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Subantarctic Fur Seal (Arctocephalus tropicalis)

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The subantarctic fur seal is a small, carnivorous marine mammal. This species is sexually dimorphic, with adult males being up to 2 m long and weighing 70-165 kg. Adult females are 1-1.5 m long and weigh 25-67 kg with a mean of around 50 kg. Newborns weigh 4-6 kg (Goldsworthy & Shaughnessy 1995a; Laws 1993 cited in DEH 2003g).

The subantarctic fur seal has a distinctive colouration. It is a chocolate brown with a contrasting yellow face and chest and long white vibrissae (sensory whiskers). Adult females can be distinguished from adult males as the latter have a thick mane, barrel chest, broad shoulders, darker brown dorsum (back) and richer, yellow ventral (underparts). Males also have a distinctive ‘mo-hawk’ crest. Pups are glossy-black with a dark chocolate brown belly (DEH 2003g).

Australian Distribution

In Australian waters, the subantarctic fur seal breeds, molts and hauls out mainly on Macquarie Island, but individuals range widely and occasionally reach the beaches of Tasmania and mainland Australia (DEH 2003g). Breeding colonies are only found at Macquarie Island (Shaughnessy et al. 1988a; Goldsworthy 1999). Subantarctic fur seal individuals haulout at Heard Island, and one pup was born in each of 1987, 2000 and 2003 (Woinarski et al. 2014). Very few immigrants from large breeding colonies in the western Indian Ocean visit Australia (Woinarski et al. 2014).

More than 50 subantarctic fur seal individuals have been reported on the coastline of southern Australia, from Western Australia to Queensland (Kirkwood et al. 1992; Gales et al. 1992a; Llewellyn et al. 1994; Warneke 1995b; Mawson & Coughran 1999; Ross 2001 pers comm., unpublished observations).

The subantarctic fur seals is widely distributed in the Southern Hemisphere. They breed in the Southern Ocean on islands north and south of the Antarctic Polar Front, including Amsterdam, Crozets, Gough, Macquarie, the Prince Edward Islands, Saint Paul and Tristan da Cunha. They have also been recorded breeding on Heard Island (Hofmeyr & Kovacs 2008).

This species is classified as LEAST CONCERN according to the IUCN's Red List.
This species is classified as LEAST CONCERN according to the IUCN’s Red List.

Population Information

The Macquarie Island population was estimated at between 90 and 130 mature individuals in the mid 1990’s, however, DNA analysis has indicated that there are critically low levels of pure subantarctic fur seals (Goldsworthy 2002 cited in DEH 2003g). It is estimated that less than ten purebred subantarctic fur seals pups are born per year on Macquarie Island (Goldsworthy 2002 cited in DEH 2003g). Globally the population estimate for sub-Antarctic fur seals is 277, 000-356, 000 (Hofmeyr et al. 1997 cited in DEH 2003g).

The subantarctic fur seal was hunted by sealers in the 18th and the 19th century and its numbers were reduced to the brink of extinction at the beginning of the 20th century (Hofmeyr & Kovacs 2008). At Macquarie Island over 200, 000 fur seal skins were taken, and the colony was extirpated within approximately 10 years after its discovery (DEH 2003g). It is thought the original species on Macquarie Island prior to the seal harvesting was the subantarctic fur seal (Shaughnessy & Shaughnessy 1987 cited in Lancaster et al. 2006).

At Macquarie Island breeding began again in about 1955, however it has had a slower recovery than elsewhere (Shaughnessy & Goldsworthy 1993 cited in DEH 2003g; Goldsworthy & Shaughnessy 1995a). The size of the population on the island is increasing steadily at 8% per year (Woinarski et al. 2014).

Habitat

The subantarctic fur seal utilizes rocky coastal habitat containing rock platforms and beaches with exposed boulders (Bester 1982; Goldsworthy and Shaughnessy 1995a cited in DEH 2003g).  At Macquarie Island, breeding seals occur on rocky shores, and non-breeding seals also utilize tussock slopes above the colonies (Shaughnessy et al. 1988a). Where the subantarctic fur seal and the Antarctic fur seal are sympatric on breeding beaches at Macquarie Island, females of the former species prefer rocky shores and Antarctic fur seal females prefer cobble beaches (Goldsworthy et al. 1999). Suitable terrestrial habitat on Macquarie Island can be found at Secluded Beach and Goat Bay on North Head Peninsula (Shaughnessy 1999). There is potential for animals to utilize other rocky beaches elsewhere on the island (Robinson et al. 2002).

Important feeding habitat for the species includes the waters immediately surrounding Macquarie Island (Copson et al. 1994 cited in DEH 2003g), where females occasionally feed while nursing. Two important feeding areas for lactating cows have been identified at 30 and 100 km north of Macquarie Island (Robinson et al 2002 cited in DEH 2003g). These waters adjacent to breeding colonies are also used for access to land, for respite and refuge,  and these waters may have importance for pups learning to swim and feed in the shallows (DEH 2003g).

