"Some 15,000 gray seal pups are born annually on a 25-mile-long sand bar on an island off the coast of Nova Scotia. This is far from the seals' feeding grounds, and both males and females fast during the mating and birthing season. The pups gain huge amounts of weight, in the form of blubber, when they are nursing. The female's milk contains 10 to 15 times as much fat as in human milk. The blubber keeps them warm and becomes their energy supply for 3-4 weeks after weaning and before they can hunt for their own food."
Links:Mammal Species of the World
Original description: Fabricius, 1791. Skrivter Naturhist. Selskabet Copenhagen, 1(2):167.