Origin and abundance of lake whitefish (Coregonus clupeaformis) congregating below a hydroelectric control dam in northern Canada

Abstract

AbstractThe abundance and origin of lake whitefish (Coregonus clupeaformis) congregating downstream of the Missi Falls control dam at the outlet of Southern Indian Lake (SIL) in northern Manitoba, Canada were studied during two successive open water seasons. In 1986 the number of lake whitefish below the dam increased to almost 90000 in the autumn and most of these fish were physiologically ready to spawn. Morphological comparisons indicated that most of these fish originated from SIL and were apparently attempting to return to it. Flows through the dam in this year were high and similar to those before the diversion of the Churchill River. In 1987 there were fewer fish of SIL origin below the control dam and the numbers decreased over the summer. Discharge through the dam was much lower in 1987 than before diversion. The number of lake whitefish below the dam that appeared to originate from lakes downstream of Missi Falls on the lower Churchill River varied from 2000 to 12000 over the whole study period. These fish may have been attracted to the control dam by local environmental conditions such as cool water temperatures. The effects of the control dam on lake whitefish movements and distribution was not predicted despite extensive pre‐project studies. These effects should receive more attention in the prediction of impacts of boreal hydroelectric projects.