DARRINGTON — Fisheries biologist Pete Verhey waded through the cold, clear creek that feeds into the North Fork of the Stillaguamish River, scanning riffles and side channels looking for evidence of fish eggs.
“We got one!” he shouted, pulling pink tape from his waders and marking the spot where a steelhead trout had buried eggs in the gravel.
The redd, or spawning nest, is an encouraging sign that steelhead trout may be making their way upstream from Oso — above where a massive landslide decimated a riverside neighborhood a month ago and pushed several football fields worth of sediment down the hillside and across the river.
As search crews continue to look for two missing people in the slide, scientists also are closely monitoring how the slide is affecting federally endangered fish runs, including chinook salmon and steelhead.
It’s too early to know the slide’s long-term effects, but so far scientists are hopeful about the immediate prospects: adult steelhead are spawning in clear waters above the slide area, and typical numbers of baby fish are migrating downstream to the marine waters.
“It’s still a human tragedy, and we’re respectful of that,” said Jenni Whitney, a district fish biologist with the state Department of Fish and Wildlife. “We’re doing our best to monitor fish because eventually people will want to know.”
Water samples tests also have turned up low levels of fecal coliform, nitrates and other pollutants, easing concerns about chemical contamination for people and fish, said Dick Walker, a senior spill responder with the Department of Ecology.
The state and Stillaguamish Tribe were already in the midst of yearslong efforts to monitor and restore fish runs when the slide struck. That wealth of historical data will help them gauge future changes.
A few days after the March 22 slide, biologists working with the tribe saw a spike in dead juvenile salmon migrating out to Puget Sound. They saw more deaths than usual in its smolt trap, essentially a water wheel in the river near Stanwood that allows scientists to trap, count, measure and then release baby fish.
“We were really concerned the first few days,” but it was an isolated event, said Jason Griffith, a fisheries biologist with the tribe.
The slide had temporarily dammed up the river, and he and others were initially worried that the dam could break. A flash flood warning issued downstream of the slide was in effect for the first few days.
Once the river cut a channel and pushed through, a ton of silt began moving downstream. The waters down from the slide turned murky and gray. Muddy waters make it difficult for fish to survive. Sediment can damage fish gills and make it harder for fish to see their food.
Fish holding in pools near the area of the slide and any eggs in the gravel at the time likely were damaged, said DFW’s Whitney.
“It’s hard to know how long it will take for sediment to move out of system, and how long it will take for (fish) to return. How will it affect fish long into the future?”
Those are some questions scientists hope to answer as they continue monitoring fish in the months and years to come.