This article was originally on Hakai magazine, an online publication about science and society in coastal ecosystems. Read more of these kinds of stories hakaimagazine. com.
Of all the traits that make salmon extraordinary migrants — their jumping power, their tolerance for both fresh and salt water, their attunement to Earth’s magnetic fields — their sense of smell is perhaps the most impressive. Guided by the scents they imprint on in their youth, most adult salmon return to spawn in the stream where they were born. No one knows exactly what scents smolts remember, but it is likely a combination of mineral and biological cues, such as signature metals and the smell of their own relatives.
However, if scientists at the Oregon Hatchery Research Center have their way a few years from now, some chinook salmon will be chasing an entirely different scent: the rich, beer-like bouquet of brewer’s yeast. The enticing smell of beer is an attempt to solve a sticky conservation problem: How do you get salmon home from the hatchery?
Although the vast majority of salmon return to their birthplace to spawn, they sometimes slip. A small portion naturally wanders to other streams. “From an evolutionary standpoint,” says Andy Dittman, a Seattle, Washington, biologist with the U.S. National Oceanic and Atmospheric Administration, “it’s an important alternative strategy” that helps populations survive disasters and expand their range.
After Washington’s Mount St. Helens erupted in 1980, for example, trout, a close relative of salmon, drained the ash-choked Toutle River and breed in nearby watersheds. And as climate change shrinks Alaskan glaciers, so do salmon trickle into newly exposed streams and lakes.
But salmon raised in the brooder takes it to the extreme. Many hatchery fish are released into unfamiliar streams or are released during developmental stages when they are not easily imprinted. As adults, these fish often sail past their breeding grounds and mate with wild-born fish, disrupting wild gene pools which have been refined through thousands of years of natural selection. On the Elk River, this problem was historically acute. For some years, Dittman recalls, more than half of the breeding fish were brood chamber salmon roaming wild spawning grounds.
In 2016, the Oregon Department of Fish and Wildlife commissioned the state’s hatchery research center to solve the problem. Could scientists imprint young hatchery-raised fish on a scent of their choice, one that would lure them home years later?
Finding the perfect scent largely fell to researcher Maryam Kamran. Just like Pavlov trained his dog drool at a sound, Kamran dropped various smelly substances into tanks full of pinky-length salmon roasts and then added food pellets to get the fish to associate the smells with their meals. Then if she could just add the scent to the water and still see the fish firing excitedly, she knew they would be able to recognize that scent.
Kamran tested a huge — and sometimes weird — range of flavors, including shrimp extract, watercress tincture, steelhead skin, and minnow gall. She mixed and matched different proteins and hormones and pheromones. You try things that give the fish information, says Kamran. “Is there a predator? Is there a partner? Is there food? What is the quality of the living environment?”
In his Seattle lab, Dittman complemented Kamran’s efforts. He placed electrodes on the salmon’s odor receptors, then sprinkled them with Kamran’s chosen odors to see how their neurons reacted. “Whatever scents we chose,” says Kamran, “we had to see if the salmon noses could actually detect it.”
After several years, a leading candidate emerged: a cocktail of amino acids purchased from a commercial lab. In 2021, managers at the Elk River Hatchery released the first quinoa salmon pressed on those acids into the wild, along with others raised on minnow bile and other compounds. Yet, for all its promise, the amino acid mixture proved prohibitively expensive to use in large quantities. So the search for a cheap scent continued, which led the scientists to beer this spring.
The idea came from Seth White, director of the Oregon Hatchery Research Center. White, an amateur beer maker, knew that brewer’s yeast contains glutamate, an amino acid that salmon can latch onto. And he knew exactly where to find it in large quantities.
One day in March, White visited Newport, Oregon, where the Rogue Ales brewmaster flipped a handle on two kegs of beer and poured out pitchers of trub—the yellowish sediment of malt particles, solidified proteins, and sedimented yeast left behind by the brewing process. White wrapped plastic bags of trub in a cooler and drove the hour to the hatchery research center. “I felt like Ulysses on a quest,” says White.
His journey was not in vain, as Dittman soon discovered that young salmon are very sensitive to the mess. “It seems to be a good candidate,” says White. “It’s going really well so far.”
Of course, it is one thing to get young fish to press a scent, but it is quite another to get adult salmon to chase it back to their birthplace. Last winter, the first males pressed on the amino acid cocktail began to trickle back into the Elk River, though scientists have yet to analyze the data. On the beer side, White says the Oregon Hatchery Research Center still needs to conduct experiments before hatchery managers consider exposing their fish to trub. If it ever works out, he’s already picked a name for the brew: Olfaction Pale Ale.
This article first appeared in Hakai magazine and is republished here with permission.