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Brown fur seal

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Brown fur seal
Hauling-out on the Hippolyte Rocks off the east coast of Tasmania
CITES Appendix II (CITES)[2]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Clade: Pinnipedia
Family: Otariidae
Genus: Arctocephalus
Species:
A. pusillus
Binomial name
Arctocephalus pusillus
(Schreber, 1775)
Subspecies
  • A. p. pusillus (Cape/South African fur seal)
  • A. p. doriferus (Australian fur seal)
Distribution of the brown fur seal, dark blue: breeding colonies; light blue: nonbreeding individuals

The brown fur seal (Arctocephalus pusillus), also known as the Cape fur seal, and Afro-Australian fur seal, is a species of fur seal.

Description

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Skull of male

The brown fur seal is the largest and most robust member of the fur seals. It has a large and broad head with a pointed snout that may be flat or turned up slightly.[3] They have external ear flaps (pinnae) and their whiskers (vibrissae) are long, possibly growing back past the pinnae, especially in adult males. The fore-flippers are covered with sparse hairs over about three-quarters of their length. The hind-flippers are short relative to the large body, with short, fleshy tips on the digits.[3] The size and weight of the brown fur seal depends on the subspecies; the Southern African subspecies is, on average, slightly larger than the Australian subspecies. Males of the African subspecies (A. p. pusillus) are 2.3 m (7.5 ft) in length on average and weigh 200–300 kg (440–660 lb).[4] Females are smaller, averaging 1.8 m (5.9 ft) in length and typically weighing 120 kg (260 lb).[5] Males of the Australian subspecies (A. p. doriferus) are 2.0–2.2 m (6.6–7.2 ft) in length and weigh 190–280 kg (420–620 lb).[6] Females are 1.2–1.8 m (3.9–5.9 ft) length and weigh 36–110 kilograms (79–243 lb).[5]

Adult male brown fur seals are dark gray to brown, with a darker mane of short, coarse hairs and a lighter belly, while adult females are light brown to gray, with a light throat and darker back and belly. The fore-flippers of the fur seal are dark brown to black.[3] Pups are born black, molting to gray with a pale throat within 3–5 months.[3] The skull of the African subspecies has a larger crest between the mastoid process and the jugular process of the exoccipital.[5]

  • Male A. p. doriferus
    Male A. p. doriferus
  • Female A. p. doriferus
    Female A. p. doriferus
  • Juvenile A. p. doriferus
    Juvenile A. p. doriferus

Ecology

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Baby seal
A fur seal colony at Duiker Island, South Africa
Fur seal underwater at Agulhas Bank
Cape Cross colony, Namibia

The African fur seal inhabits the southern and southwestern coast of Africa, from Cape Cross, Namibia to around the Cape of Good Hope and from Black Rocks, near Port Elizabeth in the Eastern Cape province.[3] The Australian fur seal lives in the Bass Strait, on four islands off Victoria (southeastern Australia), and five islands off Tasmania.[3] Brown fur seals prefer to haul-out and breed on rocky outcrops and small islands, rock ledges and exposed reefs, as well as on rocky, pebble or boulder beaches. However, some larger colonies can be found on sandy beaches, such as in South Africa.[3] Fur seals spend most of the year at-sea, but are never too far from land. They have been recorded 160 km from land, but this is not common.[5]

The African fur seal's diet is made of up to 70% fish, 20% squid, and 2% crab.[7] Also eaten are other crustaceans, cephalopods and sometimes seabirds.[5][7] In rare instances, they have even been documented attacking and eating sharks. A recent incident occurred off Cape Point, South Africa, where a large male was observed attacking and killing five blue sharks between 1.0 and 1.4 m long. Observers concluded that the seal likely killed the sharks to eat the fish-rich contents of their stomachs, as well as their livers, as a source of energy.[8] The Australian fur seal mostly eats squid, octopus, fish, and lobsters.[5][7] The brown fur seal dives for its food. The African subspecies can dive as deep as 204 m (669') for as long as 7.5 minutes.[9] The Australian subspecies generally feeds at lower depths, diving an average of 120 m[7] (394'), and going as deep as 200 m (656').[9]

The brown fur seal's main predators are the great white shark, and orcas (killer whales), as well as occasionally vagrant southern elephant seals.[10] African land-based predators, primarily of pups, include black-backed jackals, brown hyenas and occasionally lions[11] on the Skeleton Coast in Namibia. In addition, seagulls and other seabirds are thought to peck the eyes out of baby seals, especially sick or injured individuals, to render them helpless and disabled, as they begin to feast on their flesh.[12]

