Table 8. — Estimated mortality rates due to Hock Island Darn based on Wenatchee sockeye recoveries 



[95 Percent confidence limits] 



Table 9. — Upstream returns of tagged spring and summer 

 chinook by area of released at Rock Island Dam, 1954-56 



of mortalities when comparing total returns from 

 above and below the dam. 



In view of these similar recoveries of tagged 

 chinook salmon released above and below Rock 

 Island Dam, we cannot conclude that there is a 

 substantial mortality caused by the dam. For 

 spring chinooks, there are indications of a loss of 

 fish released below the right bank ladder in 1956. 

 Data are not available for determining if this loss 

 exists for the other 2 years. 



RETURNS AT ROCK ISLAND 

 Identity of Tags and Species 



The correct identity of tag returns at Rock 

 Island Dam depended upon the fish counters' 



LOSS AND DELAY OF SALMON PASSING ROCK ISLAND DAM 



353 



