Apparent fishing effort
Global Fishing Watch analyzes AIS data collected from vessels that our research has identified as known or possible commercial fishing vessels, and applies a fishing detection algorithm to determine “apparent fishing activity” based on changes in vessel speed and direction. The algorithm classifies each AIS broadcast data point for these vessels as either apparently fishing or not fishing and shows the fishing on the Global Fishing Watch apparent fishing effort heat map.
Fishing events use those data points as input and summarize them into one event for easier analysis. Fishing events are defined using the following restrictions:
- Consecutive positions identified as fishing are grouped together
- Fishing positions which appear consecutively, but are 10 km apart or more than 2 hours apart are separated.
- Fishing events within 1 hour and 2 km of another fishing event but that may have intermittent transit points are grouped together.
Finally, the dataset is restricted by removing fishing events that are brief and fast, and thus possibly less likely to indicate a realistic fishing event. The following short fishing events are removed:
- Events less than 20 minutes;
- Events comprised of 5 or fewer positions;
- Events that cover distance of less than 0.5 km (for all gears except estimated squid gear);
- Events that cover distance of less than 50m (for estimated squid gear) in distance; and
- Abnormally fast moving vessel events with an average vessel speed of 10 knots per hour or greater.