3 days ago
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Scientists have recorded New Zealand’s rig sharks making noises in the world’s first documented case of active sound production by any shark species.
Until now, over a thousand fish species are known to produce sounds in several contexts, such as mating and for defence against predators.
While cartilaginous fish like sharks and rays are known to use sound for communicating, tracking prey, and for safely moving underwater, they are not known for producing sounds voluntarily.
A 2022 study showed for the first time that a stingray species produces clicks when approached by a diver.
Now, a new study has found that rig sharks handled by researchers deliberately make short, sharp clicks of relatively high peak frequencies.
The recordings, published in a new study in the journal Royal Society Open Science, hint that the sounds are created by these small sharks forcefully snapping their flattened teeth.
Rig sharks grow to about 150cm (5ft) in length and are endemic to shallow estuaries around New Zealand.
They mainly feed on crabs and other small crustaceans and are preyed upon by larger sharks.
Scientists suspect these small sharks produce these sounds in response to disturbance or distress.
In the study, researchers assessed recordings captured from 10 rig sharks as they were handled underwater in tanks at the Leigh Marine Laboratory in New Zealand.
“During this brief handling time, rigs were opportunistically observed to produce clicking sounds underwater,” scientists observed.
They assessed the number of clicks the sharks produced during every 10-second interval of recording.
On average, the sharks produced 9 clicks every 20 seconds, with most sounds made along with body movements like moving from right to left, researchers observed, hinting that they were likely a “startle response”.
“Roughly 25 per cent of the clicks co-occurred with an explosive sway (vigorous bending of the head and body from side to side), about 70 per cent co-occurred with calm swaying (slow side to side movements), and 5 per cent of clicks occurred in the absence of any obvious body movements,” scientists noted.
“To the best of our knowledge, this study would be the first to show that sharks can produce sounds,” they wrote.
However, researchers call for further studies to confirm the mechanism and determine the sound’s other use and biological significance.
It also remains unclear whether the rigs can sense their own clicks.
“Further behavioural observations are needed to test this hypothesis and verify whether rigs produce clicks under more natural conditions without human interference,” scientists concluded.
