Leopard seal

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Leopard seal in Antarctica

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). Along with all of the other earless seals, it belongs to the family Phocidae. It is in the tribe of Lobodontini seals, and is the only species in the genus Hydrurga. The name hydrurga means "water worker" and leptonyx is the Greek for "small clawed". It is second only to the killer whale among Antarctica's top predators.

Description

The leopard seal has a distinctively long and muscular body shape, when compared to other seals. This species of seal is known for its massive head and jaws that allow it to be one of the top predators in its environment. A notable key feature of leopard seals are their counter-shaded coats. A counter-shaded coat is when the dorsal side of the coat is darker, than ventral side. So, in leopard seals they have a silver to dark gray blended coat that make up its distinctive "leopard" coloration. Whereas, the ventral side of the coat are paler in color- ranging from white to light gray. Females are slightly larger than the males. The overall length of this seal is 2.4–3.5 m (7.9–11.5 ft) and weight is from 200 to 600 kilograms (440 to 1,320 lb). They are about the same length as the northern walrus, but usually less than half the weight.

Its front teeth are sharp like those of other carnivores, but its molars lock together in a way that allows them to sieve krill from the water, in the manner of the crabeater seal.

Distribution

Leopard seal distribution

The leopard seal lives in the cold waters surrounding the Antarctic continent. Where most seals remain restricted within the pack ice throughout the year, some (mostly young animals) move further north in the austral winter to subantarctic islands and the coastlines of the southern continents. They are difficult to survey by traditional visual techniques because they spend long periods of time vocalizing under the water during the austral spring and summer - when visual surveys are carried out. This trait of vocalizing underwater for long periods however has made them available to acoustic surveys. Leopard seals are solitary and widely distributed throughout the pack ice. Higher densities of leopard seals are seen in the Western Antarctic than in other regions.

While solitary animals may appear on areas of lower latitudes, females rarely breed there.

Behavior

Acoustic behavior

Leopard seals are very vocal underwater during the austral summer. The male seals produce loud calls (153 to 177 dB re 1 μPa at 1 m) for many hours each day. While singing the seal hangs upside down and rocks from side to side under the water. Their back is bent, the neck and cranial thoracic region (the chest) is inflated and as they call their chest pulses. Adult male leopard seals have only a few stylized calls, some are like bird or cricket-like trills yet others are low haunting moans. The leopard seals have age-related differences in their calling patterns, just like birds. Where the younger male seals have many different types of variable calls - the adult male seals have only a few, highly stylized calls. Each male seal produces individually distinctive songs. They arrange their few call types into individually distinctive sequences (or songs). The acoustic behavior of the leopard seal is believed to be linked to their breeding behaviour. In male seals, vocalizing coincides with the timing of their breeding season, which falls between November and the first week of January; captive female seals vocalize when they have elevated reproductive hormones.

Breeding and habits

The females give birth to a single pup during the austral summer on the floating ice floes of the Antarctic pack ice, and protect their pups until they are able to fend for themselves.

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 leopard seal bringing live, injured, and then dead penguins to him, possibly in an attempt to teach the photographer how to hunt.

Foraging behavior

Leopard seal yawning

The leopard seal is second only to the killer whale among Antarctica's top predators. Its canine teeth are 2.5 cm (1 in). It feeds on a wide variety of creatures. Young leopard seals probably eat mostly krill, squid, and fish. Adult seals probably switch from krill to more substantial prey, including king, adelie, rockhopper, gentoo, emperor, and chinstrap penguins, and less frequently, Weddell, crabeater, Ross, and young Southern elephant seals. Leopard seals have also been filmed eating fur seal pups.

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 taken as prey.

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 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 tearing and ripping it into smaller pieces.

Attacks on humans

Comparison of the size of a leopard seal (average size of 2.4–3.5 m (7.9–11.5 ft)) and a human (assumed height of 1.82 m (6 ft)).

Leopard seals are potentially highly dangerous towards humans, but attacks are rarely reported. Examples of aggressive behavior, 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. The "sea leopard", 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, Frank Wild, 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 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.