Last modified: Tuesday September 22nd, 1999

Fur Seals

Juan Fernandez fur seal

 Arctocephalus philippii (Peters, 1866)

Nomenclature

This species was placed, together with Arctocephalus townsendi, in the separate genus Arctophoca, but it is now included in the genus Arctocephalus.

Appearance

Males are about 200 cm long and weigh around 140 kg. Females are much smaller: 140 cm and 50 kg. There are no recorded measurements for pups. The external characteristics of this species are very similar to those of Arctocephalus townsendi. The fur is black with a lighter ventral and chest. Snout and flippers are elongated.

Distribution

This species can be found in the Juan Fernandez Archipelago and on the Desventuradas Islands off the coast of Chile.

Feeding

The diet consists of fish, cephalopods and lobster.

Population dynamics and life history

no data available.

Trophic relations

no data available.

Interactions

none recorded.

Population size

This species was nearly exterminated in the 16th to 19th century. It was rediscovered in 1965. A census in 1970 indicated about 750 fur seals present in the Juan Fernandez Archipelago. On the Desventuradas Islands only 2 were sighted. According to local fishermen the actual population of the Desventuradas may be higher, because this species tends to hide in sea caves. There seems to be a yearly population increase of 16-17%.

Exploitation

There is no harvest of this species. There is some illegal catch for lobster bait and fur. Poaching is prohibited since 1965.

Threats to the population

Because of its limited size, the population is vulnerable. Lack of genetic diversity may be an additional problem.

References

Aguayo L., A. (1979)
Juan Fernandez Fur Seal. in: Mammals in the Seas, volume II: pinniped species summaries and report on sirenians. FAO Fisheries Series No. 5, Vol II, pp. 28-30
Bonner, W.N. (1981)
Southern Fur Seals, Arctocephalus (Geoffroy Saint-Hilaire and Cuvier, 1826), in: Ridgway, S.H. and Harrison, R.J. (eds.): Handbook of Marine Mammals, vol. 1: The walrus, sea lions, fur seals and sea otter, pp. 161-208, Academic Press Inc., Ltd, London
King, J.E. (1983)
Seals of the world, 2nd edition. British Museum (Natural History), London and Oxford University Press, Oxford, 240pp.

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South American fur seal

 Arctocephalus australis (Zimmerman, 1783)

Nomenclature

Two subspecies have been described: Arctocephalus australis australis (Zimmerman, 1783) for the Falkland population and Arctocephalus australis gracilis (Nehring, 1887) for the mainland population. The validity of these subspecies is disputed.

Appearance

Of this species the males are usually about 200 cm long and weigh 160 kg. Females measure 150 cm and weigh 50 kg. Pups weigh between 3 and 5 kg at birth. Adult males are blackish grey in colour and have some manes. Females and immature males are greyish black with a lighter ventral.

Distribution

This species usually lives on rocky coasts. There is a population on the Falkland Islands. On the South American mainland, this species ranges from Recife des Torres in Southern Brazil down to Terra del Fuego on the Atlantic side and on the Pacific side up to Lima, Peru.

Feeding

The diet contains a wide variety of organisms, including fish (among others anchovy), cephalopods, crustaceans, lamellibranchs and sea snails.

Population dynamics and life history

Females become mature at the age of 3, males at 7 years. The pregnancy rate is 82%. Gestation lasts 1 year. Lactation lasts 6 to 12 months. Longevity is unknown. Pups mortality varies with local circumstances, ranging from 4 to 82.5%. Adult mortality is unknown.

Trophic relations

no data available.

Interactions

Occasionally South American fur seals are caught in fishing nets, but this is not common, since this species is not a boat follower like Otaria or Arctocephalus pusillus.

Population size

Ground, boat and aerial counts have been carried out in several areas. The Falkland population totals 15-16,000 animals. On the mainland, the largest population is in Uruguay: 252,000 animals. This population is still increasing. The total mainland population is about 307,000. For some areas there are no accurate counts available, but for most areas the population seems to be stable or even increasing.

