New footage shows for the first time that seals clap underwater to ward off competitors and show off to potential mates.

The action was captured on film for the first time by Dr. Ben Burville, a Visiting Researcher with Newcastle University, U.K. While it is not so unusual to see trained seals clap in a zoo or aquarium, the action had not previously been recorded in the wild and underwater.

Burville’s clip, described in the journal Marine Mammal Science, shows a male gray seal clap two times underwater in front of another male, creating a “cracking” noise.

Gray seals are gregarious and social creatures. Verbal signals (growls, hisses, hoots and caterwauls, etcetera) are often used by individuals to navigate group situations, while nonverbal signals such as flipper slaps and breaches play a role but were thought to be limited to the surface of the water.

After 17 years of trips to capture this very motion on camera, Burville filmed the underwater clapping on October 17, 2017 near the Farne Islands in northeast England. Burville witnessed similar behavior on five separate occasions and has heard it more than 20 times within a 20-year period.

The clap itself lasts for a fraction of a second (<0.1 seconds) and makes a high-frequency sound (>10 kHz), similar to a cymbal. The tone cuts through background noise, say researchers, to deliver a clear message to passing seals.

Based on researchers’ observations, the claps are performed by males and appear to be directed at others in the vicinity. The claps typically appear in bursts of one or two.

The study’s authors “tentatively” identify the clapping as male behavior, performed to deter competition from other males and attract females by displaying their strength.

“Depending on the context, the claps may help to ward off competitors and/or attract potential mates,” lead author Dr David Hocking from Monash University’s School of Biological Sciences said in a statement.

“Think of a chest-beating male gorilla, for example. Like seal claps, those chest beats carry two messages: I am strong, stay away; and I am strong, my genes are good.”

Similar displays have been observed in other marine mammals at a surface level. Harbor seals, for instance, slap their flippers to draw attention from females and warn males off their territory. While, humpbacks have been known to use flipper slaps as a sign of aggression or competition. However, these displays tend to involve just one flipper at a time.

“What makes grey seals different is thatlike humansthey literally clap their forelimbs together, and they do it entirely underwater,” the study’s authors wrote for a piece in The Conversation.

Whatever the reason for it may be, this clapping seems to be an important social behavior, the study’s authors argue. That means that anything that disturbs the clapping could have a negative impact on the breeding and survival of gray seals.

“Human noise pollution is known to interfere with other forms of marine mammal communication, including whale song,” said Hocking.

“But if we do not know a behaviour exists, we cannot easily act to protect it.”

In previous research, scientists discovered gray seals are capable of mimicking human speech and song. One, Zola, was especially good at humming Twinkle Twinkle Little Star and the Star Wars theme tune.

“Copies were not perfect but given that these are not typical seal sounds it is pretty impressive,” lead researcher Dr Amanda Stansbury told the BBC at the time.