| Antarctic fur seal | |
|---|---|
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| Male Antarctic fur seal onSouth Georgia | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Carnivora |
| Parvorder: | Pinnipedia |
| Family: | Otariidae |
| Genus: | Arctocephalus |
| Species: | A. gazella |
| Binomial name | |
| Arctocephalus gazella Peters, 1875 | |
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| Antarctic fur seal range | |
TheAntarctic fur seal (Arctocephalus gazella) is one of eight seals in the genusArctocephalus, and one of nine fur seals in the subfamilyArctocephalinae. Despite what its name suggests, the Antarctic fur seal is mostly distributed inSubantarctic islands[3] 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 theKerguelen Islands.[4]
Antarctic fur seals are member of the genusArctocephalus. Recently, a proposal was made to reassign this species to the resurrected genusArctophoca.
Antarctic fur seals may be confused with southernotariids that share their range, like Subantarctic (A. tropicalis), New Zealand (A. forsteri), and South American fur seals (A. australis), and the Juan Fernandez fur seal (A. phillippii), as well as the South American (Otaria flavescens) and New Zealand sea lions (Phocarctos hookeri).[5] Genetic studies on population structure suggest that there are two genetically distinct regions: a western region including the islands of theScotia Arc,Bouvet Island, andMarion Islands, and an eastern region, including Kerguelen andMacquarie Islands. Seals from theCrozet Islands andHeard Island are mixtures from both regions.[6]
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Thefur seal is a midsizedpinniped with a relatively long neck and pointed muzzle compared with others in the family. The nose does not extend much past the mouth, the external ears are long, prominent, and naked at the tip. Adults have very longvibrissae, particularly males, up to 35 to 50 cm. The fore flippers are about one-third, and hind flippers slightly more than one-fourth of the total length.[7]
Adult males are dark brown in colour. Females and juveniles tend to be paler, almost grey with lighter undersides. Colour patterns are highly variable, and scientists reported that somehybridization between Subantarctic and Antarctic fur seals has occurred.[8][9] Pups are dark brown at birth, almost black in color. However, a very small number of partiallyleucistic Antarctic fur seals have been found.[10]
Males are substantially larger than females. Males grow up to 2 m (6.5 ft) long and with a mean weight of 133 kg (293 lb). Females reach 1.4 m (4.6 ft) with a mean weight of 34 kg (74.9 lb). At birth, mean standard length is 67.4 cm (58–66) and mass is 5.9 kg (4.9–6.6) in males and 5.4 kg (4.8–5.9) in females.[11]
Antarctic fur seals live up to 20 years with a maximum observed for female of 24.[12]
Antarctic fur seals are believed to be the most abundant species of furseal.[13] The largest congregation occurs on the island ofSouth Georgia in the southern Atlantic Ocean, which holds approximately 95% of the globalpopulation.[14] The current best estimate of the South Georgia population is between 4.5 and 6.2 million animals.Bouvet Island has the second largest population with 46,834 animals.[15] However, there are regional differences in population trends: some colonies are increasing in size (e.g.Kerguelen Islands,McDonald Islands), some are stable (e.g.Macquarie Island, Heard islands), and some are showing a decrease (e.g. Bouvet Island).[15]
Antarctic fur seals have acircumpolar distribution and breed from 61° S to theAntarctic Convergence. Breeding colonies are found atSouth Georgia and the South Sandwich Islands,South Orkney Islands,South Shetland Islands and Bouvet Island in the SouthernAtlantic Ocean;Marion Island,Crozet Islands,Kerguelen andHeard Island in the SouthernIndian Ocean; and Macquarie Island in the SouthernPacific Ocean.[16] Duringwinter, Antarctic fur seals range widely from the Antarctic continent to theFalkland Islands, and southernArgentina reaching as far as the Mar del Plata and Gough Island.[17][18]
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Antarctic fur seals are one of the better-studied Southern Ocean predators. However, the vast majority of information has been collected during summerbreeding months. The breeding system of the Antarctic Fur Seal ispolygynous, and dominant breeding males mate with as many as 20 females during a successful season. Males establish breeding grounds in October to early November.[19] Females generally reach the colonies in December and give birth to a single pup several days later.[20]Gestation lasts between 8 and 9 months and it has been observed a high breeding synchrony across the species' range, concentrating 90% of pup births in a 10-day window. Pups are weaned at about four months old.[21] Juveniles may then spend several years at sea before returning to begin their breeding cycles.
