Recovery Strategy for the Atlantic Walrus
1.1 Species Assessment Information from COSEWIC
Date of Assessment: May 2000 Common Name (population): Atlantic walrus - Northwest Atlantic population Scientific Name: Odobenus rosmarus rosmarus COSEWIC Status: Extirpated Reason for designation: Extirpated by exploitation Canadian Occurrence: Québec, New Brunswick, Nova Scotia, Newfoundland and Labrador, Atlantic Ocean COSEWIC Status History: Extirpated around 1850. Designated Extirpated in April 1987. Status re-examined and confirmed in May 2000. Last assessment based on an existing status report.
Walruses are large, gregarious marine mammals with front and hind limbs that have developed into flippers. Although related to the seals and sea lions, the walrus can be distinguished from all other species of marine mammals by its tusks, which are long upper canine teeth, and by its moustache of quill-like whiskers. Adult males are larger than females and have longer, broader tusks. The skin, covered sparsely with hair, is cinnamon brown but can appear pink on a warm day or almost white after a long, cold dive. At birth Atlantic walruses are about 120 cm long and weigh about 55 kg; males grow to about 315 cm and 1100 kg, females to about 280 cm and 800 kg. The walrus can support itself upright with its front flippers, like sea lions.
Walruses are polygynous (each male has several mates) and males compete for females at breeding time. Mating occurs in the water from February through April. Most young are born the following year in May-June and suckle for 25-27 months. Maternal care is very well-developed and walrus herds are protective of young, which may lead to high juvenile survival rates. Females give birth about every 3 years.
Maximum age in walruses may be greater than 35 years. Females mature at age 5-10 years, males at age 7-13 years. Because of the low rate of production of young (annual gross production of about 10%) walruses are susceptible to mortality caused by humans, including hunting.
Walruses “haul out” (i.e., come ashore for a period of time) on ice and land, sometimes in large herds. Walruses haul out to rest, for social interactions, and to give birth and rear pups. Ice is preferred for hauling out. It has been hypothesized that one of the benefits of hauling out on land is that it provides a stable temperature in the skin and appendages, which promotes regeneration of the skin and healing of wounds. Little is known of the physiological requirements of walrus or their ability to adapt to changes in food availability or environmental conditions.
1.3 Populations and Distribution
The walrus has a discontinuous circumpolar distribution in the Arctic and sub-Arctic, with distinct Atlantic (Odobenus rosmarus rosmarus) and Pacific (O. r. divergens) subspecies. The historical distribution of Atlantic walruses ranged from the central Canadian Arctic in the west to the Kara Sea (Russia) in the east, north to Svalbard (archipelago in the Barents Sea north of Norway) and south to Nova Scotia. Within this range there are two well separated populations, one to the east of Greenland and the other to the west, to which all Canadian individuals belong. The western population can be further subdivided and includes the Canadian populations described below.
Within Canada the Atlantic walrus currently ranges from Bathurst and Prince of Wales islands in the west to Davis Strait in the east, and from James Bay in the south to Kane Basin in the north. Historically, at the time non-aboriginal people first made contact with the species, the Atlantic walrus ranged south along the Labrador coast to the Gulf of St. Lawrence, Newfoundland and Nova Scotia (Figure 1). During the ice ages, walrus may have ranged as far south as the Carolinas and Georgia.
Figure 1. Approximate historical distribution of Atlantic walrus in Canada. (Source: COSEWIC in press.)
Five populations of Atlantic walrus, ranging from Nova Scotia to the high Arctic, have been recognized in Canada. Four extant populations are currently recognized by DFO for management purposes based on geographical distribution, changes in abundance, contaminants and lead isotope ratios and signatures: 1) south and east Hudson Bay; 2) northern Hudson Bay-Davis Strait; 3) Foxe Basin and 4) Baffin Bay (High Arctic) (COSEWIC 2006). The degree of genetic isolation between these four extant populations is not known, and each may consist of sub-units that mix little or not at all.
A fifth population, the Northwest Atlantic population, was formerly found at Sable Island, the eastern coast of Nova Scotia, and in the Gulf of St. Lawrence. Originally thought to number in the tens of thousands, this Northwest Atlantic population was heavily harvested for at least a hundred years in the 17th and 18th centuries and extirpated by the late-18th century.
All Canadian populations may once have been continuously distributed. Walrus are able to move long distances, by swimming or by drift on ice, but overall movements are little known.
Although five populations of Atlantic walrus are currently recognized in Canada (COSEWIC 2006), this recovery strategy follows COSEWIC (in press) which identified two Canadian populations for designation: an extant eastern Arctic population, and an extirpated Northwest Atlantic population. It is this Northwest Atlantic population which is on the federal List of Wildlife Species at Risk (i.e., SARA Schedule 1) and for which this recovery strategy is written.
1.4 Life History Requirements
All information on the habitat and biological requirements of the Northwest Atlantic population of Atlantic walrus is based on what is known about the extant Atlantic walrus population in the eastern Arctic.
