Arctocephalus gazella (Peters, 1875)
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publication ID |
https://doi.org/ 10.5281/zenodo.6604474 |
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DOI |
https://doi.org/10.5281/zenodo.6604425 |
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persistent identifier |
https://treatment.plazi.org/id/965C87FE-1E5E-564C-9922-9B0B86DAFE17 |
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treatment provided by |
Diego |
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scientific name |
Arctocephalus gazella |
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Antarctic Fur Seal
Arctocephalus gazella View in CoL
French: Otarie antarctique / German: Kerguelen-Seebar / Spanish: Lobo marino antértico
Other common names: Kerguelen Fur Seal
Taxonomy. Arctophoca gazella Peters, 1875 ,
“von Seehunden aus Kerguelenland.” Restricted by V. B. Scheffer in 1958 to “Anse Betsy (49° 09’ S, 70° 11" E)” (= south-east of Africa, halfway to Antarctica).
A. gazella was once considered a subspecies of A. tropicalis . Monotypic.
Distribution. Subantarctic and Antarctic waters S of, or just N of, the Antarctic Convergence, and scattered islands in this zone, mainly South Georgia. Regular haul-out areas include the Antarctic Peninsula. View Figure
Descriptive notes. Total length mean 188 cm but up to 200 cm (males) and 120-140 cm (females); weight 130-204 kg, mean 188 kg (males) and 22-51 kg, mean 40 kg (females) Newborns are 63-67 cm and 6-7 kg. Dental formula 13/2, C 1/1, PC 6/5 (x 2) = 36. Antarctic Fur Seals are strongly sexual dimorphic. Mature males weigh 4-5 times as much as females and are 1-4-1-5 times longer. Muzzle is of moderate size and length, tapering to slightly pointed nose that reaches just past mouth. Pale ear pinnae are long and conspicuous. Vibrissae are pale and quite noticeable; adult male Antarctic Fur Seals have some of the longest whiskers of any pinniped, up to 50 cm. Subadults have darker vibrissae that become paler as they grow to adulthood. Adult males have mane of long guard hairs reaching from head to chest, and broad and muscular shoulders and neck. Adult females and subadults are hard to distinguish from males until they are 4-6 years old. Flippers have dark, sparse, short fur that extends beyond wrists and ankles onto dorsal surface of flippers that are otherwise covered in black leathery skin. Fore and hindflippers are long, and first digit is longer than the rest and curves back. Adult males are dark gray to charcoal, with creamy orsilver grizzling on mane and sides. Underfur is buff-colored. Fur of adult females and subadults ranges from gray to brown and may be paler on chest, abdomen, and sides than adult males, with tints of buff or ruddy brown. Pale color can also continue from chest to neck and onto face, including base of ear pinnae and muzzle where vibrissae originate. Newborns are black, with some pale areas on head and, at times, on abdomen. Juveniles molt into the adult female pattern but have silver tints where furis pale. At South Georgia, very pale, or leucistic, Antarctic Fur Seals occur at the rate of one or two per thousand. These cream-colored individuals are not true albinos because they have normally pigmented eyes.
Habitat. Pelagic, using large regions of the Southern Ocean and sea ice. On land, Antarctic Fur Seals prefer rocky areas, but they will come ashore on sandy beaches and even move higher up into tussock grass. Predators include Killer Whales (Orcinus orca) and Leopard Seals (Hydrurga leptonyx), which prey on offspring in the South Shetland Islands. At Macquarie Island, young Antarctic Fur Seals are preyed on by New Zealand Sea Lions ( Phocarctos hookeri ).
Food and Feeding. The diet of the Antarctic Fur Seal varies depending on the area and time of year. At their main colony at South Georgia, breeding females feed nocturnally on krill in summer. At other islands where krill is not available, they eat mainly squid, lanternfish ( Myctophidae ), and cod icefish ( Nototheniidae ). During winter, males at South Georgia eat krill or fish, with squid and lanternfish accounting for only a fraction of their diet. Antarctic Fur Seals will prey on penguins, including king penguins (Aptenodytes patagonicus) on Marion Island and macaroni penguins (Eudyptes chrysolophus) and Gentoo penguins (Pygoscelis papua) off Heard, Macquarie, and South Georgia islands.
