Sockeye salmon 'sense magnetic field of home'

Each year millions of fish make the journey home in one of the toughest migrations of the animal kingdom. The memory of the magnetic field where they first entered the sea helps them find their way back, say US scientists.

The data, in Current Biology, provide the first direct evidence that salmon use geomagnetic cues in migration.

Other marine animals, including turtles and seals, may also use the same homing mechanism.

Researchers studied fisheries data spanning 56 years charting the return of salmon to the Fraser River in British Columbia. The route the fish chose to swim around Vancouver Island matched the intensity of the geomagnetic field near their home rivers.

Nathan Putman, a researcher at Oregon State University, told BBC News that for salmon to find their way back home, they remember the magnetic field that exists where they first enter the sea as juveniles, and once they reach maturity, they seek that same coastal location, with the same magnetic field.

"In other words, salmon remember the magnetic field where they enter the ocean and come back to that same spot once they reach maturity."