Research Article: Climate vulnerability assessment for Pacific salmon and steelhead in the California Current Large Marine Ecosystem

Date Published: July 24, 2019

Publisher: Public Library of Science

Author(s): Lisa G. Crozier, Michelle M. McClure, Tim Beechie, Steven J. Bograd, David A. Boughton, Mark Carr, Thomas D. Cooney, Jason B. Dunham, Correigh M. Greene, Melissa A. Haltuch, Elliott L. Hazen, Damon M. Holzer, David D. Huff, Rachel C. Johnson, Chris E. Jordan, Isaac C. Kaplan, Steven T. Lindley, Nathan J. Mantua, Peter B. Moyle, James M. Myers, Mark W. Nelson, Brian C. Spence, Laurie A. Weitkamp, Thomas H. Williams, Ellen Willis-Norton, João Miguel Dias.


Major ecological realignments are already occurring in response to climate change. To be successful, conservation strategies now need to account for geographical patterns in traits sensitive to climate change, as well as climate threats to species-level diversity. As part of an effort to provide such information, we conducted a climate vulnerability assessment that included all anadromous Pacific salmon and steelhead (Oncorhynchus spp.) population units listed under the U.S. Endangered Species Act. Using an expert-based scoring system, we ranked 20 attributes for the 28 listed units and 5 additional units. Attributes captured biological sensitivity, or the strength of linkages between each listing unit and the present climate; climate exposure, or the magnitude of projected change in local environmental conditions; and adaptive capacity, or the ability to modify phenotypes to cope with new climatic conditions. Each listing unit was then assigned one of four vulnerability categories. Units ranked most vulnerable overall were Chinook (O. tshawytscha) in the California Central Valley, coho (O. kisutch) in California and southern Oregon, sockeye (O. nerka) in the Snake River Basin, and spring-run Chinook in the interior Columbia and Willamette River Basins. We identified units with similar vulnerability profiles using a hierarchical cluster analysis. Life history characteristics, especially freshwater and estuary residence times, interplayed with gradations in exposure from south to north and from coastal to interior regions to generate landscape-level patterns within each species. Nearly all listing units faced high exposures to projected increases in stream temperature, sea surface temperature, and ocean acidification, but other aspects of exposure peaked in particular regions. Anthropogenic factors, especially migration barriers, habitat degradation, and hatchery influence, have reduced the adaptive capacity of most steelhead and salmon populations. Enhancing adaptive capacity is essential to mitigate for the increasing threat of climate change. Collectively, these results provide a framework to support recovery planning that considers climate impacts on the majority of West Coast anadromous salmonids.

Partial Text

Anthropogenic climate change poses a direct threat to existing global biodiversity. In fact, climate-related population extinctions have already occurred in 47% of 976 plant and animal species surveyed in a recent review of the literature [1]. Moreover, local extinction percentages are higher in freshwater (74%) than in terrestrial (46%) or marine habitats (51%) [1]. Such impacts are expected to increase in the future [2–4], and managers are actively seeking information regarding the species or populations most vulnerable to climate change. Information of this kind is needed to prioritize resources for restoration and climate adaptation efforts. Climate vulnerability assessments are an important tool in these efforts because they provide systematic summaries of the relative threat level to a set of species or populations [5–7].

Our approach followed the climate vulnerability assessment method developed by Hare et al. [35], which is now being implemented for U.S. marine and anadromous species by NOAA Fisheries [36]. This method was designed for rapid assessment across a wide variety of taxa using available qualitative and quantitative data. It assumes that vulnerability will be periodically re-assessed, and methods refined as status reviews are updated and more information can be considered for individual DPSs.

Loss of the southernmost populations within a species’ range is widely predicted with climate change [259], but our assessment also highlighted that unique life histories are at high risk. Both the late-fall and winter-run Chinook ecotypes exist only at the southern end of the species range, and both face extinction without continued intensive management. Similarly, for chum salmon, the summer-run is rare and faces relatively greater vulnerability than the more common fall or winter-run life history types in northern regions. Local adaptations to distinct flow and temperature conditions are the characteristics that contribute to high vulnerability for these life history types and make them particularly sensitive to climate change.