Brown fur seal - Arctocephalus pusillus

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There are two widely-separated subspecies: A. p. pusillus in southern Africa, and A. p. doriferus in southern Australia.

These two subspecies are the largest fur seals and have a high degree or sexual dimorphism. Cape fur seals are 3.5 to almost 4.5 times heavier, and approximately 1.3–1.9 times longer, than females. Both sexes of Australian fur seals are heavier than their Cape fur seal counterparts, but have a weight relationship between males and females that is similar to the relationship in the Cape fur seal. For length, Australian adult females average a bit longer, and males slightly shorter than Cape fur seals, and the relationship between males and females is closer, with males being approximately only a 1.1–1.8 times longer than females.

Both subspecies have been described as the most sea lion-like fur seals. In both, the head is large and wide, and the crown rounded in adult males and flatter in females. There is a sloping forehead that is more prominent in adult males, and less steep, but still present, on females. The muzzle is robust and long, flat and wide on top, tapering only somewhat in width and thickness to the large conspicuous nose. The rhinarium is large, wide and rounded in adult males, less so in adult females, and extends beyond the end of the mouth. The ear pinnae are long and prominent. The vibrissae are moderately long, pale, and regularly extend to the ear pinnae. Adult males are greatly enlarged in the neck and shoulders, with a mane of longer guard hairs from the nape and neck to shoulders and chest. Adult females, subadults, and juveniles are robust, but normally proportioned in the neck and shoulders.

The fore flippers have a dark, sparse, short fur that extends beyond the wrist onto the middle of the dorsal surface of the flipper in a “V” pattern that does not reach the rounded tip. The rest of the dorsal surface, and the palms of both fore flippers are covered with a hairless black leathery skin. The first digit is the longest, widest and thickest, and curves posteriorly, giving the flipper a swept-back look. Digits 2-5 are successively shorter. There is a small opening in the skin at the end of each digit for a claw that is usually reduced to a vestigial nodule, and rarely emerges above the skin. The claw openings are set back from the free edge of the flippers by cartilaginous rods that extend the length of each digit, and expand the size of the flippers.

The hind flippers have dark, short, sparse hair covering part of the proximal end of the flipper, and the rest of the dorsal surface, and the entire sole is covered in black leathery hairless skin. The hind flippers are long and each digit has a cartilaginous rod that adds a flap-like extension to each toe. The bones of the three central toes terminate at the position of the small nails that emerge through the skin on the dorsal surface, set back from the end of the flipper. The claws of digits 1 and 5 are vestigial, like the claws on the fore flippers, and may or may not emerge from small openings set back from the end of the flaps. All of the flaps at the end of the flipper are of relatively equal length. The first toe or hallux and the fifth toe are somewhat wider than toes 2–4.

Adults are tan to grayish brown with yellowish to orange highlights above and on the neck, and variably paler with reddish brown shades on the abdomen. Males are usually darker than females and darken as they age. Cape fur seals are generally darker than animals from Australia. The guard hairs have a grizzled appearance especially on bulls. Females, subadults, and juveniles can be lighter in the chest region. The mystacial area can be paler. The tops of the flippers are very dark. Part of the ear pinnae and the area around the insertions of the pinnae are paler, however the tips of the pinnae are naked and dark in older animals. Pups are blackish, with variable hints of silver overall, and can be paler below. They first molt at 4-5 months to an olive gray coat. As juveniles, they molt a year later into a silvery gray coat.

Adult male Australian fur seals average just less than 2 m, and can reach 2.3 m in length. They attain an average weight of 279 kg, and can weigh up to 360 kg. Adult females are 1.2 –1.8 m in length, and attain an average weight of 76 kg, and can weigh up to 110 kg. Newborns average 73 cm in length, and females average 7.1 kg, and males 8.1 kg. Adult male Cape fur seals are 2–2.3 m long, average 247 kg in weight, and may reach 353 kg. Adult females are 120–160 cm long and weigh an average of 57 kg, with a maximum of 107 kg. Pups are born around 6 kg and are 60–70 cm long.