Exploitation

In Uruguay there is an annual harvest of immature males, upto 12,000 per year (Vaz-Ferreira, 1982). Other populations are not exploited.

Threats to the population

Currently none. Increased offshore oil exploitation may create ecological problems that could affect the population.

References

Bonner, W.N. (1981)
Southern Fur Seals, Arctocephalus (Geoffroy Saint-Hilaire and Cuvier, 1826), in: Ridgway, S.H. and Harrison, R.J. (eds.): Handbook of Marine Mammals, vol. 1: The walrus, sea lions, fur seals and sea otter, pp. 161-208, Academic Press Inc., Ltd, London
King, J.E. (1983)
Seals of the world, 2nd edition. British Museum (Natural History), London and Oxford University Press, Oxford, 240pp.
Vaz-Ferreira, R. (1979)
South American Fur Seal. in: Mammals in the Seas, volume II: pinniped species summaries and report on sirenians. FAO Fisheries Series No. 5, Vol II, pp. 34-36
Vaz-Ferreira, R. (1982)
Arctocephalus australis Zimmermann, South American Fur Seal. in: Mammals in the Seas, Volume IV: small cetaceans, seals, sirenians and otters. FAO Fisheries Series, No. 5, vol. IV, pp. 497-508

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Subantarctic fur seal

 Arctocephalus tropicalis (Gray, 1872)

Nomenclature

This species is occasionally confused with Arctocephalus gazella, with which it breeds synpatrically, but it is clearly a different species. It is sometimes also called the Amsterdam Island fur seal.

Appearance

Males are usually about 180 cm long and weigh about 165 kg. Females measure 145 cm and 55 kg. Pups are 65 cm at birth and weigh about 5 kg. This fur seal is brown to dark grey in colour, with a yellow chest and throat area and a dark brown ventral. Bulls are usually darker than females.

Distribution

The subantarctic fur seal can be found on the following island groups: Tristan da Cunha, Cough Island, Prince Edward Island, Marion Island, Crozet Island, Amsterdam Island and Saint Paul Island. Shaughnessy (1982) distinguishes three different breeding groups: the Tristan da Cunha-Cough group, the Prince Edward group and the New Amsterdam-Saint Paul group. There is no breeding in the Crozet Archipelago.

Feeding

The diet consists of several fish species, cephalopods, euphasiids and penguins.

Population dynamics and life history

No data are available about the onset of maturity and about the pregnancy rate. Gestation lasts 51 weeks and lactation 7 months. Longevity is unknown. The mortality rates are as follows: neonatal: 0.9%; 1-3 weeks: 32-63%; 3 weeks-5 months: 1-2%. This results in an average mortality for the first 5 months of 47%. Mortality from weaning to the age of 2 years ranges from 40 to 50%. Adult mortality is unknown.

Trophic relations

This species breeds sympatrically with Arctocephalus gazella on Marion Island. There competition for space and food can be expected. There are some indications that interbreeding occurs between these two species. The subantarctic fur seal is predated upon by sharks and the killer whale.

Interactions

None recorded.

Population size

Bonner (1979) estimates the total population at 123,500. He mentions for Tristan da Cunha: 13,500; Cough: 100,000; Prince Edward: 4,600; Saint Paul/Amsterdam: 5,300. Shaughnessy (1982), basing his estimates on earlier censuses comes up with a total population of 23,400, a much lower estimate. The main difference with Bonner's estimate is the Cough population: according to Shaughnessy this population totals some 13,000 animals. Also his estimate for Prince Edward is lower: 1,110. These discrepancies needs further investigation.

The total population has been severely over-exploited in the past but seems to be recovering well now.

Exploitation

There is currently no harvest of this species. Some animals have been taken for display purposes. All the colonies are protected. Marion and Prince Edward resort under the Sea Bird and Seal Protection Act of South Africa. Cough and Tristan resort under the Tristan da Cunha Conservation Ordinance of 1976. New Amsterdam and Saint Paul are regulated by the French Chamber of Deputies.

Threats to the population

No data available.

