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