Magnetic fields let sea turtles navigate

CHAPEL HILL, N.C. — Research from North Carolina biologists shows that loggerhead sea turtles use the Earth’s magnetic fields to navigate back to their home beaches.

But sometimes, another beach has such a similar magnetic field, the sea turtles head to that one instead, as if their internal GPS has just slightly mixed up addresses — even if the beaches are far away from each other.

A new study from University of North Carolina biologists Kenneth Lohmann and J. Roger Brothers shows that loggerhead sea turtles that nest on beaches with similar magnetic fields are genetically similar to each other.

In fact, according to the research, magnetic fields are the strongest predictor of genetic similarity among nesting loggerhead sea turtles, no matter how far away or dissimilar their home beaches are.

This new finding supports previous research from Lohmann and Brothers that indicated adult sea turtles use magnetic fields to find their way back to the beaches where they themselves were hatched.

The new research implies that sometimes, the sea turtles mistakenly nest at a beach with a similar magnetic field, even if that beach is far away from their home beach — such as on the opposite coast of Florida.

The research could be helpful in conservation efforts for the turtles. Conservationists can take into account the importance of a beach’s magnetic field for attracting loggerheads, and understand that sea walls, power lines and large beachfront buildings can alter the magnetic fields, possibly changing the “address” in the turtle’s internal “GPS.”

And the research is of particular relevance to North Carolina, since it explains how loggerhead sea turtles hatched on Tar Heel beaches find their way back home after migrating across the entire Atlantic Ocean basin.

“Loggerhead sea turtles are fascinating creatures that begin their lives by migrating alone across the Atlantic Ocean and back. Eventually, they return to nest on the beach where they hatched — or else, as it turns out, on a beach with a very similar magnetic field,” said Kenneth Lohmann, professor of biology in the College of Arts and Sciences at UNC-Chapel Hill. “This is an important new insight into how sea turtles navigate during their long-distance migrations. It might have important applications for the conservation of sea turtles, as well as other migratory animals such as salmon, sharks and certain birds.”

There are only seven species of sea turtles worldwide, and six are listed as threatened or endangered in the United States, according to the North Carolina Wildlife Resources Commission.

The study was published April 12 in the journal Current Biology.