The world’s smallest, rarest dolphin lives in New Zealand. After the expansion of gill-netting in 1970, the population and range of Hector’s dolphin diminished rapidly. One extremely isolated subspecies, Māui dolphin, now numbers barely 100 individuals. Yet science has revealed that the species may yet recover, even from the brink of oblivion.
Ten nautical miles to the east, breakers beat against the foaming shore of Namibia’s Skeleton Coast. But here, keeping watch on a moonless night, rising and falling in the long Atlantic swell, I’m witnessing a quiet symphony.
Green water, alive with bioluminescence, peels around the heaving bow, and on the displacement wave, Heaviside’s dolphins ride in light, their fusiform flanks cloaked in iridescent plankton. They spiral and cavort, luminous jetstreams traced by their pectoral fins cutting through the cold Benguela Current like fireworks through a night sky.
Although Heaviside dolphins are now geographically restricted to Namibia and the southern tip of Africa, they are a remnant population of a small, robust cetacean which dispersed around the planet two million years ago. They rounded Cape Agulhas, crossed the Indian Ocean, established in New Zealand, then crossed the Pacific and split into two groups to populate the southern tip of South America.
All four groups have since evolved separately, shaped by their new habitats and food sources, becoming four separate species. Hector’s dolphin (Cephalorhynchus hectori) is New Zealand’s only endemic cetacean, and on the basis of current knowledge is the smallest and rarest of all marine dolphins in the world.
Until 1970, there were an estimated 30,000 Hector’s dolphins around the New Zealand coast. Then everything changed. Commercial and recreational fishers began using nylon gill-nets, and Hector’s dolphins, which forage mostly in shallow coastal waters, became entangled in these and drowned. It is estimated that in just three decades, 70 per cent of Hector’s dolphins were killed nationwide.
One isolated population on the west coast of the North Island was found to be genetically distinct from the rest and given the name Māui dolphin, a subspecies of Hector’s dolphin. Gill-nets killed 90 per cent of them.
Now numbering barely 100 individuals, the Māui dolphin is classified as critically endangered, and almost all are found on a stretch of coastline a mere 40 km long. Near obliterated by nylon nets, this pint-sized dolphin might seem to need a miracle to recover, but science suggests that it may have avoided the spectre of catastrophic genetic decline, and paints a single, clear route to salvation.
In 1978, all that was known about Hector’s dolphin was written in a scientific paper just four pages long.
Seeking to add to this scant knowledge, Steve Dawson and Elisabeth Slooten started their studies by taking to sea in an inflatable boat. In five months, they surveyed the dolphin’s entire known range.
After running more than 8000 km of transects, searching the sea for the distinctive curved dorsal fin of Hector’s dolphin, the pair produced a sobering analysis.
“In the North Island, the dolphins were so rare that on most days we didn’t see any,” says Dawson. “The log of each day’s transects would typically read, ‘zero, zero, zero, zero, zero, zero, one, zero, zero, zero…’”
Recent aerial and boat surveys resulted in a population estimate of just over 7000 Hector’s dolphins in the South Island, while in the North Island, the Māui subspecies numbered about 110. The most troubling finding was that gill-nets were being used throughout the dolphins’ range.
“On the east coast of the South Island, there was an almost perfect overlap between gill-netting for rig and elephant fish and the natural distribution of Hector’s,” says Dawson. “Even recreational fishers make a difference. Fishermen would admit to hauling up one or two once every year or so and not think much of it; it was just one or two. But they didn’t realise there might be only 50 in their local population.”
Twenty-five years on, Slooten and Dawson—now associate professors at Otago University—continue to study the species and the ecological problems it faces. Hector’s dolphins reach sexual maturity at about seven to nine years old, produce a calf only every two to three years, and live to about 20. In that time, they may give birth to between three and five calves, meaning that the best possible growth rate in any given population is just 1.8 per cent a year.
This is just enough growth to compensate for natural impacts such as disease, predation and lean years. South Island Hector’s dolphins can sustain a total human impact, including by-catch and other impacts such as pollution, of just 13 dolphins a year. For Māui dolphin the maximum sustainable loss is just one individual every 6.4 years. Any more than this and the species is doomed to eventual extinction.
Yet, until recently, actual by-catch was estimated at 110–150 dolphins a year.
In 1988, a marine mammal sanctuary was established around Banks Peninsula with the express purpose of protecting Hector’s dolphins, but fishers simply shifted their effort to areas immediately north, south and offshore of the sanctuary, and continued to catch dolphins. They caught fewer, but it was still an order of magnitude higher than what the population could sustain.
