Harp seals are part of the family Phocidae, known as the "true" or "earless" seals because they lack external ear flaps.
They have a robust body, a relatively small, broad, flat head, and a narrow snout that contains eight pairs of teeth in both the upper and lower jaws.
Their front flippers have thick, strong claws. On their hindflippers, the inner and outer digits are longer and have small, narrow claws.
Phocids are unable to rotate these back flippers underneath them to walk, and instead use their front flippers to pull themselves along on land.
Adults are approximately 5-6 ft (1.7 m) long, and weigh around 300 lbs (135 kg). They have light gray fur, with a black face and a horseshoe-shaped black saddle on their back.
Their common name refers to this pattern, which looks like a harp.
Harp seals are modest divers by pinniped standards. The average maximum dive is to about 1,200 feet (370 m), with a duration of approximately 16 minutes.
They eat a variety of fish and invertebrates, but mainly focus on smaller fish such as capelin, arctic and polar cod, and invertebrates including krill.
Females give birth to pups near the southern limits of their range from late February to mid-March.
Pups nurse on high-fat milk for approximately 12 days, during which they gain about 5 lbs (2.2 kg) per day and develop a thick blubber layer.
At birth, harp seals are just under 3 feet (1 m) long, and weigh about 25 lbs (11 kg).
Called "whitecoats," newborns have long, wooly, white fur known as "lanugo", and undergo a complicated series of "molts" before reaching adult coloration.
Harp seal pups are abruptly weaned from their mothers when they weigh approximately 80 lbs (36 kg).
Adult females leave their pups on the ice where they remain without eating for approximately 6 weeks.
Pups can lose up to half of their body weight before they enter the water and begin feeding on their own.
After pups are weaned and left alone, adult harp seals begin mating.
Adult females undergo a period of suspended development known as "delayed implantation" during which embryos do not attach to the uterine wall for three months or more.
This allows all females to give birth during the limited period of time when pack ice is available.
During breeding in February and March, and when molting in late spring, harp seals aggregate in large numbers of up to several thousand seals on the pack ice.
During extensive seasonal migrations, large groups may feed and travel together.
Harp seals are prey for polar bears, killer whales, and sharks.
Harp seals occur in the pack ice throughout much of the North Atlantic and Arctic Oceans. They can be found from Newfoundland to northern Russia.