Leopard seal

Name and taxonomy

The French zoologist Henri de Blainville described the species in 1820 as Phoca leptonyx. He worked from a stuffed skin in Le Havre, which had come from the seas around the Falkland Islands. He could not find the ear opening, and he thought the head looked like that of a monk seal. Johannes Gistel created the genus Hydrurga in 1848. The leopard seal is the only species in that genus, and it has no subspecies.

The common name comes from the spotted coat. GBIF lists only two English names, leopard seal and sea leopard. Blainville believed that his new species was the animal that southern sailors called the sea calf.

Evolution and relatives

The leopard seal is a true seal of the family Phocidae, in the order Carnivora. Like all true seals it has no outer ear flaps, only an ear canal that opens on the skin. The Ross, crabeater and Weddell seals are its nearest relatives. Together they form the tribe Lobodontini, the Antarctic seals. The name of the tribe refers to their lobed cheek teeth, which lock together to sieve krill.

The crabeater seal shares this sieve, but the leopard seal adds large canines for big prey. Fossils show that leopard seals reached South Africa in the Late Pleistocene. It swims with its long front flippers, in the way that sea lions do, which is unusual for a true seal.

Appearance

The leopard seal has a longer and more muscular body than other seals. Adults measure 300 to 380 centimetres, and males weigh about 300 kilograms while females reach 500 kg. Wikipedia gives a wider spread of 2.4 to 3.5 metres and 200 to 600 kg. Females can be up to 50% larger than males. That makes the leopard seal as long as a walrus but usually under half its weight.

The head is large and narrow, with a long snout and a very wide gape. Many people say it looks like a reptile. The canine teeth reach 2.5 cm, and the cheek teeth carry three sharp cusps each. The whiskers are short and clear. The front flippers are very long for a true seal, and the body tapers quickly behind the chest.

The coat is dark grey on the back and silver to pale grey on the belly. Dark spots and blotches cover the back, and the belly is heavily spotted too. A thick blubber layer keeps the seal warm and gives the body a smooth outline for fast swimming. A newborn pup measures about 120 cm and weighs around 30 kg.

Habitat and range

The leopard seal is an ice-loving species of the Antarctic pack ice, between about 50 and 80 degrees south. Densities are highest in West Antarctica. Most animals stay within the pack ice all year. Satellite tags show them moving north as the ice grows in autumn and south again as it melts in spring.

In the southern winter, mothers with pups may move north to sub-Antarctic islands and southern coasts. A population appears to live and breed in Patagonia. Seasonal visitors and vagrants reach South Georgia, Kerguelen, Heard, Macquarie and the Falkland Islands. Single animals have turned up in Western Australia, New Zealand, Argentina, Brazil, Uruguay, South Africa and Easter Island. GBIF holds records from 20 countries, which include these wanderers.

The seal spends most of its time in the water, hunting near the surface. It hauls out on ice floes, icebergs and beaches to sleep. At Bird Island, South Georgia, seals even sleep in kelp beds with their heads above the water. One female, Owha, lived around New Zealand's North Island for a decade, from 2012 until at least 2022.

Diet and hunting

The leopard seal has the widest diet of any Antarctic seal. Young seals eat mostly krill, squid and fish. Adults add penguins, including emperor, king, Adelie, gentoo and chinstrap penguins. They also kill young crabeater, Weddell and Ross seals, elephant seal pups and fur seal pups. Around South Georgia the Antarctic fur seal is the main prey, taken mostly from late December to mid-February.

To catch a penguin, the seal waits almost submerged near the edge of the ice. It grabs the feet of a swimming bird, then shakes it and beats it on the water surface until it dies. It cannot cut meat into pieces, so it thrashes the carcass from side to side to tear it apart. Old reports that it skins a penguin before eating are wrong.

Krill is taken by suction and strained out through the locking cheek teeth. This lets one animal switch between big prey and tiny prey as the season changes. Most dives are shallow, but the seal can go deeper than 80 metres, and the longest known dive lasted about 15 minutes. It collapses its lungs on a deep dive and reinflates them at the surface. Vagrants in New Zealand have eaten elephantfish, ghost sharks and spiny dogfish.

Behaviour and social life

The leopard seal lives alone. The only lasting bond is between a mother and her pup, and it ends at weaning. During surveys, adults seen near one another showed no interaction at all. Seals gather more densely on the pack ice in the breeding season and when pups are born.

In the water the seal is fast and agile, steering with its big front flippers. On ice and land it moves clumsily. It sleeps on floes, on beaches and among kelp. It keeps to open water and does not travel far under solid ice, as Weddell seals do.

