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NW Fishletter #389, January 7, 2019

[1] NW Climate Scientists Prepare To Help Fish Survive As Region's Rivers Warm

Salmon and steelhead in the Pacific Northwest will face many challenges as the climate warms, according to the Fourth National Climate Assessment released by 13 federal agencies on Nov. 23.

From ocean acidification and toxic algae blooms to earlier runoff and lower summer flows in rivers and streams, migratory fish will have numerous hurdles to overcome as the Earth warms.

But to Daniel Isaak--a fisheries research scientist at the Rocky Mountain Research Station whose studies were cited in the federal report--rising water temperatures in rivers and streams will be at the heart of their struggles.

That's why Isaak and other scientists developed a regional database for stream temperature, compiled by hundreds of biologists and hydrologists, logging in more than 200 million hourly water temperature readings at more than 20,000 stream sites.

Already, the information has been used to help scientists determine how much water temperatures in the Columbia Basin have increased, and to predict how much they will continue to rise under different climate change models.

Now, it's being used to figure out where fish and other aquatic species will have the best chance at survival as conditions worsen. "It's important for how we restore habitat, and where we might derive the most bang for the buck," Isaak told NW Fishletter.

Isaak said he started focusing on how fish will be impacted by changing stream temperatures 12 years ago. His ongoing work includes a website with GIS databases that highlight and summarize the streams that are predicted to be key climate refuges for bull trout and cutthroat trout. The same methods can be used to develop specific locations for preserving other species, he said. "I feel like we've built a good foundation, and proven the concept with a few species. Now, we can go down the same road with other species."

A look back to 2015 with its massive fish die-offs provides a good reason to be prepared. Isaak noted that 2015 brought weather conditions that, in the past, the Northwest might expect once every 100 years. Under climate change models, similar conditions will be likely every 10 years by 2050, and every five years by the end of the century, he said.

The federal climate report, too, points to 2015 as a glimpse of what's to come in the Pacific Northwest. An exceptionally warm winter left record-low mountain snowpack, and a dry spring led to severe drought, mega-wildfires and heat waves on land and at sea. Overall, temperatures were 3.4 degrees above normal, with wintertime temperatures at 6.2 degrees above normal.

"The warm 2015 winter temperatures are illustrative of conditions that may be considered "normal' by mid-century (higher scenario, RCP8.5) or late century (lower scenario, RCP4.5)," the report says.

But it was the warm summer temperatures that warmed the Columbia River to more than 70 degrees in July, resulting in the death of an estimated 250,000 adult sockeye as attempted their journey to spawning areas upstream.

According to a report on the die-off by NOAA Fisheries, flows and water temperatures in the Columbia River in June resembled conditions normally seen in late July and August. The impact was especially harsh between Bonneville and Lower Granite dams, where 95 percent of the Snake River sockeye listed under the Endangered Species Act perished.

NOAA's recommendations for avoiding a similar die-off in the future revolve mostly around monitoring water temperatures and setting triggers for taking action, developing plans to trap and transport sockeye when mainstem temperatures signal a problem, and finding ways to cool water in the river and at fish ladders.

Isaak agrees that the mainstem rivers at lower elevations will be more troublesome when it comes to helping migratory fish survive. "Those are going to be the places where we see the biggest, most dramatic impacts," he said.

This realization is relatively new. Many studies had previously predicted that--like the arctic--widespread extinctions would occur in higher elevations and cold mountain streams. But those predictions relied on small datasets and imprecise water temperature information.

As lead author of a 2016 study published in the Proceedings of the National Academy of Sciences, Isaak used the water temperature database from a network of 222,000 km of streams to show that "thermal habitat in mountain streams is highly resistant to temperature increases and that many populations of cold-water species exist where they are well-buffered from climate change."

That means instead of losing cold-water species at the highest elevations first, those areas can become important refuges which can be used to help preserve a species. Isaak noted that this was a revelation for scientists working in the headwaters, and it offers more hope that cold-water species can survive.

Indeed, despite the dire tone of the federal report, and the many challenges for salmon and steelhead--which depend on many different habitats throughout their lifecycle--Isaak believes salmon and steelhead will survive to the end of this century.

"Fish can adapt, to a certain degree," he said. "Migratory fish can migrate earlier in the year, or shift to migrate later in the year, and there's good evidence that's been happening over multiple decades," he said. There are tradeoffs that come with the adaptations, however.

Returning to spawn earlier can mean less time in the ocean to grow, resulting in smaller fish, Isaak also noted. Other changes made to accommodate warmer water temperatures may affect the health of the population. "So there's wiggle room, but there's a breaking point, too," he said.

Ultimately, Isaak believes that some runs will be detrimentally impacted as water temperatures in the Columbia Basin increase. "Summer Chinook, fall Chinook and summer steelhead--because they're migrating during peak temperatures--they're going to be a little more vulnerable," he said. Others, like winter steelhead, spring Chinook and coastal species like chum, won't be as vulnerable, he noted.

But, he added, there's a lot of diversity in the Columbia Basin, with five different salmon species and steelhead, and different runs within those that can adapt and survive. As some runs decline, others may be able to take advantage of the resulting loss of competition, and increase in numbers.

In the end, it will come down to how well-suited they are to adjusting to a warming climate, he said, predicting, "There's always going to be salmon somewhere." -K.C. Mehaffey

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NW Fishletter is produced by NewsData LLC.
Publisher/Editor-in-Chief: Mark Ohrenschall, Editor: K.C. Mehaffey
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