Marine fisheries provide around 20% of animal protein consumed by man worldwide, but ineffectivemanagement can lead to commercial extinction of exploited stocks. Fisheries that overlap nationally controlled and highseas waters cause particular problems, as few management data are available for the high seas. The Argentinean shortfinnedsquid, Illex argentinus, exemplifies such a “straddling stock”. Here we demonstrate that light emitted by fishingvessels to attract squid can be detected via remote-sensing. Unlike conventional fisheries data, which are restricted bypolitical boundaries, satellite imagery can provide a synoptic view of fishing activity in both regulated and unregulatedareas. By using known levels of fishing effort in Falkland Islands waters to calibrate the images, we are able toestimate effort levels on the high seas, providing a more comprehensive analysis of the overall impact of fishing on thestock. This innovative tool for quantifying fishing activity across management boundaries has wide-ranging applicationsto squid fisheries worldwide.