Ross seal

The Ross seal (Ommatophoca rossii) is a true seal (family Phocidae) 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 (Ommato- meaning "eye", and phoca meaning "seal"), and complex, trilling and siren-like vocalizations. Ross seals are brachycephalic, as they have a short broad muzzle and have the shortest fur of any other seal.

Ross seal
Ross-seal
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Clade: Pinnipedia
Family: Phocidae
Genus: Ommatophoca
Gray, 1844
Species:
O. rossii
Binomial name
Ommatophoca rossii
(Gray, 1844)
Ross Seal area
Ross seal range

Taxonomy and evolution

The Ross seal shares a recent common ancestor with three other extant Antarctic seals, which are together known as the lobodontine seals. The other species are the crabeater seal (Lobodon carcinophaga), leopard seal (Hydrurga leptonyx) and Weddell seal (Leptonychotes weddelli).[2] These species, collectively belonging to the seal tribe Lobodontini, share teeth adaptations, including lobes and cusps useful for straining smaller prey items out of the water column. The ancestral Lobodontini likely diverged from its sister clade, Mirounga (elephant seals) in the late Miocene to early Pliocene, when they migrated southward and diversified rapidly in relative isolation around Antarctica.[2] However, the only fossils of Ross seals so far known date from much later, during the early Pleistocene of New Zealand.[3]

Description

Ross seals reach a length of about 1.68–2.09 m (5.5–6.9 ft) and weight of 129–216 kg (284–476 lb); females are slightly larger at 1.96–2.5 m (6.4–8.2 ft).[1] A molecular genetic based technique has been established to confirm the sex of individuals in the laboratory.[4] Pups are about 1 m and 16 kg at birth. The coat is colored dark-brown in the dorsal area and silvery-white beneath. At the onset of the Antarctic winter, the coat fades gradually to become light brown. At close range, the Ross seal can be easily identified by its large eyes, which are up to 7 cm in diameter.

The Ross seal is able to produce a variety of complex twittering and siren-like sounds that are performed on ice and underwater, where they carry for long distances.[5] The underwater siren sound can be composed of two harmonically unrelated superimposed tones that are pulsed with the same rhythm. Uniquely, the vocalizations, whether on ice or in water, are made with a closed mouth - emitting no air. The purpose of these sounds is unknown, though their distinctive nature and long range are likely to facilitate either encounters or avoidance of individuals.[5]

Range and population status

Although its close relatives Weddell seals, crabeater seals and leopard seals are ubiquitous in Antarctic waters, the Ross seal is an uncommon and relatively unknown animal, considered to be the least common pack ice seal. It almost never leaves the Antarctic Ocean, with the very rare exception of stray animals found around subantarctic islands, and uniquely, off the south coast of Australia. Nonetheless, its distribution is circumpolar, with individuals found in low densities - usually singly - in very thick pack ice in all regions of the continent.

The total Ross seal population is estimated at around 130,000 individuals, but there is great uncertainty in this estimate (reported 95% confidence intervals range from 20,000 to 227,000).[6] Thus, very little is known about trends in the population. A genetic survey did not detect evidence of a recent, sustained genetic bottleneck in this species,[7] which suggests that populations do not appear to have suffered a detectable and sustained decline in the recent past.

Interactions with humans have been limited. They have been collected historically by Antarctic expeditions and for scientific collections. Their range does not generally overlap with commercial fishing.

Feeding and reproductive behavior

Ross seal feeds primarily on squid and fish, primarily Antarctic silverfish, in the pelagic zone.[8] Ross seals are presumed to be preyed upon by killer whales (Orcinus orca) and leopard seals, large predators that share their Antarctic habitat, though there are no documented observations of predation.

Females give birth to their young on the ice in November. Pups are nursed for only four weeks before weaning. Mating is thought to occur underwater shortly after the pup is weaned, but has never been observed. Ross seals mature sexually at approximately three years of age, and are thought to live around 20 years in the wild.[8]

