Different types of seals:

Weddell seal

Their fat protects seals efficiently from the cold, both at sea and outside. They can weight up to 600kg, a good portion of which is fat. As an additional protection against the cold the have a thin layer of very dense fur. The male is bigger than the female, up to 3m long, but is not seen too often on the ice. They are very good divers, able to dive down to 600m and hold their breath for an hour. Their only predator is the killer whale, sometimes seen off the shores of Antarctica. During those dives they catch and eat mainly fish, squids, octopuses, krill, crabs and shrimp.

When seals are young, they like to be scratched under the 'arms'. Baby seals have never been hunted in Antarctica and big ones have not been hunted for about a century (whalers used to catch them when they couldn't find enough whales). From the dark color of baby seals, it's easy to tell they don't have land predators: baby seals from the arctic are white to try to hide from the sight of polar bears...

If the ice is not too thick, Weddell seals can drill a hole in it by opening their mouth wide and turning it repeatedly against the ice. They normally never venture inland, but mummified remains of seals have been found in the dry valleys, hundreds of km away from the sea.

Crabeater Seal

Although very abundant around Antarctica, they are not very common around DdU and I saw only a couple of them. The only thing I know about them is that they don't particularly eat crab but krill which they filter out of the water with their uniquely shaped teeth. They may reach up to 2.5m and weigh more than 200kg. They often have scars from leopard or killer whales attacks.

Leopard Seal

When they catch one, they play with it just like a cat with a mouse. You wouldn't want one to mistake you for a penguin (it's happened a few times to people standing on the shore !). They come to DdU mainly when the chicks go to the sea for the first time, still learning to swim. Penguins are extremely tough animals, though, I've seen several that survived such attacks with no feet or tails that successfully manage to raise chicks every year.

Their name comes from their spotted fur and also from their huge mouth and powerful jaws. Females are larger than males and may reach 4m and weight up to 450 kg. They are solitary predators and eat just about everything, from krill to other seals but particularly appreciate Adelie penguins. They often attack penguins that are walking on broken floating ice by bursting through the ice; you can tell penguins are nervous when walking on broken ice by the speed they go ! And they don't stand near the shore. It's also something that has cause more than a few scares in my colleagues when they saw a leopard seal burst out of the water at their feet, probably thinking they were some kind of fat penguin.

source:

http://www.gdargaud.net/Antarctica/Animals.html