魚類学雑誌
Online ISSN : 1884-7374
Print ISSN : 0021-5090
ISSN-L : 0021-5090
中禅寺湖流入河川におけるサケ科魚類3種の産卵生態
若林 輝中村 智幸久保田 仁志丸山 隆
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2002 年 49 巻 2 号 p. 133-141

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Microhabitats of spawning sites of the three salmonids (honmasu salmon Oncorhynchus masou, which was a probably hybrid of masu salmon O. m. masou, red-spotted masu salmon O. m. ishikawai and biwa salmon O. m. subsp., brown trout Salmo trutta and Japanese charr Salvelinus leucomaenis) were investi-gated from mid September to early December in 1995 and from mid September to late November in 1996 in four rivers (Toyamasawa, Yanagisawa, Yokokawa and Kannonsui rivers), which discharge into Lake Chuzenji, central Japan. Spawning behaviors of honmasu salmon, brown trout and Japanese charr were observed from mid September to late October in all rivers, from late October to early December in all rivers and from late October to early December in the Toyamasawa River, re-spectively. Spawning redds of honmasu salmon and brown trout were observed in a wide range of reaches in the three rivers, while those of Japanese charr were re-stricted in the upper reach of the Toyamasawa River. Honmasu salmon spawned in deeper sites with larger sized substrates than do brown trout. Japanese charr spawned in sites with slow current velocities. Redd superimpositions were ob-served in all species and brown trout and Japanese charr frequently superimposed on the redds of honmasu salmon. The results suggest that the competition between honmasu salmon and brown trout-Japanese charr for spawning sites is reduced by their different spawning periods, but redd superimpositions by brown trout and Japanese charr decrease the breeding success of honmasu salmon.

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