References

  1. ^ a b Southwell, C. (2008). "Ommatophoca rossii". IUCN Red List of Threatened Species. Version 2008. International Union for Conservation of Nature. Retrieved 28 January 2009.
  2. ^ a b Fyler, C. A.; Reeder, T.W.; Berta, A.; Antonelis, G.; Aguilar, A.; Androukaki, E. (2005), "Historical biogeography and phylogeny of monachine seals (Pinnipedia: Phocidae) based on mitochondrial and nuclear DNA data", Journal of Biogeography, 32 (7): 1267–1279, doi:10.1111/j.1365-2699.2005.01281.x
  3. ^ Berta, A.; Churchill, M. (2012). "Pinniped Taxonomy: evidence for species and subspecies". Mammal Review. 42 (3): 207–234. doi:10.1111/j.1365-2907.2011.00193.x.
  4. ^ Curtis, Caitlin; Stewart, Brent S.; Karl, Stephen A. (2007-05-01). "Sexing Pinnipeds with ZFX and ZFY Loci". Journal of Heredity. 98 (3): 280–285. doi:10.1093/jhered/esm023. ISSN 0022-1503. PMID 17548861.
  5. ^ a b Watkins, William A.; Carleton Ray, G. (1985), "In-air and underwater sounds of the Ross seal, Ommatophoca rossi", The Journal of the Acoustical Society of America, 77 (4): 1598–1600, doi:10.1121/1.392003, retrieved 2010-06-06
  6. ^ Southwell, C.J.; Paxton, C.G.M.; Borchers, D.L.; Boveng, P.L.; Nordøy, E.S.; Blix, A.S.; De La Mare, W.K. (2008), "Estimating population status under conditions of uncertainty: the Ross seal in East Antarctica", Antarctic Science, 20 (2): 123–133, doi:10.1017/s0954102007000879
  7. ^ Curtis, Caitlin; Stewart, Brent S.; Karl, Stephen A. (2011-07-07). "Genetically effective population sizes of Antarctic seals estimated from nuclear genes". Conservation Genetics. 12 (6): 1435–1446. doi:10.1007/s10592-011-0241-x. ISSN 1566-0621.
  8. ^ a b Skinner, J.D.; Klages, NTW (1994), "On some aspects of the biology of the Ross seal Ommatophoca rossii from King Haakon VII Sea, Antarctica", Polar Biology, 14 (7): 472, doi:10.1007/bf00239051

External links

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Crabeater seal

The crabeater seal (Lobodon carcinophaga) is a true seal with a circumpolar distribution around the coast of Antarctica. They are medium- to large-sized (over 2 m in length), 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 name, crabeater seals do not eat crabs. As well as being an important krill predator, the crabeater seal is an important component of the diet of leopard seals (Hydrurga leptonyx), which consume about 80% of all crabeater pups.

Earless seal

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East Antarctica

East Antarctica, also called Greater Antarctica, constitutes the majority (two-thirds) of the Antarctic continent, lying on the Indian Ocean side of the continent, separated from West Antarctica by the Transantarctic Mountains. It lies almost entirely within the Eastern Hemisphere and its name has been accepted for more than a century. It is generally higher than West Antarctica and includes the Gamburtsev Mountain Range in the centre.

Apart from small areas of the coast, East Antarctica is permanently covered by ice. The only terrestrial plant life is lichens, mosses and algae clinging to rocks, and there are a limited range of invertebrates including nematodes, springtails, mites and midges. The coasts are the breeding ground for various seabirds and penguins, and the leopard seal, Weddell seal, elephant seal, crabeater seal and Ross seal breed on the surrounding pack ice in summer.

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King Haakon VII Sea

King Haakon VII Sea (Norwegian: Kong Haakon VII Hav) is a proposed name for part of the Southern Ocean on the coast of East Antarctica.

Leopard seal

The leopard seal (Hydrurga leptonyx), also referred to as the sea leopard, is the second largest species of seal in the Antarctic (after the southern elephant seal). Its only natural predators are the killer whale. It feeds on a wide range of prey including cephalopods, other pinnipeds, krill, birds and fish. 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 "small clawed".

Lobodontini

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Lutrogale

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Mephitis (genus)

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Nyctereutes

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Paradoxurus

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Queen Maud Land

Queen Maud Land (Norwegian: Dronning Maud Land) is a c. 2.7 million square kilometre (1.04 million sq mi) region of Antarctica claimed as a dependent territory by Norway. The territory lies between 20° west and 45° east, between the claimed British Antarctic Territory to the west and the similarly claimed Australian Antarctic Territory to the east. On most maps there had been an unclaimed area between Queen Maud Land's borders of 1939 and the South Pole until 12 June 2015 when Norway formally annexed that area. Positioned in East Antarctica, the territory comprises about one-fifth of the total area of Antarctica. The claim is named after the Norwegian queen Maud of Wales (1869–1938).

Norwegian Hjalmar Riiser-Larsen was the first person known to have set foot in the territory, in 1930. On 14 January 1939, the territory was claimed by Norway. From 1939 until 1945, Nazi Germany claimed New Swabia, which consisted of part of Queen Maud Land. On 23 June 1961, Queen Maud Land became part of the Antarctic Treaty System, making it a demilitarised zone. It is one of two Antarctic claims made by Norway, the other being Peter I Island. They are administrated by the Polar Affairs Department of the Norwegian Ministry of Justice and Public Security in Oslo.

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Ross expedition

The Ross expedition was a voyage of scientific exploration of the Antarctic in 1839 to 1843, led by James Clark Ross, with two unusually strong warships, HMS Erebus and HMS Terror. It explored what is now called the Ross Sea and discovered the Ross Ice Shelf. On the expedition, Ross discovered the Transantarctic Mountains and the volcanoes Erebus and Terror, named after his ships. The young botanist Joseph Dalton Hooker made his name on the expedition.

The expedition inferred the position of the South Magnetic Pole, and made substantial observations of the zoology and botany of the region, resulting in a monograph on the zoology, and a series of four detailed monographs by Hooker on the botany, collectively called Flora Antarctica and published in parts between 1843 and 1859. The expedition was the last major voyage of exploration made wholly under sail.Among the expedition's biological discoveries was the Ross seal, a species confined to the pack ice of Antarctica.

Extant Carnivora species

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