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
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
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
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
“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.”