study reaches are unreliable. Suggested ways for improving the accuracy of 

 the WUA values and the resulting recommendations for adult trout include 

 modifying the existing IFC model to use bottom velocities rather than the 

 mean velocities for computing the WUA, developing probabillty-of-use curves 

 from data collected for river trout populations and incorporating cover into 

 the IFG model. 



Non-Field Method 



Data presented in this study suggest that flow recommendations based on 

 a fixed percentage of the mean annual flow of record may be valid for Mon- 

 tana's trout rivers. The percentage selected as a flow recommendation for 

 adult trout appears to depend on the channel morphology with the wider, shal- 

 lower rivers such as the Madison requiring a higher percentage of the mean 

 annual flow. The more typical rivers of the study area (Beaverhead, Gallatin 

 and Big Hole Rivers) require instream flows equal to about 33% of the mean 

 during the low flow or non-runoff months. 



Recommendations of the Tennant method are based on a fixed percentage 

 of the mean annual flow of record. However, Tennant applies his recommended 

 percentages uniformly to all waterways without regard to differences in chan- 

 nel morphology. Based on the study results, channel morphology should be a 

 major consideration when using a fixed percentage method to formulate flow 

 recommendations . 



ACKN0V7LEDGEMENTS 



The author wishes to thank Al Elser, Ron Marcoux, Bruce May, Dr. William 

 Miller, Norman Peterson, Barry Schaplow, Harold Stevenson, Richard Vincent, 

 Jerry Wells and Al Wipperman, present and former biologists with the Montana 

 Department of Fish, Wildlife and Parks, for collecting and summarizing much 

 of the trout population data used in deriving flow recommendations for this 

 study. The author also wishes to thank personnel of the USGS, Helena, Montana 

 for providing flow data and Dr. Clair Stalnaker and Ken Bovee of the Coopera- 

 tive Instream Flow Service Group for their technical assistance. This study 

 was funded by the U. S. Fish and Wildlife Service. 



LITERATURE CITED 



Bovee, K, D. 1978. Probability-of-use criteria for the family salmonidae. 

 Cooperative Instream Flow Service Group, Fort Collins, CO. 80 pp. 



Bovee, K. D. and T. Cochnauer. 1977. Development and evaluation of weighted 

 criteria, probablllty-of-use curves for instream flow assessments; fisher- 

 ies. Cooperative Instream Flow Service Group, Fort Collins, CO. 39 pp. 



