Michigan Department of Natural Resources
Fisheries Research Report No.1811, 1974
Population Dynamics of Trout, with Crayfish as Food, in Three Pothole Lakes in Michigan
Howard Gowing
and
Walter T. Momot
Abstract.-In the fall of 1965, populations of brook trout (juvenile and adult) were established in three pothole lakes in the Pigeon River area, art densities of 188, 411, and 1,399 fish per hectare. The lakes were closed to fishing; fish removal was limited to monthly samples for study of food consumption and growth. Population estimates were made periodically of surviving trout, and of an abundant species of crayfish. The trout populations diminished drastically (by 89 to 99%) over a 2-year period, due mostly to natural mortality rather than to our sampling. Heaviest mortality occurred during either the first winter, or the first summer, related to high vs. low density. Growth was related to trout density and to food consumption. Crayfish made up 13% of the trout's diet in one lake, and a high of 71% in the third lake. Trout ate only age-0 crayfish; obviously the older crayfish were too large. Trout consumed as little as 1%, but as much as 43%, of the annual production of age-0 crayfish in the three lakes, but apparently did not "stress" the crayfish population. During a second 2-year period, rainbow trout and brook trout were compared in two lakes, starting with like stocking rates and size of fish. The rainbow did better in survival and in production (44 kg/ha) than did the brook trout (14 kg/ha). The rainbow fed more on cladocerans; the brook trout more on crayfish.