Steelhead Trout, Salmo gairdneri 



The steelhead trout count of 7,078 fish in 

 1963 was slightly more than twice the 30-year 

 mean of 3,336 (table 1). 



In 1963, the greatest number of steelhead 

 passed through the fishways in September 

 when 2,634 fish were recorded (table 2). Peak 

 monthly movement of these fish in 1962 was 

 also in September when 3.429 fish were counted. 



Of the stee.lhead passing Rock Island Dam in 

 1963, 76/3 percent used the left ladder, while 

 8.0 and 15.7 percent ascended the middle and 

 right ladders, respectively (table 8). In 1962, 

 percent utilizationby ladder was left, 70.7; mid- 

 dle, 12.1; and right, 17.2 percent. Additional 

 data pertaining to the movement of steelhead 

 trout at Rock Island Dam are in tables 9-14. 



Maximum day's count in 1963 was 201 on 

 September 15 (table 3), compared to 284 on 

 September 28 in 1962. 



Miscellaneous Fish 



In 1963, species of fish passing Rock Island 

 Dam other than salmon and steelhead trout 



were counted as in former years. Data per- 

 taining to these fish are in tables 15-20. No 

 claims are made as to complete accuracy of 

 identification of these fish; however, the de- 

 gree of accuracy is consistent with that main- 

 tained at other dams on the Columbia River 

 and the data may be used as a rough index of 

 abundance of these fish. In 1963, about 138,000 

 fish other than salmon and steelhead trout 

 passed the dam. In 1962, 165,000 such fish 

 were counted. These species included large- 

 scale sucker, Catostomus macrocheilus ; long- 

 nose sucker, Catostomus catostomus ; squaw- 

 fish, Ptychocheilus oregonense ; Rocky 

 Mountain whitefish, Prosopium williamsoni ; 

 Columbia River chub, Mylocheilus caurinus ; 

 chiselmouth, Acrocheilus alutaceus ; carp, 

 Cyprinus carpio; lamprey, Entosphenus tri- 

 dentatus ; shad, Alosa sapidissima ; Dolly 

 Varden trout, Salvelinus malma ; and rainbow 

 trout, Salmo gairdneri. The number of mis- 

 cellaneous species of fish passing through the 

 fishways in 1963 exceeded the count of salmon 

 and steelhead by about 30,800 fish. 



Table 8 . —Semimonthly number and percent of steelhead trout counted over each ladder, Rock Island 



Dam, 1963 



1 Middle ladder inoperative from May 1-20. 



2 Right ladder inoperative for several hours on Sept. 1. Closure was made in order to permit 

 removal of debris. 



