Exploring Nighttime Fishing and Its Impact Factors in the Northwestern South China Sea for Sustainable Fisheries

The South China Sea (SCS) is an important region of fishery resources. However, its fishery resources have been threatened, mainly because of overfishing. In this study, we explored the distribution of night-time fishing boats and analyzed the relationship between fishing activities and marine environmental factors in the northwestern SCS (NWSCS). Firstly, the spatiotemporal variations in nighttime fishing boats in each month of 2021 in the NWSCS were studied. Meanwhile, a fishery activity center index was used to analyze the overall fishery activity trend in the NWSCS. Finally, the spatiotemporal distribution patterns of corresponding environmental factors (i.e., Chl-a, SSS, SST, latitude, longitude) were analyzed, and the nonlinear relationship between environmental factors and fishery activities was quantitatively studied using the generalized additive model. The results showed that fishery activities were mainly distributed in the waters of Beibu Gulf and the southwest of Hainan Island. Meanwhile, there were obvious seasonal differences (i.e., trimodal distribution) in the intensity of fishery activities in the NWSCS. Chl-a was the most important impact factor with a contribution of 21.7%, followed by SSS, longitude, SST, and latitude, with contributions of 12.8%, 9.4%, 4.2%, and 0.5%, respectively. Fishery activities in the NWSCS were mainly distributed in the area with Chl-a of 0~0.35 mg/m3, SST of 21.2~26.4 °C, and SSS of 32.9~33.8 Practical Salinity Unit. This study reveals that more efforts are required to prevent IUU fishing activities for the sustainable development of marine ecosystems in the NWSCS. It is also necessary to improve remote sensing technology to support making sustainable fishing plans.