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Overview

Distribution

Range Description

Subantarctic Fur Seals are widely-distributed in the southern Hemisphere. They breed on sub-Antarctic islands north of the Antarctic Polar Front, including Amsterdam (Guinet et al. 1994), the Crozets (Guinet et al. 1994), Gough (Bester et al. 2006), Macquarie (Shaughnessy 1993), the Prince Edward Islands (Bester et al. 2003, Hofmeyr et al. 2006a), Saint Paul (Guinet et al. 1994) and Tristan da Cunha (C. Glass pers. comm. in SCAR EGS 2004). They have also been recorded breeding on Heard Island (Goldsworthy and Shaughnessy 1989). Vagrants have been recorded on the coasts of Antarctica (Shaughnessy and Burton 1986), southern South America (Aguiar-dos Santos and Haimovici 2001, Bastida et al. 1999), southern Africa (Bester 1989, Shaughnessy and Ross 1980), Madagascar (Garrigue and Ross 1996), Australia (Gales et al. 1992), and New Zealand (Taylor 1990), and on Bouvetøya (Hofmeyr et al. 2006b), the Comores (David et al. 1993), the Juan Fernandez Islands (Torres and Aguayo 1984), Îles Kerguelen (Wynen et al. 2000), Mauritius (David and Salmon 2003) and South Georgia (Payne 1979).
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Geographic Range

Arctocephalus tropicalus, the Subantarctic Fur Seal, can be found on islands near the South Pole just north of the Antarctic Convergence. These include the islands of Amsterdam, Crozet, Grough, Marion, Prince Edward, St. Paul, and Tristan (King, 1983).

Biogeographic Regions: ethiopian (Native ); neotropical (Native ); australian (Native ); oceanic islands (Native ); atlantic ocean (Native ); pacific ocean (Native )

  • King, J. 1983. Seals of the World. Ithaca, New York: Comstock Publishing Associates.
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Physical Description

Morphology

Physical Description

Subantarctic fur seal males measure between 1.5 and 1.8 meters in length and weigh from 95 to 140 kilograms (King, 1983: 46). The coat on the male is a dark gray or brown in color dorsally while the underside and face area are paler and a little more orange. The males also have a crest of slightly longer and rougher white tipped hairs on top of their head. The females of the species are slightly smaller, measuring between 1.2 and 1.3 meters in length and weighing approximately 50 kilograms (King, 1983: 46). The female's coat is very similar to the male's, the notable difference being their lack of the white tipped crest. Both males and females have long white whiskers (King, 1983: 46). Subantarctic fur seal pups are colored differently from their parents. Pups are black with pale orange fur on the underside. Their whiskers are also black. This coat is replaced by an adult coat during the pups' first molt between 8 and 12 weeks of age (King, 1987: 47).

Range mass: 50 to 140 kg.

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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
Subantarctic Fur Seals are sexually dimorphic, with adult males being up to 1.8 m long and weighing 70-165 kg; adult females are 1.19–1.52 m long and weigh 25-67 kg, with a mean of around 50 kg. Newborns weigh 4-4.4 kg (Laws 1993). Females attain maturity at 5 years of age (Bester 1995). Gestation lasts 51 weeks. Longevity is unknown (Reijnders et al. 1993).

Subantarctic Fur Seals are polygynous; males defend territories with vocal and postural displays and fighting (Bester 1981, Kerley 1983). They prefer rough rocky or boulder beaches with sources of shade or exposure to prevailing winds (Bester 1982). Pups are born from late October to early January, with a peak in mid-December. Females give birth within 6 days of arriving at the colony with oestrous and mating occurring 8-12 days later. Females spend the time between the births of their pups and oestrous, with their newborn before mating and departing for the first of a series of foraging trips they will make before weaning their pup at approximately 11 months of age (Bester 1981, Kerley 1983). Trip durations of mothers increase over the course of lactation from 6-10 days to 23-28 days (Georges and Guinet 2000, Kirkman et al. 2002). Dives become deeper and slightly longer over the summer, starting at a mean depth of 16.6 m and increasing to 19 m. Dives are seldom deeper than 100 m or longer than 4 minutes (Georges et al. 2000).

Subantarctic Fur Seals are sympatric with other species of fur seals at three sites. Hybridization with Antarctic Fur Seals occurs at the Prince Edward Islands (Hofmeyr et al. 2006a) and the Îles Crozet (Guinet et al. 1994), and with both Antarctic Fur Seals and New Zealand Fur Seals at Macquarie Island (Goldsworthy et al. 1999).

