Study on Fish Migration through a Stone-Embedded Fish Passage Based on Preference

Abstract

A stone-embedded fish passage (SEF) allows fish to pass a barrier by reducing the velocity in the slope. The efficiency of SEFs has however not been evaluated well and the design parameters are not clear. The efficiency of SEFs for fish therefore needs to be evaluated and analyzed. In this research, we attempted to develop a simple equation to estimate the passability of an SEF for Ayu (Plecoglossus altivelis), which is applicable in the SEF’s designing stage. We reproduced the SEF conditions experimentally. The set-up consisted of a pool and a channel, and evaluated its passability based on physical conditions such as air bubbles, velocity, and depth. With the results, we developed a decision tree to explain the passability using design variables such as discharge, channel slope, and pool size and depth. Then, to estimate the whole SEF, we proposed an equation which calculated the average of the decision tree outputs throughout the SEF’s whole ascending routes. Lastly, we verified the equation through field experiments. The equation showed good agreement with the observed fish ascent success rate. This technique could therefore be used to evaluate a SEF in its designing stage.