Global Fishing Watch launched in 2016 as a way to track fishing boats around the world. The core data comes from boats’ automatic identification system (AIS), a GPS system that pings out its location every 30 seconds to satellites. Most large boats around the world (not just fishing boats) are required to have AIS onboard for monitoring purposes and safety. Global Fishing Watch collects AIS data on all boats around the world to “determine the type of ship (e.g., cargo, tug, sail, fishing), its size, what kind of fishing gear (e.g. longline, purse seine, trawl) it’s using, and where and when it’s fishing based on its movement patterns.” It is an impressive way to collect fishing data and shows some promise for curbing illegal fishing. You can read more about it here.

One of the first major publications to come out of these AIS data attempted to map the ‘global footprint’ of fishing. It concluded that 55% of the global ocean was fished. However a recent paper, using the exact same data, concluded that only 4% of the global ocean is fished. An order of magnitude difference! What is going on here?