Colours of Wildlife: Southern Elephant Seal

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Southern Elephant Seal

Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"

Southern Elephant Seal by Willem

As promised, I bring you the Southern Elephant Seal, Mirounga leonina, the largest member of the Phocidae or True Seal family, and also the world's largest Carnivoran (that is, not just a carnivore in general, but a member of the order Carnivora, which includes cats, dogs, bears, badgers, weasels, otters, raccoons, mongooses, civets, genets and more) and the world's largest non-whale marine mammal. There is also a Northern Elephant Seal, Mirounga angustirostris, which is a tad smaller and differs in a few other respects also. They replace each other at opposite ends of the world, the southern living around Antarctica while the northern inhabits the North Pacific Ocean. Elephant seal fossils going back to the Pliocene are known, and they apparently evolved back then in the Pacific region, the southern species evolving and separating from the northern thanks to a successful long-range colonization effort. The genus name Mirounga is a name for the seal from some Aboriginal Australian language, apparently, while 'leonina' means 'lion-like'.

The name 'Elephant Seal' is highly appropriate. First, in size, they are almost as big as elephants, a bull elephant seal sometimes achieving a full length of 6.5 m/21' and a weight of 4000 kg/9000 lbs, with a record of perhaps 5 tonnes. The cow is much smaller, reaching 3 m/10' and 900 kg/2000 lbs. But the bull makes the elephantine resemblance even more striking by possessing a 'trunk' of sorts! This is a lengthened, prehensile, and inflatable snout. It is not used the way an elephant uses its trunk, though, but is mainly a display feature. Inflated, it makes a kind of amplifier for the bull's roaring calls during its beach display and combat. But it also functions as a 'rebreather' that absorbs exhaled moisture. This helps the bulls to maintain body fluids to avoid dehydration during their stay on land as they fight and defend their territories. Females have more typical seal-faces.

Though elephant seals come onto land for some very important reasons, they spend more than 80% of their lives in the water. They mainly use their rear 'fins' (feet with extensive webbing) for underwater propulsion. A full-grown bull can hold his breath for an incredible two hours (imagine being able to watch a long movie without having to breathe even once) and can dive to a record depth of 2388 m/7 835'. This compares well with the Sperm Whale, which can hold its breath for about three hours, and dive to over 3 km/10 000'. They only come up to the surface to rest and breathe for a period of 2-3 minutes in between dives. What they do to survive their dives is to store a very large amount of oxygen in their blood. They have a very large volume of blood in their huge bodies, much of it kept in special blood-storing cavities in their abdomens. Additionally, they have a greater number of red cells per volume of blood. Finally, they are also able to store some oxygen in their muscles themselves.

At the depths to which these mammals dive, the water pressure is intense, the water is freezing cold, and it is pitch dark. Elephant seals have very sensitive eyes, with more rods compared to cones (the rods being more light-sensitive) and a reflective layer at the back called a tapetum lucidum, to reflect ingoing light to traverse the retina a second time. Sharp as their eyes are, they wouldn't be able to see prey at all in the pitch black depths if it wasn't for the fact that many deep-ocean fish species actually emit their own light, a phenomenon called bioluminescence. Down there the elephant seals also use their very keen sense of hearing, and their sensitive snout whiskers, to find food. To keep warm, they have thick blubber and a blood circulation system that maintains heat around the heart and vital organs. They also slow their heart-rate and slow down their whole metabolism during dives, to save on energy. They feed on fish, octopuses and squid, and even on some krill (small crustaceans) and algae, but many details of their feeding are unknown due to the difficulty of observing them at such great depths. They don't always go that deep; typical dives are 400m to 1 000m/1300' to 3 300'. But even that is very deep for us humans.

