標津川下流域で行った試験的な川の再蛇行化に伴う魚類と生息環境の変化

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.

特集：標津川再生事業の概要と再蛇行化実験の評価
Feature: Shibetsu River Restoration Project