Every year, Wageningen Marine Research carries out shellfish surveys in the Dutch coastal waters (Wadden Sea, Oosterschelde, Westerschelde and Coastal Zone), investigating the distribution and size of the most important commercial shellfish species. These are mainly mussels, cockles, knife hives and Japanese oysters, but also other species with a certain importance for ecology or fishing are included. In addition, catch data from professional fishing are also collected. The data is used by the government when deciding whether or not to permit fishing.