Loggerhead turtles mysterious navigation tracked in 3D

All sorts of marine animals can navigate hundreds, or thousands, of kilometres across the ocean to find the right breeding and foraging grounds. Scientists are frequently perplexed by how creatures can do this.

A team from the French island of Réunion, 800km east of Madagascar in the Indian Ocean, has used three-dimensional data of ocean currents to figure out how loggerhead turtles migrate. The researchers have fascinating, but still perplexing, results.

They’ve published their findings in Journal of the Royal Society Interface.

The researchers fitted tracking devices to 25 young loggerhead turtles which migrated north over the Indian Ocean, from Réunion to the Arabian Peninsula.

They combined the tracking data with ocean current data to assess how the turtles navigated. Typically, ocean migration is examined in 2D, which the researchers say can lead to errors – they took advantage of newer tracking methods to look at the turtle movements in 3 dimensions.

They found that the turtles used a “map and compass” method of navigating, where animals head to distant targets in a straight, or close to straight, line at a stable swimming speed. The turtles occasionally changed course slightly to correct their heading.

This matches with the methods other turtles, like hawksbill and green turtles, use to navigate, suggesting it’s a strategy that’s used across species.

They found that ocean currents below the surface had a big influence on how the turtles moved.

“In further studies, exploring the diving behaviour associated with this two-dimensional movement offer exciting perspectives to provide better understanding of sea turtle ecology during migrations,” write the researchers in their paper.

“It is clear that exploring the third dimension through the improvement of the animal-born technologies open a new path to the understanding of sea turtle ecology as well as for other marine animals.”

Exactly how they navigate remains a mystery for another day.

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