How would you like to hop in the water with a giant sea creature that can grow almost 25 feet across and weigh up to two tons? For marine biologist and National Geographic grantee Joshua Stewart, it’s all in a day’s work. He has a soft spot for giant oceanic manta rays and is fighting to protect these gentle giants.
“They look like giant B-52 stealth bombers cruising in over the reef. They’re one of the most inquisitive, gentle and curious animals that I’ve ever spent time with,” says Stewart, who went with a team to the remote Revillagigedo Islands, 300 miles off the coast of Mexico, to attach Crittercams to giant mantas for the very first time. “The mantas swim right over your head, as if you’re wearing them like a sombrero. They’ll play in your bubbles, they make eye contact—it really feels like you’re having a personal interaction with them.”
But Stewart didn’t travel 30 hours by boat to hang out with giant mantas just because of their charming personalities. The Crittercams, which attach with noninvasive suction cups and stay on the mantas for up to six hours, allow Stewart to witness the hidden lives of these majestic creatures. For biologists, learning about the behavior of any animal is exciting in and of itself, but knowing where mantas go and what they do is also helping scientists protect mantas from a grizzly fate.
“Over the last 10 to 15 years, there’s been an increase in demand for manta ray gill plates, which are the cartilaginous structures that allow mantas to filter out zooplankton. That demand for gill plates has led to, as far as we can tell, ongoing population declines,” Stewart says. “The demand is coming almost exclusively from China and Southeast Asia, and the gill plates are used as a pseudo-remedy cure-all for everything from bronchitis to acne—you name it. It’s not a traditional remedy; this is a new development. It’s not in the ancient texts, which have a lot of cultural importance.”
Mantas also often end up as bycatch due to commercial fishing, so Stewart hopes the Crittercam data can help researchers develop strategies to limit both bycatch and targeted fishing of manta rays. “This is what makes the oceans wild, having these kind of amazing animals,” Stewart says. “But if you’re not already convinced that we need to save mantas because of their beauty, grace, and charisma, which I hope you are, then there’s definitely the economic argument to be made as well. The value of manta rays in fisheries is minimal, a few million dollars a year, whereas the value of manta rays to dive and snorkeling tourism is hundreds of millions of dollars every year. The short end of that is that mantas are just worth more alive.”
So far, the Crittercams have returned some surprising data. While most big animals living in open ocean environments tend to migrate a fair amount, it seems like giant manta rays are actually homebodies. Stewart thinks the mantas are hanging out where they’re most likely to find their number one meal: zooplankton. “We’re hypothesizing that mantas might be shifting their movements vertically instead of horizontally to find food,” he says. The mantas preference to stay put might be a big benefit for their conservation, since protection strategies could be effectively implemented locally, rather than coordinating at an international level among many different countries with different interests.
Learning about giant manta rays has long been cost-prohibitive, due both to manta rays’ remote habitats and expensive research technology, but thanks to developments like Crittercam, we’re able to see more and more into the lives of these fascinating ocean giants and other marine life. “Here’s this megafauna, this beautiful animal that we know so little about,” Stewart says. “And there are so many opportunities to break ground and learn about what’s happening, learn about their ecology, learn about their biology. For a biologist, it’s exciting to find something new that you can explore.”
Stewart is an associate director of the Manta Trust, a member of the Gulf of California Marine Program, and a grantee of the National Geographic Society/Waitt Grants program. Learn more about the science and exploration supported by the nonprofit National Geographic Society at natgeo.org/grants, and see more amazing explorer moments in the rest of the Expedition Raw series.
Video Producer/Editor: Nora Rappaport
Series Producer: Chris Mattle
Crittercam footage: Kyler Abernathy and Greg Marshall