The dental formula is I 3/2, C 1/1, PC 6/5.

Cape and Australian fur seals both share their range with vagrant Subantarctic fur seals, and in the case of the Australian fur seal with 2 other otariid species resident near their range.

For the Australian fur seal, New Zealand fur seals and Australian sea lions pose a regular chance for confusion. New Zealand fur seals are grayer and darker, have a thinner and proportionately longer, more pointed muzzle, a more flattened crown, and are stocky, but smaller overall. The mane of Australian fur seal males is more conspicuous. On land, New Zealand fur seals often move forward by jutting both fore flippers ahead at the same time and bounding. Australian fur seals move one fore flipper forward at a time, and the head sways from side to side with the alternating gait like many sea lions when they move slowly.

Australian sea lions have large blocky heads with a very wide blunt ended muzzle. Females, subadults, and juveniles are generally fawn with a grayish or silver tan back. Adult male sea lions are unmistakable with very large muzzle, dark facial mask and pale color on the crown and upper mane.

Subantarctic fur seals are uniquely colored. The back and rump of adult males is dark gray to brownish black, and the chest and neck through the muzzle, face and area around the eyes are cream with yellow to orange shading. The ear pinnae are short, mostly bare skin and dark, and attach in the dark pelage of the upperparts. There is also a tuft of longer pale fur in the dark crown above the eyes and behind the dark forehead. Although the adult male is enlarged and thick in the shoulders and neck, he does not have a mane. Adult females have similar coloration to the males, but have less well-defined pale facial markings that can be shaded with dull yellow orange to light brown. In both sexes the top of the fore flippers is darker as is the area where the flippers attach to the sides. The underside of the abdomen is dark ginger to reddish brown. The fore flippers and hind flippers are proportionately short and wide.

Cape fur seals are found along the south and southwestern coasts of southern Africa, from South Africa to Angola. Australian fur seals are found along the coast and in continental shelf and slope waters from western Victoria, east along the coast to the southeast corner of Australia, then north through most of New South Wales. The range also includes Tasmania, and the islands of Bass Strait. They travel up to 160 km offshore. On land, they have a decided preference for rocky habitat.

Both subspecies are highly polygynous. Adult males arrive at the colonies first. Breeding is from late October to the beginning of January. Males establish and defend territories with vocalizations, ritualized postures and fighting. The territories of bulls are a mean of 62 m2 and hold about 9 females on average. Male vocalizations include a bark or whimper, and a guttural threat. Females have a threat and a bawling pup attraction call.

Female Australian fur seals come ashore and give birth 1.5–2 days after arrival. The peak is in the first week of December, although there is some variation between colonies. Females attend the pup for 8-9 days before coming into estrous, mating, and departing on their first foraging trip. Foraging trips get longer as the season progresses from summer to winter, changing from a mean of 3.71 to 6.77 days. Periods of attendance stayed the same from birth to weaning, and had a mean length of 1.7 days. Pups are usually weaned at 10–12 months even though some pups begin to forage at 7 months, and others are nursed for 2–3 years. The data are similar in most regards for Cape fur seals except that foraging intervals are much shorter, probably reflecting greater availability of food near the colonies in the nutrient rich areas off southwest South Africa.

Foraging dives by lactating Australian fur seal females are usually to 65–85 m with a maximum of 164 m, and last 2–3.7 minutes with a maximum duration of 8.9 minutes. Unlike many other fur seals, considerable foraging occurred during the day. Two lactating female Cape fur seals dove shallower averaging 41 and 49 m respectively, but had much deeper maximum dive depths of 191 and 204 m.

At sea, these seals are found alone or in small groups of up to 15 animals, often gathering in huge rafts adjacent to rookeries. They adopt a variety of poses while resting in the water, including the "jug-handle." These fur seals also purposely entangle themselves in rafts of kelp, possibly using the kelp as an anchor and for camouflage. When traveling rapidly, they sometimes porpoise. Neither of the populations is migratory; they move more locally within their restricted ranges. Predators include killer whales and great white sharks at sea, and black-backed jackals and brown hyenas for Cape fur seals at mainland colonies in southern Africa.

