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Pinnipednesday - Arctocephalus tropicalis Edition

January is creeping away from us on flippered feet.

The Subantarctic Fur Seal (Arctocephalus tropicalis) is a medium-sized pinniped that can be found in the southernmost parts of the Atlantic, Pacific and Indian Oceans. If you're thinking that the "tropicalis" part of its specific name is therefore somewhat inappropriate, you are correct. It was named and described in 1872 by a naturalist who was basing his description on a single specimen which had somehow found its way to northern Australia, thus giving the impression that it was a tropical species.


Subantarctic Fur Seals have distinct coat coloration, regardless of sex. They are darker-colored on their backs, ranging from dark brown to a gray-brown, and are lighter-colored on their bellies and chests, ranging from tawny ginger to a burnt orange color. Males also have a little tuft of dark fur sticking up on their foreheads, and their coloring tends to be more pronounced. Adult male Subantarctic Fur Seals are slightly larger than females, growing up to 6 feet (1.8 meters) in body length and weighing about 330 pounds (150 kg). Females can grow up to almost 5 feet (1.45 meters) in length and weigh much less, around 110 pounds (50 kg).

The diet of Subantarctic Fur Seals consists of mesopelagic fish, which they hunt at night when those types of fish (like lanternfish) are likely to ascend closer to the surface of the water. Night hunting is facilitated by their large, light-sensitive eyes and sensitive vibrassae. They can also feed on krill by straining water through their teeth, and will occasionally take penguins and squid when they can get them. Juveniles tend to be a little more adventurous in straying from the breeding beaches, and will sometimes go as far as the coasts of South America.


Breeding and pupping season for Subantarctic Fur Seals takes place in December, but males will arrive on the isolated breeding beaches as early as October, to establish their territories and and forming harems of about 8 females, which tend to stay within the male's territory. Trespassing males are driven away with prejudice, although it doesn't often escalate past aggressive displays and threats. Females will give birth to the previous year's pup, nursing them non-stop for about a week and then leaving the pups on shore while they make forays into the water to hunt for food. Pups are weaned after six weeks, which is when they first go into the water themselves.


Subantarctic Fur Seals were close to extinction in the 18th and 19th centuries, after they were heavily hunted like so many of their fellow pinnipeds. They have made a significant recovery since the 1830s, when the demand for their fur started to die down, and now number about 300,000 in total. The bulk of the population resides around Gough Island, and they are currently considered to be a species of least concern by the IUCN.


Source for all images used in this post.

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