What, if anything, is a Maui’s dolphin?

Maui’s dolphin | © WWF & Will Rayment

Everyone wants to save the Maui’s dolphin. It’s either the world’s smallest dolphin or smallest marine mammal (depending who you read), and supposedly the most endangered: there are only about 55 left. A petition is doing the rounds to save the “most critically endangered marine species in the world” from extinction, partly by stopping iron ore mining on the seabed.

There’s one big problem, though. Maui’s dolphins don’t really exist, not in the same way that takahe or kakapo or short-tailed bats do. They’re not a distinct species, just a subspecies of Hector’s dolphins—in fact, it would be perfectly accurate to call them “North Island Hector’s dolphins”. And this has implications for their conservation.

Part of the problem is that people who should know better use technical terms like subspecies and species as if they were the the same thing, but there’s a world of difference. A subspecies is a population of animals or plants that looks a bit different from its relatives nearby. Critically, members of the subspecies are still perfectly-well able to breed with other members of their species. If a subspecies is isolated for long enough and become so different they it can’t interbreed any more, we call it, by definition, a different species. A species is a real thing, reproductively isolated and distinct from its nearest relative; a subspecies is just a formally-named variety, and what counts as a subspecies can be a matter of personal taste, reflecting how picky a biologist is. Some biologists refuse to even countenance subspecies and say, with some justification, that they’re not real.

Because biologists, like everyone else, are fond of large charismatic animals, it’s mostly mammals and birds that get fussily sorted into subspecies. This whole debate would be a non-issue if we were talking about an insect, or reptile, or fungus. The problem is if you split something into multiple subspecies you are almost guaranteed to create at least one rare, localised population, which then becomes in urgent need of conservation, and it’s problematic if ever-decreasing conservation funds have to be allocated to saving something that doesn’t really exist.

So what sort of thing is a Maui’s dolphin, then? Alan Baker and two colleagues measured bones of a dozen or so Hector’s dolphins from the North Island and few dozen from the South, and also compared their genetics. North Island Hector’s dolphins are a bit bigger, have a longer snout, and show some differences in their DNA—the sort of differences you would see if they’d been evolving separately from the southern dolphins for a few thousand years. (Thousands of years sounds like a lot, but it’s really nothing in evolutionary time.) Baker et al. (2002) named the northern population Cephalorhynchus hectori maui, and decided it would henceforth be called Maui’s dolphin, with the South Island population, confusingly, remaining Hector’s dolphin (Cephalorhynchus hectori hectori). Notice the triple-barrelled Latin names, which indicate both forms are just subspecies of Cephalorhynchus hectori.

(Maui’s dolphin is actually a pretty terrible name, as Maui didn’t identify, know about, or even see them, being, as he was, mythical. Baker et al. were naming them after the North Island, Maui’s fish—Te Ika a Maui—as that’s where they live, but the South Island is Maui’s canoe, and they live there too; it would be more appropriate, but a bad idea, to call them fish dolphins, or ika dolphins. Personally I think we should go back to cumbersome-but-accurate North Island and South Island Hector’s dolphins.)

Does all this pickiness about the difference between species and subspecies matter? Yes. Cephalorhynchus hectori are distinctive, unique beasts, not very much like other dolphins, and they’re only found here in New Zealand. Losing them would be a tragedy, because there’s no way to get them back. Maui’s dolphins are just those slightly-bigger Hector’s dolphins that live in the North Island, and if they died out the species would be be a little less varied, but, critically, it would still be here. It’s awful to lose a subspecies, but it doesn’t even compare to an actual species extinction; we’ve had plenty of those in New Zealand, and will be hard-pressed to prevent more.

It’s also important to look at these subspecies on a longer, evolutionary, timescale. The north/south split is, as you would guess, caused by Cook Strait; it isn’t a complete barrier, but Hector’s dolphins are coastal animals that prefer water less than 100 m deep, and most of the Strait is deeper. They can and do cross it, though, as the 2010 DoC survey found some South Island dolphins along the North Island coast. This species prefers cool water, so Maui’s dolphins are currently living close to the edge of their comfortable range, and population numbers might never have been very high.

