Migrating turtles have limited sense of direction, study finds

One turtle scientists tracked swam more than 800 miles to reach an island just 100 miles away

The hawksbill turtles involved in the study are generally found in the tropical waters of the Atlantic, Indian and Pacific Oceans (Getty)

Some migrating sea turtles don’t know where they are going, new research suggests, with one of the creatures swimming more than 800 miles to reach an island just 100 miles away.

An international team of scientists tracked the behaviour of 22 hawksbill turtles as they swam across the Indian Ocean.

They found that the turtles often swam via indirect routes and typically travelled twice the distance needed to get to their next location.

The navigation and migration patterns of animals in the ocean have for many years puzzled scientists and biologists, including Charles Darwin.

The report authors said that sea turtles often migrate to different places in order to forage, mate and nest, but the new study suggests that they have a “relatively crude map sense in the open ocean”.

Hawksbill turtles are one of the most recognisable species of turtle (Getty/iStock)

Professor Graeme Hays, chair in marine science at Deakin University and the study’s first author, told The Guardian that the turtles his team observed didn’t eat for prolonged periods of time as a result of their undirected travelling.

Professor Hays said the research suggested that the turtles “almost certainly are using a geomagnetic map” – a map that relies on or relates to the magnetic field of the Earth.

“So, it doesn’t allow pinpoint straight-line migration, but it does tell them when they’re getting a long way off route,” Prof Hays said.

The turtles rely on the Earth’s magnetic field to navigate distances, say the study’s authors (Getty)

Despite the new study suggesting the turtles’ geomagnetic map may not be reliable enough to target specific locations, the animals will later rely on other means to get to their destination.

“In the final stages, they can smell an island that they’re headed to,” Prof Hays said.

“As they get some sort of visual landmark – for example, the water starts to get a bit shallower and they can see the seabed – then they’ve probably got some sort of cognitive map of that area.

“They could probably just recognise the sea floor, just like you would recognise visual landmarks in the area where you live.”

Hawksbill turtles also face navigational difficulties when the islands or submerged banks they are looking for are small or remote.

The research was published in the Journal of the Royal Society Interface.