Feeding, Growth, and Productivity of Northwest Atlantic Harp Seals (Pagophilus groenlandicus)

Abstract

The food of harp seals inhabiting the northwest Atlantic consists chiefly of pelagic fish, especially capelin, Mallotus villosus, and pelagic and benthic Crustacea (Euphausiacea, Mysidacea, Amphipoda, Decapoda), with smaller quantities of benthic fish. Feeding has been observed to take place on individual items by suction, and small fish are taken tail first. Feeding is intensive in winter and (by deduction) in summer, less intensive during spring and autumn migration, and in spring during whelping and moult. A weight loss in spring due chiefly to loss in thickness of subcutaneous fat (blubber) is most intensive in adult females as a result of lactation. This loss is made up slowly in summer. The preparturient females are partly segregated in midwinter on what may be the best feeding grounds. During lactation, and immediately following it when they are again segregated from other age-sex groups, adult females tend to feed on decapod Crustacea. In spring, the only time when all age classes are in the same geographic area, there is a stratification of feeding by size of organism and by depth, from chiefly Euphausiacea taken in surface waters by the weaned young, through capelin taken probably at intermediate depths by the immature animals, to herring, cod, and other groundfish taken by the moulting adults to depths of perhaps 150–200 m. Social feeding begins at about 1 year of age with the change from Crustacea to pelagic fish. From knowledge of the rate of feeding, body weights, and reproductive rates, the ecological efficiency of harp seals (i.e. weight of annual increment of population/weight of annual food eaten) is calculated at 0.005, a low figure. Annual weights of food items eaten by the northwest Atlantic population of harp seals are roughly estimated as: all organisms, 2 × 106 metric tons; capelin, 0.5 × 106 tons; and herring, 2 × 104 tons. Predation by harp seals on capelin stocks off eastern Canada occurs only during the winter months when pack ice is present as a resting substrate, the same resource being consumed in the summer months by the great whales (Balaenopteridae).

Important prey species of marine vertebrate predators in the northwest Atlantic:proximate composition and energy density

“…Traditionally, capelin has been reported as the predominant prey of harp seals in the western Atlantic (Fisher & Mackenzie 1955, Sergeant 1973, Murie & Lavigne 1991. However, the diet of these seals from nearshore northeastern Newfoundland since 1986 has been dominated by Arctic cod instead .…”

Feeding habits of harp and hooded seals in Greenland waters

“…Fabricius (1780Fabricius ( , 1790, Winge (1902), and Vibe (1950), supplemented by Sergeant (1973), Kapel (MS 1973), Kapel and Geisler (MS 1979) and Kapel (1982 (Kapel 1982(Kapel , 1995.…”

“…NAMMCO Scientific Publications, Volum e 2 ------------------------------------------------- Sergeant (1973) reviewed available information on harp seal feeding in the Northwest Atlantic, and included more recent studies in his monograph on harp seals (Sergeant 1991). Another review of studies of harp seal feeding in the Northwest Atlantic was presented by Wallace and Lavigne (1992).…”

“…Sergeant (1973) presented stomach contents data on 16 harp seals caught in the Canadian Arctic (at four different localities). Polar cod occurred in 6 of these, mysids in 5, Parathemisto in 4, and euphausids in 3 stomachs.…”

Predation by Harp Seals in Atlantic Canada: Preliminary Consumption Estimates for Arctic Cod, Capelin and Atlantic Cod

“…Harp seals (Phoca groenlandica) are a migratory species found throughout the North Atlantic where they feed upon a variety of fish and invertebrate species (Sergeant, 1973(Sergeant, , 1991Smith et al, 1979;Beck et al, 1993;Lawson and Stenson, 1995, in press;Kapel, 1995;. Recent studies indicate that their numbers have been increasing in the Northwest Atlantic since the early 1970s and were in the order of 4.5-4.8 million in 1994 (Shelton et al, 1996).…”