Researchers: Salmon Memorize Magnetic Fields to Guide Them Back to Spawning Grounds

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February 08, 2013

Researchers: Salmon Memorize Magnetic Fields to Guide Them Back to Spawning Grounds

By Chad Love

How salmon manage to find their way back to the river of their birth is one of the great mysteries of the natural world. Now scientists believe they may have solved this mystery.

From this story in the (UK) Daily Mail:
Ever wondered how salmon navigate across thousands of miles of ocean without getting lost? After years feeding at sea, the fish swim through vast expanses of featureless water back to the rivers where they hatched. Now scientists may have finally answered a mystery that has baffled them for decades, after finding evidence suggesting salmon use the Earth’s magnetic field to guide them back to their spawning grounds. Researchers believe that when the fish first enter the sea, they memorise the location’s magnetic field and use it as a home address. The magnetic field varies across the globe, allowing animals to use it as a ‘map’ and determine their location.

According to the story, salmon imprint on and basically remember the magnetic fields that exist when they first enter the sea. When they return to spawn, they seek out that same magnetic signature. Scientists tested the theory by looking at historical data for the Fraser River in British Columbia. Vancouver Island sits at the mouth of the Fraser river, so returning salmon must either swim to the north or the south of the island to enter the river.

Since the earth's magnetic field is constantly undergoing minor shifts and variations, scientists correlated the preferred route of the salmon with the magnetic field data from the same year the fish went to sea.

What they found was that salmon tended to choose their route around Vancouver Island based on the distinct magnetic signature of the river when they first went to sea two years earlier.

Prety cool stuff. But I always just assumed the salmon used GPS like the rest of us. Doesn't everyone?

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from Ontario Honker ... wrote 18 weeks 1 day ago

I was always told that they smelled their way home once they got close to the river. My late wife and I marveled at an incredible phenomenon one calm evening when we were fishing in the Straits of Juan de Fuca on fall day back in 1987 just before we were married. It was a slack tide near sundown and the sea was flat as a mirror. As far as we could see in any direction coho salmon were swimming lazily right at the the surface with fins actually sticking up out of the water. A biologist later told me they do that to catch a "smell" of their home stream in the fresher, less dense water near the surface. It was really something to see. Beautiful memory.

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from labrador12 wrote 18 weeks 1 day ago

I wonder how they recolonize systems after glacial periods. Many streams that had runs obliterated by fish traps in the 1800s recolonized themselves. All the small Great Lakes tributares are self colonized too.

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from Ontario Honker ... wrote 18 weeks 1 day ago

Labster, the classic study for that was after Mt St Helens blew. One fork of the Turtle River was absolutely ruined for habitation by mud flows. So what would happen to the salmon that were supposed to migrate up there that fall to spawn? They chose instead to go up the forks that were not contaminated (they were tracked by their microchip ID pins inserted in nose as fingerlings). Obviously that water smelled closest to what they were trying to key on. We now know that a certain percentage of all salmon runs are "adventurers" who actually do not return to the stream from whence they were spawned but go somewhere else. The percentage of errant spawners varies from species to species. As I recall, sockeye are the most adventuresome. Of course, this would be an inherent survival trait that has no doubt survived since glacial times, as you suggested. Colonists also ensure the genetic integrity of the species in general. If conditions in a particular drainage become fatal for the strain of salmon in it, there's at least some possibility that colonizers from somewhere else will bring in fresh genetic resources that might not be as vulnerable.

And then there are those who still insist Charles Darwin was nuts. Pfffft. I say put them on a strict diet of green chili burritos so they'll have a chance of blowing their heads out of their butts. Education hasn't yet seemed to be able to do the job.

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