Small-island countries accidentally subsidize foreign fishing fleets. We show how these subsidies can be measured from space, and we propose a strategy for recovering some of the lost value. The waters of small-island countries tend to have less fishing pressure and healthier fish populations than nearby high seas. As a result, fish flow across the territorial boundaries, and foreign fishing effort concentrates near these boundaries, to benefit from the fish spillover. This spillover is effectively a subsidy to foreign fishing fleets from the small-island countries, at a cost to their domestic fish populations. We show that small-island countries can recover some of these losses, with minimal impact on their fish populations, by leasing a small amount of fishing rights within their waters to foreign vessels. We also show how simple proportional measures of current foreign fishing effort near the territorial boundary—obtainable globally from new satellite data—can be used to project the economic potential and ecological tradeoffs of such a leasing policy.