References

Bonner, W.N. (1979)
Subantarctic fur seal. in: Mammals in the Seas, volume II: pinniped species summaries and report on sirenians. FAO Fisheries Series No. 5, Vol II, pp. 52-54
Bonner, W.N. (1981)
Southern Fur Seals, Arctocephalus (Geoffroy Saint-Hilaire and Cuvier, 1826), in: Ridgway, S.H. and Harrison, R.J. (eds.): Handbook of Marine Mammals, vol. 1: The walrus, sea lions, fur seals and sea otter, pp. 161-208, Academic Press Inc., Ltd, London
King, J.E. (1983)
Seals of the world, 2nd edition. British Museum (Natural History), London and Oxford University Press, Oxford, 240pp.
Shaughnessy, P.D. (1982)
The status of the Amsterdam Island fur seal. in: Mammals in the Seas, Volume V: small cetaceans, seals, sirenians and otters. FAO Fisheries Series, No. 5, vol. V, pp. 411-421

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Antarctic fur seal

 Arctocephalus gazella (Peters, 1875)

Nomenclature

This species is occasionally confused with Arctocephalus tropicalis, with which it breeds sympatrically. Early account refer to the Antarctic fur seal as Arctocephalus australis. An alternative common name for this species is the Kerguelen fur seal.

Appearance

Adult males range in length from 170 to 200 cm and in weight from 90 to 200 kg. For females these ranges are 120 to 140 cm and 20 to 51 kg respectively. Pups are 60-70 cm at birth and weigh 5-6kg. The back and sides of adult fur seals are grey to brownish, with a creamy throat and chest and a dark gingery ventral. Males have manes with a lot of white hairs, which give the manes a grizzled look. Pups are very dark brown or black.

Distribution

This fur seal can be found on the islands south of the Antarctic Convergence and north of 65°S. The major breeding area is in South Georgia. Other breeding colonies can be found on the South Sandwich Islands, Bouvetya, South Shetland, Marion Island, Heard, McDonald Islands and possibly on Kerguelen. This species apparently does not migrate.

Feeding

The Antarctic fur seal feeds mainly on krill (euphasiids), but also takes fish, squid and birds. Feeding dives occur mainly at night, between 20:00 and 21:00 hrs and between 02:00 and 03:00 hrs. These peaks correlate with the nocturnal rise of krill, the major summer prey. In diving bouts, the seal make about 19 dives per hour. All dives are shallow (21-30m, maximum recorded: 101m) (Kooyman et al, 1986).

Population dynamics and life history

Females become mature at 3-4 years, males at 6-7 years. Gestation lasts 51 weeks and lactation 100-120 days. The pregnancy rate is unknown. Longevity for males is in excess of 13 years, for females over 23 years. Female mortality while breeding is 10%. The breeding season extends from November through April. Weaning occurs at on average 117 days. The weaning period is short and fixed and is initiated by the pups. Thus pups born earlier in the season suckle longer than pups that are born later (Doidge et al, 1986).

Trophic relations

In part of the range this species breeds sympatrically with Arctocephalus tropicalis and may be competing for space and food. The leopard seal, Hydrurga leptonyx, predates on pups of this species.

Interactions

no data available.

Population size

From surface counts, aerial sample counts and capture-recapture tests a population estimate of 350,000 was derived (Bonner, 1979), the majority of which was located in South Georgia. There was a rapid increase in population size noted. Later Bonner (1982) estimated the population of South Georga alone at 369,000.

Exploitation

Currently there is no harvest of this species on land. It is possible that some animals are taken at sea. The Antarctic fur seal is protected throughout its range. South Georgia and South Sandwich are included in the Falkland Islands Dependencies Conservation Ordinance, Bouvetya is protected by Norway and Kerguelen by France. Harvest is prohibited south of 60S by the Antarctic Treaty and the Convention for the Conservation of Antarctic Seals.

Threats to the population

Currently the population is not treathened. A future expansion of krill exploitation in this area could seriously affect this species, since it would affect its main food source.

