- Scientists believe salmon memorise magnetic fields to remember locations
- Research found they use the Earth’s magnetic field to guide them to their spawning grounds
- Other animals believed to use Earth’s magnetic field to navigate include birds, turtles, and termites
7 February 2013
Magnetism: Scientists have found evidence suggesting salmon use the Earth’s magnetic field to guide them back to their spawning grounds
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.
‘To find their way back home across thousands of kilometres of ocean, salmon imprint on the magnetic field that exists where they first enter the sea as juveniles,’ said lead researcher Dr Nathan Putman of Oregon State University. ‘Upon reaching maturity, they seek the coastal location with the same magnetic field.’
To test the theory, they looked at fisheries data going back 56 years, documenting the return of sockeye salmon to the Fraser River in British Columbia.
But to reach the river mouth, the fish must either swim around the north or south side of Vancouver Island.
Scientists, who published their findings in the journal Current Biology, discovered their decision was influenced by the Earth’s magnetic field, which shifts slightly each year.
The fish showed greater preference for the inlet that most matched the magnetic value of the Fraser River when they left it two years earlier
If it was closer north of the island, then the fish were more likely to opt for that route, while if it was south there was an increased chance they would migrate using that course.
‘When they attempt to return, they are confronted with a giant obstacle: Vancouver Island is blocking direct access to their river,’ said Dr Putman. ‘So the fish must make a choice: Do they use the northern inlet or the southern inlet in their detour?’
He added: ‘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.
‘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.’
Other animals believed to use Earth’s magnetic field to navigate include birds, turtles, and termites.
And if you are ever lost in the countryside without a compass, don’t panic. Just look for a herd of cows and see which way they are pointing.
After monitoring the behaviour of thousands of cattle, scientists have found that they tend to face north, after using the magnetic field to align themselves.
The behaviour is thought to be a relic of the days when the wild ancestors of today’s domesticated cattle used inbuilt compasses to find their way across the plains of Africa, Asia and Europe on long migrations.
Animals are thought to use internal magnets – made of crystals of magnetite – to find their way around. Homing pigeons, for instance, have a tiny blob of these crystals in their beaks.