Depending on the season and where they are, their diet varies—some orcas eat more fishes and squid than seals and penguins. But wherever they are in any of the world's oceans, average-sized orcas may eat about 500 pounds (227 kilograms) of food a day. Orcas have many hunting techniques, and bumping seals off ice is just one of them.

http://kids.nationalgeographic.com/kids/animals/creaturefeature/orca/