Posted by admin | 02.04.2015 | Marine Science, Turtle Talk

Loggerhead Migration – Understanding the Mysteries

For centuries humans have been trying to navigate the oceans. Early attempts by the Phoenicians relied on celestial navigation over 4,000 years ago, and as ship design advanced, so did the navigational materials from early compasses, sextants, and astrolabes to modern-day radar, sonar, and GPS. While humans have been striving for a more efficient way to plot a course through the global oceans, one of our tetrapod friends has been doing this successfully, long before ancient or modern technology evolved.

We have long know that sea turtles have some kind of mapping system allowing them to travel long distances, yet return to natal beaches. Hatchling loggerhead sea turtles take a transoceanic trip, swimming from nesting beaches to the subtropical Sargasso Sea. They remain in this subtropical gyre for several years to mature, and then return back to beaches to nest. Over the years we were able to discern that they can interpret magnetic cues to determine their latitudinal position, but that is only half the picture. How were they able to orient themselves along the east-west longitudinal gradients?

In a new article from Current Biology, researchers from Chapel Hill have now provided that answer. Loggerhead sea turtles apparently use a bi-coordinate map with magnetic cues providing both latitudinal AND longitudinal information. Using a large water pool with a magnetic control field, the researchers would alter the magnetic field to mimic either a Puerto Rican orientation or a Cape Verde Island orientation. By using these two locations on opposite sides of the Atlantic, they were testing to see if sea turtles would swim in the proper direction to reach the Sargasso Sea. And it seems they did: turtles with the Puerto Rican magnetic field swam northeast and turtles with the Cape Verde Island field swam southwest.

It is remarkable to think that the hatchlings popping out of nests along our coast have an advanced navigation system in their tiny bodies. It is an innate ability, not something that they learn from migratory experience. Reaching the Sargasso Sea is an extremely difficult endeavor as they have to avoid both natural and manmade threat, but it is comforting that there is something guiding them along this journey.