The sky is a glossy midsummer blue as the motorboat rounds Omaha Spit and heads out into the shimmering waters of the Hauraki Gulf. We skim northeast into the slight swell, circling the forested bulk of Te Hauturu-o-Toi/Little Barrier Island, with its plunging valleys and bright cliffs, and a lone cloud thatching its heights. Our destination—the triangle between Hauturu, Aotea/Great Barrier Island and the Mokohinau Islands—is New Zealand’s manta ray hotspot.
Our boat is bright red, emblazoned with stylised manta rays, and belongs to Mark Erdmann, a 50-something marine biologist from Conservation International with an American drawl and a single crystal earring. The animal we’re looking for is as wide as the boat is long—6.3 metres—and is part of the pantheon of New Zealand marine megafauna, along with whales and dolphins and great white sharks. But few people know that oceanic manta rays are even here.
Until recently, little scientific or government attention was paid to the species. In 2010, Department of Conservation (DOC) marine scientist Clinton Duffy published a paper proving that oceanic manta rays frequent New Zealand waters, at least in the summer months, and in 2011, manta rays were protected under the Wildlife Act. But they’ve never been comprehensively studied. “There are lots and lots of unanswered questions,” Erdmann says.
Like, do manta rays live here year-round? If they don’t, where do they go? How many are there? Do they give birth here? Are there nurseries for baby manta rays somewhere off Northland? How deep do they dive, and why? How do they use these waters? Where do they go to get their parasites cleaned off by other fish? Researchers are only just starting to uncover the answers.
Originally a mantis shrimp specialist, Erdmann spent more than two decades living in Indonesia, where he logged more than 12,000 dives and recorded more than 200 new-to-science species of reef fish, corals and crustaceans. Ten years ago, he got roped into studying manta rays in Raja Ampat, in West Papua. Underwater, the animals would sometimes stay with him for an hour or more, the adults moving like graceful Balinese dancers, the newborns like floppy, curious puppies. “It didn’t take more than about a month and a half of spending serious time with mantas to absolutely fall in love,” Erdmann says. “They became my favourite animal of all.”
They’re among the smartest fish in existence, Erdmann tells me from the wheel, gunning for the hotspot before the tide turns. Manta rays have huge brains, he says, even relative to their body size. Recent research suggests they communicate with each other using their cephalic fins—the flat lobes around their mouth. They form long-term friendships, and may even be able to recognise themselves in a mirror: a form of self-awareness seen in only a few animals, such as dolphins and apes.
You can see that intelligence in their eyes when you dive with them, adds Edy Setyawan, who is hanging on beside me, wearing dark wraparound glasses and a backwards cap. An Indonesian PhD student at the University of Auckland, Setyawan has spent his research career diving with manta rays in West Papua and elsewhere. “You can actually see them observing you, trying to scan you, thinking, ‘What is this fish?’”
The same question could be turned on the manta rays themselves. Erdmann and Setyawan aim to fill in some of the manta ray unknowns using a combination of smart technology, swashbuckling snorkelling and a whole lot of staring at the sea.
“MANTA!” yells New Zealand Geographic photographer Richard Robinson from the bow mid-morning, and Erdmann swings the boat around. There’s a fin slicing the water, a brown shape. It’s a hammerhead shark.
At lunchtime, we jump into a school of trevally at Simpson’s Rock—the fish elude Erdmann’s attempts to spear one for dinner—but see no mantas.
In the early afternoon, we edge up to a yacht with a red sail and a herb garden hanging off the stern, and Lydia Green leaps aboard our boat with her salty blonde hair flying behind her cap. In 2017, British-born Green set up Manta Watch New Zealand, a non-profit dedicated to researching and protecting the animals, as well as recruiting the public as citizen scientists to report sightings and identify individual manta rays.
Manta Watch encourages people to take photos and videos of mantas, and record the time and coordinates of each encounter. It’s early January, and Green has been receiving five or six manta ray sightings every day between East Cape and Northland.
“I just want to make everyone stoked on the ocean,” Green says. “And people are! You tell them that we have mantas in Aotearoa and their eyes widen and their jaws drop.”
Māori have lived around these waters for centuries, and have always known the manta rays were here. The ancestors of Ngāti Rehua and Ngāti Manuhiri frequently criss-crossed the seaways between Aotea, Te Hauturu-o-Toi, the Mokohinau Islands and the mainland in their waka, and later in sailing boats. They call the mantas whai rahi.
