Atlantic walrus (Odobenus rosmarus rosmarus) COSEWIC assessment and status report: chapter 2

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Species Information

Walruses are large gregarious pinnipeds with front flippers that can support them upright, like otariids, hind flippers that are structured and function like phocid seal hind flippers, upper canine teeth that grow into long tusks, and a moustache of quill-like vibrissae. They are about 120 cm long and 55 kg at birth; males can grow to about 315 cm (~1100 kg) and females to about 277 cm (~800 kg). Their sparsely haired skin is cinnamon brown but can appear pink on a warm day or almost white after a long, cold dive. The Atlantic walrus, Odobenus rosmarus rosmarus (Linnaeus, 1758) is one of two extant subspecies of the walrus, the other being the Pacific walrus (O. r. divergens). The taxonomic status of walruses inhabiting the Laptev Sea is uncertain.

Distribution

The Atlantic walrus ranged historically from the central Canadian Arctic in the west to the Kara Sea in the east, north to Svalbard and south to Nova Scotia. Four populations have been identified in Canada: 1) South and East Hudson Bay, 2) Northern Hudson Bay-Davis Strait, 3) Foxe Basin, and 4) Baffin Bay (High Arctic). A fifth population--the “Southeast Gulf of St. Lawrence and Scotian Shelf” or “Maritime” population--was abundant along the Atlantic coast of Canada but has been extirpated. The Baffin Bay population is shared by Canada and Greenland. There may also be exchange between the Northern Hudson Bay–Davis Strait and Central West Greenland populations. The four Canadian populations are distinguished by geographical distribution, changes in abundance, contaminants, and lead isotope ratios and signatures but the degree of genetic interchange between them is uncertain. Moreover, each may consist of sub-units that mix little or not at all. Wintering areas at polynyas in pack ice or at ice edges have been documented within the range of each of the putative populations. Walrus distribution appears to have shifted to areas that are less accessible to people.

Habitat

Atlantic walruses occupy a large area but relatively narrow ecological niche. In the absence of humans, they probably require large areas of shallow water (80 m or less) with bottom substrates that support a productive bivalve community, the reliable presence of open water over these feeding areas, and suitable ice or land nearby upon which to haul out. Little protection is afforded to walrus habitat by existing National Parks, Wildlife Areas, Bird Sanctuaries, or other federal lands.

Biology

Walruses haul out on ice and land, sometimes in large herds. They can travel long distances by swimming or by riding ice floes but their seasonal movements are poorly understood. They feed predominantly on bivalve molluscs, for which they may compete with bearded seals (Erignathus barbatus). Little is known of their physiological requirements or ability to adapt to changes in food availability or environmental conditions.

Walruses are polygynous. Males compete intensely for females on the ice or in the water from February through April. The stability of the sea ice may be an important determinant of breeding behaviour. Implantation of the embryo is delayed until late June or early July, and gestation is active for about 11 months. Most young are born in late May and early June; some suckle for 25–27 months. Females mature between the ages of 5 and 10 years and give birth to a single calf about once every three years until they reach reproductive senescence. The resulting birth rate is about 0.30 calves per fecund female per year and an annual gross production rate of about 10%. Generation time may be about 21 years. From counts of growth layers in the teeth, walruses may live over 35 years.

Rates of mortality from predation by humans, polar bears (Ursus maritimus) and killer whales (Orcinus orca) are unknown. Fighting during the breeding season and selective hunting may increase male mortality. Little is known of diseases of walruses or of their response to pathogens.

Population Sizes and Trends

Five populations ranging from Nova Scotia to the high Arctic are recognized for managing hunting based on geographical distributions, genetics and lead isotope data.

South and East Hudson Bay population. Opportunistic counts suggested there were 270+ animals in the late 1990s, which was lower than earlier estimates of “410+” in 1988 and "500“ in 1995. Data are insufficient to assess whether the population really declined.

NorthernHudson Bay-Davis Straitpopulation. The most recent reconnaissance survey (August 1990) counted 1376 animals in the Coats Island–Southampton Island area and 461 in the Nottingham Island-Salisbury Island area. The number of animals present was roughly estimated in 1988 at 4850–5350 animals, and in 1995 at 6000 animals, based on a few sightings in a wide geographical area over a long period.

Foxe Basinpopulation. In August 1983, 2722 walruses were counted during a helicopter reconnaissance of northern Foxe Basin. In July 1989, a systematic visual aerial survey of central Foxe Basin counted 475 walruses and estimated that 5500 (95%CI 2700-11200) animals were present. These surveys did not cover all of northern Foxe Basin or correct for animals that were submerged beyond view. They provide indices against which change can be measured rather than estimates of the overall population. The 1989 data also provide the best available estimate of abundance.

Baffin Bay (High Arctic) population. In the 1970s and 1980s, 1700–2000 walruses from the Baffin Bay population may have summered in Canadian waters. This estimate was based on data from different seasons and years, most over 20 years old.  An aerial survey in 1999 combined with best guesses for areas not counted suggest the population may have numbered about 1500 animals.

