Weddell seal

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Weddell seal
Mikkelsen Harbour-2016-Trinity Island (D'Hainaut Island)-Weddell seal (Leptonychotes weddellii) 03.jpg
At the D'Hainaut Island, Mikkelsen Harbour, Trinity Island
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Clade: Pinnipedia
Family: Phocidae
Genus: Leptonychotes
Gill, 1872
Species:
L. weddellii
Binomial name
Leptonychotes weddellii
(Lesson, 1826)
WeddellRange 1.PNG
Weddell seal range
  Water
  Ice
  Range

The Weddell seal [2] (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. [3] 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. [4] It is the only species in the genus Leptonychotes.

Contents

Description

Skull Weddell Seal skull 1844.jpg
Skull

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). [5] [6] They are amongst the largest seals, with a rather bulky body and short fore flippers relative to their body length. [7] 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. [8] However, the male seal tends to have a thicker neck and a broader head and muzzle than the female. [9] A molecular genetic-based technique has been established to confirm the sex of individuals in the laboratory. [10] 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. [9]

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. [8] This coat moults around the beginning of summer. [9] 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. [9] 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). [8]

Behaviour

Movements

A Weddell seal at a breathing hole Weddell seal.jpg
A Weddell seal at a breathing hole

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. [11] In the winter, they stay in the water to avoid blizzards, with only their heads poking through breathing holes in the ice. [8] 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. [12] 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. [13] They have been observed to dive as deep as 600 m for up to an hour. [12] These seals exhibit a diel dive pattern, diving deeper and longer during the day than at night. [14] 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. [15]

Weddell seals are top predators in the Antarctic. They eat an array of fish, bottom-feeding prawns, cephalopods and crustaceans. [16] A sedentary adult eats around 10 kg (22 lb) a day, while an active adult eats over 50 kg (110 lb) a day. [8] 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. [17]

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. [18] 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. [19]

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. [8]

Breeding

Baby Weddell seal, Adelie Land Bebe Phoque de Weddell - Baby Weddell Seal.jpg
Baby Weddell seal, Adélie Land

Weddell seals return to fast ice colonies during the spring for birthing and breeding. [20] Weddell seal populations will often return to the same breeding sites over consecutive breeding seasons. [21] 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. [12] Weddell seals usually give birth to one pup per year, [12] however the Weddell seal is one of the only species of seals that can give birth to twin pups. [3] 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. [12] The pups take their first swim around one to two weeks of age. [12] During the first two weeks, mother Weddell seals distinguish their pups through olfactory smells, and specialised vocalisations, and stay in the same spatial area. [22] After six to seven weeks, pups are weaned and begin to hunt independently. [8]

Weddell seal pup with its grey natal coat, Deception Island Antarctic,Weddell seal-puppy (js) 44.jpg
Weddell seal pup with its grey natal coat, Deception Island

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. [23] Additionally, fast ice breeding grounds cause females to cluster in large aggregations, making it easier for males to control their harem. [21] The mating season occurs during austral spring between late November and December after pups are weaned and females begin ovulating. [12] During the mating season, Weddell seals make noises loud enough to be felt through the ice. [3] Males defend underwater territories during the breeding season and have been observed to fight. [24] 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. [25] The seals are normally around six to eight years old when they first breed, but this can be much earlier for some females. [9] Weddell seals undergo delayed implantation. The embryo is not implanted into the uterus until the beginning of austral summer, between mid-January and mid-February, allowing for birth under more favourable environmental conditions. [12] Juvenile Weddell seals (0–2 years old) have a high 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). The maximum lifespan of the species is estimated at least 25 years.

Newborn Weddell seals have different thermoregulatory strategies from other species of seals. Weddell seal pups are not born with brown fat, which is used in other seal species for thermoregulation. [26] Instead, they rely heavily on lanugo, a fine layer of hair on the surface of their skin, to keep warm. [27] 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. [27] The activity of metabolic enzymes including citrate synthase, ß-hydroxyacyl CoA dehydrogenase, and cytochrome c oxidase were measured and determined to be significantly active in newborn Weddell seals' longissimus dorsi, a large and major swimming muscle. [27] Research has also suggested that pups have high mitochondrial densities in the muscle, which may serve a thermogenic role. [26]

Vocalisation

Video of a reclining Weddell seal on pack ice in Adélie Land

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 with each other through different mediums. Weddell seals on ice can hear the calls of Weddell seals in the water as long as the noise level on land is low and they are nearby 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. [28] 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 when observed. [29] 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. [30] Weddell seals commonly produce ultrasonic vocalizations. However, the functional significance of these high-frequency sounds is yet unknown. [31]

Taxonomy

Rice [32] 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

At Neko Harbour, Antarctica Weddell Seal (js)1.jpg
At Neko Harbour, 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. [33]

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. [34]

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. [35]

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. [1]

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. [36] 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. [37] 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. [1]

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. [1] 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. [1] This species is not listed by CITES.

