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article imageStudy finds salmon use magnetic fields to find their way home

By Martin Laine     Feb 8, 2013 in Science
Long before humans discovered magnetic north and invented the compass, Pacific sockeye salmon were using the Earth’s magnetic fields to guide them back to their home rivers.
The scientists found a strong correlation between known salmon migration patterns over the past 56 years and shifts in the earth’s magnetic fields over the same period. The researchers studied the migration of salmon that had spawned on the Fraser River in British Columbia, Canada. After spawning, the young fish swim out into the open ocean, swimming as much as 4,000 miles into the Pacific where they spend two years before returning to the Fraser River as adults.
The study was published in this week's issue of Current Biology.
Scientists have long wondered how salmon accomplish the journey without any apparent landmarks or other guidance. The theory that they might use the Earth’s magnetic field to direct them was first advanced in 2008 by marine biologists at the University of North Carolina in Charlotte, N.C., according to an article in the Science Daily.
“These results are consistent with the idea that juvenile salmon imprint on the magnetic signature of their home river, and then seek that same magnetic signature during their spawning migration,” said Nathan Putman, a researcher at Oregon State University and the study’s lead author, in an article on the National Science Foundation website. The study was partly funded by the NSF.
The Earth’s magnetic fields vary considerably, so each field has a unique pattern or signature. This study is the first to show that an animal has the ability to learn this signature and to use it to find a particular location, in this case the home river.
“For the salmon to be able to go from some location out in the middle of the Pacific 4,000 miles away,” Putman said. “They need to make a correct migratory choice early – and they need to know which direction to start going in.”
Still unknown is how often the fish “check in” on the magnetic field. Putman thinks that they would need to check in from time to time to correct their course during the early stages, and then more frequently as they get closer.
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