Breeding. The Antarctic Fur Seal has the same general polygynous breeding system as described for the Northern Fur Seal ( Callorhinus ursinus ). Delayed implantation allows gestation of only 8-9 months to synchronize to an annual breeding cycle. Life span is up to 15 years for males and 23 years for females. Breeding of Antarctic Fur Seals occurs from late November to late December. Males arrive at rookeries in late October, establishing territories as small as 20 m* with up to 19 females. At the largest rookery island, South Georgia, males hold territories for an average of 34 days. Females arrive in mid-November and bear young 1-2 days later. They nurse their young for 6-7 days and then enter estrus. Within hours of copulating, they leave on their first feeding trip, which usually lasts 4-5 days before they return to nurse their young for 2-3 days. Offspring are weaned at c.4 months old. Antarctic Fur Seals achieve sexual maturity threat c.3 years in females and c.7 years in males. They hybridize with Subantarctic Fur Seals (A. tropicalis ) at Prince Edward Islands and Crozet Islands and with New Zealand Fur Seals (A. forsteri ) and Subantarctic Fur Seals at Macquarie Island.
Activity patterns. At sea, Antarctic Fur Seals groom, rest, and feed as described for the Northern Fur Seal plus an inverted posture with hindflippers up in the air. When traveling rapidly, Antarctic Fur Seals can “porpoise” clear of the water’s surface in low leaping arcs. They typically make numerous shallow foraging dives, mostly during the night. Dives of lactating female Antarctic Fur Seals are to 8-30 m and last less than two minutes; maximum dives are to 181 m, and the longest dives last ten minutes.
Movements, Home range and Social organization. Major colonies of Antarctic Fur Seals are at South Georgia and Bird Islands, with smaller numbers on other island groups including South Shetlands, South Orkney, South Sandwich, Prince Edward, Crozet, Kerguelen, Heard, McDonald, Macquarie, and Bouvetgya. Movements in winter are not well known. After weaning offspring, females leave the colony areas until the following breeding season. Males mostly disperse, but some subadult and adult males remain at South Georgia throughout the year. In summer, males haul out on the Antarctic Peninsula, and they can be found at the edge of the pack ice. Vagrants have reached Gough Island, Brazil, southern South America; Juan Fernandez Islands, Australia; and Mawson Station in East Antarctica.
Status and Conservation. CITES Appendix II. Classified as Least Concern on The [UCN Red List. The South Georgia rookery of Antarctic Fur Seals, representing 95% of the total population, supports 4:5-6-2 million individuals and is stable or increasing. The next largest rookery is Bouvetgya, with ¢.66,000 individuals. Hunting in the 19" century nearly exterminated Antarctic Fur Seals, but a few survived at South Georgia, Bouvetgya, and the Kerguelen islands. The Antarctic Treaty provides protection for all species of fur seals below 60° S latitude. The remote seas used by Antarctic Fur Seals are not heavily fished, but commercial operations, including krill harvesting, could develop in the future. Injuries from marine debris and discarded fishing gear are current risks, and the fraction of the population that becomes entangled, mostly young individuals,is estimated to be 0-1%. The population bottleneck of the 19" century reduced genetic diversity of the Antarctic Fur Seal, possibly making it more vulnerable to disease or stresses of climate change. Ocean acidification also could impact Antarctic Fur Seals if krill is affected by altered marine chemistry that makes it more difficult for these crustaceans or their prey to form their calcified exoskeletons.
Bibliography. Acevedo et al. (2011), Arnould (2009), Aurioles & Trillmich (2008b), Bester & Wilkinson (1989), Bonner (1981), Boveng et al. (1998), Boyd (1999), Boyd & Croxall (1992), Boyd, Lunn & Barton (1991), Boyd, Mc-Cafferty et al. (1998), Costa et al. (1989), Croxall et al. (1990), Doidge & Croxall (1989), Doidge etal. (1986), Duck (1990), Forcada & Staniland (2009), Goldsworthy & Shaughnessy (1989a), Goldsworthy et al. (2009), Green et al. (1991), Guinet, Jouventin & Georges (1994), Guinet, Lea & Goldsworthy (2000), Hoffman & Forcada (2012), Jefferson et al. (2008), Kirkwood et al. (2003), Klages & Bester (1998), Klages et al. (1999), Lancaster, Gemmell et al. (2006), Lancaster, Goldsworthy & Sunnucks (2010), Lavigne & Schmitz (1990), Lunn et al. (1994), McCann & Doidge (1987), North et al. (1983), Reijnders et al. (1993), Rice (1998), Robinson etal. (2003), Scheffer (1958), Staniland et al. (2011), Wickens & York (1997), Wynen et al. (2000).
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