T&ble 8. Semimonthly number and percent of steelhead trout counted over each ladder, Rock Island 



Dam, 1964 



±1 Middle ladder closed from Oct. 14-24 in order to make repairs. 



Maximum day's count in 1964 was 129 on 

 September 17 (table 3), as compared to 201 

 on September 15, 1963. Additional data per- 

 taining to the movement of steelhead trout 

 at Rock Island Dam are contained in tables 

 9-14. 



Miscellaneous Fish 



In 1964, species of fish passing Rock Island 

 Dam other than salmon and steelhead trout 

 were counted as in former years (tables 

 15-20). No claims are made as to complete 

 accuracy of identification of these fish; how- 

 ever, the degree of accuracy is consistent 

 with that maintained at other dams on the 



Columbia River. Such data should only be 

 used as a rough index of abundance of these 

 fish. 



In 1964, 118,284 fish other than salmon 

 and steelhead trout passed Rock Island Dam. 

 This number, as compared to 138,000 in 

 1963, exceeded the count of salmon and steel- 

 head trout by about 4,000. The species in- 

 cluded are largescale sucker, Catostomus 

 macrocheilus ; longnose sucker, Catostomus 

 catostomus ; squawfish, Ptychocheilus 

 oregonense ; Rocky Mountain whitefish, 

 Prosopium williamsoni ; Columbia River chub, 

 Mylocheilus caurinus ; carp, Cyprinus carpio ; 

 lamprey, Entosphenus tridentatus ; Dolly 

 Varden trout, Salve linus malma ; and rainbow 

 trout, Salmo gairdneri . 



