Walruses are found in all Arctic waters, in areas that are seasonally ice-covered, in the Atlantic (Atlantic walrus, O. rosmarus rosmarus), in the Pacific (Pacific walrus, O. rosmarus divergens) and off the North coast of Asia, particularly in the Laptev Sea (Laptev walrus, O. rosmarus laptevi), three subspecies being geographically isolated.
Atlantic walruses are found in the northern waters of Canada, Greenland, Norway and Russia.
Summer distributions of walruses in Greenland and Canada. Known wintering areas shown in white.
Summer distribution of walruses in Svalbard-Franz Josef Land and the Barents/Kara Seas.
Habitat use by walruses varies according to the season. For most of the year walruses are widely dispersed over vast areas where they usually occur in clumped groups (Heide-Jørgensen et al. 2013). In spring and summer, walrus are generally found in coastal areas throughout their distribution area, where water depths are relatively shallow and they can access their favoured benthic foods. Summer habitat use is also driven by available haulout areas (Freitas 2009). Proximity to human settlements is also a factor in habitat choice, as walruses that are disturbed or displaced from an area tend not to return.
Walruses prefer hauling out on sea ice when they can, rather than on land (Lydersen et al. 2008). In the summer when ice is not available, groups of walruses haul out onto land at traditional sites, called uglit in Inuktitut. These are often located close to their feeding grounds, although walruses have been observed travelling up to 100 km from these sites to feed (Witting and Born 2005). Some sites may be used year after year, while others are more transient. There is considerable variation in site use by walruses both within and between years (Stewart et al. 2013c).
Walrus haul out on the ice...
or on land when ice is not available. Photos: J. Blair Dunn
Walruses seem to be fairly consistent across their geographic range in spending about 25% of their time hauled out, at least during late summer (Lydersen et al. 2008). Diurnal variation in haul-out patterns has also been observed, with a tendency for walruses to haul out during the afternoon and evening (Stewart et al. 2013a).
Off western Greenland, areas of preferred habitat are offshore banks (<200 m deep) with suitable food items. One such area is west of Disko Island (69.75° to 70.75° N) while another is Store Hellefiske Banke (66.50° to 68.25° N) in the Sisimiut-Aasiaat area (Andersen et al. 2013). Store Hellefisk Banke has water depths ranging from 20 to 200 m and is frequented by walruses during spring (Dietz et al. 2013). These two shallow areas are separated by the entrance to Disko Bay where water depths exceed 200 m and where walruses are generally not found (Heide-Jørgensen et al. 2013).
Walruses spend from fall to spring in these two areas, but are absent from them in summer. Once the sea ice has melted, walruses will migrate the roughly 450 km across Davis Strait towards SE Baffin Island (Andersen et al. 2013, Heide-Jørgensen et al. 2103).
As well as varying by season, habitat use varies by sex. Males have larger home ranges than females, and tend to occur farther offshore, farther from the ice edge and at greater depths than females. Frietas et al. (2009) documented quite regular annual movement patterns for 17 male walruses around Svalbard. During summer, walruses were most often found in coastal areas with a median distance to the coast of 4.6 km. In the winter, most of the tagged males performed long distance movements, up to 840 km from the tagging locations, and returned sometime between late February and late June.
The choice of summer haulout sites also appears to differ between males and females. Adult females with calves occur more frequently at sheltered inshore haul-out sites whereas the off-shore exposed rocks facing deeper waters have a higher proportion of adult males (Dietz et al. 2013).
Similar results were seen in a more recent tagging study of adult male walruses from Svalbard. During the winter, they moved into areas of >90% ice concentration, traveling as far as 600 km from ice-free water (Lydersen and Kovacs 2013). It is thought that these males moved into their breeding areas in the winter, based on the timing of the occupancy and diving behaviour in that area. When the breeding season was over, walruses with satellite tags that were still transmitting locations returned to the Svalbard coast, showing high site fidelity to the previous year’s summering area (Lydersen and Kovacs 2013).
Winter habitat use, especially for males, seems to be driven by breeding needs and appears to be independent of water depth and distance to shore (Frietas 2009). Males seem to feed little during the breeding season and their habitat selection is probably mainly affected by the presence of females. (Lydersen and Kovacs 2013, Frietas 2009).
Differences between male and female habitat use is also seen in other areas. Along Southeastern Baffin Island in the fall, dispersal of walruses along the coast was more condensed and there was greater segregation seen between males and females. Females remained farther north and farther east, and males were more often located offshore in areas with greater water depths. Males had also had larger home ranges than females during both seasons (Dietz et al. 2013). Females and calves seem to prefer to remain in association with drifting ice as much as is possible, but they are also found in coastal areas in summer throughout the range of the species (Freitas et al. 2009). Another consideration for females which will influence their habitat choices is their need to feed throughout the year, including times when they are pregnant or nurturing young.
Sea ice is important habitat for walruses. In several studies, the preferred percentage ice for walruses in West Greenland was found to be 50-60% cover, with some variation according to sex, season and year (Dietz et al. 2013, Born et al. 1994). In the Svalbard-Franz Josef Land region some walruses winter in very dense pack ice (Lydersen and Kovacs 2013, Freitas et al. 2009). Walruses are unable to break through ice that is thicker than about 20 cm (Fay 1982) but in both West Greenland and SE Baffin Island shallow polynya and pack-ice areas with dynamic leads exist where walruses can overwinter.
Photo: J. Blair Dunn