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Researchers Profiling Cooler Areas In Yakima River That May Act As Salmon Safe Havens
Posted on Thursday, August 30, 2018 (PST)

Researchers from the Benton Conservation District, Yakama Nation, and U.S. Geological Survey are profiling cooler areas in the lower 100 miles of the Yakima River that may serve as safe havens for fish during warm weather.


Funded by Washington Department of Ecology, the survey will help protect these sites and meet environmental enhancement objectives of the Yakima River Basin Integrated Plan


For 12 days this July, average daily river temperatures at Prosser were above 80 degrees. Historically, the monthly mean temperature for July at Prosser is 69.3 degrees.


Over the last four years, the rise in river temperatures is notable. In fact, 20 of the 30 warmest river temperatures recorded since 1990 at Prosser were from the years 2015 to 2018, says WDOE.


These “thermal blocks” are stalling the migration of sockeye salmon. Recently reintroduced to the river by the Yakama Nation, the sockeye are pausing their migration, waiting at the mouth for conditions to improve.


Temperatures above 73-77 degrees are considered lethal to salmon. Survival of late spring smolts is also influenced by rapid water warming, especially in drought years.


Fish are able to detect water temperature differences within a half a degree. They move to areas that are cooler and more favorable in an activity called "behavioral thermoregulation." Of all Pacific salmon, sockeye prefer the coldest water.


Enhancing thermal refuge locations on the lower Yakima may support late spring and summer migration of anadromous species when water temperatures are otherwise too warm for fish passage.


Benton Conservation's water resources specialist Marcella Appel is leading the multi-agency project to map the thermal profile of the river from Wapato to Richland. Data will be used to identify areas where cool water is introduced to the river, be it from shallow groundwater or subsurface flows influenced by irrigation.


“We want to learn where these temperature refuges exist because they are so important to salmon,” Appel explained. “The information will provide one more piece of the puzzle as partners of the integrated plan seek to restore water conditions on the Yakima River for people and salmon.”


It’s also believed these refuges provide beneficial warmer water for out-migration of juvenile smolts during the winter and spring months.


The conservation district, Nation, with Ecology staff and local community volunteers, have completed eight of nine floats, already covering 80-plus river miles. The study team has one more float to log information, planned in early September.


With anticipated climate change impacts in the basin resulting in higher river temperatures and lower springtime flows, thermal refuge locations will become increasingly important for migratory species, says WDOE.


“The support and collaboration for this project have been amazing,” Appel said. “We could not have completed the rigorous summer float schedule without the help of our partners and local citizens.


“It is satisfying to see everyone working together on solutions for the lower Yakima River. I look forward to the next phase as we analyze the data. We anticipate the efforts of this two-year study will lead to future projects aimed at helping cool water species navigate an otherwise hot river,” Appel concluded.


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