RELATIONS OF FISH HABITAT TO ENVIRONMENTAL STRUCTURES OF A SMALL STREAM IN VIEWS FROM ECOLOGICAL CONTINUITY

Abstract

Environmental structures and fish habitat were compared between reaches of a spring-fed small stream, the Hinakura Stream which has been used for agricultural irrigation, a branch of the Nagara River in Gifu Prefecture. Many ground sills inside the Stream have divided fish habitat for the ecological continuity. As a result of the cluster analysis of the environmental factors; height of ground sill, undercut bank, riparian plants, overhanging vegetation, submerged plant, sediment and substrate composition, the Stream was divided into eight parts. The nektonic fishes inhabited mainly in the all section, benthonic fishes were closely related with riparian plants, submerged plants, sediment and substrate composition. For fishway design, cruising speed (sustained speed) and burst speed (maximum swimming speed) characterize the swimming ability of fish. In general, cruising speed is 2-4BL (body length)/sec, and burst speed, 10-15BL/s, although results of the measurement of swimming speed in a non-uniform flow channel, the duration for which a fish can maintain a certain swimming speed. To minimize the activity of white muscle, fishway should provide current velocities lower than the cruising speed at some part of any cross section of fishway. Ability or function of fish swimming speed, have been dealt in fishway design such as flow characteristics in a life stage.