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 an d an additional 8 are threatened. In the two southernmost counties, salmon is eradicated. Due to the high acid sensitivity, production of salmon was g reatly reduced as early as 1920, several decades before acid rain was recog nized as an environmental problem. International agreements on reduced atmo spheric 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. Lim ing is an effective measure to protect and restore fish populations in acid ified waters. Liming of acidified salmon rivers has become important in Nor way in recent years which in combination with reduced emissions will be an important contribution to protection of the Atlantic salmon species. In thi s paper we give an overview of the effects of acidification on Norwegian sa lmon and discuss different aspects of mitigation measures; the expected eff ect of international agreements on reduced atmospheric emissions, the expec ted effect of liming on salmon production and the possibilities of re-estab lishing self sustaining salmon stocks in limed rivers.