A recent study by researchers at the University of Auckland’s Leigh Marine Laboratory revealed a fascinating find. They first noticed Rig sharks, endemic to New Zealand, producing unique clicks while doing their regular behavioral assays. These small, bottom-dwelling sharks, scientifically known as Mustelus lenticulatus, were found to produce these sounds while being handled underwater by scientists. The results imply some sort of distress defensive mechanism present in these juvenile sharks.
In the experiment, ten juvenile Rig sharks were studied, with researchers inadvertently capturing the clicking sounds made by the sharks. Those clicks were uniform over a wide swath of people. In close to 70% of instances, these clicks were paired with soothing, swaying body movements. Interestingly, even some clicks with zero visible movement detected were made, showing the nuance behind this behavior.
The clicks, averaging 48 ms each, were mostly single bursts in about three quarters of the recordings. The other cases were resolved with a double-click and a drag. Most significantly, the volume levels of these clicks even reached upward of 155 decibels, Myer said — similar to the sound of a shotgun blast. Despite this intensity, the clicks' frequencies are far higher than the Rig sharks' own hearing range, which is largely below 1 kilohertz.
"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 Carolin Nieder, a researcher involved in the study.
This difference in click rate implies that the clicks may not be a method of communication between Rig sharks. The scientists suggest that these audible cues serve as momentary interruptions. This strategy allows for juvenile Rig sharks to minimize predation when they are caught. The strikingly similar pattern and intensity of the clicks from each volunteer lends credence to this hypothesis.
Increasingly they hope future studies will determine if other closely related shark species make noise, and learn what type of sounds they might be producing. Their collective research will allow us to better understand the evolutionary adaptations of sharks and the sensory mechanisms involved.
