Abstract
The effects of pool type fishways on stream fish distribution in the Ishizaki River, Hokkaido, Japan, were evaluated from the view point of population density, estimated by mark and recapture experiments. The population densities of six diadromous species (Salvelinus leucomaenis, Oncorhynchus masou, Gymnogobius urotaenia, Rhinogobius sp.CO, Cottus hangiongensis and Plecoglossus altivelis) were estimated, only S. leucomaenis occurring above check dams that lacked fishways. Three species (O. masou, P altivelis and R. sp.CO) were present above dams with associated fishways, but their population densities were fre-quently lower than below the dams. G. urotaenia and C. hangiongensis were col-lected only below dams with fishways, whereas S. leucomaenis was present above dams that lacked fishways, suggesting that they were landlocked by those dams. It was concluded that pool type fishways are not necessarily the best aid for the mi-gration of diadromous fishes, most benthic fishes, in fact, not being able to use them.
