Lost turtles cut laps in tricky migrations

·2-min read

The popular misconception that sea turtles are guns at global navigation has been busted with researchers finding they often swim in circles trying to get home.

Australian turtle expert Graeme Hays says GPS trackers attached to migrating hawksbill turtles in the Indian Ocean have revealed hardly any go in a straight line.

One critter that left its nesting site in the remote Chagos Archipelago travelled more than 1300km to reach its island home, which was only 176km away.

In fact only four of the 22 turtles that were tracked travelled in a vaguely straight line and Professor Hays says that may have been more out of luck than good judgement.

The findings put paid to the idea that sea turtles always know where they're going with pinpoint accuracy, a myth that arose from earlier research by an American team.

They were able to show that baby turtles could perceive components of the earth's geomagnetic field, allowing them to use it as a map.

Headlines about baby turtles having the built-in GPS systems flashed around the world.

But the Americans also said they weren't at all sure about the resolution, or quality, of the map and turtles may only have a very broad sense of where they are.

Prof Hays says it now seems likely that migrating turtles use a hierarchy of tools to get home.

Their geomagnetic maps give them a general sense of whether they have strayed off course.

When they get closer to home, searching behaviours kick in and they begin travelling in a circuitous manner as they look for specific islands or sand banks.

"When they get close to their target, the geomagnetic map is no good because its not a fine enough scale so they've got to switch to alternatives," Prof Hays says.

"Those really long migrations are surprisingly easy for turtles to complete from a navigation perspective. It's the journey to small isolated targets that are the tricky ones."

Prof Hays is Alfred Deakin professor and chair in marine science at Deakin University.

The study has been published in the Journal of the Royal Society Interface.

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