Sharks are thought of as silent killers, associated with no other sound but the "duunnn dunn, duuuunnnn dunn" of the Jaws theme song. But humans might have been long ignorant of the sound sharks truly make, which new research suggests is, in the case of the rig shark, similar to the clicks of whales and rays. Marine biologist Carolin Nieder was working on her PhD on sharks' hearing capabilities in 2021 when she handled some rig sharks and noticed them making some odd crackling noises. "At first we had no idea what it was because sharks were not supposed to make any sounds," Nieder tells Scientific American.
Many fish species produce sounds by vibrating their swim bladder, but sharks don't have one. Curious, Nieder and colleagues experimented with handling juvenile rig sharks, native to the coastal waters of New Zealand, in tanks outfitted with sound recorders. As the sharks were touched, they produced high-frequency clicks (listen here) lasting an average of 48 milliseconds, faster than the blink of a human eye, per CNN. Researchers believe the clicks are generated by the rig shark snapping its overlapping rows of flattened teeth, according to the study published Tuesday in Royal Society Open Science. Why the shark produces these sounds is more of a mystery.
The consistent pattern and frequency of the clicks suggest the sounds are intentional, Nieder tells CNN. But the frequencies "were mostly outside the rigs' hearing range, which casts doubt that the sharks use them to communicate," per Scientific American. It's possible the sounds are meant to spook predators, including several toothed whales that would've been able to hear them, the outlet notes. As several ray species produce clicklike sounds when approached by divers, this could be a similar defense mechanism or warning signal. Nieder, who notes the sharks stopped producing the sounds once they got used to handling, next plans to test whether the sounds can be heard in a more natural environment. (More sharks stories.)
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