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The Weddell seal (''Leptonychotes weddellii'') is a relatively large and abundant Earless seal, true seal with a Subantarctic, circumpolar distribution surrounding Antarctica. The Weddell seal was discovered and named in the 1820s during expeditions led by United Kingdom of Great Britain and Ireland, British Seal hunting, sealing captain James Weddell to the area of the Southern Ocean now known as the Weddell Sea. The Life history theory, life history of this species is well documented since it occupies fast ice environments close to the Antarctica, Antarctic continent and often adjacent to Antarctic bases. This is the only species in the genus ''Leptonychotes''.
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 landform, glacial movement and tidal action, may increase fluctuations in distributions.
Weddell seals return to fast ice colonies during the spring for birthing and Breeding in the wild, 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 Olfaction, olfactory smells, specialized Animal sound, vocalizations, 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 Genetics, genetic analyses of mating success have suggested how factors such as size, diving ability, site-specific experience enhances success in male Weddell seals. Additionally, fast ice breeding grounds cause females to cluster in large aggregations, making it easier for males to control his own Harem (zoology), 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 (zoology), Copulation has only been observed to occur under water, 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 are normally around six to eight years old when they first breed, but this can be much earlier for some females. Weddell seals undergo delayed Implantation (human embryo), implantation. The embryo is not embedded into the uterus until the beginning of Summer, austral summer, between mid-January and mid-February, allowing for birth under more favorable environmental conditions.
Juvenile Weddell seals (0–2 years old) have a high Mortality rate, mortality probability, whereas no differences can be found between the mortality rate of animals older than 2 years and that of adults (Hastings et al., 1999). Maximum lifespan of the species is estimated at least 25 years.
Weddell seals are the second most Abundancy index, 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.
Voices in the Sea - Sounds of the Weddell SealInformation on Weddell sealsAustralian Antarctic GovernmentBiology of Weddell seals Fun facts about Weddell seals
{{Taxonbar, from=Q313166 Lobodontins Pinnipeds of Antarctica Pinnipeds of South America Pinnipeds of Australia Mammals of Chile Mammals of South Australia Carnivorans of South America Least concern biota of Oceania Least concern biota of South America Mammals described in 1826 Taxa named by René Lesson Articles containing video clips
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 (dog), 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 show a counter-shaded coloration that varies from bluish-black to dark gray dorsally and to light gray/silver ventrally. Coats may change to shades of brown before the annual molt. Adult males usually bear scars, most of them around the genital region. Weddell seal pups are born with a lanugo of similar Coloration evidence for natural selection, coloration and they Moulting, moult after 3–4 weeks; later, they turn a darker color similar to that of adults. The pups are around half the length of their mother at birth, and Weight, 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).Behavior
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 landform, glacial movement and tidal action, may increase fluctuations in distributions.
Foraging
Weddell seals dive to Foraging, 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 Apex predator, top predators in the Antarctic. They eat an array of fish, bottom-feeding prawns, cephalopods and crustaceans. A Sedentary lifestyle, sedentary adult eats around 10 kg (22 lb) a day, while an active adult eats over 50 kg (110 lb) a day. Antarctic toothfish, Antarctic cod and Antarctic silverfish, silverfish constitute the majority of their diet. Cephalopods are common Predation, 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 Hunting, hunt in different parts of the water column depending on prey availability. Weddell seals hunt in both Pelagic zone, 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 Earless seal, phocids are known to be seabird predators, resulting in implications that penguin hunting is a learned behavior. There are recordings of four different penguin species being attacked by Weddell seals: gentoo penguins, 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 Whiskers, 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 in the wild, 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 Olfaction, olfactory smells, specialized Animal sound, vocalizations, 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 Genetics, genetic analyses of mating success have suggested how factors such as size, diving ability, site-specific experience enhances success in male Weddell seals. Additionally, fast ice breeding grounds cause females to cluster in large aggregations, making it easier for males to control his own Harem (zoology), 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 (zoology), Copulation has only been observed to occur under water, 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 are normally around six to eight years old when they first breed, but this can be much earlier for some females. Weddell seals undergo delayed Implantation (human embryo), implantation. The embryo is not embedded into the uterus until the beginning of Summer, austral summer, between mid-January and mid-February, allowing for birth under more favorable environmental conditions.
Juvenile Weddell seals (0–2 years old) have a high Mortality rate, mortality probability, whereas no differences can be found between the mortality rate of animals older than 2 years and that of adults (Hastings et al., 1999). Maximum lifespan of the species is estimated at least 25 years.
Vocalization
Male and female Weddell seals communicate through a variety of sounds, specifically males sometimes use “trills” to communicate. Weddell seals are also able to communicate to each other through different mediums. Weddell seals on ice are able to hear the calls of Weddell seals in the water as long as noise level on land is low and they are in close proximity of one another. Sound waves can be transmitted either through the ice itself or from water to breathing holes where female Weddell seals are usually breeding. There have been recordings of Weddell seal vocalizations 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 own unique song, but singing behavior is not common when observed. Vocalizations are also important in mother-pup Weddell seal interactions. Mother Weddell seals use Animal sound, vocalizations 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 vocalizations when hungry to alert their mothers to feed.Taxonomy
Rice noted that the scientific name was Spelling, misspelled in the past as ''L. weddelli'' and this synonym (taxonomy), synonym is no longer accepted, although it is still found commonly in the scientific literature prior to 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
Weddell seals are the second most Abundancy index, 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 Seal hunting, sealing in the 1980s. However, the effects of global climate change on Antarctic seals are still to be fully determined. Research estimates seal populations may decline as the availability of their habitat is extremely temperature sensitive thus making them potentially Vulnerable species, vulnerable. Climate changes affecting the duration and the extent of the sea ice and nutrients availability could potentially reduce pups’ survival and may have important implications for population Growth rate (group theory), growth rates. The fact that some populations breed on land (e.g., at South Georgia), could demonstrate an ability in the species to colonize different environments, although the extent of such Plasticity (physics), 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 behavior, distribution, and foraging are still unknown. Currently there are no reports of significant Fishery, 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 System, 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
*Warren ZapolReferences
External links
Voices in the Sea - Sounds of the Weddell Seal
{{Taxonbar, from=Q313166 Lobodontins Pinnipeds of Antarctica Pinnipeds of South America Pinnipeds of Australia Mammals of Chile Mammals of South Australia Carnivorans of South America Least concern biota of Oceania Least concern biota of South America Mammals described in 1826 Taxa named by René Lesson Articles containing video clips