Sea turtles may use the sunrise to show them the way home.

That’s what scientists at James Cook University have found after analysing satellite tracking data of the animals.

Dr Takahiro Shimada, from JCU’s College of Science and Engineering, said scientists caught and tagged 22 turtles and transported them between eight and 28 kilometres from their usual home.

The aim of the project was to learn more about turtles’ exceptional navigational and orientation abilities.

Changing directions

“They frequently travel between areas that are a long distance apart and we know they are capable of travelling through unknown waters and returning to where they were captured,” Dr Shimada said.

But, he said, they found something unusual during the project.

“The most striking thing was the alternation of travelling and stationary periods.  It appears the turtles reassess their heading direction in the hours around sunrise and adjust the direction of their movement accordingly.”

The turtles would travel for an average of eight hours and then rest for an average of nine hours. Data from the tracked turtles showed them changing direction when the resting period ended, usually early in the morning.

Turtles and the sun

Dr Shimada said there was strong evidence turtles use geomagnetic and possibly wind or current-borne cues for orientation, but this study showed something else may be at play as well.

“Orientation should not have been restricted to the hours around sunrise if geomagnetic cues, chemical cues and a cognitive map had been the exclusive sources of directional information.”

Dr Shimada said given the time of day when they changed course, the turtles may have been using the position of the sun as a cue.

“They may obtain critical cues for directing short-distance movement in the hours around sunrise given significant corrections were only observed to occur at this time of day. They may also use polarised light to recalibrate their internal compass at sunrise.”

A new and important finding

He said it was the first time this had been observed.

“Our findings will advance understanding of the mechanisms of fine-scale orientation by sea turtles and in general provide valuable implications for animal orientation.”

This article was first published by James Cook University.

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