But the North Island/South Island split is quite recent, and only temporary. Over the last couple of million years, New Zealand has been through about 20 ice ages, in which the world sea level dropped dramatically and our three main islands were joined into a single land mass. Back then, Hector’s dolphins would have lived as one continuous population in the cool waters around the entire coastline of that big island. Twenty times there has been a comparatively short warm period, called an interglacial (we’re in one right now), when the waters have risen, the islands have separated, and the North Island dolphins have been isolated from their kin and begun to evolve slightly differently. Twenty times they’ve been reabsorbed back into the fold. Maui’s dolphins have appeared and disappeared repeatedly for millions of years.

The species Cephalorhynchus hectori is in trouble: it’s been classified as Endangered since 2000 (IUCN 2011), and the population has dropped by 75% in the last 40 years, down to about 7000, largely from accidental bycatch in fishing nets. The response has been to ban commercial gillnetting in much of the dolphin’s habitat—coastal waters less than 100 m deep—though numbers continue to drop. I think it’s more important to stabilise the dolphin population than worry about whether or not they persist in the North Island. Most whales and dolphins, as their numbers recover, can recolonise their former range without assistance, and the fact that South Island Hector’s dolphins are still crossing Cook Strait suggests that would happen here too. Rather than worrying about seabed mining near Raglan, which is surely a comparatively minor threat, we should be fighting for Liz Slooten’s proposal: a gillnet and trawling ban across Cook Strait shallow waters so dolphins can get to the North Island unhindered.

Hector’s dolphin in Akaroa Harbour | Harald Selke / Tewahipounamu

Hector’s dolphins do need protection, but conservation organisations, journalists, and even the Department of Conservation are treating the North Island dolphins as if they were a distinct species about to go extinct, even comparing them to the moa. That’s irresponsible, and plays fast and loose with the facts at a time when we need to have those facts on our side.


Baker, Alan N., Smith, Adam N. H., and Pichler, Franz B. 2002. Geographical variation in Hector’s dolphin: recognition of new subspecies of Cephalorhynchus hectori. Journal of the Royal Society of New Zealand 32(4): 713–727

IUCN. 2011. Cephalorhynchus hectori. IUCN Red List of Threatened Species. Accessed 20 March 2012.

The Science Media Centre provides a good overview of recent stories on Maui’s dolphin, and the WWF has a series of fact sheets that are informative although they don’t agree with my argument above.

And for journalists who claim Cephalorhynchus hectori is the “smallest” or “rarest”:

  • Smallest marine mammal: the sea otter (Enhydra lutris), up to 45 kg.
  • Smallest cetacean: probably the vaquita (Phocoena sinus), from the Gulf of California, 40–55 kg.
  • Rarest cetacean species: the vaquita again (100–300 left).
  • Rarest other marine mammals: the Hawaiian monk seal (Monachus schauinslandi), 1100 remaining, and the Mediterranean monk seal (Monachus monachus), less than 600.

7 thoughts on “What, if anything, is a Maui’s dolphin?

  1. Anton van Helden

    Thanks for this Mike, you are pretty accurate about what you say. Sub-species is a bit of a curly one, it is the signalling of speciation in action and some people describe sub-species as management units. That Baker et al. made the decision to give this sub-species its own common name I have always found to be interesting. It certainly gives something for people to rally behind.

    Hector’s dolphin populations have been in decline for some time, they suffer at the hands of humans on a regular basis, through negative interactions with fisheries and some pretty indiscriminate fishing practices like set-netting.

    Cephalorhynchus hectori can rightly claim to be the smallest oceanic dolphin, the Vaquita is a porpoise, family Phocoenidae.

    Hector’s dolphin is our only endemic dolphin; if we lose it from here it is gone. That the North Island population, which has some distinctive characters and so yes actual genetic difference is as you rightly say a Hector’s dolphin, that it has sub-species attached is a fact of history now. That we should think it okay for them to go locally extinct from the North Island’s West coast then I think that would be a very sad day….one we are on the way towards.

