Photo credit: www.smithsonianmag.com

New Insights into Shark Communication: Rig Sharks Recorded Making Sounds

For years, scientists believed sharks to be silent creatures gliding through the oceans. A recent breakthrough challenges this perception by revealing that rig sharks, a small species residing off the coast of New Zealand, are capable of producing sounds. This discovery suggests that auditory communication may be more significant in sharks’ lives than previously understood.

The research team, whose findings were published in the journal Royal Society Open Science, recorded unusual clicking sounds from these sharks. As stated by the authors, this study is believed to be the first of its kind to showcase a shark’s ability to generate sounds.

Lead researcher Carolin Nieder from the Woods Hole Oceanographic Institution noted that sharks possess highly developed sensory systems beyond just hearing, which include electroreception and an acute sense of smell. However, she challenges the previous understanding that sound plays an insignificant role in their behavior.

The discovery first occurred incidentally during Nieder’s PhD research at the University of Auckland in 2021. While handling rig sharks for testing, she noticed a distinct chirping noise. “The sounds reminded me of electric sparks,” Nieder recounted, reflecting on her initial observations.

Despite the unexpected nature of the sounds, research was limited at that time. However, Nieder’s curiosity persisted, leading her to closely examine the phenomenon from May 2021 to April 2022. During this period, she studied ten juvenile rig sharks in a lab setting, aiming to uncover the mysteries behind their crackling sounds.

To capture the sounds, the researchers placed each shark in a recording-equipped tank, holding them individually for 20 seconds. The sharks responded by producing clicking noises, each lasting approximately 48 milliseconds and reaching sound levels exceeding 155 decibels, equating to the volume of a shotgun. The clicks generally consisted of single pulses, with about a quarter appearing in pairs. Intriguingly, around 70% of the sounds were correlated with smooth body movements, while the remaining were associated with vigorous thrashing or occurred when the shark was still.

Furthermore, the frequency of clicking decreased as the sharks became accustomed to their surroundings, leading the researchers to hypothesize that this could be a learned behavior rather than an involuntary response linked to captivity.

Interestingly, the frequencies emitted by the rig sharks fall outside their hearing range, suggesting that the sounds may not serve inter-shark communication. The purpose behind this sound production remains uncertain. It may potentially serve as a warning mechanism against predators, particularly since some toothed whales, known to hunt rig sharks, can detect these sounds.

Adrian Gutteridge, a shark biologist with the International Union for Conservation of Nature and not involved in the study, commented on the ambiguous nature of these sounds, noting it is too early to determine whether they function as a defense signal or are mere byproducts of nervous system activity producing clicks of their teeth and jaws.

Unlike many fish species that utilize a swim bladder to generate sounds—an organ that enables buoyancy and communication—sharks lack this anatomical feature. Scans of rig sharks revealed no other structures capable of sound production, indicating that their sounds likely originate from their teeth. Confirming this theory would require direct, close-up observations of the sharks’ jaws during sound production.

As research progresses, scientists are keen to explore whether these sounds occur in the wild, raising essential questions about the rig sharks’ behavioral patterns outside the laboratory setting. Marine biologist Dennis Higgs from the University of Windsor emphasized the need for further exploration into whether rig sharks utilize sound in natural habitats.

The revelation that rig sharks can produce sounds opens up new possibilities for understanding shark behavior and communication, ultimately enhancing the scientific community’s view of these fascinating marine creatures.

Source
www.smithsonianmag.com