Hydrological habitat simulation analysis for spawning and hatching of four major Chinese carps in middle reaches of Changjiang River

It is an important measure to promote the restoration of fish resources by optimizing streamflow and providing suitable hydrological conditions for the spawning and hatching of drifting egg fishes such as the four major Chinese carps in the middle reaches of the Yangtze River through the ecological operation of the Three Gorges Reservoir (TGR). In order to quantitatively analyze the hydrological distribution characteristic of the spawning and hatching areas of the four major Chinese carps during the TGR ecological operation, a one-dimensional and two-dimensional coupled hydrodynamic model was developed, covering the Yichang-Luoshan reach of the middle Yangtze River and the Dongting Lake area. The model was used to simulate the hydrodynamic conditions during ecological scheduling and non-scheduling periods from 2011 to 2024. The results show that the TGR ecological operation have significantly improved hydrological and hydrodynamic conditions at key ecological nodes, including Yichang, Shashi, Jianli, and western Dongting Lake. Specifically, the ecological operation extended the duration of continuous water level rise, increased the rate of water level ascent (mostly exceeding 0.25 m/d), and enhanced flow velocity while maintained it within the suitable velocity range for spawning (0.6~1.3 m/s).Represented hydrological stations in different river sections all met the hydrological requirements of the key life cycle of the four major Chinese carps hatching (velocity>0.3m/s), with the Yichang-Jianli reach showing the most pronounced improvement. This study quantitatively demonstrates the positive regulatory effects of the ecological scheduling on spawning and hatching processes of the four major Chinese carps, providing scientific support for the evaluation and optimization of future ecological scheduling strategies.