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Odobenus rosmarus ssp. divergens 

Scope: Global
Language: English
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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Mammalia Carnivora Odobenidae

Scientific Name: Odobenus rosmarus ssp. divergens (Illiger, 1815)
Parent Species:
Common Name(s):
English Pacific Walrus
Synonym(s):
Odobenus rosmarus ssp. laptevi Chapskii, 1940
Taxonomic Notes: The Walrus, Odobenus rosmarus, has generally been divided into three subspecies: the Atlantic Walrus (O. r. rosmarus), the Pacific Walrus (O. r. divergens) and the Laptev Walrus (O. r. laptevi), although the status of the Laptev subspecies has been uncertain (Fay 1982, Rice 1998). The Laptev Walrus has been described as intermediate in size between the Pacific and Atlantic forms, with skull morphology most similar to the Pacific subspecies (Fay 1982). Recent analyses of mitochondrial DNA and morphometric data show that the taxon O. r. laptevi should be abandoned and the Laptev Walrus should be recognized as the westernmost subpopulation of the Pacific Walrus subspecies (Lindqvist et al. 2009).

Elemental analysis of Pacific Walrus teeth has provided evidence for separate subpopulations corresponding to breeding concentrations in the southeast and northern Bering Seas (Jay et al. 2008). But, this separation is not supported by mitochondrial DNA analysis (Sonsthagen et al. 2012).

Assessment Information [top]

Red List Category & Criteria: Data Deficient ver 3.1
Year Published: 2015
Date Assessed: 2014-09-30
Assessor(s): Lowry, L.
Reviewer(s): Kovacs, K.M.
Facilitator/Compiler(s): Ahonen, H., Pollock, C.M., Chiozza, F. & Battistoni, A.
Justification:

Past estimates of Pacific Walrus abundance suggest a total population size of more than 200,000. However, current abundance and population trend are largely unknown. Population modeling suggests that abundance was likely declining in the 1980s and 1990s. Climate warming and reduction in sea ice coverage are occurring and because Pacific Walrus depend on sea ice for birthing and caring for their young, and for access to feeding areas, population declines are expected. Directed harvest may also impact future population trends. Based on reports from various sources Pacific Walrus are still numerous. But, because of a paucity of data on actual abundance and trend over recent decades, the Pacific Walrus should be listed as Data Deficient at this time.

Geographic Range [top]

Range Description:Walruses have a discontinuous circumpolar Arctic and sub-Arctic distribution. The Pacific subspecies ranges from the Bering and Chukchi Seas, which constitute the centre of its range, to the Laptev Sea in the west and the Beaufort Sea in the east, with vagrants occurring in the North Pacific Ocean south to Japan and to southcentral Alaska (Fay 1982). They are usually found in relatively shallow areas over the continental shelf and only seldom occur in deeper waters.
Countries occurrence:
Native:
Russian Federation; United States
Vagrant:
Canada; Japan
FAO Marine Fishing Areas:
Native:
Arctic Sea; Pacific – northwest; Pacific – northeast
Additional data:
Estimated area of occupancy (AOO) - km2:2617280Continuing decline in area of occupancy (AOO):No
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:8643598
Continuing decline in extent of occurrence (EOO):NoExtreme fluctuations in extent of occurrence (EOO):No
Upper elevation limit (metres):5Lower depth limit (metres):250
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:The Pacific Walrus population recovered from a depleted state in 1950 to a historically high level in the 1980s (Fay et al. 1997). Abundance of the Bering-Chukchi segment of the population was estimated several times during 1975-1990 by researchers from the USA and USSR/Russia. Those surveys involved visual counts of Walrus hauled out on ice or on land, and the estimates had low precision (Hills and Gilbert 1994, Gilbert 1999). Walruses that were hauled out but missed by observers, or were not counted because they were diving, were not accounted for. The most recent aerial survey in 2006 used substantially different methods: thermal scanners were used to locate and estimate the numbers of Walrus hauled out on ice along strip transects, and models were used to account for animals missed by the scanner or in the water and not detectable (Speckman et al. 2011). However, because of poor weather conditions, the 2006 survey covered only about half of the potential Walrus habitat. The population estimates derived from all the major survey efforts to date are summarized as follows: fall 1975, 220,000-248,000 (Fay et al. 1997); fall 1980, 291,000–311,000 (Fay et al. 1997); fall 1985, 244,000 (Fay et al. 1997); spring 1987, 208,000 (Fedoseev et al. 1988); fall 1990, 201,000 (Gilbert et al. 1992); and spring 2006, 129,000 with 95% confidence limits 55,000 to 507,000 (Speckman et al. 2011). For surveys in 1975, 1980, 1985 and 1990 the 95% confidence limits were generally from zero to 500,000 (Hills and Gilbert 1994). While these counts seem to suggest that the population may be reduced compared to 20-30 years ago, the incomplete nature of the 2006 survey, differences in methods between years, and the imprecision of all the estimates make it impossible to say for certain whether or not the population has declined (Garlich-Miller et al. 2011).

