Northern Prawn Fishery Fishing Effort Estimated from VMS Data

The dataset comprises GIS grids of fishing effort of the Northern Prawn Fishery (NPF) estimated from vessel monitoring system (VMS) data. The VMS is operated by the Australian Fisheries Management Authority (AFMA). It periodically records the location of each vessel in the fishery. Note that the activity of the vessel at the time is not recorded. The system's primary purpose is to monitor compliance with fishing regulations, but the data can also be used for research. To estimate fishing effort from the VMS records, we estimated the track of each fishing vessel by joining successive vessel locations with lines. We divided the track into apparent trawling and non-trawling sections (e.g. based on date, time and vessel speed), and calculated the time each trawling section spent in each cell of a GIS grid covering the managed area of the fishery. This method for estimating fishing effort from VMS data has limitations. Because a vessel may have taken a path other than a straight line between the polls, our straight line path (a) may only partially match the real path of the vessel, (b) may underestimate the length of the path traversed by the vessel, and (c) may underestimate the speed of the vessel. Note that (a) and (b) would affect which particular grid cells the trawling time was allocated to, but not the total trawling time that was added to the grid. The use of vessel speed to filter out non-trawling activity is imperfect because vessels may carry out other activities at speeds less than the maximum trawling speed.

本数据集包含基于船舶监控系统（VMS）数据估算得到的北方虾类渔业（NPF）捕捞努力量地理信息系统（GIS）网格。该船舶监控系统由澳大利亚渔业管理局（AFMA）运营，会定期记录该渔业内每艘作业船舶的位置。请注意，系统并未同步记录船舶彼时的作业活动类型。该系统的核心初衷为监控渔业合规情况，但相关数据亦可用于科研用途。为基于船舶监控系统记录估算捕捞努力量，研究团队通过直线连接连续采集的船舶位置，还原每艘捕捞船舶的航行轨迹；随后依据日期、时间及船舶航速等信息，将轨迹划分为疑似拖网与非拖网作业区段，并统计每个拖网区段在覆盖该渔业管控海域的地理信息系统网格各单元格内的停留时长。此种基于船舶监控系统数据估算捕捞努力量的方法存在一定局限：由于船舶在相邻记录点位之间未必沿直线航行，因此（a）我们还原的直线轨迹仅能部分匹配船舶实际航行路径；（b）该方法可能低估船舶实际航行总航程；（c）亦可能低估船舶实际航速。请注意，（a）与（b）类局限仅会影响拖网作业时长的网格单元格分配结果，不会改变计入网格的总拖网作业时长。以船舶航速筛选非拖网作业的方式存在缺陷，因为船舶可能以低于最大拖网航速的状态开展其他作业活动。