Study on diurnal and nocturnal variation of fish resources in marine ranching by fixed-point monitoring based on acoustic technology

To thoroughly evaluate the effectiveness of artificial reefs in marine ranching, and to promote the sustainable use and effective management of marine resources, we conducted the fixed-point acoustic monitoring of fish resources by using a split-beam scientific echosounder (Simrad EK80) in two research areas: the artificial reef area of Zhuhai Dazhizhou Marine Ranch in July 2023 and the artificial reef area of the southern Beihai Yintan Marine Ranch in December 2023. The study systematically analyzed the distribution of target strength (TS), diurnal variations in the nautical area scattering coefficient (NASC), and current conditions within the monitored marine areas. The results show that in the Beihai artificial reef area, the TS of fish resources ranged from −51.9 to −31.0 dB, with an average of −44.8 dB. In the Zhuhai Dazhizhou Marine Ranch, the TS of fish resources ranged from −51.7 to −25.5 dB, with an average of −45.4 dB. Diurnal monitoring data indicate that the TS variation range and average values of fish resources in the artificial reef areas were generally better than those in the control areas, with fish resources primarily distributed at depths greater than 5 meters, more abundant in the artificial reef areas. In the Beihai artificial reef area, the correlation coefficient between the bottom NASC and current speed was 0.416 74, indicating a significant positive correlation between them (p<0.05). The results demonstrate the diurnal and nocturnal variation patterns in the fishery resources of marine ranching, further enrich the research methodology for monitoring the fishery resources of marine ranching, and provide a reference basis for the dynamic management of the fishery resources of marine ranching.