Both subspecies are opportunistic feeders that take a wide variety of prey, including pelagic, mid-water, and benthic animals. Australian fur seals take squid, octopus, barracouta, whiting, flathead, red mullet, parrot fish, leather jackets, pilchards, and rock lobsters. For Cape fur seals, the predominant food taken by type was fish (75%), cephalopods (17%), and crustaceans (8%). Important species are cape hake, horse mackerel, pelagic goby, pilchards, anchovy, squid of the genus Loligo, rock lobster, shrimp, prawns, and amphipods. Cape fur seals have also been reported to occasionally take jackass penguins and several species of flying seabirds.

Cape and Australian fur seals were hunted heavily in the 19^th century and both populations were driven to very low levels. With protection, both have recovered, although the Cape subspecies to a much greater extent than the Australian. Cape fur seals numbered approximately 1.7 –2 million animals in 1990, and the population was estimated to be increasing at a rate of 3% per year. Australian fur seals were estimated to number 30,000–50,000 in 1991.

Seal harvests in South Africa were suspended in 1990, but are ongoing in Namibia. The Cape fur seal is considered to be very detrimental to commercial fisheries, costing large sums in damaged gear and stolen and damaged catch annually. Some seals are taken incidentally in fishing operations every year. More significantly, Cape fur seals are known to become entangled in marine debris such as packing bands, discarded lines and nets, and other material that can become a collar around an animal’s neck. Rates of entanglement vary by colony, but have been estimated to be between 0.12–0.66%. The effect of human disturbance from tourism at several large colonies is unknown.

Australian fur seals are protected from all harvest. There are conflicts with local commercial fisheries from seals stealing catch, damaging gear, and becoming entangled in nets and traps. They are considered a pest species by some, and are shot under permit to protect fishing gear and catch. Mortality is highest and more significant for younger age classes. They also live close to human population centers and agricultural areas and are exposed to a wide variety of pollutants through their food chain.

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• World Register of Marine Species (WoRMS)
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Arnould, J.P.Y. and M.A. Hindell. 2001. Dive behaviour, foraging locations, and maternal-attendance patterns of Australian fur seals (Arctocephalus pusillus doriferus). Canadian Journal of Zoology 79:35-48.

Arnould, J.P.Y. 2002. Southern fur seals Arctocephalus spp. pp. 1146-1151 in W.F. Perrin, B. Würsig and J.G.M. Thiewissen, eds. Encyclopedia of marine mammals. Academic Press.

David, J.H.M. 1987. South African fur seal, Arctocephalus pusillus pusillus. pp. 65-71 in J.P. Croxall and R.L. Gentry eds. Status, biology, and ecology of fur seals proceedings of an international workshop Cambridge, England, 23-27 April 1984. National Oceanic and Atmospheric Administration Technical Report National Marine Fisheries Service 51.

Pemerton, D., R. Kirkwood, R. Gales and D. Renouf. 1993. Size and shape of male Australian fur seals, Arctocephalus pusillus doriferus. Marine Mammal Science 9(1):99-103.

Shaughnessy, P.D. and R.M. Warneke. 1987. Australian fur seal, Arctocephalus pusillus doriferus. pp. 73-77 in J.P. Croxall and R. L. Gentry eds. Status, biology, and ecology of fur seals proceedings of an international workshop Cambridge, England, 23-27 April 1984. National Oceanic and Atmospheric Administration Technical Report National Marine Fisheries Service 51.

Warneke, R.M. and P.D. Shaughnessy. 1985. Arctocephalus pusillus, the South African and Australian fur seal: Taxonomy, evolution, biogeography, and life history. pp. 53-77 in J.K. Ling and M.M. Bryden, eds. Studies of sea mammals in south latitudes. South Australian Museum, Adelaide.