A beaded shark surrounding its prey is a classic scene known by many ocean lovers. It looks like according to a new study that whales, penguins and sea turtles swim in circles, in addition to this captivating circular behavior.
“We found that a wide range of marine megafauna exhibited similar circular behaviors, in which animals circled more than twice in a row at a relatively constant velocity,” says marine biologist and lead author Tomoko Narazaki of the University of Tokyo, Japan.
The researchers tracked their movements in three dimensions and looked at where and when tagged animals tend to circle, with a number of possible reasons. But of course the research offers more possibilities for reflection than it has answers, so let’s dive in.
The researchers first spotted this mysterious circular behavior in green sea turtles, which were spotted using 3D data loggers and tracked down as part of another study.
“To be honest, I doubted my eyes when I first saw the data because the turtle circles so constantly, just like a machine,” says Narazaki, who also studied why sea turtles swim so slowly.
“When I got back to my lab, I reported this interesting discovery to my colleagues who use the same 3D data loggers to study a wide variety of marine megafauna taxa.”
What they found was that sea turtles were not alone: whales, sharks and penguins showed more or less the same circular motions.
To study this wide variety of marine animals, the researchers collaborated with local scientists and field volunteers in Japan, the Comoro Islands off the east coast of Africa, and the Crozet archipelago, further south in the Indian Ocean, with the help of the British. Antarctic survey.
They tracked down a total of 19 animals, including tiger sharks, king penguins, Antarctic fur seals, one goose whale and a whale shark.
Previously, marine life was detected far and wide, but to gravure heights or horizontally across the ocean surface, using depth sensors or satellite images.
Multisensor data loggers, as used by this study team, have now made it possible for researchers to measure fine-scale animal movements over depth, latitude and longitude and up to a time scale of seconds – an impressive achievement in the vast earth oceans.
You would think that swimming in a straight line is the most efficient way to move around – and that is from the perspective of energy saving. But in an open ocean that is blue in all directions, animals that move from one place to another may swim directly past a festival of an event, so be curious.
Some of the circular exhibits were taken in areas where the animals usually look for food. For example, four tiger sharks (Galeocerdo cuvier) marked off the coast of Hawaii, surrounded up to 30 meters (426 feet) up to 30 times in their feeding areas.
The Antarctic fur seals (Arctocephalus gazella) circled mainly during the day, although they feed mainly at night; meanwhile, a group of playful king penguins (Aptenodytes patagonicus) mostly searched at the surface between the deep dives, so there is clearly more to the story than food.
That said, other marine animals use extraordinary circular motions to catch prey.In 2019, humpback whales (Megaptera novaeangliae) has been seen creating a ‘net’ of bubbles as they swam in rings to catch fish. So each to their own.
Mating rituals could be another possible explanation, with one tagged male tiger shark trying to help a female mate by swimming in circles around her.
But the most surprising finding for Narazaki was to see some home turtles swimming in circles as they approached their nesting beaches. One turtle in the study circled 76 times one day and 37 times the next, choosing the right direction to swim into after intense deliberation.
This observation leads the research team to think that circular behavior may also play a role in navigation. Their idea is that migrating sea turtles can swim in circles to detect slopes in the Earth’s magnetic fields that they use to navigate through the oceans and find their way home.
There is probably not just one answer to this water puzzle, as the animals can circle for several reasons.
“For example, some animals can move in circles to improve prey while simultaneously collecting geomagnetic information,” the researchers write.
“Others, such as elephant seals falling off like falling leaves, can maintain directionality by geomagnetic scanning while resting in seemingly characteristic mesopelagic depths.”
All in all, this study is large on cooperation, but only small, and it did not lack information on the presence of nearby animals that could influence the behavior of the animals.
Marine scientists around the world need to be able to make good use of this new technology in search of more clues as to why marine animals swim in circles.
The findings may also help establish a clear baseline for later identification of the impact of external factors – such as shipping – on animals’ movements, behavior and navigational ability.
The research was published in iScience.