Richard Robinson

The special case of our smallest dolphins

Hector’s and Māui dolphins are dying in nets—but their biggest foe might be a virus carried by cats. Can transformative tech cut through the tangle and save the creatures at the heart of it?

Written by       Photographed by Richard Robinson

A Hector’s dolphin killed by a fishing net is laid to rest near Karitāne, on the North Otago coast. It’s not the first Hector’s dolphin the Kāti Huirapa rūnanga have had to bury in these dunes. A 2019 report estimated, based on modelling, that 58 of these dolphins are killed in commercial fishing nets each year.

The waka paddles slice placid water, a dozen of us pulling in unison, ferrying a body across the Waikouaiti awa to her final resting place. We beach the vessel on Ōhinepouwera, the sandspit opposite Karitāne, where hundreds of whales were butchered back when Johnny Jones ran his empire of blubber and bone. Now, it’s a place of peace, the waves patiently cleaning the sand of its grisly past.

It’s earthquake weather, the nor’west sculpting spaceships in the sky.

The kaikaraka’s wailing cry leads us up the dunes, the deceased dolphin in the place of honour, at the front. She’s gently lowered into a hole, wrapped in a korowai of rimurimu, a kelp cloak. Children add seashells to the offering.

To the strains of ‘Te Aroha’, spadefuls of sand cover the dolphin and she begins her long rest.

This Hector’s dolphin died a bit more than four nautical miles from here, just beyond the invisible line in the sea that might have saved her.

Their playfulness makes them popular with surfers at Porpoise Bay, where Nick Smart runs a small surf shop.

According to fishing rules designed to protect her, she shouldn’t have been there. And yet she was, hunting fish on the continental shelf. In the murk, her finely tuned echolocation failed to detect the net that snared her. With her small lungs working hard and screaming for air, she could only remain underwater for a short time—her struggle would have been brief.

As per legal requirement, the dolphin’s body was brought to shore and delivered to the Ministry of Fisheries office in Dunedin. They arranged for her transport to Palmerston North. There, she was held in cold storage before being dissected under necropsy, cleaned and prepared for the long overland journey home. Back in Dunedin, Department of Conservation  (DOC) staff carried her on the back of a ute out to Karitāne.

For most people, she’s a statistic now, paperwork, acronyms and existential maths swirling around her death. She’s one of two Hector’s dolphins that make up this year’s FRML, or fishing-related mortality limit, for the Otago region. Her death will factor into the PST, or population sustainability threshold, a theoretical measure of the number of deaths these dolphins can sustain.

For some, this dead animal is a symbol of everything that’s wrong with New Zealand’s fisheries management. For others, she represents a tragic but unavoidable loss on a busy coast where fishing and dolphins intersect. To the people of Kāti Huirapa ki Puketeraki, whose ancestors lived alongside Hector’s dolphins for centuries, and whose wharenui is fronted by an exact, exquisite replica of one that washed up when the meeting house was being carved, she’s an old friend who’s been away, come home at last.

[Chapter Break]

A gentleman visitor to the seaside village of Brighton, South Otago in the 1860s might have been well advised to carry with him a copy of Paul Diver’s Guide to Brighton and Its Environs.

“While lady relatives and friends are inhaling the breezes on the Parade,” suggests the author, “let the marksman sit at either side of the boat-harbour on a fine day, at high tide, and he will soon see a shoal of porpoises, at which if he is quick, he will be able to get a fair shot. The bodies of these tenants of the deep, when hit, can be recovered at low tide, and a considerable quantity of oil taken from them.”

University of Otago science communication researcher Gemma McGrath spent years trawling such old books, articles and papers, and interviewing people for her master’s thesis, which attempts to gauge just how common Hector’s dolphins once were. So common, she found, “that people wouldn’t be able to imagine them ever becoming rare”.

Her thesis functions as a snapshot of abundance, of a time when many thousands of dolphins thrived around the coast of New Zealand. It tells of dolphins feeding far up rivers, lighthouse keepers harpooning them for fun—and of a mysterious white-faced variety of Hector’s dolphin that seems to no longer exist.