See also

Related Research Articles

<span class="mw-page-title-main">Earless seal</span> Family of mammals

The earless seals, phocids, or true seals are one of the three main groups of mammals within the seal lineage, Pinnipedia. All true seals are members of the family Phocidae. They are sometimes called crawling seals to distinguish them from the fur seals and sea lions of the family Otariidae. Seals live in the oceans of both hemispheres and, with the exception of the more tropical monk seals, are mostly confined to polar, subpolar, and temperate climates. The Baikal seal is the only species of exclusively freshwater seal.

<span class="mw-page-title-main">Fur seal</span> Subfamily of mammals

Fur seals are any of nine species of pinnipeds belonging to the subfamily Arctocephalinae in the family Otariidae. They are much more closely related to sea lions than true seals, and share with them external ears (pinnae), relatively long and muscular foreflippers, and the ability to walk on all fours. They are marked by their dense underfur, which made them a long-time object of commercial hunting. Eight species belong to the genus Arctocephalus and are found primarily in the Southern Hemisphere, while a ninth species also sometimes called fur seal, the Northern fur seal, belongs to a different genus and inhabits the North Pacific. The fur seals in Arctocephalus are more closely related to sea lions than they are to the Northern fur seal, but all three groups are more closely related to each other than they are to true seals.

<span class="mw-page-title-main">Eared seal</span> Marine mammals in the family Otariidae

An eared seal, otariid, or otary is any member of the marine mammal family Otariidae, one of three groupings of pinnipeds. They comprise 15 extant species in seven genera and are commonly known either as sea lions or fur seals, distinct from true seals (phocids) and the walrus (odobenids). Otariids are adapted to a semiaquatic lifestyle, feeding and migrating in the water, but breeding and resting on land or ice. They reside in subpolar, temperate, and equatorial waters throughout the Pacific and Southern Oceans, the southern Indian, and Atlantic Oceans. They are conspicuously absent in the north Atlantic.

<span class="mw-page-title-main">Pinniped</span> Taxonomic group of semi-aquatic mammals

Pinnipeds, commonly known as seals, are a widely distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals. They comprise the extant families Odobenidae, Otariidae, and Phocidae, with 34 extant species and more than 50 extinct species described from fossils. While seals were historically thought to have descended from two ancestral lines, molecular evidence supports them as a monophyletic lineage. Pinnipeds belong to the suborder Caniformia of the order Carnivora; their closest living relatives are musteloids, having diverged about 50 million years ago.

<span class="mw-page-title-main">Crabeater seal</span> Species of carnivore

The crabeater seal, also known as the krill-eater seal, is a true seal with a circumpolar distribution around the coast of Antarctica. They are medium- to large-sized, relatively slender and pale-colored, found primarily on the free-floating pack ice that extends seasonally out from the Antarctic coast, which they use as a platform for resting, mating, social aggregation and accessing their prey. They are by far the most abundant seal species in the world. While population estimates are uncertain, there are at least 7 million and possibly as many as 75 million individuals. This success of this species is due to its specialized predation on the abundant Antarctic krill of the Southern Ocean, for which it has uniquely adapted, sieve-like tooth structure. Indeed, its scientific name, translated as "lobe-toothed (lobodon) crab eater (carcinophaga)", refers specifically to the finely lobed teeth adapted to filtering their small crustacean prey. Despite its common name, crabeater seals do not eat crabs. As well as being an important krill predator, the crabeater seal's pups are an important component of the diet of leopard seals (H. leptonyx). They are the only member of the genus Lobodon.

