Abstract
Evaluation methods for fishways in Japan were reviewed and some proposals were made on their improvement. A major problem in the methods was lack of a holistic view in the role of fishways. Most of previous fishway evaluations were based on experiments using stocked fish in the fishway to examine possibility of their upstream movement. In the case of the fishway of Komaki dam with 79.2 m in height, fish passing through the dam were few in number in spite of the effectiveness of the fishway itself. The monitoring data on the fishways of the Nagara Rivermouth Barrage have been examined by several scientists and arguments on the environmental influence of the barrage were made based on their evaluation. They claimed that environmental change accompanied with the construction of the barrage made degradation of the fish population in spite of the ability of the fishways. These results suggested that we should consider a number of factors for estimating on fishway performance, including those outside the fishway. This means fishways should be evaluated from the aspect of the survival of fish populations. The function of fish passage is not the purpose of a fishway but a part of conservation of fish population. We should include dam effect estimation in a fishways evaluation program. For this purpose, required are approaches from fish population ecology such as investigation of longitudinal distribution and seasonal pattern of migration in each age of the fish population. Now practical guidelines for the method of evaluation should be developed.
