| The masu salmon is a rare species of fish found in Hokkaido (Japan’s cold region). It migrates to mountain streams to spawn. As the consideration of the environments of such rivers、 requires an understanding of suitable spawning conditions for these fish. Past studies of masu salmon spawning environments were conducted with a focus on physical river elements (riverbed slope、 penetration flow、 etc). However、 it is very difficult to create and maintain such physical elements. [*]This study aimed to clarify the relationship between the spawning environments of masu salmon and river topography、 focusing on the area of sandbar geomorphology in which、 sandbars are formed by the natural effects of the river’s flow.[*]The survey reach was located in the Hidarimata River and Toshibetumena River within the Shiribeshi Toshibetu river basin in Hokkaido. The length investigated in each river was 350 m、 and included areas of two sandbars and two non-sandbars geomorphology. Spawning bed and river topography were investigated in each river.[*]The major findings of this study are as follows. [*]1.Riverbed undulations in areas of sandbar morphology were significantly larger than those in areas of non-sandbar morphology. [*]2.13 beds were confirmed in the survey reach、 and 12 of these (about 92%) were concentrated in areas of sandbar morphology. Furthermore、 within this sandbar morphology、 10 spawning beds (about 83%) were concentrated in the range of bed slope of relatively gentle.[*]3.Riverbed undulations worked effectively for the microhabitat that the masu salmon uses as a spawning-bed. These results indicate that the area of sandbar morphology is important for spawning habitat of masu salmon. |
