Turtle secrets uncovered

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.

He said researchers are particularly interested in sea turtles because they have exceptional navigational and orientation abilities.

“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 they found something unusual in this case.

“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 median travelling period of eight hours was followed by a median resting period of close to nine hours. The turtles would change direction when the resting period ended, usually early in the morning.

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.”

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.”

The paper is available on request from Dr Shimada.

Images – including video of turtle ‘rodeo’ capture: http://bit.ly/2iaQhJ8

Note: Pictures are of Dr Takahiro Shimada during capture and release operations with turtles.

They are for single use only with this media release and not available to be archived or reused. (Tracking units featured in the pictures are either recovered or fall off in time).