Sharks recorded making terrifying sounds while hunting - despite not having vocal cords

For centuries, sharks have stirred fear and fascination. They glide through water with quiet power. Unlike whales or dolphins, they never seem to speak. Scientists assumed that sharks lived in a world of silence – masters of stealth with no sound.

That idea was rooted in biology. Sharks lack swim bladders, organs that help many fish produce sound.

They also don’t have vocal cords or specialized structures like drumming muscles. So the conclusion felt safe: sharks don’t make noise.

But nature is full of surprises. A recent discovery made at the University of Auckland’s Leigh Marine Laboratory has rewritten what we know about these ancient predators.

Sharks might not be voiceless after all.

The first recorded shark sounds

In a study published in Royal Society Open Science, scientists shared the first known recordings of active sound production by sharks.

The species involved, the rig shark (Mustelus lenticulatus), is a small, bottom-dwelling shark native to New Zealand.

During routine hearing experiments, ten juvenile rig sharks produced distinct clicking sounds when handled underwater. These weren’t random splashes or incidental noise. They were consistent, sharp clicks — deliberate and audible.

“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… But I think the original notion that we had that sound isn’t important at all is also likely not true,” said Carolin Nieder, lead author of the study.

Clicks as stress or warning signals

The clicks didn’t happen while the sharks swam freely. They didn’t appear during feeding or rest. They only occurred when the sharks were briefly handled. Most clicks happened in the first ten seconds of handling and dropped off after that.

This suggests the sounds may be a reaction to stress. The sharks could be trying to defend themselves or confuse potential predators. Some clicks coincided with physical movements, like swaying or sudden bends. Others came with no visible movement.

The researchers counted an average of nine clicks per shark in a 20-second window. About three-quarters of those clicks were short, single-pulse bursts. The remaining were double-pulse clicks, produced in rapid succession.

“Maybe they weren’t afraid for their lives anymore,” Nieder said, noting the decline in clicks over time. This behavior may resemble a natural escape tactic in the wild, used as a quick distraction.

Teeth, not vocal cords

So how do sharks make these sounds without sound-producing organs? The team examined this closely. Using microCT scans and detailed dissections, the researchers studied the cranial structure of the rig shark. The teeth emerged as the most likely mechanism.

Rig sharks have blunt, interlocking teeth arranged like flat plates. These teeth snap together during rapid jaw movements. This snapping action likely creates the broadband clicks observed in the study.

The sounds recorded had an average duration of 48 milliseconds, with frequencies between 2.4 and 18.5 kHz.

Most clicks peaked around 9.6 kHz, far above the rig’s hearing threshold, which tops at around 800 Hz. Yet, the first burst of each click contained low frequencies that might be audible to the sharks themselves.

Are these shark sounds meaningful?

The purpose of the clicks remains uncertain. Are they a biological signal – a warning, alarm, or defensive cry? Or are they simply a byproduct of muscle contractions and jaw tension under stress?

The study notes that rigs did not produce sounds during other behaviors, like swimming or feeding. This supports the idea that the clicking is linked to disturbance, not daily communication.

Still, comparisons with other fish species are revealing. Teleost fish, like cod and piranhas, often emit clicks when threatened or approached by predators. These “predator-related” sounds serve no obvious communicative role but may momentarily confuse or startle attackers.

Similar sounds in other species

This discovery also echoes recent findings in rays. Since 2022, several studies have reported click-like sounds in stingrays and skates when divers approached.

Species like the mangrove whipray and the blonde ray produce sharp broadband clicks, seemingly in reaction to disturbance.

These clicks share many traits with the rig’s clicks: short duration, high frequency, and apparent links to stress. While the anatomical mechanisms may differ, the pattern is striking.

In rays, the movement of spiracles and fins has been observed during sound production. In rigs, however, no clear body movement could be linked directly to the clicks. This raises the need for better underwater observation – perhaps through close-up video – to pinpoint exactly how the sound is made.

Not all sharks click

Interestingly, not all sharks show this behavior. The study tested three dusky smoothhounds (Mustelus canis), close relatives of the rig. These sharks, when handled under the same conditions, produced no clicks.

This may point to differences in species behavior, evolutionary paths, or simply varying sensitivity to human presence. The dusky smoothhounds had been in captivity longer, which might explain their lack of response.

The researchers noted that Mustelus as a genus includes many species with similar tooth shapes. It’s possible that other species may also produce clicks under the right circumstances.

Can rig sharks hear their own sounds?

This question remains unresolved. Rigs are most sensitive to very low frequencies, far below the peak of their clicks. Yet, each click begins with a powerful burst that includes frequencies under 1 kHz. These lower frequencies may fall within the shark’s hearing range.

Whether the clicks carry a message for other sharks is unclear. But it’s possible the clicks aren’t meant for sharks at all. The energy-rich sounds could affect predators with better hearing, like toothed whales or large marine mammals.

Some fish also produce similar sounds that deter or confuse predators, even if they aren’t always effective.

New voices from the deep

For years, researchers assumed that sharks lacked the ability – or need – to make sound. This study shifts that narrative. It reveals not only a sound, but a potential signal – a cry, a warning, or perhaps an instinctive snap.

The rig shark now holds the title of the first confirmed sound-producing shark. And its clicks may not be alone for long. As scientists look closer, more species may reveal their hidden voices.

In the quietest corners of the ocean, even sharks might have something to say.

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Click this link to hear the noises made by these sharks during the hunt…

The study is published in the journal Royal Society Open Science. 

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