The cockle Cerastoderma edule has been collected by traditional fishing methods for many decades in the Bay of Saint-Brieuc, a 2 900 ha tidal bay, without any evaluation or management of this resource. Since 2001, the National Natural Reserve of the bay of Saint-Brieuc has carried out an annual assessment of the stock and a mapping of the cockle fishing grounds. The assessment takes place between the end of July and mid-August on a regular sampling network of 131 stations 500m apart and covering the whole of the 2900 ha inter-tidal foreshore. Cockles are harvested for each station within a square of 0,25m² and measured in laboratory. This led to the development of a predictive model on the fishing grounds production using the growth stages of each individual and the biomass. The model provides benefits for managers, in particular: * A mid-term prediction (1 to 2 years) of the fishable part of the cockle fishing ground. This allows requests from institutional organizations to be answered , who meet every year with professionals and scientists to rule on the next fishing season * A means to assess quickly the impact of any change to the minimum legal fishing size on the fishable part of the cockle fishing ground * A means to estimate the potential impact of a managment project which could interfere with the way of the fishing ground functions This approach can be easily transfered to other co-managment shemes of Cockle fishing grounds.