It Turns Out Sharks Make Noises, and Here's What They Sound Like

Sharks have long been believed to be silent, stalking their prey and wolfing them down without comment. They're ruthless and efficient.

But a team of marine biologists in New Zealand are challenging that assumption. In a new study published in the journal Royal Society Open Science, the researchers report that they've recorded the first ever instance of a shark actively producing a sound, in the form of sharp, abrupt clicks.

The sharks that produced the noise were rig sharks, a species which are common to the coastal waters of New Zealand. Locals often refer to the relatively small sharks, which grow up to five feet long, as "lemon fish" (not to be confused with much more formidable lemon sharks) — or simply "rigs."

Lead author Carolin Nieder said that she made the discovery while handling the rig sharks during her research into their hearing capabilities.

"At first we had no idea what it was because sharks were not supposed to make any sounds," Nieder, who works at the famed Woods Hole Oceanographic Institution, told Scientific American. "I remember coming home and just thinking more and more about how weird those sounds were."

To confirm it wasn't a fluke, Nieder and her colleagues gathered ten juvenile rig sharks, separately placing them into tanks equipped with microphones. As the sharks were either being gently held or transferred between tanks, all of them emitted the high frequency, sub-second clicks, the researchers found. 

The clicks occurred underwater, and almost always as the sharks were moving their body in some way. Brief as the clicks were, they reached an appreciable volume of 156 decibels.

Some species of fish use their swim bladders to generate noise by vibrating them. Marine mammals like whales use vocal cords. But sharks don't possess a specific organ for making sounds. In the rigs' case, it appears that they're making the noise by snapping together their dense rows of flattened teeth, which are specialized to chomp through shells.

Notably, the sharks didn't produce the clicks while swimming or feeding. Their high frequency also puts the sounds outside the rig shark's limited hearing range, making it unlikely that they use the noises to communicate.

"I think it's more likely that they would make those noises when they get attacked," Nieder told the New York Times. Other fish snap their teeth or jaws in an attempt to ward off predators, she added.

To be sure, the circumstances that the recordings were made in raise questions about whether these are sounds that the sharks would produce in the wild. But the fact that they were made at all warrants further investigation.

"This study opens up the possibility of these smaller sharks 'sounding the alarm,'" Neil Hammerschlag, president of Atlantic Shark Expeditions and executive director of the not-for-profit Shark Research Foundation, told CNN.

"While we really don't know if the sound produced by the rig sharks was simply a byproduct of being handled... it does open up some new questions, possibilities and avenues for future research."

More on marine life: Behold Rare Footage of What Narwhals Actually Use Their Tusks For

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