Title

Fallback by adult sockeye salmon at Columbia River dams

Publication Date

2006

Keywords

adult, Bonneville Dam, Columbia River, dams, future research, injuries, Oncorhynchus nerka, salmon, sockeye salmon, spawning, spillway, survival

Journal or Book Title

North American Journal of Fisheries Management

Abstract

We implanted radio transmitters into sockeye salmon Oncorhynchus nerka in 1997 to determine the (1) fallback percentage and rate at eight Columbia River dams, (2) effect of fallback on adult counts at each dam, (3) relations between spillway discharge and fallback, (4) relations between injuries and fallback, and (5) relations of fallback and survival to spawning tributaries. The rate of fallback, that is, the total Dumber of fallback events at a dam divided by the number of fish known to have passed the dam, ranged from 1.9% to 13.7% at the eight dams. The rate of fallback was highest at Bonneville Dam, the dam with the most complex fishway. Fallback produced overcounts of 2% to 7% at most dams. Fallback was weakly related to spill volume at Bonneville Dam. Significantly more sockeye salmon with head injuries fell back than fish without head injuries. About 40% of the sockeye salmon had injuries from marine mammals, but these injuries were not associated with the rate of fallback. The rate of survival was similar between fish that fell back (68.0%) and fish that did not fall back (67.5%). We suggest that fisheries managers adjust counts for fallback but note that these relationships were obtained under high-discharge conditions. We conclude that fallback biases dam counts and that the relationship between spawning success and fallback should be an area of future research.

Pages

380-390

Volume

26

Issue

2

This document is currently not available here.

Share

COinS