The harp seals diet varies with age, location, season, and year. When young seals first begin to forage for themselves, they feed primarily on small, shrimp-like crustaceans called euphausids. As their swimming skills improve, they broaden their diet to include a variety of larger crustaceans (zooplankton) and small fish.
Location also determines a harp seals diet to a large extent. Generally, when harp seals are summering in west Greenland and northern Canadian waters, they feed on pelagic crustaceans and small fishes, especially Arctic cod, polar cod and capelin. During the southern (fall) migration along the Labrador coast, fish are preyed upon more than invertebrates. No one species predominates, although capelin and small gadids (codfishes) are commonly eaten.In the St. Lawrence, harp seals feed intensively on capelin during the winter months. During the breeding season, they feed less frequently and on a wider variety of species. Lactating females and moulting harp seals feed infrequently, although mothers feed intensively on capelin after weaning their pups. Although harp seals in nearshore waters off Newfoundland and Labrador feed on a variety of fish and invertebrate species, the bulk of their diet consists of relatively few species such as Arctic cod, capelin, redfishes, Atlantic herring, Atlantic cod, and some decapod crustaceans.
Further offshore, capelin predominates in the diet, followed by sand lance, Greenland halibut and other flounders. During the northern (spring) migration, harp seals feed along the Labrador coast on a variety of species, including euphausids, various codfishes, capelin and shrimp, while in the Gulf migrating seals feed less frequently, primarily on capelin and herring.