Subantarctic Fur Seals are opportunistic and pelagic foragers. They feed on myctophid and notothenid fish, cephalopods, and small numbers of crustaceans at the Prince Edward Islands (Klages and Bester 1998) and at Macquarie Island (Robinson et al. 2002). At Amsterdam Island they are know to take Rockhopper Penguins (Paulian 1964).

Systems
  • Terrestrial
  • Marine
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The males of the species spend most of the year out at sea, hauling out on the rookeries only during the mating season. Females spend much of their time close to the rookeries, hauling out at regular intervals for nursing and again during the breeding season. Breeding occurs on land and rocky coastal areas are preferred for the rookeries (King, 1983; Riedman, 1990).

Aquatic Biomes: coastal

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Depth range based on 24 specimens in 1 taxon.
Water temperature and chemistry ranges based on 24 samples.

Environmental ranges
  Depth range (m): 0 - 0
  Temperature range (°C): 1.883 - 15.471
  Nitrate (umol/L): 3.046 - 26.539
  Salinity (PPS): 33.870 - 35.265
  Oxygen (ml/l): 5.787 - 7.723
  Phosphate (umol/l): 0.445 - 1.800
  Silicate (umol/l): 3.083 - 19.880

Graphical representation

Temperature range (°C): 1.883 - 15.471

Nitrate (umol/L): 3.046 - 26.539

Salinity (PPS): 33.870 - 35.265

Oxygen (ml/l): 5.787 - 7.723

Phosphate (umol/l): 0.445 - 1.800

Silicate (umol/l): 3.083 - 19.880
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Trophic Strategy

Food Habits

The Subantarctic fur seal's diet consists mainly of squid and is supplemented by krill, fish and, at times, penguins or other birds (Riedman, 1990; King, 1987). Like most marine mammals, A. tropicalus finds at least some of its food in the ocean.

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Life History and Behavior

Life Expectancy

Lifespan, longevity, and ageing

Observations: Little is known about the longevity of these animals, but one wild born specimen was still living in captivity at about 18.5 years of age (Richard Weigl 2005).
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Reproduction

The breeding season for A. tropicalus begins in September when the males haul out on shore at the breeding grounds, or rookeries, to establish territories by displays, sparring, or actual battle. The females come ashore in October and November and choose male territories within which to bear their young. They later mate with the male possessing that territory. It is also at this time that immature animals begin avoiding the rookeries.

Pups are born beginning in late November through January. Most pups are born in early December. Cows give birth to a single pup and begin lactation almost immediately. Lactation is almost continuous for the next 8-12 days, after which the cow mates and begins returning to the sea. She will spend increasing amounts of time at sea over the next year, returning only to nurse her pup. Lactation continues throughout the pup's first year or until the cow's next pup is born. Copulation occurs between 8 and 12 days after the cow gives birth, but there is a delay of about 4.3 months in the implantation of the blastocyst (Riedman, 1990: 250). The pups are approximately 4.5 kilograms and 60 centimeters at birth, the males being slightly larger than the females. Females reach sexual maturity between 4 and 6 years of age while males reach sexual maturity earlier, between 3 and 4 years of age (Riedman, 1990: 237).

Average birth mass: 4420 g.

Average gestation period: 357 days.

Average number of offspring: 1.

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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
LC
Least Concern

Red List Criteria

Version
3.1

Year Assessed
2008

Assessor/s
Hofmeyr, G. & Kovacs, K. (IUCN SSC Pinniped Specialist Group)

Reviewer/s
Kovacs, K. & Lowry, L. (Pinniped Red List Authority)

Contributor/s

Justification
Due to its large and apparently increasing population size, the Subantarctic Fur Seal should remain classified as Least Concern.

IUCN Evaluation of the Subantarctic Fur Seal, Arctocephalus tropicalis
Prepared by the Pinniped Specialist Group

A. Population reduction
Declines measured over the longer of 10 years or 3 generations
A1 CR > 90%; EN > 70%; VU > 50%
Al. Population reduction observed, estimated, inferred, or suspected in the past where the causes of the reduction are clearly reversible AND understood AND have ceased, based on and specifying any of the following:
(a) direct observation
(b) an index of abundance appropriate to the taxon
(c) a decline in area of occupancy (AOO), extent of occurrence (EOO) and/or habitat quality
(d) actual or potential levels of exploitation
(e) effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.

All subpopulations of Subantarctic Fur Seals are currently either increasing or stable.

A2, A3 & A4 CR > 80%; EN > 50%; VU > 30%
A2. Population reduction observed, estimated, inferred, or suspected in the past where the causes of reduction may not have ceased OR may not be understood OR may not be reversible, based on (a) to (e) under A1.

All subpopulations of Subantarctic Fur Seals are currently either increasing or stable.

A3. Population reduction projected or suspected to be met in the future (up to a maximum of 100 years) based on (b) to (e) under A1.

