Climate impacts on Oregon coastal coho salmon, Oncorhynchus kisutch: integrating freshwater and marine ecosystems at daily to centennial time scales

Peter W. Lawson

Northwest Fisheries Science Center, National Oceanographic and Atmospheric Administration, 2032 S.E. OSU Drive, Newport, Oregon, 97365, U.S.A.

Email: peter.w.lawson@noaa.gov

Effects of climate on ocean conditions in the California Current system are becoming well understood. In particular, relationships between marine conditions and coho salmon, Oncorhynchus kisutch, survival have received much attention. Interannual variability of Oregon production index area coho salmon marine survival is related to winter sea surface temperature, spring transition, and upwelling. However, coho salmon spend half their life-cycle in freshwater. In freshwater, interannual variability of coho smolt production is related to air temperature, timing of winter storms, and stream flow in the second winter and spring. Freshwater and marine environmental factors are largely concurrent and correlated; good marine survival is likely to occur in the same years as good freshwater smolt production. In addition to the interannual and decadal scale variation attributable to these factors, climate affects freshwater production through a second, unrelated mechanism; changes in the freshwater ecosystem through landscape processes of fire, mass wasting (landslides), and forest growth. Early modeling efforts indicate that these processes alone can result in a two-fold variation in smolt production with a 100 year cycle. There is likely to be a similar-scale effect in ocean ecosystems, with some components of the system (long-lived groundfish, pelagic predators) responding on decadal to centennial time frames, creating (primarily) top-down trophic effects. In both marine and terrestrial systems we need to explore links between climate effects and long-term responses of ecosystems. Such a long-term perspective could aid in developing ecosystem-level management in the California Current system.