Author(s): Shigeo Morita; Makoto Kuwahara; Shoji Yamashita
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Abstract: The masu salmon (Oncorhynchus masou), a rare species of fish found in Hokkaido (Japan’s cold region), migrates to mountain rivers to spawn, lives in these rivers for more than a year after being born, and then migrates downstream to the sea. Rivers in Hokkaido are covered with ice and snow during the winter season, and their rate of discharge is considerably less. Therefore, under these conditions during winter season, it is very important to assist with the conservation and creation of wintering habitats for their life history. Many studies of masu salmon have been conducted focusing on the relationship between wintering habitats and physical river elements (water depth, flow velocity, and coverage, etc). According to these studies, masu salmon prefer places with a low flow velocity and a high degree of coverage of wintering habitats. However, physical river elements are affected by the conditions caused by ice and snow in the river channel, and because such conditions very so much according to the topography of each river, few studies have focused on these effects. This study aimed to clarify the relationship between river topography and wintering habitats, and a survey of wintering habitats was conducted focusing on the condition caused by ice and snow in the river channel in the areas with varying topography. Additionally, in the reaches with few locations suitable for wintering, an experiment to create wintering habitats using riverbed boulders was examined. As a result, the characteristics of wintering habitats in the areas with varying topography were shown. In particular, in the reach with few wintering habitats, artificially created wintering habitats gather ice and snow easily, the cover is formed around these places, and these wintering habitats functioned well in the winter season. Additionally, the majority of the structure of artificially created wintering habitats remained secure after the winter season.
Year: 2010