Sharks aren’t silent after all

At least one shark species has a bark to go along with its bite. It can make clicking noises, scientists report, a first among an animal group once thought to be totally silent.

During her doctoral research at the University of Auckland in New Zealand, Carolin Nieder, now at Woods Hole Oceanographic Institution in Massachusetts, was studying sharks’ hearing. When handling the sharks during experiments, she noticed one species – a houndshark called the rig (Mustelus lenticulatus) – appeared to make metallic clicking sounds.

“I was just kind of ignoring it because sharks are not supposed to make sounds,” says Nieder. “And it just kept happening.”

The ability to produce sounds intentionally is common among land vertebrates, as a world full of bird chirping and mammalian bellowing illustrates. But underwater, many fish emit sounds by scraping objects or vibrating their muscles, and in 2022 researchers reported that some rays – close relatives of sharks – will click when disturbed by divers. No shark sounds had been formally described yet.

To confirm the existence of the rig’s noisiness, Nieder and her colleagues brought 10 juvenile rigs caught in the waters off New Zealand’s North Island into the lab. There, they were placed in tanks with sensitive sound recording instruments. The team gently handled the sharks and found that all of them made a clicking noise in response. The rig appears to be the first shark known to produce sounds that aren’t associated with other actions, such as feeding or bumping into something.

The researchers think the sharks may be producing the sounds by snapping their jaws together. Much like the clicking rays, the rig has flattened teeth, which might create a sharp sound upon impact. Listen below.

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Further research may confirm the source of the clicking and if it has a function. Nieder points out that the rig is a small shark and potential prey for larger animals, so it’s possible the clicking has a role in defence when the animal is bitten or grasped.

“It could be to disorient the predator a little bit,” she says. It’s also possible the clicking has a role in hunting, she adds, such as scaring or discombobulating the sharks’ crustacean prey.

“This is a long-overlooked but potentially really important area of shark biology,” says Aaron Rice at Cornell University in New York, who was not involved with the research.

If sound production is widespread among sharks, their clicks may be useful for studying their often steeply declining populations, says Rice. There is a great wealth of sound data recorded from fish and whale studies that might have also captured shark sounds, he says. These could be used to determine if sharks were in the area, adding another tool for monitoring the imperilled predators.

“[The finding] represents what is truly a new discovery in basic biology,” says Rice. “It highlights the fact that there’s so much we don’t know about the ocean.”