Bychkov (1975) estimated the number of Walrus in the Laptev Sea to be 4,000-5,000 and the same figures are given in NAMMCO (2005) as a “best guess” for the size of the population in that area. In spite of the numerous uncertainties, it is likely that the total abundance of the Pacific Walrus population is at least 200,000, and the number of mature individuals is at least 100,000.

Other lines of evidence (e.g., changes in harvest patterns, condition indices and life-history parameters) suggest that the Pacific Walrus population increased rapidly during the 1960s and 1970s, and may have exceeded the carrying capacity of its environment in the early 1980s (Fay et al. 1989, 1997). Samples from Walrus harvested in the Bering Strait region during 1952-2002 showed higher reproductive rates and earlier maturation in females in the 1990s, suggesting that the population was again below carrying capacity and no longer constrained by density dependent mechanisms, either due to a decline in population size, changes in environment conditions, or a combination factors (Garlich-Miller et al. 2006).

Taylor and Udevitz (2015) analysed the demography of the Pacific Walrus population using a Bayesian model that integrated estimates of population size, harvest, age structure and reproductive rate. Their results suggest that a population decline began no later than 1981, became more severe in the mid-1980s, and moderated from the late 1980s through 2005. They suggested that the steep decline in the early 1980s could be due to high harvest levels described by Fay et al. (1989), or a change in the environment’s capacity to support Walruses. While Jay et al. (2011) describe a mechanism whereby sea ice loss could cause the Pacific Walrus population to decline, this is a relatively recent phenomenon that is probably not related to population changes in the 1980s and 1990s (M. Udevitz pers. comm.).

Jay et al. (2011) developed a Bayesian network model that integrated potential effects of changing environmental conditions and other stressors on the future status of the Pacific Walrus population. They found a progressive increase in outcome states of vulnerable, rare and extirpated combined from a level of 10% in 2004, to 22% by 2050, and 40% by 2095. In this model, changes in summer-fall sea ice habitat and harvest levels had the greatest effect on status outcomes.

Pacifici et al. (2013) calculated that the generation time for O. rosmarus is 15.2 years. This is the same as the average age of female Pacific Walrus in the Alaska Native harvest of approximately 15 years (Garlich-Miller et al. 2006).
Current Population Trend:Unknown
Additional data:
Number of mature individuals:100000Continuing decline of mature individuals:Unknown
Extreme fluctuations:NoPopulation severely fragmented:No
No. of subpopulations:2Continuing decline in subpopulations:No
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:No

Habitat and Ecology [top]

Habitat and Ecology:Walruses are one of the largest pinnipeds. In the Pacific, males reach about 3.6 m in length and weigh 880-1,656 kg; adult females are about 3 m long and weigh 400-1,250 kg. Newborns are 1-1.2 m long and weigh 45-77 kg. Walrus are characterized by their large tusks, that are well-developed in both males and females. Tusks are used for interspecific aggression, defence against predators (Polar Bears and Killer Whales), and as an aid for hauling-out on ice (Fay 1982).

