Turtles tracked as they expertly navigate the open ocean

Sea turtles travel thousands of kilometres between feeding and breeding grounds. In a paper published today in Proceedings of the Royal Society B researchers have tracked turtles as they find their way across long distances of the featureless landscape in the North Atlantic Ocean.

Leatherback turtles show remarkable navigation capabilities and are able to locate the beaches they were born on even after several years’ absence. How they manage this impressive feat of navigation is still not well understood. A paper published today suggests that it might be a combination of magnetic orientation and using the sun’s position in the sky as a compass that helps turtles stay on track.

For two years the researchers monitored 15 leatherback turtles using satellite tags whilst they migrated across open-ocean in the Northwest Atlantic. In this region leatherbacks make long journeys through the subtropical gyre, a large circular current system, where the featureless open ocean landscape contains few known sensory cues which could guide the turtles in their travels.

The team found that on average turtles travel through the gyre for 32 days and covered between 1105 km and 2290 km. The adult leatherbacks the team studied travelled slightly faster at 60 km per day than the subadults who travelled an average of 47km per day. The team found that despite the featureless landscape the turtles stayed on course. They travelled in approximately the same direction and on average had a heading of 154 degrees, south south east.

The team’s results show that adult and subadult leatherbacks can consistently maintain their southwards bearing despite the featureless landscape, most probably by orienting themselves using something other than topographic features or landmarks.

The researchers say that although at the moment they do not know for certain how leatherbacks keep on course, they might be using the Earth’s geomagnetic field to help guide them, setting this magnetic compass using the position of the sun on the horizon to keep track of their direction as they migrate across the open ocean.