In False Bay, the seals employ a number of defensive strategies while in shark-infested waters, such as:

  • Swimming in large groups, and harassing sharks in the vicinity.
  • Low porpoising, to increase subsurface vigilance.
  • Darting in different directions, to cause confusion when attacked.
  • Using their agility to stay out-of-reach.
  • Swimming near the dorsal fin to stay clear of the shark's jaws, when pursued.[13]

Behaviour

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Brown fur seal colony at Friar Islands, Tasmania
Brown fur seals in Cape Cross

Acoustic behavior

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Australian fur seals are social animals that use vocalizations in a broad range of contexts. These vocalizations have been shown to contain individually unique properties important for enabling individual recognition.[14] This is particularly important for the reunion of mothers and pups that experience repeated separations whilst mothers are out at sea foraging, sometimes for days at a time. Upon their return, mothers need to locate their pups.[15][16] This reunion process may also be facilitated through a combination of smell and spatial cues.

In males, increases in testosterone and calling rates are seen in conjunction with the onset of the breeding season.[17] Males can also differentiate neighboring males from stranger males, responding more aggressively to the vocalizations of strangers.[18] This difference in response is suspected because the threat posed by a stranger is unknown and potentially greater than their neighbor, which they would have previously encountered while establishing their territories.[19][20]

Breeding behaviour

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Brown fur seals often gather into colonies on rookeries in numbers ranging from 500 to 1500, at least for the Australian subspecies.[5] While fur seals spend most of the year at sea, they never fully evacuate the rookeries, as mothers and pups return to them throughout the year. No dispersal from a colony is established, although some fur seals from one colony have been found at another. True boundaries do not exist between the colonies. When at sea, they travel in small feeding groups. Brown fur seals begin to breed in the middle of October, when males haul out on shore to establish territories though display, vocalisations, sparring, and sometimes actual combat.[21] They fast at this time and do not eat until after mating in November or December. When the females arrive, they fight among themselves for territories in which to give birth. Female territories are smaller than those of males and are always located within them. Females within a male's territory can be considered part of his harem. However, males do not herd the females, which are free to choose their mates and judge them based on the value of their territories. For the Australian fur seals, 82% of copulations are performed by males whose territories are located directly at the water's edge.[9] Copulation between the male and his females begins 6 days after they give birth to their pups conceived from the previous year. However, a delay occurs in the implantation of the blastocyst, which lasts 4 months in the African subspecies and 3 months in the Australian subspecies.[9] Gestation for the brown fur seal typically lasts a year less a few days.[9]

Suckling

After mating, females begin alternating brief periods of foraging at sea with several days ashore nursing their pups.[3] Foraging trips last about 7 days in winter and about 4 days in summer and autumn. When a mother returns from sea to feed her pup, she emits a loud call which attracts all the nearby pups, but she only responds to her pup. She possibly can recognize her pup by smell.[9] When left alone, pups gather in groups and play during the evening.[5] Pups are usually weaned at 4–6 months old.[3]

Human interactions

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Brown fur seal Gaston in Prague Zoo
Fur seals used for tourist attraction in Namibia

This species is an inquisitive and friendly animal when in the water, and often accompanies scuba divers. They swim around divers for periods of several minutes at a time, even at a depth of 60 m. On land, they are far less relaxed and tend to panic when humans come near them.

Australian fur seals were hunted intensively between 1798 and 1825 for commercial reasons. Seal hunting stopped in Australia in 1923, and their population is still recovering, causing increasing friction with South Australian fishermen as their range expands.[22] Breeding and haul-out sites are protected by law. South African fur seals have a very robust and healthy population. Harvesting of seals was outlawed in South Africa in 1990.

Brown fur seals are still harvested in Namibia. Permits are issued for the killing of pups for their luxurious fur and adult males for their genitalia, which are considered an aphrodisiac in some countries. It is also considered necessary to limit seal numbers in Namibia because of the supposed effect seals have on the country's fish harvest. Research by environmental groups disputes this.[23]

Unexplained aggression

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In January 2023, media reports indicated that seals have been attacking humans in South Africa, particularly in Cape Town area. Scientists believed it was due to the presence of a brain-altering poison in the fish they consume. The poison affects their behaviour making them more aggressive towards humans. Some attribute the aggressive behaviour to the surge of toxic red tide algae, fuelled by pollution and climate change. The incidents have increased in recent times, leading to concern and calls for further investigation.[24][25]

