The estimates of junvenile (age 1+) brown trout appear 

 to reflect the flow patterns during this period. Standing 

 crops of wild rainbow trout and adult (age 11+ and older) 

 brown trout during portions of 1967-1978 were affected by 

 the stocking of catchable, hatchery rainbow trout and intense 

 fishing pressure. These groups were eliminated from the anal- 

 yses since population fluctuations are not directly correlated 

 to flow variations. 



The USGS gage at the head of the study section was not 

 operating during much of the 1967-1978 period. The approxi- 

 mate flows for the section were obtained by adjusting those 

 for the USGS gage below Hebgen Reservoir. 



The approximate distribution of the average daily flows " 

 during the 12-month period preceding each estimate of age 1+ ;• 

 brown trout is given in Table 7. It is assiimed that these 

 standing crops primarily reflect the magnitude of the flows 

 during the 12-month period preceding each estimate and not 

 the flows during spawning, incubation, and the first simuner of 

 growth for that particular year class. 



The lowest standing crop estimate (1,643 age 1+ trout 

 weighing 405 lbs in 1967) followed the lowest flows. Between 

 October 1966 and September 1967, approximately 17% of the 

 average daily flows were less than 650 cfs compared to to -: 

 1.5% for the other years and approximately 19% of the average 

 daily flows were less than 750 cfs compared to to 3.5% for 

 the other years. ' '.-? . 



The highest standing crop estimate (7,876 age 1+ trout 

 weighing 1,696 lbs in 1976) followed the highest flows. Be- -. 

 tween October 1975 and September 1976, approximately 95% of 

 the average daily flows exceeded 1,150 cfs and none were less ..' 

 than approximately 1,088 cfs. 



The estimated numbers of age 1+ brown trout for years 

 other than 196 7 and 19 76 were relatively stable, ranging from 

 3/012 to 4,410. The biomass estimates for these years were 

 more variable, ranging from 583 to 1,044 lbs. 



The data suggest that flows greater than approximately ': 

 1,150 cfs would sustain the highest standing crops of juvenile 

 brown trout while flows less than approximately 650-750 cfs 

 appear to severely reduce their numbers. The optimum flow for 

 juvenile (age 1+) brown trout probably exceeds 1,150 cfs. 



A 6-mile section of reach #3 between the mouths of Wolf 

 and Squaw creeks (Figure 1) has been closed to angling since 

 February 1977. This section was established in conjunction 





31 



