Different Adaptation Strategies of Atlantic Salmon (Salmo salar) Populations to Extreme Climates with Special Reference to some Cold Norwegian Rivers

Some of the salmon rivers on the western and northern coasts of Norway are very cold, and the sea temperature outside these rivers is almost always higher than that in the river. Growth rates of Atlantic salmon (Salmo salar) parr and smolt ages and sizes have been examined in three such cold rivers. We found indications that the lower temperature limit for growth of Atlantic salmon is not a fixed temperature, but varies from population to population according to the temperature regime of their environment. Smolts are small, with average sizes of 12–13 cm total length. Females dominated in number among the smolts, but the dominance was less pronounced than in most other rivers. Strategies used by Norwegian salmon in cold rivers are therefore different from those employed by salmon in the northern extremes of the salmon's range in Canada.