A long tradition of research has proven that common property resources may be protected by a ‘firewall’ of regulations. Open access resources, however, seem to be doomed for certain due to their lack of institutions. What happens in between? Can resources be handled in a sustainable manner if a user community maintains cultural institutions which influence only the resource distribution while at the same time access to the resource itself is not restricted? An island community in the Ha‘apai-Group of Tonga has been chosen to illustrate the principle. In Tonga, unlike other Pacific countries, everybody has free access to all marine resources. With a gradual transition from subsistence to more commercial fishery, non cooperative strategies of resource use are generally arising now as opportunities to sell fish redirect aims towards gain-maximizing. Thus, on the one hand, such non-cooperative strategies are expected to culminate in resource depletion. On the other hand, cooperation (fetokoni‘aki) has always been a highly cherished value in the traditional culture, and the institution of foodsharing has been particularly strong among community members (including fishermen) due to a tight social net. Therefore, villages still can be found where the cultural institution of foodsharing enhances cooperativeness and sustainable resource use. The case study took place in Lofanga. Although they have the same opportunities and economic incentives as the commercial fishermen in neighboring ‘Uiha, the vast majority of fishermen in Lofanga still harvests on a subsistence basis. The few commercial fishermen hold special positions within the village structure as well as within the social net and try to maintain or improve their position by complying with the sharing rule to an above average degree. Giving all their neighbors access to their yield legitimizes their efforts while at the same time it reduces the efforts of other community members. Nevertheless, these open access resources are threatened by commercial fishermen from neighboring islands. Some of these have even started to over-exploit their own resources and to compete with other villages for their fishing grounds. It seems plausible that in order to enable traditional institutions in Tonga to work more efficiently, the open access nature of marine resources should be changed to community-based management.