの資源保全と有効利用」の一環として行った。

6～8月にかけて主に沼田川中流域で採集したアユ30尾の耳石Sr/Ca比を調べ，由来判別を行った。その結果，30尾中12尾が天然遡上アユであることが判明した。また，支流の椋梨ダム湖（白竜湖）より上流の椋梨川で採集した13尾は，全ての個体で耳石Sr/Ca比の変動が認められなかったことから，これらはダム湖で再生産した陸封アユと考えられた。 Ayu, Plecoglossus altivelis altivelis, is a commercially important species of amphidromous fish. Thus it is being targeted for stock replenishment to sustain harvest numbers. Stock identification between amphidromous and hatchery fish was conducted using the otolith Sr/Ca concentration ratio on fish taken from the Nuta River in Hiroshima Prefecture, where 170,000 hatchery ayu had been previously released. Of 30 fish sampled from the middle-reaches, 12 were identified as an amphidromous form. Of the 13 fish sampled from the Mukunashi River, a branch of the Nuta River, all were identified as landlocked fish that would have completed their life cycle between the Mukunashi River and the artificial lakes formed by the Mukunashi Dam. 本研究は平成19年度広島大学地域貢献研究において，東広島市沼田川漁業協同組合より課題提案された「東広島市沼田川におけるアユの資源保全と有効利用」の一環として行った。

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.