Density and Condition of Subyearling Chinook Salmon in the Lower Columbia River and Estuary in Relation to Water Temperature and Genetic Stock of Origin

Abstract

We examined the hypotheses that density and morphometric condition of subyearling juvenile Chinook Salmon Oncorhynchus tshawytscha would decline during periods of high water temperature in the lower Columbia River and estuary. The hypotheses were tested using salmon density measurements and a condition anomaly calculated from residuals of the length–weight linear regression based on 5,536 subyearlings collected from brackish estuarine and tidal freshwater (TFW) habitats. We captured Chinook Salmon at all temperatures encountered (4.2–23.5°C). In the TFW zone, densities were highest at optimal temperatures and lowest at suboptimal and supraoptimal temperatures; in the estuary, density did not differ among temperature regimes. Fish condition was lowest in winter, when temperatures were suboptimal, and highest in summer, when temperatures were supraoptimal. Pairwise comparisons of fish condition between periods of optimal temperature (spring) and supraoptimal or stressful temperature (summer) showed little change in the estuary but a large, positive increase with temperature in the TFW zone. Similarly, we examined seasonal differences in the condition of 50–60-mm fry and again found condition to be lowest in winter and highest in summer. Finally, using genetic information, we identified stock‑specific differences in migration timing and concluded that most large yearlings and many subyearlings migrated in late winter or spring and therefore were never exposed to high temperatures. Other prevalent stocks persisted in the estuary during periods of elevated temperature; however, the condition of those fish also tended to be higher or neutral in summer than in spring. High temperatures appeared to influence migration timing, as evidenced by reduced density in TFW reaches during summer. However, we found little support for the hypothesis that condition of juvenile Chinook Salmon is reduced during periods of high water temperature in the lower Columbia River and estuary.

Received April 5, 2014; accepted April 11, 2014

ACKNOWLEDGMENTS

We thank C. Seaton (Oregon Health and Science University) for compiling the temperature data from estuarine mooring stations. Many people assisted in beach seine collections, including P. Bentley, D. Bottom, L. Campbell, S. Hinton, G. McCabe, R. McNatt, and R. Nelson. We appreciate the reviews and manuscript improvements provided by B. Beckman, K. Fresh, L. Johnson, and R. Zabel (National Oceanic and Atmospheric Administration Fisheries) and three anonymous reviewers. This research was funded by the U.S. Army Corps of Engineers and the National Oceanic and Atmospheric Administration.