In 2003, a second protected area was established on the North Island’s west coast, prohibiting gill-nets within four nautical miles. The no-netting limit was extended to seven nautical miles in 2008, and new measures were put in place in the South Island, banning gill-netting within four nautical miles of the east and south coasts and within two nautical miles of the west during three months of summer. In addition, trawling was prohibited within two nautical miles of shore on the west coast of the North Island and east coast of the South.
Slooten’s projections suggest that the 2008 measures will be enough to see a very slow recovery in some areas, especially on the south coast of the South Island, depending on how well fishers comply with the new regulations. However, the largest and least protected population on the South Island’s West Coast will still lose 1000 dolphins by the year 2050, representing a continuing overall decline in the species. This situation would be in breach of New Zealand’s own legislation for marine mammal protection, which requires population recovery to “non-threatened” status within 20 years.
Māui dolphins will take more than two centuries to recover to half their abundance before fishers began setting gill-nets, and more than 1000 years to fully recover to that 1970 population, if at all.
As a species, Hector’s dolphin will never fully recover from the damage that nylon filament has wrought in a few decades.
And even as the nets are moved offshore, other potential impacts are replacing them. Iron sand is being mined in the zone whereMāui dolphins are most common, and applications have been lodged for geophysical exploration and seismic surveys just a little offshore. At the northern end of their range, an electricity project based on a field of 200 large tidal turbines has been planned for the mouth of Kaipara Harbour.
“We don’t know what the impact might be of any of these intrusions,” says Dawson, “though they are unlikely to benefit Māui dolphins.”
Raglan simmers under the mid-summer sun, perfumed by a gusty north-westerly blowing over Waikato pasture.
This coast is a regular pilgrimage for surfers hungry to ride what is arguably the finest point break in the country, surfers who remember riding with groups of up to 30 Māui dolphins. But that’s changed. Raglan now represents the southern extent of the now much-decreased range of the Māui dolphin, and few are seen.
Waves patter on the hull like a thousand drumming hands as DOC’s survey vessel Tuatini skips out past the breakers on the harbour bar. On board is marine mammal specialist Marc Oremus, a Frenchman who has made something of a career shooting dolphins. However, loaded in the breach is not a cartridge of powder and shot, but a dart with a hollow tip that excises a cylinder of skin and blubber, five millimetres in diameter, seven millimetres deep.
Over the past two months, Oremus and DOC colleague Martin Stanley have surveyed the entire range of Māui dolphins and collected 36 biopsies. Oremus hopes that some of these samples may match those taken between 2001 and 2006, so that scientists can better estimate the range and abundance of the population. It’s a little like walking down a city street and expecting to bump into the same person you met a decade ago. Except this is a ghost town, and residents are few, so the chances are relatively good.
Over both the 2010 and 2011 seasons, the researchers will determine the DNA profile of some 41 dolphins. It may not seem like a large sample, but it represents almost half the population. This is a mammal so rare that today, we will survey fully a quarter of its known range and find just three individuals.
Between Raglan and the Manukau Harbour—the home range of 90 per cent of the Māui dolphin population—the barricade of chalky cliffs is broken only by the settlement of Port Waikato and a series of vertical scars where creeks and rivers arrive at the edge of the North Island, and simply fall off.
Waves hammer at this wall, tearing it down inch by inch and delivering the sediment back into the Tasman. As a result, the sea has the opalescent quality of a glacial lake, shimmering and inscrutable.
We first search south of the harbour, and turn up nothing, then run northwards along shore, with four pairs of eyes scrutinising every wavelet, every splash, for signs of life.
To the south I can see Taranaki, a monument to the former southern extent of Māui dolphins’ historic range.
When nylon nets arrived, the range of the dolphins was made obvious by the carcasses strewn on the shore—like gauging the number of ships by the number of shipwrecks.
There were numerous beachcasts in the New Plymouth region, dolphins washed up in nets, or with scars indicating net entanglement. Now, the beachcasts, the sightings—the population itself—seem confined to a stretch of coast from Raglan to Manukau Harbour, just one-third of the historic distribution.
After two and a half hours of retina-searing surveillance, Stanley lets out a whoop from the starboard side. Three Māui dolphins cut along the coast under a monumental escarpment, just seaward of the surf line. They move quickly, breaching the surface with cascades of spray, and as we idle inshore, they turn towards the boat.
