Leopard seals frequently grow up to 12 feet long and weigh up to 1300 pounds, with only one predator to fear: killer whales. There are anecdotal accounts of sharks hunting leopard seals, but there are no records of this happening on a regular basis.
Leopard seals are sometimes referred to as top predators, like lions and bears, but they are not a true apex predator. Killer whales feed on leopard seals and larger prey. They are very efficient hunters and, according to Wikipedia, prey on walruses, whales, dolphins, porpoises, otters and 20 different species of seals including elephant seals, the largest seal in the Antarctic. When hunting for prey, killer whales spy-hop to locate animals resting on pieces of ice, then they swim as a group to create waves that wash over the ice. When the prey is washed into the ocean, they attack it.
Unlike killer whales, leopard seals don’t hunt in packs. They are not social animals and form groups only during mating season. After a seal pup is born, the female protects it on her own until it is self-sufficient.
According to National Geographic, leopard seals are the only seal species to hunt warm-blooded food such as penguins and other seals, as well as fish and squid. Leopard seals have earned a reputation for playing with their food because they have been observed tossing penguins around. Leopard seals are known to attack pontoons on boats and occasionally have attacked humans.