Fish community structure and environmental impact factors in Three Gorges Reservoir during summer and autumn

The Three Gorges Reservoir (TGR) is a critical area for fish biodiversity conservation in the Yangtze River due to its rich fish resources. However, significant changes in fish communities have occurred following the impoundment and increasing human activities in the TGR area. Thus, based on the surveys conducted in summer and autumn of 2018, we analyzed the dominant species composition, distribution patterns, and environmental relationships of fish species in four sections of the TGR, namely Mudong, Fuling, Yunyang, and Wushan section, so as to provide a scientific basis for the subsequent assessment of the effectiveness of the fishing ban. A total of 94 fish species from 9 orders and 21 families had been recorded, including 13 exotic species and 15 species endemic to the upper Yangtze River. The results reveal significant spatial differences in fish community structures across the four sections (p<0.05), while seasonal differences were not significant (p<0.05). Dominant species results indicate a trend towards smaller-sized fish communities. The abundance-biomass comparison curves show that the W values for Mudong, Yunyang, and Wushan were −0.022, −0.078, and −0.225, respectively, indicating varying levels of disturbance, whereas Fuling had a W value of 0.040, suggesting a relatively stable community structure in this section. Kendall's Tau correlation and redundancy analysis demonstrate that the abundance of Saurogobio dabryi and Rhinogobio cylindricus increased with distance from the Three Gorges Dam and shallower water depths, while Pelteobagrus nitidus, Culter alburnus, and Coilia brachygnathus were more abundant closer to the Three Gorges Dam and in deeper water. Hemiculter bleekeri showed a significant negative correlation with water transparency, while Pseudobrama simoni was positively correlated with water temperature and chlorophyll a concentration.