Arctocephalus tropicalis, the Subantarctic Fur Seal, is distributed throughout the southern hemisphere from the southern Atlantic to the Indian Ocean. For breeding they mostly remain north of the Antarctic Polar front on subantarctic islands, but sightings have been recorded on the Antarctic continent, as well as in southern South America, southern Africa, Australia, New Zealand, Tasmania and Madagascar. ‘Arctocephalus’ translates to ‘bear head’ in Greek, and ‘tropicalis’ hails from the fact the first specimen was discovered in Australia. The species are widely distributed and Least Concern at present. Estimated population size = 400,000.
Fur seals are slightly smaller eared seals than sea lions, and are highly sexually dimorphic. A. tropicalis is a medium sized fur seal (males ♂ up to 2 m long/ 165 kg, females ♀ up to 1.5 m/ 67 kg). Fur seals differ from sea lions largely by their dense underfur and smaller size, but they also have shorter noses, longer ear flaps and proportionately longer flippers. A. tropicalis is a solid bodied fur seal with short, broad flippers, and a short, snub muzzle. Males have neck manes and tufted crests often visible on their heads, while the females are noticeably smaller. Facially, the head is small, with prominent ear pinnae, and long, white vibrissae. The eyes are relatively small and the nose is small and short, and they have a characteristic lighter face ‘mask’. Males tend to be a dark olive brown colour (ranging from dark grey to black) with a pale creamy underbelly and sometimes lighter patches on the crown. The face mask can be a yellowish-orange colour. Females are generally a greyer shade but also have creamy-orange chests and faces.
A. tropicalis are opportunistic feeders, taking advantage of available resources in their location. They forage in the open ocean and have been recorded taking a variety of fish, cephalopods, crustaceans, and even the occasional penguin. Commonly fished types include lanternfish, icefish, and squid, which are caught near the surface nocturnally.
Sexual maturity – males ♂ 4-8 years old/ females ♀ 4-6 years old.
A. tropicalis are polygynous. Males form territories first at large rookeries and defend them by vocalising, posturing and fighting. Mating takes place with an average of 4-12 females. Gestation lasts a year, and females give birth from late October to early January, in austral summer. The pups are born with black lanugo which is moulted at around 3 months into a dark brown colour, almost resembling that of an otter. The pup will be attended continuously for the first 1-2 weeks before the mother returns to the sea to make foraging trips. These trips will be short at first, but increasing in length over time until eventually they can be as long as a month. Weaning will occur at around 11 months of age. Interestingly, A. tropicalis has been known to interbreed with both Antarctic Fur Seals and New Zealand Fur Seals. The adult fur seals moult their coats between March and May. Average longevity in this species is 20-25 years, with females tending to live longer than males.