Flows in Section II during the summer of' 1977 were less 

 than those in the siammer of 1976. The minimum suirimer flow 

 measured in 1977 (250 cfs) was 63% of the minimum flow 

 measured in 1976 (396 cfs). -'' ■ 



Fall estimates of brown trout, the dominant trout species , . 

 in Section II, could not be compared since no estimate was 

 made in September 1976. However, the summer (April - Septem-::-' 'I 

 ber) rate of population decrease, referred to as the mortality 

 rate, is available for comparison to the rate for Section I. 

 In 1977, a summer mortality of 65% for age III+ and older 

 brown trout was measured in Section II, which had a minimum 

 summer flow of 250 cfs, while Section I, which had a minimum 

 summer flow of 393 cfs, showed a summer mortality of only 26% -■* 

 for age III+ and older brown trout. The summer mortality rate 

 in Section II was elevated when compared to the rate for Sec- 

 tion I, the least dewatered study section. This elevated 

 summer mortality of older trout coincided with a 36% reduction 

 in the minimum summer flow between Sections I and II. Mor- ^, 

 tality rates for younger trout are not available for compari- -; , 

 son. 



The lowest summer flow measured in Section III in 1976 

 was 198 cfs. Section III was totally dewatered for a 5-day 

 period in July 19 77. Prior to 19 77, the total dewatering of 

 Section III last occurred in 1973. The September 1976 

 estimate of brown trout, the dominant trout species in Sec- 

 tion III, followed three successive above average water years 

 and preceded total dewatering. 



,. While differences in angling pressure and habitat may 

 be contributing to the variation in standing crops of trout 

 between study sections, data collected in this study suggest 

 that summer flow is the major factor limiting trout popula- 

 tions. Simple linear regression analyses show that the minimum 

 summer flows measured in Sections I, II, and III in 19 76 and 

 1977 explain 99.6 and 95.0%, respectively, of the variation .. ,,1.^ 

 in the September estimates of numbers and biomass of age 11+ 

 and older trout (Figure 19) . Both relationships are signifi- 

 cant at the 9 5% confidence level. 



Figure 19 shows that the study section having a minimum 

 summer flow of 52 3 cfs supported about two times the number 

 and biomass of adult trout that occurred in the study section 

 having a minimum summer flow of 250 cfs. It appears that sum- 

 mer flows of approximately 52 3 cfs and greater would sustain 

 the highest standing crops of trout, while summer flows of 

 approximately 250 cfs are judged undesirable on the basis of 

 the approximate 50% reduction of the trout standing crop. 



41 



