Relationship between physical environment and distribution of juvenile masu salmon in early summer in the Atsuta [Japan] River, Hokkaido

We investigated the relationships between channel units and number or density of juvenile masu salmon in early summer of 1999 and 2000 in the Atsuta River in Hokkaido, northern Japan. Densities of juvenile masu salmon were higher in the channel units, where there were shallow, slow and sandy habitats with underwater and overhanging covers 50 cm in height, than in other units, in both years. The abundance of riparian forest is thought to be important as source for juvenile habitats, since woody debris was related to the formation of those channel units.