Marine mammals are both permanent and seasonal members of the Arctic and include baleen and toothed whales, seals, walrus, and Polar bear.  The following section focuses on those mammals closely linked to the marine food webs.

Bowhead whales are circumpolar, residing in the high latitudes from late April to October.  In the spring months, bowheads migrate northward as the sea ice breaks up.  Five stocks have been identified, including the Spitsbergen, Baffin Bay-Davis Strait, Hudson Bay-Fox Basin, Sea of Okhotsk, and Bering-Chukchi-Beaufort stocks (Rugh et al. 2003).  The latter stock overwinters in the Bering Sea.  In the spring, the Bowheads move north and east, past Point Barrow into the western Beaufort Sea (Lowry et al. 2004).  The majority of whales move into the Canadian Beaufort Sea for the summer months; however, some Bowhead whales will either remain in the eastern Alaskan Beaufort or move into the Arctic Ocean.  While Bowhead whales appear to favor continental slope waters in the spring and summer, they appear to favor the inner shelf waters (<200 m depth) of the western Beaufort in September and October (Moore et al. 2000).  As the ice cover increases in late fall, the whales migrate into the Bering Sea for the winter months. 

Bowhead whales are considered to be second order consumers (Hoekstra et al. 2002), with a diet dominated by euphausiids and calanoid copepods (Bluhm and Gradinger 2008).  Stomach content analyses indicate that, while benthic crustaceans and fish occur, their consumption is either occasional or incidental (Frost and Lowry 1984; Lowry et al. 2004).  In the Bering-Chukchi-Beaufort system, there appears to be some seasonality in the diet which is dominated by euphausiids in spring and by copepods in the summer and autumn months.  This distribution of diet is likely to be a result of opportunity, rather than selection.  Dominant species in stomach contents included the euphausiids Thysanoessa raschii and the copepods C. hyperboreus and C. glacialis (Frost and Lowry 1984; Lowry et al. 2004).

The White whale, or Beluga, is a circumpolar species inhabiting cold waters of the Arctic and subarctic waters (Rice 1998; NAMMCO 2005a).  During the winter months, White whales retreat to subarctic regions with loose pack ice and winter polynyas (Barber et al. 2001).  During the summer months, White whales live in coastal waters, estuaries, shelf breaks and deep basins.  In the Alaskan Arctic, White whales move into the Beaufort Sea in May, moving east into the Canadian Beaufort or north to the Arctic Ocean for much of the summer (Loseto et al. 2006).  In the fall as the Arctic cod congregate in the nearshore waters, White whales cross along the Alaskan mid-shelf in late August and September (Suydam and Moore 2004).  The  Eastern Chukchi White whale typically remains in the more open waters (>200 m depth) throughout the year, whereas the Eastern Beaufort Sea White whales move closer to shore when in the eastern Beaufort Sea (Suydam et al. 2001).

White whales are considered to be third order consumers (Hoekstra et al. 2002), with a diet dominated by Arctic cod (B. saida and A. glacialis), and to a lesser extent whitefish (Coregonidae) in the Russian and Greenland Arctic.  A variety of other prey items have been observed in stomach contents, including capelin, herring, smelt, sculpins, cephalopods and benthic invertebrates (Bluhm and Gradinger 2008).  Nitrogen and carbon isotope signatures indicate that they also feed on copepods and euphausiids, particularly in the spring and fall (Hoekstra et al. 2002; Frost and Lowry 1984).  Known predators of White whales include Orca whales, Polar bears, and humans (NAMMCO 2005a).

Narwhal occur in the deep and offshore waters of the Canadian High Arctic, the Barents and Kara Seas, eastern Laptev Sea and the waters surrounding Greenland (Sherman and Hempel 2008).  Narwhal appear to have high site fidelity, remaining in close association with the ice in winter.  Winter feeding grounds appear to be more important than summer feeding areas, with remarkable aggregations of narwhals found in polynyas.  In winter, a large number of whales can share the limited open water areas; near Greenland, between 17,000 and 19,000 narwhals were found to occupy 2% of the surveyed area (approximately 73 whales per km² of open water (Laidre, personal communication).  Narwhals feed mostly in deep water and possibly at or near the bottom. Dives of up to nearly 1,500 m and 25 minutes are documented (Laidre et al. 2003), and there are some seasonal differences in the depth and intensity of diving (Laidre et al. 2002, Laidre et al. 2003).  Arctic cod (B. saida and A. glacialis) and the squidGonatus fabricii dominate the narwhal diet, with lesser amounts of Greenland halibut and other deep-sea fish (Laidre and Heide-Jørgensen 2005a; Bluhm and Gradinger 2008). Predators include Orca, Polar bears and humans (Hay and Mansfield 1989). 

