Leopard Seals are among the most wide-varied eaters of the Antarctic. They wouldn't mind eating Krill, Petrels, Fish or Penguins.
The only competitor they need to worry about are smaller-toothed whales.
Baleen Whales, as big as they may look, only feed on Krill.
They only swim away from Smaller-Toothed whales and maybe even humans.
Antarctic Sperm Whales like to eat Squid. They have no predatory fears.
And last but not least, Smaller-Toothed Whales, such as the Killer Whale, are the kings of the food chain. They eat Baleen Whales, Elephant Seals, Squid, Penguins, Leopard Seals and many other Seals.
Just like Sperm Whales, they have no predators.