Migrating turtles don’t really know where they’re going, study shows

Since Charles Darwin, biologists have wondered how animals like sea turtles navigate hundreds to thousands of kilometres across the open ocean. New research suggests that some sea turtles don't know where they're going.

The movements of hawksbill turtles as they swam from their nest in the Chagos Archipelago to their destinations in the Indian Ocean were mapped by an international team of scientists.

The turtles were found to travel in circuitous routes when they migrated short distances.

The turtles travel twice the distance to their targets. A person swam 1,306 km to reach an island that was a mere 176 km away.

Satellite 22 hawksbill turtles were tracked by the team after they had finished snoozing.

Sea turtles do not nest in the same area. The animals would have already migrated from their grounds and laid multiple clutches of eggs before heading back.

If the turtles were perfect navigators, they would probably travel in direct paths from their nest sites to areas where they could find food.

The magnetic field of the birth area of turtles is thought to be the reason why they return to lay eggs there.

Hays said the new study suggested the turtles are using a geomagnetic map, but it is a coarse resolution.

He said that it doesn't allow straight-line migration, but it does tell them when they're getting a long way off route.

Hawksbill turtles migrate a modest distance compared to green turtles.

The green turtles that nest in the Chagos Archipelago have been tracked.

Although it is a long journey, it is an easy task because the turtle only has to swim vaguely west to reach Africa.

Hawksbill turtles had a harder time locating small, specific places like isolated islands or submerged banks.

The turtles' geomagnetic map sense isn't fine-grained enough to locate specific targets according to new research.

The smell of an island in the final stages is a sign that the animals are close to their intended locations.

As they get a visual landmark, the water starts to get a bit deeper and they can see the seabed, which is a cognitive map. They could probably just recognize the seafloor, like you would recognize visual landmarks in the area where you live.

The research was published in a journal.