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Dolphins

by  Gerard Hutching

Most of the dolphin species that breed, feed and frolic in New Zealand waters can be found around the world. There have been some remarkable individuals – notably Pelorus Jack, who accompanied ships travelling between Wellington and Nelson, and Opo, the beloved bottlenose who let children ride on her back. There is also a species unique to New Zealand – Hector’s dolphin, and a subspecies, Māui’s dolphin. Fully protected by law, they are among the rarest of these intelligent, fascinating marine mammals.


Common dolphins

Dolphins belong to the family Delphinidae. This family belongs to the order Cetacea, which includes all whales and dolphins. In New Zealand there are 10 species and one subspecies of dolphin, the most prevalent being the dusky and the common dolphin. Hector’s dolphin is the only species confined to New Zealand waters. The bottlenose, although well known, has a relatively small local population. Other dolphins are occasional visitors. The larger members of the Delphinidae family, such as orcas, are commonly called whales because of their size; five of these are also found in New Zealand.

One of the less common but more unusual-looking dolphins takes its name from a whale. Like its namesake, the southern right whale dolphin lacks a dorsal fin.

All dolphins are totally protected under the Marine Mammal Protection Act 1972, administered by the Department of Conservation. The most significant conservation issue is the accidental catching of Hector’s and Māui’s dolphins in fishing nets.

Common dolphin

The short-beaked common dolphin (Delphinus delphis) is probably the most abundant in the world, although globally in decline. Most of the dolphins depicted in ancient Greek and Roman art are common dolphins.

This species has a tall dorsal fin and pale yellow side patches. It is found in coastal waters in New Zealand and elsewhere, as well as in deep waters of the Atlantic and Pacific. It is the most numerous dolphin around the New Zealand coast. It reaches 1.7–2.4 metres in length, and weighs 70–110 kilograms.

Squid and small schooling fish are its main food. Groups, or pods, range from several individuals to several thousand. Tourist operators searching for common dolphins are alerted to their presence by the mass feeding of gannets and terns on small schooling fish such as pilchards and saury. The birds take advantage of the bonanza when the dolphins herd the fish to the surface. In spring the dolphins and birds are sometimes joined by Bryde's and sei whales. As the whales cruise at speed through the massed fish, the dolphins ride their pressure waves.

In a survey carried out between 1962 and 1964, scientist David Gaskin discovered the largest concentrations in summer were from Kaikōura to Hawke Bay, although they were also abundant around the Hauraki Gulf and Northland. Winter sightings were confined mainly to Marlborough and points north.

An intensive survey off the West Coast in the summer of 1996–97 revealed them to be widespread and in good numbers. About a third of the groups, spotted in shallow waters, included calves; it is speculated that these nursery pods seek shelter from menacing deep-water sharks.

Females breed every two years, and calves suckle for six months. Their lifespan in the wild is unknown, but in 2004 two common dolphins at Marineland, Napier, were still alive 30 years after being captured.

Relative size

While male Hector's dolphins weigh only 40 kilograms, their testes tip the scales at 1.2 kilos. A human male, on the other hand, is much heavier, but his testes weigh only 40 grams.

Mixing with other species

Off Kaikōura, common dolphins cavort with dusky dolphins, fishing together and forming close bonds. Sometimes individuals of the two species can be seen caressing each other, clapping jaws and mating. Hybrids can result – with a common dolphin’s beak and a dusky’s stripe below the dorsal fin – but it is uncertain whether these offspring can reproduce.

Around Northland common dolphins occupy a separate niche to the bottlenose dolphins, and the two are almost never sighted together, even if they are sometimes separated by only a few kilometres. Like the bottlenose, in spring and summer the common dolphin plies the warm waters of the East Auckland Current for food, moving closer to the Bay of Islands in autumn and winter. In contrast, common dolphins off Whitianga stay closer inshore during summer but move further out in winter.


Dusky dolphins

Appearance

Dusky dolphins (Lagenorhynchus obscurus) are slightly smaller than common dolphins at 1.6–2.1 metres long and 50–90 kilograms in weight. They have tapered diagonal stripes along their side. Their main foods are krill, copepods and small fish. The average size of pods is 6–15, but groupings of several hundred or even thousands are often seen.

Breeding and lifespan

Breeding begins at 4–6 years, and after a gestation of about 11 months calving generally takes place in spring. The mother feeds her calf for 18 months. Dusky dolphins live for 30 years or more.

