Stream Fish Habitat Science and Management in Japan: A Review

Abstract

Japanese freshwater fish habitats can be generally categorized into 1) rivers and streams, 2) ponds and lakes, and 3) rice fields and small irrigation channels connecting them. Of these, reviewing studies on stream fish habitat is the primary objective of this paper. Streams in Japan have widely received severe habitat alterations through construction of artificial instream structures as well as modification of riparian vegetations. As a result, streamdwelling fishes that require natural flow regimes, substrates, and riparian vegetation have declined their populations in great deal in many parts of the country. Recent studies have found riparian forests control water temperature and provide woody debris creating cover structures for the stream fishes resulting in enhancing their carrying capacity. Differences in riparian vegetation types (forest versus grass) played an important role in determining the local distribution of salmonids. Also, experiments removing concrete-lined channel and installing log-drop structures demonstrated that such the treatment greatly improved fish habitat.

As the general public became aware of the serious degradation of aquatic habitats, river management policy has gradually shifted to include conservation and improvement of river environment as habitat for wildlife during the last two decades. For fish migration, installation of fishway on dams has been prevailing, and research efforts have been made to design more effective fishway and passable weirs. In many cases, however, such restoration work lacks ecological data for assessment of their effectiveness. When such knowledge on fish habitat are accumulated, a vital issue will be how it is accounted into actual management. Future studies on fish habitat should shift toward treating habitat network at larger spatial scales to seek better designs for distributing appropriate habitats over a whole catchment. Such studies should also include clarifying the habitat requirements of endangered species and effects of non-native on native species.