Sharks captured making terrifying sound in first evidence they're not silent killers

Throughout history, sharks have sustained a reputation of being silent killers, with the top ocean predators relying on their stealth. 

Scientists have long believed the creatures don’t make any noise because they lack the sound-producing organs found in many other mammals.

That was until now, as a groundbreaking new study has uncovered what is believed to be the first-ever recordings of sharks making sounds.

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In the study, published in the journal Royal Society Open Science on Wednesday, researchers detailed evidence that rig sharks - small, bottom-dwelling sharks found off the coast of New Zealand - make a distinct clicking sound when handled by researchers underwater.

The researchers believe the sharks create the sound by forcefully snapping their flattened teeth together and that it may be a stress or warning signal.

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"Sharks have sensory systems that are more refined than their hearing, like their electroreceptors, their smell, and the way they propel themselves through the water," Carolin Nieder, the study’s lead author told Live Science. "But I think the original notion that we had that sound isn't important at all is also likely not true."

Nieder accidentally came across the sounds during routine behavioral experiments at the University of Auckland's Leigh Marine Laboratory. The study detailed how researchers have observed ten juvenile rig sharks making sounds.

All 10 sharks produced audible clicks when being handled by the researchers. The recordings mark the first known evidence of a shark making sounds.

During the first few handlings, the clicks were frequent but they stopped as the experiments progressed. “Maybe they weren't afraid for their lives anymore," Nieder theorized as she noted that in the wild, juvenile sharks may use loud clicks as a quick distraction to escape from predators.

Most sharks were believed to be silent because they lack swim bladders, the air-filled sacs fish commonly use to make sounds, and scientists have not found any obvious sound-producing organs. The new study proposes that the sound may be coming from their teeth.

Rig sharks have broad, blunt teeth that are tightly packed and ideal for crushing prey. But Nieder notes that until researchers directly observe the sharks’ jaws during the clicking sound, the definite method will remain a mystery.

Around three-quarters of the clicks observed were single bursts while the rest consisted of shot double-clicks. The researchers noted that the sharks made calm, swaying movements during around 70% of the clicks.

Adrian Gutteridge, a shark biologist who was not involved in the study said more research would be needed to determine what the clicks could mean. "It's too early to tell whether it's a response, kind of saying, 'go away,' or if [it's] just their nervous system is firing off which just happens to make their teeth and jaws click," he said.