SPATIAL-TEMPORAL DISTRIBUTION CHARACTERISTICS OF FISH RESOURCES IN YICHANG-CHENGLINGJI RIVER SECTION OF THE YANGTZE RIVER IN THE EARLY PERIOD OF FISHING BAN

In this study, we investigated fish resources in the Yichang to Chenglingji reach of the middle Yangtze River using the SIMARD EY60 echo detector in July 2022 (during the high-water season) and January 2023 (during the low-water season). Additionally, we integrated the results of net fishing surveys to assess the spatial and temporal distribution characteristics of fish resources in this reach during the initial ten-year fishing ban period. The results revealed that during the wet season and dry season of the fishing ban period, fish densities were 128.69 ind./1000 m³ and 38.43 ind./1000 m³, with mean target strengths (TS) of –57.54 and –60.18 dB, and mean fish lengths of 5.22 and 3.85 cm, respectively. Significant differences in fish density and TS values were observed between the two seasons. Horizontally, fish distribution was uneven, with higher fish densities observed in meandering and winding sections compared to straight river segments. The sections with the highest fish densities during both surveys were found in the Gongan to Shishou and Zhijiang to Jingzhou reaches. Vertically, fish densities showed a pattern of bottom layer > middle layer > surface layer, and significant differences were observed in fish densities among these layers during both seasons. Combining net fishing data and historical survey data from previous years, fish resources in the Yichang to Chenglingji reach were dominated by Cyprinidae and Bagridae, while there was some recovery of fish resources during the initial fishing ban period, small individual fish still dominated. The spatial and temporal distribution of fish resources in the middle Yangtze River was correlated with factors such as habitat preferences and aquatic ecological conditions. These findings provide valuable data support for future evaluations of the effectiveness of the fishing ban.