A population reduction of Subantarctic Fur Seals is not expected in the future. It is possible, however, that global climate change may alter environmental conditions to the detriment of this species.

A4. An observed, estimated, inferred, projected or suspected population reduction (up to a maximum of 100 years) where the time period must include both the past and the future, and where the causes of reduction may not have ceased OR may not be understood OR may not be reversible, based on (a) to (e) under A1.

All subpopulations of Subantarctic Fur Seals are currently either increasing or stable. While a population reduction is not expected in the future, it is possible that global climate change may alter environmental conditions to the detriment of this species.

B. Geographic range in the form of either B1 (extent of occurrence) AND/OR B2 (area of occupancy)
B1.
Extent of occurrence (EOO): CR < 100 km²; EN < 5,000 km²; VU < 20,000 km²

The EOO of Subantarctic fur seals is > 20,000 km².

B2. Area of occupancy (AOO): CR < 10 km²; EN < 500 km²; VU < 2,000 km²

The AOO of Subantarctic fur seals is > 2,000 km².

AND at least 2 of the following:
(a)
Severely fragmented, OR number of locations: CR = 1; EN < 5; VU < 10
(b) Continuing decline in any of: (i) extent of occurrence; (ii) area of occupancy; (iii) area, extent and/or quality of habitat; (iv) number of locations or subpopulations; (v) number of mature individuals.
(c) Extreme fluctuations in any of: (i) extent of occurrence; (ii) area of occupancy; (iii) number of locations or subpopulations; (iv) number of mature individuals.

Subpopulations are not severely fragmented. Subantarctic Fur Seals are found at numerous breeding rookeries on eight islands or island groups. This species is not experiencing continuing decline or extreme fluctuations in extent of occurrence, area of occupancy, number of subpopulations, number of mature individuals or area, extent or quality of habitat.

C. Small population size and decline
Number of mature individuals: CR < 250; EN < 2,500; VU < 10,000
AND either C1 or C2:
C1.
An estimated continuing decline of at least: CR = 25% in 3 years or 1 generation; EN = 20% in 5 years or 2 generations; VU = 10% in 10 years or 3 generations (up to a max. of 100 years in future)
C2. A continuing decline AND (a) and/or (b):
(a i) Number of mature individuals in each subpopulation: CR < 50; EN < 250; VU < 1,000
or
(a ii)
% individuals in one subpopulation: CR = 90–100%; EN = 95–100%; VU = 100%
(b) Extreme fluctuations in the number of mature individuals.

The current abundance of Subantarctic Fur Seals is well in excess of 10,000. The number of mature individuals in 5 of 8 subpopulations is estimated to be over 1000. Approximately 50 % of individuals belong to the Gough Island subpopulation.

D. Very small or restricted population
Number of mature individuals: CR < 50; EN < 250; VU < 1,000 AND/OR restricted area of occupancy typically: AOO < 20 km² or number of locations < 5

The current abundance of mature Subantarctic Fur Seals is well in excess of 1,000, the AOO is far larger than 20 km² and the number of locations is > 5.

E. Quantitative analysis
Indicating the probability of extinction in the wild to be: Indicating the probability of extinction in the wild to be: CR > 50% in 10 years or 3 generations (100 years max.); EN > 20% in 20 years or 5 generations (100 years max.); VU > 10% in 100 years

There has been no quantitative analysis of the probability of extinction of Subantarctic Fur Seals.

Listing recommendation — Estimates indicate a Subantarctic Fur Seal abundance of several hundred thousand individuals breeding at numerous sites on eight islands or island groups. 95% of Subantarctic Fur Seals breed at just three of these sites: Gough Island, the Prince Edward Islands and Amsterdam Island. Two other subpopulations are estimated to contain of more than a 1,000 adults. All subpopulations are either stable or increasing. No major threats currently affect any subpopulations and it is unlikely that any will do so in the near future. This being said, Subantarctic Fur Seals may be affected by global climate change should it impact upon their abiotic environment or prey species. It should also be noted that Subantarctic Fur Seals experienced a severe population bottleneck during the 19th and 20th Centuries that has reduced their genetic variation and which may render this species vulnerable to disease or climate change. Under present conditions Subantarctic Fur Seals qualify for listing in the category Least Concern.
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Much of the subantarctic fur seal populations had been taken by sealers by the 1830s, but enough of the animals survived in order to make a comeback. A majority of the population, which was estimated at 214,000 individuals in 1983, is located on Gough Island (King, 1983: 46). In 1990 the population was estimated at 300,000 individuals (Riedman, 1990: 60). More recently the population was estimated at 310,000 individuals and rising. Currently there are no recognized threats to the subantarctic fur seal population.