    But perhaps there is more going on than we think. We have had sightings of animals on the Whanganui coast, animals occasionally seen up the East coast of the North Island. Where are those animals from? are they there year round? Do Hector’s dolphins only live 9 nautical miles from the coast? Surveys for marine mammals are difficult but this endemic dolphin of ours should be a priority. I look at the studies that have been done and I am concerned, that for the most part they have been driven it seems by external researchers (mainly Universities) or a few individuals within regional offices of DOC. I am not sure what money is available for this, or what became of proposals to put satellite transmitters on some so we could look at their range. But we are working in a data deprived world and people are being asked to make management decisions about these animals. Broad management tools are used because better data would be necessary to make other responses. I am not sure why anyone would commission a study to see if the likely recovery of this group of animals based on current rates of human induced mortality…..if the population is what they say it is then losing 1 animal is enough to put it in decline. The point is what is the population? what bounds the population? There is geneflow of the species across Cook Strait, animals seen in Wellington harbour up the West and East Coasts, none of which are in the survey area.

    I notice that the extension to the range of the marine mammal sanctuary in the proposal is in response to an animal being caught in a net, where the species has not been identified and the capture point despite not being in the survey area of any of the studies, is suggested to be “Maui’s dolphin” based on known range of these animals. What is the real range? the current range? what active programmes are there to survey these animals?

    Please don’t get me wrong here, I think we should make every effort to manage even this little sub-species, sub-population and as you suggest the whole species. But I ask what and how is it being managed?

    Sub-species or not these animals are special whether you agree or disagree with Baker’s rationale for a name.

    The management issues that face the North Island Hector’s dolphin population are also affecting the others in the waters around our coast and action rather than inaction is better. A conservative approach, closing areas to fishing or mining or whatever…..perhaps a good thing in the short term, if we are going to also invest in finding out more about these animals. There are a lot of other species out there even much bigger species that we know much less about.

    The marine environment is a difficult thing to manage and less than 1% of our EEZ is protected. We are a bunch of islands in the middle of a vast EEZ, one of the biggest…and yet we have a minister of racing but not one for oceans.

    It would be a tremendous shame to lose this population, it would be worse to lose the species, in learning to manage this little sub-population of one, perhaps we can do something to slow the other from reaching this condition.

    These are just a few personal thoughts.

  2. Anton van Helden

    Actually if we go back to North Island Hector’s dolphin and then South Island Hector’s dolphin it changes little….to go back to the North Island population of Hector’s dolphins then I think that would be more accurate…since you are suggesting abolishing the sub-species. You could go the other way also and break them into smaller management units as there are some clear and distinctive genetic markers that follow other geographical boundaries….with some geneflow between them…..the degree of geneflow it the question I guess. Still interesting piece and thanks for writing it!

  3. Mike

    Thanks so much, Anton, for sharing your perspective. It does look like we need a more thorough research programme to work out the actual range of these animals and what sort of genetic structure there is in the population. It’s very clear from reading the survey literature that the population estimates depend on many assumptions and models, but the numbers produced are promptly quoted by the media as if they were exact and certain.

    I hang my head for getting dolphins and porpoises mixed up: have amended it to “cetacean”.

    One problem that occurred to me with the common name: according to Baker et al. 2002, Maui’s are those dolphins living in the North Island, and Hector’s in the South. So what’s the common name for the species Cephalorhynchus hectori as a whole? It actually doesn’t have one any more, unless we call it “Hector’s-and-Maui’s Dolphin”. This makes it quite hard to talk about the biological species and have a single management plan for it; no wonder people mistake Maui’s for a separate species. Perhaps we really should go back to talking about the two subspecies as Northern and Southern Hector’s dolphins.

    ALso, Baker et al. found the dolphins in the southern South Island are fairly genetically distinct, though not as much as the North Island ones, and I wonder if we looked hard enough we couldn’t find something distinctive enough in their morphology to justify calling them a subspecies too. Since there are probably only a few hundred of them, that would demand a new conservation campaign.

  4. David Winter

    Hi Mike,

    I can’t find much to disagree with in this. I’m very much pro-conservation, but being inaccurate in making a case for conservation is not helping.

    I’m in the “not real” camp for subspecies, but that doesn’t mean a largely disjunct population with some unique characters shouldn’t be a conservation priority. A conservation geneticist might say the fixed mitochondrial DNA differences between the North and South island populations can be used as a proxy to suggest there are other genetic variants between these populations, and losing the Northern population would lose that diversity. The goal of conservation biology is often stated as “maintaining the evolutionary processes acting on a species” or similar, and since genetic diversity makes species more resilient to change, managers often focus on genetically diverse or distinct populations.