References

Bonner, W.N. (1979)
Antarctic (Kerguelen) fur seal. in: Mammals in the Seas, volume II: pinniped species summaries and report on sirenians. FAO Fisheries Series No. 5, Vol II, pp. 49-51
Bonner, W.N. (1981)
Southern Fur Seals, Arctocephalus (Geoffroy Saint-Hilaire and Cuvier, 1826), in: Ridgway, S.H. and Harrison, R.J. (eds.): Handbook of Marine Mammals, vol. 1: The walrus, sea lions, fur seals and sea otter, pp. 161-208, Academic Press Inc., Ltd, London
Bonner, W.N. (1982)
The status of the Antarctic fur seal, Arctocephala gazella. in: Mammals in the Seas, Volume IV: small cetaceans, seals, sirenians and otters. FAO Fisheries Series, No. 5, vol. IV, pp. 423-430
Doidge, D.W., McCann, T.S. and Croxall, J.P. (1986)
Attendance behavior of Antarctic fur seals. In: R.L. Gentry and G.L. Kooyman: Fur seals - Maternal strategies on land and at sea, pp.: 103-114, Princeton University Press.
King, J.E. (1983)
Seals of the world, 2nd edition. British Museum (Natural History), London and Oxford University Press, Oxford, 240pp.
Kooyman, G.L., Davis, R.W. and Croxall, J.P. (1986)
Diving behavior of Antarctic fur seals. In: R.L. Gentry and G.L. Kooyman: Fur seals - Maternal strategies on land and at sea, pp.: 115-125, Princeton University Press.

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South African fur seal

 Arctocephalus pusillus pusillus (Schreber, 1776)

Nomenclature

This is one of the two subspecies of Arctocephalus pusillus, that are currently recognized. The other is A.c. doriferus. A common name that is frequently used for this species instead of South African fur seal is Cape fur seal.

Appearance

The males measure about 230-235 cm and weigh about 360 kg, although weights upto 700 kg have been mentioned. Females are about 180 cm and weigh 120 kg. Pups measure 60-80 cm and weigh 6 kg at birth. The fur of the males is dark grey on the dorsal side and lighter ventrally. Females have a brownish grey dorsal and a light brown ventral. Pups are black at birth.

Distribution

This species can be found along the coasts of South Africa and Southwest Africa (Namibia). There is no migration.

Feeding

The South African fur seal forages of pelagic shoaling fish and cephalopods. Among the fish maasbanders (Trachurus) and pichards are the most common, but also anchovies and hakes are eaten. Among the cephalopods Loligois the most common. Stomachs that were examined contained 70% fish, 20% cephalopods and 2% crustaceans; the other 8% was made up of miscellaneous matter. They consume an estimated 270 kg of fish per animal per year, which means a total consumption of over 170,000 metric tons of fish per year for the whole population. While feeding, the seals dive on average 2.1 minutes, with a maximum of 7.5 minutes. The dives usually go to less than 50m. The deepest recorded dive was to 204m (Kooyman and Gentry, 1986).

Population dynamics and life history

Females become mature at the age of 3. The age at maturity for males is unknown. The pregnancy rate is 74%. Gestation lasts about 1 year, which includes a delay of implantation of about 4 months. Lactation can last upto 12 months, but usually is 9-11 months. The breeding season lasts from November through December (David and Rand, 1986). There are no data available on longevity or natural mortality.

Trophic relations

The fur seal competes for food with dolphins and porpoises and several bird species, such as cape gannetts, jackass penguins and cormorants. Increases in the fur seal population have caused displacement of several bird colonies. The fur seal are predated upon by sharks and killer whales. Pups are taken by the black-backed jackal.

Interactions

There is a high degree of interference with commercial fisheries, especially in the purse seine fisheries for pilchard and anchovy and the trawler fisheries for hake. They have been seen taking fish from the nets, or even from the ship and chasing the fish out of the net. Occasionally some seals will get entangled in the nets and drown. Fur seals also get entangled in lost gear, such as nets and fishing lines. In a survey 0.12% of the population was in some way entangled in lost gear (Shaughnessy, 1985).

