Spatiotemporal distribution of fishing grounds in 

the Bohai Sea and its adjacent waters based on AIS

Abstract: Automatic identification system (AIS) is a new type of navigation aid system applied to shiptoship and shiptoshore. It can monitor vessel activity in real time and plays an increasingly important role in vessel collision avoidance, vessel monitoring, and maritime management. In the past ten years, the popularization and application of AIS transmitters has made AISbased dynamic trajectory data valuable for scientific research in marine traffic management, marine fisheries management, and marine spatial planning management. With its high spatial and temporal resolution, AIS data provides a good source to reveal the characteristics of maritime traffic activities and fishing intensity. Since the introduction of AIS, significant progress has been made regarding the use of AIS data for identifying fishing behavior, quantifying fishing intensity, and assessing marine ecological stress. However, previous studies lack a description of the overall spatial and temporal distribution pattern of fishing activities in coastal sea areas, which affects the efficiency of marine fishing activity management and marine ecological protection in regional waters. The Bohai Sea and its adjacent waters is one of the important distribution areas of fishing grounds in China, with abundant fishing resources, extensive distribution of fishing ports and fishing vessels, and intensive fishing activities. Nevertheless, in recent decades, due to the impact of overfishing and landsource pollution, fishery resources have been seriously degraded. It is an urgent need to understand the distribution and level of overall fishing activity in regional waters, so as to provide decisionmaking support for marine fishing activities, marine ecological environment protection, and the restoration of marine fisheries resources. Based on AIS data from marine vessels in the Bohai Sea and its adjacent waters in 2014 and 2018, this study mapped the range of the fishing ground, and analyzed the temporal and spatial distribution characteristics of fishing grounds and their influence factors. First, the speed threshold under fishing states was determined based on the speed frequency density distribution of fishing vessels and a Gaussian mixed model. Secondly, the kernel density estimation and hot spot analysis were combined to map fishing grounds. The standard deviation ellipse method was used to calculate the spatial distribution center of fishing grounds. Then the distribution of fishing grounds for the months and quarters of 2018 and the same MMSI information for 2014 and 2018 were mapped. Finally, based on the statistical analysis and the aggregation index, the quantitative structure and spatial distribution characteristics of fishing grounds were analyzed, and the factors that caused the differences in the spatial and temporal patterns of fishing grounds were discussed. The results showed that there were significant monthly and quarterly differences in the spatial distribution of fishing grounds in the Bohai Sea and its adjacent waters. It was mainly distributed in Yanwei nearshore area and sea area near the Bohai Strait. Except for the summer fishing moratorium period from May to August, the average percentage of the sea area near the Bohai Strait and Yanwei nearshore fishing grounds in the total area of all fishing grounds each month was about 52.10%. While the scale of fishing activity in the Bohai Sea was small, it was scattered only in the coastal waters of Qinhuangdao, northern areas of Huanghua, and Laizhou Bay. The largescale fishing activities were mainly concentrated from September to December after the summer fishing moratorium, with widespread fishing grounds and marked changes in spatial morphology. Among them, the fishing grounds in September were the largest, with an area of about 15 355.29 km2. In October, fishing grounds had the highest level of clustering, and the aggregation degree index reached 37.49. Autumn was the most active season for fishing activities in the sea area, and the gathering area accounted for about 16.48% of the total study area, showing the characteristics of contiguous distribution in the sea area near the Bohai Strait. The spatial distribution center of fishing activity in summer was the most to the west, and the spatial distribution centers of fishing grounds from shifted eastward with the changes of spring, autumn and winter. Based on the AIS information statistics of the same MMSI fishing vessels, it was found that compared with 2014, the distribution of fishing grounds in 2018 changed slightly, but the spatial range of fishing grounds in 2018 was expanded and the spatial distribution was more concentrated, with the area of fishing grounds approximately 1.8 times that in 2014. Fishing grounds in the coastal waters of the Bohai Sea increased significantly. The center of spatial distribution shifted to the west. The spatial and temporal variation of fishing grounds was comprehensively affected by some factors, such as seasonal change, ecological habits of fishery organisms, the summer fishing moratorium, space regulation of fishing zones, and stock enhancement. For example, affected by the monsoon climate of medium atitudes and the Spring Festival, the distribution of fishing grounds was relatively small from January to February. As an important migratory channel for fishery organisms in the Bohai Sea and its adjacent waters, the migration fish in the sea area near the Bohai Strait and Yanwei nearshore showed obvious gathering from October to November, making largescale fishing activities in these two months possible. The summer fishing moratorium obviously limited the monthly and seasonal distribution characteristics of fishing activity, which was one of the effective measures to control the fishing activities. From the regional scale and overall perspective, the study quantitatively revealed the spatial and temporal variability characteristics of fishing activities in the Bohai Sea and its adjacent waters based on AIS data. The results can provide decisionmaking support for the regulation of fishing activities, the sustainable development of marine fishing industry, the restoration of fishery resources, and marine spatial planning management in the Bohai Sea and its adjacent waters. This study also further confirms that AIS big data has good application value in marine fishery scientific research, which can realize rapid identification and monitoring of fishing intensity and its distribution pattern in regional waters, and further expand the application research field of AIS data.

Keywords: fishing activity; fishing behavior; fishing vessel; AIS; Bohai Sea