Brown Trout (Salmo trutta) Status and Chemistry from the Norwegian Thousand Lake Survey: Statistical Analysis

Abstract

Substantial negative impacts of acidic precipitation on freshwater fishes have been recorded over the last 50 yr in Norway. We analyzed the present status and historical trends of brown trout (Salmo trutta) populations in relation to water chemistry in 584 Norwegian lakes. Since the 1940s, 39% of the lakes have lost their trout populations, and another 17% of the lakes have declining trout populations; thus, 56% of the populations have been adversely affected. The results of analysis of variance, principal components analysis, and discriminant analyses converge on the variables pH, monomeric inorganic aluminum, and alkalinity as most strongly related to trout status. Lakes whose trout populations are extinct have an average aluminum concentration of 133 μg/L, an alkalinity of −34 μeq/L, and a pH of 4.8 versus 11 μg Al/L, + 27 μeq/L, and 6.0 for lakes with healthy populations. Also, nitrate and sulfate levels are significantly higher in affected versus unaffected lakes. Calcium and sulfate appear to influence trout status moderately as individual variables, but strongly in combination, since they are the major determinants of alkalinity in these lakes. Models based on discriminant analyses showed good success (up to 89%) in predicting trout population status categories from water chemistry.