Population size

Using aerial photography and tag recapture techniques the population has been estimate at a total of 850,000 (Shaughnessy, 1979&1982). The annual pup production is around 211,000. The number of breeding bulls is 13,000 (the average harem size is 28 animals, range: 7-66). The pup production for 1976 was between 188,500 and 249,100 (Cressie and Shaughnessy, 1987).

Exploitation

Every year between 60,000 and 80,000 pups, aged 6-10 (after the first moult) are taken for furs. Also about 2,000 males are killed each year. The average pup kill for 1970-1979 was 73,400 per year (Cressie and Shaughnessy, 1987). The harvest seems to be at MSY level, which is 35% of the female pups and 40% of the male pups born annually. Apart from the hunting, the fur seal population is exploited as a major tourist attraction. The South African fur seal is managed under the Sea Birds and Seal Protection Act and a quota system is inforced.

Threats to the population

None. The problem of entanglement in lost fishing gear should be looked into. This is an unnecessary increase in mortality and is non-specific: other species of marine mammals will be affected by it as well.

References

Bonner, W.N. (1981)
Southern Fur Seals, Arctocephalus (Geoffroy Saint-Hilaire and Cuvier, 1826), in: Ridgway, S.H. and Harrison, R.J. (eds.): Handbook of Marine Mammals, vol. 1: The walrus, sea lions, fur seals and sea otter, pp. 161-208, Academic Press Inc., Ltd, London
Cressie, N.A.C., Shaughnessy, P.D. (1987)
Statistical methods for estimating numbers of Cape fur seal pups from aerial surveys. Mar. Mamm. Sci. 3(4): 297-307
David, J.H.M. and Rand, R.W. (1986)
Attendance behavior of South African fur seals. In: R.L. Gentry and G.L. Kooyman: Fur seals - Maternal strategies on land and at sea, pp.: 126-141, Princeton University Press.
King, J.E. (1983)
Seals of the world, 2nd edition. British Museum (Natural History), London and Oxford University Press, Oxford, 240pp.
Kooyman, G.L. and Gentry, R.L. (1986)
Diving behavior of South African fur seals. In: R.L. Gentry and G.L. Kooyman: Fur seals - Maternal strategies on land and at sea, pp.: 142-152, Princeton University Press.
Shaughnessy, P.D. (1979)
Cape (South African) Fur Seal. in: Mammals in the Seas, volume II: pinniped species summaries and report on sirenians. FAO Fisheries Series No. 5, Vol II. pp. 37-40
Shaughnessy, P.D. (1982)
The status of seals in South Africa and Namibia. in: Mammals in the Seas, Volume IV: small cetaceans, seals, sirenians and otters. FAO Fisheries Series, No. 5, vol. IV, pp. 383-410
Shaughnessy, P.D. (1985)
Interactions between fisheries and Cape fur seals. in: Beddington, J.R., Beverton, R.J.H. and Lavigne, D.M. (eds.): Marine Mammals and Fisheries, pp. 119-134, George Allen & Unwin (Publishers) Ltd, London

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Australian fur seal

 Arctocephalus pusillus doriferus (Wood Jones, 1925)

Nomenclature

This one of the two subspecies of Arctocephalus pusillus, to which also the South African fur seal belongs. The Australian fur seal has also been described as a separate species as Arctocephalus tasmanicus and Arctocephalus doriferus, but its inclusion in Arctocephalus pusillus is now widely accepted. Another common name for this species is Tasmanian fur seal.

Appearance

The males measure 200-225 cm and weigh 220-360 kg. Females are 125-170 cm and weigh 36-110 kg.At birth, male pups measure 64-81 cm and weigh 5-12 kg, and female pups measure 62-79 cm and weigh 4-10 kg. There is a marked sexual dimorphism in this fur seal. Males are dark greyish brown with a paler ventral and a coarse mane. Females are a pale fawn to greyish brown with a pale throat and a brown ventral. At birth pups are black. After the moult they are greyish fawn with a pale throat.