Like all the other crucial elements of the ecosystem—the whales, the seaweed, the hāpuku and the plankton—whai rahi are the mauri of the ocean, the life-force of the Hauraki Gulf, Ngāti Manuhiri chief executive Nicola MacDonald tells me. Whai rahi have special significance for the seafaring hapū of this area, featuring in the maramataka (lunar calendar), many pūrākau (legends) and even in Ngāti Manuhiri’s contemporary logo.
MacDonald, who is also a descendant of Ngāti Rehua, tells me a Ngāti Rehua pūrākau about two brothers: Te Whai Rahi, the manta ray, and Te Whai Repo, the eagle ray. Te Whai Rahi, the elder, was born in the pure waters of the Kaitoke wetland, on Aotea’s east coast—waters so clear and pure they gave him his superlative wingspan. The tōhunga at Kaitoke asked the brothers to look after the ocean and all Tangaroa’s children. Te Whai Repo went north, to Motukōkako in the Bay of Islands (also known as the Hole in the Rock). Te Whai Rahi stayed in the south, to take care of the waters in what is now the Hauraki Gulf.
“Te Whai Rahi is like a sentinel,” MacDonald says. And he has lessons for humans, who are also entrusted with being kaitiaki for the oceans. “You have to have great stamina and fortitude to navigate huge ocean spaces.”
Huge ocean spaces like the one we’re in now, looking for a manta ray. Studying the animal requires stamina and fortitude, too. We climb onto the roof of the little red boat as it traces a white wake back towards the Mokohinau Islands. We gaze at the sea. For hours.
By late afternoon, the horizon is a hard line between the cobalt sea and the pale sky. It becomes hypnotic—the motor, the sloshing ocean, the fairy prions and shearwaters dipping and fluttering, the tiny storm petrels bouncing off the waves with legs askew.
I feel I’m in a sort of trance, staring out at the blue.
“You’ve got to look at everything, and nothing,” advises Robinson.
I’m supposed to trust my instincts to alert me to a change in the pattern. But there’s just so much ocean that even a six-metre-wide manta ray is a tiny black needle in a big blue haystack.
Part of the difficulty is that mantas spend only a small proportion of the day feeding at the surface, Green says. If they’re even one metre below, you won’t see them.
“They’re everywhere,” she says, “and nowhere.”
The sea is a satin sheet beneath the cloudy sky. The water looks molten, and Hauturu is a slate-grey silhouette on the horizon. A raft of blue penguins bob next to the boat, then dive in unison.
“I like this, Edy,” says Erdmann. “It’s looking good. We’re gonna find some if it stays like this.”
With the sea this glassy, any manta that comes to the surface should be clearly visible. Robinson is eagerly scanning the horizon. He’s convinced today is going to be Manta Monday.
In a normal year, Erdmann spends months overseas—often in Raja Ampat, but all over the world, too—conducting research, supervising students and wooing donors. The pandemic paused all that, so he bought the red boat and dedicated his summers to the manta ray project. Any day the conditions are right, he assembles a crew and heads out into the gulf.
Every sighting and every satellite tag adds to what we know about Aotearoa’s manta rays. Their DOC conservation status is “data deficient”, because we still know so little about them, but according to Erdmann, our manta ray population is probably in good shape. “This might be one of the few oceanic manta populations in the world which isn’t getting hammered, so that makes it even more important for us to have a close look at it.”
Globally, oceanic manta rays are in trouble, and were recently categorised as “endangered” on the International Union for Conservation of Nature’s Red List. Their populations can be quickly and permanently decimated by fishing, as they don’t start reproducing until they are 15 years old, gestation takes more than a year, and they usually have only one baby at a time. What’s more, scientists don’t yet know how often they breed.
“Any form of exploitation, populations just can’t cope with it,” says Green.
Mantas are targeted in many countries by fishers hoping to sell their gill rakers—the thin cartilage filaments they use to filter plankton out of the water—for use in traditional medicine.
They can also become entangled in set nets or fall victim to ghost-fishing, killed by the discarded nets that now haunt the world’s oceans.
“Manta rays can’t swim backwards,” says Green. They’re designed to travel forward, mouth first—they can’t reverse their way out of a net.”
Bycatch in commercial fisheries isn’t a problem in New Zealand waters like it is on the high seas worldwide, but manta rays observed here sometimes have fishing-line scars. One seen off the Poor Knights Islands had a game-fishing hook and lure attached to its head, fetchingly encrusted with barnacles. And in 2019, Green was called to the Far North to inspect a dead manta ray washed up on Rarawa Beach. It may have been struck by a boat. “I have had reports of people just bashing into them because they’re so hard to see.”
