The Milky Way is blazing in the moonless sky as our inflatable bounds across the chop of Ari Atoll’s remote lagoon, the lights aboard M/V Four Seasons Explorer slipping away behind us.

For three days we’d cruised south through the Maldives aboard Explorer, the resort chain’s luxury liveaboard that each September hosts expeditions of the Manta Trust research and conservation organization. Although the diving had often been spectacular, mantas had proved elusive, and my best look had been on our first dive, when a lone manta glided around our group before disappearing over the reef.

Now, as our pilot edges us up to the anchored dhoni, the traditional Maldivian wooden boat that will be our dive platform, we can see a procession of immense ghostly shapes rise to the surface, spin gracefully and spiral down again. A crew member meets us at the rail with an ear-to-ear grin: “We have mantas!”

The Manta Trust now operates in 16 regions around the world, with a mission to conserve mantas through research, awareness and education. Its staff and volunteers have identified, cataloged and tracked thousands of individual reef (Manta alfredi) and oceanic (M. birostris) mantas from the Maldives to Mexico, studied their migration, behavior and mating, and documented their economic value for tourism and the threats to their survival. Both species are listed as vulnerable by the International Union for Conservation of Nature.

The Trust’s liveaboard expeditions provide an opportunity to dive with mantas and other megafauna alongside an expert — in our case, marine biologist Guy Stevens, the Trust’s chief executive and co-founder.

The Maldives location is particularly fitting because, although the Trust has a growing global presence, the Maldives and Four Seasons Explorer claim a special role in the organization’s creation.

In 2003, a year after graduating from Plymouth University with a marine biology degree, Stevens was looking for a job when he found a posting for a marine biologist at the Four Seasons Kuda Huraa resort in North Male Atoll.

“What did I know about the Maldives?” Stevens says. “Nothing, really, except that it was in the tropics and I thought it would be a really cool place to be. Once I got here, I fell in love with it.”

The job combined the duties of divemaster with answering guests’ questions about the creatures they encountered. But in his first encounters with the Maldives reef mantas, Stevens was struck by their grace and beauty, their apparent intellect and their distinct personalities.

Stevens had as many questions as the tourists: How many mantas exactly were there? Where do they go when they disappear? How long do they live? Are they as intelligent as they seem?

After one of those dives with mantas, he said to a co-worker on Explorer: “These mantas are just incredible. What do you know about them?”

“She told me, ‘Nobody knows anything about them.’ And I said, ‘Wouldn’t it be amazing to start a research project about mantas?’”

MANTA FINGERPRINTS

In 2005, Stevens founded the Maldivian Manta Ray Project as a way to support the conservation of mantas in Baa and North Male atolls by learning about their life cycle and habitat. The effort spread first through the Maldives, then went global in 2011, when he founded the Manta Trust with marine biologist and nature photographer Thomas Peschak.

Read about the Manta's Trust's work to end the manta gill-raker trade.

In the 10 years since the MMRP began, the project has documented and cataloged more manta encounters than anywhere else in the world — 35,000-plus total sightings, with more than 3,850 individual mantas identified, named or numbered and recorded in the project’s database — more than half the 5,000 to 6,000 estimated population.

The key to assembling that huge amount of information with limited resources was using what Stevens calls a “citizen science” model — essentially underwater crowdsourcing.

A manta can be identified by the unique markings each has on its underside. The Trust’s IDtheManta Initiative allows divers to upload to the Trust’s website photos and details of sightings, which are used to identify new or familiar mantas, with the aim of using biometric recognition software to eventually create fully automated identifications.

In the Maldives, many mantas have now been sighted numerous times (Stevens can recognize an astonishing number of them on sight), and the data about the times and locations of their encounters have begun to help researchers piece together the mysteries of their lives and their travels.

The research shows that, although they were previously believed to stay within a relatively small territory (unlike their larger cousin, the oceanic manta), reef mantas covered surprisingly long distances. One-fifth of the recorded Maldives mantas have been sighted in multiple atolls of the sprawling archipelago, and in 2013, the project documented the movement by a juvenile female named Ewok from Baa Atoll in the north to the southernmost atoll — a journey of more than 400 miles.

LEFT-HANDED MANTAS

Although much about mantas’ lives remains a mystery, years of observation have allowed researchers to witness the elaborate courtship rituals of the Maldives’ reef mantas, in which as many as 25 males compete to mate with a single female. The winner eventually seizes in its mouth the end of the female’s winglike pectoral fin to hold them together while mating.

That explains what causes the scars common on the tips of mature females’ wings: the rows of small, cusplike teeth in the male’s bottom jaw. But it poses another question: Why are more than 95 percent of female mantas’ mating scars, everywhere in the world, on the left fin?

The females give birth to a single pup (rarely two) after a gestation of 12 to 13 months. Female mantas in the Maldives don’t reach sexual maturity until they’re at least 10 years old — perhaps even 15, Stevens says — and repeated observations of mature females suggest they average only one pregnancy every five or six years. Evidence of such a slow reproduction rate lends urgency to conservation efforts.

“After a decade of research, there’s a lot that we’re really just now starting to figure out,” Stevens says. “But one thing we do know is there’s no such thing as a sustainable fishery for mantas.”

