"Movement Ecology" to Explain Salmon Homing?

John Roach
for National Geographic News
December 2, 2008

Sea turtles and salmon may use their sensitivity to Earth's magnetic field to guide them home at the end of their epic coming-of-age journeys.

Juvenile sea turtles and salmon leave their birthplaces with an inescapable wanderlust, swimming hundreds or even thousands of miles away.

But after years on the high seas, the biological urge to reproduce calls them home. And so they return to the very spots in which they were born.

Exactly how the marine animals find their way home is an enduring scientific puzzle.

Kenneth Lohmann, a marine scientist at the University of North Carolina, Chapel Hill, says the secret may lie in the variability of Earth's magnetic field.

Each coastal area has a unique magnetic signature, he said.

"What we're proposing is the sea turtles and salmon, when they begin life, basically learn or imprint on the magnetic field that marks their home area," he said.

"They retain this information. And years later, when it is time for them to return, they are able to exploit this information in navigating back to their home area."

Once the animals reach their native coastal areas, other senses, such as vision or smell, may guide them the rest of the way.

Lohmann and colleagues propose the theory in a paper published today in a special package about the field of movement ecology in the journal Proceedings of the National Academy of Sciences.

An Ancient Idea

Some 2,300 years ago, the Greek philosopher Aristotle searched for common features that unified animal movements of all types, noted Ran Nathan, an ecologist at The Hebrew University in Jerusalem.

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