Temperature, flow, and the migration of adult sockeye salmon (Oncorhynchus nerka) in the Columbia River

Abstract

We related the arrival timing of adult sockeye salmon (Oncorhynchus nerka) at a series of dams on the Columbia River (Bonneville, McNary, and Rock Island) and Snake River (Ice Harbor) to the changing flow and temperature regimes over the last several decades. The temperatures experienced by sockeye salmon have increased in the lower but not upper reaches of the system, and the flows experienced by the fish have decreased. The Bonneville-McNary travel rate increased from about 22 to 49 km/day, and sockeye salmon now pass McNary Dam about 11 days earlier than in 1954. Both travel rate and arrival date were correlated with temperature increases and flow decreases at McNary during that period. Sockeye salmon arrival at Rock Island Dam (14 days earlier from 1933 to 1994) was also correlated with temperature and flow there. However, the travel rate between McNary and Rock Island dams did not change from 1955 to 1994, despite a decrease in estimated water velocity from 85 to 23 km/day. Sockeye salmon arrival at Ice Harbor Dam has sometimes been bimodal; the first mode's date has not changed, but annual mean dates have been positively correlated with flow and negatively with temperature.