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. Natural predators of the harp seal include polar bears, sharks, walruses, and humans. Harp seals have been hunted since the beginning of time by people inhabiting the arctic and subarctic areas. Harp seals have been exploited primarily for their meat and skin.