Date of Award:

1972

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Advisor/Chair:

William T. Helm

Abstract

Exponential rates of digestion are described for brown trout and whitefish for July, October, December (1969), and April (1970). The slope of the line fitted to the digestion data from each month was defined as the instantaneous rate of digestion and applied to an exponential growth model to determine the instantaneous consumption rate.

The digestion and consumption rates were applied to field measurements of percent fullness to determine the amount of food material ingested during a 24 hour period. Brown trout consumed 127, 24, 19, and 84 mean percent of their stomach capacity in the July, October, December, and April studies. Whitefish consumed 74, 21, 46, and 51 mean percent of their stomach capacity in the same respective study periods. Mean daily ration from four major collection periods was calculated on fish in the 50 gram to BOO gram size range. Brown trout daily ration varied between 1.35 percent and 2.59 percent. Whitefish daily ration varied between 0.44 percent and 0.83 percent.

Brown trout diets were quite variable with 44 percent of their caloric intake comprised of terrestrial invertebrates in October, 55 percent of the December calories comprised of fish eggs, and 39 percent of the April calories made up of Leptoceridae larvae.

Emerging imagoes were important items in the brown trout diets, contributing as much as 62 percent and not less than 11 percent of the numeric intake for one collection period.

Whitefish did not rely upon emerging imagoes as a significant food source. Their stomachs consistently contained mayflies, chironomids, and caddis larvae. Both fish species occasionally consumed substantial amounts of the large stonefly, Pteronarcys.

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