Predation on migrating smolt as a regulating factor in Baltic salmon, Salmo salar L., populations

The results of three investigations, two with wild smolt and one with hatchery‐reared smolt of altic salmon, were analysed with regard to mortality due to predation during river and estuarine migration. This mortality was found to be high, at least 50% of the initial number of smolt was estimated not to reach marine waters. Smolt mortality may be important in population regulation, analoguous to other animal species having the same life strategy with two life stages and a transfer to a new habitat connected to the shift in life stage.