a 



Rainbow trout responded more favorably .to the flow in- 

 creases than did brown trout. In 1971 numbers and biomass of 

 age II and older rainbow trout were 198 and 152%, respectively, 

 of those in 196 7 while brown trout numbers and biomass were 

 160 and 116%, respectively, of those in 1967. Younger rain- 

 bow trout (age II and III) responded more favorably to the -""-.■ 

 flow increases than age IV and older rainbow trout and age * ' 



III brown trout responded more favorably than age II and age j 



IV and older brown trout. .< — 



The distribution of the average daily flows for the ap- 

 proximate 12-month period preceding each estimate shows the 

 magnitude of the flow increases following the 1967 estimate 

 (Table 6). The lowest estimate of trout numbers and biomass , •. 

 (in 1967) followed the 12-month period containing the lowest 

 flows. Between spring 1966 and spring 1967, 7% of the average 

 daily flows were less than 900 cfs versus 0% for the other 

 years and 18% were less than 1,100 cfs versus 0-3% for the 

 other years. The highest estimate of trout numbers (in 1970) 

 followed the 12-month period containing the highest flows. 

 Between spring 1969 and spring 1970, 97% of the average daily 

 flows exceeded 1,400 cfs and none were less than 1,240 cfs. 

 The estimated trout biomass peaked in 1969 and remained stable 

 through 1970 and 1971. During the 12-month period preceding 

 each of these three biomass estimates, 94 to 100% of the 

 average daily flows exceeded 1,200 cfs and none were less 

 than 923 cfs. 



The population and flow data for the 1966-71 period 

 suggest that standing crops of trout were reduced by flows 

 less than approximately 900-1,100 cfs. During this period, 

 the highest trout standing crops were preceded by flows 

 greater than approximately 1,200-1,400 cfs. The optimum "' 

 flow in reach #1 for adult rainbow and brown trout probably 

 exceeds 1,200 cfs. o !*"_;:; . 



-i ' ?' ■ -' 



Madison River - Reach #3 '~ S 



Standing crops of brown trout, the dominant trout 

 species, and rainbow trout in a 5-mile section near reach #3 

 of the Madison River were estimated in fall 1967 through 

 fall 1978. The study section begins 12 miles downstream of 

 the lower boundary of reach #3 at river mile 60 (Figure 1) . 

 The section provides a measure of the flows needed to maintain 

 trout populations in the upper river even though it is not 

 located within reach #3. 



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