<span class="mw-page-title-main">Bearded seal</span> Species of Arctic dwelling marine mammal

The bearded seal, also called the square flipper seal, is a medium-sized pinniped that is found in and near to the Arctic Ocean. It gets its generic name from two Greek words that refer to its heavy jaw. The other part of its Linnaean name means bearded and refers to its most characteristic feature, the conspicuous and very abundant whiskers. When dry, these whiskers curl very elegantly, giving the bearded seal a "raffish" look.

<span class="mw-page-title-main">Leopard seal</span> Macropredatory species of Antarctic seal

The leopard seal, also referred to as the sea leopard, is the second largest species of seal in the Antarctic. Its only natural predator is the orca. It feeds on a wide range of prey including cephalopods, other pinnipeds, krill, fish, and birds, particularly penguins. It is the only species in the genus Hydrurga. Its closest relatives are the Ross seal, the crabeater seal and the Weddell seal, which together are known as the tribe of Lobodontini seals. The name hydrurga means "water worker" and leptonyx is the Greek for "thin-clawed".

<span class="mw-page-title-main">Elephant seal</span> Genus of aquatic carnivores

Elephant seals or sea elephants are very large, oceangoing earless seals in the genus Mirounga. Both species, the northern elephant seal and the southern elephant seal, were hunted to the brink of extinction for oil by the end of the 19th century, but their numbers have since recovered. They are the largest extant carnivorans, weighing up to 4,000 kilograms (8,800 lb). Despite their name, elephant seals are not closely related to elephants, and the large proboscis or trunk that males have was convergently evolved.

<span class="mw-page-title-main">Macaroni penguin</span> Species of bird

The macaroni penguin is a species of penguin found from the Subantarctic to the Antarctic Peninsula. One of six species of crested penguin, it is very closely related to the royal penguin, and some authorities consider the two to be a single species. It bears a distinctive yellow crest that resembles macaroni, from which its name is derived. Its face and upperparts are black and sharply delineated from the white underparts. Adults weigh on average 5.5 kg (12 lb) and are 70 cm (28 in) in length. The male and female are similar in appearance; the male is slightly larger and stronger with a relatively larger bill. Like all penguins, it is flightless, with a streamlined body and wings stiffened and flattened into flippers for a marine lifestyle.

<span class="mw-page-title-main">Hooded seal</span> Species of carnivore

The hooded seal is a large phocid found only in the central and western North Atlantic, ranging from Svalbard in the east to the Gulf of St. Lawrence in the west. The seals are typically silver-grey or white in color, with black spots that vary in size covering most of the body. Hooded seal pups are known as "blue-backs" because their coats are blue-grey on the back with whitish bellies. This coat is shed after 14 months of age when the pups molt. It is the only species in the genus Cystophora.

<span class="mw-page-title-main">Harp seal</span> Species of mammal

The harp seal, also known as Saddleback Seal or Greenland Seal, is a species of earless seal, or true seal, native to the northernmost Atlantic Ocean and Arctic Ocean. Originally in the genus Phoca with a number of other species, it was reclassified into the monotypic genus Pagophilus in 1844. In Greek, its scientific name translates to "ice-lover from Greenland," and its taxonomic synonym, Phoca groenlandica translates to "Greenlandic seal." This is the only species in the genus Pagophilus.

<span class="mw-page-title-main">Antarctic fur seal</span> Species of carnivore

The Antarctic fur seal is one of eight seals in the genus Arctocephalus, and one of nine fur seals in the subfamily Arctocephalinae. Despite what its name suggests, the Antarctic fur seal is mostly distributed in Subantarctic islands and its scientific name is thought to have come from the German vessel SMS Gazelle, which was the first to collect specimens of this species from Kerguelen Islands.

<span class="mw-page-title-main">Ribbon seal</span> Species of mammal

The ribbon seal is a medium-sized pinniped from the true seal family (Phocidae). A seasonally ice-bound species, it is found in the Arctic and Subarctic regions of the North Pacific Ocean, notably in the Bering Sea and Sea of Okhotsk. It is distinguished by its striking coloration, with two wide white strips and two white circles against dark brown or black fur.

<span class="mw-page-title-main">Ross seal</span> Species of mammal

The Ross seal is a true seal with a range confined entirely to the pack ice of Antarctica. It is the only species of the genus Ommatophoca. First described during the Ross expedition in 1841, it is the smallest, least abundant and least well known of the Antarctic pinnipeds. Its distinctive features include disproportionately large eyes, whence its scientific name, and complex, trilling and siren-like vocalizations. Ross seals are brachycephalic, as they have a short broad muzzle and have shorter fur than any other seal.