In New Zealand, hunting manta rays is illegal. Any caught accidentally must be released alive and unharmed—a rule that mirrors traditional Māori practices. Whai, the general term for all rays, are not considered kai, says MacDonald. Her father and grandparents, who were all fishers, taught her that any whai caught alive must be immediately released. But one Ngāti Manuhiri kaumātua, Ringi Brown, told her of another tradition: if a whai is accidentally caught and does not survive, it should be cooked and eaten—a way of showing more respect for its mana than throwing it overboard as though it were a piece of rubbish.
Erdmann tagged his first two New Zealand mantas in 2019, on an expedition with Clinton Duffy off Whangaroa, supported by the Auckland-based Tindale Marine Research Charitable Trust. At the time, Erdmann was hoping to prove that we had our own population of manta rays. Evidence from Indonesia, Sri Lanka and Mexico indicated that, though oceanic mantas could migrate long distances, they mostly stayed close to home. Erdmann aimed to convince DOC that mantas were local—and therefore worthy of more conservation funding than is typically given to a migrating species. What he discovered surprised him.
One tag popped off after a week. But the other stayed stuck to its ray, a 3.6-metre female dubbed Emmy. She tracked north, then travelled 1982 kilometres to Fiji—much further than oceanic manta rays had ever been recorded migrating. Conveniently, she went to the Lau Islands, where Erdmann’s employer, Conservation International, has an office. The tag popped off Emmy’s back, and Erdmann’s colleagues went straight to the lagoon it was floating in and picked it up.
This kind of satellite tag transmits limited information while it’s attached to the manta, and only when the animal happens to be resting at the surface on a calm day. When the tag falls off (as it’s supposed to after four to six months, or if the manta dislodges it), it floats on the surface and sends data summaries until its battery runs out. Most of the time, Erdmann never sees the tag again. But if he can recover one “it’s a goldmine”, he says. It carries the full record, in real time, of everything the animal did.The tag revealed that Emmy had dived deeper than oceanic manta rays were known to go, reaching 1248 metres below the surface. She stayed down for less than a minute, then swam back up again. Other mantas have since been recorded diving even deeper, but researchers still have no idea why. Are they cooling down? Scratching their bellies on the bottom to remove parasites? They’re down there too briefly to be feeding. The leading theory is that they dive for navigation: it may be easier to detect the Earth’s magnetic field in the depths, and the mantas could be checking that they are heading in the right direction.
In early 2021, Erdmann and Setyawan managed to tag five more manta rays in the Hauraki Gulf. One spent a month cruising around in the hotspot, and two others headed north towards Fiji and Tonga before the tags ran out of battery or fell off. This doesn’t mean the entire population is migrating—it’s possible that some individuals live here all year round, while others head to the tropics.
Mantas are almost certainly mating here. Male and female pairs have been observed courting, and last summer, the team photographed a female with fresh mating scars on her left wing. Manta mating is “not super romantic”, says Green. “But it’s over quickly.”
One day at the end of summer in 2021, Erdmann’s team encountered seven heavily pregnant females together. Manta mothers develop a pronounced baby bump, Erdmann explains. “By the time they have a 1.8-metre animal folded up inside of them, you can absolutely see it. At that time, it’s the easiest you’ll ever approach one because they just couldn’t give a damn. Like, ‘Oh, faaaark, when is this going to come out?’” Seeing the expectant mantas together as a group suggested to Erdmann that mothers may actually be giving birth somewhere in our waters. “There’s no way those moms were going to swim all the way to Fiji.”
There must also be cleaning stations scattered around the coastline. In Indonesia, Setyawan and other scientists have mapped the places oceanic mantas go to be cleaned by small fish, and have a good idea of the animals’ preferred times of day and tides. That predictability makes it much easier for scientists—and tourists—to see the animals. Oceanic manta rays don’t require quite as much pampering as their tropical cousins, but they’re still prone to hangers-on. “They get a lot of ectoparasites because they have so much surface area. They’re a big dinner plate, basically,” says Erdmann.
It’s just a matter of learning the animals’ patterns.
“We keep feeling like we’re getting closer and closer to cracking the code,” he says. “It’s like it’s always just out of reach.”
As the day progresses, there are a few false alarms. Dark shapes jumping and splashing turn out to be bottlenose dolphins. Shearwaters flutter en masse over a school of kingfish. Gannets are sitting on the water like decoys, waiting for something to happen.
Green sends word of a recent manta sighting to the south of Hauturu. We hoon around the island and find a Bryde’s whale there instead.
Out here, the water temperature is 24.9 degrees Celsius—abnormally warm for the gulf in January. A marine heatwave is turning sea-temperature maps bright red. Could that be a problem for the manta rays?
