A steelhead trout in an Oregon stream. A new agreement restores buffer zones along streams where pesticides cannot be sprayed.

Columbia River steelhead runs have plummeted in the past decade.

Oregon Department of Fish and Wildlife

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It’s an extremely tough year to be a steelhead.

Fish are returning from the Pacific Ocean back to their freshwater spawning grounds in some of the lowest numbers on record, prompting widespread fishery closures and dire warnings of a race toward extinction.

On the Columbia River, just about 54,000 steelhead have made it past Bonneville Dam as of this week. The count so far this year is less than a third of what it’s been the past 10 years on average.

“It seems like the bottom has just dropped out on steelhead,” said Laurie Weitkamp, a research fisheries biologist with the National Oceanic and Atmospheric Administration in Newport.

Columbia River steelhead runs have been gradually shrinking for the past decade, so a small run this year comes as little surprise in that regard. The dismal state of this year’s runs have exposed a critical gap in our understanding of steelhead and how they live.

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Like salmon, steelhead are anadromous. Steelhead are born in freshwater ecosystems and undertake a long migration out to sea when they’re about the size of a grocery-store zucchini. They navigate waters through deserts and forests, over mountains and dams, and out to sea.

After spending a few years in the ocean growing big and strong, steelhead return to freshwater to spawn, and the cycle starts again.

“There are many places in the life cycle of steelhead and salmon where things can go wrong because they use this incredible landscape and waterscape throughout their lives,” said Nate Mantua, a research scientist for NOAA in Santa Cruz, California.

Steelhead are not salmon; they’re trout, but the two are so similar that they’re often spoken of in the same breath. Pinpointing what’s going wrong for steelhead requires close examination of how the fish are different.

Thomas Buehrens is a senior research scientist with the Washington Department of Fish and Wildlife and said coho salmon, in particular, provide the best point of comparison.

“In previous years, steelhead and coho haven’t been perfectly positively correlated,” Buehrens said, “but good years for one have often been good years for the other.”

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Coho salmon and steelhead both exit river systems into the ocean around the same time of year at around the same size. They initially face the same predators and the same ocean conditions.

But then comes the key difference: Coho, as well as other salmon species, typically remain close to shore for their marine life. Steelhead, on the other hand, jet way out into the deep blue, off the continental shelf.

Coho are having a relatively good year, with returns well above the 10-year average so far.

Dams in the Columbia Basin have severely disrupted salmon and steelhead habitat, which has been perhaps the single-largest contributor to the fish’s long-term population decline. Overfishing hasn’t helped either. But Buehrens noted it’s difficult to attribute rapid swings in run size to either of those factors.

“We haven’t made any major changes to those variables on the timescales that we’ve seen this short-term collapse of steelhead or the short-term uptick in coho,” he said.

That’s led many researchers, including Buehrens, to think this year’s steelhead struggles started somewhere in the ocean.

“It implies the problem’s not where [coho and steelhead] are found together, but it’s once the steelhead are parting ways with the coho,” he said.

The ocean life of steelhead is clouded in mystery.

Conducting research that far out in the ocean is hard and labor-intensive. The ocean is huge, and NOAA’s Laurie Weitkamp said even finding steelhead — let alone learning the more intricate details of their marine life — is a tremendous challenge.

“The whole steelhead ocean ecology is a black box,” she said. “We really do not know anything.”

Steelhead could be having a bad year because of increased predation, insufficient food, marine heat waves, disease or any number of things. Weitkamp said scientists can’t know for sure until they figure out where steelhead are.

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Filling in the knowledge gaps about steelhead can help us understand how the fish will respond to increasingly volatile oceans, added NOAA’s Nate Mantua. Humans’ relentless burning of fossil fuels has driven climate change that’s contributing to turbulent ocean conditions.

“We’re not going to be able to turn that around any time soon,” he said. “Not in our lifetimes. We might put the brakes on it and get on a better track for what the future holds, but these fish are going to have to deal with a lot of climate change, a lot of ocean change.”

Mantua added that we already have a clear picture of what steelhead — and salmon, for that matter — need to survive and adapt in a changing climate.

“They need that incredible diversity of life histories that existed in the best populations,” he said. “And we know that that diversity of life histories comes from really diverse and connected habitats … and that is sorely lacking in the Columbia Basin and on the Washington side, the coast and Puget Sound.”

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