Scientists buried these tools in a WA river. Then the atmospheric rivers hit

SQUIRE CREEK, near Darrington - Michaela Lowe wielded an antenna on a long handle, scanning the creek bottom early this year. She and her fellow scientists trudged through the water in dry suits and life vests.

A pulsing chime cut through the rushing creek: they'd found salmon eggs. Well, not real eggs.

To mimic nests where salmon lay their eggs, the scientists buried a series of boxes and chains in gravel across the Stillaguamish River watershed last fall. Then, this winter, torrential rain and record flooding hit the region. These storms, a part of life in the Northwest, are expected to become more extreme, bringing more frequent and severe flooding as the climate warms.

The research team with the Washington Department of Fish and Wildlife is hoping the tools they retrieved here can help them better understand threats to the life cycle of imperiled Stillaguamish Chinook.

A box laden with fine sediment could indicate real salmon eggs were entombed, suffocated, while a chain of exposed beads could signal salmon eggs were blown out of the gravel.

A lot is at stake.

While Chinook have been struggling across Puget Sound, Stillaguamish Chinook are in an especially precarious place. About 1,200 Chinook have returned to the river to spawn on average each year over the past decade, roughly 10% of returns a century ago. There hasn't been a commercial fishery here for decades.

The Stillaguamish Tribe is capturing wild adult Chinook and raising juveniles in captivity to sustain salmon genetically rooted to the river while habitat is restored, Stillaguamish Tribe fisheries director Kadi Bizyayeva said.

A healthy river moves in broad, slow pulses amid heavy rainfall: rising then dissipating as it fans around logjams over a wide flood plain. Floodwaters carry big trees and sediment downstream, providing habitat for fish as the flood recedes.

But these meandering Puget Sound rivers were largely evicted from these wet valleys, severed from their messy family of oxbows, sloughs and braided channels, and confined to simple channels like aqueducts during European settlement as people built their lives and livelihoods in the flood plain. In heavily altered watersheds, such as the Stillaguamish, most of the energy of a flood shoots downstream like a fire hose, which can be catastrophic for people and fish.

The Stillaguamish Tribe has led restoration efforts, bringing in partners and working to "decolonize" the river: removing or setting back human-made levees and dikes and reintroducing large wood to recover hundreds of acres of the river's historic estuary and flood plain.

In the past, these salmon may have faced a year or two of poor freshwater conditions, or poor ocean conditions, but salmon could rebound when things would turn up. Now, they face more frequent threats.

Stillaguamish Chinook often see a climate double whammy of drought and low river flows while spawning in the river, and winter flooding that can smother or wash out incubating eggs, Bizyayeva said. As flooding gets more severe, even more habitat restoration needs to be done just to maintain the status quo, said Jason Griffith, a longtime environmental manager with the tribe.

In the short term, he said, "we're just trying to keep them from going extinct. Puget Sound residents, Griffith said, have the opportunity to turn things around in the freshwater, while there are very limited options to change conditions in the ocean, he said.

At a project site where the flood plain has been reconnected, Griffith explained, sediment spreads over the land instead of barreling down the river and smothering eggs.

"I have never been able to use my treaty rights to fish for Chinook," Bizyayeva said. "For me, the only way I can really access treaty rights on Chinook is to serve in a way that will bring that back for future generations."

Bizyayeva said she hopes Lowe's study will help quantify much of the traditional knowledge that tribal elders have passed on about impacts in the system, and inform future targeted restoration.

In the Stillaguamish watershed earlier this year, Lowe combed through the creek bed until her fingers struck the edge of the plastic egg box. She pulled fellow researcher Stefan Woodruff in closer.

Woodruff swooped a plastic tote under the box as it began bleeding fine sediment. He waded to shore with his catch.

Each sample was poured into a bucket and sealed in with a lid. Woodruff, Derek Dewey and Nick Mankus, scientific technicians with the state, schlepped the buckets to the back of their pickup and hauled them to an Ellensburg lab to be processed.

The small boxes were buried about a foot deep, roughly the depth Chinook dig to lay their eggs. A couple of feet downstream of each box, scientists placed a beaded chain in a pipe and pounded it into the creek bed, leaving the last bead at the top of the chain just below the surface.

They attached tags typically used to track fish so they could identify each box and chain.

Previous research in tributaries of the Columbia River helped define the relationship between scour (when eggs are washed away), sedimentation (when eggs are buried) and salmon survival. While it likely varies between east- and west-side streams, lead researcher Chris Johnson said, it allows scientists to apply a link between environmental conditions and Chinook salmon survival in research such as Lowe's.

In the Columbia basin, scientists found, on average, that egg-to-fry survival declined nearly 17% for every centimeter - about the width of a pea - of scour. They also found that with every percentage increase of fine sediment within a redd, the baby fish survival decreased about 1%.

Lowe's study, which began in 2023, updates similar research led by the Stillaguamish Tribe and Snohomish County in the early 2000s. Lowe aligned some of her 20 study sites across the basin with those from the previous research.

Since that study, there have been landslides, as well as changes in logging practices and road management in the watershed. Her research will revisit the original hypotheses about how sedimentation and scour affect egg survival, and offer clues about changes over time and the impacts that persist.

So far, some data suggests it's not necessarily a big flood that causes the most damage, Lowe says. It's a complex relationship. Multiple storms back to back can hit just as hard as one big event, and survival may also depend on where the redd is in the watershed.

The boxes the researchers pulled from the river this year showed dramatic variation in how much fine sediment had collected across the 20 locations. These results, along with the scour data, will be used to estimate salmon survival from eggs to fry.

Salmon have persisted in these often volatile Northwest rivers for millennia. Through volcanic eruptions, landslides, drought, earthquakes, tsunamis and certainly flooding, salmon have evolved and adapted. But now humans are changing things faster than ever before.

"Allowing rivers to have their natural processes and dynamics, it's messy and it's stressful sometimes, but that's how these ecosystems are supposed to behave," Lowe said, "and fish can respond to that appropriately if we let them."

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