Effectiveness of Fish Pool and Confluence Structures as Refuge Sites Constructed at Intervals in Agricultural Drainage Channels

Abstract

A marked and recapture survey was conducted to clarify the effectiveness as fish refuges during flooding of the fish pool structure and four confluence structures constructed in a drainage channel with a length of approximately 2,035 m as part of the land consolidation project. A total of 8.3% of the fish were recaptured after the flooding of water. The proportion of small individuals decreased in some fish species and sites after rainfall compared to before rainfall. In the case of Oryzias latipes, the peak of the length distribution at the time of recapture was larger than that at the time of marked release. Therefore, it was inferred that small individuals were swept away due to the increase in flow velocity associated with rainfall. In addition, individuals marked at upstream sites were recaptured at downstream sites. These indicating that the construction of multiple refuge sites on the same drainage line was effective in preventing runoff from the drainage channel during flooding.