Geomagnetic Migration

AAAS: "Migrating sea turtles only sort of know where they’re going."

"When Charles Darwin visited Ascension Island in 1836, he was perplexed by the vast numbers of green sea turtles (Chelonia mydas) nesting on its beaches." Every mating season, these intrepid reptiles leave their feeding grounds along the coast of Brazil and journey > 2000 km across the sea to lay their eggs on this tiny, remote island. 'How, Darwin later mused in a letter to Nature, did the animals find their way to a “speck of land in the midst of the great Atlantic Ocean?”'

Decades later, scientists uncovered convincing evidence that sea turtles can sense components of Earth’s geomagnetic field. 'Kenneth Lohmann, a marine biologist at the University of North Carolina at Chapel Hill ...[and] his team previously conducted laboratory studies demonstrating turtles can sense the strength of geomagnetic fields as well as their angle relative to the surface of Earth—potentially providing migrating turtles with a “bicoordinate” geomagnetic map of their surroundings.'

Just as wind can blow a bird off its flight path, ocean currents may divert a migrating turtle from its intended course. Apparently, sea turtles have only “an approximate idea of where they are and where they’re going.” Annual variations in magnetic field intensity + inclination, changing currents + the potential survival value of finding a new island all factor into the value of an imperfect navigation system.

The updated tracking devices have a compass sensor that measures the direction a turtle is facing with respect to true north + a satellite transmitter that relays information about the animal’s location—and correct heading for Ascension—to the Argos satellite system, which is equipped to receive data from around the globe. The real beauty of the system is the remarkable speed with which it transmits data—essential when tracking an animal that spends most of its time beneath the waves, surfacing only briefly to catch its breath before diving down again. “You’ve only got a fraction of 1 second.”

Of course, when I'm swimming I take pretty quick breaths as well.