Overfishing is increasingly threatening the world's marine ecosystems (1, 2). The search for the social causes of this crisis has often focused on inappropriate approaches to governance and lack of incentives for conservation (3, 4). Little attention, however, has been paid to the critical impact of sequential exploitation: the spatially expanding depletion of harvested species (5). The economist Mancur Olson (6) argued that local governance creates a vested interest in the maintenance of local resources, whereas the ability of mobile agents--roving bandits in Olson's terminology--to move on to other, unprotected resources severs local feedback and the incentive to build conserving institutions. Distant water fleets and mobile traders can operate like roving bandits (7), because global markets often fail to generate the self-interest that arises from attachment to place.