For years, sharks were considered silent predators, navigating the oceans without producing sounds. This assumption has been overturned by recent research revealing that rig sharks (Mustelus lenticulatus), native to New Zealand's coastal waters, emit distinct clicking noises. Marine biologist Carolin Nieder from the Woods Hole Oceanographic Institution first observed these sounds inadvertently during studies on shark hearing.

The new recordings captured distinct popping and clicking noises, ranging from 80 to 500 milliseconds in length, produced voluntarily by captive individuals. 

Purpose unclear

While the precise purpose of the sounds remains unclear, their repeatability and apparent control suggest they may be a form of deliberate acoustic behaviour. The researchers noted that the clicks may serve as a form of startle defence, a territorial signal or a form of intraspecific communication. 

Sound-producing mechanisms are incredibly diverse in fishes. The most important group of mechanisms involves the swim bladder and various types of sonic (drumming) muscles that induce swim bladder vibrations.

Image

Unlike many fish that utilise swim bladders for sound production, rig sharks lack this organ. The researchers hypothesise that the clicking noises result from the forceful snapping of the sharks' uniquely flattened, plate-like teeth, which are typically used to crush crustaceans.

The findings challenge long-standing assumptions and invite further investigation into how sharks interact with their environment—and with each other—through sound as well as motion. Whether rigs can acoustically sense their click sounds is not yet understood.