Four population groups of Pacific salmon in California, Oregon/Washington, and Idaho are especially vulnerable to climate change, according to a new study.

Two of the four populations cited are spring Chinook salmon in the interior Columbia and Willamette River basins, and Snake River sockeye.

The NOAA Fisheries study, “Climate vulnerability assessment for Pacific salmon and steelhead in the California Current Large Marine Ecosystem” was published in PLoS ONE last week.

“Salmon have always adapted to change, and they have been very successful, otherwise they wouldn’t still be here. What we are trying to understand is which populations may need the most help with anticipated future changes in temperature and water availability, and what steps we can take to support them,” said study co-author Lisa Crozier of NOAA Fisheries.

The results will be useful for prioritizing protection efforts for salmon populations along the entire U.S. West Coast.

The broad range of environments in which salmon dwell make them especially sensitive to environmental change, notes the study.

To better understand the vulnerability of Pacific salmon, the authors studied 33 threatened or endangered population groups of Pacific salmon, encompassing local populations from the Mexican border to the Canadian border.

For each population group, the authors looked at 20 different attributes in order to assess the group’s vulnerability to change. These attributes measured the magnitude of expected change in local environmental conditions, the capacity of the population group to adapt phenotypically to new climatic conditions, and the sensitivity of specific population groups to current environmental conditions.

Four population groups were found to be most at risk: Chinook in California’s Central Valley, coho in northern California and Oregon, Chinook in the Columbia and Willamette River basins, and sockeye in the Snake River basin of Idaho.

All 33 studied population groups were found to be vulnerable to elevations of stream and sea surface temperatures as well as ocean acidification. However, some population groups were more affected than others by local conditions, such as barriers to migration such as dams.

“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,” says the study.

As part of an effort to provide such information, researchers conducted a climate vulnerability assessment that included all anadromous Pacific salmon and steelhead population units listed under the U.S. Endangered Species Act.

Using an expert-based scoring system, researchers 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.

“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,” says the study.

“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.”

The populations that scored highest in adaptive capacity were:

Puget Sound steelhead, Chinook and coho salmon.

Lower Columbia River steelhead and Chinook salmon. Snake River spring/summer and fall Chinook salmon.

Northern California steelhead.

The varied life histories of these population groups give them more flexibility to respond to climate change, said researchers. Although existing diversity may help these populations, ultimately some of that diversity will be lost.

Other adaptations might not affect diversity, however. Some populations might shift their migration earlier or later to avoid the midsummer heat, for example. And habitat restoration projects — including removing dams that prevent adequate fish passage — could provide some species with more of a buffer against changing temperatures and flows.

“The fish will change; we have to be prepared for that,” Crozier said. “Given a chance to persevere, they will take advantage of it.”

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(1) comment


I am a biologist in British Columbia studying a virus in the Atlantic salmon farms called piscine orthoreovirus. In reviewing the Head Recovery Data I see that salmon from the Columbia, Willamette River and Snake River have been caught in this area, which means they have been exposed to this Norwegian virus. It infects the red blood cells of Chinook and causes them to rupture enmasse. I think it would be worth screen fish in these rivers for this virus.

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