Upstream migration of fishes downstream of an under-construction hydroelectric dam and implications for the operation of fish passage facilities

Abstract

Fish behavior measurements are important for river and fishery scientists to protect fish resources and for ecological engineers to guide ecosystem conservation but they can pose a practical challenge. In this study, an acoustic camera was used to observe the migration patterns of fish species downstream of an under-construction hydroelectric dam, the Lianghekou dam in the middle Yalong River, China. The fixed-point method was employed to continuously measure fish migration using a dual-frequency identification sonar (DIDSON) during the spawning periods from April to August. The fish number and length measured by sonar were in fairly good agreement with the results of manual counting and field fishing, respectively. The results showed that the number of fish individuals migrating upstream (NFU) and fish length varied monthly and diurnally, and the NFU measured at dark twilight were 2–3 times greater than those measured during the daytime. The analysis showed that the upstream migratory behavior is dominated by the combined actions of river discharge, water temperature, and time of day. Based on the results, we suggest that the suitable operation time for future fish passage facilities could be when the river discharge ranges from 500 m3/s to 1500 m3/s and the water temperature ranges from 13 °C to 16 °C when the fishes in the study area mostly migrated upstream. The optimal operation time could be at night when the river discharge and water temperature are approximately 1000 m3/s and 15 °C, respectively. Although the indirect evidence of fish migration was recorded at a single location, this study reveals the great potential of acoustic cameras for measuring fish migration behavior downstream from hydropower stations which could be helpful for fish passage studies and fish resource conservation in China.