ヨシノボリが選好する載り石環境の成立条件と形成メカニズム

抄録

Substrate condition is an important factor for fish habitat evaluation. Especially, the substrate condition for spawning redd of Rhinogobius is quite strict. They need riverbed with loose stone on fine materials (Nori-Ishi in Japanese). To clarify the forming conditions and processes of the environment, gravel size distributions of runs in Kanto district was investigated. One of the substrate measurement methods is an area grid sampling method, and the other is a volumetric sampling one. Comparing the results of these two methods, vertical deposition patterns can be understood. The forming conditions can be analyzed based on hierarchical scale structure. To form the suitable environment, geological condition must be volcanic rock, slope changing must develop well, enough large materials concentrates, outer bank side of run must not be eroded, and the point must be inner bank side. It was clarified that percentage of large boulders in riverbed subsurface layer is a quantitative parameter for the forming condition of loose stone on fine materials and buried stone.