Occurrence of salmonid parr and eel in relation to water quality in small streams on the west coast of Sweden

Abstract

In the summer of 1983 twelve streams on the west coast of Sweden were electrofished, and water samples were collected. In three of the streams water sampling was continued throughout the winter of 1983–84. Although summer pH showed little variation between stations there were large differences in fish abundance. The abundances of salmonid parr and eel were correlated with the alkalinity, and were significantly greater at stations with summer alkalinity above 0.25 meq·1¹⁻¹. The winter water sampling programme showed drastic and rapid drops in the alkalinity during the snow-melt. Electrofishing data compiled from 7 streams during 1956–84 showed decreasing parr abundances in small streams (catchment area <1000 km²) with low (<0.25 meq·1⁻¹) alkalinity. It is suggested that the negative effect on fish is mainly due to toxic forms of A1 and to a lesser extent on the direct toxicity of low pH levels.