Scientists have long speculated how salmon manage to make their way back to the exact same river they were born in after traveling up to 4,000 miles and spending years in the open ocean. A new study from Oregon State University (OSU) reveals that sockeye salmon use a magnetic map to find their way back home to spawn. Scientists have suspected that animals like fish and sea turtles use magnetic fields to help in navigation, but this is the first time that a correlation has been clearly found.
“To find their way back home across thousands of kilometers of ocean, salmon imprint on the magnetic field that exists where they first enter the sea as juveniles,” explained lead author Nathan Putman of OSU’s Department of Fisheries and Wildlife. “Upon reaching maturity, they seek the coastal location with the same magnetic field.”
Putman and colleagues studied sockeye salmon from the Fraser River in British Columbia. These salmon, just like any other, leave their river for the ocean. Their return, however, is more challenging…
“When they attempt to return, they are confronted with a giant obstacle: Vancouver Island is blocking direct access to their river!” he said. “So the fish must make a choice: Do they use the northern inlet or the southern inlet in their detour?”
By studying 56 years of fisheries data collected since the 1950s, the researchers found that the salmons’ preference for the northern or southern route changed with the natural shifting in Earth’s magnetic field. The data showed that the salmon picked which ever direction most closely matched the magnetic value of Fraser River when they left two to four years earlier.
The magnetic field “gets them to within 50 to 100 kilometers of their own river system and then olfactory cues or some other sense kicks on,” Putman said.
In addition to shifting magnetic fields, their route also changed with water temperature. Putman points out that salmon are cold-water fish so they prefer a route with colder water.
“Salmon have to get it right because they only have one chance to make it back to their home river, so it makes sense that they may have more than one way to get there,” he said. “The magnetic field is amazingly consistent, so that is a strategy that can withstand the test of time. But they may also use the sun as a compass, track waves breaking on the beach through infrasound, and use smell.”
To learn more:
- Read the full story from OSU: Salmon May Use Magnetic Field as a Navigational Aid
- Find the study, published in Current Biology, here: Evidence for geomagnetic imprinting as a homing mechanism in Pacific salmon
- Check out this article from BBC: Sockeye salmon ‘sense magnetic field of home’
Copyright © 2013 by Marine Science Today, a publication of Marine Science Today LLC.