One rule of thumb is that a seal needs to eat about 4 to 6 percent of its weight every day, but how much a seal actually eats depends on whether it is active or sedentary. Seals who are breeding or molting don’t eat at all for long periods of time. A Weddell seal that is sedentary can eat about 22 pounds of food every day while a seal that is active can eat over 100 pounds a day. A grown Weddell seal can weigh between 880 and 1320 pounds. The harbor seal, which is small for a seal, needs 12 to 18 pounds every day.
The gray seal usually needs between 35 and 52 pounds every day, but as stated, a large gray seal can kill and eat a harbor porpoise. The huge elephant seal needs to chow down on 180 to 270 pounds of seafood daily while it’s at sea, for when it hauls out it will fast, often for weeks. This is because it can’t enter the water when it’s mating, fighting, giving birth, nursing a pup or shedding its skin, and the water is where the food is.