Eems vissen in Beeld

Over a million of barriers, e.g. dams or weirs, are present in european waterways that physically obstruct migratory fish species to migrate between vital habitats to fulfill their life cycle. An ongoing effort to remove or bypass such barriers to restore longitudinal connectivity is taking place to restore the physical connectivity. Nevertheless, there is little knowledge on less visible barriers that may not be as obvious as physical structures. In a small lowland stream system that is freed from all physical barriers from sea to source, the Westerwoldse Aa (The Netherlands), we study migratory fish species on how the species recolonize the restored parts, as well as aim to identify whether any remaining barriers to fish migration exist. To evaluate the efficacy of nature restoration and enhancement efforts, the entire stream basin is evaluated in perspective to the worst ecological state the system was at before the restoration efforts were implemented. In addition, fish populations, as well as individuals are studied through a strategic sampling design throughout the whole stream basin as well as PIT tagging of individual fish. Also, the size and quality of habitat patches along the entire gradient is mapped which will provide insight to types of habitat that are used by the migratory fish species.