Abstract:To determine the distribution of fish resources in the Hongchaojiang Reservoir and its correlation with environmental factors, the fish resources available in the Hongchaojiang Reservoir were evaluated in April 2018 using an echo detector (EY60, 200 kHz). According to the results, there was no significant difference in fish density between day and night in the Hongchaojiang Reservoir (P>0.05); however, the mean target strength was greater in the daytime than in the nighttime (P<0.05). The mean target strength in the day and at night was (–43.30±0.32) dB and (–44.50±0.26) dB, respectively, because small fish between –60 dB and –54 dB (–60 to –57 dB and –57 to –54 dB increased by 9.25% and 4.76%, respectively) increased during nighttime, while fish between –54 and –48 dB increased during the daytime (–54 to –51 dB and –51 to –48 dB increased by 7.42% and 5.27%, respectively). Fish distribution in the Hongchaojiang Reservoir displayed significant spatial variation (P<0.05). Fish density was characterized by higher density upstream than downstream, and higher density in the Reservoir branch than in the Reservoir center. Average fish density was 109.52 ind./1000 m3 and the maximum density was observed in the upstream S3 site, with a density of 330.21 ind./1000 m3, while the minimum density was observed in the downstream S8 site, with a density of 21.50 ind./1000 m3. Correlation analysis revealed that fish density distribution was positively correlated with total phosphorus (TP), permanganate index (CODMn), and chlorophyll a, and negatively correlated with water depth (P<0.05). Fish target strength exhibited a significant negative correlation with water temperature, turbidity, TP and CODMn (P<0.05). The results suggest that abiotic factors such as chlorophyll a and TP drive the spatial distribution of fish in the Hongchaojiang Reservoir. In addition, the results also reflect the influence of biological factors (fish bait, escape from predators, etc.) on fish distribution. The results of the study provide insights that could enhance our understanding of the distribution of fishery resources in the Hongchaojiang Reservoir.