While elephant seals swim, dive and feed alone, they come on land in sometimes quite large groups. They come on land for two purposes. The first is moulting. Every year, adult elephant seals shed their fur and also the entire surface skin layer, the epidermis. While the old skin and fur sloughs off, new skin grows by blood vessels branching to the surface through their thick blubber. During their moult, they are sensitive to chilling. In the near-freezing southern oceans, they would lose too much heat; consequently, they haul out onto land where they stay until skin and hair have regrown. They cannot return to the water to feed until the process has completed, which takes about a month. They moult in the southern summer, typically in January to March, when outside air temperatures are at their warmest, and on islands well to the north of Antarctica. Occasionally, they turn up quite far to the north, such as the coasts of South Africa or Australia, or even the islands of Saint Helena and Mauritius in the southern tropics, and Ecuador and Peru in South America. On the occasions when elephant seals turn up on beaches in the Cape Province, they tend to provoke an influx of tourists coming down specially to catch a glimpse of them. They can actually, after a rest, make it back on their own to their feeding grounds thousands of kilometres to the south.

The second reason why elephant seals come onto land, is for breeding. Unlike whales, they can't give birth underwater, and the baby seals can't tolerate the cold when they are very young. The adults start arriving on their breeding grounds in August (late winter to early Spring). The main breeding colonies are on South Georgia, the Falkland Islands, the Valdes Peninsula in Argentina (the only mainland breeding site), Kerguelen, Marion, Prince Albert, Crozet, Amsterdam and Heard Islands, and islands south of Tasmania and New Zealand, principally Macquarie Island. In earlier times, there were breeding colonies on Tasmania, the Juan Fernandez islands off Chile, and Saint Helena.

For coming onto land, elephant seals need fairly gentle beaches of sand or pebbles. Being true seals, they cannot turn their hind limbs forward to walk, but have to 'wriggle' along on their bellies. Nevertheless, they can reach speeds of 8 km/h (5 mph) like this!

When it comes to mating, elephant seals are extreme polygamists. On a breeding beach, the bulls will contend and fight until a single 'harem master' remains. The fights consist of the bulls roaring at each other, rearing up (sometimes lifting two thirds of their full length off the ground) to intimidate each other, wrestling and shoving each other, quite regularly also inflicting deep bites that can leave their snouts in tatters and their bodies criss-crossed by scars and gouges. A fight can last for 14 minutes. The vanquished bull will deflate his snout and flee back to the water emitting high-pitched yelps. The master of the beach that emerges from these fights, will claim all the females on the beach and may mate with as many as sixty of them. If there are more females than that on the beach, he will allow one or two 'sub-masters' below him who will mate with the females he can't personally attend to. Bull elephant seals may remain on land for two or even three months over the breeding season, during which time they have to feed off their own fat reserves.

As with the Cape Fur Seal, elephant seal females also give birth to the pups from last year's mating after coming onto land, and then mate to impregnate her with the next season's pup. Some females mate at sea with non-harem-owning males.

A newborn southern elephant seal pup weighs about 40 kg/90 lbs. Its soft, curly, blackish fur keeps it warm on land but isn't waterproof yet. Its mother feeds it with a milk very rich in fat. It rapidly gains weight, reaching 130 kg/290 lbs when weaned about 23 days later. For the start of its life, it is very dependent on its blubber stores. The mother in turn loses a lot of weight while suckling her pup, since she fasts and doesn't feed at all during the process. She leaves the pup when it is weaned; the pups disperse into the oceans from November to January. Pups are preyed upon by sharks, leopard seals and killer whales. Large sharks and killer whales prey on adults also.

Both southern and northern elephant seals have suffered greatly as a result from human hunting, both species being driven close to extinction before legal measures were instituted to protect them. At present, they are recovering their numbers, but are still under pressure as a result of competition with human fishermen. They are also seriously affected by global warming. They are very dependent on deep, cold, upwelling ocean currents, which might change along with the climate. They are therefore regarded as important indicators of the impact of climate change on marine life. Most of their breeding colonies are now protected, and they do prove themselves capable of successfully meeting many challenges, and so we can consider them fairly safe for now.

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