The global view of walruses
1 May 2017
The walrus (Odobenus rosmarus) has a circumpolar Arctic and sub-Arctic distribution with two subspecies, the Atlantic walrus, O. r. rosmarus, and Pacific walrus, O. r. divergens. Walruses are widely distributed but occupy a narrow ecological niche. They require areas of shallow water with a productive bivalve community, the reliable presence of open water to access these feeding areas, and suitable ice or land for hauling out. Walruses often gather in large herds. They are associated with moving pack ice for most of the year but when ice is absent haul out on land at predictable locations. Walruses are sensitive to disturbance at these haulouts.
Their habitat use and behaviour make walruses relatively easy for hunters to locate, and vulnerable to environmental changes and disturbance. Hunting by humans has strongly influenced their distribution. Many populations were historically over-harvested, with varying levels of recovery. Suitable habitat has declined as human activities have expanded. Understanding of walrus population trajectories is limited by the difficulty and cost of surveying in remote areas. Survey coverage has typically been limited to a small subset of a population’s distribution. Few populations have been resurveyed over time using comparable methods, and the structure of some populations is poorly understood. Information on the populations and on the IUCN (International Union for the Conservation of Nature) status of each subspecies is summarized on the map. Most countries need to update the conservation status of walrus populations within their jurisdiction.
Atlantic walruses historically ranged from the central Canadian Arctic east to the Kara Sea, north to Franz Josef Land and south to Nova Scotia, Canada. Six extant populations are recognized based their genetic interchange and other factors such as geographical separation. Several are shared by Canada and Greenland, and Norway and Russia share the Svalbard-Franz Josef Land population. The historically abundant population in southeastern Canada was wiped out by hunting ca. 1850, and is unlikely to re-establish due to the increase in other human activities in the region.
Two Pacific walrus populations are recognized, one in Russia’s Laptev Sea and the other, shared by Russia and Alaska, in the Bering and Chukchi seas. The Laptev Sea population was once considered a separate subspecies but recent studies support its recognition as the westernmost population of Pacific walruses. These populations may have formed a continuum prior to commercial exploitation. Little information is available on the Laptev Sea population and its abundance and trends are unknown. The Bering and Chukchi Seas population occurs throughout the continental shelf waters of both seas and ranged farther south prior to excessive hunting. Population size has fluctuated markedly in response to varying levels of human exploitation.
Key threats and factors limiting walrus populations stem from subsistence hunting, industrial development and resource extraction, tourism and other disturbances, and climate change. Stressors from these threats, such as habitat disturbance and hunting mortality, can alter walrus distribution or reduce walrus abundance, with ecological impacts and socioeconomic costs. Subsistence hunting affects Atlantic walrus populations in Canada and Greenland and Pacific walrus in the Bering and Chukchi seas. Atlantic walruses in Norwegian and Russian waters are not hunted for subsistence, nor are Pacific walruses in the Laptev Sea.
Industrial development and disturbance by human activities may become increasingly important threats. Hydrocarbon exploration and development has the potential to affect Atlantic walruses east and west of Greenland and in the Barents Sea, and Pacific walruses in the Chukchi Sea. Shipping on a massive scale from iron mine development may soon disrupt Atlantic walrus habitats in Canada year-round. Loss of sea ice is helping to enable these activities and others such as ship-based tourism.
Climate change has the potential to affect all walrus populations through declines in sea ice habitat that alter their seasonal distribution, ocean acidification that causes shifts in species, and changes in human access. Pacific walruses in the Bering and Chukchi seas appear to be particularly vulnerable to ice loss, which is forcing them ashore earlier in the season in very large numbers. Greater use of coastal haulouts limits their access to offshore feeding areas, may facilitate the spread of disease, and has resulted in trampling mortalities when they are disturbed.
Research is ongoing for all populations but many information gaps and uncertainties remain related to walrus ecology and population dynamics. Some of these, such as population-specific growth rates and hunting loss rates (i.e., animals struck and lost) apply to most populations; others to a few. Two conservation and management measures are overarching: the need for international cooperation in managing shared populations, and the need for a proactive approach to the assessment of potential impacts from human activities. The importance of both measures will increase as human activities further encroach on walrus habitat in response to climate change.
Human activity coupled with diminishing sea ice means walrus herds are being forced to look for new platforms for feeding, mating and resting. MADS PETER HEIDE-JØRGENSEN says walrus distributions around Greenland have changed alongside past and present human activities and climate change.
Counting walruses is difficult, complex and labour intensive usually requiring repeat visits to haulout sites. Even then there are numerous variables swaying the numbers. MIKE HAMMILL says good record keeping is integral to good management of declining herds.