We love a good ocean mystery!

By Meghan Overdeep
March 26, 2021

Scientists are one step closer to unlocking the dizzying truth behind why certain marine animals occasionally swim in circles.

Animals, ranging from whales to penguins, have all been observed exhibiting this perplexing behavior. According to the results of a new study published in the journal iScience, however, there isn't a one-size-fits-all answer for every species—at least not yet.

In a recent article for Vice, Becky Ferreira explains how it all started with green sea turtles. Hoping to gain insight into how they navigate across vast, seemingly featureless oceans, Tomoko Narazaki, an ocean researcher at the University of Tokyo, and her team displaced a group of green sea turtles. They then observed their journey back to their home waters using 3-D tracking tags.

Narazaki was surprised to find that even with a destination, the turtles still often swam in circles. One turtle even circled repeatedly 76 times. Perhaps, the team hypothesized, the circling was related to magnetic-based navigation. Afterall, dogs have been found to make similar movements to align themselves with the earth's geomagnetic fields.

Narazaki encouraged her University of Tokyo colleagues who studied different marine animals to look at their tracking data as well. They found that sharks, penguins, whales, and seals all performed circling behavior.  

For the most part, circling was recorded in places where the animals forage for food. Humpback whales are known to hunt by encircling their prey and capturing it in a net of air bubbles. But the researchers are convinced that feeding isn't the whole story.

"[M]any circling events appear unrelated to foraging," they write. "For example, a shark-mounted video showed a male tiger shark circling to approach a female for courtship."

While some observations might appear mysterious, Narazaki and her team suggest that it all comes back to navigation. Animals need to have their bearings while performing any number of tasks, including foraging and breeding.

"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," the researchers explain in the study. "Animals might circle to derive directional/positional cues from the geomagnetic field, especially in navigationally challenging situations."

Going forward, scientists hope to study the different animals' "internal states," as well as environmental conditions which might play a role in this puzzling, shared behavior.