Operation improvement of the river mouth barrage to increase the population of Ayu-fish in the Yodo River System.

Abstract

Annual total number of Sweetfish (Ayu) migrating upstream from the Shin-Yodogawa River have been recorded up to 30,000 -1,600,000 for these 6 years. However, the upstream migration of Ayu from the Okawa River is prevented by the high current velocity caused by the difference in water level at the Kema water gate. We investigated measures for promoting the upstream migration by improving operation of the Yodogawa-ozeki Weir. Experimental measures for decreasing the water level difference conducted in 2017 increased the available time for Ayu to make upstream migration up to 100 hours in the season and a total of ca. 60,000 Ayu passages were recorded. This operation improvement is expected to play a part in increasing the natural resources of Ayu in the Yodogawa river system.