When harp seal pups are born, they have a yellow coat, which is stained from the amniotic fluid and blood. After the first molt, harp seals molt annually. Harp seals begin molting in early April and each molt lasts about four weeks. The mature pelage is achieved at 7 years of age in males and 12 years of age in females. Harp seals are a gregarious species.
Individuals reach maturity at four years of age.
Harp seals mate in the water from mid to late March. The pupping season is from late February to mid-March and occurs on the pack ice. Females give birth to a single pup every year on the pack ice. Harp seals feed primarily on decapods, amphipods, euphausiid crustaceans, and pelagic fishes. Adult harp seals can dive as deep as 750 feet to feed.