Now, a study has broken that silence. Videos reveal that two species of stingray—the mangrove whipray (Urogymnus granulatus) and cowtail stingray (Pastinachus ater), both native to the Indo-West Pacific—produce striking, unmistakable clicks.
In fact, in one of the videos, the stingray’s click was so boisterous, it caused the photographer to drop his camera, says Lachlan Fetterplace, a marine ecologist at the Swedish University of Agricultural Sciences who led the study, published recently in the journal Ecology.
While nearly a thousand species of bony fish make some sort of noise, sharks, rays, and skates had, until now, been thought of as silent outliers. And that’s surprising, because scientists and divers are in the water with these animals all the time. (Read more about nature’s novel noisemakers.)
“That’s kind of the strange thing,” Fetterplace says. “I dive a lot with some other species of rays, and now I’m second guessing myself. Could I have missed this?”
“This just shows we don’t know everything,” he adds. “We’re in the year 2022, and you can discover something no one has ever seen just by going out and doing observations in natural history.”
How does a stingray make a sound?
Before the new study, the only verified evidence of rays making sounds came from a study of captive cownose rays. Published in 1970, this research recorded short, sharp clicks coming from the fish, but only after scientists forcefully prodded them. It wasn’t until 2017 and 2018 that several of the new study’s co-authors happened to record high-quality video while diving in Indonesia and Australia that captured the noises.
Even though the video evidence these rays make noises seems to be a slam dunk, the researchers are not certain how the animals produce the sounds.
“They don’t have vocal cords, and there’s no clear mechanism for how they do it,” Fetterplace says.
In the videos, the rays’ spiracles—two holes on their heads used to move water across their gills—appear to contract as the clicking sound is heard. This suggests the fish might be creating friction between the spiracles and the surrounding tissue, not unlike when we snap our fingers. It’s also possible the rays are forming sounds by creating a vacuum, like when we click our tongues, Fetterplace explains.
Whatever is going on, it is likely to be revealed soon, as other scientists are already planning studies to look at ray anatomy more closely.
What are stingrays trying to say?
For their research, Fetterplace and his colleagues compared the bandwidth and frequencies of the sounds to the known range of stingray hearing. They confirmed stingrays can indeed hear these sounds, which could mean they’re a form of communication.
At the same time, the scientists’ work showed that reef sharks and sicklefin lemon sharks—predators of both ray species—can also hear the clicks. That suggests stingrays may issue the sounds when they sense a predator approaching as a warning, perhaps to stay away from the rays’ venomous barbs.
Similarly, the quick, loud sounds may simply be a diversion that surprises a predator and gives the stingray a chance to escape. (Like how the clicks worked on that underwater photographer.)
There is another possibility, though.
When photographer and co-author Javier Delgado Esteban witnessed a wild mangrove whipray making sounds in 2018 in Geoffrey Bay, Australia, he noted another interesting behavior. After making the clicks, the juvenile was quickly joined by a number of other stingrays. (See the enormous stingray that set the record for world’s largest freshwater fish.)
“The others would come in and pile around it, and all have their tails with spikes sticking up,” says Fetterplace, suggesting the clicks could be a way to call in reinforcements.
‘Really, really exciting’
Audrey Looby, a doctoral candidate and marine community ecologist at the University of Florida, recently published a scientific review of noise-making in fish. She sifted through more than 800 references dating back to 1874 and found very few references to elasmobranchs, the group that includes sharks, rays, and skates.
“So seeing a study come out like this, where there’s video and a comprehensive description of behaviors associated with those sounds, it’s just really, really exciting,” Looby says.
As to how this ability has gone overlooked for so long, Looby says it could be explained by any of several factors. For instance, perhaps stingrays make sounds occasionally, or only certain species can do it, or the fish are more likely to produce noise at a specific time or season. (Read fascinating facts about stingrays.)
“They can also be quite difficult to study because they are often highly mobile and elusive,” says Looby.
Because many species of stingray are threatened with extinction, Fetterplace offers a word of caution. While he and his co-authors hope their research will uncover more examples of sound-producing stingrays, “we don’t want the public to go out and get really close to a ray just to get this sort of noise.”
“That’s not good for the ray,” he says, “and it’s potentially dangerous.”