1.4.1 Habitat and biological needs
Atlantic walruses require large areas of relatively shallow water (80 m or less), with bottom substrates that support a productive bivalve community, open water over the feeding areas, and suitable ice or land nearby on which to haul out. In the north they are associated with moving pack ice for much of the year but when ice is lacking in summer and fall, they congregate and haul out on land in a few predictable locations. Suitable land habitat is on low, rocky shores with steep or shelving subtidal zones where animals have easy access to the water.
Atlantic walruses feed mostly on benthic (bottom-living) prey at depths of 10m to 80m. Dives can last up to 24 minutes. They identify suitable prey using their sensitive whiskers, and bottom sediment patterns suggest that prey are identified by rooting with the snout and then excavated using jets of water from the mouth.
Although bivalve molluscs are the preferred prey, gastropod molluscs, sea cucumbers and sea urchins, polychaete worms, amphipod and isopod crustacea, brachiopods and priapulids have also been found in stomach contents. Over a 97-hr period a 1200 kg male Atlantic walrus dove 412 times and consumed an average of 53 bivalves per dive, equivalent to an intake of 57 kg wet weight of bivalve biomass per day. Walruses are also known to eat ringed and bearded seals, fishes and squids, and seabirds.
1.4.2 Ecological role
Atlantic walrus are an important predator of bottom invertebrates, particularly bivalve molluscs. The closely related Pacific subspecies, which is currently much more abundant than the Atlantic walrus (ca 200,000 individuals in the Bering Sea and adjacent areas), is considered to have a major role in the marine ecosystem, strongly influencing productivity and ecological function through predation on benthic invertebrates, disturbance to bottom sediments and facilitating flow of nutrients from the bottom to the water column (Ray et al. 2006). Nutrient flow from water in bottom sediments to the water column is estimated to be increased by two orders of magnitude by Pacific walruses.
It is not known whether competition for resources with other animals was a significant ecological factor historically.
1.4.3 Limiting factors
The low intrinsic capacity of the population to increase, mainly due to infrequent production of young (every three years), means that Atlantic walrus are particularly susceptible to additional mortality from human activities.
1.5.1 Description of potential threats
The principal threat to existing Atlantic walrus is human hunting. Hunting in the 17th and 18th centuries (for meat, oil and hides) was the cause of extirpation of the Northwest Atlantic population. However, this might not be an important potential threat to a re-established walrus population in southeastern Canada. Commercial harvesting of Atlantic walrus has been forbidden in Canada since 1928, and there was apparently no documented Aboriginal harvest in the past in southeastern Canada (COSEWIC 2006), although given the long time period since the population was extirpated, evidence may have been lost or not collected.
Human disturbances (noise from ship traffic and aircraft, oil and gas exploration, human settlements, and other human activities) could be potential threats to a re-established walrus population in southeastern Canada. Disturbances that cause walruses to leave their haul-outs may impact populations by causing stampedes (with associated juvenile mortality), interfering with feeding, increasing energy expenditures, masking communications, impairing thermoregulation and increasing stress levels. Oil spills would be a significant potential threat to walrus herds given their need for habitat near the water’s edge.
Entanglement in fishing gear, particularly gillnets, would be a potential threat to a re-established walrus population in southeastern Canada. Fishing for prey species preferred by walrus, or disturbance to habitat of prey species from fishing, might also be potential threats. These would probably be of limited importance however, since there are currently no fisheries for molluscs (clams and scallops) which live within benthic sediments in subtidal areas at depths where walrus forage in Atlantic Canada at present. Of greater potential concern however may be the perception of walrus as competitors for fisheries and the circulation of nuisance seal permits.
Predation from polar bears and killer whales are known to occur on walrus in the north, probably mainly on young; however predation is probably limited given the protective behaviour of herds to their young and the large size of adults. Killer whale predation on individuals of the Northwest Atlantic population may have occurred historically, but the importance of this is unknown. Predation would probably not be a limiting factor for a re-established Northwest Atlantic population at present because killer whales are rarely observed in the Gulf of St Lawrence. However, killer whales are reported off Newfoundland and given possible climate related shifts in whale distribution, future abundance levels, and uncertainties with regards to the numbers necessary to induce an important predation pressure on a walrus stock, the potential importance of killer whale predation on walrus cannot be dispelled.
The potential effects of climate change on walruses or the distribution of ice floes are likely limited. The impacts of warming or cooling temperatures on a re-established walrus population in southeastern Canada are difficult to predict, but could involve direct effects such as behavioural and physiological responses as well as indirect effects such as increased vulnerability to hunting and predation. Extreme summer temperatures could potentially become a limiting factor for haul-out occupancy in southern waters. That being said, the extirpated Northwest Atlantic population of walrus presumably was able to survive in the absence of ice for much of the year, since ice cover in its area of distribution was only present in winter.
Unless otherwise stated, material in this section is drawn from COSEWIC (in press) and COSEWIC (2006).
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