EVALUATION OF INITIAL EFFECT OF THE TEN-YEAR FISHING BAN IN THE YANGTZE RIVER: RESPONSE OF STABILITY AND POPULATION STRUCTURE OF MIDDLE REACHES FISH COMMUNITIES

A ten-year fishing ban was implemented in the Yangtze River in 2021 to restore its declining fishery resources and aquatic biodiversity. To scientifically evaluate the ecological response during the early stage of the fishing ban, this study used catch data from Jingzhou, Jianli, and Huangshi sections in the middle reaches of the Yangtze River for the periods 2017 to 2019 (before the fishing ban) and 2021 to 2023 (after the fishing ban). The abundance/biomass curve (ABC curve) and W statistical value were used to analyze community stability, while systematic evaluation of population structure changes in 16 common fish species was conducted using proportional size distribution (PSD), average body length, and proportion of sexually mature individuals. The results showed that before the fishing ban (2017—2018), the community remained within the undisturbed range (W values of 0.051 and 0.093), which was actually a stress type steady state under long-term fishing pressure. In 2019, the W value dropped to 0.017, signaling moderate interference. The comprehensive fishing ban in 2021 triggered a population release response, with W values turning negative (-0.027) but still falling within the moderate disturbance range. At the community level, the number of small fish species (eg: Hemiculter bleekeri) surged, while PSD values and average body length increased significantly for certain species (eg: Siniperca chuatsi and Saurogobio dabryi), revealing asynchronous ecological processes during the early recovery stages. The abnormal increase in the W value to 0.098 in 2022 was mainly attributed to the impact of extreme drought on small fish populations, rather than a linear continuation of the fishing ban effect. By 2023, the W value declined again to 0.036, signaling a return to the true recovery trajectory. Regarding population structure, the average body length of 8 fish species increased significantly (2.4%—91.0%, P<0.05), while PSD values for S. chuatsi, S. dabryi, and Hemiculter leucisculus rose markedly (14-70, P<0.05). The proportion of sexually mature individuals in 10 fish species also increased significantly (2.6%—56.4%, P<0.05). The number of healthy species (50≤PSD<80) increased from 3 before the fishing ban to 4 after, while the number of structurally unstable species (PSD<50) decreased from 5 to 2. However, the average body length of Parabramis pekinensis, Megalobrama amblycephala, and Xenocypris argentea significantly decreased (2.8%—44.5%, P<0.05), and the proportion of sexual maturity in S. dabryi, H. leucisculus, and M. amblycephala decreased significantly (1.0%—52.9%, P<0.05), indicating species specificity of recovery. Research demonstrates that the ten-year fishing ban has initially shown positive effects in the Yangtze River, but its ecological response is a complex process of policy driven and hydrological interference. It is recommended to establish a comprehensive evaluation system with multiple indicators, supplemented by habitat restoration and other management measures, to promote the restoration of slowly recovering species populations.