ECOLOGICAL SCHEDULING OF XILUODU-XIANGJIABA CASCADE RESERVOIRS ON THE REPRODUCTION OF THE FOUR MAJOR CHINESE CARPS IN THE JIANGJIN SECTION OF THE UPPER YANGTZE RIVER

To mitigate the negative effects of hydropower operation on fish reproduction in the downstream river and maximize reservoir ecological benefits, the Xiluodu-Xiangjiaba joint ecological scheduling has been implemented since 2017. Based on early resource survey data from the Jiangjin section of the upper Yangtze River from 2017 to 2022, this study evaluates the effects of cascade reservoir joint ecological scheduling on the natural spawning of the four major Chinese carps in the downstream river section and identifies key hydrological indicators that affect the natural spawning of the four major Chinese carps. The results showed that the total egg production of four major Chinese carps in the Jiangjin section ranged from 42 to 401 million from 2017 to 2022, exhibiting a general fluctuating trend with a peak of approximately 401 million in 2022. Over the six-year period, 25 spawning peaks were observed, mainly concentrated from early June to early July. During ecological scheduling periods, the egg runoff volumes ranged from 0.001 to 108.8 million, accounting for 0.06% to 34.47% of annual totals-exceeding 30% in 2022 and 10% in 2018. In terms of ecological scheduling effectiveness, the breeding peak period that coincided with ecological scheduling accounted for 16% of the total breeding peak period, indicating that ecological scheduling effectively promoted the natural breeding activities in the downstream Jiangjin section. Hydrological demand analysis showed that the suitable flow range for spawning of the four major Chinese carps in the Jiangjin section was 6000—15000 m³/s, with a suitable water temperature of 21—23℃. Correlation analysis further demonstrated that spawning amount had a significant positive correlation with the peak flow, flow increment, and flow increase rate (<italic>P</italic>&lt;0.05). Based on these results, the study recommends conducting 2—3 ecological scheduling events in mid-late May and early June, maintaining rising water conditions in the Jiangjin section for more than 3d, and ensuring a daily fiow increase rate of at least 900 m³/s to facilitate the large-scale reproduction. The results provide a scientific basis for formulating scheduling strategies for the Jinsha River cascade reservoir system.