34 



TABLE 4. Estimated numbers of brown trout in the 1965 through 1974 year 



classes in the Hildreth Section (6455 ft) of the Beaverhead River. 



The plot of average daily flows for the Hildreth Section for the 

 1964-76 period was visually inspected to determine if the extreme variation 

 in the estimated numbers of age I brown trout was related to the magnitude 

 of flows during the 17-month period between fry emergence and the fall 

 yearling estimate. Visual inspection showed the highest yearling estimate 

 (908/6455 ft) followed a low winter flow period. Based on the large 

 number of age II trout in the spring of 1976, a conservation approximation 

 of the number of yearling brown trout the previous fall would be 624/6455 

 ft. This high number of yearlings followed the lowest winter flow 

 period of the study. Flows during the first summer of growth of the 

 1967 year class were the lowest during the study, yet year class 

 strength (474/6455 ft) was relatively high in the fall of 1968. It 

 appears unlikely that reduced flows during the 17-month period pro- 

 ceeding the fall estimates were the principle factor depressing numbers 

 of age I brown trout. 



Flows during the brown trout spawning period (September 15 - 

 October 31) were examined for a possible flow-yearling relationship. 

 Visual inspection of the plot of average daily flows during the 1964 



