At times, Antarctic seals may seem to be lumbering, inactive mounds of blubber and fur, rolling around aimlessly on the ice. In reality, like many Antarctic animals, they are highly specialized marine creatures able to thrive in one of the most extreme environments in the world.
There are only six species of seals that live in the Southern Ocean: the crabeater (Lobodon carcinophaga), leopard (Hydrurga leptonyx), Weddell (Leptonychotes weddellii), Ross (Ommatophoca rossii), elephant (Mirounga leonina) and Antarctic fur seals (Arctocephalus gazella). However, they are present in enormous numbers. In fact, the crabeater is possibly the most numerous large mammal on the planet, after humans.
Seals are part of the suborder of mammals called pinnipeds (which means fin-footed). Awkward on land, but impressive in the water, they have special muscles to close off their nostrils when they are diving and swimming. They can also slow their metabolism and heart rate during dives to conserve energy and air, and their lungs and blood vessels are especially efficient in absorbing oxygen.
Nevertheless, Antarctic seals are a diverse group. Some, like the elephant and fur seals, live in colonies where aggressive males maintain control over multiple females. Weddell and crabeater seals are somewhat less social, although they do gather occasionally in large groups, and leopard and Ross seals are solitary. Their diets and hunting strategies also vary. The slightly misnamed crabeater seal has incredibly unusual teeth that allow it to eat lots of tiny krill (a crustacean but not a crab). Weddell seals dive to depths of hundreds of meters and often catch large fish. Scientists have observed these seals bringing uninjured Antarctic toothfish to the surface, but could not explain how they did this. Antarctic toothfish can reach 2 meters in length, while Weddell seals range from 2.9-3.3 m. It is possible that they use sonic bursts to stun and catch them, a clever way to enjoy a nice toothfish dinner without a lot of effort.
Though they may be excellent predators in the water, Weddell seals aren’t the top seal predator in the Southern Ocean. That title belongs to the leopard seal, which not only eats fish and krill, but penguins and other seals. And they have occasionally attacked humans.
The somewhat less fierce fur seal also represents one of Antarctica’s biggest conservation successes. Sealing once reduced their numbers to only a few thousand, but since the end of sealing and the signing of the Convention on the Conservation of Antarctic Seals (CCAS), they have rebounded to a population size of four million. Still, like penguins, they remain vulnerable to climate change and lack of available food sources such as krill. More information is needed on how they interact within the food web to understand how to protect them for decades to come.