Effects of climate change on Snake River Chinook Salmon

Lisa Crozier and Rich Zabel

Northwest Fisheries Science Center, NOAA-Fisheries, 2725 Montlake Blvd, Seattle, WA

Many salmon have a complex life history that involves long-distance migrations between freshwater and ocean habitats. Climate change may have different effects on each life stage. For example, Snake River Spring-Summer Chinook salmon spawn and rear juveniles in high elevation streams in eastern Oregon and central Idaho, but complete most of their growth in high-nutrient ocean environments. I present evidence that stream temperature and stream flow affect fish growth, survival, and migration timing, but that habitat differences between populations and density-dependent processes mediate these effects. These freshwater effects may propagate through the life cycle, because fish size and the timing of their arrival in the estuary greatly influence ocean survival. Climate effects on ocean conditions are largely uncorrelated with the freshwater conditions for these fish, so they also experience independent climate effects in ocean stages. River conditions may also affect adult fertility, but this is difficult to quantify at this time. We used a stochastic, life-cycle model to integrate these independent and interacting processes, and scale up to population-level effects. We simulated population dynamics in historical and two climate-change scenarios to explore the potential consequences of climate change for the viability of this threatened fish.