We just got closer to the secret of how turtles navigate the open ocean

(ORDO NEWS) — How sea turtles and other aquatic life find their way in the open ocean, away from real navigational aids or natural signposts, has long intrigued biologists. Now a new study shows turtles have built-in basic geomagnetic controls – but they still rely mostly on luck and perseverance to find their destination.

Scientists equipped 22 hawk turtles (Eretmochelys imbricata) with GPS trackers to track which routes they would take to return to their feeding grounds after mating and breeding. These trackers showed that the routes were quite tortuous.

For example, one turtle traveled a total of 1,306 kilometers (812 miles) to find an island just 176 kilometers (109 miles) from its starting point. The researchers found that, in general, the animals had to do a lot of circling before they could land again.

“Our results provide strong evidence that hawk turtles only have a relatively crude mapping sense in the open ocean,” the researchers write in the published paper.

“The existence of widespread foraging and breeding grounds in isolated oceanic areas indicates that target-seeking in the later stages of migration is a common occurrence for sea turtles.”

Sea turtles are well known for their ability to migrate vast distances across the ocean, often landing on small isolated islands located far from other places, so the question arises how they find these remote places surrounded by open water.

Although previous studies have shown that these turtles sense the Earth’s magnetic field to some extent, which may help them with route planning, it has not yet been clear how accurate and reliable this magnetic mapping technique is.

As a rule, tagged turtles swam twice as far as they needed to find feeding spots. However, compared to other tortoise species, these hawksbill turtles cover relatively short migratory distances.

Changes in the strength and direction of the magnetic field around the Earth are used by many species to figure out which way to go. In the case of these turtles, this navigational tool seems to work, but only to a certain extent.

“It doesn’t pinpoint straight-line migration, but it does tell them when they deviate too much from the route,” marine ecologist Graeme Hays of Deakin University in Australia told The Guardian.

The researchers report that some evidence of course correction has been found both in open water and in shallow water closer to land. Many of the results of this study are consistent with those previously observed in green turtles (Chelonia mydas).

As far as the researchers were able to find out, ocean currents did not affect how turtles got from point A to point B. Turtles also did not expect a specific set of local weather conditions before setting off on a journey – they began their travels immediately after breeding.

The behavior and navigation of turtles is in stark contrast to some seabirds, which usually find their destination quickly and most likely use wind-blown scents to do so. It appears that sea turtles do not have such decision cues.

“Our results suggest that the navigational abilities of sea turtles are far from perfect, but rather just as good as they can be within their sensory abilities,” the researchers wrote.

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