Ice seals of the Arctic include Ringed seals, Ribbon Seals, Spotted Seal, and Bearded Arctic seals.   Ringed seals (Phoca hispida) are the most common and widely distributed ice seal in the Arctic (Reeves 1998).  Ringed seals are relatively small seals (1.5 m) that are generally found on permanent ice or large floes, maintaining breathing holes allowing it to use ice habitats when other seals cannot (NAMMCO 2005b).  Major foods eaten are Arctic cod, nektonic crustaceans (hyperiid amphipods and euphausiids), capelin, sculpin, and sea-ice and benthic crustaceans (Bluhm and Gradinger 2008).  The balance of the diet varies seasonally.  Ringed seals are a primary prey item for Polar bear, Arctic fox and Glaucous gulls (NAMMCO 2005b).

The Bearded seal (Erignathus barbatus) is a solitary seal with a circumpolar distribution.  It is most abundant where it can reach the sea bottom to feed.  The bearded seal is generally found in the pack ice where openings are common since it cannot maintain a breathing hole.  In the Beaufort and Chukchi system, E. barbatus consumed crab, shrimp, and clams (Lowry et al. 1980).  In the Kara and Barents Seas, and Sea of Okhotsk bearded seals fed primarily on Arctic cod (B. saida) as well as shrimp (Sclerocrangon boreas) and mollusks (Finley and Evans 1983).  In the areas of NW Greenland and the Canadian High Arctic, bearded seals had a varied diet including fish, crustaceans, gastropods, cephalopods and polychaetes (Finley and Evans 1983).

Other seals that are found in the Arctic include Ribbon seals (Phoca fasciata), Harp seals (P. groenlandica), and Spotted seals (P. largha).  Both the Ribbon and Spotted seals feed primarily on Arctic cod, capelin, as well as demersal fish and large benthic crustaceans.  Harp seals feed primarily on Arctic cod and shoaling fishes, such as herring and capelin (Bluhm and Gradinger 2008).

Three subspecies of walrus occur in the Arctic: the Pacific walrus (O. rosmarus divergins) in the Bering-Chukchi), the Laptev walrus (O. rosmarus laptevi) in the Laptev Sea, and the Atlantic walrus (O. rosmarus rosmarus) in the Barents-Kara, Greenland, and High Canadian Arctic waters (NAMMCO 2005c).  Walrus are extremely gregarious, often hauled out on land or ice floes, with several thousand individuals in a herd. 

Walrus feed in shallow waters (10-50 m), foraging through bottom sediments with their stiff beard bristles. Their primary diet appears to be dominated by bivalve clams, however, stomach contents analysis also indicates that other benthos are also important, including snails, echinoderms, and crabs (Outridge et al. 2003; Bluhm and Gradinger 2008).  Dominant clam species found in stomachs included Mya truncata, Serripes groenlandica, and Macoma sp.  Due to their size, tusks, and their gregarious behavior walrus predators are limited to Polar bear, Orca, and humans (NAMMCO 2005c).

Orcas occur in the Arctic during open water periods.  Orcas move northward from the Bering Sea or the North Atlantic.  Distribution likely varies, with movements tracking those of favored prey species or pulses in prey abundance of availability (such as seal pups or fish runs).  In the Arctic, Orcas rarely move close along or into the pack ice (Reeves et al. 2002).  The frequency and abundance of Orcas in the Arctic appears to increase during years with decreased ice coverage.  Orcas are a top predator and feed on a variety of large vertebrate prey including anadromous and pelagic fish, ringed seals, and whales.  Orcas are considered a significant threat to Bowhead whales (COSEWIC 2009).

Polar bears are linked to the marine habitat through diet and daily or seasonal migration.  Although they reside on the ice during the winter, polar bears are accomplished swimmers and inhabit the open waters along the ice edge; they migrate toward land once the ice melts.  Polar bears are linked to the marine pelagic food web, feeding primarily on ringed seals, although they will also feed opportunistically on other marine mammals (Thiemann et al. 2007).