Seals generally prey on fish, but they will also eat eel, squid, octopus and lobster. Leopard seals will eat penguins and smaller seals, according to Seals World. The gray seal can eat 10 pounds (4.53 kilograms) of food in one day. They sometimes skip eating for a few days, and often stop eating completely during mating season and will live off energy from their stored-up blubber for weeks.