Observations on the Age, Growth, Reproduction, and Feeding of Mountain Whitefish (Prosopium williamsoni) in the Sheep River, Alberta

The ecology of mountain whitefish (Prosopium williamsoni) in the upper Sheep River was studied during 1972 and 1973. Mountain whitefish spawned from late September to mid-October in shallow, fast, midstream areas. The number of spawning fish on each spawning site was small (two to 20 fish per site). Absolute fecundity (eggs/fish) increased as the females became older; however, relative fecundity (eggs/g of fish) remained comparatively stable for all age classes. The linear regression of absolute fecundity (Y) on fork length (X, in mm) is described by the formula: Y = 4347.6 + 50.7 (X – 301.5). Growth is rapid except in the older age classes of 7 and 8. The weight (Y, in g) length (X) relationship (sexes combined) is described by the formula: log Y = 2.1967 + 3.2108 (log X – 2.3710). The relationship of body (Y) to scale (X) growth is described by: log Y = 2.0891 + 0.9542 (log X – 2.4367). Recruitment into the population of the upper Sheep River appeared to be at 3 years of age with an annual natural mortality rate of approximately 33% on 3-year-old and older mountain whitefish. The diets of mountain whitefish consisted primarily of dipterans, ephemeropterans, trichopterans, and terrestrial invertebrates.