• Researchers found various marine animals swimming in circles
  • Foraging, navigation and courtship may be the cause of the circling events
  • Future studies could shed more light on the mysterious behavior

Various marine creatures were found to be mysteriously swimming in circles, and researchers don't know why.

When moving toward a destination, moving in a straight line is said to be the most efficient way to get there. However, the researchers of a new study published in iScience found a rather odd behavior in sea creatures: they tend to swim in circles.

It was during an experiment to test green turtles' navigation when researchers first spotted the odd behavior.

"To be honest, I doubted my eyes when I first saw the data because the turtle circles so constantly, just like a machine!" study lead Tomoko Narazaki of the University of Tokyo said in the Cell Press news release.

And when the researchers looked at other data, they found that other marine creatures, such as the tiger shark and Cuvier's beaked whale, do it as well.

Circling Events

A circling event is when the creature moves in more than two consecutive circling movements, the researchers explained. They observed a total of 272 circling events in four tiger sharks that were tagged off Hawaii, with the creatures circling from two to 30 times during each event. They did this at various depths, the researchers noted, although they remained at a constant depth at each event.

One may think that this behavior could be linked to feeding behavior since people are quite familiar with the sight of a shark circling its potential prey. Humpback whales are also known to engage in circling movements to create a "bubble-net" around their prey.

However, this particular circling behavior was also observed in a variety of other animals such as Antarctic fur seals, whale sharks and king penguins. In fur seals, the behavior was observed not at the time of day when they are known to be foraging.

Mysterious Behavior

So what could be behind the seemingly odd behavior? The researchers noted other possibilities apart from foraging.

It could be that the behavior is related to courtship or for navigation, the researchers surmised. For instance, a tiger shark engaged in the behavior when approaching a female. They also observed one turtle that circled 76 times and again 37 times 22 hours later. These circling events, the researchers said, happened when the turtle was at a location where it showed "significant navigational changes."

"We hypothesize that some circling movements are associated with examination of the geomagnetic field," the researchers wrote, noting that "diverse taxa" are known to use the geomagnetic field to navigate.

"Interestingly, submarines also circle during geomagnetic observation because accurate measurement can be achieved by using values measured from all directions to cancel noises, such as hull magnetization," they added.

Advanced Technology

Why exactly the creatures engage in the behavior remains unclear, although it's possible that it has more than one purpose, Cell Press said. What's more, the researchers noted that their study did not have any information on whether there were other stimuli that could have prompted the behavior in the creatures, such as landscapes or other creatures.

That said, the technology that the researchers used, which allowed them to track the animals' movement in three dimensions, may help provide more clues in the future. As the researchers said, marine animals move in an "inherently 3D environment" but have mostly been observed in fewer dimensions.

For instance, combining the 3D observations with video surveillance of the movements in the future could shed more light on the behavior.

Sea Turtle
Image: A sea turtle swimming close to the surface Pixabay