A first: a shark identified as a deliberate producer of underwater sounds

Long thought to be silent, sharks may not be as silent as previously thought. An international team of scientists - including Professor Éric Parmentier - has just documented the "clicks" voluntarily produced by a species of shark, the spotted shark (Mustelus lenticulatus), during captive handling. This unprecedented discovery could revolutionise our understanding of communication in elasmobranchs.

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t's a discovery that could well revolutionise our understanding of communication in sharks. For a long time, these marine predators were considered to be silent creatures, incapable of voluntarily producing sounds. Unlike many bony fish, sharks have neither a swim bladder - an air sac often involved in sound production - nor a bony skeleton, nor even firmly anchored teeth. All these anatomical characteristics seemed to deprive them of any vocal capacity.

But researchers from the Institute of Marine Sciences at the University of Auckland, in collaboration with the University of Liège, have now challenged this assumption. By observing a species of shark known as the spotted shark (Mustelus lenticulatus), they have recorded for the first time sounds clearly emitted in response to manipulation. Ten young emissoles, captured in the coastal waters of New Zealand and kept in captivity, all produced short, repeated clicks when they were briefly handled outside their resting tank," explains Prof Eric Parmentier, a marine biologist at ULiège." On average, each shark emitted nine "clicks" over a period of twenty seconds. "These sounds, recorded using a hydrophone placed in the experimental tank, are characterised by their wide frequency band (up to 24 kHz) and an average duration of 48 milliseconds. Some of the 'clicks' consisted of a single pulse, others of two successive pulses. The sound power of the initial pulses often exceeded 160 dB, a level high enough to be detected even in noisy conditions."

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But where do these sounds come from? Morphological analyses, including 3D reconstructions of the sharks' heads using micro-CT scans, did not reveal any specialised sound-producing structures. However, the scientists did identify a particular organisation of the teeth of the spotted dogfish: flat, interlocking mosaic structures, typical of species that feed on crustaceans and hard-shelled molluscs. This type of dentition, known as "squamous", could enable the production of sound by friction when the jaws contract suddenly.

This stridulation mechanism, already observed in certain species of shark-like rays, seems to apply here to the spotted emissola. Similar 'clicks' have recently been recorded in two species of ray - the cow-tailed stingray and the mangrove stingray - in response to the approach of divers.

While the exact function of these clicks has yet to be confirmed, the researchers have put forward several hypotheses. The sounds could be part of a startle or distress response, comparable to the warning calls made by other fish when they are captured or threatened. They could also act as a deterrent to predators. However, most of the acoustic energy of these clicks exceeds the known hearing capacity of the emissole, making it unlikely that they are used for communication between conspecifics - unless part of the lower, more discreet frequencies is perceived by the animal.

The scientists stress the need for further studies to verify whether these sounds are also produced in the natural environment, and in what behavioural contexts they occur. Because if this sound production turns out to be more frequent than previously thought, it could mark a turning point in the study of acoustic communication in sharks - an area that is still largely unexplored.

This first observation of active sound production in a shark opens the door to many new questions. Are the shark's clicks used in the wild to interact with other sharks or to deter predators? Do other shark species share this ability? These are all questions that researchers hope to explore in future studies. One thing is certain: the depths of the sea have not finished revealing their sonic secrets.

Scientific reference

Nieder C., Parmentier E., Jeffs A.G., Radford C., Evidence of active sound production by a shark, R. Soc. Open Sci. 12: 242212,  2025

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Eric Parmentier