ABSTRACT 



The U.S. Fish and Wildlife Service is legislatively charged by the 

 Coordination Act of 1934 as amended August 14, 1946, to investigate Federal 

 water-use influence on the fishery and to provide for the protection of these 

 resources . This is an evaluation of the Bonneville Dam influence on Chinook 

 salmon populations in the Columbia River based on the availability of the fish 

 to the gill nets. 



Breaking the fishing year into spring, summer and fall components, 

 return estimates based on the periods before and after construction of the 

 dam show mixed trends. The spring returns are better after dam construc- 

 tion, the summer returns are far worse, and the fall returns balance . 



Ratios of return to escapement for the three seasons of the year show 

 a spring improvement after dam construction, a large drop in summer, and 

 a lesser drop in the fall. Return-to-escapement ratio levels after Bonneville 

 Dam appear related to the proportion of chinooks which pass Bonneville Dam as 

 adults and again as juveniles. For example, all summer chinooks spawn above 

 Bonneville Dam while roughly two thirds of the spring chinooks spawn above the 

 dam . On the other hand, the annual abundance curve reveals no change in trend 

 before and after dam construction and the mixed trends of spring, summer, and 

 fall seasons do not appear influenced by the construction date of Bonneville Dam . 



