Arctocephalus tropicalis (Gray, 1872)

Russell A. Mittermeier & Don E. Wilson, 2014, Otariidae, Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona: Lynx Edicions, pp. 34-101 : 93-94

8.

Subantarctic Fur Seal

Arctocephalus tropicalis

French: Otarie dAmsterdam / German: Subantarktik-Seebar / Spanish: Lobo marino subantartico

Other common names: Amsterdam Island Fur Seal

Taxonomy. Gypsophoca tropicalis Gray, 1872 ,

“North coast of Australia.” Restricted by J. E. King in 1959 to “*Australasian sea’ ...to include the islands of St. Paul and Amsterdam as these are the islands nearest to Australia.”

A. tropicalis has also been known as A. elegans or considered to be the same species as A. gazella . Monotypic.

Distribution. Widespread in subantarctic waters, primarily waters N of the Antarctic Convergence from the S Atlantic and Indian oceans to SW Pacific Ocean. Breeding takes place almost entirely N of the Antarctic polar front.

Descriptive notes. Total length up to 180 cm (males) and 119-152 cm (females); weight 70-165 kg (males) and 25-67 kg, mean ¢.50 kg (females). Newborns are ¢.60 cm and 4.4-4 kg. Dental formula 13/2, C 1/1, PC 6/5 (x 2) = 36. Subantarctic Fur Seals have a distinctive appearance, with pointed muzzle and small nose (rhinarium), and crown appears flat. Adults have long cream-colored vibrissae that reach past relatively short, dark ear pinnae. Mature males are mostly deep gray to blackish-brown, but fur on face down to chest is creamy, at times tinted yellow or even orange. Long fur above eyes and in back of forehead forms pale tuft or crest that contrasts with dark fur on crown. Forehead of males is exaggerated by this tuft, which is lacking in females and juvenile males. Mature females have similar overall coloration to males, although creamy face pattern of femalesis not as sharply delineated and tints are duller yellowish orange, or even a ruddy brown. Color of abdominal area can range from ginger to ruddy brown. Young darken as they mature. Hybrid Subantarctic Fur Seals x Antarctic Fur Seals have color pattern that is a mix of the two pure species. Adult male Subantarctic Fur Seals are heavy for their length and can appear stocky, with wide, short neck that seems even heaver because of longer guard hairs. Males do not develop silvery grizzling. Subantarctic Fur Seals have short and wide fore and hindflippers; foreflippers have more rounded tips than in other species of fur seals. Flippers have dark, sparse, short fur that extends beyond wrists and ankles onto dorsal surface offlippers that are otherwise covered in black leathery skin.

Habitat. [Large areas of subantarctic South Atlantic and Indian oceans. Favored locations for rookeries include beaches with cobbles and boulders, and rocky seaside terraces and grottos. These locations usually provide some shelter from sun and wind. Predators include Killer Whales (Orcinus orca), large sharks, and Leopard Seals (Hydrurga leptonyx). At Macquarie Island, New Zealand Sea Lions ( Phocarctos hookeri ) prey on Subantarctic Fur Seals.

Food and Feeding. [.anternfish ( Myctophidae ) and cod icefish ( Nototheniidae ), cephalopodes,krill, and occasionally penguins, make up the diet of Subantarctic Fur Seals. At Amsterdam Island, they consume cephalopods,fish, and rockhopper penguins (Eudyptes chrysocome). The diet of Subantarctic Fur Seals at the Prince Edward Islands was 50% cephalopods, 45% fish, and 5% krill.

Breeding. The Subantarctic Fur Seal has the same general polygynous breeding system as described for the Northern Fur Seal ( Callorhinus ursinus ). For Subantarctic Fur Seals, breeding occurs in summer, with a births peaking in mid-December, but young can be born as early as late October or as late as earlyJanuary. Males defend territories that include 1-5 females. Females reach sexual maturity at c.5 years of age. Pregnant females give birth within six days after arriving at the rookery; they enter estrus 8-12 days later. Gestation is c.51 weeks, including the period of delayed implantation. Foraging trips of female Subantarctic Fur Seals initially are 6-10 days long. Winter foraging trips can be 23-28 days long, and dive durations increase to 1-5-6-5 minutes. Young are nursed for 10-11 months before being weaned. Hybrids with both Antarctic Fur Seals and New Zealand Fur Seals are known and occur at a relatively high rate of 0-1% with the former. The fact that Subantarctic Fur Seals and Antarctic Fur Seals prefer different breeding habitats probably serves as a barrier to greater rates of hybridization. A probable Subantarctic Fur Seal x Juan Fernandez Fur Seal hybrid has also been recorded. Hybrid Subantarctic Fur Seals x Antarctic Fur Seals have been reported to grow to adult size and successfully reproduce. Life span of the Subantarctic Fur Seal is unknown.

