Facts on Cape Fur Seal (Arctocephalus pusillus pusillus)
Cape fur seals belong to the eared seal family (Otariidae) and are a sub species of the Afro-Australian Fur seal. Sub species are genetically similar species that are separated geographically (living in different parts of the world) or ecologically (same area, different prey or habitat preferences). The Cape fur seal and Australian fur seal are almost identical in appearance but are classified as sub species because of their different geographical ranges. In South Africa the Cape fur seal is the only seal species that breeds here, however, other species such as elephant seals, Subantarctic fur seals, leopard seals occasionally occur along our coastline.
In 2004 it was estimated that around 2 million Cape fur seals occur in southern Africa and that the population had shown a stable increase since 1993 (Butterworth et al. 1995, Kirkman et al. 2007). Cape fur seal distribution extends from Algoa Bay in the east to northern Namibia on the west coast and they normally live within 160km from the coast. Occasional records from Angola and Marion Island (1,500km from South Africa)have also been recorded. There are 40 breeding colonies throughout their distributional range, with 8 on the main land and the rest on islands. The colonies can range in numbers from a few dozen individuals to several thousand seals.
Cape Fur seal are the largest fur seal species and exhibit large sexual dimorphism (males and females differ in size) (to find out more follow the link : http://oceanadventures.co.za/males-females-species-look-different/). The bulls can grow up to 2.5m in length and weigh 200-350 kg, the cows are much smaller at 1.2-1.6m and 40-80 kg. Males have a large chest and a thick mane and the smaller females have a silver-grey fur. New born pups are velvet black but after their first moult at 3-5 months of age they change to an olive grey colour. After a year their coat turns silver-grey.
Cape fur seals can live up to 21 years. Males reached sexual maturity at 4-5 years of age but normally don’t start breeding until 8-13 years of age and the females reached sexual maturity at 3-4 years of age. The males haul out from mid-October and will spend 6 weeks on land protecting their harem (up to 66 females) while living off their blubber (fat reserves). The females haul out and give birth in late November to early December and 6-10 days after giving birth, she is mated again by the dominant bull. The Cape fur seal gestation period is 8 months, but females only give birth after 12 months. This is due to a process known as ‘delayed implantation’, whereby the already fertilized egg only begins to generate after a period of 4 months. During the first 3 months after giving birth, the females will spend 2-3 days on land and 3-4 days at sea hunting. When they return to the colony females will call for their pup and the pup will answer with a unique call. When the female reaches her pup they will sniff each other and only the pup that smells right will be feed. The pups are weaned at 4-6 months, but it has been found that some can suckle for 1-2 years.
Fur seals are unique in several aspects, notably the way in which they sleep. They have two sleeping patterns, one on land and one in the water (Lyamin et al 2008). On land they sleep more like land mammals, occasionally opening their eyes to look for predators. In the ocean they rest different parts of their brain at different times and stay afloat by paddling with one foreflipper, briefly opening one eye to watch for predators (for more information flow the link http://oceanadventures.co.za/facts-whales-dolphins-sleep/).
Cape fur seals feed on shoaling fish, squid, octopus, sharks and rays. They can dive to depths of over 200m and hold their breath for up to 7.5min. They generally hunt alone but can form hunting parties of up to 15 individuals. They are very active and social in the water and territorial on land. Their main predator is the great white shark, but they (mainly the pups) are also hunted by brown hyenas (Hyaena brunnea) and black-backed jackals (Canis mesomelas) (mainly pups) on land.
In the 17th-19th centuries the Afro-Australian fur seal was heavily hunted and both sub species were reduced to low levels. Both species are now protected and the global population for the Afro-Australian fur seal is healthy so they are classified as least concern by the IUCN. However, the population in Namibia might not be healthy because of a low pup production. Cape fur seals have been protected in South Africa since 1893 but were still commercially harvested until the 1990´s by the government (Butterworth et al. 1995). Historically in Plettenberg Bay there were two colonies, one on Beacon Island (that is now joined to the main land and developed) and one at Seal Point on the Robberg peninsula (that was extinct by 1890). Seals started returning to Robberg in the 1990’s (Stewardson and Brett 2000) and the first pups where observed in 1996/1997. This started the speculation that Robberg could once again become a breeding colony (Huisamen et al. 2011). In 2012 the Robberg seal colony was classified as a breeding colony because more than 100 pups were born in one year. Since then, the overall population has fluctuated between 2500 and 5500 seals.
– Butterworth, D. S., Punt, A. E. and Wickens, P. A. 1995. The effects of future consumption by the Cape fur seal on catches and catch rates of the Cape hakes. 3. Modelling the dynamics of the Cape fur seal Arctocephalus pusillus pusillus. South African Journal of Marine Science 16: 161-183.
– Huisamen J. Kirkman S.P. Watson L.H. Cockcroft V.G Pistorius P.A 2011. Recolonization of the Robberg Peninsula (Plettenberg Bay, South Africa) by Cape fur seals African Journal of Marine Science 2011, 33(3): 453–461
– Kirkman, S. P., Oosthuizen, W. H., Meyer, M. A., Kotze, P. G. H , Roux, J.-P. and Underhill, L. G. 2007. Making sense of censuses and dealing with missing data: trends in pup counts of Cape fur seal Arctocephalus pusillus pusillus for the period 1972-2004. South African Journal of Marine Science 29: 161-176.
– Lyamin O.L. Kosenko P.O. Lapierre J.L Mukhametov L.M and Siegel J.M 2008 Fur Seals Display a Strong Drive for Bilateral Slow-Wave Sleep While on Land. The Journal of Neuroscience: 28(48):12614 –12621
– Whales dolphins and other marine mammals of the world (2006) by Hadoram Shirihai and Brett Jarrett. Prinston field guides 2006
– Smithers’ Mammals of Southern Africa a field Guide by Peter Apps Struik Nature edition 2012