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Scientists map enigmatic circle-swimming of whales, sharks, turtles, penguins

Three-dimensional tracking data suggests lots of large marine species swim in circles, and for a variety of reasons. Photo by Narazaki et al./iScience
Three-dimensional tracking data suggests lots of large marine species swim in circles, and for a variety of reasons. Photo by Narazaki et al./iScience

March 18 (UPI) -- Scientists have discovered a unique movement pattern shared by green sea turtles, sharks, penguins and other marine mammals -- they all swim in circles.

Using advanced animal-tracking technologies, scientists have managed to precisely measure the three-dimensional movement patterns of a range of marine species.

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These bio-tracking efforts -- detailed Thursday in the journal iScience -- revealed commonalities in the way many marine species explore their underwater environs.

"We've found that a wide variety of marine megafauna showed similar circling behavior, in which animals circled consecutively at a relatively constant speed more than twice," lead study author Tomoko Narazaki, researcher at the University of Tokyo, said in a press release.

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Researchers first observed the movement pattern while studying green turtles. After tagging the turtles, scientists removed them from their nesting locations to observe the navigation abilities.

"To be honest, I doubted my eyes when I first saw the data because the turtle circles so constantly, just like a machine!" Narazaki said. "When I got back in my lab, I reported this interesting discovery to my colleagues who use the same 3D data loggers to study a wide range of marine megafauna taxa."

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Many of Narazaki's colleagues described similar revelations after reexamining bio-tracking data -- they found a range of species regularly swim in circular patterns.

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The most efficient way to get from point A to point B, of course, is to follow a straight line. So why swim in a circle?

The turtle data recorded by Narazaki and his research partners showed the reptiles swam in circles near their feeding grounds, suggesting the pattern is used for finding food. Tracking data from a tiger shark study also showed circular swimming was linked with hunting.

However, tracking data showed fur seals regularly swam in circles throughout the day. Fur seals typically feed at night.

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Analysis of the track data revealed additional links between circular swimming and courtship, as well as navigation.

"What surprised me most was that homing turtles undertake circling behavior at seemingly navigationally important locations, such as just before the final approach to their goal," Narazaki said.

When recording geomagnetic data, submarines also travel in circles, and scientists suspect the swimming pattern may help some animals sense magnetic fields.

Because so many species swim in circles, scientists suspect the behavior offers a variety of advantages.

"Similar circling behaviors were observed across a wide variety of marine megafauna, suggesting these behaviors might serve several similar purposes across taxa including foraging, social interactions, and navigation," researchers wrote in their paper.

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