Hector’s dolphins were once a common sight up rivers and estuaries. Ramari Oliphant Stewart (Ngāti Awa, Rongomaiwahine, Ngāti Mahuta) is a tohunga tohorā (whale expert) and marine biologist who lives on the West Coast. She gained a glimpse of those vanished times six years ago, when a pod of 30 Hector’s dolphins took up residence along a two-kilometre stretch of the Ōkārito lagoon.

Hector’s dolphins hug bays and river mouths during summer, but in winter appear to move deeper offshore. Some conservationists say restrictions on net fishing need to be pushed much further out. Recent acoustic research by Hannah Williams at the University of Otago shows the dolphins there regularly cross the four-nautical-mile line of restriction to feed where fishers are working.

Locals and officials, she tells me, didn’t know how to deal with the incursion, with many fearing an imminent stranding. “There were locals trying to drive them out with jet skis and outboards,” she says. “I was horrified. They just had no idea what they were doing.”

She quickly discovered a nursery group of calves further up the lagoon. She convinced the local hapū to put a rāhui over the area and spent three and a half weeks camping out there, observing the dolphins as they hunted for baitfish.

“I learned so much about these animals. I saw three or four different fishing strategies they were using.” One strategy involved herding the bait brought in by each tide. The dolphins, she says, were expertly working the shifting tidal front.

“It was what I call picket fencing. The tide would drop and it’d be about a metre of water and they had all the bait fenced inside the channel.”

Māori around Aotearoa, she says, once knew such behaviour intimately. “[The dolphins] were well known to hapū up and down the coastline. Because when the health of our estuaries and harbours was there, [dolphins] were no doubt in and out of them.

“They are masters at working shallow, low-visibility environments.”

Māori have a deep and complex connection to Hector’s dolphins. “They are taonga, beheld as whanaunga [extended family] with deep respect,” explains researcher Sonia Rahiti (Ngāi Tahu). “Certain whānau and hapū had strong relationships with dolphins, who were kaitiaki [guardians]. They acted as tohu [signs] and were ecosystem indicators.”

The dolphins, Ramari tells me, were also an important food source for southern Māori.

“Hector’s dolphin in the South Island was a really important species in terms of maintaining human fat levels during the winter when you had poor harvest seasons. You needed fat otherwise you died of liver disease.

“Everyone tends to sanitise it these days. But we had a huge respect for those species because they were part of our existence.”

[Chapter Break]

In the early 1980s, marine biologists Steve Dawson and Liz Slooten were postgraduate students just starting their careers. Seeking to fill the gaping information void around Hector’s dolphins, the pair set out on one of the most ambitious marine science projects ever undertaken in New Zealand: they bought a small inflatable boat (Dawson’s mum chipped in for the trailer) and navigated huge stretches of coastline, counting dolphins.

Their epic journey took them from the sheltered harbours of Banks Peninsula to the Marlborough Sounds and the rugged west coast of the South Island. They also explored from Muriwai Beach to Raglan, following up on reports of dolphins living there. At times it got “more than a little bit scary”, says Dawson. They had no back-up motor, no radio—the VHF network wasn’t up to it.

“We ended up going out of just about all of the West Coast river bars,” he says. “We did end up coming in upside down one time. There’s no way in the world we would let graduate students do that these days.”

The survey mapped for the first time where Hector’s dolphins clustered along the coast.

Fetching up in Akaroa, on Banks Peninsula, the pair rented the old Wainui school for $12 a week, and headed out onto the harbour every good day.

“We kept finding dolphins either floating around in the water, or dead on the beach,” says Slooten. Many of these dolphins carried the telltale scars of having been caught in plastic monofilament nets.

The couple decided to start autopsies. “We thought we might get about a dozen dead dolphins,” says Slooten. “In the end we got 125. The first one, you’re shocked as hell. And after a while, which is almost more shocking, you get completely used to it.”

Around this time, Dawson interviewed more than 100 fishermen. One told him he’d caught a dolphin a day for the previous two weeks. Another reported catching five dolphins in one net. One reported catching 44 dolphins in a year.

“Those bad old days were just soul destroying,” Dawson says. “It was a tough time.”

