Why and when do white seals turn dark?

The common seal can be found on sandy estuaries, fjords and rocky inlets away from the full force of the open sea. Although they live and feed in water, they still come to the shore to breed and to maul their hair. A seal pup is born with thick white fur but will lose this shortly after it is born and it will be replaced by much darker, sleeker coat. Their diet includes all kinds of sea foods: fish, shellfish, crabs, and lobsters. The pup of a seal will suckle for 10 minutes, five or six times a day. After a month the pups have grown at an amazing rate, and then the mother will leave to mate with another bull. As this stage the pup enters the sea to feed for itself.