Atlantic salmon abundance and size track climate regimes in the Baltic Sea

Atmospheric variations on multi-decadal time scales, or climate regimes, can cause significant alterations throughout the physical environment, often with remarkable consequences for animal populations and ecosystems. Here we report that the climate regimes in the Baltic Sea area, which are based on the North Atlantic Oscillation and two more regional oceanographic variables, account for the observed dynamics of Atlantic salmon abundance and size in the sea. The changes in the salmon abundance and size followed changes in the climate regimes in the Baltic Sea area, indicating that high amplitude shifts in the Atlantic salmon performance are closely associated with longer-term patterns in the climate. During maritime, temperate regimes salmon were larger in size but low in abundance, with contrasting characteristics during continental, cold climate regimes. Therefore, Atlantic salmon seem to provide a very sensitive indicator of the biological effects of climateforced changes in the aquatic environment.