Antarctic fur seal
Introduction to Antarctic Fur Seals
The Antarctic fur seal (Arctocephalus gazelle) is one of nine species of fur seals that, along with six living species of sea lions, make up the "eared seals" or otariids. Their small external ear flaps distinguish them from the earless "true seals." The Antarctic fur seal is the only eared seal that commonly lives in Antarctic waters. They are seen frequently on Antarctica cruises—particularly at sub-Antarctic South Georgia.
Distribution and Migration of Antarctic Fur Seals
ANTARCTIC FUR SEALS VIDEO
Researchers estimate that 4 million Antarctic fur seals live within the Antarctic Convergence—the nutrient-rich transition zone between cold Antarctic water in the south and the more temperate waters to the north. Antarctic fur seals are found on several sub-Antarctic islands, with 95 percent of the world’s population breeding at South Georgia. The South Georgia population is considered the densest concentration of marine mammals on earth! Other islands with Antarctic fur seal populations include the South Shetlands, South Orkneys and South Sandwiches, and Heard Island. They are also occasionally seen on the Antarctic Peninsula and on other small islands. They disperse widely when at sea.
Antarctic fur seals were hunted to near extinction by American and British sealers in the 18th and 19th centuries for their luxurious pelts. In the early 1900s only a small population still survived and bred on Bird Island at South Georgia. All Antarctic fur seals today are believed to be descendants of this one tiny colony—which some scientists fear compromises the genetic diversity of the species. Ironically, it was an imbalance of the food chain that facilitated the remarkable recovery of the Antarctic fur seal. In the 1900s, Antarctic whaling removed the biggest krill-eating animals—the baleen whales—which caused a sudden over-abundance of krill, a major part of the diet of Antarctic fur seals.
Identifying Antarctic Fur Seals—Physical Characteristics
The Antarctic fur seals are identified by their visible earflap, dark coarse fur, and their ability to arrange themselves into a standing position by turning their rear flippers under their body and supporting most of their weight on their exceptionally strong fore flippers. This adaptation allows them to walk and run on "all fours" on land. The Antarctic fur seal also uses its front flippers for swimming.
Adult males measure 4–6 feet (1.6–2m) in length and weigh 200–460 pounds (90–210kg), with an average size of 415 pounds (188kg). Adult females are smaller at 4 feet (1.3 meters) in length and weigh 55–120 pounds (25–55kg), with an average size of 81 pounds (37kg). Males are generally four or five times larger than females, a characteristic of the species’ pronounced sexual dimorphism.
|"Blonde" Antarctic fur seal pup|
Another variation between the sexes is fur color. Adult males are dark brown in color, while females and juveniles tend to be gray with a lighter underside. Pups are black at birth and molt to a silver-gray coat at 2 to 3 months of age. An unusual blonde-fur variant occurs in about one in one thousand births in the population.
Antarctic Fur Seal Habitat
When not breeding on land, the Antarctic fur seal leads a largely pelagic (oceangoing) existence, pursuing its prey wherever it is abundant. While fur seals are capable of traveling on and hauling out onto ice, it is unusual to see them there. During the breeding season they primarily reside on sheltered rocky, sandy and gravelly beaches on sub-Antarctic islands with lush tussock grass clumps. With available food, some adult males and juveniles may hang around the breeding islands year-round.
Antarctic Fur Seal Breeding and Mating
The breeding season for the Antarctic fur seal occurs from November to January, during the Antarctic summer, with males arriving on land early to compete for breeding territory. The males are fiercely territorial, using physical threat displays, vocalizations and their formidable canine teeth to aggressively defend their access to estrus females.
Males fast during the breeding season, unwilling to leave their females or territories, losing up to 3½ pounds each day. A male Antarctic fur seal harem contains, on average, 10 females, although some prime dominant "beach master" bulls have been known to have over 100 females.
Gestation is 12 months. Females give birth during November–December, about two days after arriving onshore. The pups weigh 6–15 pounds at birth. The mother mates one week after giving birth and then leaves to feed at sea, usually for 3–5 days, before returning to shore to nurse her pup for 1–2 days. This cycle of feeding and nursing lasts about 4 months.
|Antarctic fur seals with king penguins|
Juveniles may spend several years at sea before returning to land to begin their breeding cycle. Leopard seals and orcas are known to eat Antarctic fur seal pups near the breeding beaches.
Antarctic Fur Seal Diet
Fur seals feed on moderately-sized fish, birds (including penguins), squid and krill—with krill making up the majority of the diet. In one year an individual fur seal will eat as much as one ton of krill.
Antarctic Fur Seal Behavior
While Antarctic fur seals can dive for up to 10 minutes and as deep as 800 feet (approx. 250 meters), dives usually average 3–4 minutes at 100 feet (approx. 30 meters).
The Antarctic fur seal leads a solitary life except for breeding and molting. Females live up to 23 years. Males live up to 15 years (due to the stress of the breeding season). Adult fur seals are preyed upon by sharks, orcas and occasionally by larger sea lions.
When on land the beach master bulls are very aggressive, especially during the breeding season, and can be a biting hazard to unwary or foolhardy tourists who do not treat them with caution and get too close.
Antarctic fur seals are threatened by oil spills, overfishing and entanglement in fishing nets.