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An international study led by Monash University in Australia found that wild gray seals clap underwater to communicate. A video posted to YouTube last month shows the mammals swimming and moving their flippers to create a clapping sound. The footage was filmed in October 2017 in the UK's Farne Islands. The research was published Monday in the journal Marine Mammal Science.

Marine mammals like seals and whales are known to usually communicate via calls and whistles. But researchers found gray seals can also fend off competitors and appeal to potential mates during breeding season by clapping their flippers underwater.

"The discovery of 'clapping seals' might not seem that surprising. After all, they're famous for clapping in zoos and aquaria," lead study author David Hocking said in a release. "But where zoo animals are often trained to clap for our entertainment, these gray seals are doing it in the wild of their own accord."

It took researcher Ben Burville 17 years of diving to capture the footage. This is the first time a seal has been captured clapping while fully underwater using its front flippers.

"The clap was incredibly loud and at first I found it hard to believe what I had seen," Burville said in the release. "How could a seal make such a loud clap underwater with no air to compress between its flippers?"

Hocking said this discovery shows just how much humans still have to learn about animals. It appears clapping is a key social behavior for gray seals, meaning anything that disturbs it could take a toll on breeding and the species' survival, the study notes.

"Human noise pollution is known to interfere with other forms of marine mammal communication, including whale song," Hocking said. "But if we do not know a behaviour exists, we cannot easily act to protect it."

Here's the video showing the seal clapping:

First published Feb. 3 at 2:53 p.m. PT.

Update, 3:09 p.m.: Adds more information.