A Relationship between Fish Communities and Habitat Environments in Small Erosion-controlled Rivers in the Lake Biwa Basin

The purpose of this study is to examine the relationship between fish communities and habitat environments in small, erosion-controlled rivers which until this day have been overlooked, and which have thus failed to be included in natural environment restoration zones. Thirty-one sites in three small rivers which flow into Lake Biwa were selected for investigation. As a result, six families and twelve fish species were identified. Based on the results of TWINSPAN, two categories of fish communities were established: the first comprised the communities found in the vicinity of the river mouth which included upstream migratory species such as Plecoglossus altivelis altivelis, and the second comprised the communities found in the middle course of the river which did not include upstream migratory species. It was inferred that the partition of the habitat space was the result of the existence of small dams in the river. The results of CCA indicated that although these small rivers had been significantly altered for erosion-control, a large variety of micro-habitat environments survived, and specific fish species inhabited the various habitats accordingly.