Acoustic study of fish resources in Xiangjiaba Reservoir in the lower reaches of Jinsha River during the early period of ten-year fishing ban

The Yangtze River is the longest river in China, with the richest fish resources in inland China. With the rapid economic development of the Yangtze River basin in recent decades, the intensity of human activities has been increasing, and the fish resources in the Yangtze River basin have declined sharply. To protect the ecological environment in the Yangtze River Basin, the Ministry of Agriculture and Rural Affairs has decided to ban fishing in key waters for 10 years. In order to scientifically evaluate the preliminary implementation effect of the ten year fishing ban policy in the reservoir at the lower reaches of the Jinsha River, the catch and hydroacoustic survey were carried out in Xiangjiaba Reservoir at the lower reaches of the Jinsha River in November 2020 and May 2022, and the changes of fish resources were analyzed. The results of catch survey showed that 9 species of fish belonging to 2 families were collected in November 2020, among which Hemiculter leucisculus and Pelteobagrus vachelli were dominant; In May 2022, 14 species of fish were found in 5 families, with Saurogobio dabryi and Pelteobagrus vachelli predominating. The results of hydroacoustic survey showed that there were significant differences in the distribution of fish target strength among different years, different regions and different water layers. The fish density in May 2022 (0.60 ind./1 000 m³) was higher than that in November 2020 (0.46 ind./1 000 m³). The spatial and temporal distribution of fish resources was not uniform. There were some differences in the densely populated areas of fish in different survey periods. In November 2020, there was no significant difference among most areas, while in May 2022, there was a significant difference. The density of upper layer fish in May 2022 (0.44±0.83 ind./1 000 m³) was significantly higher than that in November 2020 (0.06±0.15 ind./1 000 m³). The distribution of fish in different water layers was significantly different, and the lower layer density was higher than the middle and upper layers. The estimated fish resources in Xiangjiaba Reservoir were 3.22×10⁶ ind. (2020) and 3.53×10⁶ ind. (2022), respectively. The method of hydroacoustic survey is suitable for the monitoring of fish resources after the total fishing ban. In general, the method of hydroacoustic survey is suitable for the monitoring of fish resources in the reservoirs at the lower reaches of Jinsha River, and fish resources in Xiangjiaba Reservoir area have been recovered to some extent after the implementation of the ten-year fishing ban.