“It will not affect them in terms of their metabolism. They’re totally happy with that temperature,” says Erdmann. “What I’m not sure about is what it’s going to mean for the krill.” New Zealand’s dense swarms of red krill—small shrimp-like crustaceans—are such a rich food source the mantas travel all the way here from the tropics to eat it. “Otherwise they would just stay in Fiji.”
If the krill move further south to avoid the warm waters, the mantas will probably follow them. If krill populations diminish or disappear, that’s a problem.
Back in the hotspot, we keep looking. Often, the team has found mantas feeding at the surface on days like today, when the tide turns and falls in the afternoon. Erdmann explains his theory: this part of the gulf forms a kind of basin, and the falling tide brings a flush of warm water in from the north. In the late afternoon, krill are making their way up to the surface, where they’ll spend the night. “We think that combination of the warm water flooding in and the krill coming up to the surface triggers the massive feeding response.”
The conditions are perfect: a falling tide, warm water, a glassy sea. But no mantas. Finally, just as we’re heading home, Erdmann is sure he sees a manta wingtip break the surface. By the time Setyawan gets a drone in the air to observe it, the manta has disappeared.
On Wednesday, we’re at it all over again. Setyawan is busy, so Erdmann’s Sāmoan-Dutch Conservation International colleague Schannel van Dijken has joined us instead to help drive the boat. (Van Dijken is a National Geographic Explorer and Polynesian voyager who reckons he was the first person to give a seahorse a tattoo—he was tagging it for his master’s research.)
Robinson is optimistic, as usual: “It’s everything we ask for in a day, Mark.”
The ocean is a dark, limpid silver. The tide will turn mid-afternoon. Long ocean swells—the beginnings of distant Cyclone Cody—occasionally lift the boat to a better vantage point. But for most of the day, we see nothing but gannets flying in formation, seabirds, the scattered islands and the mercury sea.
Finally, at four-thirty in the afternoon, it happens. We’re heading south towards Hauturu when Robinson spots a triangular wake heading our way. A black wingtip slides out of the water, like a shark’s fin—but this time, it’s a manta. It cruises slowly towards the boat as Erdmann swears at the drone. At last, he launches the device. Its insect whine fades as it zooms upwards.
By now, I’ve lost sight of the manta ray. Erdmann bends over the drone’s control screen, shielding it from the sun with his body. “I’m on it!” he shouts. There it is on the screen: an unmistakable silhouette against the bright blue water, a bird’s-eye view of a black manta ray with its horn-like cephalic fins outstretched and white chevrons curling over its shoulders.
Erdmann gives the controls to Robinson, who manoeuvres the drone to follow the manta as it gently flaps across the screen, while Erdmann pulls on a wetsuit, mask, snorkel and long flippers.
Van Dijken hands him his speargun, loaded with a satellite tag, and an underwater scooter—a handheld battery-powered motor. Then Van Dijken drives the boat in a wide arc, hoping to position it ahead of the manta without spooking it. Erdmann slides into the water and speeds off.
The scooter and the drone make this entire project possible. The scooter gives the snorkeller a chance of catching up with the effortlessly fast manta, while the drone allows someone else to keep the manta in their sights. The person in the water might not be able to see the ray until they’re a few metres away, but they can swim towards the drone, knowing it’s positioned directly above the animal.
As I watch the screen over Robinson’s shoulder, willing Erdmann to swim into view, there’s a flash of white. The manta turns a backwards somersault with its mouth wide open, its pale belly flashing the sky.
A barrel roll is a sign that it’s feeding—and it’s also incredibly helpful for identifying individual animals.
Setyawan told me earlier that each manta ray has a unique pattern on its underside, and the sex is visible as well, meaning the researchers can use the drone images to compile a database of IDs. That should allow the team to track what happens to individuals over time: how fast they grow, where they go, if they get injured. “It’s like they’re saying, ‘Here, take photos of my belly and you’ll see who I am,’” said Setyawan.
Erdmann and the ray are now so close we can see them from the boat. But even with the scooter, the fish is too fast for him to tag it. (An animal needs to have a bit of curiosity, he says, for him to get close enough, and some are more skittish than others.)
Over the next few hours, in the same area, we find and follow two more manta rays, including a pregnant female.
When we’re watching on the tiny drone screen or glimpsing a distant wingtip, it’s hard to get a sense of just how big these animals are. But at last, a ray comes so close to the boat that I throw on my mask and snorkel and leap over the side.
In one electrifying moment, she’s right there, coming straight towards me, cephalic fins waving, huge in the blue gloom—but then she turns, and with a laconic flick of her wings she’s gone.
Scooterless and barefoot, I’ve no hope of following her.