Magnetic Field Is Secret to Salmon 'Compass' Say Scientists

It's long been known that birds navigate during migration by sensing the Earth's magnetic field but new research says fish can, too.

"Researchers compared records of local magnetic fields and 56 years' worth of commercial fishing data documenting routes taken by homing sockeye salmon during the annual Fraser River salmon run," writes the Wall Street Journal.

The fish sense chemical traces of their spawning grounds to find their way back once they're in local waterways, but out in the open ocean, scientists weren't sure how they navigated.

But the routes salmon took back from the ocean varied depending on the magnetic drift of the Earth. "We found that the proportion of salmon using each route was predicted by geomagnetic field drift: the more the field at a passage entrance diverged from the field at the river mouth, the fewer fish used the passage," said researchers in Current Biology.

"When sockeye have gotten nice and fat out in the Pacific and start heading home to spawn, they have to decide which way to swim around Vancouver Island," said Nathan Putman, a postdoctoral researcher at Oregon State. "There's this 300-kilometer piece of land blocking their entry into the Fraser River from the ocean, and they either have to swim north by way of the Queen Charlotte Strait, or south through the Strait of Juan de Fuca."

The salmon search for an electromagnetic signal closest to the one they remember when they left their spawning grounds as juveniles.

"I know it might seem fantastical to some people that fish have evolved compasses in their noses," Putnam said. "But remember, a sockeye only gets to do this once. They have just one chance to spawn and pass on their genes so there is huge selective pressure for them to get it right."