STUDY OF LOSS AND DELAY OF SALMON PASSING ROCK ISLAND 



DAM, COLUMBIA RIVER, 1954-56 



By Robert R. French, Fishery Biologist (Research), Bureau of Commercial Fisheries, Seattle, Washington, 

 and Roy J. Wahle, Fishery Biologist (Management), Bureau of Commercial Fisheries, Columbia Fishery 

 Program Office, Portland, Oregon 



ABSTRACT 



To determine loss or delay of salmonids in passing 

 Rock Island Dam on the Columbia River, and whether 

 such loss or delay was associated with the right bank 

 ladder, salmon were tagged and released both above and 

 below the dam in 1954-56. They were subsequently 

 observed passing through the fishways and recovered at 

 upstream points. Most tagged fish released below the 

 left and right bank fishway returned over the left, cor- 

 responding closely with the choice of ladders made by 

 the untagged populations. Point estimates of sockeye 



salmon losses ranged from to 42 percent. Tagging 

 results (one season only) on spring chinook salmon 

 indicated a loss of fish released below the right bank 

 ladder, but no loss when total tag returns from below 

 and above dam releases were compared; data failed to 

 show that the dam caused losses of summer chinook. 

 Tagged salmon released below the dam were delayed 

 2 to 4 days. Altering the right bank fishway may cause 

 more fish to use it, but there is no clear evidence that 

 such alterations will reduce overall loss or delay. 



Rock Island Dam, completed in 1934, was the 

 first dam built on the Columbia River. It is 

 about 450 miles above the river's mouth in central 

 Washington (fig. 1). A fishway was built at 

 each end of the dam to pass anadromous fish and 

 in 1936 a third was added near the middle of the 

 dam to pass salmon observed congregating there. 

 These ladders were the pool type, 20 feet wide, 

 with a gradient of 1 to 10. 



The dam was modified during 1951-53 by in- 

 stalling regulating gates in the spillway channel 

 increasing the forebay elevation approximately 

 12 feet (fig. 2). Six new generating units were 

 added in the powerhouse (located on the left side 

 of the dam). These modifications necessitated 

 changing the fishways to meet the new forebay 

 level, and fish attraction flow was increased at the 

 lower end of the left (looking downstream) ladder 

 to counteract the effect of increased flow from the 

 turbine units. Although fishery agencies re- 

 quested changes at the lower end of the right lad- 



Note.— Approved tor publication May 26. 1964. 

 FISHERY BULLETIN: VOLUME 65, NO. 2 



der to provide better entrance conditions and ad- 

 ditional attraction flow, nothing was done at the 

 time. The entrance of the right ladder at three 

 different water levels is shown in figure 3. 



The Federal Power Commission, in granting 

 a license amendment for the modification of 

 Rock Island Dam, reserved the right to require 

 altering the lower end of the right ladder if sub- 

 stantial evidence were presented that such alter- 

 ations or modifications were required for effective 

 conservation of fish life resources of the Columbia 

 River. Any such altering was to begin before 

 Dec. 1, 1960. 



The size of anadromous fish runs passing Rock 

 Island is shown in table 1. Fewer of the fish 

 have used the right ladder since the dam was 

 modified. During the period 1936-52, for ex- 

 ample, the counts of salmon and steelhead at 

 the three ladders were distributed as follows: 

 Left ladder, 47. S percent; center ladder, 22.5 

 percent; right ladder, 29.7 percent. For the 

 period 1953-56 (after modification of the dam), 

 the counts were these: Left ladder, 73.7 percent; 



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