Seals of the world, part 4: The Southern Elephant Seal

What is the largest seal in the entire world?

Moving from the northern hemisphere to the southern hemisphere, this week’s blog is about the larger, bulkier cousins of the Northern Elephant Seal. You guessed it… the Southern Elephant Seal (Mirounga leonina)! This incredible species is EVEN BIGGER than the northern version, and earns the title of not only largest pinniped in the world, but also the largest living carnivore in the world. This means it even beats the Polar Bear, who can be as little as a fifth of the weight of one of these beasts! The Southern Elephant Seal was given it’s original name by the native people of Australia, meaning ‘lion’, as a reference to both their size and their lion-like roar.

Like the northern species, male and female M. leonina are extremely sexually dimorphic. The males have the facial ‘trunk’ appendage, or proboscis, which is used to bellow out aggressive warning sounds to their counterparts and rivals, to signal that they are the largest, strongest individual who should gain access to all the females on a beach. Slightly unsightly, the males also have thick, scarred necks with many folds, which serve as protection during the many battles they will partake in during breeding season. In clashes between two males of equal standing, physical stance and vocalisations may be enough to decide a winner and stave off aggression, but in other circumstances the pair will rear up and forcibly jab their sturdy canine teeth into their opponents neck. Battles are rarely fatal, but frequently end in blood and injury. In comparison, the females are far smaller, maybe only two thirds of the length of a male, and less than a third of the weight. They lack the elephant-like trunks and instead have rounded faces with flattened muzzles.. altogether more attractive! Finally, the pups are born with black fur that is not waterproof but remarkably insulating against the cold and wind. Pups are poorly equipped to swim until they have moulted this fur into their silvery, grey-brown juvenile coat, which happens after weaning.

M. leonina is found throughout the perimeter of Antarctica, even reaching out as far as the southern tip of South America. The best time to see them is when they congregate in huge numbers on breeding beaches, the winning males with their huge harem of females numbering on average around 50 individuals. Controlling the beach and all who inhabitant it, these males are commonly called ‘beachmasters,’ and younger males chancing their arm are chased away at speed! Some of the most successful beachmasters may succeed in mating with 100 females in one season (!) though on the converse side, some of the inexperienced males may not even attain 1! Having said this, there have been reports of less dominant males grabbing an opportunity while the beachmaster’s back is turned.. a very risky game! Equally, new research has show that females may be returning to the beaches already pregnant, indicating that they are mating at sea, away from the designated beachmaster. This challenges our view of the traditional polygynous society.

The beach is a dangerous place to be during the pupping season, and as well as occasional incidences of females killed by forceful males during sexual encounters, many a pup will lose it’s life after becoming crushed under the weight of a 4 tonne male. Males Southern Elephants can be anything up to six and a half metres long and weigh nearly 4000 kg! Females on the other hand will only reach four metres, and a more modest 800 kg. To put some perspective on how huge these animals grow in their lifetime, they will only be around a metre long when first born, and weigh only between 36 and 50 kg. Due to the rich, 12 % fat fed to the pup throughout the 3 week nursing period, the youngster will be weaned already weighing more like 130 kg, that’s tripling it’s weight!

The diet of the M. leonina after weaning varies, but it is known that they spend large amounts of time at sea, often at great depths. They have no problem diving to 700 metres below the surface, and will sometimes venture far deeper. Studies have shown that animals such as lanternfish, squid and other twilight zone species make up a large bulk of the diet. The Southern Elephant Seal truly is a giant amongst animals, and one of the most interesting and uniquely adapted species you can see. We hope this blog has stirred your interest in the fascinating marine world we have in front of us, that so desperately needs protecting from the damage human life is doing. Read more on the Pinnipedia, or head straight over to www.pinniped.org/front-page/pinnipedia/southern-elephant-seal. 

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