WHOI: New Discovery Reveals Sharks May Detect and Produce Sound

Scientists are discovering for the first time that sharks may be capable of their own unique and mysterious form of sound production, a previously unconsidered occurrence.

For decades, sharks have been understood through a different array of sensory capabilities—an acute sense of smell for detecting a drop of blood over vast distances, the ability to sense the electrical fields of prey, and vision through the ocean’s dim light. Their ability to detect and produce sound may have been overlooked, though. “Look up sharks, and nothing mentions sound production—they have been thought to be ghostly silent,” says Carolin Nieder, a postdoctoral investigator at the Woods Hole Oceanographic Institution (WHOI). Studying sharks is not easy, though, as they are elusive in their natural habitats and have rarely been studied up close or while being handled.

Nieder was originally conducting research at the University of Auckland on how different types of sharks detect the direction of sound. While handling the rig shark in a tank, she captured underwater vocalizations described as “click… click… click… click.” In collaboration with researchers at the Université de Liège and the University of Auckland, this led to a discovery that when handled underwater, the rig shark isn’t silent at all. The finding is particularly surprising given that dogfish sharks have been model species for neurobiology research for decades at institutions like University of Chicago’s Marine Biological Laboratory and WHOI.

Nieder’s finding parallels research from a field study during 2022 during which the mangrove whipray and the cowtail stingray began to click when approached by divers. Both ray species belong to the ancient elasmobranch family, a class of cartilaginous fish with distinctive anatomical features. Recently, three other related species, including the blonde ray, the rough skate, and the marbled electric ray, were also reported to produce short, broadband clicks when disturbed by divers, possibly as a threat response. Tracing these evolutionary transitions that go back 450 million years, researchers began to suspect that sharks may be capable of similar sound production.

Whether rig sharks can acoustically sense their own click sounds, or what function these sounds serve, is not yet understood. Tests of this animal’s hearing range reveal that the clicks produced by rig sharks exceed their low-frequency sensitive hearing range. This raises doubts about whether these sounds play a role in communication between individuals. However, because the initial impulse contains lower frequencies, it's possible that rigs may still be able to hear at least part of them.

Nieder’s team is analyzing contextual clues to understand the clicks' purpose. While rigs that were handled produced clicks, and produced significantly more during the first 10 seconds of handling than during the subsequent 10 seconds, they were not observed to produce clicks during feeding or while free-swimming in the tank. These findings suggest that initial handling may trigger initial stress and startle the sharks, or the sound could be an anti-predator response in the wild. But as the rigs become habituated to handling, their behavioral response diminishes, resulting in fewer clicks over time.

Sharks detect sound in two ways: through their inner ears and through the movement of water, which they sense using a row of specialized cells called the lateral line. However, it's not clear yet how sound is produced by rig sharks, as elasmobranchs are not known to possess any specialized body part for sound production, and have a flexible, cartilaginous skeleton. The broadband frequency range and short duration of the rig clicks suggest that they may be generated by teeth snapping together.

Given the shared pavement-like teeth among all Mustelus species, it is likely that other members of the genus produce similar sounds. If these sounds come from jaw snapping, other sharks with strong crushing jaws may be able to do the same. While Nieder’s work has shifted to using acoustic techniques to enhance coral larval settlement in reef restoration efforts, she hopes to return to New Zealand to unravel exactly how these sharks make their sounds—and whether other local shark species might also have voices waiting to be heard.