Distribution and population

Found in coastal and continental shelf areas around the southern hemisphere, dusky dolphins are the second most numerous species of dolphin around New Zealand. Their distribution is associated with the zone where subtropical and subantarctic waters converge, as it is at the boundary between warm and cool waters that food is most plentiful. They are most abundant from East Cape down to Kaikōura, and also occur as far east as the Chatham Islands. During winter a cool current which runs up as far as Gisborne encourages the dolphins north, but that is generally their natural northern limit.

In the 1970s duskies were reported at Taranaki and Tasman Bay; by the 1990s such sightings had stopped, although the dolphins are regularly seen in and outside Wellington Harbour and in the Marlborough Sounds. In summertime duskies venture further south along the West Coast and to Southland, Otago and Stewart Island; in 1973 a researcher estimated that about 5,000 surrounded Solander Island. Occasionally, enterprising pods brave the chill waters of the subantarctic Auckland Islands and Campbell Island.

There is a notable absence of dusky dolphins between the Conway River south of Kaikōura down to just north of the Otago Peninsula. The water in this area – including Pegasus Bay and the Canterbury Bight – is shallow, and does not attract duskies’ favoured prey.

Kaikōura is considered one of the best places in the world to see dusky dolphins in their natural environment. Each pod or group can number anything between 100 and 800; in autumn and winter this can increase into the thousands.

Killer instinct

During November 1995 scientists at Kaikōura saw four orcas hunting dusky dolphins over 11 days. Most of the observed kills were adults, but the orcas also attacked younger dolphins. A dusky dolphin was flicked 10 metres out of the water and an orca leapt up to seize it in mid-air. This was not an isolated event. The dolphins rely on their skill at fleeing and hiding to avoid being killed.

Distinctive New Zealand duskies

Compared to dusky dolphins off the Argentine coast (where they are the most studied in the world), the New Zealand duskies off the Kaikōura coast are distinctive in their behaviour and feeding. DNA studies by United States scientist Frank Cipriano suggest that they may be a separate species.

Dusky dolphins do not develop pair bonds, but instead the males compete for female attention. Females may mate with a number of different males within just a few minutes.

During late spring and summer the Kaikōura duskies spend the mornings inshore resting and socialising, but by late afternoon they move between 6 and 15 kilometres offshore. At this time, too, they show off their full repertoire of leaps and somersaults. In winter they spend more time in deep water.

There may be another purpose to moving inshore during summer: since calves are born at that time of year, the dolphins may be taking shelter in shallow bays to avoid a surprise attack by a shark or killer whale.


Hector’s and Māui’s dolphins

The small Hector’s dolphin (Cephalorhynchus hectori), named after the New Zealand scientist James Hector, is also known by its Māori names tutumairekurai and tūpoupou (to rise up). Restricted to New Zealand waters, it is found along parts of the South Island coast. The usual pod size is between 2 and 12, but sometimes larger. Māui’s dolphin (Cephalorhynchus hectori maui) is a northern subspecies. Also called the North Island Hector’s dolphin, Māui’s status as a separate subspecies was proposed by scientists in 2002.

Appearance

Both weigh around 50 kilograms and are 1.2–1.5 metres long, making them among the shortest of the world’s dolphins. They are black and grey with a mainly white belly, with a distinctive rounded black dorsal fin and a blunt rostrum (beak). To casual observers, Hector’s and Māui’s dolphins look alike. However, studies have shown that they have different sized beaks, the genital patches in the males are differently coloured, and Māui’s dolphins are significantly longer.

They feed on fish, squid and crustaceans. Females have one calf at intervals of 2–4 years or more. Their lifespan is about 20 years.

Distribution and population

The population of Hector’s dolphin was estimated at around 7,000 in 2013, with the largest group off the West Coast. The other main concentration is around Banks Peninsula, with smaller groups off Cloudy Bay in the Marlborough Sounds and in Te Waewae Bay, Southland. They are classified as a vulnerable species.

Māui’s dolphin is found off the North Island’s north-west coast, between Dargaville and New Plymouth. It once ranged as far south as Cook Strait and up to Ninety Mile Beach. Categorised as critically endangered, it is one of the rarest marine dolphin subspecies in the world. In 2010–11 it was estimated that there were only 48–69 Māui's dolphins over the age of one year.

