The article raises the question of the political management of the pressures generated by the dynamics of local development on the resources of the island territories of the Iroise Sea, the island of Ouessant, the Molène archipelago and the island of Sein. A field survey consisted in 55 semi-directive interviews with three audiences: activity promoters, elected officials and managers; 254 questionnaires, 116 of which were from inhabitants and 138 from tourists, provided quantitative information on the mobilization of territorial resources. For the most part, these come from the sea. They are of course fishery resources, but also landscape resources, and even more generally geographical resources, in the sense that island life, as a living environment, constitutes a factor of attractiveness, at least the driving force behind the creation of identity and, indeed, society. The resources required today in the context of local development are natural, social, spatial and financial resources. The pressures that are exerted on the territory are expressed in two main forms: the secondarization of the habitat and the availability of land in general, on the one hand; and competition over fishery resources, on the other. The key element identified on the territory concerning the political management of these resources is a difficulty of communalization, the organization of the actors with the aim of managing the resources collectively. The marine conservation organizations do not currently seem to be able to significantly influence the management of resources, but they represent a tool, possibly an under-exploited territorial resource, in favor of this process of communalization.