The leopard seal (Hydrurga leptonyx), also referred to as the sea leopard, is the second largest species of seal in the Antarctic (after the southern elephant seal). It is most common in the Southern Hemisphere along the coast of Antarctica and on most sub-Antarctic islands, but can also be found on the coasts of southern Australia, Tasmania, South Africa, New Zealand, Lord Howe Island, Tierra del Fuego, the Cook Islands, and the Atlantic coast of South America. It can live 26 years, possibly more. Orcas and large sharks are the only natural predators of leopard seals.
Along with all of the other earless seals, it belongs to the family Phocidae, and is the only species in the genus Hydrurga. The name hydrurga means "water worker" and leptonyx is the Greek for "small clawed".
The leopard seal is large and muscular, with a dark grey back and light grey on its stomach. Its throat is whitish with the black spots that give the seal its common name. Females are slightly larger than the males. The overall length of this seal is 2.4–3.5 m (8.4–11.7 ft) and weight is from 200 to 600 kilograms (440 to 1,300 lb). They are about the same length as the northern walrus, but usually less than half the weight.
The leopard seal lives in the cold waters surrounding Antarctica. During the summer months, it hunts among the pack ice surrounding the continent, spending almost all of its time in the water. In the winter, it ranges north to the sub-Antarctic islands. Occasionally, individuals may be spotted on the southern coasts of Argentina, Chile, Australia, and New Zealand, and as far north as the Cook Islands. Juveniles are more often found in the north.
The leopard seal is a solitary creature and comes together in small groups only when it is time to mate. During the mating season, males and females make acoustic calls to each other over distances, with at least the males having individual variability in their vocalising sequence patterns. After a 9-month gestation, the female digs a hole in the ice, and gives birth to a single pup during the Antarctic summer. She protects the pup until it is able to fend for itself.
Leopard seals are not very vocal, although they occasionally make some grunting and growling noises.
The leopard seal is bold, powerful and curious. In the water, there is a fine line between curiosity and predatory behaviour, and it may 'play' with penguins it does not intend to eat. There are also records of leopard seals attacking divers. Paul Nicklen, a National Geographic magazine photographer, captured pictures of a to him, possibly in an attempt to teach the photographer how to hunt.
The leopard seal is second only to the killer whale (orca) among Antarctica's top predators. Its canine teeth are 2.5 cm (1 in). It feeds on a wide variety of creatures. Smaller seals probably eat mostly krill, but also squid and fish. Larger leopard seals probably switch from krill to more substantial prey, including king, adelie, rockhopper, gentoo, emperor penguins and chinstraps, and less frequently, other seals, such as crabeater seal.
Around the sub-Antarctic island of South Georgia, the Antarctic fur seal (Arctocephalus gazella) is the main prey. Other prey include penguins and fish. Antarctic krill (Euphausia superba), southern elephant seal (Mirounga leonina) pups and seabirds other than penguins have also been found in leopard seal scats in small quantities.
When hunting penguins, the leopard seal patrols the waters near the edges of the ice, almost completely submerged, waiting for the birds to enter the ocean. It is helped in this endeavour by the penguins themselves, which nearly always push one of their own into the water ahead of themselves. It kills the swimming bird by grabbing the feet, then shaking the penguin vigorously and beating its body against the surface of the water repeatedly until the penguin is dead. Previous reports stating the leopard seal skins its prey before feeding have been found to be incorrect. Lacking the teeth necessary to slice its prey into manageable pieces, it flails its prey from side to side to tear and rip it into smaller pieces.
The leopard seal is classified under the family Phocidae. Its closest relatives are the Ross seal, crabeater seal and the Weddell seal, which together are known as the lobodontine seals. All these seals descend from the superfamily Pinnipeda, which evolved from bear-like ancestors. They have diverged from other taxa in the order Carnivora.
The leopard seal has many features analogous to other species. For example the forearm and hand bones are similar in structure to those found in many mammal, reptile, and bird species. However, in the leopard seal, the fingers are covered in a web of skin, which they use to propel themselves through the water.
The leopard seals share homologous features with its close relatives, the lobodontine seals. They all have dark fur on the tops of their bodies and lighter fur on their underbellies. Though the colors vary between these species, the colored fur serves the same function, which is camouflage against predators and as it stalks its prey.
