'.I 



Table 3. Fall estimates of age II and older brown trout are inflated due 

 to the upstream movement of spawning fish into the Hildreth Section. While 

 fall estimates of age groups II and older may reflect numbers of brown 

 trout of spawning age, they do not reflect numbers of resident trout. 

 Fall estimates of age I brown trout are valid. These fish are sexually 

 immature and, therefore, considered residents. 



Spring estimates of age II and older brown trout are compared in 

 Figure 5. Total numbers decreased substantially between 1967 and 1968, 

 remained relatively stable between 1968 and 1974, then increased between 

 1974 and 1976. An elevated mortality of age III and older trout was 

 responsible for the decrease between 1967 and 1968. The increase 

 between 1974 and 1976 reflects strong 1973 and 1974 year classes. 



Strengths of the 1965 through 1974 year classes of brown trout are 

 shown for an 18-month period in Table 4. The data suggests that some 

 movement of brown trout into the Hildreth Section did occur following 

 a poor yearling crop. Although movement may have occurred, the number 

 of yearlings still had a strong influence on year class strength in 

 succeeding years. Simple linear regression analyses (Figure 6) show 

 that the number of yearlings explain 83 and 847, respectively, of the 

 annual variation in 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 irrigation and nonirrigation flows (Appendix 

 Table 5). 



