Southern elephant seals are named after the large proboscis (nose) of the adult males, which is used to make loud roaring sounds, especially during the mating season.
They are large ocean-going mammals with adult males weighing up to 3000 kg and adult females between 300 and 900 kg just prior to giving birth. Pups weigh about 40 kg at birth and are weaned after 24 days by which time they weigh on average 120 kg. A large weaner may weigh in excess of 220 kg.
They are big and cumbersome on land, but are superb swimmers and divers. Biologists have recorded them diving up to two kilometres deep and holding their breath under water for up to two hours.
Elephant seals can navigate very accurately to feed. They can dive to over 1500 m and can stay submerged for up to two hours. Most dives are about 30 minutes duration and of depths between 300 and 800 m. The seals can dive constantly while at sea, spending about two minutes on the surface between dives.
Elephant seals are able to accomplish these amazing diving feats because they have evolved some special adaptations, by which they conserve energy very economically.
They have a torpedo shape, which accounts for their prowess in swimming and diving. And an enormous volume of blood in which to store oxygen, which they use very efficiently. Elephant seals even have extra spaces called sinuses in their abdomens to store extra blood.
Haemoglobin in red blood cells carries oxygen, and elephant seals have a lot more red blood cells per unit of blood than other animals. Their red blood cells may, as an adaptation for diving, contain more haemoglobin than normal. These extra red blood cells make elephant seals’ blood very thick. Elephant seal muscles are also used to store oxygen. Molecules of oxygen-carrying myoglobin are present in the muscles and colour them black. The analogy of fully charging a battery is sometimes used to describe their ability to take a breath and make the oxygen last for up to two hours.
Southern elephant seals have a thick layer of blubber that sustains them during the breeding season as they do not feed during this time.
Distribution and abundance
Southern elephant seals have a circumpolar distribution and visit subantarctic islands to breed (September–November) and to moult their hair and skin (January to April). There are four main stock groups: South Georgia, Peninsula Valdez, Iles Kerguelen (including Heard Island), and Macquarie Island.
From 1950 to 1985 the elephant seal populations at Macquarie Island, Heard Island, and others of the Iles Kerguelen stock declined by about 50%. Since then the population at Heard and Kerguelen has remained relatively stable but the Macquarie population has continued to decline at about 1.2% per year.
Australian scientists have tracked these seals using plastic ear tags. Elephant seals cruise the whole Southern Ocean and can swim enormous distances. Individuals spotted on Kerguelen Island, for example, have later been seen at Davis then Casey station in Antarctica.
For many years seals were killed for their blubber which was boiled down to make oil.
Conservation status: least concern
They breed on the ice in spring, from late September to early November. Females give birth to a single pup which is weaned 3–4 weeks after birth. During this time the female spends the entire time on the ice with the pup.
During the breeding season the female and pup are usually accompanied by a male which mates with the female when she comes into oestrous. The male plays no part in bringing up the pup, and the group disbands once the pup is weaned.
Diet and feeding
Elephant seals migrate south to Antarctica, after breeding or moulting, to feed on squid and fish at the edge of the sea-ice.
They travel long distances to their foraging areas. Males forage mainly on the Antarctic continental shelf while females forage in more pelagic areas, such as off the Antarctic shelf within the pack ice, or near the Antarctic Polar Frontal Zone. Foraging areas can be several thousand kilometres away from their breeding islands.