Sharks have long been regarded as silent predators, but a new study shows that small rig sharks (Mustelus lenticulatus) can make clicking sounds when handled. Evolutionary biologist Carolin Nieder discovered the noise by accident during shark hearing tests. In lab trials, juvenile rigs emitted rapid “click…click” noises when restrained. The results, published in Royal Society Open Science, represent “the first documented case of a shark making sounds”. Nieder recalls: “At first we had no idea what it was, because sharks were not supposed to make any sounds”
Accidental Discovery in the Lab
According to the study, Nieder’s team had placed an underwater microphone in a tank to test shark hearing. During routine handling, a researcher reached in and heard a clear “click…click” coming from the shark’s mouth. Rig sharks have broad, flat, cusp-shaped teeth for crushing crustaceans, and the forceful snapping of these teeth likely produces the sound.
Nieder then followed up with systematic trials on ten rig sharks. In repeated tests, every shark emitted click bursts when grasped—averaging about nine clicks per 20-second handling episode. Notably, clicks were most frequent in early trials and largely stopped as the sharks became accustomed. Because the clicks were strongest during initial capture, the researchers speculate this might be a voluntary stress or defensive response. Nieder cautions that this hypothesis needs formal testing under natural conditions.
Implications for Shark Biology and Communication
If confirmed, these findings suggest surprising complexity in shark communication. Sharks and their relatives (rays and skates) lack the gas-filled swim bladders that most bony fish use to make sound. Sharks were long assumed silent. Yet the rig’s clicks hint that sharks may use sound for alarm or communication.
Nieder also found that rigs hear only low frequencies (below ~1,000 Hz)—far lower than the human range. “They are sensitive to electric fields, but if you were a shark I would need to talk a lot louder to you than to a goldfish,” she notes. The researchers say further work is needed to see if rigs click in the wild as an alarm or social signal.
