The Baltic salmon stock Its natural and artificial regulation

Abstract

The Atlantic salmon, Salmo salar L., is represented in the Baltic area by a commercially exploited population, practically “landlocked” in this brackish-water sea. It displays long-term catch fluctuations which seem not to be matched elsewhere. The nature of these fluctuations is discussed. A survey of possible explanations is given based on present knowledge of salmon biology and of survival limiting and mortality factors. Smolt output is determined by carrying capacity of the rivers. Mathematical correlations between catch (abundance) and climatic factors exist but the causal connection between survival of smolts to adult stages and any one factor — be it food supply, predation or diseases — is obscure.

The progressing destruction of the reproduction areas of the salmon rivers due to hydro-power developments has implied — and would continue to imply — a most serious artificial regulating factor if it was not successfully counteracted by a programme for large-scale artificial recruitment of reared smolts at present maintaining about 20% of the Baltic salmon stock.