| Vessel Monitoring System(VMS)was first proposed by the United States in the early 1990 s,can provide information on the location and activities of fishing vessels,and automatically transmit the information on the location,speed and direction of fishing vessels to the monitoring center on shore,so that the monitoring center can timely grasp and monitor the operational dynamics of fishing vessels,which has greater application potential in many fields such as fishing control,scientific research,navigation safety and maritime enforcement.Similar monitoring programmes are now used by States and various international fisheries organizations worldwide to obtain vessel data for fisheries management and control.Current VMS technology allows for more accurate monitoring of the operating status and trajectory of fishing vessels.Vessel monitoring systems can have a very positive effect in monitoring the status of fishing vessels,determining the trajectory of fishing vessels,calculating fishing effort,determining the extent of fishing grounds,calculating resource abundance,and determining the impact of fishing on marine ecology or marine species.Gillnets are one of the main fishing operations in China and occupy a relatively important position in the country's marine fishing industry.Drift gill net,also known as drift net,is the most widely used fishing gear with the largest number of gill net gear,with simple structure,easy operation,low power requirements for fishing vessels,flexible production operations,less crew required,low cost,wide range of fishing targets,high selectivity,suitable for different fishing grounds for operation.Although banned in some countries and seas,drift gillnets are still widely used in China and many third world countries,and the majority of our gillnet fishing vessels are drift gillnetters.The current VMS technology still suffers from poor data accuracy in specific areas and is not yet a substitute for traditional monitoring tools such as observers or field sampling,and most of the current research on vessel level data is focused on the application of a single area or fishing target.Due to limitations in equipment costs and data sources,as well as legal requirements,most studies have used or focused only on data from trawlers,especially large trawlers over 15 m in length,and ignored other types of fishing practices.At the same time,foreign research on the application of methods to ship position data mainly focuses on the use of interpolation to improve the accuracy of ship position data,so the existing methods are not suitable for the analysis of high time resolution Beidou satellite system ship position data.Currently,there are only a few methods of determining the fishing status of fishing vessels for the Beidou satellite,and mainly for trawlers.It is necessary to find a calculation method for other non-trawl gear,and to discern the fishing status of fishing vessels based on the Beidou vessel position data,in order to make effective use of the high-resolution vessel position data obtained from the Beidou satellite data,and to implement effective monitoring and management of vessels engaged in marine motorized operations in China.Among them,China's drift gillnet fishing vessels have a small average power,a large number of boats and a wide range of operation.If managed using traditional methods,which are costly and difficult to manage,it is particularly suitable for real-time monitoring and management using vessel position data.For this case,this paper uses data from a drift gillnet fishing vessel in Jiangsu Province for the whole year of 2016 and from 822 gillnet fishing vessels in Zhejiang Province for the whole year of 2017.The temporal resolution of the longitude and latitude ship position data transmitted by the Beidou system is 3 min,the spatial resolution is about 10 m,and the speed measurement accuracy is 0.2 m/sec.The data were comprehensively analysed and the process and characteristics of drift gillnet fishing operations were examined.This paper accomplishes the following:(1)In this paper,for the first time,a method for extracting the number of nets,as well as the length and direction of nets for drifting gillnet operation using Beidou satellite data is proposed.The method uses a combined threshold identification method to determine the status of fishing operations.The threshold values of speed,spatial distance,time interval,and change in heading are used to identify the point at which the net is closed at the time of operation,and then the point at which the net is released is determined from the beginning of the closed net status.According to the 516 nets extracted from the example,74% of the nets identified by the program are the same as those manually identified,with good consistency,high accuracy,fast processing,high real-time,and no need to use fishing log data.This method has a relatively reliable accuracy and can provide new tools for fisheries management and related research in China.(2)Using this method,in this paper,3,352 nets from 455 drift gillnet fishing vessels were obtained based on the production data of 822 gillnet fishing vessels in Zhejiang Province from January 1,2017,to December 31,2017,after data extraction.The spatial and temporal distribution of fishing behaviour in the drift gillnet fishery in Zhejiang Province was analysed.The results show that most of the drift gillnet fishing vessels are concentrated in the inshore waters,as far as 34°N to the north,located in the Lianqing Shi fishery,626 km from the home port;as far as 26°N to the south,located in the eastern Fujian fishery,309 km from the home port;and as far as 126°E to the east,located in the Jiangwai fishery,650 km from the home port.The Yangtze River Estuary Fishery,Zhoushan Fishery,Yushan Fishery,Wentai Fishery and Dasha Fishery were the main areas of operation for drift-net fishing vessels in Zhejiang Province,with fishing effort from January to April mainly distributed close to the coastline,and only a few fishing effort concentrated in more distant areas such as Dasha Fishery and Shawai Fishery.After the end of the fishing moratorium,in August,fishing effort was almost concentrated in the offshore areas of the Yangtze River Estuary,Zhoushan and Yushan fisheries,and in September-December,the overall fishing effort tended to extend out to the sea and to the south as the water temperature decreased and the resource abundance of coastal waters decreased.Fishing effort was low in January-April,peaking in August at the end of the closed season and stabilizing in September-December,but was lower in March and November relative to the size of the nets.The spatio-temporal distribution of nets and fishing effort in the fishery is a feature that has developed over time,and the production habits of fishing vessels are relatively stable because they have developed from years of experience in tracking fishery resources.Therefore,the conclusions in this paper can be considered as a relatively stable description of the production habits and characteristics of drift gillnet fishing vessels in Zhejiang Province in the absence of changes in fishing policy,which can provide some reference for fisheries management,fisheries enforcement and fisheries policy development in Zhejiang Province.(3)Subsequently,a drift gillnet vessel condition analysis system using vessel position data is designed in this paper.The system is used to automate the processing of the fishing vessel's position data,including the Beidou terminal,core server,monitoring terminal and other components,which can automatically judge the fishing status of the vessel according to the fishing vessel's operation mode,vessel length and main engine power,and can monitor,locate and alarm the fishing vessel in real time,query and display the fishing vessel data and measure the distance on the electronic chart.It is also possible to analyse historical data on vessels,track their trajectories and compare them with fishing log data.In addition,it is possible to access the vessel management system to manage the vessel's files and condition and to notify the relevant departments and units when needed for better management.The system can be applied in a number of different ways,such as calculating catch effort,analysing the behavioural patterns of fishermen at sea and studying the biological and ecological impacts of fishing in the region,or as part of a larger fisheries management and monitoring system for many different fishing practices. |
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