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Seals

by  Lloyd Spencer Davis

The story of New Zealand’s seals is the story of seals the world over – once numerous and widespread, they were hunted to near extinction, then protected, and are now making a recovery. At many sites around the coast, observant onlookers can watch these streamlined swimmers and divers in action.


New Zealand’s seals

Three species breed around New Zealand’s coastline and on its temperate and subantarctic islands. These are the New Zealand fur seal, the New Zealand or Hooker’s sea lion, and the southern elephant seal. A fourth, the leopard seal, is a frequent visitor. Leopard seals breed in the New Zealand-claimed sector of Antarctica, the Ross Dependency, along with Weddell seals, crabeater seals and Ross seals.

Seals of the savannah

Why are different seal groups named after lions, elephants and leopards? Male sea lions have dense hair around the neck and throat, like a lion’s mane. Male elephant seals have an enlarged curved fleshy snout, resembling an elephant’s trunk. And leopard seals have leopard-like spots as well as the jaws and teeth of a ferocious predator.

Near extinction

Seals played a significant role in the early New Zealand economy. They were an important source of food and skins for Polynesian settlers until depleted on accessible mainland coasts. Later, sealskin and oil were the first products exported to the northern hemisphere, after the first group of European sealers set up camp in remote Dusky Sound in 1792. The quest for seals drove much of the early European exploration of New Zealand’s southern and subantarctic regions. By 1830 the seals were close to extinction. However, enough survived for populations of each species to stage a slow recovery.

Origins

Seals evolved from land-based carnivores similar to bears, about 25 to 27 million years ago in the Oligocene period. This was long after the demise of the dinosaurs. All terrestrial vertebrates (land animals with backbones) can trace their beginnings to a moment when some lobe-finned fish walked up the banks of a muddy estuary and the evolution of their lives on land ensued. Yet the sea must have offered attractive pickings for any mammals that could venture back into it. Seals merely followed those that had already pursued such bounty: the whales, dolphins, manatees and dugongs. The earliest known seal fossils are from the eastern North Pacific.


Seal families

Some scientists place seals within the order Carnivora, and some in a separate order, Pinnipedia. But there is agreement that seals consist of three families:

  • Otariidae: fur seals and sea lions
  • Phocidae: ‘earless’ seals
  • Odobenidae: walruses.

In the past, there was greater diversity: for example, there were once another 13 species of walrus. Some evidence suggests that fur seals, sea lions and walruses are derived from bear-like ancestors, while the earless seals may have evolved from otter-like ancestors. Molecular studies, however, support the notion that all seals are descended from a common ancestor within the order Carnivora.

Adaptations to sea life

As with all marine mammals, adaptation to the aquatic environment has influenced the body shape of seals. They have become streamlined, their limbs have become flippers (the term Pinnipedia means ‘feather foot’ or ‘wing foot’), and they have a layer of fat to help insulate them in the water and to act as an energy reserve.

Life on land

Seals can be at sea for weeks at a time, sleeping, feeding, and travelling huge distances. But unlike dolphins or whales, they are tied to the land for breeding. They will also spend time on land at haul-out sites when not breeding.

Fur seals and sea lions

Fur seals and sea lions are known as otariid or ‘eared seals’. Of all the seals, they are thought to have evolved first, and yet are the least specialised for life in water. They have external earflaps and still walk on all four flippers when on land. In the water they propel themselves with their front flippers. The New Zealand fur seal and sea lion are examples of otariid seals.

Earless seals

Earless or phocid seals have no earflaps, which makes them more streamlined. They are unable to move their hind flippers under their bodies, so they move with a caterpillar motion on land. In water, they propel themselves with their hind flippers, and steer with their front flippers.

The phocid seals are more specialised for a life in water than eared seals: they dive deeper and for longer and, in males, the testicles are kept internally – a much warmer place when in chilly waters. In New Zealand the southern elephant seal and leopard seal are examples of phocid seals.


Adaptations for diving

Elephant seals and Weddell seals can go without breathing for well over an hour. During their dives Weddell seals may reach depths of 860 metres, while southern elephant seals have been known to go more than 1,500 metres down.

Storing oxygen

All life began in the sea. But despite having evolved originally from fish, land-based vertebrates face a major problem if they return to a life in the sea and act like a fish again. As air breathers, they cannot take up dissolved oxygen from water like a fish. So they can only dive for as long as they can store oxygen breathed in at the surface. Consequently, these animals developed special adaptations for storing oxygen. This was the case with the ancestors of seals.