    “Save the northern population of the Hector’s dolphin because it might be an important reservoir of genetic diversity for this highly endangered species” isn’t a great bumper sticker though.

    Interestingly enough, some snail biologists went in for subspecies in New Zealand and it’s generally considered to have had a negative effect on conservation. For “charasmatic mini fauna” like Powelliphanta there are all sorts subspecies restricted to a few valleys or mountains, and since they have a name collectors leave them alone. A a result we don’t have enough data to actually establish whether these named populations are of conservation importance and so they go on the long list of “data deficient” invertebrates on DoC’s lists.

  5. Mike

    I agree, genetic diversity is good to have, but doesn’t make for a very exciting bumper sticker. In NZ we seem to wait until we’re down to between 60 and 11 individuals before we get serious about conservation (Maui’s dolphins seem to be right on schedule), so genetic diversity is understandably not on the radar.

    Fascinating to hear about the snail subspecies problem. I had thought from reading the DoC conservation priorities plan that someone had been busily describing subspecies to create a slew of endangered populations, but would never have thought it was actually hindering conservation efforts.

  6. Liz Slooten

    What is in a name?

    I agree with Mike Dickison, Zoologist and ukulele enthusiast, that the name Maui’s dolphin was not necessarily the best choice. As he points out, Maui’s dolphin is a sub-species and ‘North Island Hector’s dolphin’ might have been a better name. Bit of a mouthful though, which may be one reason why ‘Maui’s dolphin’ was chosen. It might make sense to give the South Island populations one name (e.g. Pahu) and the North Island population another (e.g. Popoto) and there has been an attempt to rename them along those lines.

    Another option would be to call the species ‘New Zealand dolphin’. There are two endemic marine mammals in NZ, that are only found here. The other one is the NZ sealion, which was until recently known as ‘Hooker’s sea lion’. Like Hector’s dolphin it had been named many years ago, after a scientist who was well known at the time. These days, we spend quite a bit of time answering questions like ‘who was Hector’? The name ‘NZ dolphin’ would bring the species name in line with ‘NZ sealion’ and would make it clear that they are only found in NZ.

    The North Island population (Maui’s dolphin, North Island NZ dolphin, or whatever you want to call it) is listed separately by the IUCN and DOC as ‘Critically Endangered’. New information suggests that their current population numbers fewer than 80 individuals. Data recently released by DOC indicate that there are approximately 55 individuals of 1 year and older. This information has caused quite a bit of confusion in the media and the blogosphere.

    The researchers, from DOC and Auckland University, took biopsy samples from Maui’s dolphins in order to study their genetics. They then used the ratio of ‘new’ samples (individuals never biopsied before) and re-sampled individuals (who had been biopsied before) to estimate population size. This method is called ‘mark-recapture’ and is usually used to analyse data from photographic identifications (e.g. dolphins with nicks out of their dorsal fins). Imagine you have a catalogue (photo-album) of 100 marked individuals you have previously photographed. Now you take photographs of a large sample of dolphins, and find that about half of the dolphins in the population are marked (have fin nicks). That would suggest that there are about 200 dolphins in the population (2 x 100). So far, so good. The catch is that the Marine Mammal Protection Act won’t allow people to biopsy very young dolphins. Hector’s dolphin is already very small, and therefore at higher risk from biopsy sampling. The calves are tiny and much more likely to be injured by a biopsy dart. The researchers therefore took care not to sample individuals that were half adult size or smaller. The problem is, we don’t know exactly how old these individuals are. Size is not a particularly accurate way to estimate dolphin age.

    By comparison our survey in 2004, carried out by a team of Otago University and DOC staff, is simpler to explain. We used a plane with 4 observers (and a pilot!) to survey the area where Maui’s dolphins are found. The survey used the standard, world-best-practice method called line-transect surveys to estimate dolphin density (number of dolphins per square kilometre) in order to estimate total population size. Unlike the biopsy study, we were allowed to see calves as well as adults. So there are no complications in terms of the survey counting only part of the population.