A juvenile can hold its breath for only about 7 minutes, so it cannot reach deep winter krill. That may explain the rare cases of two seals hunting fur seal pups together. One female brought live, injured and then dead penguins to a photographer over four days, as if to feed him. Leopard seals also bite the black pontoons of inflatable boats, so researchers fit guards to them.

Communication and senses

Leopard seals hear in air about as well as a person does. Underwater they use hearing and their whiskers together to track prey. Most sightings come from acoustic surveys, because the seals call underwater through the southern spring and summer.

Males sing underwater for many hours each day in summer, at 153 to 177 decibels. A singing male hangs upside down, arches his back, inflates his chest and rocks from side to side. Scientists recognise five male sounds: a high double trill, a medium single trill, two low trills and a hoot. Each male strings his few calls into his own sequence, like a song. Young males have many variable calls, while mature males keep a few fixed ones, as in some birds.

The songs are thought to mark out space between males and to draw females. Captive females call when their breeding hormones rise. A mother also calls to get the attention of her pup when she returns from feeding.

Reproduction and life cycle

Much of the breeding cycle is unknown, because the pack ice is hard for people to reach. The system is polygynous, and one male mates with several females. Mating takes place in the water from December into early January, soon after the pups are weaned. Males become fertile at about 3 to 6 years and females at 2 to 7 years.

Pregnancy averages 274 days, and the embryo pauses for 2 months before it implants. The mother digs a round hollow in the ice for the pup. One pup is born in November or early December on the floating pack ice. It weighs about 30 kg at birth and measures about 120 cm. The mother nurses it on an ice floe for about 4 weeks, and then it is on its own.

The father plays no part and returns to his solitary life after mating. About 25% of pups die in their first year. Survey voyages found about one pup for every three adults in November and December. A wild leopard seal probably lives about 26 years, and the record is 30. One wild-born animal died in captivity at about 17.3 years.

Predators and threats

No animal other than the orca hunts an adult leopard seal. Even so, orcas rarely eat leopard seals. Vagrants in Australia and New Zealand carry wounds from stingrays, chimaeras and cookiecutter sharks.

People pose no direct threat today, and no hunting takes place. Early explorers killed a few for food and for their sled dogs. Soviet sealers took about 650 in an experimental harvest in 1986 and 1987. The Convention for the Conservation of Antarctic Seals now protects the species from harvest.

The larger worries are indirect. Shrinking pack ice would remove the platform on which the seal gives birth and nurses. Commercial krill fishing competes for its main prey. Tourism, tangling in marine debris and canine distemper virus add further risks.

Population and conservation

The IUCN gives the species the code LC, Least Concern. Estimates of the world population range from 220,000 to 440,000 animals. A 2012 survey gave 35,000, which the IUCN considers a serious undercount. The trend is unknown, but nothing points to a decline.

Counting these seals is hard and costly, because they are spread across the pack ice and spend long periods underwater. Visual surveys miss them in spring and summer, when they are busy calling below the surface. Acoustic surveys, of the kind used for whales, now give most of what is known about their numbers.

In New Zealand waters the Marine Mammals Protection Act protects the species. Australia's Taronga Zoo kept three rescued vagrants, Brooke, Sabine and Casey, between 1999 and 2014. They were not released, for fear of carrying disease back to the wild population.

Relationship with humans

Few people ever meet a leopard seal, and attacks on humans are rare. Most of its fierce reputation comes from the early days of Antarctic exploration. In Shackleton's expedition of 1914 to 1917, a seal about 3.7 metres long and 500 kg chased Thomas Orde-Lees across the ice. Frank Wild shot it to save him. In 1985 a seal bit the explorer Gareth Wood twice and tried to drag him into the sea.

In 2003 the biologist Kirsty Brown died while snorkelling near Rothera Research Station. A leopard seal dragged her down to about 70 metres and held her under for about six minutes. It was the first recorded human death caused by the species. An expert at the inquiry suggested the seal took her for a fur seal or attacked in fright. In 2021 a seal harassed three spearfishers off Simon's Town in South Africa for half an hour and bit them.

Researchers and tourists now keep a distance from the seals and armour their boats. The species is used in science and education, and it has no known economic harm. More people in Antarctica may bring more encounters.

In culture and myth

No people ever lived in Antarctica, so traditional myth has little to say about the leopard seal. The selkie stories of Scotland and Ireland concern northern seals, not this species. Spirit-animal writers read it as a sign of strength, independence and survival, but that reading is probably modern.

Its cultural life began with the explorers' journals. The story of the sea leopard that chased Orde-Lees became one of the famous episodes of Shackleton's expedition. Nature films later seem to have fixed its image as the penguin's chief enemy. Paul Nicklen's photographs of a female offering him penguins showed a gentler side and spread widely. In New Zealand the seal Owha carries a Maori name that means a gift from my ancestors.