Distribution

The Australian fur seal lives from 32°S to 43°S and from 152°E to 142°E. They can be found along the Australian coast from Seals Rocks in New South Wales, through South Tasmania, to Lady Julia Percy Island, Victoria.

Feeding

This fur seal is a deep diver and seems to get its food from deeper waters. It is known to dive at least 500 m deep. Its diet consists of squid, octopus and a wide variety of fishes.

Population dynamics and life history

The age at maturity is for females 3-6 years and for males 9-12 year. The pregnancy rate is 68%. Gestation lasts 51 weeks, including a delay of implantation of 3 months. Longevity and adult mortality are unknown. Pup mortality in the first 2 months is 15%.

Trophic relations

There is no overlap and hence no competition with Arctocephalus forsteri or Neophoca cinerea. The main predators of this species are the white shark and the killer whale.

Interactions

There is an intensive interaction with local fisheries. Significant numbers of immature fur seal are killed in nets or traps, or areshot by fishermen.

Population size

There have been direct counts and aerial photograpy censuses carried out. The population consists of 19,000 to 24,000 animals and is stable.

Exploitation

There is no harvesting of this species, as its territories are protected by State Law.

Threats to the population

The main problem areas for this fur seal are: increased pollution with pesticides and heavy metals of its habitat, increased disturbance and the high level of net entanglement cases.

References

Bonner, W.N. (1981)
Southern Fur Seals, Arctocephalus (Geoffroy Saint-Hilaire and Cuvier, 1826), in: Ridgway, S.H. and Harrison, R.J. (eds.): Handbook of Marine Mammals, vol. 1: The walrus, sea lions, fur seals and sea otter, pp. 161-208, Academic Press Inc., Ltd, London
King, J.E. (1983)
Seals of the world, 2nd edition. British Museum (Natural History), London and Oxford University Press, Oxford, 240pp.
Warneke, R. (1979)
Australian fur seal. in: Mammals in the Seas, volume II: pinniped species summaries and report on sirenians. FAO Fisheries Series No. 5, Vol II, pp. 41-44

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New Zealand fur seal

 Arctocephalus forsteri (Lesson, 1828)

Nomenclature

The Australian population was originally described as to belong to Arctocephalus doriferus (which is now a subspecies of Arctocephalus pusillus), but later it was realized that this animal was similar to the New Zealand fur seal, described as Arctocephalus forsteri. The Australian population is also referred to as the Australian fur seal, though this name should not be used, since it is confusing.

Appearance

Males of this species measure 145-250 cm and weigh 120-185 kg. Females are 125-150 cm, and weigh 40-70 kg. Pups are 40-45 cm at birth and weigh on average 4.3 kg. There is a marked sexual dimorphism in this species. Males have thick manes and much darker in colour than the females. They have a dark brown to black dorsal side with a lighter ventral. Females are brown to dark brown with greyish tones. Pups are black at birth, turning greyish brown after moult.

Distribution

This species is usually found on rocky coasts. There are two distinct populations. One population can be found on the southern coast of Australia, from 117°E to 136°E (West Australia and South Australia). The other population lives in New Zealand, in summer on the South Island and surroundings, south of 43°S. In winter this fur seal can be found on the North Island as well, upto 34°S.

Feeding

Analyses of stomach contents shows that 38% of the diet consists of barracouta, 27% of octopus, 24% of squid and 9% of small fish. Occasionally birds are eaten as well.

Population dynamics and life history

Females become mature at 4-6 years of age, males at 10-12 years. Lactation lasts 10-11 months. Other population dynamics parameters are unknown.

Trophic relations

Probably there is no competition for food resources. Sharks and killer whales include this species in their diets.

Interactions

In some places local populations may be tourist attractions, but most populations live in remote areas. Occasionally some are trapped in fishing nets or drown in lobster traps.