Genetic studies show there is no mixing between these populations.

Brain boxes

The brain of a 38-kilogram Hector’s dolphin weighs 640 grams. This is 1.7% of its total body weight – one of the highest proportions in the animal kingdom. It is bettered only by the typical proportion for humans of 1.9 %. But to what extent a big brain means high intelligence is not well established.

Range

Like the other Cephalorhynchus dolphins (one off South Africa, two off South America and one off the Kerguelen Islands), Hector’s and Māui’s dolphins live inshore where they catch their preferred food and are less likely to be attacked by large sharks. The furthest away from the coast any have been recorded is 60 kilometres; mostly they stay within 10 kilometres.

Researchers believe that in the past, ancestral Cephalorhynchus dolphins left an evolutionary dispersal point – assumed to be off South Africa, home today of their cousin, the Heaviside’s dolphin. Following the sea current known as the West Wind Drift, a founding population arrived in New Zealand and evolved into a separate species with a stay-at-home lifestyle. Others established populations west and east of South America, and became respectively the Chilean dolphin and Commerson’s dolphin.

Shorter length, shorter life

Hector's dolphins do not live as long as others: the smaller the species, the shorter the lifespan. Out of more than 80 Hector's which have been dissected – some of them caught in fishing nets – the oldest recorded ages have been 19 years for a female and 20 for a male. Some individuals may live longer than this, but the ages are comparable to those recorded for other Cephalorhynchus species. By contrast, larger dolphins such as the bottlenose live to between 25 and 50 years. A dolphin’s age is estimated from the layers in a cross-section of tooth.

The threat from nets

Fishing is the most significant known threat to Māui’s and Hector’s dolphins. Trawl, drift and set nets are likely to entangle them. The dolphins cannot easily detect the nets, even when using echolocation (similar to sonar). This enables them to ‘see’ the hard parts of prey, or solid objects like rocks, but because nets are soft and flexible they do not bounce sounds back to the dolphin.

Echo world

Finding food and navigating under water by vision alone is tricky in murky water. Dolphins can use echolocation as well. They send out a stream of clicks and ‘read’ the echo that bounces back from hard surfaces, such as a rock wall or the taut swim bladder of a fish. This gives them information about size, density and distance.

In 2015 there were set-netting restrictions around parts of the North and South island coasts to protect Māui's and Hector's dolphins. In addition Banks Peninsula, Catlins Coast, Clifford and Cloudy Bay and Te Waewae Bay marine mammal sanctuaries had been created to protect Hector's dolphins, and the West Coast North Island Marine Mammal Sanctuary had been established to protect both Hector's and Māui's dolphins. 

Hector's dolphins are still caught off the Canterbury coast, outside the Banks Peninsula sanctuary. One solution is acoustic alarms, or pingers, which scare off a dolphin as it approaches a net. The pingers are placed at 100-metre intervals along a net, and are activated by a battery lasting 30 days.


Bottlenose dolphins

The bottlenose dolphin (Tursiops truncatus) has a long, blunt beak. The body is different shades of grey, darker above and lighter on the belly. Globally there is wide variation in size, from 2.4 to 4 metres, and in weight from 250 to 650 kilograms.

They live in all the temperate oceans of the world. Pod size can be from 2 to 60 or more. Fish and marine invertebrates are their main foods.

Females breed every 3–5 years, and calves suckle for approximately 2–3 years. They can live for 40 years or more.

Coastal and pelagic

Two global ecotypes (adapted to local ecological conditions) have been identified: pelagic (living mainly in the open ocean) and coastal. Elsewhere, the coastal dolphin is smaller than the pelagic, which can reach almost 4 metres. But New Zealand’s coastal dolphins are also generally about this size. Scientists are conducting a genetic comparison of coastal and pelagic bottlenose dolphins in different parts of the country to determine their genetic diversity.

In New Zealand there are three main coastal populations:

  • about 450 individuals mainly in the Bay of Islands, but moving from Doubtless Bay in Northland down to Tauranga
  • about 70 in Doubtful Sound, Fiordland
  • a group in the Marlborough Sounds, some of which may stray down to Westport.

