长江宜昌江段四大家鱼产卵场亲鱼集群生境适宜性评价

[Objective] Promoting the natural spawning of fish through reservoir operation is an important and effective measure for enhancing the ecological benefits of reservoirs. From 2011 to 2025, the Three Gorges Reservoir (TGR) conducted 24 ecological operation tests over 15 consecutive years to promote the spawning of the four major Chinese carps (FMCC) and facilitate the recovery of fish resources. However, early-stage fish resource monitoring data indicate that the responses of FMCC to each ecological operation test vary, with spawning effects being pronounced in some cases but suboptimal in others. Therefore, attention should be focused on the schooling behavior of the parent fish of FMCC in the Yichang river section, and appropriate hydrodynamic conditions constitute a key ecological basis for their spawning. [Methods] To determine the appropriate ecological flow for FMCC parent fish schooling in the Yichang river section, this study began with the ecohydraulics requirements of the parent fish schooling, proposed a hydrodynamic suitability curve based on previous monitoring results and existing literature, established a three-dimensional hydrodynamic model and a Physical Habitat Simulation Model (PHABSIM) of the spawning site, analyzed the hydraulic habitat suitability of FMCC under different flow conditions, and identified the ecological flow range suitable for parent fish schooling. [Results] By simulating the weighted usable volume (WUV) of FMCC spawning schooling habitats under different outflows from the TGR, the spatial response characteristics of the schooling habitat were quantitatively evaluated. Overall, WUV first increased and then decreased as the flow of the spawning site increased. At a flow of 14 000 m3/s, WUV reached its maximum, accounting for 71.7% of the percent usable volume (PUV) of the study area. Under this flow, conditions were favorable for forming a larger, more concentrated, and well-connected schooling-suitable habitat. Under high flow conditions exceeding 22 000 m3/s, the increased flow velocity and intensified vertical velocity gradient hindered the formation of stable FMCC spawning schooling, significantly reducing the suitable habitat volume. Therefore, to promote parent fish schooling, flow should not be too high. The optimal flow range should be 10 000-20 000 m3/s, accounting for more than 64.3% of PUV, which was conducive to forming a three-dimensional habitat suitable for FMCC schooling and maintaining high ecological stability. The suitable flow velocity and depth ranges for parent fish spawning schooling in the Yichang river section were 0.9-1.4 m/s and 3.0-5.0 m, respectively. FMCC habitat suitability in the study area exhibited distinct vertical and horizontal spatial distribution patterns. At a flow of 14 000 m3/s, the average velocity in the upper layer was 1.10 m/s, while in the lower layer it was 0.75 m/s. For the upper-middle layer, flow velocity, depth, and comprehensive suitability index were 0.90, 0.91, and 0.84 respectively, whereas for the bottom layer, they were 0.89, 0.65 and 0.57. The upper-middle layer outperformed the bottom layer, particularly in terms of depth and comprehensive suitability index, indicating that the upper-middle layer provided more stable and suitable habitat conditions for FMCC. [Conclusion] Using an unstructured irregular triangular mesh, a three-dimensional hydrodynamic model of the FMCC spawning site in the Yichang river section is established. The model accuracy meets the requirements, enabling accurate simulation of the hydrodynamic characteristics of the spawning site under different flow conditions. Before spawning, parent fish tend to occupy the upper-middle layer, and their behavior is more sensitive to flow conditions. The flows of 10 000-20 000 m3/s favor parent fish schooling, with the most suitable range being 12 000-16 000 m3/s. The findings provide a scientific basis for the TGR to precisely regulate ecological water management during key life history stages, such as parent fish schooling, thereby enhancing the ecological benefits of the reservoir.