Researchers at the University of Auckland’s Leigh Marine Laboratory have just uncovered an exciting phenomenon. Of particular interest, they studied rig sharks (Mustelus lenticulatus), a small bottom-dwelling shark species native to New Zealand. It all started when researchers, while conducting routine behavioral experiments, noticed these sharks make loud, unmistakable clicks when captured and handled under water. This finding marks the first known instance of a shark actively producing sound, expanding the understanding of marine life communication.
The research consisted of ten juvenile rig sharks, each of which underwent a short period of handling by researchers. Importantly, each of those sharks made sound during these encounters, releasing loud bursts of clicks. As the initial observations determined that the clicking sounds were most prevalent during the first handfuls, as the trials continued, these sounds largely went away. Each click zipped by in less than 48 milliseconds. This would be at volumes greater than 155 decibels, similar to the sound level of a shotgun blast.
Given the rapid tooth clicks, the team initially assumed these clicking sounds were produced as the rig sharks chop down their teeth. This is supported by the unique “pavement dentition” of the species, which could serve a dual purpose: aiding in feeding and producing noise when the jaws close. Curiously, rig sharks are only responsive to sounds under 1 kilohertz. Since this range is much lower than the frequencies of their clicks, it means they probably wouldn’t use these sounds to communicate among themselves.
Many of the rig shark’s known predators including New Zealand fur seals are highly sensitive to higher frequencies. The loud clicks might shock or disorient these predators, introducing an element of natural selection to this unusual habit.
In nearly 70% of the clicks, there were fluid, rhythmic physical motions of the body. There were many more clicks that lacked any apparent movement at all. Out of these sounds, approximately 75% were single bursts of clicks and the rest were quick double click sounds.
Adrian Gutteridge, one of the academics behind the project, urged caution when it came to interpreting these noises.
“It’s too early to tell whether it’s a response, kind of saying, ‘go away,’ or if it’s just their nervous system firing off which just happens to make their teeth and jaws click.” – Adrian Gutteridge
Carolin Nieder, another researcher on the team, on the behavior the rig sharks displayed in the experimental arena.
“Maybe they weren’t afraid for their lives anymore.” – Carolin Nieder
This finding is important not just for newly documented rig shark behavior. It expands our perception of how marine animals communicate with one another. The apex predators’ capacity to create noise could have huge implications on how they interact with not only predatory threats but their surroundings.
