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We Don’t Know Why Whales, Sharks, Penguins, & Sea Turtles All Swim In Circles

Over the past couple of years, technological advances have made it possible for researchers to obtain detailed tracking movements of marine creatures.

A recent study published in the journal iScience has used 3D data loggers to discover that large ocean creatures like sharks, penguins, turtles, and marine mammals all do something weird – they swim in circles.

Lead author Dr Tomoko Narazaki at the University of Tokyo says they “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.”

The researchers used data loggers that allowed them to track the movement of sharks, turtles, penguins, and marine mammals in three dimensions. NARAZAKI ET AL. 2021/ISCIENCE.

SPIN ME RIGHT ‘ROUND

The researchers first came across the behaviour in green sea turtles when they were researching their infamous homing abilities.

They were perplexed and doubted wether what they were seeing was accurate given the mechanical and repetitive nature to the circling.

“To be honest, I doubted my eyes when I first saw the data because the turtle circles so constantly, just like a machine!” Narazaki says.

Narazaki spread news of the finding to other colleagues who use 3D data loggers on a large range of marine megafauna.

And then the results came flooding in. They found the same circular swimming in tiger sharks, a whale shark, green turtles, king penguins, Antarctic fur seals, and a Curvier’s beacked whale.

The behaviour was puzzling because, much like walking, the most efficient way to swim is more or less in a straight line. The researchers concluded that there must be some reason for the animals to circle like this and suggested a couple of theories.

BUT WHY?

The researchers recorded 272 instances of tiger sharks circling while in their feeding areas off the Hawaiin coast. The behaviour sometimes occurring while animals are foraging implies it may have something to do with locating a meal.

However, fur seals were observed to primarily circle during the day, even though they forage far more often at night. Even the tiger sharks were using the circling move at times that had nothing to do with feeding.

An alternative theory is that it has something to do with navigation. Turtles are well known for their impressive in-built navigation system that allows them to locate the exact beach they hatched from during the breeding season. Scientists are still piecing together just how they manage to do this, but suspect it has something to do with magnetic fields.

In the paper published this month, green sea turtles were seen to circle just before key navigation moments.

“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 says.

If the behaviour does aid the turtle’s navigation, it would mirror how submarines circle during geomagnetic observations.

But the behaviours could hold multiple uses, including some the researchers are yet to explore. The authors say they would like to see how the circling behaviour changes in different environmental conditions or whether certain internal states put the animals in a pirouetting mood.