Depending on the time of year, the Northland bottlenose can occupy significantly different habitats. During summer and autumn the dolphins move to the outer waters of the Bay of Islands to fish in the warm East Auckland Current, which sweeps in from the Tasman Front. At other times they stay fairly close to shore, in water with a mean depth of 23 metres (compared to 80 metres for common dolphins). Bottlenose dolphins rarely mix with other species.

The Fiordland group

The Doubtful Sound bottlenoses occupy a vastly different habitat to bottlenoses elsewhere. Not only is it much cooler in the fiords than at sea, but there is also a 3–4-metre layer of fresh water above the sea water.

Weather wise

How do Fiordland bottlenoses cope in winter, when a thin layer of ice sometimes covers the inner fiords for weeks? They move to the warmer outer reaches of the fiords and the open ocean, and do not produce their offspring until mid-summer. Tropical-dwelling bottlenoses give birth all year round, but in Fiordland they have to time calving for an optimum start in life.

These fiord-dwellers are a small group – 70-strong and practically closed: during seven years of observation (sometimes for more than 100 days a year) researchers never saw any individuals leaving the group, or newcomers entering it. As a result, the dolphins have developed extremely strong and long-lasting bonds.

Such behaviour – unique among bottlenose dolphins – is influenced by the ecology of the fiords. Food is not only scarce, it is also difficult to find. Survival depends on transferring information from one member to the other; cooperation and stable relationships are the key to continued existence.

Males tend to be more boisterous, competing for access to females by leaping high into the air. The Fiordland dolphins are larger than their tropical counterparts, following the general rule that the cooler the climate the bigger the animal. During autumn and winter they eat more in order to put on a thicker layer of protective blubber.


Humans and dolphins

Māori and dolphins

Many cultures have revered dolphins. The Greeks put people to death for killing them, and Māori often described them as taniwha, or water spirits.

The Ngātiwai people, who used to live on the Poor Knights, Great Barrier and Little Barrier, believed that dolphins acted as messengers in times of need, bearing news from the islands to the mainland. The tribes living around Cook Strait talked of Paneiraira, a taniwha that resembled a whale. It would help canoes cross the tricky strait between the North and South islands.

The taniwha Tuhirangi guided Kupe, the mythical Polynesian explorer, to New Zealand. Later, Kupe placed Tuhirangi at French Pass in the Marlborough Sounds, to guide canoes through the treacherous waters. Tuhirangi lives there in a cave called Kaikaiawaro.

In the mid-18th century a guardian dolphin accompanied Hinepoupou on her famous long-distance swim. Ngāti Kuia believe the dolphin was Kaikaiawaro, although other traditions believe it was Kahurangi. Hinepoupou, of the Ngāti Kuia tribe, had been abandoned by her husband and his brother on Kapiti Island, west of the North Island. She decided to swim to her father’s home on Rangitoto ki te Tonga, near D’Urville Island at the edge of the Marlborough Sounds – a distance of 80 kilometres across the northern approach to Cook Strait.

Friendly dolphins

In modern times, friendly dolphins – Pelorus Jack and Opo are the best known – have regularly made appearances around New Zealand’s coast. Throughout human history there have been stories of such sociable individuals; in the 21st century the media and the internet guarantee that such interactions have a high profile.

Pelorus Jack, the speedy Risso

In 1888 a 4-metre Risso’s dolphin escorted a steamer from the outer Marlborough Sounds towards Nelson. He became known as Pelorus Jack, and Māori naturally recognised him as the taniwha Tuhirangi. From then on until his disappearance in 1912, he accompanied ships for a distance of about eight kilometres to and from French Pass, the dangerous passage separating D’Urville Island from the mainland. If the dolphin had to choose between two boats he would pick the faster, and could easily outpace a vessel travelling at 30 kilometres per hour. At night his speeding outline would glow with phosphorescence from plankton in the water. He became so famous that his picture featured on the cover of the Illustrated London News. It was never established whether ‘Jack’ was male or female.

Backfire

The friendly dolphin Pelorus Jack was said to have been shot at from the ferry Penguin in the early 1900s. From then on, the story went, he would avoid it and ill luck followed the vessel. In 1909 the Penguin sank on the south Wellington coast with the loss of 75 lives, one of the worst maritime disasters in New Zealand history.

