Atlantic Salmon and Acidification in Southern Norway: A Disaster in the 20th Century, but a Hope for the Future?

Due to acidification, 18 Norwegian stocks of Atlantic salmon are extinct and an additional 8 are threatened. In the two southernmost counties, salmon is eradicated. Due to the high acid sensitivity, production of salmon was greatly reduced as early as 1920, several decades before acid rain was recognized as an environmental problem. International agreements on reduced atmospheric emissions will reduce acidification effects in Norway substantially during the coming 20 to 50 years. However, the extreme acid sensitivity of salmon makes the destiny of this species in Southern Norway uncertain. Liming is an effective measure to protect and restore fish populations in acidified waters. Liming of acidified salmon rivers has become important in Norway in recent years which in combination with reduced emissions will be an important contribution to protection of the Atlantic salmon species. In this paper we give an overview of the effects of acidification on Norwegian salmon and discuss different aspects of mitigation measures; the expected effect of international agreements on reduced atmospheric emissions, the expected effect of liming on salmon production and the possibilities of re-establishing self sustaining salmon stocks in limed rivers.