Walruses have the lowest reproductive rate of any pinniped species (Fay 1982). Male Walruses reach sexual maturity at seven to 10 years of age but they are unlikely to successfully breed until they reach full body size at 15 years of age or older. Most female Walruses attain sexual maturity at four to seven years. A calf will typically nurse for one to two years (Fay 1982, Garlich-Miller et al. 2006). Ovulation may be suppressed until the calf is weaned, increasing the birth interval to three years or more (Garlich-Miller and Stewart 1999). Courtship and mating occur mainly in the winter. It is believed that Walruses are polygynous and that the males establish small aquatic territories where they vigorously vocalize and display adjacent to females hauled-out on ice floes. Most births occur in May of the following year (Fay 1982).

The low birth rate of Walruses is offset in part by considerable maternal investment in offspring (Fay et al. 1997). Estimated survival rates for first year calves range from 0.5 to 0.9 and may be as high as 0.96-0.99 for juveniles and adults (e.g., four to 20 years old; DeMaster 1984, Fay et al. 1997). Maximum longevity is approximately 40 years (Fay 1982). Chivers (1999) developed an individual-based model of the Pacific Walrus population and estimated a theoretical maximum population growth rate of 8%.

Walruses haul out on ice floes and beaches on islands or remote stretches of mainland coastlines. They are very gregarious animals and are frequently found in tight groups that number from the tens to the thousands. Pacific Walruses spend most of their lives associated with sea ice and move with the ice as it expands and moves south in the fall and winter, and breaks up and retreats in the spring and summer. Males often separate from the females in late spring, and during the summer they use land haulouts some distance from sea ice. The females, their calves, and most of the juveniles follow the retreating sea ice north. At sea, Walruses can be found alone or in aggregations (Fay 1982).

Walruses are primarily bottom feeders and shallow divers. Most prey taken are found in the upper few centimetres of sediment, or live on or just above the bottom. Based on stomach contents, several species of clams make up the majority of the diet for most animals. In addition to clams, more than 100 taxa have been found including snails, worms, crabs, amphipods, shrimp, sea cucumbers, tunicates and slow-moving fish (Fay 1982, Sheffield and Grebmeier 2009). Some individuals prey on seals (Lowry and Fay 1984). Although Atlantic Walrus are capable of diving to depths of more than 250 m (Born et al. 2005), Pacific Walrus usually forage in depths of 80 m or less (Fay and Burns 1988). Walrus make foraging trips that last from a few hours to several days; trips are shorter in duration and distance travelled when they originate from sea ice versus land (Udevitz et al. 2009).
Systems:Terrestrial; Marine
Continuing decline in area, extent and/or quality of habitat:Yes
Generation Length (years):15
Movement patterns:Not a Migrant
Congregatory:Congregatory (and dispersive)

Use and Trade [top]

Use and Trade: Native people of the Arctic have harvested Walruses for food, hides, ivory and other materials for thousands of years, apparently with little impact on their numbers until the arrival of Europeans in the 17th century. All Walrus populations were then severely depleted by episodic commercial hunting that was greatest from the 18th through to the mid-20th centuries (Fay 1982). Since the 1970s, the Pacific Walrus has been covered by numerous international and national conservation programs that have eliminated commercial hunting and limited trade (Garlich-Miller et al. 2011), allowing the population to recover. The Pacific Walrus continues to be an important subsistence resource for indigenous people in coastal Alaska to this day (Robards et al. 2013), and harvests in recent years are likely to have been sustainable (Garlich-Miller et al. 2011, Udevitz et al.2013).

Threats [top]

Major Threat(s): As the Pacific Walrus is being considered for listing under the US Endangered Species Act, considerable attention has been devoted to identifying and evaluating threats (Garlich-Miller et al. 2011). The primary threats that have been identified are habitat changes caused by a warming climate and directed harvest.

