BOISE — In 20 years, the Chinook salmon in Idaho may lose a critical home for spawning in Central Idaho.
A new study by University of Idaho researchers predicted that Bear Valley Creek, a stream that flows into the Middle Fork of the Salmon River, will drop by nearly half by 2040, and by nearly three-quarters by the end of the century.
Warmer temperatures cause snow to melt earlier in the spring, providing less water for salmon in the summer. And for salmon, cold, freshwater streams are an important home. Smaller streamflow means smaller salmon habitats.
“Preserving this habitat is necessary for the species to survive,” Daniele Tonina, lead author of the study and professor at the Center for Ecohydraulics Research at the University of Idaho, told the Idaho Statesman.
The researchers studied Chinook salmon habitats in Bear Valley Creek with LiDAR, a type of 3D laser scanning. They also analyzed 60 years of historical data collected at nearby streams to predict how salmon habitats will change over the next 70 years.
Shrunken and fragmented habitats won’t be able to support the number of salmon that have occupied the area historically, which could make it difficult for salmon to continue living in those areas, according to the study.
As migratory fish, salmon influence many ecosystems
“Salmon were made to move, and they need to be able to do that,” Tim Copeland, Idaho Fish and Game wild salmon and steelhead program coordinator, told the Statesman.
Salmon are anadromous fish — born in freshwater, they migrate to the ocean where they spend most of their lives, and return to freshwater to spawn.
Their migratory life cycle makes them important to the ecosystems they encounter. They bring nutrients like nitrate into high elevation streams that would otherwise be nutrient-limited, Tonina said.
Bear Valley Creek is nearly 1,000 miles away from the ocean by the river network, Tonina added, meaning that salmon face many different environments throughout their journey. Larger animals, such as bears and eagles, depend on salmon for their survival and prey on them.
In other words, they “bring the productivity of the ocean up to Idaho’s mountains,” Copeland said.
Laser technology helps researchers see what salmon see
A key aspect of the study is that researchers examined salmon habitats at a scale that was meaningful to the fish, Tonina said. They looked at the environment in 1-meter by 1-meter segments and scaled those observations up to understand the full, detailed picture.
LiDAR allowed researchers to penetrate the water’s surface and take photos of the stream bed. This information allowed them to simulate what the salmon see — helping them understand whether the habitat had the right size, velocity, depth and temperature to support salmon through their life functions, such as spawning, growing and rearing.
Then, the researchers looked at historical streamflow trends with data spanning 1957 to 2016 — collected by the U.S. Geological Survey and Department of Water Resources at nearby streams.
They used this information to model what could happen to salmon habitats in Bear Valley Creek by the end of the century.
Projected reductions in summer flow could decrease spawning habitats by 38%, rearing habitat by 2.5%, and off-channel habitat by 29%. Off-channel habitats are smaller streams that typically have more food, have lower water velocity, and protect juvenile salmon from predators, Tonina said.
Additionally, they found that between 1957 and 2016, average summer flows in the studied area declined by 19%, which diminished habitats used by adults and juvenile salmon.
Shrinking habitats will hurt salmon
Reduced summer streamflow will impact where salmon move and how many will return to the stream, Tonina added.
Shrinking habitats could lead to increased competition among salmon looking for nest sites and other resources — which can impact mortality and migration timing, the researchers state in the paper. Additionally, channels in the stream may separate from each other, causing flows to become stagnant and less habitable.
Other streams within the Pacific Northwest may see similar trends in flow reduction and shrinking salmon habitat, Tonina said, since Bear Valley Creek is a typical river system for the area.
Copeland has noticed this trend. He compared two consecutive years of survey work in Big Creek, which is farther north of Bear Valley Creek: One year, stream flows were good throughout the summer, and salmon dug their nests pretty far upstream, he said. The next year had reduced snowpack, and the salmon couldn’t get as far upstream as they did before, although they still had good spawning conditions.
The Bear Valley Creek study was conservative in assessing the impact of climate change on salmon. Other factors can impact their survival, Tonina said. For example, lower streamflow means that the river will be less capable of moving sediment throughout the region, which could be detrimental to fish.
And other species, such as lamprey and rainbow trout, which migrate to sea, may also experience shrinking habitats, Tonina added.
Climate change isn’t only threat to salmon
Salmon have more than just climate change to worry about.
Salmon declines go back to the late 1800s, Emmit Taylor Jr., director of the Nez Perce Tribe’s fisheries watershed division, told the Statesman.
Canneries, fisheries, dams, human impacts on tributary habitats, overgrazing, road building and ocean fisheries are obstacles that salmon didn’t have to go through 200 years ago, he said. Since 1997, he’s been working to restore fish habitat throughout the Nez Perce Tribe’s treaty territory, which overlaps with Idaho, Washington and Oregon.
The tribe has turned hundreds of miles of habitat back for salmon and other wild fish, Taylor said, but the outlook for salmon is still daunting.
The Nez Perce Tribe has defined a quasi-extinction risk threshold — hit when 50 or fewer fish return to a spawning area for four consecutive years. And an alarming number of areas in the territory are getting close to this threshold, Taylor said.
“Personally as a tribal member, the past five years have just been hard,” Taylor told the Statesman.
Fishing provides connection to the land, Taylor said, and when there’s no fish, that connection is lost.
Taylor and his family recently took a trip to the South Fork Salmon River. It’s been five years since they were last there, because there haven’t been enough fish to harvest.
“My son was kind of losing memory of the South Fork Salmon,” Taylor said, “and that’s going to have a ripple effect down the line.”
Tribal members work hard to bring the fish back so they don’t lose the cultural connections that the fish have provided for generations, he added.
Salmon are a resilient species, Copeland said. But humans can still help them out.
Idaho Fish and Game does “cradle-to-grave monitoring” on wild salmon, Copeland said, with methods like snorkel surveys and genetic sampling.
In their everyday lives, the public can advocate for clean water and actions that protect rivers, streams and fish, Taylor said.
Salmon are a species we can’t afford to lose, Taylor said. “There’s no if, and’s or but’s about it — we just can’t lose it.”
