Sockeye salmon typically swim as much as 4,000 miles into the ocean and then, years later, can navigate back to the upstream reaches of the river in which they were born to spawn their young, they said.
Writing in the journal Current Biology, the researchers suggest salmon find those home rivers by sensing the river's unique magnetic signature.
They studied the routes salmon had taken from their ocean destinations, mostly near Alaska or the Aleutian Islands in the Pacific, to the mouth of their home river -- the Fraser River in British Columbia, Canada.
Then they gathered data on the intensity of the Earth's magnetic field at pivotal locations in the salmon's migratory route.
"These results are consistent with the idea that juvenile salmon imprint on [i.e., learn and remember] the magnetic signature of their home river, and then seek that same magnetic signature during their spawning migration," Oregon post-doctoral researcher Nathan Putman said.
Most salmon make the round-trip migration, which may total 8,000 miles, only once in their lives, typically dying soon after spawning, the researchers said.
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