In July 2024, it was confirmed that 17 seals along a 650-km stretch of coastline between Cape Town and Plettenberg Bay tested positive for rabies, and that could be the cause of the attacking behaviour in fur seals.[26] The hypothesis is the rabies was acquired from black-backed jackals who prey on the seals; rabies is endemic among southern African jackals.[27]

Threat by marine debris and industry

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A 2021 study published in The Marine Pollution Bulletin found that the Brown fur seal colonies in Namibia are vulnerable to extensive entanglement in marine debris as a result of extensive pollution in the oceans.[28] The study overall found that juveniles are more prone to become entangled in marine debris, and that 53% of all entanglements discovered were caused by fishing line.[28] Another study by the University of Stirling conducted a similar study on marine pollution and found an almost identical percentage, 52%, of entanglements of brown fur seals were caused by fishing debris.[29]

Ocean Conservation Namibia, a local animal conservation group based in Walvis Bay, was formed specifically by volunteers who capture entangled seals and free them from entanglement discarded by ships and fishing industries.[30] The organization monitors the coast regularly but their founder, Naude Dreyer, told reporters of drastically declining numbers of seals as pollution continues to increase.[31]

See also

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References

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  1. ^ Hofmeyr, G.J.G. (2015). "Arctocephalus pusillus". IUCN Red List of Threatened Species. 2015: e.T2060A45224212. doi:10.2305/IUCN.UK.2015-4.RLTS.T2060A45224212.en. Retrieved 12 November 2021.
  2. ^ "Appendices | CITES". cites.org. Retrieved 14 January 2022.
  3. ^ a b c d e f g h i Randall R. Reeves; Brent S. Stewart; Phillip J. Clapham; James A. Powell (2002). National Audubon Society Guide to Marine Mammals of the World. Alfred A. Knopf, Inc. ISBN 0-375-41141-0.
  4. ^ "The S.A. Fur Seal". Botany.uwc.ac.za. 1 February 2001. Archived from the original on 1 July 2014. Retrieved 13 April 2013.
  5. ^ a b c d e f g h King, J. (1983). Seals of the World. Ithaca, New York: Comstock Publishing Associates.
  6. ^ Arnould, John P.Y.; Hindell, Mark A. (2001). "Dive behaviour, foraging location... preview & related info". Canadian Journal of Zoology. 79: 35–48. doi:10.1139/cjz-79-1-35. hdl:10536/DRO/DU:30015951. Archived from the original on 16 February 2013. Retrieved 13 April 2013.
  7. ^ a b c d Schliemann, H. (1990). "Eared Seals and Walruses". In Grzimek, B. (ed.). Grzimek's Encyclopedia of Mammals. New York: McGraw-Hill. pp. 168–203.
  8. ^ Smithsonian Magazine; Nuwer, Rachel. "Fur Seals Caught Preying on Sharks Off South Africa". Smithsonian Magazine.
  9. ^ a b c d e f Riedman, M. (1990). The Pinnipeds: Seals, Sea Lions, and Walruses. Berkeley: University of California Press.
  10. ^ Penry, Gwenith S.; Baartman, Ashwynn C.; Bester, Marthán N. (2013). "Vagrant elephant seal predation on Cape fur seal pups, Plettenberg Bay, South Africa". Polar Biology. 36 (9): 1381–1383. Bibcode:2013PoBio..36.1381P. doi:10.1007/s00300-013-1350-4. S2CID 20350457.
  11. ^ "Beach lions again hunting seals and coastal birds in Namibia, after 35 years". 29 January 2019.
  12. ^ Palermo (2015). "Gruesome Meal: Seagulls Snack on Baby Seals' Eyeballs". Live Science.
  13. ^ "Anti-Predatory Strategies of Cape Fur Seals at Seal Island". www.elasmo-research.org.
  14. ^ Tripovich, J.S.; Canfield, R.; Rogers, T.L.; Arnould, J.P.Y. (2008). "Characterisation of Australian fur seal vocalizations during the breeding season". Marine Mammal Science. 24 (4): 913–928. Bibcode:2008MMamS..24..913T. doi:10.1111/j.1748-7692.2008.00229.x.
