Leptonychotes weddellii

The Weddell seal (Leptonychotes weddellii) is a relatively large and abundant true seal (family: Phocidae) with a circumpolar distribution surrounding Antarctica. Weddell seals have the most southerly distribution of any mammal, with a habitat that extends as far south as McMurdo Sound (at 77°S). It is the only species in the genus Leptonychotes, and the only member of the Antarctic tribe of lobodontine seals to prefer in-shore habitats on shore-fast ice over free-floating pack ice. Genetic evidence suggests that Weddell seal population numbers may have increased during the Pleistocene. Because of its abundance, relative accessibility, and ease of approach by humans, it is the best-studied of the Antarctic seals. An estimated 800,000 individuals remain today. A genetic survey did not detect evidence of a recent, sustained genetic bottleneck in this species, which suggests that populations do not appear to have suffered a substantial and sustained decline in the recent past. Weddell seal pups leave their mothers at a few months of age. In those months, they are fed by their mothers' warming and fat-rich milk. They leave when they are ready to hunt and are fat enough to survive in the harsh weather. The Weddell seal was discovered and named in the 1820s during expeditions led by James Weddell, the British sealing captain, to the parts of the Southern Ocean now known as the Weddell Sea. However, it is found in relatively uniform densities around the entire Antarctic continent. The Weddell seal shares a common recent ancestor with the other Antarctic seals, which are together known as the lobodontine seals. These include the crabeater seal (Lobodon carcinophaga), the Ross seal (Ommatophoca rossii), and the leopard seal (Hydrurga leptonyx). These species share teeth adaptations including lobes and cusps useful for straining smaller prey items out of the water. The ancestral Lobodontini likely diverged from its sister clade, the Mirounga (elephant seals) in the late Miocene to early Pliocene, when they migrated southward and diversified rapidly to form four distinct genera in relative isolation around Antarctica. Weddell seals measure about 2.5–3.5 m (8 ft 2 in–11 ft 6 in) long and weigh 400–600 kg (880–1,320 lb). Males weigh less than females, usually about 500 kg (1,100 lb) or less. Male and female Weddell seals are generally about the same length, though females can be slightly larger. However, the male seal tends to have a thicker neck and a broader head and muzzle than the female. A molecular genetic based technique has been established to confirm the sex of individuals in the laboratory. The Weddell seal face has been compared to that of a cat due to a short mouth line and similarities in the structure of the nose and whiskers. Their upturned mouths give them the appearance of smiling. The Weddell seal grows a thin fur coat around its whole body except for small areas around the flippers. The colour and pattern of the coat varies, often fading to a duller colour as the seal ages. This coat moults around the beginning of summer. Adults are generally brown, with lighter ventral (belly) pelage. They are mottled with large darker and lighter patches, those on the belly being silvery white. Adult males usually bear scars, most of them around the genital region. Young Weddell seals have gray pelage for the first 3–4 weeks; later, they turn a darker color. The pups reach maturity at three years of age. The pups are around half the length of their mother at birth, and weigh 25–30 kg (55–66 lb). They gain around 2 kg (4.4 lb) a day, and by 6–7 weeks old they can weigh around 100 kg (220 lb). Weddell seals are commonly found on fast ice, or ice fastened to land, and gather in small groups around cracks and holes within the ice. In the winter, they stay in the water to avoid blizzards, with only their heads poking through breathing holes in the ice. These seals are often observed lying on their sides when on land. They are very docile, placid animals that can be easily approached. Weddell seals are non-migratory phocids that move regionally to follow the distribution of breathing holes in the ice between seasons. Weddell seals dive to forage for food, maintain breathing holes in fast ice, and explore to find more ice holes. These seals exhibit a diurnal haul-out pattern. A higher frequency of seals haul out during the afternoon, usually around 4:00 PM, because of warmer air temperatures.