The VIIRS satellite sensor can identify bright lights at night. This is the same sensor that is used to make the maps of lights at night of the world that you may have seen. In the dark ocean, vessels using bright lights stand out to this sensor and can be tracked. Some forms of fishing, such as squid jigging, use bright lights at night and squid fleets can be easily seen in the VIIRS data. The VIIRS data on the map is a map of likely vessels – both fishing and otherwise – detected by VIIRS.
A few caveats, though, are necessary for understanding these detections. One is that not all are actually fishing vessels – some may be other large vessels. Another caveat is that many vessels fish without lights, or with dim lights and would not show up in this dataset. Finally, there are “false positives” – places where the algorithm detects a light, but which result from errors or noise. There are also some cases of the algorithm picking up airplanes on international flights, although these are rare.
Nonetheless, the VIIRS data shows some clear fishing patterns that are not visible in the AIS data. The VIIRS shows high seas, industrial squid fleets and many of these vessels are broadcasting AIS. The night lights data also show lots of fishing activity around Indonesia and some of our research partners have matched many of these lights to vessels broadcasting VMS. Finally, the data also shows intense activity throughout southeast and east Asia, revealing fishing activity in a region that has poor AIS data.