Dolphins whistle. Whales sing. Fish croak, chirp, grunt, hum and growl. But in the chatter of the sea, one voice has been missing — until now.
Sharks have long been seen as the silent killers of the water. But scientists at the University of Auckland in New Zealand recently recorded a rig shark, or Mustelus lenticulatus, making a sharp clicking sound, most likely by snapping its teeth together, according to findings published in the journal Royal Society Open Science on Wednesday. They believe it’s the first time a shark has been recorded actively making noise.
The lead researcher, Carolin Nieder, first heard the sound while she was researching the hearing abilities of sharks. While she was handling one shark, it made a clicking, snapping sound similar to that of an electric spark, she said.
The noise came from a rig shark, a fairly small shark common in the waters around New Zealand that grows to up to five feet and mainly eats crustaceans. It is eaten by bigger shark species — and by New Zealanders, who use it to make fish and chips.
Dr. Nieder was taken aback when she heard the noise.
Other sea creatures have mechanisms for making sound. Fish, for example, have a swim bladder, a gas-filled sac that is used for buoyancy but can also be used as a kind of drum. Many fish have a muscle that can vibrate the swim bladder in a way similar to a human’s vocal cords, generating sounds.
But sharks “were thought to be silent, unable to actively create sounds,” Dr. Nieder said.
For the study, she and her co-authors observed the behavior of 10 rig sharks housed in tanks equipped with underwater microphones. They found that all 10 sharks would begin to make the clicking noise when they were being moved between tanks or gently held.
On average, the sharks would click nine times in a 20-second interval, and the researchers believe they made the sound by snapping their teeth together.
They did not make the noise when they were feeding or swimming, leading the scientists to believe the clicking was more likely something they did when stressed or startled, rather than as a means of communicating with one another.
“I think it’s more likely that they would make those noises when they get attacked,” Dr. Nieder said, adding that many other fish snap their teeth or jaws in an attempt to deter or distract predators.
It was unclear whether the sharks could hear the clicks themselves; whether they made the sound in the wild or just in captivity; and whether they made it intentionally or if it was a side effect of their response to being startled, Dr. Nieder said.
Christine Erbe, the director of the Center for Marine Science and Technology at Curtin University in Australia, said that the study expanded on a growing field of research into how marine animals make and hear sounds.
“Once we start looking, we find more and more species that use sound,” she said.
Because of that, it was not surprising to find that sharks can make noise, she said.
However, she added, “I think it’s significant in the sense that we totally underestimate the communication between animals and their environmental sensing abilities, and therefore also how we can impact them with noise.”