Effects of upstream and downstream dam operation on the spawning habitat suitability of Coreius guichenoti in the middle reach of the Jinsha River

The middle Jinsha River is a crucial spawning site for Coreius guichenoti, an endemic and economically important fish. The spawning habitat has been influenced by dam construction and operation upstream and downstream of the river reach. This study evaluated the effects of dam operation on spawning habitat suitability using a physical habitat model developed by combining a fuzzy logic approach and a coupled hydrodynamic model. The hydrodynamic model was calibrated and validated with field-measured data. The habitat model was able to predict spawning habitat suitability through comparisons of weighted usable areas (WUAs) and the numbers of collected fish eggs. The habitat model was explored to evaluate the effects of upstream and downstream dam construction on spawning habitat suitability. The results showed that the operation of constructed upstream dams had negative effects on spawning habitat suitability and produced temporal changes in the available WUA. The main spawning period may be delayed from May to June as a result, and variations in the water temperature regime were likely the main influential factor. Predictions revealed that the impoundment of the under-construction Wudongde hydropower station downstream of the study area would increase the suitability of hydrodynamic factors. The suitable water discharge range for spawning was from 1500 m3/s to 2500 m3/s, and the optimal discharge was 2000 m3/s without the impacts of the Wudongde Reservoir impoundment. However, the suitable water discharge range would be extended to be from 750 m3/s to 2750 m3/s, and the optimal water discharge for spawning is estimated to range from 1500 m3/s to 1750 m3/s after the reservoir begins operation. The results of this study may help to formulate more efficient methods of improving spawning habitat suitability, such as adjusting the rate of discharged flow. Furthermore, the presented methods provide a basis for further research on the assessment of fish habitat suitability in the context of cascade dam construction.