How do salmon find their way back to the exact same stream where they hatched? The ocean is vast, and salmon travel thousands of miles up and down Alaska and the Pacific Coast. So how on earth do they find their way back to a very specific river and stream?
Well it's exactly that - the earth.
Specifically the earth's magnetic field. Researchers from the University of Washington and Oregon State University hypothesized that salmon must use the earth's magnetic field to steer themselves home. Their brains are very small, and while their other senses are magnificent, there is something special about the earth's magnetic field.
According to National Geographic, scientists took 56 years of fisheries data to study a group of sockeye salmon that spawned in the Fraser River in British Columbia and spent much of their adult lives in and around Alaska‘s Aleutian Islands. The researchers studied the likely routes the salmon took in transit between these two locations and compared it to data on the strength of the Earth’s magnetic field at the time.
The navigational choice depended largely on which route most closely matched the magnetic signature of the Fraser River when the salmon first left the area for the saltier waters of the Pacific.
“These results are consistent with the idea that juvenile salmon imprint on the magnetic signature of their home river, and then seek that same magnetic signature during their spawning migration...”
“As the salmon travel that route, ocean currents and other forces might blow them off course. So they would probably need to check their magnetic position several times during this migration to stay on track. Once they get close to the coastline, they would need to hone in on their target, and so would presumably check in more continuously during this stage of their migration.”
This study, published in “Current Biology”, was the first to document an animal’s ability to learn to navigate via the magnetic field.
These results help explain why salmon raised in hatcheries so frequently become lost in the ocean. Since many fisheries are crisscrossed with electric wires, magnets, and metallic objects—all of which alter perception of magnetism—the fish never learn the magnetic “feeling” of home.
Scientists can use this data to forecast where salmon will be in future seasons by studying how the magnetic field changes over time.
Try that at your next cocktail party conversation!