They’re painterly little torpedoes; naval grey with a snowy mantle and a charcoal bow wave from the tip of the beak down over the pectoral fin, as though they swam through ink at speed.
The chin and belly are brilliant white, a harlequin cloak of streamlined stripes topped with a sharply curved dorsal fin neatly matching the robust arc of the dolphin in flight. But it’s the mouth that’s most intriguing—a subtle crescent from the beak to where the mandible connects with the skull, downward in a visage of slight despair.
On the bow, Oremus takes aim, anticipates a dolphin surfacing and pulls the trigger. A small orange dart bounces off the flank just below the dorsal and floats, awaiting pick-up. In the tip is a tiny consignment of skin and blubber, a minute clue from which researchers can attempt to unravel the past, present and future of New Zealand’s only endemic cetacean.
Hector’s and Māui dolphins carry in their DNA the traces of their ancestry, their whakapapa, as we all do. But the unique coding of four chemical bases—adenine, guanine, cytosine and thymine—that make you you and Māui dolphins Māui dolphins may also be leading Māui to a genetic dead end.
“There’s something called the 50/500 rule,” says Scott Baker, associate director of Oregon State University’s Marine Mammal Institute and professor of molecular ecology and evolution in the School of Biology at the University of Auckland. “You need at least 500 individuals in a population to maintain existing genetic variation. And you need a minimum of 50 individuals to prevent severe loss of genetic variation.
“With a total population probably less than 100, Māui are clearly in the red-flag zone.”
In a small population, harmful mutations can accumulate, leading to a loss of fitness, decreased adaptability and a phenomenon known as inbreeding depression, where further deleterious mutations accumulate through breeding among close relatives in a downward spiral called mutational meltdown. In large populations, inbreeding is rare and harmful mutations are removed by natural selection, but in a meltdown scenario, mortality exceeds the birth rate and the population can decline. Given the perilously low potential for population growth in Māui, and the fact that there are unlikely to be more than 28 mature females in the entire population, genetic decline is yet another threat to their long-term survival.
One solution to poor genetic diversity is to introduce more variation and increase the size of the gene pool by translocating individuals from other populations, such as Hector’s dolphins from the South Island. If these individuals survive and interbreed, they will reintroduce genetic variation that has been lost in the local population.
The benefits of such a “genetic rescue” have been hotly debated, and it’s not without detractors. For one, translocating endangered species is risky. And by introducing variation into the gene pool, the unique parcel of genetic exclusivity that defines Māui dolphins could be eroded. By protecting them from genetic decline, you risk losing the subspecies—by saving their souls, you can erase their identity.
“It comes down to what you’re trying to protect,” says Steve Dawson. “The Convention on Biological Diversity emphasises conservation of genetic diversity. The moment you introduce a Hector’s dolphin to the Māui gene pool, then that diversity is compromised.
“So if we want Hector’s on the west coast of the North Island, that’s fine, but if we want Māui, we have to do something different.”
But for now, any argument is academic, because it may have already happened.
Rebecca Hamner, a PhD student at the University of Auckland, has a fridge that on first inspection may be a little alarming for a nature lover. There is a shelf labelled “Hector’s & Maui’s”, and there, carefully sorted in coloured plastic containers, are 872 tissue samples from the world’s rarest marine dolphin. Some are tiny plugs of skin and blubber from the tip of a biopsy dart. Others are small, carefully excised samples from beachcast or netted dolphins. And in a freezer on another floor, stored at minus 80ºC, are yet more samples from museum collections dating back to 1870. The Hector’s and Māui samples are part of the University of Auckland Cetacean Tissue Archive, the second-largest such collection of blubber in the world—kind of disgusting, but very useful for informing conservation strategy.
Each sample may be just millimetres in size, but that’s acres for a marine mammal geneticist. And though every sample looks identical, each carries a unique cargo of DNA, like a barcode. A long barcode.
The dolphin genome has some 3,200,000,000 base pairs—about the same as the human genome—all tangled up in a cell a tenth of a millimetre across.
But there is no need for geneticists to analyse the entire DNA complement of each sample. From the molecular variation in just one 360-base pair section of mitochondrial DNA, Hamner can deduce a dolphin’s mitochondrial haplotype, a signature used to trace lineage that is inherited only from the mother.
To date, 22 haplotypes have been identified for Hector’s dolphins. By dint of geographical isolation, genetic ‘drift’, low genetic diversity and a grossly depleted population, the Māui subspecies all belong to a single haplotype, coded ‘G’.
