Samenvatting

Worldwide, fish species are the most threatened taxa among freshwater vertebrates and have declined by 76% over the past 40 years. Anthropogenic activities such as the construction of dykes and dams are the main cause of this. These obstacles are very important for contemporary society, but they pose significant problems for the dynamics of aquatic systems. Especially for diadromous fish species such as the three-spined stickleback and eel. In Europe, the population of diadromous fish has declined by 95%. Therefore, the European Union has set up targets to combat fragmentation and to improve the fish population.