  15. ^ Tripovich, J.S.; Rogers, T.L.; Canfield, R.; Arnould, J.P.Y (2006). "Individual variation in the pup attraction call produced by female Australian fur seals during early lactation" (PDF). Journal of the Acoustical Society of America. 120 (1): 502–509. Bibcode:2006ASAJ..120..502T. doi:10.1121/1.2202864. hdl:10536/DRO/DU:30009058. PMID 16875246.
  16. ^ Tripovich, J.S.; Canfield, R.; Rogers, T.L.; Arnould, J.P.Y. (2009). "Individual variation of the Female Attraction Call produced by Australian fur seal pups throughout the maternal dependence period". Bioacoustics. 18 (3): 259–276. Bibcode:2009Bioac..18..259T. doi:10.1080/09524622.2009.9753605. S2CID 76654284.
  17. ^ Tripovich, J.S.; Rogers, T.L.; Dutton, G. (2009). "Faecal testosterone concentrations and the acoustic behavior of two male captive Australian fur seals". Australian Mammalogy. 31 (2): 117–122. doi:10.1071/AM09009.
  18. ^ Tripovich, J.S.; Rogers, T.L.; Arnould, J.P.Y. (2005). "Species-specific characteristics and individual variation of the Bark Call produced by male Australian fur seals (Arctocephalus pusillus doriferus)" (PDF). Bioacoustics. 15 (1): 502–509. Bibcode:2005Bioac..15...79T. doi:10.1080/09524622.2005.9753539. hdl:10536/DRO/DU:30008864. S2CID 83645557.
  19. ^ Tripovich, J.S.; Charrier, I.; Rogers, T.L.; Canfield, R.; Arnould, J.P.Y. (2008). "Acoustic features involved in the neighbour-stranger vocal recognition process in male Australian fur seals". Behavioural Processes. 79 (1): 74–80. doi:10.1016/j.beproc.2008.04.007. PMID 18571339. S2CID 727101.
  20. ^ Tripovich, J.S.; Charrier, I.; Rogers, T.L.; Canfield, R.; Arnould, J.P.Y. (2008). "Who goes there? The dear-enemy effect in male Australian fur seals (Arctocephalus pusillus doriferus)". Marine Mammal Science. 24 (4): 941–948. doi:10.1111/j.1748-7692.2008.00222.x.
  21. ^ Tripovich, Joy S.; Rogers, Tracey L.; Arnould, John P.Y. (2005). "SPECIES-SPECIFIC CHARACTERISTICS AND INDIVIDUAL VARIATION OF THE BARK CALL PRODUCED BY MALE AUSTRALIAN FUR SEALS, ARCTOCEPHALUS PUSILLUS DORIFERUS". Bioacoustics. 15 (1): 79–96. Bibcode:2005Bioac..15...79T. doi:10.1080/09524622.2005.9753539. ISSN 0952-4622. S2CID 83645557.
  22. ^ "Aggressive fur seals attacking rare birds, pelicans and fishing nets, SA fishermen warn". 891 ABC Adelaide. 24 April 2015. Retrieved 24 April 2015.
  23. ^ "South African and Australian Fur Seals (Arctocephalus pusillus)". www.pinnipeds.org.
  24. ^ Town, Jane Flanagan, Cape. "Seals driven mad by eating toxic fish attack Cape Town bathers". The Times. ISSN 0140-0460. Retrieved 3 February 2023.{{cite news}}: CS1 maint: multiple names: authors list (link)
  25. ^ What's behind South Africa's rise in seal attacks?, France 24, 20 January 2023
  26. ^ "'Everyone was paddling to get away': seals with rabies alarm South Africa's surfers", The Guardian, 11 July 2024
  27. ^ Dall, Nick. "Why are Cape fur seals in South Africa infected with rabies?". Al Jazeera. Archived from the original on 8 September 2024. Retrieved 9 September 2024.
  28. ^ a b Curtis, S.; Elwen, S. H.; Dreyer, N.; Gridley, T. (19 October 2021). "Entanglement of Cape fur seals (Arctocephalus pusillus pusillus) at colonies in central Namibia". Marine Pollution Bulletin. 171: 112759. Bibcode:2021MarPB.17112759C. doi:10.1016/j.marpolbul.2021.112759. PMID 34364137 – via PubMed.
  29. ^ "Plastics and pusillus - Investigating the impact of plastic pollution on Cape Fur Seals (Arctocephalus pusillus pusillus) at colonies in central Namibia" (PDF). Retrieved 5 August 2023.
  30. ^ "Namibia's seal saviour: How one man is freeing hundreds of animals from deadly debris". Beautiful News. 28 November 2019.
  31. ^ "The Havoc Of Climate Change Claimed The Lives Of Thousands Of Seals In Namibia". 16 November 2020.
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