He and Slooten worked alongside the newly formed DOC to establish New Zealand’s first marine mammal sanctuary in Akaroa in 1988.

Since then, the couple and their graduate students (there have been nearly 30) have returned to Akaroa every year to study the dolphins. “We’ve seen a nice increase in the survival rate,” says Slooten. “There are clear indications that we’ve gone from a precipitous decline to somewhere around flatlining.”

[Chapter Break]

Hector’s dolphins are the small-town Kiwi of the dolphin world, says Rochelle Constantine, a cetacean biologist with the University of Auckland. “Their average range is around 50 kilometres.”

Much of Constantine’s work focuses on genetics, a powerful tool for analysing populations and figuring out where these animals live. Genetics has reinforced what had long been suspected by researchers—that, due to Hector’s dolphins’ tendency to keep it local, the groups of dolphins around our coast are largely isolated from one another.

Each cluster of dolphins in the South Island, for example, carries a different genetic stamp. Two populations on the Kaikōura coast, less than 40 kilometres apart, are separated by the deep incursion of the Kaikōura Canyon, and as a result have different genetics.

“That’s why it’s kind of tricky talking about ‘the Hector’s dolphin’,” says Constantine, “because they are quite different.”

When Smart first paddled out into Porpoise Bay to have this photograph taken, there were no dolphins to be seen. They flocked to him within minutes. “You often see them competing with each other for waves,” he says. “They do tail slaps, or the big dolphin will push the little dolphin out of the way. It’s pretty special when you’re out there on a paddleboard and they’re just following you and playing games.”

In 2002, it was discovered that the small population of dolphins off the North Island’s west coast were so genetically different from those down south that they should be classed as a separate subspecies, the Māui dolphin. With as few as 48 individuals left, they’re one of the world’s rarest cetaceans, and their numbers are still declining.

Hector’s are faring better—our latest estimate puts their total population at about 15,000—but Dawson worries about the vulnerability of each family cluster. “These populations are small and fragmented,” he says. “They’re at very high risk.”

Since Banks Peninsula, four more sanctuaries have been set up specifically to protect Hector’s and Māui dolphins—off the west coast of the North Island, Marlborough, Southland’s Te Waewae Bay and in the Catlins, where, I discover, they are causing quite a stir.

[Chapter Break]

On a still autumn day, I join surfer Nick Smart and DOC senior ranger Ros Cole on a bench outside Smart’s one-room surf school, overlooking the wide, sandy crescent of Porpoise Bay. A group of around 40 Hector’s dolphins spend the summer here, feeding, socialising and having their babies.

The dolphins are in the bay most days through summer, easily accessible from the beach. They’ve become one of the worst-kept secrets on the international backpacker circuit.

Cole periodically calls in here to keep an eye on human behaviour. The main worry is that excited tourists will affect mother dolphins trying to nurse their babies.

While most tourists are well behaved, she says there is the odd person that gets a little too eager for a Free Willy moment. “What we’re seeing is people trying to touch dolphins and things like that. We prefer if the dolphins want to interact with people that they do it on their own terms rather than people pushing themselves into the dolphin space.”

From the shore, I watch 10 dolphins in perfect formation riding the glassy surf—silver and black missiles in cold, clear water. As the wave breaks, two leap clear of the sea.

Further out, the rest of the pod mill in the wash of the bay, their cookie-cutter fins bobbing at the surface. A few tourists with hired bodyboards are heading out for a closer look.

Smart’s surf classes are often crashed by playful dolphins. “There are some days where they just don’t leave us alone. They just want to surf with us and have fun.”

Wendi Roe of Massey University and masters student Vivian Lee begin the necropsy on the dolphin that was later buried at Karitāne.
Having necropsied more than 150 of these dolphins, Roe is convinced the parasite Toxoplasma gondii (detected in the tissue samples), poses a serious threat. “It’s just one of the cleverest parasites there is,” she says.

For his students, it’s an unforgettable experience. “Some of them have never seen a dolphin. Some of them haven’t even been in the ocean. I often get students telling me it’s the best thing they’ve ever done in their life.”

