In a remarkable breakthrough, researchers have captured the first-ever sounds made by sharks, as detailed in a new study published in the journal Royal Society Open Science. The study, which was released on Wednesday, reveals that the rig shark, also known as the spotted estuary smoothhound, generates clicking sounds when handled, challenging previous perceptions of these marine creatures as silent.
According to Carolin Nieder, a marine biologist at Woods Hole Oceanographic Institution and the lead author of the study, the discovery was serendipitous. While conducting research on the hearing abilities of sharks for her doctorate at the University of Auckland in New Zealand, Nieder stumbled upon this intriguing auditory phenomenon. “I had never considered that any of the sharks I was studying could make any sort of sound,” she explained. “I was under the assumption that sharks are silent fish, so they wouldn't make any active sounds,” she added.
The research involved capturing seven rig sharks from the Kaipara Harbour in New Zealand, along with three more sourced from a local commercial fisherman. These sharks were then housed in a marine laboratory using circular flow-through holding tanks. After a week of acclimatization, the sharks were moved to an experimental tank for handling, where the sound production was observed.
During the handling process, researchers noted that the rig sharks produced clicking sounds underwater. On average, each shark emitted about nine clicks in a span of 20 seconds, with a notable increase in clicks during the initial 10 seconds of handling. The average duration of these clicks was measured at just 48 milliseconds. The study found that approximately 25% of the clicks occurred during vigorous movements of the sharks’ heads and bodies, while around 70% were recorded during calmer swaying. Notably, 5% of the clicks happened without any visible body movements.
The study indicated that the initial handling triggers a stress response in the sharks, leading to heightened clicking activity. As the sharks became more accustomed to being handled, the frequency of clicks diminished, suggesting a correlation between stress levels and sound production.
Nieder highlighted the significance of this discovery, particularly for smaller sharks like the rig, which are vulnerable to predation. “Maybe if a small shark like this gets attacked, these clicks could disorient the predator for just a split second to allow for an escape,” she explained. The rig shark’s ability to produce clicking sounds is attributed to its unique flat teeth, which differ from the teeth of other shark species.
Neil Hammerschlag, president of Atlantic Shark Expeditions and not involved in the study, expressed enthusiasm over the findings. “The idea that some sharks are making sounds is exciting because it suggests they could communicate through sound,” he remarked. This discovery opens up new avenues for future research into shark communication and behavior.
Nieder expressed hope that this initial observation will inspire further research into shark communication and encourage curiosity about other species traditionally thought to be silent. “We should continue to listen to other animals and species that are deemed silent,” she concluded, urging a deeper exploration into the auditory capabilities of marine life.
