Assessment of damage to fish population in Norwegian lakes due to acidification

We assessed the current status of fish populations (N = 39 093) in 32 303 N orwegian lakes in relation to the effects of acidification. The number of l ost and reduced populations of the 6 most common species of fish in Norwegi an lakes greater than 3.0 ha (0.03 km(2)) in acidic areas were estimated to be 9630 and 5405, respectively. Brown trout, which is the most widespread and common species of fish in Norwegian lakes, has suffered the most severe damage. A manual delineation method gave a total affected area of 1417 km( 2) in 1940, which had risen to 51 530 km(2) in 1990. Acidification has affe cted fish populations in southernmost Norway most seriously. The damage was also estimated in grid cells of 12 x 12 km, which was based on an estimate d damage index for each cell. This analysis yielded a total damaged area of 84 166 km(2) in 1990 or about 25% of the total land area of Norway.