This paper examines the discrepancies between national policy objectives for the development of shellfish farming in France and the results of this policy at the local level. National legislation is claimed to favour a ‘people-oriented’ policy and the sustainable use of marine coastal resources. In practice, stakeholders implement this policy under local institutional arrangements. A case study in the Mont-Saint-Michel Bay compares the economic, social and environmental performances of both mussel and oyster industries. Local management arrangements have avoided overexploitation. Conversely, performances in terms of rent distribution, job retention and contribution to public budgets are inconsistent with national objectives. This suggests that the existence of conflicting interests, information asymmetries and unequal bargaining powers was not sufficiently envisaged when the national regulation framework was drafted. However, when combined with an opaque and weakly regulated system of transferable use-rights, those factors are likely to influence local management processes and their socio-economic results.