Study: Animals find their way magnetically

Researchers at the University of North Carolina at Chapel Hill have proposed a new theory to explain how sea turtles and salmon find their way back to their birthplace after journeys of thousands of miles.

Migratory animals such as sea turtles and salmon imprint on the Earth’s unique magnetic signature of a stretch of coast and retain that information to guide them back there, according to the theory developed by Kenneth Lohmann, a professor of biology at UNC-Chapel Hill and others.

Lohmann who has spent 20 years studying how sea turtles navigate, said the Earth’s magnetic field varies predictably and each area of the coast has its own magnetic address. The homing instinct may be explained in terms of migratory animals such as turtles learning that unique magnetic signature and using that data to navigate years later.

“It’s a new explanation for how the turtles and salmon might find their way back,” Lohmann said. “We think it’s a good one. This is really the first plausible explanation for how it might work.”

The new research appears in the latest issue of the journal Proceedings of the National Academy of Sciences. It was funded by the National Science Foundation.

Why turtles and salmon migrate long distances only to return to their birthplace is not known. Scientists speculate the homing instinct evolved because of a survival strategy that if the birthplace was good enough for the adult, it will be safe for their offspring also.

Commenting on the theory of magnetic imprinting, Andrew Dittman, a research fishery biologist at the National Oceanic & Atmospheric Administration's Northwest Fisheries Science Center in Seattle, said, “I think it’s a reasonable idea, but it’s indeed purely hypothesis .... People have discussed these notions for some time. We clearly know that salmon can detect magnetic fields and use them to orient.”

Dittman said scientists have concluded that salmon are guided by olfactory cues once they reach their home rivers, but it’s unreasonable to expect those cues could extend thousands of miles into the ocean. He said how the fish traverse thousands of miles of ocean to find the home river has been unknown.

Lohmann said he hoped the paper would stir discussion among scientists and eventually lead to a way of testing the theory.