Nova Scotia–Newfoundland–Gulf of St Lawrence (Maritime) population. This--formerly numerous--population used land haul-outs in Newfoundland, the Gulf of St Lawrence; Sable I. off Nova Scotia was also frequented. Heavy harvesting, especially in the 17th and 18th centuries extirpated this population. Occasional recent sightings are not considered a sign of its re-establishment.

Limiting Factors and Threats

Atlantic walrus populations in Canada may be limited or threatened by hunting activities, noise disturbance, and industrial activities. Their narrow ecological niche and restricted seasonal distribution make walruses relatively easy to hunt and vulnerable to environmental changes. Hunting is the cause of most known mortality among Atlantic walruses. It probably poses the most consistent limiting factor and threat to populations in Canada. Managers do not know the size or structure, survival rate, sustainable harvest rate, or rate of removal for any of the currently defined Canadian populations.

The ability of these populations to sustain the existing harvest is unknown. Data on the landed harvests of walruses in Canada are incomplete and vary widely in quality. Total removals may be underestimated by as much as 32%. Average annual Canadian takes since 1989–90 are believed to be 15 from the South and East Hudson Bay population (slight drop in take from 1977 to 1990), 247 from the Northern Hudson Bay–Davis Strait population (abrupt decline in kills, mostly in Nunavut, between 1997 and 2002), 276 from the Foxe Basin population (modest drop from 1977 to 1990), and 24 from the Baffin Bay Population (abrupt decline from 1997 to 2002). It is not known whether the decreases in takes are due to less effort, lower hunter success, or uneven reporting. The contribution of changes in the quality of the harvest data and of uneven reporting are also unknown. The Canadian Baffin Bay population may be vulnerable to hunting in Greenland waters, but this is also not well known. There is a pressing need to obtain better estimates of the walrus populations and removals to ensure that declines in recorded harvests do not signal population depletion.

Human disturbances that cause walruses to leave their haul-outs may impact population dynamics by causing stampedes, interfering with feeding and increasing energy expenditures--particularly among calves--masking communications, impairing thermoregulation and increasing stress levels. Prolonged or repeated disturbances may cause walruses to abandon their haul-outs. Their ability to recolonize areas and to adapt to non-threatening disturbances is unknown. The rarity of animals along the Atlantic coast of Canada since that population was extirpated suggests that re-colonization is at best very slow.

Threats posed to walruses in Canadian waters by industrial activities are low at present. Commercial fisheries could affect them by competing directly for food, damaging areas of seabed where walruses feed, and causing audio and visual disturbances; however, scallop fisheries that might have posed the most direct threat have been tried, and have proved non-viable. Machine noise, particularly from aircraft, disturbs walruses and can cause stampedes into the water. Climatic warming or cooling may expose walruses to greater hunting pressure. The effects of chemical contaminants on walruses are unknown but tissue levels are typically low, except for cadmium and lead from natural sources and organochlorines in animals that eat seals. The vulnerability of the species to disease is unknown.

Special Significance of the Species

Walruses traditionally provided important staples in the subsistence economy of the eastern Canadian Arctic and Greenland. The hunt and the sharing of its proceeds continue to be of great social and cultural significance, and the economic value of the meat and ivory is substantial. Ecologically, the walrus is important as the only species in its genus and a key link in the Arctic food chain between bivalve molluscs and humans.

Existing Protection or Other Status Designations

Atlantic walruses in Canada are afforded limited protection by regulations that manage the hunting, movement, and sale of walrus products (Fisheries Act, Marine Mammal Regulations SOR/93-56, Registered 4 February 1993). Hunts in Nunavut are co-managed by the Nunavut Wildlife Management Board with scientific advice and support from the Department of Fisheries and Oceans (DFO), which manages walrus in other jurisdictions in cooperation with other agencies. Four settlements in the Canadian Arctic have community quotas: Coral Harbour 60/yr, Sanikiluaq 10, Arctic Bay 10, and Clyde River 20. Elsewhere, Inuit and Indian natives of Canada can kill up to four walruses per year without a licence; non-natives require a licence. Trade in edible walrus parts is prohibited in Canada, except among Indians and Inuit, and a DFO permit is required to transport walrus parts within Canada, except for Indians or Inuit who are returning home after the hunt. The regulations prohibit disturbing, killing ineffectually, hunting without equipment to retrieve, waste of edible parts, and abandoning a killed walrus without making a reasonable effort to retrieve it. Invasive research, such as tagging, and live capture are permitted only under licence.

The Atlantic walrus is listed on Appendix III of the Convention on International Trade in Endangered Species (CITES). Anyone wishing to export walrus parts or derivatives from Canada must obtain an export permit from the Canadian CITES administration.

There is no formal cooperation between Canada and Greenland in the management of shared Atlantic walrus populations.

The Atlantic walrus was previously assessed by COSEWIC in 1987 and given two designations: the "Northwest Atlantic" or "maritime" population of Atlantic walruses in Canada was considered extirpated and the Arctic population was designated as not at risk.