CITES: appendix ii

IUCN Red List of Threatened Species: least concern

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Population

Population
The total population was estimated to be greater than 310,000 animals in 1987 and all indications are that it has been steadily growing since that time (SCAR EGS 2004). Subantarctic fur seals breed at numerous sites on eight islands or island groups. Some 95% of Subantarctic Fur Seals breed at three of these sites: Gough Island, the Prince Edward Islands and Amsterdam Island (Bester et al. 2003, Bester et al. 2006, Guinet et al. 1994, Hofmeyr et al. 2006a). Two other subpopulations are estimated to contain more than 1,000 adults (Guinet et al. 1994). All subpopulations are either stable or increasing (SCAR EGS 2004).

Population Trend
Increasing
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Threats

Major Threats
Similar to all of the other southern fur seals, Subantarctic Fur Seals were over-exploited by sealers in the 18th and 19th century and were reduced to the brink of extinction at the beginning of the 20th century. Since then their population has increased rapidly and they have reoccupied much of their former range. This population bottleneck has reduced their genetic variation and may render this species vulnerable to disease or climate change (Wynen et al. 2000).

Tourist visits at Subantarctic Fur Seal haulout sites are rare and thought to cause minimal disturbance (Kirkwood et al. 2003, Shirihai 2002). Few fisheries take place in waters occupied by this species (Hanchet et al. 2003). Entanglement in marine debris occurs at the Prince Edward Islands, but with incidences of less than 1% (Hofmeyr et al. 2002).

While the impact of climate change on fur seals is unknown, it is potentially detrimental (Chown et al. 1998, Learmonth et al. 2006). Fur seals are also at risk of mass mortality from infectious diseases, though breeding on isolated islands affords some species a higher degree of protection from disease (Chown et al. 1998, Lavigne and Schmitz 1990).
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Management

Conservation Actions

Conservation Actions
Subantarctic Fur Seals live in some of the most remote oceanic areas and breed on many of the most isolated islands on earth. All of the breeding islands are managed as protected areas or parks by the governments that claim these territories. Seals on the Prince Edward Islands are protected by the South African Sea Bird and Seal Protection Act of 1973 and also inhabit a special nature reserve (PEIMC 1996). Seals on Gough and Tristan Islands are protected by the Tristan da Cunha Conservation Ordinance of 1976. Amsterdam and Saint Paul Islands are regulated by the French Chamber of Deputies, while at Macquarie Island, the fur seals are protected by the Tasmanian Department of Parks, Wildlife, and Heritage (Reijnders et al. 1993). Listed on CITES Appendix II.
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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Positive

In the past, these seals were hunted for their fur.

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Wikipedia

Subantarctic fur seal

The subantarctic fur seal (Arctocephalus tropicalis) is found in the southern parts of the Indian, Pacific, and Atlantic Oceans. It was first described by Gray in 1872 from a specimen recovered in northern Australia—hence the inappropriate specific name tropicalis.

Contents

Description[edit]

The subantarctic fur seal is medium-sized compared with other fur seals. Males grow to 2 m and 160 kg, whereas females are substantially smaller—1.4 m and 50 kg. Both sexes have distinctive, creamy-orange chests and faces. Their bellies are more brownish. Males have a dark grey to black back. The females are lighter grey. Pups are black at birth, but molt at about three months old. The snout is short and flat. The flippers are short and broad. Subantarctic fur seals live for about 20–25 years.

Distribution[edit]

Subantarctic fur seals are geographically widespread. As their name implies, they generally breed in more northerly locations than the Antarctic fur seals. The largest breeding colonies are on Gough Island in the south Atlantic and Île Amsterdam in the southern part of the Indian Ocean. Breeding grounds are also found at Marion Island in the Prince Edward Islands (where there is an overlap with Antarctic fur seals), Crozet Islands and the Macquarie Island. Where grounds overlap, the subantarctic species can be identified by the orange colour on the chest.

About 300,000 of the species alive today, probably substantially down from when they were first discovered in 1810, as they were hunted for their pelts throughout the 19th century. Populations are recovering rapidly, though, in most areas whilst under the protection of the Convention for the Conservation of Antarctic Seals. A small population on Heard Island is endangered. Unlike the Antarctic fur seal, whose genetic variation is low due to hunting making all but one breeding colony extinct by 1900, the diversity amongst subantarctic specimens remains high.

Diet[edit]

Subantarctic fur seals hunt in shallow waters at night, when myctophid fish come close to the surface. They also feed on squid.

References[edit]

  1. ^ Hofmeyr, G. & Kovacs, K. (2008). Arctocephalus tropicalis. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 30 January 2009.

Further reading[edit]

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