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Why marine creatures swim in circles

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Why marine creatures swim in circles

Tue, 23/03/2021 - 19:21
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Animals might swim in circles to collect navigational information. Movement patterns may represent an intuitive connection to Earth’s geomagnetic field.

Pixabay / Public Domain
Pixabay / Public Domain

Thanks for advancements in tracking technologies, scientists have discovered an intriguing behavioural trait amongst some marine species: They sometimes swim in circles.

When studying the navigational abilities of sea turtles, Tomoko Narazaki, a marine researcher at the University of Tokyo, observed that the turtles in her study would swim in circles so constantly “just like a machine.”

She shared her observations with her colleagues, who disclosed that the animal species which they were studying (like sharks, whales, seals and penguins) also demonstrated somewhat similar circular movements.

For marine animals in the wild, the act of swimming in circles would waste precious energy reserves, as opposed to swimming in a straight line from Point A to Point B (which was more efficient).

So, why were they doing it?

The scientists set out to find out, and recently published a paper in the iScience journal on their findings.

It was found that there were several situations in which marine animals exhibit circling behaviour. For instance, they may circle one another during courtship and social interactions, or when foraging for food as they surround the prey animal.

However, there were many other occasions when circling behaviour could not be explained, like when they did so outside of their feeding grounds or during times when they were not hunting.

On such occasions, the researchers suggested that they swam in circles to collect navigational information and speculated that such movements may signify an intuitive connection to the planet’s geomagnetic field.

T. Narazaki, et al / iscience / CC BY-NC-ND 4.0
Similar circling movements were observed across marine megafauna. Source: T. Narazaki, et al / iscience / CC BY-NC-ND 4.0

 

Similar to how submarines circle during geomagnetic observation to cancel out “noise” (say, caused by hull magnetisation) to obtain an accurate measurement, the marine animals might do so to gather directional and positional cues from the geomagnetic field, particularly in navigationally challenging situations.

“Homing turtles did the turning behaviour at seemingly navigationally important points,” said Tomoko Narazaki, in a New Scientist article.
 

Incidentally, the discovery was made possible due to recent advances in tagging and 3D-biologging technologies. Now, scientists can record detailed geographic and behavioural data that can be used to hone in on the precise features of animal movements like pitch, heading, small changes in depth.

To further understand the behaviour, the scientists hope to integrate the short-term data from tags with long-term satellite tracking, and to work with more species. They also hope to use video cameras and sensors during their observations to provide environmental context.

“We would like to examine animal movements in relation to animals’ internal state and environmental conditions to examine why they circle,” said Narazaki.

Sources
iScience
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