Activity patterns. Most of what is known about activities of Subantarctic Fur Seals comes from their time spent ashore during the breeding season. While at sea, Subantarctic Fur Seals groom, rest, and feed as described for the Antarctic Fur Seal. The few studies of diving behavior of Subantarctic Fur Seals show that lactating females on foraging trips may reach maximum dive depths of up to 208 m, but most dives are to 100 m or less and average four minutes.

Movements, Home range and Social organization. Subantarctic Fur Seals are found at Gough, Prince Edward and Marion, Crozet, and Macquarie islands, and at St. Helena, Tristan da Cunha island group, and Saint Paul and Amsterdam Islands in temperate waters north of the subtropical front. Ninety-five percent of the population breeds at three main rookeries: Amsterdam Island, Gough Island, and Prince Edward Islands. Females with offspring stay near rookeries for most of the winter and spring. Lactating adult females feed within several days traveling distance of rookeries. Little is known of travel outside of the breeding season. At sea, Subantarctic Fur Seals are generally encountered alone or in small groups. In February-April, they come ashore for their annual molt. Stranded animals and apparently healthy individuals have been recorded as vagrants as far away as Brazil;Juan Fernandez Islands; southern cone of South America; Gabon; southern Africa, including Namibia and Angola; Madagascar; Comoros; Mauritius; southern Australia and Tasmania; Antipodean Islands; and South Island of New Zealand. Subantarctic Fur Seals have also been known to occur south of the Antarctic Polar Front at South Georgia, South Sandwich Islands, Bouvetgya, Kerguelen Islands, MacDonald Island, and the Antarctic Peninsula. They also occur at Davis and Mawson stations on the eastern Antarctic continent. Their northern distributional limits at sea are not well known.

Status and Conservation. CITES Appendix II. Classified as Least Concern on The [UCN Red List. The latest worldwide population estimate for the Subantarctic Fur Seal from 1987 exceeded 310,000 individuals and showed an upward trend. Breeding colonies are increasing in size, or are at least maintaining their size. Subantarctic Fur Seals suffered unsustainable hunting by sealers in the 19" century, which led to population crashes. Faced with near extinction at the beginning of the 20" century, Subantarctic Fur Seals have now come back to reoccupy much of their former distribution. Human-caused disturbance to Subantarctic Fur Sealsis presently low—a result of their remote oceanic habitat, where they breed on some of the most isolated islands on the planet. Breeding rookeries are all within government-protected areas or parks. Tourism and research activities are minimal. Although not a major hazard, fisheries may have a small impact through bycatch or gear entanglement. While no major threats are on the immediate horizon, the Subantarctic Fur Seal may face future challenges. Population reductions of the 19" and 20" centuries led to a genetic bottleneck, reducing population variability and perhaps increasing vulnerability to disease or climate change. Fortunately, the fact that they breed on several widely separated remote islands reduces risk of mass mortality due to contagious diseases. Climate change has the potential to affect the marine environment in ways that may negatively impact the Subantarctic Fur Seal.

Bibliography. Arnould (2009), Berta & Churchill (2012), Bester (1981, 1982, 1995), Bester, Ryan & Dyer (2003), Bester, Wilson et al. (2006), Bonner (1981), David & Salmon (2003), David et al. (1993), Gales et al. (1992), Garrigue & Ross (1996), Georges & Guinet (2000), Georges et al. (2000), Goldsworthy (1999), Goldsworthy & Shaughnessy (1989b), Goldsworthy et al. (2009), Guinet et al. (1994), Hofmeyr & Kovacs (2008), Hofmeyr, Bester & Kirkman (2006), Hofmeyr, De Maine et al. (2002), Jefferson et al. (2008), Kerley (1983a), King (1959), Klages & Bester (1998), Lancaster et al. (2006), Lancaster, Goldsworthy & Sunnucks (2010), Lavigne & Schmitz (1990), McDonald et al. (2012), Payne (1979), Reijnders et al. (1993), Rice (1998), Robinson et al. (2003), Shaughnessy & Burton (1986), Shaughnessy & Ross (1980), Taylor (1990), Torres & Aguayo (1984), Wickens & York (1997), Wynen et al. (2000), Zanrae & Bester (2011).

Figures

1. Northern Fur Seal (Callorhinus ursinus), 2. Antarctic Fur Seal (Arctocephalus gazella), 3. Juan Fernandez Fur Seal (Arctocephalus philippii), 4. Guadalupe Fur Seal (Arctocephalus townsendi), 5. Galapagos Fur Seal (Arctocephalus galapagoensis), 6. South American Fur Seal (Arctocephalus australis), 7. New Zealand Fur Seal (Arctocephalus forsteri), 8. Subantarctic Fur Seal (Arctocephalus tropicalis), 9. Afro-Australian Fur Seal (Arctocephalus pusillus)

Distribution. Widespread in subantarctic waters, primarily waters N of the Antarctic Convergence from the S Atlantic and Indian oceans to SW Pacific Ocean. Breeding takes place almost entirely N of the Antarctic polar front.