Global warming and any associated reduction in the extent, timing and characteristics of seasonal sea ice cover could negatively affect Pacific Walruses. Declining sea ice reduces suitable haulout and breeding habitat and limits access to offshore feeding areas (Tynan and DeMaster 1997, Laidre et al. 2008). The duration of the ice-covered season has already been substantially reduced within the Pacific Walrus range (Laidre et al. 2015). Global climate models suggest moderate changes for winter-spring ice conditions in the Bering Sea by the mid-2000s (20-30% loss) and major changes by the late-2000s (60-90% loss). Summer sea ice in the Chukchi Sea is predicted to show major losses (>80%) by the mid-2000s (Garlich-Miller et al. 2011). In prior years, Walrus in the Chukchi Sea spent the summer hauling out mostly on sea ice and foraging over a wide area on the shallow continental shelf (Fay 1982). In recent years with little or no summer ice cover, animals have begun to haul out on land in large groups and go to sea to forage from there (Robards and Garlich-Miller 2013). Coastal haul-outs are less suitable for Walruses because of increased energy required to reach prey resources and mortality due to crowding, disturbance events and predation (Jay et al. 2011, Garlich-Miller et al. 2011, MacCracken 2012). Reduced sea ice cover will also allow for a greater diversity and intensity of potentially disruptive human activities (e.g., shipping and coastal development) in Pacific Walrus habitat, bringing additional potential threats to the population. As an example, low-level aircraft over-flights and near shore passage of vessels can have serious effects on Walruses at land haul-out sites, as they are highly susceptible to disturbance and easily panicked into stampedes (Fay and Kelly 1980). Mortality of calves on haul-outs caused by trampling could have a substantial effect on the future population size (Udevitz et al. 2013).

Human harvests have had major impacts on abundance of Pacific Walrus over the past 200 years (Fay 1982, Fay et al. 1997). All Walrus populations were severely depleted by episodic commercial hunting that was heaviest from the 18th through to the mid-20th centuries (Fay 1982). Since the 1970s, the Pacific Walrus has been covered by numerous international and national conservation programs that have eliminated commercial hunting and limited trade (Garlich-Miller et al. 2011), allowing the population to recover. The Pacific Walrus continues to be an important subsistence resource for indigenous people in coastal Alaska to this day (Robards et al. 2013), and harvests in recent years are likely to have been sustainable (Garlich-Miller et al. 2011, Udevitz et al.2013). The future, however, is uncertain, and as warming and sea ice declines impact the Walrus population harvest levels could become an important influence (Jay et al. 2011).

The Pacific Walrus faces additional threats, including environmental contaminants, oil and gas industry activities, fisheries and shipping. These are not considered to represent significant threats to the population at this time, but all of them have potential to impact Pacific Walrus in the future. Of greatest concern is a large oil spill associated with oil and gas development activities or shipping. While the probability of a large oil spill is low, a spill could have significant impacts if it contacted large aggregations of Walrus along the Arctic coast or offshore, or if oil impacted the benthic communities in which they feed (Garlich-Miller et al. 2011).

Conservation Actions [top]

Conservation Actions: A variety of conservation measures are in place that help protect the Pacific Walrus (Garlich-Miller et al. 2011). Walruses are listed on Appendix III of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) which allows for control of global trade in Walrus ivory. Within the USA, the Marine Mammal Protection Act (MMPA) prohibits most taking of Walruses unless it is by an Alaska Native for subsistence or production of handicrafts. The MMPA does not impose quotas or limits on subsistence harvest, but all animals taken are required to be harvested in a non-wasteful manner, and harvest levels are documented. Alaska Natives work with the responsible management agency (the US Fish and Wildlife Service) to co-manage Walrus hunting. MMPA regulations are used to control impacts caused by commercial fishing, oil and gas development, and other human activities. A number of other US laws can be, and are, used to limit human impacts on Walruses and their habitats. The Pacific Walrus is currently under consideration for listing under the US Endangered Species Act which would provide additional protections. Within the US there are currently no legal mechanisms to regulate discharge of greenhouse gas emissions, the primary cause of climate warming and sea ice loss (Garlich-Miller et al. 2011).

In Russia, Walruses were commercially harvested through the 1980s, but harvests ended in 1991 due to economic collapse of the industry. The “Law of Fisheries and Preservation of Aquatic Resources” provides for subsistence harvest of Pacific Walruses by aboriginal Russian peoples, and an quota is determined annually. Russian legislation prohibits sport hunting of Pacific Walruses, and a variety of protections are afforded to major haulout sites along the Russian coast (Garlich-Miller et al. 2011).

Citation: Lowry, L. 2015. Odobenus rosmarus ssp. divergens. The IUCN Red List of Threatened Species 2015: e.T61963499A45228901. . Downloaded on 16 January 2018.
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