Predation on Larval Lake Whitefish (Coregonus clupeaformis) and Lake Herring (C. artedii) by Adult Rainbow Smelt (Osmerus mordax)

Rainbow smelt (Osmerus mordax) predation on larval lake whitefish (Coregonus clupeaformis) and lake herring (C. artedii) in Twelve Mile Lake, Ontario, was intense in 1984. Coregonid larvae hatched in early April as smelt spawning was ending. Predation was continuous for a 7-wk period, beginning at the onset of hatching. Numbers of coregonid larvae observed in smelt stomachs were directly proportional (p ≤ 0.005) to their abundance in the lake. During the week when the larvae were most abundant, they occurred in 93% of the smelt stomachs containing food. The corresponding average daily consumption was 8.4 larvae per smelt. Simulation of the combined effects of smelt predation and "natural" mortality indicated that mortality of lake whitefish may be 100%. Survival of herring larvae must be greatly reduced as well. Rainbow smelt became established in Twelve Mile Lake in the 1950's; their effect on larval whitefish survival may have been aggravated by intensified dipnetting of spawning lake whitefish during the 1960's. There has been little or no recruitment of young whitefish to the population since 1975, although dipnetting for adults ceased in about 1970. Our results support the hypothesis that the primary cause of recruitment failure of this whitefish population is predation by smelt.