The ecology of adult amago salmon (Oncorhynchus masou ishikawae) after their upstream spawning migration being largely obscure, the study sought to reveal seasonal changes in the longitudinal distribution and abundance of salmon in the upstream spawning area in the Nagara River, Honshu Island, central Japan. The 2004 fish catch record by commercial fishermen and recreational anglers indicated a high level of migration of the salmon from the Ise Bay to the lower section of the Nagara R. in May, with a similarly high level of subsequent upstream migration in late May. Underwater observations in a tributary of the upper Nagara R. revealed that the salmon occupied large deep pools over summer. However, a considerable decrease in salmon numbers occurred in the pools during August, possibly due to bycatch fishing. To maintain wild amago salmon populations, such pool habitats are important refuges and fishing regulations to deter bycatch fishing must be considered.
