Evaluation of fish habitat in Oto river by IFIM

Abstract

Recently, the request for ecological aspect in river improvement works becomes gradually stronger in order to offer higher quality of natural space to people. We adopted the Instream Flow Incremental Methodology (IFIM) to determine a conservation flow for freshwater fishes. Habitat variables (velocity, depth, and substrate) are utilized to derive a habitat suitability criteria for pale chub, dark club, and river lizard goby observed in 1994 in Oto River. And we surveyed macro-habitat variables, that are water temperature and cover (i. e. shadowed area on water surface by trees along the riverside), during the summer in 1995 to enhance the IFIM model by introducing the relation with target fishes. To apply the IFIM to a study reach, we developed a one-dimensional mathematical model for a gradually varied flow. We derived accurate and objective habitat suitability criteria between target fishes and habitat variables and found that density of fish species was related to cover according to each fish's food pattern. However, water temperature data during one day were not sufficient to explain a relation with target fishes. Variation in WUA, which shows a quantitative estimate of fish habitat, is found out to be closely related to density of target fishes and a conservation flow for pale chub in summer in Oto river is evaluated about 4m3/sec.