No one really knows how many of the world’s seas are being fished by commercial vessels—some scientists say nearly all of them. Researchers decided to tap the vast amount of data generated by anticollision beacons on ships—some 22 billion messages from 2012 to 2016. There were several obvious fishing hotspots—the South China Sea, and the coastal areas of Europe, East Asia, and South America. Together with activity on the high seas, they covered some 55% of the ocean surface, the researchers report today in Science.