Attacks on humans
Leopard seals are potentially highly dangerous towards humans, but attacks are rarely reported. Examples of aggressive behaviour, stalking and attacks have been documented. Notable incidents include:
- A large leopard seal attacked Thomas Orde-Lees (1877–1958), a member of Sir Ernest Shackleton's Imperial Trans-Antarctic Expedition of 1914–1917 when the expedition was camping on the sea ice. A large "sea leopard" of about 12 ft (3.7 m) long and 1,100 lb (500 kg) chased Orde-Lees on the ice. He was saved only when another member of the expedition shot the animal.
- In 1985, Scottish explorer Gareth Wood was bitten twice on the leg when a leopard seal tried to drag him off the ice and into the sea. His companions managed to save him by repeatedly kicking the animal in the head with the spiked crampons on their boots.
- In 2003, a leopard seal dragged snorkeling biologist Kirsty Brown of the British Antarctic Survey nearly 200 ft (61 m) underwater to her death, in what was identified as the first known human fatality from a leopard seal.
Leopard seals have shown a particular predilection for attacking the black, torpedo-shaped pontoons of rigid inflatable boats, necessitating researchers to equip their craft with special protective guards to prevent them from being punctured.
Notes and references
- Wozencraft, W. C. (2005). "Order Carnivora". In Wilson, D. E.; Reeder, D. M. Mammal Species of the World (3rd ed.). Johns Hopkins University Press. ISBN 978-0-8018-8221-0. OCLC 62265494. http://www.bucknell.edu/msw3/browse.asp?id=14001042.
- Southwell, C. (2008). Hydrurga leptonyx. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 28 January 2009.
- "Leopard Seal Description & Characteristics". The Antarctic Connection. http://www.antarcticconnection.com/antarctic/wildlife/seals/leopard.shtml. Retrieved 2007-12-10.
- Hill, Anna. (2013) Hydrurga leptonyx. Animal Diversity Web. Accessed February 24, 2013.
- Tunstall, T. "Hydrurga leptonyx". Animal Diversity Web. University of Michigan Museum of Zoology. http://animaldiversity.ummz.umich.edu/site/accounts/information/Hydrurga_leptonyx.html. Retrieved 2009-04-27.
- Nowak, Ronald M (2003). Walker's Marine Mammals of the World. Johns Hopkins University Press: Baltimore, MD.
- Leopard Seals, Hydrurga leptonyx. marinebio.org
- Rogers, Tracey L. and Cato, Douglas H. (2002). "Individual Variation in the Acoustic Behaviour of the Adult Male Leopard Seal, Hydrurga leptonyx". Behaviour 139 (10): 1267–1286. doi:10.1163/156853902321104154. JSTOR 4535987.
- Kindersley, Dorling (2001,2005). Animal. New York City: DK Publishing. ISBN 0-7894-7764-5.
- Walker, T.R., Boyd, I.L., Mccafferty, D.J., Huin, N., Taylor, R.I., Reid, K. (1998). "Seasonal occurrence and diet of leopard seals (Hydrurga leptonyx) at Bird Island, South Georgia". Antarctic Science 10 (1): 75–81. doi:10.1017/S0954102098000108. http://www.researchgate.net/publication/231850677_Seasonal_occurrence_and_diet_of_leopard_seals_%28Hydrurga_leptonyx%29_at_Bird_Island_South_Georgia.
- Carrington, Damian (2003-07-24). Inquiry into fatal leopard seal attack begins. NewScientist.com. Retrieved on 2013-02-24.
- Owen, James (August 6, 2003). "Leopard Seal Kills Scientist in Antarctica". National Geographic Society. http://news.nationalgeographic.com/news/2003/08/0806_030806_sealkiller.html. Retrieved 2007-12-10.
- Rogers, Tracey L. (2002). Leopard Seal. In William F. Perrin, Bernd Würsig & J.G.M. Thewissen eds. Encyclopedia of Marine Mammals San Diego: Academic Press. 692–693.
- National Geographic Magazine, November 2006 Leopard Seals
- King, Judith E. (1975). Seals leopard on Lord Howe Island. Journal of Mammalogy, 56(1), pp. 251–252
- Saundry, Peter. (2010) http://www.eoearth.org/wiki/Leopard_seal Leopard Seal]. Encyclopedia of Earth. Topic ed. C.Michael Hogan, ed. in chief Cutler Cleveland, NCSE, Washington DC