Population size

The Australian population has been overexploited in the past, but is now estimated to consist of "several thousands" of animals and seems to be stable. Robinson and Dennis (1988) mention estimates of 2,500 and "less than 5,000" for the Australian populations. The New Zealand population is estimated at 30,000-50,000 and seems to be increasing.

Exploitation

This species is protected throughtout its range and is not exploited.

Threats to the population

None known.

References

Bonner, W.N. (1981)
Southern Fur Seals, Arctocephalus (Geoffroy Saint-Hilaire and Cuvier, 1826), in: Ridgway, S.H. and Harrison, R.J. (eds.): Handbook of Marine Mammals, vol. 1: The walrus, sea lions, fur seals and sea otter, pp. 161-208, Academic Press Inc., Ltd, London
Crawley, M.C., Warneke, R. (1979)
New Zealand Fur Seal. in: Mammals in the Seas, volume II: pinniped species summaries and report on sirenians. FAO Fisheries Series No. 5, Vol II, pp. 45-48
King, J.E. (1983)
Seals of the world, 2nd edition. British Museum (Natural History), London and Oxford University Press, Oxford, 240pp.
Robinson, A.C. and Dennis, T.E. (1988)
The status and management of seal populations in South Australia. In: M.L. Augee (ed.): Marine Mammals of Australasia: Field biology and captive management, pp: 87-110. Royal Zoological Society of New South Wales.

Note on the photographs

All the pictures of New Zealand fur seals on this page were taken in November 1996 at Seal Bay on Kangaroo Island, Australia.

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Northern fur seal

 Callorhinus ursinus (Linnaeus, 1758)

Nomenclature

Other common names often used for this species include Alaskan fur seal and Pribilof fur seal.

Appearance

Males of this species are on average 210 cm long and weigh 180-270 kg. Females measure 140 cm and weigh 43-50 kg. At birth male pups are 66 cm and weigh 5.4 kg, while female pups are 63 cm long and weigh 4.5 kg. This species is characterized by its short down-curved rostrum, long pinnae and long rear flippers. Males vary in colour from grey to reddish brown to black. Females have a silvery grey dorsal and a reddish brown ventral side with a white to grey balze on the chest. Pups are black with a white spot on the oxilla.

Distribution

There are 5 stocks based on the following locations: Pribilof Islands, Commander Islands, Robben Island, Kuril Islands and San Miguel Island. In winter there is a southbound migration.

Feeding

Northern fur seals are opportunistic feeders: they usually take the most abundant fish and cephalopod species available (Kajimura, 1985). The diet includes squid, hake, anchovy, herring, sand lance, capelin, pollack, mackerel and smelt. They consume about 10% of their body weight in fish per day. This means an estimated total annual consumption of the Pribilof stock alone of about 965,000 tonnes.

Some seals appear to make deep feeding dives exclusively, some make only shallow dives and others make both deep and shallow dives. Deep diving occurs throughout the day, whereas shallow dives occurs just after dusk and just before dawn. About 69% of all dives occurs at night. Diving seems to occur in bouts. In a diving bout about 10 dives are made per hour and a diving lasts on average 2.2 hours. Average dive time is 2.6 minutes. Maximum dive time is 5-7 minutes. The most frequent dives are to 50-60m and to 175m. The deepest recorded dive was to 207m (Gentry et al, 1986)

Population dynamics and life history

This species has a high commercial value and consequently it has been extensively studied. Females reach maturity at the age of 3 in Asian populations and at 4 in North American stocks. Males become mature at 9 to 15. The pregnancy rate is 60% for the North American stocks, slightly higher in Asia. Gestation lasts 51 weeks, which includes a delay of implantation of 3 to 4 months. Lactation lasts 4 months. Longevity of this species is 25 years. Pup mortality is variable, but on average it is about 10%. Total first year mortality is 50%. For age groups 1 to 3 mortality is 20%. For age groups 3 to 7 the mortality for males is 20% and for females 11%. Adult mortality for males is 38% and for females 11%.

