36 



through 1973 spawning periods (Figure 7) indicates that gradually decreas- 

 ing flows devoid of violent fluctuations yielded the highest yearling 

 estimates two years later. 



The variance of the 47 average daily flows during each of the 1964 

 through 1973 spawning periods was calculated. Variance, a coarse measure 

 of the fluctuation of spawning flows, was regressed against the estimated 

 number of age I brown trout two years later. The estimated numbers of 

 age I brown trout in 1966, 1967, and 1968 may reflect water quality 

 problems in addition to spawning flows. When these three observations 

 are removed, the variance of spawning flows explains 71% of the annual 

 variation in numbers of age I brown trout (Appendix Figure 8). 



Results of this study suggest the degree of fluctuation of spawning 

 flows is the dominant factor influencing numbers of age I brown trout, 

 which in turn influence numbers of age II and age III brown trout in 

 succeeding years. Numbers of age IV and older brown trout were not 

 related to the numbers of age III and older brown trout the previous 

 spring nor to the magnitude of mean irrigiation and nonirrigation flows. 

 Those factors influencing the numbers of older brown trout, which remained 

 relatively stable throughout the study, were not identified. 



Rainbow Trout 



Estimated numbers of rainbow trout by age groups are given in 

 Table 6. Due to the movement of spawning fish into the Hildreth 

 Section, spring estimates of age II and older rainbow trout are not 

 valid estimates of resident fish. 



Fall estimates of age I and older rainbow trout are compared in 

 Figure 9. Total numbers remained relatively stable between 1966 and 



