Every broadcast AIS and VMS position that we receive from a fishing vessel is classified by the Global Fishing Watch fishing detection algorithm as either likely fishing or non-fishing. This classification takes into account the vessels movement in the days before and after the broadcast position as well as other information we have on the vessel. Total fishing hours for all vessels on the selected time period are then determined based on assigning an amount of time to each AIS or VMS point calculated from the time between each position broadcast. Because data from AIS is not evenly spaced in time, the amount of time assigned to each AIS point varies.
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