|Document Type:||Journal Article|
|Title:||Study of loss and delay of salmon passing Rock Island Dam, Columbia River, 1954-56|
|Author:||Robert R. French, Roy J. Wahle|
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, corresponding closely with the choice of ladders made by the untagged populations. Point estimates of sockeye salmon losses ranged from 0 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.