Dynamic monitoring and analysis of number of fishing vessel voyages in Hainan Province based on Beidou position data

China's offshore fishing vessel monitoring system which is based on the Beidou satellite navigation system (contains position, time, speed, navigation and other information) plays an important role in the management and rescue of fishing vessels. In this paper, the sea and land boundary was divided into a number of 0.1°×0.1° port grids. According to the relationship between the grids and the tracks of fishing vessel, we have determined the total number of voyages of fishing vessel in Hainan Province in 2016. Hainan fishing vessels are mainly small ones and 1–5 day voyages accounted for 71.8% of the total number of voyages (average voyage time of each fishing type is about 5 d). Since moratorium, holidays, typhoons and other factors affect the number of voyages, the frequency of voyage in each month had three peaks and three valleys. The three Hainan return ports in Danzhou, Sanya and Wenchang accounted for 62.9% of the total number of voyages. The voyages departed from Hainan but not returned to Hainan are mainly in Beihai, Yangjiang, Huizhou and other ports. The extraction method of number of fishing vessel voyages based on Beidou position data is universal, which can be directly applied to the fishing vessels installing Beidou terminal in other provinces near the offshore.