Analysis of the Spawning Response Characteristics of Four Major Chinese Carps to Eco-Hydrological Processes in the Three Gorges Reservoir

The middle reaches of the Yangtze River are a crucial breeding habitat for four major Chinese carps. The ecohydrological characteristics of their spawning grounds are crucial factors influencing spawning for these species: black carp (Mylopharyngodon piceus), grass carp (Ctenopharyngodon idella), silver carp (Hypophthalmichthys molitrix), and bighead carp (Aristichthys nobilis). To investigate the impact of ecohydrological processes within the Three Gorges Reservoir on spawning, this study focused on the spawning grounds of the four major Chinese carps in the Yichang–Yidu section of the Yangtze River. By identifying key ecohydrological indicators and leveraging hydrological and spawning monitoring data from 2013 to 2024, the response characteristics of the four major Chinese carps’ spawning to these hydrological processes were analyzed. The results showed that the key ecohydrological indicators currently stimulating spawning for the four major Chinese carps are the fish-perceived daily flow rate increase, the fish-perceived cumulative flow rate increase, and the daily flow rate increase. These three indicators are significantly positively correlated with the scale of spawning for the four major Chinese carps. The thresholds for spawning at least 20% of the annual spawning total are: a perceived daily flow increase (Pda) of 4.52–36.05%; a perceived cumulative flow increase (Pcu) of 36.15–180.23%; and a daily flow increase (Qav) of 588–2825 m3/s. The optimal water temperature for the reproduction of the four major Chinese carps is 21–23 °C. Overall, since the Three Gorges Reservoir’s normal operation, the frequency and scale of spawning for the four major Chinese carps have been highest during periods of rising water. It is recommended that, within the corresponding thresholds, ecological operation be conducted twice a year, once in mid-June and once in early July or late June. Daily flow increases can be controlled within the range of 588–2000 m3/s. This study analyzed the correlation between eco-hydrological indicators and the stimulation of spawning of the four major Chinese carps, providing optimized flow ranges and habitat conditions for ecological operation, which is conducive to promoting the reproduction and spawning of the four major Chinese carps in the Yichang–Yidu spawning grounds in the middle reaches of the Yangtze River.