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Weddell Seal Science Biography & Facts

The Weddell seal (Leptonychotes weddellii) is a relatively large and abundant true seal with a circumpolar distribution surrounding Antarctica. The Weddell seal was discovered and named in the 1820s during expeditions led by British sealing captain James Weddell to the area of the Southern Ocean now known as the Weddell Sea. The life history of this species is well documented since it occupies fast ice environments close to the Antarctic continent and often adjacent to Antarctic bases. It is the only species in the genus Leptonychotes. Description 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). They are amongst the largest seals, with a rather bulky body and short fore flippers relative to their body length. 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. 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 vary, often fading to a duller colour as the seal ages. This coat moults around the beginning of summer. Adults show a counter-shaded colouration that varies from bluish-black to dark grey dorsally and to light grey/silver ventrally. Coats may change to shades of brown before the annual moult. Adult males usually bear scars, most of them around the genital region. Weddell seal pups are born with a lanugo of similar colouration and they moult after 3–4 weeks; later, they turn a darker colour similar to that of adults. 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). Behaviour Movements 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. Weddell seals are non-migratory phocids that move regionally to follow the distribution of breathing holes and exit cracks within the ice changes between seasons. The species is primarily restricted to Antarctic waters: physical factors, such as glacial movement and tidal action, may increase fluctuations in distributions. Foraging Weddell seals dive to forage for food, maintain breathing holes in fast ice, and explore to find more ice holes. They have been observed to dive as deep as 600 m for up to an hour. These seals exhibit a diel dive pattern, diving deeper and longer during the day than at night. After dropping away from a breathing hole in the ice, the seals become negatively buoyant in the first 30 to 50 m, allowing them to dive with little effort. Weddell seals are top predators in the Antarctic. They eat an array of fish, bottom-feeding prawns, cephalopods and crustaceans. A sedentary adult eats around 10 kg (22 lb) a day, while an active adult eats over 50 kg (110 lb) a day. Antarctic cod and silverfish constitute the majority of their diet. Cephalopods are common prey, and crustacean remains are sometimes found in Weddell seal scat, but at much lower rates than other prey species. They are opportunistic feeders that hunt in different parts of the water column depending on prey availability. Weddell seals hunt in both pelagic and benthic-demersal habitats. Although seabirds are not usually part of their diet, there have been several sightings of them chasing and killing penguins in the wild. Other Antarctic phocids are known to be seabird predators, resulting in implications that penguin hunting is a learned behaviour. There are recordings of four different penguin species being attacked by Weddell seals: a gentoo penguin, an emperor penguin, an Adélie penguin, and a chinstrap penguin. It has not been confirmed, however, if the penguins were consumed after being killed. Scientists believe Weddell seals rely mainly on eyesight to hunt for food when there is light. However, during the Antarctic winter darkness, when there is no light under the ice where the seals forage, they rely on other senses, primarily the sense of touch from their vibrissae or whiskers, which are not just hairs, but very complicated sense organs with more than 500 nerve endings that attach to the animal's snout. The hairs allow the seals to detect the wake of swimming fish and use that to capture prey. Weddell seals have no natural predators when on fast ice. At sea or on pack ice, they are prey for killer whales and leopard seals, which prey primarily on juveniles and pups. Breeding Weddell seals return to fast ice colonies during the spring for birthing and breeding. Weddell seal populations will often return to the same breeding sites over consecutive breeding seasons. Depending on the latitude it inhabits, this marine mammal gives birth from early September through November, with those living at lower latitudes giving birth earlier. Weddell seals usually give birth to one pup per year, however the Weddell seal is one of the only species of seals that can give birth to twin pups. Birthing of the pup takes only one to four minutes. Newborn pups weigh about 25–30 kg and grow to two times their weight within their first week of life. The pups take their first swim around one to two weeks of age. During the first two weeks, mother Weddell seals distinguish their pups through olfactory smells, and specialised vocalisations, and stay in the same spatial area. After six to seven weeks, pups are weaned and begin to hunt independently. Weddell seals show moderate polygyny and genetic analyses of mating success have suggested how factors such as size, diving ability, and site-specific experience enhance success in male Weddell seals. Additionally, fast ice breeding grounds cause females to cluster in large aggregations, making it easier for males to control their harem. The mating season occurs during austral spring between late November and December after pups are weaned and females begin ovulating. During the mating season, Weddell seals make noises loud enough to be felt through the ice. Males defend underwater territories during the breeding season and have been observed to fight. Copulation has only been observed to occur underwater, where the female submits to the male as he approaches her dorsal side. The female is often bitten on the neck by her partner if she tries to escape or terminate copulation. The seals ar.... Discover the Weddell Seal Science popular books. Find the top 100 most popular Weddell Seal Science books.