Salmon use the Earth's magnetic field to navigate across thousands of miles in open water as they locate their river of origin to breed, suggests a new study.
Salmon are cold-water fish that enter the sea as juveniles and when they mature, they make their journey across the ocean to locate their home river. Every year, millions of salmon fish make their journey back home, in what might be called as one of the toughest migrations of the animal kingdom, reports BBC.
Until now, it was not known how the salmon find their way back to their home river. But a new study has found that salmon use geomagnetic cues in migration.
A team of researchers led by Nathan Putman, from Oregon State University, examined 56 years of fisheries data documenting the return of sockeye salmon to the Fraser River in British Columbia.
Salmon returning to the Fraser River must detour around the massive Vancouver Island to reach the mouth of the river, by choosing either a southern or a northern route. The research team found that the route the fish chose around the island correlated with changes in the intensity of the geomagnetic field near their home rivers.
When the intensity level of the geomagnetic field for the Fraser River shifted to the north, the sockeye chose a northern route to return to their home river. When the field shifted slightly south, they chose a southern route.
Putman and his colleagues suggest that the salmon remember the magnetic field and use it as a navigational aid to come back to their home river, once they reach maturity.
"What we think happens is that when salmon leave the river system as juveniles and enter the ocean, they imprint the magnetic field - logging it in as a waypoint," Putman said in a statement.
"It serves as a proxy for geographic location when they return as adults. It gets them close to their river system and then other, finer cues may take over."
Other aquatic animals like sea turtles, seals, eels and tuna are using a similar migration strategy. It is not clear as to how the salmon sensed magnetic fields when they were born. But scientists believe that the change from fresh to saltwater might be triggering some kind of neurological process, the BBC report said.
Once the salmon locates its home river using the magnetic field, it then uses chemical cues to locate its birth stream.
The details of the study appear in the Current Biology journal.
Researchers are planning to study more about how salmon navigate through magnetic fields, which could be useful for commercial fisheries.