Opo, the friendly dolphin

Opo was a young female bottlenose dolphin who first came to notice in June 1955. Named after the town of Opononi on the Hokianga Harbour, she followed boats and was playful around people. Always alone, it seems she had become separated from her pod and may have sought human company as a substitute. She had a favourite among the local children, called Jill, whom she would pick up and take for short rides. Opo and her antics drew crowds of many hundreds to the tiny seaside town. As she grew used to human attention, Opo responded to cheers by increasing the complexity of her tricks and games. Her life was short, however; she died in March 1956, to the sorrow of the entire nation.

Dolphins in captivity

Dolphins which survive the stress of capture and are then held in oceanariums, may be subject to poor hygiene, sanitation and feeding. Even in better equipped institutions, it is said, they do not adjust to life in captivity, suffering high stress and boredom.

Napier’s Marineland, opened in 1965, managed to keep common dolphins, a difficult marine mammal to house. However, in September 2008 its last dolphin died. In May 2008. the government had rejected a petition asking that Marineland be allowed to replace its dolphins.

Communing with wild dolphins

Since the 1980s swimming with wild dolphins has become popular. Each year over 100 commercial tourism operators apply to the Department of Conservation for approvals to either watch or swim with dolphins, seals or whales.

The bottlenose dolphins in the Bay of Islands are the most popular for these activities, although dusky, common and Hector’s dolphins are also visited. Out of concern that the dolphins might be disturbed by this attention, a long-term study was undertaken. This showed that most dolphins are generally not interested in interacting with humans. Swimmers should enter the water off to the side, not in the dolphins’ path.


Ancient dolphins – the fossil record

New Zealand provides important clues to the evolution and ancestry of modern whales and dolphins (cetaceans), thanks to an abundant fossil record dating back to the Oligocene period of 24–34 million years ago.

Pakistan has the earliest fossils of cetaceans, dating from about 50 million years ago. These animals were probably at home both in shallow waters and on land.

Over the next 15 million years ancient cetaceans evolved into diverse forms, exploiting the rich resources in the sea. They had well-developed legs and were dependent on the land for breeding, but their long, whale-like heads were adapted to searching the ocean for food. These toothed animals had not yet evolved sonar hunting methods (like modern dolphins), or filter-feeding (like baleen whales).

The cetacean species recognisable to us appeared about 5 million years ago. Between 12 and 15 million years ago the first true dolphins emerged, and there were key changes to body shapes in all species before they took on their present-day appearance.

Explosion of species

New Zealand fossils have played a key role in unravelling the secrets of cetacean evolution during the crucial Oligocene period. This saw an explosion in the diversification of species, and the appearance of the first toothed whales. The trigger was a cooling of the climate and the opening of the Southern (Antarctic) Ocean, which led to the development of massive quantities of krill and other small crustaceans – the favoured prey of baleen whales.

New Zealand fossil sites

There are dolphin and whale fossils in limestone and other marine rocks at sites at Punakaiki, Karamea, north-west Nelson, Wairarapa, Hawke’s Bay, Taranaki, and the South Auckland coast. But nowhere compares to North Otago’s Waitaki River valley for such fossils, partly because of the geological stability of the region. The rocks are less compacted than in the rest of the country, so the ancient bones are better preserved.

Here the sea reached 70 kilometres inland from the present-day coastline. Whales and dolphins used these calm waters for breeding, and as they died, their carcasses became embedded in marine sediments that turned to rock. Millions of years later the rocks were uplifted above the sea and then began to erode, leaving the fossil bones exposed.

Fossil finds around New Zealand

From the rocks, more than 30 Oligocene species have been uncovered. Among the finds are:

  • a 34-million-year old baleen whale with characteristics of ancient and modern forms
  • a shark-toothed dolphin (so-called because of its large triangular teeth) which was part of a widespread but now extinct group. Scientists speculate it was an agile fish eater which may also have preyed on penguins.
  • a dolphin sporting a lance-like, 20-centimetre tusk. This fossil, closely related to the endangered Ganges River dolphin of India, is evidence that the ancestors of river dolphins were once widespread in the oceans.
  • a fragmentary fossil of a sperm whale from early in the Miocene Epoch (23–24 million years ago). The sperm whale belongs to one of the oldest living whale families.

Hononga, rauemi nō waho

More suggestions and sources


How to cite this page: Gerard Hutching, 'Dolphins', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/dolphins/print (accessed 15 October 2019)

Story by Gerard Hutching, published 12 Jun 2006, updated 1 Sep 2015