EVALUATION OF FISHING BAN EFFECT IN THE CHISHUI RIVER BASED ON BODY LENGTH STRUCTURE ANALYSIS

The prohibition on fishing in the Chishui River, implemented in 2017, serves as a pioneering demonstration zone for the 10-year fishing ban in the Yangtze River. To assess the effectiveness of the fishing ban in the Chishui River, we analyzed the average body length, proportional size distribution (PSD), and changes in the proportion of sexually mature individuals for 20 major fish species over the first five years before the ban (2012—2016) and the subsequent five years after the ban (2017—2021). The results showed that after five years of the fishing ban, there was a preliminary alleviation of the downsizing trend in the individuals of major species, characterized by an increase in the proportion of larger individuals and sexually mature individuals, thereby optimizing the population structure. Specifically, the average body length of 16 fish species increased by 1.7% to 104.5% (P<0.05); PSD values for the populations increased by 1 to 57 (P<0.05); and the proportion of sexually mature individuals increased by 1.0% to 81.4% for 13 fish species. However, consistent performance across all species was not observed. Two fish species showed no significant changes in average body length and PSD values, while two fish species experienced a decrease of 2.4% to 6.2% in average body length (P<0.05) and a decrease of 3 to 15 in PSD values (P<0.05). The proportion of sexually mature individuals decreased by 0.8% to 18.1% for seven fish species. Following the commencement of the fishing ban, variations in body length structures were observed among different species, although the population structure of some of the major fish species had been effectively improved, the full recovery of fish species in the Chishui River had not yet been realized. While promoting the recovery of some fish resources, the fishing ban also changed the structure of the fish community and contributed to the dynamic adjustment of the entire aquatic ecosystem. Consequently, we recommend the continuation of the fishing ban in the Chishui River, along with long-term, continuous, and targeted monitoring and research. Such efforts are crucial for achieving the effective recovery of fishery resources in the Chishui River and enhancing ecosystem service functions. Furthermore, this study provides a reliable theoretical and technical foundation for evaluating the 10-year ban on fishing in the Yangtze River and guiding future resource management and ecological conservation.