Walruses are large marine mammals, recognizable by their prominent tusks, inhabiting the frigid, shallow waters of the Arctic and Subarctic regions. Walruses are considered migratory animals, but their seasonal journeys are distinct from the long-distance migrations of some whale species. Their movements are generally shorter, less predictable, and are primarily driven by the annual advance and retreat of the sea ice and the need to access feeding grounds.
Sea Ice Dependency and Seasonal Movement
The movement of walruses is dictated by the presence of sea ice, which serves as a mobile platform for resting, nursing, and giving birth. They spend a significant portion of their lives on the ice, using it as a stable, drifting base between foraging bouts. Walruses are specialized feeders, relying almost exclusively on benthic invertebrates, such as clams and mussels, found on the continental shelf. Because they are not deep divers, they must remain close to these shallow feeding grounds, usually less than 80 meters deep.
The seasonal shift in Arctic ice cover forces a corresponding movement in walrus populations. In the spring, as the pack ice begins to melt and retreat northward, the walruses follow the receding edge to stay above productive feeding areas. This seasonal following allows them to continuously exploit rich food sources. This reliance on sea ice is an energy-efficient strategy, as the ice essentially transports them over their foraging territory.
When the sea ice advances southward in the autumn and winter, walruses make the return journey to remain at the southern periphery of the ice edge. This continuous association with the ice is so ingrained that the movements are often described as tracking the ice edge rather than a true migration to a specific destination. However, recent environmental changes are disrupting this pattern, forcing walruses to adapt their movements as the summer ice melts earlier and further than in previous decades.
Contrasting Migration Patterns of Walrus Subspecies
Walruses are divided into two primary subspecies, the Pacific Walrus and the Atlantic Walrus, and their distinct geographical distributions necessitate different migratory strategies. The Pacific Walrus population, which is significantly larger in number, undertakes the most extensive seasonal movement of the species. This group typically winters in the central and southern Bering Sea, where the ice remains stable enough to support them.
In late spring, the majority of the Pacific population, particularly the females and young calves, begins a large-scale northward migration into the Chukchi Sea. They often move passively with the melting ice floes, traveling hundreds of kilometers across the Bering Strait to their summer feeding grounds. This long journey is also a critical part of the life cycle, as females typically give birth to their calves during this northward movement.
In contrast, the adult male Pacific Walruses often exhibit a partial migration pattern, separating from the females and young. Many of the bulls remain in the southern Bering Sea or migrate to coastal areas like Bristol Bay, hauling out on land to rest throughout the summer.
The Atlantic Walrus, found in the eastern Canadian Arctic, Greenland, Svalbard, and western Russia, generally displays a more localized and less extensive movement. The Atlantic subspecies’ movements are characterized by shorter, more regional shifts, often remaining closer to coastal areas throughout the year. While they also depend on sea ice, their migration is often a localized response to changes in ice cover or proximity to traditional haul-out sites.
Hauling Out and the Physical Journey
The physical journey involves a constant cycle of resting and foraging, a behavior known as “hauling out.” This refers to leaving the water to rest on a solid substrate, ideally a large, stable ice floe. Walruses use these floating platforms as mobile nurseries and resting points, which allows them to drift over new feeding grounds without the energetic cost of continuous swimming.
When the sea ice is unavailable or has retreated beyond the shallow continental shelf where their food lies, walruses are forced to haul out on coastal land masses, often forming massive aggregations. These terrestrial haul-outs can number in the tens of thousands of individuals, creating extremely dense gatherings on rocky beaches or outcrops. While walruses are powerful and efficient swimmers, capable of sustained long-distance travel in the water, their movement on land is slow and clumsy.
The necessity of using land haul-outs presents significant physical and safety challenges for the herd, particularly for the youngest members. The sheer density of the animals in these crowded coastal locations increases the risk of a stampede if the herd is suddenly disturbed by a predator or human activity. Tragically, many calves can be crushed and killed in the ensuing rush to the water, a danger that is largely absent when they are resting on dispersed sea ice platforms.