Fish Populations of a Trout Stream in Relation to Major Habitat Zones and Channel Alterations

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Abstract
The relationship of fish populations to major habitat zones and channel alterations was studied in Little Prickly Pear Creek, Montana, during the summers of 1965 and 1966. Five major zones were defined as follows: headwater, meadow, mountain, lower meadow, and Wolf Creek Canyon, with at least one representative study section in each. Approximately 23% (6 of 30 miles) of the stream has been altered. Field measurements showed no pool‐riffle periodicity in the altered mountain sections, while successive riffles were spaced at intervals of 5.7 widths, in the unaltered areas. Altered sections of the mountain zone consisted, by area, of 87% shallow‐fast with no deep‐slow water, compared to 49 and 14%, respectively, for the unaltered sections. Amount of cover per acre of stream was about 80% greater in the unaltered mountain section than in the altered. Rock deflectors in the altered section of Wolf Creek Canyon rendered the physical characters of the stream nearly comparable to the unaltered sections. Fish populations were estimated by means of a simple mark‐and‐recapture census. Non‐trout species were absent from the altered sections, but made up 30 and 58% of the total number and weight, respectively, in the unaltered mountain sections. Trout were 78% more abundant in the unaltered mountain sections than in the altered, and a statistical test indicated a significant difference between the two trout populations. Standing crops of trout ranged from 40 to 226 pounds per acre, and the total stream supported an estimated 20,400 trout greater than 4.0 inches long weighing 9,500 pounds. Channel alterations resulted in a total loss of 4,700 trout with a total weight of 2,200 pounds.

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