It has a silver-gray fur covering its body, with black harp or wishbone-shaped markings dorsally, accounting for its common name.

[5] This behavior allows the mother harp seal to conserve energy and avoid the harsh conditions of the fast-ice while remaining near her pup.

As with most phocids, she requires vast amounts of energy to ensure sufficient mass transfer to her growing, weaning pup.

[6] The insulating quality of this fur depends on its ability to keep a layer of air trapped inside or between the hairs.

Harp seals combine anatomical and behavioral approaches to managing their body temperatures, instead of elevating their metabolic rate and energy requirements.

Brown fat warms blood as it returns from the body surface as well as providing energy, most importantly for newly weaned pups.

Its retina is rod-dominated and backed by a cat-like and reflective tapetum lucidum, enhancing its low light sensitivity.

Its cones are most sensitive to blue-green spectra, while its rods help sense light intensity and may provide some color discrimination.

The lack of tear ducts to drain secretions to the nasal passages contribute to the harp seals "eye rings" on land.

They provide a touch sense with labeled line coding, and underwater, also respond to low-frequency vibrations, such as movement.

[16] As in other populations and foraging areas, diet varies with distance from shore, with arctic cod comprising more of it nearshore and capelin more of it offshore.

[17] Courtship peaks during mid-March and involves males performing underwater displays, using bubbles, vocalizations, and paw movements to court females.

[20] The fertilized egg grows into an embryo which remains suspended in the womb for up to three months before implantation, to delay birth until sufficient pack ice is available.

[19] In order to cope with the shock of a rapid change in environmental temperature and undeveloped blubber layers, the pup relies on solar heating, and behavioral responses such as shivering or seeking warmth in the shade or even water.

During the approximately 12-day long nursing period, the mother does not hunt, and loses up to 3 kilograms (6.6 lb) per day.

[2] Harp seal milk initially contains 25% fat (this number increases to 40% by weaning as the mother fasts) and pups gain over 2.2 kilograms (4.9 lb) per day while nursing, quickly thickening their blubber layer.

[19] During this time, the juvenile's "greycoat" grows in beneath the white neonatal coat, and the pup increases its weight to 36 kg (79 lb).

Weaning is abrupt; the mother turns from nursing to promiscuous mating, leaving the pup behind on the ice.

[19] During this time the ice begins to melt leaving them vulnerable to polar bears and other predators including killer whales and large sharks.

[20] Juveniles molt several times, producing a "spotted harp", before the male adults' harp-marked pelt fully emerges after several years.

[2] Seals congregate annually on the ice to molt, pup and breed before migrating to summer feeding grounds.

A third stock breeds on the "East Ice" in the White Sea, which is off the north coast of Russia below the Barents ea.

[23] There are two recognised subspecies:[23] Harp seals are strongly migratory, the northwest population regularly moves up to 4,000 kilometres (2,500 mi) northeast outside of the breeding season;[24] one individual was located off the north Norwegian coast, 4,640 kilometres (2,880 mi) east northeast of its tagging location.

The latter was linked to a mass movement of harp seals into Norwegian waters; by mid-February 1987, 24,000 were reported drowned in fishing nets and perhaps 30,000 (about 10% of the world population) had invaded fjords as far south as Oslo.

[29] Harp seals can strand on Atlantic coasts, often in warmer months, due to dehydration and parasite load.

Several centers are active in seal rescue and rehabilitation, including IFAW, NOAA, and the New England Aquarium.

Most sealing occurs in late March in the Gulf of St. Lawrence, and during the first or second week of April off Newfoundland, in an area known as "the Front".

[33] In 2006, the St. Lawrence hunt officially started on March 25 due to thin ice caused by the year's milder temperatures.

The identified annual Canadian Total Allowable Catch (TAC) levels were 425,000 assuming harvest age structures of 95% young of the year (YOY).