    Research using both genetics and ‘normal’ (visual) surveys indicates that the current population size used to be 1000 or more individuals. i.e. The Maui’s dolphin population has been seriously depleted and is currently only about 10% of its original size. This is a serious risk factor, in itself. A population of fewer than 100 dolphins (let alone fewer than 80) is very unlikely to pull through on its own.

    Just before anyone goes off on a tangent and concludes that the new population size estimate is ‘invalid’ and therefore we don’t need to worry about Maui’s dolphin, let me clarify: The new information is totally consistent with a very small population size, and may indicate a population decline. A population of 100 Maui’s dolphins (or 200 for that matter) would already be ample reason to be extremely cautious about their conservation. Several years ago, DOC and the IUCN listed Maui’s dolphin as Critically Endangered. That means, by definition, that they are at an extremely high risk of extinction. The IUCN has recently started listing subspecies and even individual populations that are not genetically distinct, because listing only entire species is not sufficiently sensitive. For example, I’m a member of an international expert panel advising on the conservation of the Taiwan population of humpback dolphins (Sousa chinensis). This species is widespread, throughout Asia. As a species, it is much more secure than Hector’s dolphin (which is only found in one country). But there are several individual populations of humpback dolphins that are at serious risk. The Taiwan population is one of those. Again, the IUCN has listed this population as Critically Endangered (even though, in this case there is no evidence that it’s genetically distinct from humpback dolphins in China). Basically, what the international science community is saying is that you can’t go eliminating one population after another and expect the species as a whole to survive. Anton van Helden made some similar comments in his response on 21 March (above).

    I’m struggling to think of a good analogy. But I’m always amazed about people who continue to smoke, even after they’ve had a leg amputated due to health impacts from smoking. Sure, they could keep going until they’ve lost both legs and both arms. But this doesn’t seem very rational. I don’t think anyone is suggesting that we can do without North Island Hector’s dolphin. This would be like saying we don’t mind about having lost North Island Takahe or South Island Kokako. Clearly both of these species would be a lot more secure if we still had the North and South Island subspecies. Clearly, we can’t just eliminate a species from large parts of its range and expect the species as a whole to continue as normal. So, assuming that New Zealand wants to save Maui’s dolphin, what would be the best way to achieve this?

    Thankfully, the answer to this question is simple. Several people have already pointed out that the area between the Maui’s dolphin population and South Island Hector’s dolphin populations is still unprotected. The Maui’s dolphin killed off Cape Egmont in January shows that any Maui’s dolphin that ventures south of the protected area (and any Hector’s dolphin that ventures north) is at a very high risk of fisheries mortality. Until Taranaki is added to the protected area, as proposed by the Minister of Fisheries, Maui’s dolphins are extremely unlikely to pull through. Likewise, protecting Tasman Bay and Golden Bay, on the north coast of the South Island, would help to provide a healthy population immediately south of the Maui’s dolphin’s distribution. This would make Maui’s dolphin much more secure. The Auckland Uni team have described this as ‘the need for protecting corridors’ within and between populations of Maui’s and Hector’s dolphins.

    Perhaps even more importantly, these dolphin deaths are totally avoidable. If the Ministry of Fisheries were to help fishermen make the change to selective, sustainable fishing methods, this problem could be solved almost overnight. This would benefit not only Hector’s and Maui’s dolphins but also seabirds (including yellow-eyed penguins, shags, shearwaters) and even the fishing industry itself. There is no long-term future for NZ fisheries if we continue to use fishing methods that cause a heavy impact on fish stocks as well as other marine species. The sooner we change to selective, sustainable fishing methods the better. This will have long-term economic benefits for the fishing industry as well as environmental benefits.

    Luckily, there is no need to ‘close’ areas to fishing. The only change needed is to stop using fishing methods known to kill dolphins and switch to fishing methods (already in widespread use) that are more selective – and sustainable in the long run.

    Mike also provided some pointers for journalists, eager to call any species the ‘largest’, ‘smallest’, ‘rarest’, ‘most intelligent’ etc. Most of your comments are correct. Technically, Hector’s dolphin is the ‘smallest and rarest marine dolphin species’. I have seen every possible variant on this theme (often in error), with people leaving out the word ‘marine’ or replacing the word ‘dolphin’ with ‘species’ or ‘mammal’ and pretty much every other possible version.

