12 

 CONCLUSIONS 

 The following conclusions pertain to the Beaverhead River between 

 Clark Canyon Dam and the confluence of Grasshopper Creek (mile to 12). 



1. The survival of age III and older rainbow trout is directly 

 related to the magnitude of flows during the nonirrigation 

 season (approximately October 15 to April 15). During this 

 period, Clark Canyon Reservoir is storing water for irrigation 

 and releases into the Beaverhead River are minimal. Results 

 of this study suggest that one average daily flow <^ 150 cfs 



is sufficient to adversely affect the survival of older 

 rainbow trout. Average daily flows greater than approximately 

 250 cfs are needed to provide a high quality, trophy rainbow 

 trout fishery. 



2. Flows were not sufficiently reduced during this study to 

 adversely affect the survival and numbers of older brown 

 trout. 



3. The reproductive success of brown trout, as measured by the 

 estimated numbers of age I brown trout, appears to be 

 related to flow patterns during the brown trout spawning 

 period. Spawning flows devoid of violent fluctuations and 

 gradually decreasing to a minimum of approximately 150 cfs 

 during the 47 day spawning period (September 15 through 

 October 31) yielded the highest estimates of numbers of 

 age I brown trout two years later. The number of age I 

 brown trout in turn was the major factor influencing numbers 

 of age II and age III brown trout in succeeding years. 



