Mammals

The islands of the Arctic ocean play an important role in marine ecosystems by providing breeding and hauling out opportunities for marine birds and mammals. Among mammals, the Arctic Ocean islands are particularly significant for polar bears Ursus maritimus and walrus Odobenus rosmarus which are found on all the archipelagos, although walrus are absent from the western and northern Queen Elizabeth Islands.

Walrus haul out on sea-ice when it is present, but once the seasonal ice has gone, they haul out on shore in dense aggregations which can number thousands of animals. They persist in areas of extensive winter ice cover by exploiting polynyas—areas of water kept open by strong currents and upwellings, but some populations are migratory, particularly the Pacific subspecies (O. r. divergens), which commutes between winter in the Bering Sea and summer in the Arctic Ocean, when large numbers occur at Wrangel Island (Aug–Oct; Fay, 1982). Despite this very large biomass of marine animals coming on land periodically, walrus have little impact on terrestrial ecosystems. Their droppings are deposited very close to the high-water mark and are mostly washed into the sea. They may provide prey for polar bears and carcasses, either killed by bears or other causes, may provide food for scavengers, such as ravens and gulls.

In contrast, polar bears may have significant impacts on terrestrial ecosystems. While ashore in summer, after the retreat of sea ice, they feed on grasses and forbs, as well as on birds’ eggs and nestlings, on lemmings and caribou and on freshwater fishes. They frequently congregate in the vicinity of walrus haul-outs and kill smaller animals, especially dependent pups. Females frequently dig maternity dens on shore, in persistent snow drifts, usually within a few kilometers of the coast (Stirling, 1988).

The existence of the Arctic Ocean islands extends enormously the area of the Arctic Ocean accessible to both walrus and polar bears. The islands give access to haul-out and denning sites and, with their indented coastlines, provide excellent habitat for ringed seals Pusa hispida, the primary prey of the polar bear, as well as creating the type of narrow straits through which tidal currents maintain year-round polynya necessary for overwintering walrus.