Afro-Australian Fur Seals are the largest of all Fur Seals. Mean asymptotic mass and length of males is 229 kg (range 218-360 kg) and 221 cm (range 201-227 cm), and females are 85 kg (range 41-113 kg) and 163 cm (136-171 cm; Arnould and Warneke 2002, Kirkwood and Goldsworthy 2013). Pups at birth are 60-80 cm in length and weigh 5-12 kg. The Cape Fur Seal is slightly smaller (Warneke 1995).
Females become sexually mature at three to six years and males at nine to 12 years. Maximum longevity recorded is 16.9 years for males and 20.9 years for females (Arnould and Warneke 2002). The annual pregnancy rate of females has been estimated at 71% for Cape Fur Seals and 73% for Australian Fur Seals (Warneke and Shaughnessy 1985, Wickens and York 1997). Gestation lasts 51 weeks, including a three-month delay of implantation. Adult mortality rates are unknown (Butterworth et al. 1995, Reijnders et al. 1993).
Cape Fur Seals are highly polygynous. The breeding season is highly synchronous, taking place between late October and the beginning of January, with adult males arriving at the colonies first. Females give birth 1.5-2 days after arrival ashore. The peak of pupping is in the first week of December (Warnecke and Shaughnessy 1985, David 1987a, De Villiers and Roux 1992). Adult females attend the pup for about six to nine days before coming into oestrous, mating, and departing on their first foraging trip (Rand 1955, Warnecke and Shaughnessy 1985). Foraging intervals are shorter for Cape Fur Seals (an average of 5.2 days) than Australian Fur Seals (six days), probably reflecting greater availability of food (Gamel et al. 2005, Kirkwood and Arnould 2011). While some pups may start foraging at seven months, they are usually weaned at 10-12 months, with suckling rarely continuing for two to three years (Warneke and Shaughnessy 1985, David and Rand 1986).
While Cape Fur Seals forage in both pelagic and benthic environments (Kooyman and Gentry 1986, David 1987b, Stewardson 2001), Australian Fur Seals are primarily benthic feeders (Arnould and Kirkwood 2008, Kirkwood and Arnould 2011, Kirkwood and Goldsworthy 2013). Characteristics of dives vary between sites (Kooyman and Gentry 1986, Stewardson 2001, Arnould and Kirkwood 2008, Kirkwood and Arnould 2011). The majority of recorded dives of Cape Fur Seals on the west coast of South Africa are to less than 50 m depth (Kooyman and Gentry 1986), while those on the southeast coast are to more than 60 m (Stewardson 2001). Mean dive duration of Cape Fur Seals varies between one minute (Stewardson 2001) and 2.1 minutes (Kooyman and Gentry 1986). Foraging dives by lactating Australian Fur Seal females are usually to 65–85 m with a maximum depth of 164 m, and dives usually last from 2.0-3.7 minutes, with a maximum duration of 8.9 minutes (Arnould and Hindell 2001). The diurnal frequency of Cape Fur Seal dives shows a bimodal distribution with most dives taking place at dusk or during the first half of the night, with a smaller peak after dawn (Kooyman and Gentry 1986, Stewardson 2001). The maximum recorded diving depth is 204 m (Kooyman and Gentry 1986).
Cape Fur Seals are generalist foragers that take a wide variety of prey, including Cape Hake, Horse Mackerel, Pelagic Goby, Pilchards, Anchovy, squid of the genus Loligo, Rock Lobster, shrimp, prawns and amphipods (David 1987b, de Bruyn et al. 2003, Mecenero et al. 2006). They have also been reported to occasionally take African Penguins and several species of flying seabirds (Makhado et al. 2006). Australian Fur Seals eat a wide range of fish species including Redbait, Leatherjacket species, Jack Mackerel, Barracouta, Red Rock Cod and Flathead (Goldsworthy et al. 2003, Hume et al. 2004, Page et al. 2005, Littnan et al. 2007, Kirkwood et al. 2008, Deagle et al. 2009). Cephalopods are also important prey with key species being Gould’s Squid, Octopus spp., and Cuttlefish (Hume et al. 2004, Page et al. 2005, Kirkwood et al. 2008).
Great White Sharks (Pemberton and Kirkwood 1994, Martin et al. 2005) and Killer Whales (Rice and Saayman 1987) are predators of Afro-Australian Fur Seals at sea. On shore, Cape Fur Seal pups are preyed on by Black-backed Jackals and Brown Hyenas (Skinner et al. 1995, Oosthuizen et al. 1997, Kuhn et al. 2008).
Estimates indicate that approximately two million Cape Fur Seals bred at some 40 colonies or colony groups in 2009. However, there have been substantial changes in distribution during this time period with an increase in the number of colonies, a northward shift in range and an increase in abundance in some areas (northern Namibia and northwestern South Africa; Kirkman et al. 2013). In 2004 some 75% of Cape Fur Seals bred at three sites: the Atlas Bay-Wolf Bay-Long Islands Complex and Cape Cross in Namibia, and Kleinzee in South Africa (Kirkman et al. 2007). All of these sites have experienced small declines in abundance since that time (Kirkman et al. 2013). Most of the smaller rookeries are estimated to contain more than 1,000 adults. While the abundances of the larger rookeries are relatively stable, they do experience fluctuations. Fluctuations are greater in southern Namibian rookeries (Kirkman et al. 2013) which have experienced major mortality events due to the impact of poor environmental conditions on prey populations (Gammelsrød et al. 1998, Gerber and Hilborn 2001). Smaller rookeries tend to experience greater fluctuations than larger rookeries (Kirkman et al. 2007, 2013).
Australian Fur Seal pup production has been assessed during three national surveys at approximately five-year intervals since 2002/03. These have indicated a mean annual increase in pup production between 1986 and 2002/03 of 5%, slowing to 0.3% per year between 2002/03 and 2007/08 seasons. It is not clear if the apparent 6% per year decline between the 2007/08 and 2013/14 estimates is due to a poor pupping season in 2013/14, or represents a real decline in population over that period, as no colonies are monitored on an annual basis. The most recent estimate (2013/14) of pup production was 15,063 (McIntosh et al. 2014). Based on the 2007/08 surveys, two colonies adjacent to the Victorian coast, Seal Rocks (5,660 pups) and Lady Julia Percy Island (5,574 pups), account for 51% the total pup production. Based on these surveys the total Australian Fur Seal population is estimated to be 120,000 individuals (Kirkwood et al. 2010).
In terms of national distributions, approximately 55% of pup production for this species takes place at 23 sites in Namibia, 38% at 16 sites in South Africa, less than 2% at a single site in Angola and 5% at 17 sites in Australia (Kirkman et al. 2007, Kirkwood et al. 2010, Shaughnessy et al. 2010, Kirkman et al. 2013, McIntosh et al. 2014, Shaughnessy et al. 2014).
While rookeries of Cape Fur Seals are separated by between a few to several hundred kilometres, tag data (Oosthuizen 1991) and genetic evidence (Matthee et al. 2006) indicate substantial movement between them and no distinct subpopulations.
Generation length has been calculated at 9.1 years (Pacifici et al. 2013). Population change for the species over three generations from 1982-2009 has been positive (Kirkman et al. 2013, McIntosh et al. 2014).