Life Cycle

Life Cycle Timeline

Beginning in October, adult subantarctic fur seal males return to breeding sites to establish territories. The largest and most aggressive males compete vigorously for territories, which may contain 4-12 females (Goldsworthy et al. 1999 cited in DEH 2003g). The number of males ashore at any one time increases through October and November. Subordinate bulls and bachelors are forced to the fringes of colonies, but sometimes obtain mating opportunities. Females are gregarious and males discourage them from leaving the territory. From late November to February, females haul out to give birth to a single pup, with a peak in birth at around 10-15 December. Twins are rarely born. Females give birth one year after mating and will mate again seven to 12 days after pups are born. Implantation is delayed for four months before a gestation period of eight months (Bester 1995 cited in DEH 2003g).

The pups grow quickly on the energy-rich milk of their mother and start to swim in rock pools and shallows after 6 weeks, they will first got to sea after weaning at approximately 11 months. Females reach sexual maturity at 4-6 years of age and males at 4-8 years, although males do not achieve territorial status until 10-11 years of age.

At Macquarie Island females with pups make short, nightly trips of around eight hours, interspersed with more extended foraging journeys averaging 3.8 days (Goldsworthy 1999a cited in DEH 2003g).

Hybridisation

Hybrids have been found in small numbers at Macquarie Islands and hybridization is likely to persist at low levels (Hofmeyr et al. 2006). Hybridization is thought to be anthropogenically induced and quite recent, with the more extensive current hybridization rates (as compared to those occurring pre-sealing) being a result of sealing pressure (Lancaster et al. 2006). At Macquarie Island the hybridization occurs between Antarctic, Subantarctic and New Zealand fur seals (the latter being just males). However, at this site the proportion of hybrids has fallen over time. This is due in large part to increased immigration of pure Antarctic and subantarctic individuals and non-random mating (caused by biological resistance to complete homogenisation) (Goldsworthy et al. 1998).

Feeding

Subantarctic fur seals are opportunistic and pelagic foragers. They feed on myctophid and notothenioid fish, cephalopods, and small numbers of crustaceans at the Prince Edwards Islands (Klages & Bester 1998 cited in Hofmyer & Kovacs 2008) and Macquarie Island (Robinson et al. 2002 cited in DEH 2003g). The subantarctic fur-seal forages mainly at night on surface, mid-water and bottom-dwelling fish, squid and octopus. The diet varies seasonally and according to location.

This species is known to forage at oceanographic frontal zones where food is expected to be most abundant. At Macquarie Island, lactating cows concentrated their foraging trips in two areas; 30km and 100 km north of the Island (Robinson 2002 cited in DEH 2003g; Robinson et al. 2002 cited in DEH 2003g). Shorter, overnight trips are usually within 10 km of the island.

Lactating cows are estimated to have nutritional needs 1.5-1.8 times those of non-lactating females (Costa 1991 cited in DEH 2003g).

Movement Patterns

This species is not reported to be migratory, although individuals have been reported to make long movements. For example, two animals tagged as pups on Marion Island were sighted at Heard Island almost 3000 km distant (Goldsworthy & Shaughnessy 1989) and a few have been reported at sea in the South Indian Ocean (Tynan 1996 cited in DEH 2003g).

Threats

Historical threats

On Macquarie Island, between 1810 and 1820, approximately 193 300 fur seals were harvested. By 1850, Fur Seals were overharvested almost to extinction on the Island (Gerber & Hilborn 2001).

Potential Threats

Fishing Practices

There are two fisheries operating in the Australian Subantarctic, both of which are managed by the Australian Fisheries Management Authority (AFMA). They are the Heard Island and McDonald Islands Fisheries (HIMI), and the Macquarie Island Fishery. Both are directed at Patagonian Toothfish (Dissostichus eleginoides), however Mackerel Icefish (Champsocephalus gunnari) are also targeted in the HIMI. Two vessels operate in the HIMI and one operates in the Macquarie Island Fishery. Fishery observers are present, and information on these fisheries is collated by the AFMA (2001). Few seals have been caught by these fishing vessels. In four years of fishing, the HIMI has caught two seal skeletons, one dead Antarctic Fur Seal and a live specimen that was released.

According to the 2004 recovery plan for this species there is low potential for sub-Antarctic fur seals to interact with fisheries. Operational interactions between seals and fisheries are well informed in sub-Antarctic fisheries but biological interactions are not well understood. As seal populations recover, the likelihood of interaction with mainland fisheries will increase (DEH 2003g).

Oil Spills

Several ships visit Macquarie Island each summer to re-supply the Australian Antarctic Division base. The large quantities of fuel pumped ashore near the main seal colony (at Secluded Beach), just north of the base, presents a possible hazard. Tour ships also visit these Islands and are another potential source of oil spills (Shaughnessy 1999). There is potential for increased visitation to the reserve, but the management and timing of visits currently affords protection to the seals (DEH 2003g).

Climate change

Fur seals are highly sensitive to changes in sea surface temperature. A 1% increase in sea surface temperature can result in a greater than 10% reduction in fecundity (Goldsworthy et al. 2002b cited in DEH 2003g). Global warming may be a threat to seals if it drives fur seal prey to greater depths or locations far from breeding colonies (Trillmich and Ono 1991 cited in DEH 2003g).

Genetic Swamping

Hybrids between the Antarctic, New Zealand and sub-Antarctic fur seal has occurred at a number of sites (including Macquarie Island) and may threaten the integrity of the species (Shaughnessy 1999).

(Australian government)

-TSF-

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