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Why do Sharks, Turtles Move in Circular Fashion? New Study Claims to Have Finally Solved the Mystery

Image for representation. (Credits: AFP).

Image for representation. (Credits: AFP).

According to a new study, some predators like sharks move in circles as they forage for food. Others do it as part of courtship or navigating the ocean to impress mates.

A particularly interesting feature about sharks is that these marine giants seem to swim in a circular motion all the time. Whether it’s a prey they are circling or a group of them in the ocean waters. Other famous ‘circlers’ include turtles and penguins and whales. But why do they do it? Is it random or a result of adaptational evolution, or something completely mysterious?

According to a new study, it’s not just one single reason. Some predators like sharks do it as they forage for food. Others have a more romantic reason—a part of courtship or navigating the ocean to impress mates. The study was led by Tomoko Narazaki at the University of Tokyo and included tiger sharks, whale shark, green turtles, king penguins, Antarctic fur seals, and Cuvier’s beaked whale as samples. It has been published in the journal iScience.

The study is the first of its kind to use emerging 3D technology to resolve the mystery behind this circular movement pattern.

According to Narazaki, these sea-dwelling creatures are capable of detecting geomagnetic fields in the ocean (to help with movement/direction). “We hypothesized that some circling may be related to magnetic-based navigation because circling movements seem to be well-suited to examination of the geomagnetic field,” she told the Inverse. It is a way of drawing a map of their surroundings, using the geomagnetic field.

While other studies have been conducted on the subject, this project used “dead reckoning,” multi-sensor marine technology, which helped them reconstruct the underwater movements in 3D. The smallest movement, variable, nuance etc became clearer with the help of this technology, such as animal speed and change in ocean depth.

While penguins, sharks used it to map available food, the turtles use it to map a way back home. This study of marine megafauna and their similar adaptations can be a result of convergent evolution. This theory suggests that unrelated species who evolved in a shared habitat develop or adapt similar behaviour to their common environmental pressures.

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