Elephant seals
Elephant seal huddle From 1950 to 1985 the elephant seal populations at Macquarie Island, Heard Island, and others of the Iles Kergulen 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.
Southern elephant seals breed in colonial groups called harems. A single dominant male usually can control a harem of up to 50 females. Once harems get larger than this the dominant beachmaster will allow assistant beachmasters to reside within the harem. Harems can grow to over 1000 females with over 30males.
Southern elephant seals 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.
Southern elephant seals feed on squid and fish.
Southern elephant seals have a thick layer of blubber that sustains them during the breeding season as they do not feed during this time. For many years seals were killed for their blubber which was boiled down to make oil.
Adult elephant seals return to subantarctic islands for the breeding season (September-November) and to moult their hair and skin (January to April).
Adult males can weigh up to 3000kg while adult females weigh between 300 and 900kg just prior to giving birth. Pups weigh about 40kg at birth and are weaned after 24 days by which time they weigh on average 120kg. A large weaner may weigh in excess of 220kg.
Southern elephant seals can dive to over 1500m in depth and can stay submerged for up to 2 hours. Most dives are about 30minutes duration and of depths between 300 and 800m and can dive constantly while at sea spending about 2 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. They have an enormous volume of blood in which to store oxygen and they use this oxygen very efficiently. Elephant seals even have extra spaces called sinuses in their abdomens to store all their extra blood. Red blood cells, with their haemoglobin constituent, carry 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 myoglobin, an oxygen-carrying molecule similar to haemoglobin are present in the muscles and colour the muscles black. When the elephant seal takes a breath it is like a fully-charge battery which can make oxygen last for up to two hours.
Links
Taxonomic information on the elephant seal
Australian Antarctic Science (AAS) projects relating to Southern Elephant Seals
Australian Antarctic publications relating to Southern Elephant Seals
Studying elephant seals
See more information on the Australian Antarctic Research Biology program
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