In animals such as humans, oxygen is carried from the lungs to the body’s organs and muscles via the blood. But in a seal’s muscles there are much higher concentrations of a protein called myoglobin, which can also bind to oxygen. This turns its muscles into oxygen stores that can power the metabolism while it is diving. As well, compared to land-based mammals, seals have much more blood, a higher proportion of red blood cells, the ability to reduce their heart rates while diving, and much greater control over the distribution of blood within the body.

Water pressure

Diving to such extraordinary depths creates its own problems because of the enormous pressure. Humans are likely to suffer the bends from much shallower dives, and sometimes need treatment in a recompression chamber. But unlike us, seals do not use any air remaining within the lungs once they have dived to about 70 metres. The lungs collapse, and the seal relies on oxygen stores in the blood and muscle.


Seal watching

Where can you see seals in New Zealand? One hundred and fifty years ago there were so few places, you could have written the answer on the blunt end of a sealer’s club. Today, protected almost continuously since 1916, seals are making a remarkable comeback and there are many places to spot them – including Wellington’s Red Rocks and Sinclair Head, and various South Island sites.

Fur seals

In the South Island there is a fur seal colony at Kaikōura, at the tip of the peninsula and accessible by foot at low tide. Perhaps the most easily accessible site is at Ohau Point, 17 kilometres north of Kaikōura, where the seals are visible close to State Highway 1. At Cape Foulwind, on the West Coast near Westport, there is a viewing platform overlooking seals some 12 metres below. A scenic spot for seal watching is at Nugget Point in the Catlins, and on the Otago Peninsula there are several accessible places where seals sleep on the rocks, and pups frolic in tide pools. There are several seal colonies in the southern North Island, including Red Rocks, on the south coast near Wellington city, Turakirae Head, and Palliser Bay in the southern Wairarapa.

Keep your distance

Seals are more closely related to bears than we are. Adult male fur seals are highly territorial during the breeding season and will attack virtually anything that moves, if they think it threatens their access to the females. Seals might appear awkward on land, but over a short distance they can move a lot faster than we can. Their strong jaws, and teeth laced with vile bacteria, mean that a bite would be unforgettable.

Other seals

The best places to find New Zealand sea lions are the sandy beaches of the Otago Peninsula, such as Sandfly Bay and Allans Beach. You will mostly see the large, dark brown males, but increasingly there are some small, pale females among them.

Elephant seals are less readily spotted, but you might see one on the south-eastern coastline of the South Island, from Ōamaru south. Leopard seals are even less predictable, but each year one or two show up on beaches frequented by elephant seals and sea lions.


New Zealand fur seal

Distribution

New Zealand fur seals (Arctocephalus forsteri, or kekeno) are found around New Zealand and its offshore islands, and southern Australia. Excavation of midden sites shows that when Polynesians arrived about 1300 AD, fur seals became an important source of food. By the time Europeans arrived in the late 1700s the seals had been all but wiped out, save for colonies on the South Island’s sparsely inhabited south-western coast. The pale-faced sealers finished off the remaining few and severely depleted numbers on the Chatham Islands, Bounty Islands and subantarctic islands – all for their pelts and the oil rendered from their blubber.

On the tiny Bounty Islands, numbers went from 52,000 in 1800 down to five by 1831. There has been considerable recovery since: 16,000 were estimated there in 1980.

Food

Their prey is fish, cephalopods such as squid and octopus, and crustacea including krill. Most dives last one or two minutes. Fur seals will forage up to 200 kilometres beyond the continental slope, often diving as deep as 200 metres.

Breeding sites

The seals breed on steep boulder beaches with plenty of crevices and tidal pools. Their layer of fat and thick fur coats, which enable them to endure long periods in water, can cause overheating on land. Crevices provide shade, and tidal pools a place to cool off.

The dominant male mates with numerous females, so many males do not get a chance to breed in every season. They often have sites where they haul out (rest), away from the breeding colonies. These sites may become breeding colonies if females visit them.

Breeding

Adult males are the first to arrive at the breeding colonies, from late October to early November. They establish territories that they defend aggressively, and remain on land, fighting but not feeding, until mid-January. This inter-male competition has promoted the evolution of large males, weighing up to 185 kilograms (an average female weighs 40 kilograms).

Females arrive from foraging at sea in late November, and give birth to a single pup (conceived the year before) by early January. About eight days later she will mate – usually with the dominant male. The female does all the nurturing of the newborn. She stays with the pup constantly for about 12 days, then alternates between feeding at sea and suckling. As the pup grows, the mother needs more food to make enough milk. Pups are weaned in July or August, and the pregnant females go to sea to fatten once again. The young pups then head out to sea, coming ashore at times. Females start breeding at around four years.

