Benthic Habitats and the Effects of Fishing

Symposium Abstract: Fishing for Shellfish in an Internationally Important Nature Reserve: Do Current Policies Achieve Their Objectives?

B. J. Ens, A. C. Smaal, and J. De Vlas


The Dutch Wadden Sea is a nature reserve of international significance. Fishing for shellfish is allowed as long these activities do not cause significant harm to the natural values of the area. In 1993 this objective was implemented in a new shellfishing policy via two management policies: closed areas and food reservation. Thus, 26% of the intertidal mudflats are permanently closed for fishery to restore important habitats, particularly intertidal mussel beds and seagrass beds. To prevent food shortages for shellfish eating birds, mainly oystercatchers and eider ducks, caused by shellfish fishery, fishing for shellfish is not allowed when shellfish stocks are below a threshold value. In 2003, this new shellfishing policy must be evaluated. To this end, a major research program was initiated. It includes testing the hypothesis that mechanised fishing for cockles has long-term negative effects on the recruitment of cockles and other bivalves mediated by a loss of fine sediments. It also includes detailed investigations whether declining numbers of oystercatchers and recent high mortality among eider ducks can be related to food shortages and if so, whether these food shortages are linked to the current shellfishing practices. While the program relies heavily on massive long-term monitoring of shellfish stocks, shellfish fishery (including continuous registration of all fishing activities), benthic habitats and bird numbers in combination with mathematical modelling, some field experiments are also conducted. Most notable is an experimental test of the hypothesis put forward by the fishermen that fishing on mussel seedbeds helps to stabilise these beds. Preliminary results of the project will be discussed.