Sharks Were Thought To Swim In Silence, But A New Recording Shows They Might Make Sounds
Sharks have long been thought to swim in silence, but now, a new recording has shown that they might actually make sounds.
For the first time, a team of researchers captured clicking noises from the rig shark, a small species that inhabits the waters off the coast of New Zealand.
The discovery suggests that audible noises play a bigger role in sharks’ lives than previously believed. It is the first known recording to show that sharks can produce sounds.
“Sharks have sensory systems that are more refined than their hearing, like their electroreceptors, their smell, and the way they propel themselves through the water,” said Caroline Nieder, the lead author of the study and a researcher at the Woods Hole Oceanographic Institution.
“But I think the original notion that we had that sound isn’t important at all is also likely not true.”
The sounds were first detected in 2021 by accident. Nieder had been conducting her PhD research at New Zealand’s University of Auckland. She noticed that the rig sharks would make chirping sounds when she handled them between lab tests.
At first, she had no idea what the sound was. Nieder was unable to investigate the noises further at the time, but she never forgot about them. Between May 2021 and April 2022, she and her team studied 10 juvenile rig sharks in the lab.
They transferred each shark into a tank equipped with recording devices. The animals were held one at a time for 20 seconds. The sharks started to make short clicking sounds as they were being moved.
Each lasted only around 48 milliseconds. However, the noises were loud, reaching a volume above 155 decibels, which is comparable to a shotgun. Most of the clicks were single pulses, but roughly a quarter occurred in pairs.
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About 70 percent of the noises were accompanied by a calm, swaying movement of the body, while 25 percent came with the thrashing of the head or body.
The remaining five percent happened when the shark was still. The sounds were also more frequent in the first 10 seconds of the handling sessions.
“As the animals got used to the daily experimental protocol, they then stopped making the clicks altogether, as if they got used to being in captivity and the experimental routine,” said Nieder.
“This led us to consider that maybe we are observing a sound-making behavior rather than a strange artifact.”
The frequencies of the sounds were too high for the rig shark’s hearing range, which suggests that the animals were not making the noises to communicate with each other. So far, it is unclear what the purpose of the sounds is, but it could serve as a defense against predators.
The study was published in the journal Royal Society Open Science.
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