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Background 



Drawdown of John Day Reservoir in 1996 is one action recently 

 proposed in an effort to increase survival of outmigrating juvenile 

 salnonids in the Colioaibia River Basin. Hydroelectric development 

 of the Columbia River Basin has altered the timing and magnitude of 

 water flows that juvenile salmonids are exposed to during 

 outmigration. Historically, smolt emigration coincided with high 

 spring and early suauoer discharges (Park 1969) . Travel time during 

 smolt migration is an important factor governing in-river survival 

 of juvenile salmon and steelhead (Raymond 1979) . Delays during 

 outmigration can prolong smolt exposure to predators and disease 

 (Raymond 1979) . Smolt travel time i^ influenced by a complex array 

 of factors; however, many fisheries scientists believe that more 

 closely approximating a natural hydrograph through reservoir 

 drawdowns will decrease travel time and increase outmigrant 

 survival. 



Many questions, however, remain about the ecological 

 consequences of drawdown. Of particular importance are questions 

 concerning physical alteration of the aquatic environment and 

 trophic level interactions, particularly predator-prey 



