Table 20 • Comparison of the optimum instream flow recommendations 

 derived by the IFG Incremental Method and the standing 

 crop and flow data for five reaches of the Madison, 

 Beaverhead, Gallatin and Big Hole Rivers. 



<i 



Reach 



Madison (#1) 

 Madison (#3) 



Beaverhead (#2) 



Gallatin(#2) 



Big Hole{#l) 



Life Stage 

 and 

 Species 



adult brown trout 

 adult rainbow trout 



juvenile brown trout 

 adult brown trout 

 adult rainbow trout 



adult brown trout 

 juvenile rainbow trout 

 adult rainbow trout 



adult brown trout 

 adult rainbow trout 

 adult mountain whitefish 



adult brown trout 

 adult rainbow trout 



Optimum Instream Flows (cfs) 



i 



The IFG method also generated optimum flow recommendations for 

 other life stages of rainbow trout, brown trout and mountain white- 

 fish (Table 21) . Since flow recommendations based on biological 

 data are not available for comparison, no attempt will be made to 

 evaluate the reliability of these predicted optimums. It should be 

 noted that the IFG optimum flow recommendations were generally 

 highest for the adult life stage. An obvious exception occurred 

 in the Gallatin reach in which the IFG optimum flows for spawning 

 brown and rainbow trout greatly exceeded those for the other life 

 stages including adults. In this case, the optimum flow recommen- 

 dations for spawning trout are misleading. Examination of the 

 weighted usable areas shows that spawning habitat for all flows 

 of interest was extremely limited for this particular subreach. 



The IFG optimum recommendations for adult mountain whitefish 

 were considerably higher than those for adult brown and rainbow 

 trout. When compared to the recommendations derived from the stand- 

 ing crop and flow data, the IFG predicted optimums for whitefish 

 appear to be more realistic estimates of the actual flow needs of 

 adult trout than were the IFG predicted optimums derived for trout. 



66 



