Quantifying Vegetation on a Rock-Ramp Fishway for Fish Run-Up and Habitat Enhancement: The Case of the Miyanaka Intake Dam in Japan

Abstract

The Miyanaka Intake Dam fishway underwent improvements in 2012, and we established a new rock-ramp fishway called the Seseragi Fishway, cognizant of its utility as a passage and a habitat for bottom-dwelling and small fish with weak swimming ability. However, the fishway is occasionally submerged by floods, causing sediment accumulation that leads to changes in the vegetation composition. In addition, the arrival and inflow of seeds from upstream and the surrounding areas result in vegetation changes. In this study, the inside and outside of the rock-ramp fishway were divided into eight areas, and the vegetation succession after 2012 was determined. A correlation was observed between the results of fish catch surveys during the same period and the vegetation. Based on these results, we reported on the process of steadily operating the rock-ramp fishway while devising and improving specific management methods. Changes in vegetation, such as an increase in upright vegetation and a decrease in flow-obstructing vegetation, contributed to an increase in the population of bottom-dwellers, weak swimmers, and juvenile fish. The existence and management of appropriate vegetation are important for maintaining fishways inhabited by a variety of fish species.