But the interest in the Porpoise Bay dolphins is a double-edged sword. “Quite often when I meet people and they’ve had a good time, I say, ‘Don’t tell too many people’, which I shouldn’t say because I have a tourism business, but I just like the numbers at the moment. I’d hate to see this place get overrun.”

Making sure there are no dolphins nearby, I swim out past the breakers and tread water. In the 20 minutes I spend out there, three or four dolphins come past just metres away, cruising the surf line, looking for food. Each time, I duck my head under, hoping for a glimpse through the gloom.

[Chapter Break]

Dolphin lives are largely invisible to us. But new scientific tools are allowing us to see more than ever.

Genetic studies reveal that every now and then, one of these notorious homebodies “busts a move”, as Constantine puts it. One Hector’s dolphin, it seems, swam from Westland all the way around Fiordland to Te Waewae Bay in Southland, leaving its genetic signature in the population there. Others travelled to the west coast of the North Island, into Māui habitat.

Figuring out where the dolphins are, and when, is critical to protecting them. These small mammals are not only vulnerable to gillnets, but also to trawl nets, which are regularly used around the coasts of our country to catch species like snapper, gurnard and tarakihi.

Commercial gillnets are now banned inshore to four nautical miles around roughly half the country. Along a swathe of the North Island’s west coast, in the heart of known Māui dolphin habitat, protection extends out to 12 nautical miles offshore. Similar restrictions are in place around Banks Peninsula. Trawl netting closures are less severe, extending four nautical miles offshore in Māui dolphin habitat and offering only partial protection elsewhere. These closures have pushed many fishing operators out of business, and some think it’s all for nothing, arguing that they never see Māui dolphins out in deeper water. Conservationists, however, say the restrictions don’t go far enough.

It’s not only nets the dolphins are up against. “Things we do on land have impacts in the sea as well,” says DOC science advisor Anton van Helden.

Steve Dawson, who with Liz Slooten has devoted much of his life to Hector’s dolphins, says they are so inquisitive that often the best thing to do is “find a group, turn everything off and let them come to you”.

He says sediment pouring out of rivers may be damaging the seafloor, causing the dolphins’ food sources to move elsewhere. For highly localised dolphins that hug the coast, this is a problem. In Southland, Ros Cole tells me, “We’ve got four big river catchments, and all of them have Hector’s dolphins hanging out off the river mouths. Everything that goes down those rivers ends up in dolphin habitat.”

Pollutants and heavy metals accumulate in the dolphins’ bodies. “Anything in the fat reserves of a female tends to get metabolised into the milk, so the calf gets that pollution. There’s evidence overseas to suggest that it can have an impact on reproductive success and breeding condition.”

Then there’s us. The ports we build, our ships and boats, the sheer amount of noise we send rippling through the water—they’re all likely to be stressors, says van Helden. “If an animal’s having to deal with a particular stress, it can reduce their capacity to cope with other things. If there’s a lot of noise in the environment, for example, it can make them less aware of predators. It may make them more vulnerable to being caught in nets. It may even bring their immune levels low enough that they’re more susceptible to disease.”

[Chapter Break]

Tens of thousands of years ago, humans shared the jungles of South America with a tenacious and adaptable parasite called Toxoplasma gondii. The parasite spends the first part of its life cycle in the body of a mammal or bird, where it enters the host’s nervous system and alters the host’s behaviour, making it less afraid of predators, particularly cats. This is the parasite’s intent—it needs a feline to call home. Once inside a cat, it reproduces, shedding thousands of oocysts (equivalent to eggs) that are released through the cat’s faeces and urine. These enter the soil and waterways and stay there, sometimes for up to a year, until some hapless creature ingests them and the cycle starts again.

As humans cleared forests, developed agriculture and domesticated cats, the parasite evolved too. It has found a comfortable niche in the cosy triangle between cats, mice and humans. Thanks to humans, these domestic strains of Toxoplasma spread around the world. We now live alongside it on a daily basis. Many of us even carry it.

Toxoplasma oocysts survive for up to two years in salt water—so the parasite also plagues the ocean. Oocysts enter streams and rivers and are washed out to sea, where they’re ingested by filter-feeding animals like cockles and mussels, as well as by fish. From there, the parasite works its way up the food chain.

