What Does Home Smell Like?

Salmon’s powerful, ingrained sense of smell allows them to return to the exact stream of their birth for spawning.

A biologist with a salmon tracking device
A biologist with a salmon tracking device Image courtesy of the U.S. Fish and Wildlife Service

Please welcome our new Food & Think blogger, Peter Smith. He replaces Lisa Bramen and joins Jesse Rhodes as a regular contributor to the blog.

When salmon swim into the open ocean, the fish essentially disappear. They travel thousands of miles for one to seven years and then, against all odds, they head home—and not just home in the general sense of the word. Salmon go back to the exact location, the exact river, lake, or stream where they were born. The fish launch themselves hundreds or thousands of miles upstream, then dig a little nest called a “redd” and mate, often their final act before dying.

For years, scientists wondered: How do salmon find their way home? What is the mechanism that they use? Do they navigate using the ocean’s currents, temperature gradients, a solar compass, the polarity of light underwater, or the earth’s magnetism? “There had been many suggestions because it’s a great question,” says Gene Likens, an ecologist at the Cary Institute of Ecosystem Studies in New York. “How does that work?”

Here’s where Arthur Hasler comes in. Hasler grew up in Utah. As a boy he hiked in the Rocky Mountains and eventually went out on mission to Germany (he’s a Mormon). He ended up in Madison, Wisconsin, where he studied zoology and founded lakes studies in the United States. One day in 1946, he went back to Utah on a vacation, to the Wasatch Range, where he had spent much of his time as a boy.

As Likens told me: “He was riding a horse in Utah, on a trail, and came up over a ridge, and he noticed that there was a familiar smell. It smelled like an area that he was used to—that was familiar.” As Likens writes,

He suddenly had what he called a déjà senti experience, “as a cool breeze, bearing the fragrance of mosses and columbine, swept around the rocky abutment, the details of this waterfall and its setting on the face of the mountain suddenly leapt into my mind’s eye.”

“So that was his ‘Aha’ moment!” Likens told me. “He thought, ‘Well, maybe salmon do the same thing, maybe they can smell their home river.’

Others had previously speculated that fish used of odors as homing cues, but Hasler and Warren Wisby introduced the idea of olfactory imprinting in the American Naturalist in 1951. They then went on to show that salmon had an extremely sensitive sense of smell: They could detect one or very few molecules in their nasal chambers. Salmon with plugged nostrils (olfactory pits) were unable to find their way home. The fish’s powerful, ingrained sense of smell allows them to return to the exact stream of their birth for spawning.

“If you think about it, we all do that,” Likens says. “When you come into your house and put on a familiar jacket, it may have a familiar smell.”

It’s almost seems like Hasler took a page from Proust—only if Proust dipped his Petite Madeleine in tisane, then Hasler immersed himself in his waterfall.

I generally don’t believe in epiphanies. In my experience, discoveries and breakthroughs tend to be the result of a slow process, a large accumulations of small things, so that’s why I think Hasler’s revelation is worth sharing—for any of us, trying to find our way home, wherever and whenever that might be.

As Smithsonian’s newest contributor, I’m excited to find a new home to explore the wonder and awe found in our food, where science intersects with storytelling, where epiphanies can cross species and senses and where what we put in our mouths can reveal something greater about the world. I look forward to you joining me in Food & Think.