The walrus (Odobenus rosmarus) is a massive marine mammal, easily recognized by its long tusks and prominent whiskers, occupying a discontinuous, circumpolar range across the Arctic Ocean and subarctic seas. This species is an integral part of the Arctic ecosystem, depending heavily on the region’s sea ice and shallow ocean floor for survival. Walrus populations are divided into distinct geographic areas determined by their evolutionary history and environmental needs. Understanding their habitat helps define the two separate populations and the specific environmental factors that govern where they can successfully live, feed, and reproduce.
The Two Walrus Subspecies and Their Global Ranges
The global walrus population is separated into two recognized subspecies: the Pacific walrus (Odobenus rosmarus divergens) and the Atlantic walrus (Odobenus rosmarus rosmarus). These two groups are geographically isolated, with the deep Arctic Basin acting as a natural boundary separating their distributions. The Pacific subspecies is concentrated in the western Arctic, while the Atlantic subspecies is spread across the eastern Arctic and North Atlantic.
The Pacific walrus represents the majority of the species’ population, with recent estimates suggesting their numbers range between approximately 129,000 and 257,000 individuals. Their range is centered around the shallow continental shelves that span the Bering, Chukchi, and East Siberian Seas, situated between Alaska and Russia. During the winter, this population aggregates along the pack ice of the Bering Sea, moving north through the narrow Bering Strait as the ice recedes in the spring and summer.
Conversely, the Atlantic walrus population is significantly smaller and more fragmented, with an estimated total abundance of around 30,000 to 40,000 animals. This subspecies occupies a much broader yet more scattered range across the eastern Arctic. Key areas include the Canadian Arctic archipelago, the waters around Greenland, the Svalbard archipelago, and the western part of Arctic Russia, including the Barents and Kara Seas.
Critical Habitat Requirements
The distribution of walruses is strictly governed by a narrow set of ecological requirements involving both a stable resting platform and accessible food sources. Walruses depend on sea ice as a platform for resting between feeding dives, giving birth, nursing their young, and molting. This ice must be stable enough to support their bulk but also dynamic enough to provide open water leads for feeding access.
Their diet consists almost entirely of benthic invertebrates, which are organisms living on or in the seafloor. This feeding habit necessitates a habitat over shallow continental shelf waters, typically those less than 100 meters deep. The walrus uses its sensitive, quill-like whiskers to locate bivalve mollusks, such as clams, which are the primary component of their diet, buried in the sediment.
The deep Arctic Ocean basin is largely avoided because the water depth prevents them from reaching the necessary food source on the seabed. This ecological constraint ties the walrus population directly to the relatively narrow, shallow shelf areas that rim the continents.
Seasonal Movements and Haul-Out Behavior
The annual cycle of walrus movement is closely linked to the advance and retreat of the Arctic sea ice. In the Pacific population, females and their dependent young undertake an extensive migration, following the receding edge of the pack ice northward into the Chukchi Sea for summer foraging. In the fall, they reverse this course, moving southward into the Bering Sea ahead of the advancing winter ice.
When the sea ice retreats completely beyond the edge of the continental shelf, walruses are forced to come ashore in massive aggregations called “haul-outs.” This behavior is particularly pronounced in the Pacific subspecies during late summer along the coasts of Alaska and Russia. A haul-out is a place where marine mammals leave the water to rest, and these walrus gatherings can reach tens of thousands of individuals.
These land-based congregations carry inherent risks due to the sheer density of the animals. When the herd is suddenly startled by a sound or a disturbance, the walruses may rush toward the safety of the water in a stampede. Tragically, in these events, smaller or younger animals, particularly calves, can be trampled to death by the panicked adults. Consequently, the availability of resting platforms, whether ice or land, directly impacts the population’s ability to forage safely.