Habitat Uses of Freshwater Fishes on the Scale of Reach System Provided in Small Streams

Synopsis

Before we can conserve freshwater fish communities, we must first elucidate the habitat uses of each species. We investigated the relationships between the habits of freshwater fishes and environmental factors in small streams located in western Toyama Prefecture, Japan. We found 30 species – 11 fluvial, 5 brackish water, 2 anadromous, 11 amphidromous, and 1 catadromous – by a semi-quantitative collecting method. Using binary data (occurrence/non-occurrence of dominant fish), we conducted logistic regression analyses to construct predictive models. Stepwise logistic regression analyses on the basis of eight biotic and abiotic factors showed that the occurrence of dominant fish was explained by environmental conditions. The flow variation, ratio of stream bed slope to the surrounding area, distance from sea, and drift plant richness were relevant. Freshwater minnow, Phoxinus oxycephalus jouyi, preferred the gentle slopes of upstream catchments. The freshwater goby, Rhinogobius flumineus, appeared to prefer steeper slopes relative to the surrounding area. In contrast, diadromous gobies preferred reaches near the sea. These suggest a correspondence between lifestyle and preferred habitat. Consequently, the maintenance of various habitat conditions is necessary for the conservation of freshwater fishes.