Enigmatic circulating behavior caught in whales, sharks, penguins and turtles

Technological advances have made it possible for researchers to track the movements of large animals living in the ocean in three dimensions with incredible precision both in time and space. Researchers report in the journal iScience on March 18 now used this biological technology to find out, for reasons the researchers still don’t understand, that green sea turtles, sharks, penguins and marine mammals all do something very unusual: swimming in circles.

“We have found that a wide variety of marine megafauna exhibited similar circulating behavior, in which animals rotated one after the other at a relatively stable speed more than twice,” said Tomoko Narazaki from University of Tokyo.

Narazaki’s team first discovered the secret circulating behavior in homing green turtles during a movement test. They had moved nesting turtles from one place to another to check their sailing abilities.

“To be honest, I blinded my eyes when I first saw the data because the turtle is orbiting so regularly, just like a tool!” Narazaki says. “When I got back in my lab, I reported this interesting discovery to my colleagues who use the same 3D data loggers to analyze a wide range of support. megafauna mara. “

The next thing surprised the researchers even more: they realized that several species of cetaceans showed more or less the same circulatory movements. This finding is somewhat surprising because swimming in a straight line is the most effective way to move around. He suggests that there must be a good reason for animals to circulate.

The Narazaki team reports that some circulating incidents have been recorded at animal supply fields, suggesting that it may have some benefit for foraging. For example, they note that 272 circulating incidents were observed in four identified tiger sharks off Hawaii. However, fur seals have been found circulating mainly during the day although they usually feed at night. Other circulating events also appeared unrelated to hunting. For example, they have seen a male tiger shark roam to approach a female for courtship, and the evidence in sea turtles indicates that roaming may play a role in sailing.

“What surprised me the most was that courtship turtles were doing circulating behavior in places that seemed to float, such as just before the final approach to the goal,” Narazaki says.

It is possible that the rotation helps the animals to find the magnetic field for navigation; interestingly, the researchers say, submarines also orbit during geomagnetic observation. But it is also possible that the circulation serves more than one purpose.

The researchers say studies of such movements, including circulation, in more marine species could lead to important behaviors that are otherwise overlooked. In future studies, they would like to study the movements of animals in terms of the indoor condition and environment of the animals, finding more clues as to why they are circulating.

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This work was supported by IPEV, the JSPS Research Fellowship for Young Scientists, a grant from JSPS, and Bio-Logging Science, University of Tokyo.

iScience, Narazaki et al .: “Similar circulation trends observed across marine taxa megafauna” https://www.cell.com/iscience/fulltext/S2589-0042(21)00189-9

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