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Study: How Warmer Columbia/Snake Water Temps Affect Adult Salmonid Migration Timing, Survival
Posted on Friday, October 12, 2018 (PST)

A recent study that summarizes adult salmon and steelhead body temperatures as they migrate upstream in the Columbia River and into the Snake River found that spring and summer chinook salmon body temperatures largely match stream temperature, causing few delays as they migrate.

 

However, as the river temperature warms, some fall chinook and most steelhead sought out cool water refuges and that tends to delay their migration.

 

“Warm summer and fall river temperatures currently delay upstream migration for many Snake River populations, and we expect that thermal barriers to migration are likely to increase in future warmer years,” said Matthew Keefer, research scientist in the Department of Fish and Wildlife Sciences, College of Natural Resources, at the University of Idaho.

 

The paper describes how changing river temperatures are likely affecting the adult migration timing and survival of many Snake River populations, he said.

 

“Warm temperature exposure in the hydrosystem correlates with adult mortality along the migration route, prespawn mortality on spawning grounds, and reduced survival and fitness of progeny,” Keefer said. The higher river temperatures also contribute directly to upstream migration delays, most notably at some adult fishways, such as at Lower Granite Dam before the cooling system was implemented, he added.

 

“We expect that water temperature management at the adult fishways will become increasingly important. The results also clearly demonstrate that conservation and enhancement of cool-water refuges sites should be a management priority,” Keefer said.

 

“Thermal exposure of adult Chinook salmon and steelhead: Diverse behavioral strategies in a large and warming river system” was published online September 21, 2018, in the journal PLOS one (https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0204274).

 

Keefer’s co-authors are Tami Clabough, research support scientist, and Michael Jepson, research specialist, University of Idaho; Eric Johnson, formerly at the University of Idaho, now a project leader at the Eagle Fish Genetics Lab, Idaho Department of Fish and Game; Christopher Peery, formerly University of Idaho, now a fish biologist at the Northwest Division of the U.S. Army Corps of Engineers in Walla Walla; and Christopher Caudill, associate professor at the University of Idaho.

 

Data used by the researchers were from two years around 2000, which were relatively cool migration years, Keefer said. “Rivers in the region have continued to warm since the original study and those warming trends are expected to continue. We anticipate that mitigating temperature-related stressors will be increasingly important for salmonid managers and researchers in the CRB.”

 

Migration and reproduction are traits often considered as sensitive to climate change, according to the study. Recent climate predictions for Northwest states are for a reduced snowpack and a shift from snow to rain-dominated runoff, lower summer flow conditions and higher river temperatures.

 

While traits of adult migration timing “reflect historical adaptation to river discharge and temperature patterns,” the study says, there is also “accumulating evidence that recent phenological shifts in many salmonid populations have occurred in response to climate-driven warming and have been accompanied by genetic changes.”

 

What is less clear, the study continues, is whether population-level adaptation can keep pace with climate change.

 

“There is also considerable uncertainty about how behavioral and phenotypic plasticity, as opposed to genetic adaptation, contributes to the observed phenological changes in some salmonid populations,” the study says. “Plasticity is critically important for how animals respond to short-term (e.g., within-generation) environmental fluctuations, whereas genetic adaptation is likely necessary when environmental change is unidirectional, as appears to be the case with recent climate warming.”

 

The researchers used temperature loggers on 212 adult chinook salmon and 200 steelhead and collected about 500,000 temperature records as the fish migrated from downstream of Bonneville Dam on the Columbia River to Lower Granite Dam on the Snake River. The fish were on their way to spawn in Oregon, Washington and Idaho streams.

 

The study looked at Snake River spring-, summer-, and fall-run chinook and summer steelhead, all listed as threatened under the federal Endangered Species Act.

 

They found that spring and most summer run chinook migrated before river temperatures reached their annual highs and so their body temperatures largely matched that of stream temperatures.

 

However, the later arriving fish – fall run chinook and most steelhead – hit water that reached their maximum thermal tolerance of 20 to 22 degrees Centigrade (68 to nearly 72 degrees Fahrenheit) in the lower Columbia River.

 

“High temperatures elicited extensive use of thermal refuges near tributary confluences, where body temperatures were 2 to 10 degrees C cooler than the adjacent migration corridor,” the study says. “Many steelhead used refuges for weeks or more whereas salmon use was typically hours to days, reflecting differences in spawn timing.”

 

The researchers also found a 260 kilometer reach (161 miles) they call a thermal migration barrier where there were few or no refuges. That, they said, may develop in future warmer years.

 

The coldest thermal refuges were in the lower reaches where fish temperatures were frequently 3 to 10 degrees C cooler than the main stem Columbia River, the study says. Salmon and steelhead in the Deschutes River refuge were typically 1 to 5 degrees C cooler than in the Columbia River. Unfortunately, the Deschutes River was the only significant thermal refuge in the more than 250-km reach from The Dalles Dam to Lower Monumental Dam.

 

“The paucity of refuges upstream from the Deschutes River confluence portends that significant thermal barriers to adult migration may occur in this reach in future warmer years,” the study says. “Similar thermal bottlenecks have threatened the sustainability of salmon populations in other locations.”

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