For a long time, sharks were considered mute creatures, relying on their stealth to hunt and avoid predators. But now, for the first time, shark sounds have been recorded.
New recordings show whitetip reef sharks (Mustelus lenticulatus) – small bottom-dwelling sharks native to New Zealand – making distinct clicking sounds when researchers hold them underwater. The sounds were consistent and repeated across individuals, and may be linked to stress responses or defence, according to the authors of the study, published Wednesday (March 26) in the journal Royal Society Open Science.
The recordings represent the first known instance of a shark actively producing sound. “Sharks have sensory systems that are more advanced than hearing, including electroreceptors, olfaction, and the way they move through the water,” Caroline Nieder, lead author of the study and a research scientist at the Woods Hole Oceanographic Institution, told Live Science. “However, I think the original idea that sound doesn’t matter is also probably wrong.”
Ten young reef sharks were accidentally observed making sounds during routine behavioural experiments at the University of Auckland's Leigh Marine Laboratory. When the researchers briefly held them underwater, all 10 sharks made audible clicks.
The clicks were most frequent during the first few manipulations, but then stopped as the experiments continued, Nieder said. “They may have stopped being afraid for their lives,” she added, noting that in the wild, loud clicks may serve as a short-term distraction for young sharks, helping them escape predators.
Most sharks are considered quiet because they lack swim bladders, the air sacs that fish typically use to make sounds. Micro CT scans and 3D reconstructions of reef sharks have also found no obvious organs or structures capable of producing sounds.
Scientists detected a clicking sound when they touched sharks during standard behavioral experiments.
The team suggested that the sounds might come from sharks snapping their teeth.
Reef sharks have broad, blunt teeth organized into tightly packed plate-like structures that are ideal for crushing hard-shelled prey like crabs. Researchers speculate that this “sidewalk dentition” may also serve a secondary function — producing sound when the jaws snap shut.
However, Nieder noted that without direct observation of sharks' jaws during snapping, this mechanism remains speculative.
Each click lasted approximately 48 milliseconds and sometimes exceeded 155 decibels, comparable to a shotgun blast.
About three-quarters of the clicks were single clicks, and the rest were short double clicks. The scientists noticed that about 70% of these clicks were accompanied by gentle, swaying body movements, but a few occurred without any visible movement at all.
It is currently unclear whether the click is an accidental side effect of interacting with the device or an intentional behavior.
The hearing range of sharks is mostly below 1 kilohertz, which is well below the frequencies of their clicks, so it is unlikely that the clicks are intended to communicate with other sharks.
However, some well-known reef shark predators, such as New Zealand fur seals (Arctocephalus forsteri), are sensitive to higher frequencies and may be startled or confused by sharp clicks.
Several species of rays and skates, close relatives of sharks, are also known to make clicking sounds when disturbed by divers. These sounds are thought to serve as warning signals or distress signals.
Nieder noted that future research could focus on closely related shark species to see if they can also make sounds and whether they make sounds in response to
Sourse: www.livescience.com
