■m 



The four September estimates, while not directly compar- 

 able to one another due to the different groups of trout esti- 

 mated in each year, do indicate that standing crops of trout 

 were highest following the summer of 1978 when flows were 

 highest. The estimated nxamber of brown trout in 1978 was 

 about 133 to 15 3% of those in previous years and the estimated 

 biomass was about 122 to 128% of those in previous years. The 

 estimated nxomber of rainbow trout in 19 78 was about 132 to 

 312% of those in previous years and biomass was about 164 to ' " 

 26 8% of those in previous years. The rainbow trout popula- 

 tion responded more favorably to the 1978 summer flow increases 

 than did the brown trout population. 



The study section was extended an additional 5.5 miles in 

 19 77. Standing crop estimates by age-groups for the 10-mile 

 extended section in September 1977 and 1978 are given in 

 Table 14. In 1978 the estimated number and biomass of age 11+ 

 and older brown trout were 109 and 109%, respectively, of those 

 in 1977, while the number and biomass of age 11+ and older 

 rainbow trout were 207 and 165%, respectively, of those in 

 1977. Total trout numbers and biomass in 1978 were 119 and j_ 

 114%, respectively, of those in 19 77. Again, adult rainbow . '/ 

 trout responded more favorably to the 1978 summer flow in- 

 creases than did adult brown trout. . .' 



All age-groups of brown trout increased in number between 

 1977 and 1978 with age IV+ and older showing the greatest in- 

 crease (18%) and age III+ the least (5%) . Nijmbers of age 11+ 

 rainbow trout increased by 173% and those of age III+ rainbow 

 trout by 91%. Numbers of age IV+ and older rainbow trout 

 remained about the same. 



The flow and limited population data for the 1969 to 19 78 

 period suggest that standing crops of rainbow and brown trout 

 in the study sections were reduced by summer flows less than 

 approximately 400 cfs. Until more definitive data become 

 available, a minimum flow of 4 00 cfs is recommended. 



47 



