Winter Observations on Bottom Organisms and Trout in Bridger Creek, Montana

Effects of temperature, ice, and fluctuating water levels on bottom organisms and on the movements of rainbow trout were investigated in a 900-foot section of Bridger Creek in southwestern Montana from October 21, 1959, to September 12, 1960. Ninety-six bottom samples and 27 drift samples were studied. Limnephilidae were the most abundant aquatic organisms in the area. Surface ice cover had no effect on the abundance of bottom organisms except for the loss of a small number frozen in the ice at the stream edge. High flows during the spring reduced the number of bottom organisms in situ, and increased the number taken in drift samples. Floating surface ice did not appear to increase the number of organisms in drift samples. Sixty-one percent of the trout captured and tagged in the study section were recaptured no more than 150 feet from the original place of capture. More trout were recovered downstream than upstream during each month of study. Trout moved as far as 2 miles upstream from the study section, and 55 miles downstream. During the spring, summer, and autumn, trout were mainly found in pools, while in winter many were collected in riffle areas under surface ice.