<span class="mw-page-title-main">East Antarctica</span> Part of Antarctica that lies within the Eastern Hemisphere

East Antarctica, also called Greater Antarctica, constitutes the majority (two-thirds) of the Antarctic continent, lying primarily in the Eastern Hemisphere south of the Indian Ocean, and separated from West Antarctica by the Transantarctic Mountains. It is generally greater in elevation than West Antarctica, and includes the Gamburtsev Mountain Range in the center. The geographic South Pole is located within East Antarctica.

<span class="mw-page-title-main">Hauling-out</span> Marine mammal behaviour

Hauling-out is a behaviour associated with pinnipeds temporarily leaving the water. Hauling-out typically occurs between periods of foraging activity. Rather than remain in the water, pinnipeds haul-out onto land or sea-ice for reasons such as reproduction and rest. Hauling-out is necessary in seals for mating and giving birth. Other benefits of hauling-out may include predator avoidance, thermoregulation, social activity, parasite reduction and rest.

<span class="mw-page-title-main">Southern elephant seal</span> Species of marine mammal

The southern elephant seal is one of two species of elephant seals. It is the largest member of the clade Pinnipedia and the order Carnivora, as well as the largest extant marine mammal that is not a cetacean. It gets its name from its massive size and the large proboscis of the adult male, which is used to produce very loud roars, especially during the breeding season. A bull southern elephant seal is about 40% heavier than a male northern elephant seal, which is nearly twice the weight of a male walrus, or 6–7 times heavier than the largest living mostly terrestrial carnivorans, the Kodiak bear and the polar bear.

<span class="mw-page-title-main">Pagophily</span> Preference or dependence on water ice

Pagophily or pagophilia is the preference or dependence on water ice for some or all activities and functions. The term Pagophila is derived from the Ancient Greek pagos meaning "sea-ice", and philos meaning "-loving".

<span class="mw-page-title-main">Lobodontini</span> Tribe of carnivores

The true seal tribe Lobodontini, collectively known as the Antarctic seals or lobodontin seals, consist of four species of seals in four genera: the crabeater seal, the leopard seal, the Weddell seal, and the Ross seal. All lobodontine seals have circumpolar distributions surrounding Antarctica. They include both the world's most abundant seal and the only predominantly mammal-eating seal. While the Weddell seal prefers the shore-fast ice, the other species live primarily on and around the off-shore pack ice. Thus, though they are collectively the most abundant group of seals in the world, the combination of remote range and inaccessible habitat make them among the least well studied of the world's seals.

References

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  22. ↑ Opzeeland IC, Parijs SM, Frickenhaus S, Kreiss CM, Boebel O (2012). "Individual variation in pup vocalizations and absence of behavioral signs of maternal vocal recognition in Weddell seals (Leptonychotes weddellii)". Marine Mammal Science. 28 (2): 158–172. doi:10.1111/j.1748-7692.2011.00505.x. S2CID   16621622.
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  24. ↑ Thomas JA, DeMaster DP (1983). "Diel haul-out patterns of Weddell seal (Leptonychotes weddelli) females and their pups". Canadian Journal of Zoology. 61 (9): 2084–2086. doi:10.1139/z83-273.
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  26. 1 2 Elsner, R. W.; Hammond, D. D.; Denison, D. M. (1977). "Temperature regulation in the newborn Weddell seal, Leptonychotes weddelli". Adaptations in Antarctic Ecosystems. pp. 531–540. ISBN   9780872010000. OCLC   3813893.
  27. 1 2 3 Pearson, Linnea E.; Liwanag, Heather E. M.; Hammill, Mike O.; Burns, Jennifer M. (2014-12-01). "To each its own: Thermoregulatory strategy varies among neonatal polar phocids". Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. 178: 59–67. doi:10.1016/j.cbpa.2014.08.006. ISSN   1095-6433.
  28. ↑ Terhune, John M. (2017-04-13). "Through-ice communication by Weddell seals (Leptonychotes weddellii) is possible". Polar Biology. 40 (10): 2133–2136. doi:10.1007/s00300-017-2124-1. ISSN   0722-4060. S2CID   23069267.
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  35. ↑ "Researchers and citizen scientists complete first-ever Weddell seal count". University of Minnesota College of Science and Engineering. September 24, 2021.
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