When it lodges in the body of a marine mammal, it can do enormous damage. Toxoplasmosis, the disease the parasite causes, kills sea otters in California, spinner dolphins in Hawaii and Hawaiian monk seals. It’s even been detected in seals in Antarctica. Seabirds, too, are likely at risk.

And in New Zealand, it’s killing our endangered dolphins.

Whenever a Hector’s or Māui dolphin is found dead on a beach or in a fishing net anywhere in the country, veterinary pathologist Wendi Roe gets a phone call. The dolphin will be shipped to her lab at Massey University, and she’ll attempt to establish what killed it.

“I’m a problem-solving kind of person,” she says. “On an individual animal basis, I’m quite motivated by wanting to know why an individual animal died, but the bigger driver, really, is the hope that you’ll be able to do something about it.”

In almost a quarter of the Hector’s or Māui dolphins Roe examines, she finds evidence of a Toxoplasma infection.

Of the 150-odd she’s necropsied, 10 have died from toxoplasmosis, including three of the eight Māui dolphins she’s been able to fully necropsy since 2007.

In fatal cases, the parasite, she says, infects pretty much every organ in the animal’s body. As it reproduces, it causes irreparable damage. Dolphins that die of toxoplasmosis do not die well.

Roe believes the disease could be a crucial factor in the species’ survival. “The proportion of deaths caused by Toxoplasma is higher than any of the other diseases I find.”

In sheep, toxoplasmosis can cause miscarriage. It could be doing the same in dolphins—we just don’t know. There’s also the distinct possibility that dolphin behaviour may be in some way altered by the parasite. Toxoplasmosis may cause humans to become less risk averse. For a dolphin swimming in a sea of nets and predators, that could be deadly.

As of 2019, some officials consider toxoplasmosis a significantly greater threat to Māui dolphins than commercial fishing. This is highly contentious.

Mark Johnson attaches a suction cup-mounted ‘D-tag’ to a Hector’s dolphin in Marlborough’s Cloudy Bay. The tags, which Johnson designed, watch and listen as the dolphin hunts. While dung samples and biopsies can tell us about diet, these cups give us context: like where and how the dolphin hunts, and how often.
The grave of the Hector’s dolphin is planted with three “eyebrows” of pīngao, in acknowledgement of Tāne and Tangaroa, along with the children’s seashells. This dolphin came from a hapū that has dwindled to about 40 individuals. Every untimely death matters.

Some conservationists accuse the fishing industry of amplifying the disease risk to shift attention away from fishing nets. “If you’re looking at animals that are found dead on beaches, by definition, they’re going to be unwell, so you’re looking at a pretty biased sample,” says Dawson.

But Roe points out that we only see a small fraction of the animals that die, so toxoplasmosis could be a bigger problem than we realise. One of the key things we need to know, she says, is where oocysts are entering waterways.

Researchers are now studying kākahi/freshwater mussels, to see if they’re ingesting the oocysts, and if so, whether mussels could be used to help detect places where the oocysts are getting into the water.

Meanwhile, a PhD thesis by Alicia Coupe sampled cats across the country and found that around 1.6 per cent of feral and stray cats were shedding Toxoplasma gondii oocysts. The numbers are huge: an estimated 51 to 62 trillion oocysts were being released into the environment annually. We don’t know how many of these make their way into the food chain. But Toxoplasma gondii is everywhere, from city parks and suburban gardens to rural areas, remote forests and tussock grasslands.

[Chapter Break]

We came close to losing some populations of Hector’s dolphins. We may still lose the Māui dolphin. But, says Constantine, if we stop killing them—catching them in nets by mistake—the populations can bounce back. We’re already watching it happen.

Protection measures, she says, have turned things around in some areas. Some groups of dolphins are now nearly as genetically diverse as they were before the nets. Crucially, though, we still don’t know for sure how many dolphins continue to be killed in nets. Reliable data comes from fisheries observers—independent people on fishing boats, charged with reporting bycatch—or cameras on boats. But observer coverage is still low in many areas and the introduction of cameras has been delayed repeatedly.