Delayed implantation

After fertilisation, the embryo’s growth is suspended for two to four months. It then implants in the mother’s uterus, and development resumes. This enables females to give birth and then mate during the same episode ashore, while still allowing for a normal gestation of about nine months. The female can therefore recover from rearing one pup before developing the next. The pup’s birth is also synchronised with the female’s return to the breeding ground the next season.

Delayed development occurs in all New Zealand’s seals, and most likely in all seals. The longest known life span of a New Zealand fur seal is 15 years.


New Zealand sea lion

The New Zealand sea lion (Phocarctos hookeri) is also known as Hooker’s sea lion, and to Māori as whakahao. Its main food is fish and cephalopods such as squid and octopus.

Appearance

The males are much larger than fur seals and have a distinctive blunt nose. Dark brown, with a mane of thick hair about the neck and shoulders, they can tip the scales at over 400 kilograms. Females weigh about half that, and are creamy yellow.

Breeding sites

The main breeding grounds are in the Auckland Islands. A small number breed on Campbell Island, the Snares Islands and in isolated cases on the Otago coastline.

The sea lions like sandy beaches, of which there are plenty, but 95% of the population breeds on three beaches in the Auckland Islands. Such a concentration makes them vulnerable: in 1998 a mystery illness killed over half that year’s pups and perhaps 20% of the adults. A squid fishery, which started around the islands in the 1980s, has killed thousands of them in trawl nets, and continues to do so. They are the world’s most threatened sea lion species, with about 10,000 individuals remaining in 2015.

Little is known of where they used to breed. The sites were probably more widespread until the early 19th century when sealers, faced with dwindling catches of fur seals, began exploiting them. While sea lions have long hauled out (rested) along the Otago–Southland coastline, it is encouraging that females have also begun pupping on the Otago Peninsula and in the Catlins, on the South Otago coast.

When not breeding, sea lions can be found scattered around the coasts of the islands where they breed, but at any time a large part of the population will be away at sea.

Breeding

The breeding pattern of sea lions is very similar to that of fur seals, with males arriving in November to set up territories. Pregnant females arrive a month later, and mate 7–10 days after giving birth. Pups may be weaned anywhere from nine months to over a year. Females start mating at four years, and males later.

The maximum recorded age is 23 years for males and 18 for females.


Southern elephant seal

Known to Māori as ihupuku or ihu koropuka, the southern elephant seal (Mirounga leonina) feeds mainly on fish, squid and crustaceans, which they catch by diving to great depths. Adult males are identifiable by their large inflatable noses.

Breeding

These seals breed mainly on subantarctic islands and the Argentine coast, especially at Península Valdés. Within New Zealand’s territorial waters, the main breeding sites are Campbell Island and the Antipodes Islands, although isolated pupping occurs along the Otago coastline. Pups are usually born between September and October, and the mothers leave them after just three weeks. Females start breeding at about 4 years.

The maximum recorded age is 20 years, but the usual life span is 18 years for males and 10–13 years for females.

Natural selection for size

At up to 3,700 kilograms of quivering blubber, the male southern elephant seal is the world’s largest seal. There is intense competition for the sections of beach on which the females breed, and the adult males seem to regard fighting as just another form of communication. Consequently only a few, larger males mate with the females. This has produced strong selection for the characteristic most likely to ensure success: size.

Males can be up to 10 times heavier than females, which often weigh less than 400 kilograms (although at sites like South Georgia, near the Antarctic Peninsula, they may weigh up to 900 kilograms).


Leopard seal

The leopard seal (Hydrurga leptonyx, or pakaka) is a creature of the Antarctic pack ice. Immature seals in particular also frequent the waters around subantarctic islands as they migrate north during winter.

Vagrants haul out (rest) sporadically on New Zealand beaches, particularly along the Otago coastline. They are fearsome predators capable of killing penguins and even other seals with the same ease as the fish and krill they also take.

Appearance

The sleek leopard seal is distinguished by a square, solid head resembling that of Tyrannosaurus rex, an olive green back, and a pale belly with dark spots – like a leopard. Unusually for seals, the females are larger than the males, measuring up to 3.4 metres long, while males are around 3 metres. Weights vary from 300 to 500 kilograms.

Population and breeding

Largely protected from hunting by their isolation amongst the pack ice, leopard seals may number anything from a quarter to half a million worldwide.

They breed around Antarctica, including the Ross Dependency (the New Zealand-administered sector), along with Weddell seals, crabeater seals and Ross seals. Little is known of their breeding habits, but it seems that mating takes place in the water, and pups are born on the ice from November to December.


Hononga, rauemi nō waho

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How to cite this page: Lloyd Spencer Davis, 'Seals', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/seals/print (accessed 18 November 2019)

He kōrero nā Lloyd Spencer Davis, i tāngia i te 12 Jun 2006