But when analysing the biopsies shot off the coast between Manukau Harbour and Raglan, Hamner hit a snag. Along with the familiar parade of Māui ‘G’ haplotypes, she found two samples corresponding to haplotypes ‘I’ and ‘J’. She ran the analysis again. And again. Then she had two other researchers in two other labs analyse it. The results were unambiguous.
But more startling were the possible reasons for the anomaly. Either the I and J dolphins were hitherto undocumented haplotypes in the Māui population, substantially increasing the assumed genetic diversity of the group, or she had discovered intruders—Hector’s dolphins, far from home—a discovery that might change the prospects for Māui dolphins, perhaps the description of the subspecies itself.
To find the answer, Hamner had to dispense with the comparatively coarse tool of mitochondrial DNA and delve deep into the nucleus of the cell to harvest nuclear DNA, inherited from both parents. This is the DNA used in forensic genetics to identify a suspect from traces of blood or tissue found at a crime scene—the CSI stuff.
Hamner was looking for microsatellites, genetic markers used to determine kinship, patterns that might connect the I and J haplotype dolphins to either Māui population or another. She extracted, amplified, genotyped and compared the genetic material from 267 dolphins, building on the genetic work of a team of previous researchers, then sifted nucleotide strings though mathematical algorithms looking for patterns—looking for millions of needles in billions of haystacks.
It took months.
Hamner leans on a pile of paperwork, eyes alight. She looks fair ready to burst.
She places a bar chart carefully in front of me, as someone might present a murder weapon. It’s a stack of coloured boxes, as cryptic to me as the Rosetta Stone. Hamner draws lines with her fingers, tracing out the membership coefficients for each of the four regional populations, and the genetic signature of the two “rogue” haplotypes.
“They were from a different population,” she whispers, barely able to contain her excitement. “They were Hector’s. They were from the West Coast.” She raises an eyebrow to underscore the sense of conspiracy: South Island Hector’s dolphins, mixing with the North Island Māui.
“We don’t know if these individuals will survive, or even stay,” says Hamner. “But this is good news. Most small populations won’t survive without periodic contact with larger populations.”
If the Hector’s dolphins survive to interbreed, the I and J haplotypes will be added to the signature of Māui dolphin, along with their nuclear genetic diversity. This could prop up the genetic health of the subspecies, but might also erode its distinctiveness—Māui dolphin may be redeemed by its cousins, only to be absorbed into their ranks.
My last encounter with a Māui dolphin was on a calm autumn day off Manukau Heads. A single one-metre-long juvenile—the only dolphin we had sighted in eight hours of searching the coast—was lolling in the sun, corkscrewing under the bow, appearing to play to the camera.
Like us, this dolphin began life connected to a placenta, it suckled from its mother, and under normal circumstances lives in family groups and maintains complex social interactions. In fact, this dolphin shares more DNA with you and me than any other endemic species in New Zealand.
Even if the spectre of genetic decline has been assuaged for now, the Māui dolphin will certainly perish if New Zealanders continue catching them in nets. Gill-netting is still allowed on the Taranaki coast, inside Kaipara Harbour and the inner Manukau—parts of the Māui dolphin’s historic range. If the conservation strategy requires the population to increase and disperse, we can’t continue to net them at the boundaries.
And if we can’t save Māui—a large, sociable flagship species for marine conservation that lives, breeds and perishes entirely within our exclusive economic zone—what hope is there for the rest of the species edging towards the precipice of extinction in Aotearoa?
The little Māui left us after 45 minutes, the deeply radiused dorsal fin scything through the southerly chop. A single juvenile alone in the Tasman Sea. It’s a vision that irked me deeply at the time, and has come back to haunt me on numerous occasions since. It’s hard to know what will become of him.
Yet, there’s a small vein of hope in Slooten’s run of population recovery probabilities. She presented an ‘Option C’, a hypothetical scenario in which New Zealanders responded to their apparently strong conservation ethic, a model in which fisheries by-catch was nominally reduced to zero. Under that optimistic assumption, a world without nets inside the known range of Hector’s dolphins, the entire population, every group nationwide, would recover to around 15,000 individuals—half of the population size before gill-netting became widespread. And it would take just 39 years.
“I think the prospects for Hector’s and Māui are potentially good,” says Dawson. “As New Zealanders, we just have to decide if we want them or not. If we don’t, then at least it’s explicit. If we do, then we need to start doing things differently.”