He’s almost close enough to touch as he follows her, flapping gently through the water. Suddenly, she darts away, soaring into a barrel roll. Dutifully, he follows, the sun dazzling as he turns his belly to the surface. But he’s no longer in the lead. Two other males are now in front, jostling to show their prowess.

This underwater ballet is among hours of new footage captured by Crittercams—cameras with depth and temperature sensors attached to manta rays with a surprising adhesive: peanut butter. The devices allow scientists to learn what these elusive animals do when humans aren’t around.

The study documents the deepest recorded manta courtship train—when males follow a female in an elaborate, synchronized chase trying to show their suitability as a mate.

Cameras were attached to 26 manta rays—16 reef mantas (Mobula alfredi) in the Maldives and 10 oceanic mantas (Mobula birostris) in Mexico—and showed four reef mantas in the Maldives’ Raa Atoll in a courtship between 83 and 219 feet deep.

To get the data, Nicole Pelletier, project leader at the Manta Trust, analyzed about 40 hours of footage, twice as long as all the Harry Potter movies combined. Her “labor of love” involved meticulously examining each video in detail, regularly stopping, starting, and rewatching sections to annotate each frame.

Deepest recorded manta train 

The study also recorded new deep-sea behaviors including manta rays hugging the bottom of the seabed—perhaps to reduce predation risk, improve hydrodynamics, or navigate using the Earth’s magnetic field. But the most spectacular footage “by far,” Pelletier says, is seeing courtship “from the animals’ perspective.”

Michelle Carpenter, a marine biologist at the University of Cape Town who was not involved in the study, says this “astonishing” discovery highlights the importance of technology in “unraveling more mysteries surrounding these incredibly intelligent, complex creatures.”

While previous studies have given important insights into the rays’ behavior, satellite and acoustic tags—which collect data and transmit them to overhead satellites, or listening stations or hydrophones in the water, respectively—tend to be very expensive, while in-water observations are restricted to recreational scuba diving limits (130 feet).

Crittercams add “a whole new level” to what we can learn, she says, because they “can go to places researchers and citizen scientists can’t.” Now we can see why these rays might be visiting certain areas.

“Until we actually have a video, we have no idea what’s happening” says Pelletizer. The new footage shows that rays barrel rolling in deep waters—which could be interpreted as feeding at this depth—can also indicate courtship.

Cams stuck to critters

Animal-borne cameras, called Crittercams, were invented by marine biologist Greg Marshall in 1986. While diving, he saw a shark with a remora—a fish which uses suction to hitchhike on larger species—attached to its body, and he had an idea.

If he could reconfigure his camera to “look and feel like that remora,” it might provide a way of unobtrusively filming underwater species. He didn’t want to use a “messy harness” or a tag penetrating into the animal’s skin.

Six months later, he’d developed his first prototype. Since then, Crittercams have made countless discoveries about the lives of sharks, whales, seals, and other animals.

Adapting the devices for manta rays proved difficult, however. “We had quite a bit of failure,” recalls Marshall.

The longer you film, the more chance of capturing unique, natural behavior, so Marshall and his colleagues needed the cameras to stick for several hours at a time. But the suction cups wouldn’t stick to the rays’ mucus-covered dermal denticles—tooth-like scales that cover the bodies of sharks and rays.

Eventually they found a powerful enough sealant in a surprising place: peanut butter. This was their most effective method in Mexico, but in the Maldives, the suction cups kept sliding off. This may have been because reef mantas have smaller dermal denticles and so there was less friction to keep the cups in place. Instead, they attached the device to the mantas’ jaw with a small dissolvable wire and plastic hook that would eventually pop off so the camera could be retrieved.

Most rays “weren’t that bothered” by the cameras Pelletier says, but three individuals breached—jumping clear of the water—potentially an attempt to dislodge the device, like an irritating remora.

Challenges and camera malfunctions are to be expected, she says. “You’re using pretty new technology at some serious depths in interesting conditions with giant animals, so you can’t expect everything to be perfect.”

Capturing a new world

Further studies analyzing even more videos—ideally using 360 cameras—will be “massively important” for research. “I have no idea if this manta had 12 others following behind it,” Pelletier says, so there may have been even more social behaviors just out of sight.

The relatively small sample size doesn’t take away from the findings, she says, because the footage “tells a story of what the cameras can record.” Another application of Crittercams could be to see if divers properly follow Codes of Conduct during encounters, Pelletier adds, especially in heavily touristed areas like Mexico where the manta rays filmed lots of divers in the videos, she says.

Understanding that deep waters are likely much more important than we realize for crucial behaviors like courtship highlights the need to protect them alongside shallow water habitats. Activities such as dredging and trawling could impact the animals that live in these areas by changing the contours of the seabed, water currents, and how food accumulates.

Carpenter hopes this sneak peek into the lives of these “charismatic, smart, and complex creatures” will also help the species get the attention they deserve. “Most people are much more aware of sea turtles, dolphins, and whales because of the amount of research on their social behavior, complexity and how smart they are,” she says. “Manta rays are quickly gaining that.”

She’s excited for what secrets they might unveil next, wondering if we might finally witness something marine biologists have long sought: a manta ray giving birth.

Whatever they discover, Marshall still feels privileged when his devices capture a new glimpse of animals living out their full lives when humans aren’t around. “35 years later and I’m like a kid about it,” he says. “I still feel that sense of wonder and awe and inspiration.”