BAD MEDICINE

Mantas probably only still exist by a stroke of luck — they simply don’t taste very good.

But despite growing support for their protection through the efforts of groups like Manta Trust, including the 2013 listing of mantas in the Convention on International Trade in Endangered Species, they’re now threatened by the trade in their gill rakers. The cartilage filaments that strain plankton from their gills, rakers are sold as a dubious medical cure in Chinese markets.

The Trust’s members have traveled to the markets to document the sales and helped create a field guide to identify the various species of manta and mobulid rays by their gill rakers. They’ve also questioned the purchasers of the medical concoctions.

“What we found was that the buyers of these gill raker medicines don’t know about the threat posed to manta populations by the practice, and when they learned about it, they didn’t want it to happen,” Stevens says.

Building awareness — and assembling hard facts to back up the argument for conservation — is the key to success, Stevens says.

Asking coastal communities in cultures without a strong environmental heritage to protect mantas just because they should is a lost cause, Stevens says. But show them that a manta that is worth a few hundred dollars for its gill rakers has a tourism value of $1 million over its lifetime and they’ll protect it because its future is theirs.

JAVIER, BUBBLES AND SQUIRT

Our afternoon dive had been on a reef with water like bottomless blue crystal, but now the night ocean is like soup, thick and green, alive with swarms of plankton drawn by the lights. We kneel on the bottom as the mantas barrel through in a train with their mouths agape, inches from our masks, twirling and spinning, nearly colliding.

An hour later we surface and gather at the stern rail to watch the mantas. As they roll their bellies to the surface, Stevens picks out the familiars.

“That’s Javier,” he says. “See the four spots between his gills? His dorsal surface is also quite dark.”

Still a juvenile, Javier has been a reliable regular at night feedings in the lagoon. But nothing’s certain.

In Stevens’ early years here, a favorite was a female named Bubbles who was often at North Male Atoll. “She was very friendly, and she would hover a few inches over your head and use your bubbles to back-flush her gills,” he says. But she disappeared with the others that frequented the site.

A small, friendly female named Squirt was first recorded in Baa Atoll in 2006 and was the project’s most sighted manta. But she didn’t return in 2015.

What’s become of them? Stevens shrugs.

“There’s no way of knowing,” he says. “It could be something’s happened to them, but not necessarily. With mantas, you just don’t know.”

Where can you dive with mantas and sharks? Read our story Wings and Fins: 12 Places to Dive with Mantas and Sharks.

MORE THAN JUST MANTAS

Although mantas were the focus of our expedition, the stunning diversity of marine life means you never know what you’ll encounter in the Maldives. That lesson struck home on the last day of the cruise, when we were searching for whale sharks off the southern end of Ari Atoll. The whale sharks come to the sunlit surface waters to warm and rest after diving deep in the cold water offshore to feed. But in two hours of motoring offshore we’d seen no signs of them. Finally giving up, the boat had turned for home when there was a shout from the bow: “Blue whale!” Blue whales are the largest animals on Earth — their tongues alone can weigh as much as an elephant. For an hour, we trailed along behind it until, with a whoof, it blew for the last time, curled its back and lifted its immense fluke from the water as it dived deep.

How You Can Help

You can donate to conservation organizations, such as the Manta Trust and Manta Ray of Hope. But the best way for divers to support manta conservation is to dive with mantas. Demonstrating the long-term economic value of manta tourism has become a powerful incentive for their conservation around the world. However, rapid tourism development poses its own hazards for mantas through uncontrolled tourist interactions or by the environmental pressures of increased tourism development on their fragile habitats. The Manta Trust has created codes of conduct for operators and tourists to minimize impacts on mantas. In addition to the Maldives trips, the Trust also organizes expeditions to other manta hot spots, including Mexico, Raja Ampat and Yap.

Divers Guide to the Maldives

Average water temp: Low to mid-80s

What to wear: 3 mm wetsuit

Average viz: In the 100-foot range, but seasonal plankton blooms can lower viz

When to go: Year-round

For more info go to sportdiver.com/maldives

Four Seasons Explorer

All-inclusive seven-day expeditions (with the option of shorter three- and four-night cruises possible) aboard this luxury yacht immerse participants in every aspect of the Manta Trust’s research efforts. The 129-foot yacht can carry a total of 22 passengers in 11 cabins.

Get There: Qatar Airlines (qatarairways.com) offers flights from several U.S. gateways, including New York, Atlanta and Los Angeles.

DON’T-MISS DIVES

Hanifaru Bay, Baa Atoll

A cul-de-sac bay the size of a football field traps swarms of plankton from upwelling currents, drawing as many as 200 mantas in a day. The iconic site is protected by strictly enforced limits to boats and tourists, and is snorkel-only.

Muthafushi Thila, Baa Atoll

This thila, or coral pinnacle, is home to huge schools of snapper and triggerfish. Laced with crannies and overhangs, it’s topped with beds of vibrant anemones.

Rasdhoo Madivaru, Ross Atoll

Drop to the ridge at 60 feet on the flood tide and watch as sharks, dogtooth tuna, jacks, eagle rays and everything large and small gather to feed.

Fesdhu, Ari Atoll

A remote lagoon offers a protected spot ideal for night dives with reef mantas.