Navigating the High Seas - A Magnetic Theory

Sea turtles and salmon possess an astonishing ability to migrate vast distances from their birthplace and, years later, return to their home territory to reproduce. This navigational feat, known as natal homing, has baffled scientists for many decades. Just how do these animals remember the location of their birthplace with such precision?

A research team from the University of North Carolina at Chapel Hill thinks they may have the answer to that question. The team, led by UNC Professor Kenneth Lohmann, proposes that marine animals such as sea turtles and salmon imprint the magnetic signature of their birthplace early in their development and recall that information when they are ready to return to their home ground to breed. Since the magnetic field of the Earth varies continuously over the planet's surface, each location has a unique magnetic fingerprint—if an animal can remember the unique magnetic identifier of its birthplace, then it holds a map that could someday lead it back home.

The idea that magnetic fields are of navigational use to marine animals is not all that new to Lohmann and his colleagues. In 2001, Lohmann's team published research that indicated young loggerhead turtles use magnetic fields to follow the currents of the North Atlantic. But loggerhead turtles are not the only sea turtle species to tap into the Earth's magnetic field for navigational information. In 2004, Lohmann and colleagues went on to show that green sea turtles (Chelonia mydas) also have their own version of a global positioning system.

The underlying reason marine animals return to their natal home ground remains open to speculation. Professor Lohmann suggests is may be a matter of risk reduction:

"For animals that require highly specific environmental conditions to reproduce, assessing the suitability of an unfamiliar area can be difficult and risky. In effect, these animals seem to have hit on a strategy that if a natal site was good enough for them, then it will be good enough for their offspring." ~ Kenneth Lohmann, PhD, University of North Carolina at Chapel Hill

One thing is certain, there is much to learn about the role the Earth's magnetic field plays in the ability of marine animals to navigate the vast reaches of our planet's oceans and find their way home.

View photographs from the study →

Find out more:

• Lohmann, KJ, Cain SD, Dodge SA, Lohmann C. 2001. Regional Magnetic Fields as Navigational Markers for Sea Turtles. Science. 294: 5541(364-366).
• Lohmann KJ, Lohmann C, Ehrhart LM, Bagley DA, and Swing T. 2004. Geomagnetic Map Used in Sea Turtle Navigation. Nature. 428: 909.
• University of North Carolina. 2008. No Place Like Home: New Theory for How Salmon, Sea Turtles Find Their Birthplace. December 3, 2008.

Photo © Ken Lohmann / University of North Carolina at Chapel Hill.