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Scientists Monitoring Oso Slide’s Effects On Stillaguamish Fish Runs

As the search for victims of the Oso mudslide continues, scientists are monitoring its effects on endangered fish runs.

The cloudiness of the Stillaguamish River due to sediment washing down after the slide is a big concern. But it looks like initial fears of devastation are giving way to optimism. 

'Fairly Alarming' At First

Credit Bellamy Pailthorp / KPLU
The smolt trap's design is based on the Archimedes screw principle.

At river mile 6, upstream from where the Stillaguamish meets the ocean and several miles downstream from the slide, a large screw-shaped waterwheel on a barge slowly turns, pulling baby fish from the river into an 8-foot-long trap. Biologists have been counting smolts here since 2001.

“So there’s a couple chum and some pink and a Chinook salmon in there,” said Jason Griffith, a fisheries biologist with the Stillaguamish Tribe.

Griffith oversees the young technicians at work aboard the smolt trap. They catalogue hundreds of tiny fish each week and measure them before letting them go back on their way out to sea.

Credit Bellamy Pailthorp / KPLU
Maggie Taylor and Katie Moyers are fisheries technicians with the Stillaguamish Tribe.

Maggie Taylor, who was working on the day of the Oso mudslide and in the week afterwards, says there were a lot of concerns. First, there was the danger that the dam of debris might break and release a big wall of water. That didn’t happen, but after the river cut through the debris, she says they did see a lot of dead fish coming into the trap.

“The first couple of days after, it was fairly alarming. There was one day when I would say about 20 percent of the fish we caught were mortalities,” Taylor said.

Concerns Over Heavy Sediment

A fish pathologist examined some samples and found two causes of death related to the heavy sediment coming downstream.

Credit Bellamy Pailthorp / KPLU
Fish death after the slide has slowed now; some mortalities are normal.

The first, says Griffith, was that the particles made it more difficult for the fish to breathe, and may have damaged their gills.

“It’s like us being in a really smoky room or something like that; it’s harder to breathe. So the fish were experiencing that, but also having trouble feeding. So the fish he (the pathologist) examined had very little in their stomachs,”  he said.

The theory is that the fish couldn’t see their prey because of the very dark and turbid waters, which is still cloudier than normal.

That’s an even bigger concern upstream in the slide area, where fish returning from the ocean normally spawn and need clear, clean gravel. Surveys of areas above the slide have so far found evidence of very few adult steelhead coming through.

Fish Have Adapted In The Past

But it’s early days yet. Salmon aren’t expected to return for a couple of months. And the fish deaths at the smolt trap subsided after the first week. Griffith, cautiously optimistic, is taking that as a good sign. 

Credit Bellamy Pailthorp / KPLU
Tiny salmon less than a year old are captured and cataloged before they are allowed to return on their way out to sea.

“It’s easy for people when they see these big events and landslides to despair and think all is lost," he said. "But salmon have been around a long time and they are good at occupying niches and exploiting the good habitat that is there. And they’ll find it and use it, and they’ll spawn and come back, like they have been for thousands of years.”

He says they will certainly monitor the situation carefully and expect a dip in the numbers coming back. But he says the Stillaguamish has seen many slides before, and the fish have adapted.

Bigger concerns are longer-term pressures from developments and warmer water temperatures that limit fish habitat in the area.

Bellamy Pailthorp covers the environment beat for KNKX, where she has worked since 1999. From 2000-2012, she covered the business and labor beat. Bellamy has a deep interest in Indigenous affairs and the Salish Sea. She has a masters in journalism from Columbia University.
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