Notes on the biology of juvenile masu salmon (Oncorhynchus masou) during winter in the Chihase River, Hokkaido

Abstract

1. The biology of juvenile masu salmon (Oncorhynchus masou) during winter was investigated in the Chihase River which enters into Japan Sea, in southern Hokkaido, from the 13th to the 15th of December, 1967.
2. In the Chihase River system, juvenile masu salmon exhibited a tendency to gather in the tributary (Hiyamizunosawa) in which the water temperature is comparatively high during winter.
3. As the result of the examination of stomach contents, it appeared that juvenile masu salmon ate larvae and nymphs of aquatic insects including Ephemeroptera, Trichoptera, Plecoptera and Diptera during winter.
4. The feeding behavior of O-year fish was more active than that of 1-year fish. Therefore, the ecology of juvenile masu salmon during winter seemed to differ by age group.