Rocch, the french "mussel watch", provides regulatory data for shellfish area quality management. Once a year, molluscs (mainly mussels and oysters) were sampled at fixed periods (currently mid-February, with a tolerance of one tide before and after the target date) on 70 to 80  monitoring stations in areas used as bivalve molluscs production. For each monitoring station, molluscs are collected in wild beds or facilities, ensuring a minimum stay of 6 months on-site before sampling. The individuals selected are adults of a single species and uniform size (30 to 60 mm long for mussels, 2 to 3 years old for oysters, and commercial size for other species). A minimum of 50 mussels (and other species of similar size) or 10 oysters is required to constitute a representative pooled sample. Lead, mercury, cadmium, PAHs, PCBs, dioxins and, since 2023, regulated PFASs are analysed in molluscs tissues.