A contribution to the ecology of the whitefishes Prosopium cylindraceum and Coregonus clupeaformis of Algonquin Park, Ontario

The distribution of Prosopium cylindraceum (Pallas) and Coregonus clupeaformis (Mitchill) in Algonquin Park, Ontario, suggested that there may be some interaction between these species. In large lakes where both species are present the C. clupeaformis population is always dominant; in small lakes only, one species is present. During the summer of 1963 the ecological relationships between these species were studied. Lakes Opeongo and Lavieille each contained both species, while in Lakes Redrock and Happy Isle only P. cylindraceum was present. Gill nets were set at frequent intervals, to determine the depth range occupied by the two species and to provide material for stomach analysis and age and growth data. Temperature and dissolved oxygen levels were recorded regularly using standard limnological techniques. The depth range occupied by both species was not strongly correlated with the thermal structure or oxygen level of the lake. P. cylindraceum in sympatric situations invariably occupied a shallower depth range than did C. clupeaformis. Where the latter species was absent P. cylindraceum were frequently found in a wide range of depths. P. cylindraceum from Lake Opeongo fed heavily on larval insects and to a lesser extent on bottom-dwelling crustacea. C. clupeaformis from the same lake fed mainly on bottom-dwelling crustacea plus some insects and molluscs. P. cylindraceum in Lakes Redrock and Happy Isle fed almost entirely on plankton crustacea. Zooplankton was of importance as a primary food source for whitefish. Age and growth data have shown that there is a direct correlation between the relative importance of plankton in the diet and the rate of growth of the fish. Fish from Lakes Redrock and Happy Isle had a much higher growth rate in both length and weight than the two species in Lake Opeongo. In the latter lake C. clupeaformis grew faster than P. cylindraceum. Large lakes with adequate zooplankton production will support both P. cylindraceum and C. clupeaformis, but the better adaptation of C. clupeaformis to plankton feeding may account for its greater success as indicated by its wide distribution, large numbers, and high rate of growth.Science, Faculty ofZoology, Department ofGraduat