A Trout Population Study on a Small Creek in Gallatin County, Montana

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Abstract
A direct current shocker was used for sampling a brook, rainbow and brown trout population. Brook trout predominated in the uppermost of 4 study sections; rainbow trout in the others. Rainbow trout (yearlings and older) declined in number through the calendar year. Brook trout (uppermost section) and brown trout markedly increased during their spawning season. Low recoveries of marked fish indicated a population turnover greater than expected from normal mortality and recruitment. The estimated standing crop per acre in August 1951 was 4,586 (106 lbs.); 85 and 80% of the rainbow and brook trout respectively being in age group 0, 13 and 18% in I, and 2% of each in II. At that time average total lengths (inches) for the age groups of these two species were: 0[long dash]2.1 and 2.9, I[long dash]5.5 and 6.1, and II[long dash]8.6 and 8.8. There were an estimated 5867 young of year per mile in fall 1950; 5468 in August 1951. A collection of brook trout during their spawning season showed some young of year males were ripe and at least 72% of the fish over 6 inches were males. Of 1016 4-inch brook trout planted in August 1950, an estimated 5% remained in the 2 1/2 mile study area during the following calendar year.

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