Estuaries and coastal areas are subject to anthropogenic activities, as the largest harbours and economic activities are located along river banks and close to shore. Known to have a high habitat diversity, estuaries and coastal areas play a key role in the life cycle of many organisms, including diadromous fish. As such, these areas can serve as transport routes, foraging or nursery areas. In order to conserve these areas in a cost-efficient and sustainable way, a better understanding of the ecosystem functions and services is needed. The Western Scheldt estuary and adjacent coastal area of Belgium are an important migration route and resident area for diadromous. We selected the European eel (Anguilla anguilla) as an economic important indicator species for diadromous fish species, to assess the importance of estuarine and coastal areas as a key habitat for this species. The results of this study will be useful for management measures for the conservation and restoration of the eel population.