49 



TABLE 14. Estimated biomass (lbs/6455) of rainbow trout in the 1965 

 through 1974 year classes in the Hildreth Section of the 

 Beaverhead River. 



Annual spring to spring rates of population change of brown trout 



by age groups are given in Table 15. Annual population increases probably 



reflect the immigration of younger age groups following poor yearling 



crops. Significant relationships between the annual rates of change for 



any age group of brown trout and the magnitude of mean nonirrigation 



flows were not demonstrated by simple regression analyses. The elevated 



rate of population decrease of older brown trouL between 1967 and 1968 



reflects water quality problems in addition to reduced flows. 



TABLE 15. Annual rates of population change (%) of brown trout by age 



groups in the Hildreth Section of the Beaverhead River between 

 1967 and 1976. 



