13 



4. Spawning flows also appear to affect the numbers of age I 

 rainbow trout. Spawning flows devoid of violent fluctuations 

 and increasing from approximately 200 cfs to approximately 

 700 cfs during the 61 day spawning period (March 1 through 

 April 30) yielded the highest estimates of age I rainbow 

 trout 18-months later. The number of age I rainbow trout 



in turn was the major factor influencing the number of 

 age II rainbow trout the following fall. 



5. Poor reproductive success was the major factor limiting 

 the total numbers and biomass of trout throughout much of 

 this study. 



6. With flow releases favorable to both reproduction and the 

 survival of older trout, this portion of the Beaverhead River 

 is capable of supporting greater numbers and biomass of 

 trout of all age groups than those which existed throughout 

 much of this study. 



7. Relationships between the magnitude of flows and trout growth 

 were not demonstrated during this study. 



8. The physical and hydraulic characteristics most affected by 

 flow reductions were cross sectional area and current 

 velocity. Top width and wetted perimeter were least 

 affected. The rate of loss for all six of the measured 

 characteristics was greatly accelerated at flows less than 

 approximately 200 cfs. 



