Abstract
We investigated effects of experimental channel re-meandering on river ecosystem in lower reaches of the Shibetsu River, Hokkaido, northern Japan. Field samplings before and after re-meandering were conducted to compare fish species abundance and physical conditions of instream habitat to those in a straightened main channel (control reach). The reach used for re-meandering, an isolated old channel of the river, had been a stagnant lentic zone. Physical conditions in the past channel therefore were extremely different from those in control reach. Whereas a large number of lentic fish and crustaceans were found in past channel, only a few lotic fish were found in control reach. After re-meandering, physical conditions of past channel were dramatically changed and showed similar depth and velocity distributions to those in control reach. Re-meandering also greatly lowered lentic fish abundance. On the other hand, many masu salmon were also found in re-meandering reach. We recorded large-sized salmonids at a concave part of re-meandering reach, which were not found in control reach. The channel re-meandering improved its planar geometries and successfully restored diverse instream habitats complex in longitudinal and cross sectional structure. However, unlike past channel, limited availability of slow-flow habitats in re-meandering reach hindered lentic species to colonize.
