Occurrence patterns of freshwater fish during spring-summer period in the Ohbetsu River, the tributary of the Bekanbeushi River, flowing through wetland, eastern Hokkaido, Japan

Abstract

In the Ohbetsu River, the tributary of the Bekanbeushi River, eastern Hokkaido, Japan, 20 species of freshwater fishes were collected from May to July in 2000-2003. Freshwater type of Pungitius pungitius and Gymnogobius castaneus were collected throughout the study period, suggesting that sampling areas constituted major habitat for these species during May-July period. In contrast, anadromous fishes such as Pacific Ocean form of Gasterosteus aculeatus, Osmerus eperlanus mordax and Salvelinus leucomaenis, were thought to migrate upstream for breeding and get through the Ohbetu River during spawning migration. These differences in occurrence pattern of fish species in the river appeared to be related to various life history patterns of fishes. It is also conceivable that the vast estuary of the river provides diverse habitat environment, enabling many fishes with various life history patterns to inhabit this river.