Assuming that inshore trawling and gillnet fishing continues, some level of dolphin bycatch, for now, is inevitable. Constantine can live with that. With caveats.

“We must always be working towards zero bycatch,” she says. “Every now and then a dolphin will die in a net. If it’s from a large, robust, healthy population, I’m not bothered by that. As long as there’s learning from it. And that we try to make sure it doesn’t happen again.”

One day, technology might mean that bycatch is impossible to hide. But it could also help prevent it in the first place by giving us a much better picture of how these dolphins operate.

Cawthron Institute researcher Deanna Clement recently led a pilot study that put digital acoustic recording tags (D-tags) on 11 Hector’s dolphins in Marlborough’s Cloudy Bay. The tags, developed by expat New Zealand engineer Mark Johnson, attach to the dolphins via suction cups and are programmed to detach after a day or two. They have transformed our ability to study these animals.

“They record with very high resolution all movements of the animal, and at the same time, they record the sounds that the animal makes,” says Johnson.

By listening in to the dolphins’ echolocation clicks, scientists can tell when the animals are hunting. Like a Geiger counter in a fallout zone, the clicks get closer together as the dolphin homes in on its prey.

“What we’re addressing is the second-by-second fine-scale behaviour of the animal,” says Johnson. “How do they go about finding food? How often do they find food? What do they do when they find  food?”

The answers will illuminate the lives of these dolphins. They might also save some. “Are there things they do that, for example, could lead to an elevated risk of entanglement in fishing gear?”

As the tags on the dolphins pinged back, scientists started to realise how limited our understanding of the species was.

New technologies are changing the game for keeping track of dolphins. In Marlborough, Johnson listens out for a recently deployed D-tag.

Hector’s dolphins, so the accepted wisdom goes, hug the coast, preferring cloudy waters around river mouths, perhaps because the murk protects them from predators like orca.

But one of the tagged animals went offshore at night and started feeding in waters 120 metres deep. “What are you doing out there?” thought Clements. “You don’t go offshore!”

She suspects the dolphins head offshore to feed in a layer of water teeming with prey animals which rises closer to the surface at night. “It makes sense, but we’ve always told ourselves this other story.”

The discovery could have profound implications for management. If dolphins are crossing the line we’ve drawn in the sea, does that mean we should redraw the line?

Another surprise: the dolphins regularly make long resting dives, staying underwater, almost motionless, for up to an hour, and while hunting, they roll over on their backs. “All we can assume is it’s something to do with their echolocation, that it’s more of an advantage if you’re searching for something near the bottom to turn around and focus on it that way,” says Clement.

We also now watch these dolphins from the air. In 2022, a non-profit group named Maui63 launched a hi-tech drone that can fly far offshore for up to six hours at a time and use artificial intelligence to spot Māui and Hector’s dolphins. Constantine leads the project.

“When it detects a Māui or a Hector’s dolphin it lets us know on land, where we’re piloting it from,” she explains. The drone is not bothered by rough seas or big swells—the pragmatics that hamper research from boats. It’s hoped the drone will show researchers where Māui dolphins go during winter, something that still largely eludes us.

There may be other applications for this tech, too.

At Karioitahi beach near Auckland, the Maui63 team prepare to launch their $300,000 drone. Using petrol and battery power, it can fly up to 160 kilometres an hour and stay up for six hours.

“We’re working alongside the Ministry for Primary Industries and some of the fishing companies [to ask]: could we use this as something that could monitor an area to look for animals before fishing is being done?” she says. “Or could it fly backwards and forwards while fishing is being undertaken? It’s very exciting.”

Eyes underwater. Eyes in the sky. Decades spent in small boats on cold, choppy seas, and in the lab, scrutinising skin samples and ruined organs. Taken altogether, it’s the sort of science that just might save a species.

“I’m really optimistic for Hector’s dolphins,” says Constantine. “I like to remain optimistic for the Māui dolphin. Every time you go out and see them, they’re bouncing around and doing all the fun things that they do. They don’t know they’re on the edge of extinction, they don’t know they’re the world’s rarest dolphin. I always have faith when I see them.”

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