NOAA Scientists Publish Climate Vulnerability Assessment for Pacific Coast Salmon and Steelhead Populations

The number of distinct population segments (DPSs) in each vulnerability rank by species.

Crozier LG, McClure MM, Beechie T, Bograd SJ, Boughton DA, Carr M, et al. (2019)

August 2019 - Twenty-eight of the 52 distinct populations of seven Pacific salmon and steelhead species in the continental US are either threatened or endangered. Three more are considered species of concern. A team of NOAA-led scientists recently completed a climate vulnerability assessment for all of these populations, plus a couple more. Such assessments offer a systematic way of assessing populations’ relative vulnerability to climate change and identifying patterns that may aid in conservation decision-making.

The NOAA scientists sought experts to rank each population according to 20 different climate change sensitivity and exposure attributes. Sensitivity attributes include things like life history traits (e.g. time spent in freshwater), and the presence of non-climate stressors. Exposure attributes, such as stream and ocean water temperatures, were ranked based on how much they are expected to change by mid-century under the IPCC business as usual emissions scenario.

The authors found Chinook salmon to be the most highly vulnerable as a species. Five distinct Chinook populations ranked very high (the highest of four ranking categories) in climate change vulnerability. One coho population (the Central California Coast population) and one sockeye population also ranked as very highly vulnerable.

Broad patterns that emerged included that interior fish populations, those with unique life histories (e.g. those that spawn at different times of year than others of their species), and those at the southernmost extent of their species ranges were among the most vulnerable to climate change. In addition, the most vulnerable populations tended to spend more time in fresh water, and in estuaries or coastal rearing habitat, and be more exposed to rising water temperatures and streamflow variability. At sea, virtually all of the populations are expected to face very high exposure to sea surface temperature rise and ocean acidification.

Central California Coast coho ranked very high in climate change sensitivity, and high in climate change exposure, leading to their overall ranking as very highly vulnerable to climate change.

Already high extinction risk and and the fact that summer and fall seasons already place a lot of stress on juveniles are among the factors that contributed to their very high sensitivity score. Very high exposure to flooding and rising water temperatures were among the many factors that contributed to the high climate change exposure ranking.

The authors noted that one of the best ways of mitigating climate change vulnerability is to reduce other kinds of anthropogenic stress on fish populations. In the case of our local coho populations, efforts like the current Salmon Habitat Enhancement Project at Muir Woods are helping to do just that. Restoring a more natural shape to Redwood Creek is expected to have far-reaching benefits like slowing the flows during flood events and raising the water table. Such benefits can only help young salmon in the creek deal with the increase in wet and dry extremes that they are likely to confront as a result of climate change.

Check out the full study on PLOS ONE to learn more. Specific information on the Central California Coast coho and steelhead populations is available in the Supporting information section.

See more from the Bay Area Nature & Science Blog