Background: Chinook salmon are highly vulnerable to climate change (Crozier et al 2019, Crozier et al 2021). As NOAA moves toward an ecosystem-based approach to fisheries management, there is increasing recognition that a better understanding of predator-prey dynamics within the California Current Ecosystem (CCE) is needed. Salmon is a key component of the ecosystem. The salmon fishery is highly managed and subject to frequent closures in recent years due to impacts from climate change and declines in protected species. Salmon is also in an intermediate trophic position during their smolt stage, making trophic interactions especially complicated. They respond to bottom-up forcing through climate impacts on primary production, competition with forage fish, jellyfish, and important fishery targets such as hake and top-down forcing from marine mammals, sea birds, and piscivorous fish. Fisheries on forage fish, hake, rockfish, and sport fish are affected by salmon productivity. Other species of management concern, especially Southern Resident Killer Whales, also depend on salmon as a primary prey species. Finally, freshwater actions related to hydrosystem management and habitat restoration have carryover effects for salmon marine survival. Improving our understanding of the constraints on salmon survival and productivity serves several management objectives.

Approach: Our proposed research has 3 over-arching objectives: 1) Identify species interactions that have especially high impact upon juvenile salmon survival and sensitivity to climate change. 2) Estimate the relative importance of top-down predation pressure upon juvenile salmon compared to that of environmental (climate regime), phenological (timing of seasonal smolt entry to the ocean), bottom-up (prey availability), and competitive pressures using a multi-model approach. 3) Identify management actions that could affect important drivers of salmon survival. The primary focus of the postdoctoral fellowship will be to conduct analyses in an ecosystem model, EcoTran (Ruzicka et al 2016), exploring the scenarios that describe alternative hypothesized ecological drivers and management actions. We will conduct thorough sensitivity analyses within the model platform to identify the levels of perturbation among predator-prey relationships that would be detectable from observational data. We will identify types of observational data that would be necessary to better constrain model results.

We will explore salmon-specific and ecosystem-level responses to climate change within the California Current under a variety of GCM projections, using ROMS modeling described in Pozo Buil et al. (2021), and species distribution models conducted by Barb Muhling (NOAA SWFSC). This work will lead to directly to improvements throughout the portfolio of ecosystem models of the Northern California Current.

Crozier, L. G., B. J. Burke, B. E. Chasco, D. L. Widener, and R. W. Zabel. 2021. Climate change threatens Chinook salmon throughout their life cycle. Communications Biology 4:222

Crozier et al 2019 Climate vulnerability assessment for Pacific salmon and steelhead in the California Current Large Marine Ecosystem. Plos One 14(7):e0217711

Ruzicka, J. J., K. H. Brink, D. J. Gifford, and F. Bahr. 2016. A physically coupled end-to-end model platform for coastal ecosystems: Simulating the effects of climate change and changing upwelling characteristics on the Northern California Current ecosystem. Ecological Modelling 331:86-99

Pozo Buil et al 2021. A Dynamically Downscaled Ensemble of Future Projections for the California Current System. Frontiers in Marine Science 8