Weddell seal

Weddell seals measure about long and weigh . 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 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 . They gain around a day, and by 6–7 weeks old they can weigh around . ==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. 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. After dropping away from a breathing hole in the ice, the seals become negatively buoyant in the first , allowing them to dive with little effort. They hunt in different parts of the water column depending on prey availability. Weddell seals hunt in both pelagic and benthic-demersal habitats. 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 are opportunistic feeders, who 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. Weddell seals are top predators in the Antarctic. They have no natural predators when on fast ice. At sea or on pack ice, they are prey for the Antarctica's apex predators (killer whales and leopard seals) which prey primarily on juveniles and pups. 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. After six to seven weeks, pups are weaned and begin to hunt independently. Additionally, fast ice breeding grounds cause females to cluster in large aggregations, making it easier for males to control their harem. Copulation has only been observed to occur underwater, after the male approaches the female from the dorsal side. The female is often bitten on the neck by her partner if she tries to escape or terminate copulation. The seals are normally around six to eight years old when they first breed, but this can be much earlier for some females. Instead, they rely heavily on lanugo, a fine layer of hair on the surface of their skin, to keep warm. Studies also revealed high levels of enzyme activity in the muscles of newborn Weddell seals, suggesting that a primary thermoregulatory strategy of these seals includes muscle thermogenesis, or shivering. There have been recordings of Weddell seal vocalisations that are described as songs. Their songs consist of repetitive sequences of the same vocal elements, and they only vary slightly over time. Individual Weddell seals can each produce their unique song, but singing behaviour is not common. Vocalisations are also important in mother–pup Weddell seal interactions. Mother Weddell seals use vocalisations to call their pups from further distances when smell can no longer be used efficiently (Opzeeland et al., 2011). Pups also use higher, more urgent vocalisations when hungry to alert their mothers to feed. Weddell seals commonly produce ultrasonic vocalizations. However, the functional significance of these high-frequency sounds is yet unknown. ==Taxonomy==

Rice noted that the scientific name was misspelt in the past as L. weddelli and this synonym is no longer accepted, although it is still found commonly in the scientific literature before 1988. Weddell seals can be confused with other two phocids that share the same range: Ross seal (Ommatophoca rossii) and crabeater seal (Lobodon carcinophagus). ==Population status==

, Antarctica Weddell seals are the second most abundant species of Antarctic phocid, after the crabeater seal. The most recent estimate suggests a population of about 202,000 female seals, based on high-resolution satellite images from November 2011 that cover the full habitat range of the species. This number includes females only, as males are mostly underwater guarding their territories in November. There are likely to be fewer males than females, as the ratio skews towards females with increasing age. Previous estimates, with lower geographic coverage and thus relying more heavily on extrapolations, tended to be much higher, reporting numbers in the range of 800,000 or so. Because of the widespread distribution of Weddell seals, population assessments are difficult and expensive to conduct, and therefore infrequently undertaken. However, thanks to the availability of higher-resolution satellite imagery and crowdsourced data, future counts may be simplified with automated image recognition. ==Threats==

During the early periods of Antarctic exploration, Weddell seals suffered dramatic declines as they were hunted for food and oil. Populations have since recovered after the elimination of commercial sealing in the 1980s. Climate changes affecting the duration and the extent of the sea ice and nutrient availability could potentially reduce pups' survival and may have important implications for population growth rates. The fact that some populations breed on land (e.g., in South Georgia), could demonstrate the ability of the species to colonise different environments, although the extent of such plasticity is uncertain. In the past, the establishment of Antarctic research bases has caused a measure of disturbance to these seals. In January 1998 the Environmental Protection Protocol to the Antarctic Treaty was ratified, implementing environmental measures such as the banning of mining and oil drilling in Antarctica for at least 50 years, along with the banning of refuse disposal and the use of pesticides in the region. However, the disturbance effects of the increasing seasonal tourism in the Antarctic and Sub-Antarctic on Weddell seal behaviour, distribution, and foraging are still unknown. Currently, there are no reports of significant fisheries interactions. Although, the development of new fisheries in Antarctic waters, particularly one targeting the Antarctic toothfish, could have an impact on Weddell seal nutrition, and potential operational interactions should be considered in the management plans. ==Conservation status==

The Weddell seal is protected by the Antarctic Treaty and the Convention for the Conservation of Antarctic Seals (CCAS). It is classified as being of "least concern" by the IUCN. This species is not listed by CITES. == See also==