The breeding season extends through June and July. No females attend the breeding sites in winter. Weaning is abrupt and total and is initiated by the pups. Weaning occurs before the pup is 125 days old (Gentry & Holt, 1986). Suckling occurs in bouts: females spend 7 days on shore, nursing the pups and then return to sea and come back for 2-day suckling periods. Fur seal milk is composed of 44% fat, 42% water and 14% protein by mass at the start of a suckling period. The fat content decreases during that suckling period. Male pups take significantly more milk than female pups: 4270 ml vs. 2650 ml per 2-day bout (Costa and Gentry, 1986).

Trophic relations

There is competition for food with Northern sea lions, Eumetopias jubatus, and harbour seals, Phoca vitulina. Adults fall prey to sharks and killer whales, while pups can be taken by Northern sea lions.

Interactions

There is competition with commercial fisheries. As a result quite some fur seals are drowned in gill nets. At least 3,500 animals are killed this way each year, although this number may be as high as 7,000. Also drift nets and fishery-related debris take their toll among the fur seal. 0.17-0.51% of the seals harvested on the Pribilof Islands are in some way entangled in debris.

Population size

This species has been severely over-exploited in the past but has now recovered. Stock estimates for 1982 were (Lander and Kajimura, 1982): The total population is therefore an estimated 1,765,000 animals.

Exploitation

The Northern fur seal is harvested under the regulations of the North Pacific Fur Seal Commission, which aims at Maximum Sustainable Yield (MSY). The harvest consists mainly of subadult males of ages 3 and 4. The harvest rates are: Robben Island: 22-44% of the male pup production, with a maximum of 3,000; Commander Islands: 32-42% of the male pup production, with a maximum of 2,000; Pribilof Islands: 20-31% of the male pup production (which means an average harvest of 30,000).

Threats to the population

Potential threats include a reduction in food supply by over-exploitation of the fish stocks, negative ecological effects of the oil exploitation in the Bering Sea and the driftnet-fisheries debris problem.

References

Bonner, W.N. (1982)
Seals and Man. A study of interactions. University of Washington Press, Seattle, 170pp.
Costa, D.P. and Gentry, R.L. (1986)
Free ranging energetics of Northern fur seals. In: R.L. Gentry and G.L. Kooyman: Fur seals - Maternal strategies on land and at sea, pp.: 79-101, Princeton University Press.
Gentry, R.L. (1981)
Northern Fur Seal, Callorhinus ursinus (Linnaeus, 1758). in: Ridgway, S.H. and Harrison, R.J. (eds.): Handbook of Marine Mammals, vol. 1: The walrus, sea lions, fur seals and sea otter, pp. 143-160, Academic Press Inc., Ltd, London
Gentry, R.L. and Holt, J.R. (1986)
Attendance behavior of Northern fur seals. In: R.L. Gentry and G.L. Kooyman: Fur seals - Maternal strategies on land and at sea, pp.: 41-60, Princeton University Press.
Gentry, R.L. Kooyman, G.L. and Goebel, M.E. (1986)
Feeding and diving behavior of Northern fur seals. In: R.L. Gentry and G.L. Kooyman: Fur seals - Maternal strategies on land and at sea, pp.: 61-78, Princeton University Press.
Kajimura, H. (1985)
Opportunistic feeding by the Northern fur seal (Callorhinus ursinus). in: Beddington, J.R., Beverton, R.J.H. and Lavigne, D.M. (eds.): Marine Mammals and Fisheries, pp. 300-318, George Allen & Unwin (Publishers) Ltd, London
King, J.E. (1983)
Seals of the world, 2nd edition. British Museum (Natural History), London and Oxford University Press, Oxford, 240pp.
Lander, R.H. (1979)
Alaskan or Northern Fur Seal. in: Mammals in the Seas, volume II: pinniped species summaries and report on sirenians. FAO Fisheries Series No. 5, Vol II, pp. 19-23
Lander, R.H., Kajimura, H. (1982)
Status of Northern Fur Seals. in: Mammals in the Seas, Volume IV: small cetaceans, seals, sirenians and otters. FAO Fisheries Series, No. 5, vol. IV, pp. 319-345

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