A SMALL FISHWAY THAT ALLOW YAMAME TO MOVE UPSTREAM FOR EXISTING HEAD CONSTRUCTIONS

Abstract

 Existing head constructions in rivers with marked differences in the height of their upstream and down sections have a detrimental effect on fish ecosystems as they prevent the up- and downstream migration of fishes. The installation of fishways is one method that has been used to resolve this problem. However, although the gentler gradient created by fishways makes it easier for fishes to move upstream, it also makes fishways longer and increases construction costs. If it were possible to construct fishways that could work well on steep gradients, then the area and costs associated with their construction could be reduced. Here we describe the design and implementation of a small fishway constructed on a steep gradient in a small river, and verify its effectiveness. The fishway has several unique characteristics, one of which is a low notch in the partition wall over which water flows. The fishway was constructed at an existing head construction and a release experiment using Yamame (Oncorhynchus masou) was performed to assess the efficacy of the structure. The results showed that the fishway permitted the upstream movement of Yamame, demonstrating that the structure is effective for improving Yamame habitat.