Passage problems of Atlantic salmon in regulated rivers

River regulations affect the complex migrations of salmonids and interfere both with adult and juvenile passages at hydro-power constructions. To minimize the negative impact on fish migrations various structures are built, e.g. fish-ladders and bypasses. These constructions do on the other hand not always secure safe fish passages and might lead to a delay in the natural migration and cause increased mortality. The general problems for the adult fish is to find the appropriate upstream migration routes and for the juveniles to avoid turbine or spillway mortality during their downstream migration. This report summarizes the salmonid lifecycle and refers to various passage problems that occur for both adult and juvenile salmon in regulated rivers. Different techniques used to study fish migrations are mentioned and possible future research topics discussed. 2