Theecology of Antarctic fur seals during the non-breeding winter is poorly understood. Adult and subadult males may form groups whilemoulting along the Antarctic Peninsula in late summer and early autumn. Adult females aregregarious but relativelyasocial other than the strong bond they establish with their pups, although there are occasional aggressive encounters with nearby females or other pups and brief interactions with adult males to mate. These seals appear to besolitary when foraging and migrating.[19]
The usual food source for individuals in the Atlantic Region isAntarctic krill (Euphausia superba); while in the Indian Ocean the diet is mostly based on fish andsquid. The fishprey are principallymyctophids,icefish, and Notothenids, althoughskates andrays are also consumed.[4] Penguins are occasionally taken by Antarctic fur seal males.[22] Seasonal differences indiet have been recorded across colonies, seasons and years.[23][24] Female Antarctic fur seals can undertake wide-rangingforaging migrations during winter.[18] Interannual differences appear to be related to differences in local oceanographic conditions.[25][26]
Antarctic fur seals feed primarily onkrill,fish, andsquid.Birds are eaten occasionally outside the breeding season. Nursing mothers nearSouth Georgia are dependent onkrill during the breeding season, therefore the availability ofkrill is important to the reproductive success of this animal. The colonies atMacquarie Island and theKerguelen Islands rely more on a diet offish andsquid. Antarctic fur seals dive at night to feed.[27]
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South Georgia islands, which hold approximately 95% of the global population,[14] had a total population in 1999/2000 between 4.5 and 6.2 million.[15] The South Georgia population reached carrying capacity fairly recently and may thus be spilling over into relatively nearby, lower density sites.[6] However, theabundance of adult females is estimated to have declined by some 30% between 2003 and 2012, and by 24% since 1984 to around 550,000. The population trend according to theIUCN Red list is 'decreasing'[1] and it has been suggested that this decline is due to the effects of globalclimate change on preyavailability.[28]
Historically the species were decimated by thesealing industry for itsfur and its population was driven close toextinction by the 19th century.[29] Since sealing operations ceased in the early 20th century, the species has recovered at different rates across its former geographic range.[15]
Waters inhabited by Antarctic fur seals are exploited by few fisheries, but these may expand in their range in the future.[30] A 1997 study at South Georgia indicated that several thousand Antarctic fur seals were entangled in man-made debris such as discarded fishing line, nets, packing bands and anything that can form a collar.[31] Consequently,CCAMLR campaigned for compliance with MARPOL provisions relating to waste disposal at sea, and for cutting of any material jettisoned which could form collars to entangle seals. Subsequent monitoring of entangled fur seals confirmed that entanglement is still a persistent problem, but it has halved in recent years.[32]Trawling activities developing around Macquarie Island may affect the prey base of the primarily fish-eating Antarctic fur seals that breed on those islands. Recent work indicates that there is significant overlap between foraging areas and fisheries activities, suggesting a potential for competition for prey resources may exist.
Leopard seals have been noted to take as many as a third of the Antarctic Fur Seal pups born at sites in the South Shetland Islands.[33] Levels ofpredation may be high enough to cause a population decline at these sites.[34]
As well as the effects ofhunting andfishing, the numbers of humans visiting the Antarctic and sub-Antarctic each year for tourism and scientific expeditions have risen. This increase in visits has led to greater interaction between the localfauna and humans.[35] With this greater interaction comes the risk of affecting the territoriality of seals especially during themating season. This can also increase the possibility of 'exotic' injuries to humans. In 2015 a man was rescued from a South Georgia Island by British Forces after receiving a serious bite from a fur seal.[36] Due to the remote location of where these injuries occur, this can lead to complications in getting people to a physician with the relevant experience in treating exotic animal bites. This issue is compounded by the complexity of fur seal behavior and how serious a bite can be[37] and the risk of transfer of diseases.[38]The implication for Antarctic Fur Seals but this species is considered to be one of several pinnipeds at high risk of future disease outbreaks because of their tendency to congregate in large dense aggregations and the effect of environmental changes associated withglobal warming on the spread of diseases.[39]
Finally, the 19th centurypopulation bottleneck led to reduced genetic diversity, leaving it again morevulnerable to disease andstresses of climate change. In particular, the Antarctic fur seal's primary prey base,krill, could be reduced as a result ofocean acidification, or the distribution could be altered by climate change.
IUCN Conservation status: Least Concern.[1]
The species is protected by the governments in whose waters it resides (Australia,South Africa,France) and by the Convention for the Conservation of Antarctic Seals in waters south of 60° S.[40] The animal is also listed in Appendix 2 of CITES.[41]
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