This Shark Challenges Everything We Thought About Shark Silence

Until recently, the scientific community believed that sharks were silent. Like many other marine life, they communicate through body language and swim patterns. However, one shark is challenging everything researchers once believed. As it turns out, this species is noisier than everyone previously thought.

Meet the Shark That Responds to Human Touch

Rig sharks, or Mustelus lenticulatus, are native to New Zealand. They’re also called “lemon fish” or spotted dogfish and dwell mainly on the sea floor. Their diet consists primarily of bottom feeders like crustaceans and small fish, drawing them to many estuaries in the Pacific. The rig’s teeth are ideally suited for its prey of choice. Plate-like rows of flat, pointed teeth line the inside of its mouth, making it highly efficient at crushing shellfish. This defining shark tooth type sets the rig apart from other species, many featuring teeth designed to tear and slice into prey.

A rig’s teeth keep it from being a threat to humans, and it has no interest in prey bigger than itself. However, fishermen catch rigs for their rich meat and high oil content. Because of this, the sharks are easily fished and easily studied. During a recent expedition, marine biologist Carolin Nieder discovered these sharks can even make noise — but only when handled.

A Loud Discovery

In the study published in The Royal Society Publishing journal, Nieder explains what she and her team heard when handling a rig shark. The clicking noise, determined to come from the shark’s teeth, was a threat response. It’s still true that sharks don’t communicate with one another using sound, but the rig shark is the exception to the silent predator ideology. Nieder and her team confirmed that, when stressed, the shark clicks its teeth together to produce a clacking sound, which serves as a defense mechanism against potential predators.

To further test this theory, Nieder’s team captured several more sharks. Each one presented with the same clicking sound as the first. As the sharks were handled more, the clicking became less. This indicates that as the sharks become familiar with being handled, they feel less threatened. However, it’s important to note that this noise has nothing to do with communication within the species. According to People, the clicking noises reached 156 decibels, which is relatively loud underwater. This noise level is outside the range of sharks, meaning they can’t hear it like humans (and other predators) can.

How Effective Is the Rig Shark’s Noise?

Since sharks are sensitive to low-frequency sounds, this high-frequency noise wouldn’t be effective against intra-species predation. That doesn’t mean it’s ineffective; some fish can hear nearly 1,000 hertz. This is well within the range of 150 decibels, which makes the rig’s clicking a valuable defensive tool. Since they’re fished regularly, the sharks may respond to being caught with this noise.

During Nieder’s study, the team discovered that some rigs incorporate body movements with teeth-clicking. It’s estimated that 25% of clicking noises were accompanied by “explosive sway.” This means a shark aggressively thrashed its body and head from side to side. Additionally, about 70% of clicking noises were accompanied by a calmer swaying motion. Only 5% occurred with no movement whatsoever. This thrashing indicates a prey response, where sharks pivot their bodies to evade enemies. It can also be a means of intimidation, with the shark thrashing back and forth to display dominance. According to the study’s conclusion, it’s likely the former as a response to distress.

Opposing Opinions on Shark Communication

In an interview with ABC News, Nieder also says the rig shark’s size could be a factor in its noise-making. Rigs only grow to about five feet, which leaves them vulnerable to attack by larger species. Clicking might be a last-ditch effort to confuse or disorient a predator, giving the rig enough time to swim away. This would only work on predators with good hearing, raising the question once again of its purpose. Neil Hammerschlag, president of Atlantic Shark Expeditions, also spoke to ABC News. He believes this noise could open a door into communication between marine life, potentially in other shark species.

Alternatively, Dennis Higgs, a marine biologist at the University of Windsor in Ontario, spoke with Scientific American about the rig’s new sounds. In the interview, he questions whether it would make this noise in open water. It’s an important question, as it could be a vocal response to the threat of human handling. Nieder plans to research this with sharks beyond just the rig to further the study. All experts agree that this noise could be a revolutionary discovery in marine biology, but its true purpose remains a mystery.

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