    The other contender for the ‘smallest marine dolphin’ title is the Tucuxi (now there’s a cool name!) also known as Sotalia fluviatilis. The Tucuxi is lighter (in weight) than Hector’s dolphin, but has a longer snout – so it’s slightly longer. This is a river dolphin in South America, that is also found on the open coast near the Amazon. I’ll leave it to you to decide whether ‘smallest’ means shortest or lightest.

    As Anton van Helden has already pointed out, the Vaquita is a porpoise, not a dolphin. It is very rare, but not quite as rare as the Yangtze River dolphin or Baiji which is thought to have recently gone extinct. The last (very intensive and extensive) survey for Baiji failed to see a single individual. The IUCN has not yet declared this species extinct. But this is likely to happen if future surveys also fail to see any Baiji.

    Thanks, Mike for your help in correcting some of these errors. By far the best source of erroneous information about Hector’s and Maui’s dolphins is the Seafood Industry Council’s website. It would take a couple of days to describe and correct all the mistakes. For example, I have seen repeated comments in the media confusing the number of OBSERVED dolphin deaths (reported by independent observers on fishing vessels) with the TOTAL number of dolphin deaths. Needless to say, this error has repeatedly been pointed out by DOC, MAF and others. But some people just keep saying it. In most areas, fewer than 10% of inshore fishing vessels carry observers, so the number of observed or reported dolphin deaths is the tip of the iceberg.

    Another, common ‘myth’ about Hector’s dolphin is that very little is known about them. There is actually far more known about Hector’s dolphins (including the North Island population) than about most other dolphin species. For example, there is only one other small cetacean for which a total population size estimate is available (the vaquita) and only two dolphin species for which a reliable survival rate estimate is available (bottlenose dolphins and orca – yes killer whales are actually ‘dolphins’).

    In a nutshell:

    • Maui’s dolphin (or North Island Hector’s dolphin) is Critically Endangered
    • Hector’s dolphin (the species as a whole) is Endangered
    • Dolphin mortality in gillnets and trawl fisheries is the number one threat identified in the Threat Management Plan (published by DOC and MAF after several years of consultation with fishing industry, iwi, NGOs, etc)
    • This problem can be solved easily and at little if any long-term economic cost by changing to selective, sustainable fishing methods

    Dr Liz Slooten, Otago University

  7. Mike

    Thanks so very much, Liz, for all that information! Lots there I hadn’t heard. I wish the media were paying attention to online discussions like this, because none of the complexities of the issue seem to be finding their way into newspapers.

    I agree with what you say, but would make one observation about using North Island and South Island takahe as an analogy for the Hector’s dolphin situation. We used to think that there was only one species of takahe, and the last survivors were living in the South Island. In fact Trewick (1996) revised takahe into two species (the extinct Notornis mantelli in the north, and N. hochstetteri in the south, each derived independently from pukeko in separate flightlessness events). What had been seen as a range reduction was upgraded to an actual species extinction.

    Range reductions, and even loss of genetic diversity, are ultimately reversible. Extinction isn’t. To extend your metaphor, being limbless is a qualitatively different thing from being dead!

    When we have limited conservation dollars (which are being cut every year, but that’s a different story) and we have to choose between species that are in immediate danger of extinction—no shortage of these in NZ—and those in danger of losing some genetic diversity, shouldn’t preventing extinction take priority? The reason I wrote the blog post is the media seem keen to portray Maui’s dolphin as an impending extinction event, whereas it’s actually a genetic-diversity loss. I agree it might be a bit much to ask conservation biologists to correct reporters: “Don’t use the word extinction, no species is going extinct here.”

    If we’re sloppy about treating subspecies as conservation units equal to species we could run into the same problems as under the Endangered Species Act in the USA; both the Northern Spotted Owl and the Dusky Seaside Sparrow, which became huge conservation causes, were “just” subspecies of a species that was not itself threatened. The ESA defines a “species” as a true taxonomic species, a subspecies, or, in the case of vertebrates, a “distinct population segment.” Which opens the floodgates, rather. (And, incidentally, why do vertebrates get special treatment?)

Leave a Reply

Your email address will not be published. Required fields are marked *