Scientists don’t know why all these sea creatures swim in circles

Marine researchers in Japan and elsewhere have uncovered yet another conundrum of the aquatic world. In a new article published Thursday, they detail their discovery that various species of large marine animals, from turtles to sharks to seals, swim in circles for no clear reason. These circles could have several purposes for the animals, such as making it easier to navigate or foraging for food, the researchers say.

Recent advances in technology, the researchers say, have allowed scientists to get a more complete picture of how marine animals move around their environment with much better precision than ever before. Lead author Tomoko Narazaki, University of Tokyo, and his colleagues decided to put this technology to good use by examining the movements of green sea turtles during their nesting season, when female turtles return to their location. from birth to lay eggs.

They moved the turtles from their nesting place to another location, so they could observe how they returned to the place of origin. But once they did, they spotted a peculiar pattern: Turtles would often spin at a relatively constant speed at least twice, then return to their normal swimming on the way home.

Curious, Narazaki shared the discovery with others in her domain. Finally, she teamed up with some of those researchers to look back at motion data that had been collected earlier on a range of other marine animals across different branches of the evolutionary tree. And of course, they found that the same kind of circular behavior happened over and over again. These whirling animals included fish (tiger sharks), birds (king penguins), and mammals (Antarctic fur seals and Cuvier’s beaked whales).

Their job is published in iScience.

“All of the data used in our study was initially collected for different purposes (eg to study the foraging behavior of sharks, etc.). The data for each species has been analyzed by different co-authors for different aspects, ”Narazaki told Gizmodo in an email. “So it took us a while to realize that this vicious cycle is a behavior common to many species, until we worked together.”

On the surface, making circles is hardly practical for the survival of these animals, as the most energy efficient way to travel anywhere in the ocean is usually a straight line. This probably means that it has one or more important functions that are worth the extra effort. Right now, however, all the team has are educated guesses about what’s going on, which can vary from species to species.

Sharks, for example, seem to revolve around where they feed most often, indicating that this offers some advantage for the hunt. Meanwhile, further research has shown that some species of whales will use the circles in groups to create “bubble nets” to catch their small fish prey. But feeding is probably not the only goal of the circles.

In at least one male tiger shark, the team found evidence that the circles were part of their courtship ritual in front of a female. Seals and penguins seem to rotate near the surface of the water most often or outside of their usual foraging hours, indicating that this is not part of their foraging technique. The team also cited previous research that found northern elephant seals circling around during their drift dives – lazy, passive dives that help them rest or prepare their last meal.

In turtles, circles can help them reorient their navigation skills, which rely on smell, sight, and sensing magnetic fields. Turtles rotated frequently just before the last part of their trip, and for some time as well. A turtle was observed spinning 76 times before continuing.

“Since similar circular behavior has been observed across a wide variety of marine megafauna taxa, it is possible that this is a behavioral convergence with similar goals,” Narazaki said. “But, for now, the purpose and function of this behavior remains unknown.”

Of course, we know that many animals on earth circulate for various reasons (just ask your closest dog before he poops). But the darkness of the vast ocean means that there are probably all kinds of common behaviors in these animals that we just haven’t been able to see yet. By studying more closely the how and the why of sea circles, the researchers hope to shed more light on this almost alien world.

“For the next step, we would like to look at the movements of the animals in relation to the internal state of the animals and the environmental conditions to examine why they are spinning,” Narazaki said. “Some hypothesis testing experiments would be needed to understand the function and mechanism underlying circular motions.”