A Walrus at the Edge of the Ice
Laura Nielsen for Frontier Scientists
Sea ice is the foundation of an entire Arctic ecosystem. Algae flourishes where the ice is active, providing sustenance for hordes of zooplankton. Birds feed on schools of small fish sustained by the zooplankton. There are species of seabirds which live here and nowhere else, and others whose natural rhythms are dictated by presence or absence of ice. Fish populations support a variety of seals and larger fish. Bowhead whales filter-feed on tiny zooplankton, while orcas prowl for bigger prey. All these organisms live and die, drifting down to the seafloor where their detritus helps make a new meal for bottom-dwellers like mollusks and tubeworms.
Walruses live here. Blubberous and ungainly on land, adroit swimmers in water, the big toothy pinnipeds are iconic in the cold north, an Arctic keystone species. Pacific walruses live on Arctic sea ice in the Bering and Chukchi Seas, between Alaska and Siberia. In Alaska only Native hunters are permitted to take walrus. Walrus meat is eaten, walrus hide used for clothing and other subsistence-living necessities like rope and hide bags. Other parts, like bones and ivory, are crafted into beautiful artwork. Populations of walruses in the Atlantic have still not recovered from past over-hunting, but Pacific walruses were not subjected to the same exploitation, and number over 200,000.
Sometimes walruses are taken by poachers for their fine ivory-like canine teeth, which grow to long tusks in both males and females. The tusks are useful in helping walruses haul-out (drag their massive bodies onto land to rest). They also allow the creatures to root through silt on the seafloor for mollusks, their favored meal. Tusks can break holes in ice for breathing, and are used in mating rituals as males posture, fight, and sing to attract members of the opposite sex.
Apart from poachers, the walrus faces natural threats from orcas (killer whales) and polar bears, though a full-grown walrus is a formidable foe and even polar bears seldom commit to an attack. Polar bears prefer instead to pick off infirm individuals, or to charge a group of walruses and cause a panic, sending the large creatures en-mass into the water. The rush of huge bodies -male walruses have a weight averaging over 2,700 lbs- has been known to cause fatalities among calves and juveniles who are sometimes crushed by the bulk of the poorly-sighted and panicked herd.
Polar bears, though, are not the walruses' true threat. It is loss of sea-ice habitat caused by climate change which likely poses the most dire challenge to the mighty walrus.
Walruses rely on ice platforms. They are a staging ground where females give birth to calves, and where calves rest. There they can to nurse - far from land predators and near to the food source which their mothers rely on. Adults let the traveling ice floes carry them along to new foraging grounds, diving to the shallow sea floor which hosts a rich food supply of musels and clams. Finished feeding, the walruses return to the ice above to rest or care for young.
The benthic zone, a muddy, silty sea floor which rests below the relatively shallow waters of a continental shelf, plays host to numerous organisms. Tubeworms, clams, and crabs are only some of the critters which inhabit the muddy realm. Walruses can be found feeding in these zones, snuffling through mud, gouging trenches with their tusks to stir up the sediment and expose a meal. While they favor clams, walruses are opportunistic feeders and will eat most any sea creature they can find hiding in the mud on the sea floor. The stiff whiskers on their snouts are vibrassae, not mere hair but highly sensitive tools which allow them to locate prey in stirred-up silt. They have agile jaws and gums, and can swiftly root out a clam, maneuver it into their mouths, and suction-out the muscle's meaty foot before spitting out the empty shell.
Rising temperatures cause the ice pack to melt, and the ice receeds north from shore to the open ocean. As the ice edge moves away from shore, it no longer provides easy access to the relatively shallow continental shelf where walruses feed. Instead, it floats over deep ocean, where the sea floor is too deep and cold for the mussels that walruses need to flourish. When this happens walruses must abandon the diminishing ice floes and swim to shore. They haul-out on land (congregate to rest, nurse calves, and mate) instead of on ice.
This leads to crowded coasts in northern Alaska and eastern Russia. Walruses are social animals, and shore groups congregate in numbers ten thousand strong or more. All those walruses foraging and feeding in nearby waters can use up local food sources very quickly, forcing individuals to swim further and further from shore to find prey, further and further back to rest on land. It is especially troubling for mothers, who nurse calves for as long as two years. The distance makes for a longer time between nursing for calves and a more arduous journey for adults. Instead of riding near-shore ice, being carried happily to new foraging grounds, the walruses must expend precious energy in travel. This creates a food strain.
It also poses dangers: more humans and predators are present on dry land. Walruses are cautious creatures, and can be spooked into a stampede not only by polar bears but by loud noises or strange smells, especially in response to industrial disturbances. Loud noises from factories, drilling or mines, low-flying airplanes and nearby boats can unsettle the group. Since so many are congregated on shore rather than spread out on a multitude of ice floes, local panics can cause trampling deaths among the herd.
Potential oil spills, increasingly likely in the Arctic as we open offshore developments in Arctic waters to shipping and drilling, also poses a grave threat to walruses; oil settling on the silty sea floor where they forage would be disastrous. Yet we have opened about 1m hectares (2.7m acres) in the Chukchi Sea to oil and mineral exploration. In the U.S. Geological Survey's 2012 walrus radio-tracking data, you can see walruses congregate in the oil lease sale area.
The Walrus is a marvelous and intelligent animal, highly social. Much like humans and elephants, the walrus has a long childhood. Calves are not weaned for two years, and may stay with their mothers for up to five years. They learn complex social skills. Male walruses seeking a female's attention produce a stunning variety of sounds. New York Times reporter Natalie Angier describes meeting a walrus and being instructed to blow into its face, because walruses huff in each other's face as a form of social communication. They like so much to be near each other that when the Alaska Sealife Center cares for rescued walrus calves, they make sure humans are with the calves 24/7, provide a walrus-like companionship by sitting with their very large baby charges ...warm living creatures to cuddle... in order to maintain the calves' mental wellbeing.
Looking ahead, we'll need more information. Supporting walrus studies will help researchers learn more about how current global changes are changing the walruses' lives, and anticipate the best ways to protect their habitat. Let us be cautious of the choices we make regarding offshore drilling in Alaska's waters, and remember this iconic Arctic species, our toothy friends, as we plot a course to our climate future.
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National Snow & Ice Data Center : "All about Sea Ice - Wildlife : Mammals" http://nsidc.org/cryosphere/seaice/environment/mammals.html
National Snow & Ice Data Center : "Arcic Sea Ice News & Analysis" http://nsidc.org/arcticseaicenews/
U.S. Fish & Wildlife Service : "Marine Mammal Management - Walrus" http://alaska.fws.gov/fisheries/mmm/walrus/nhistory.html
U.S. Geological Survey : "Walrus radio-tracking in the Chukchi Sea 2012" http://alaska.usgs.gov/science/biology/walrus/2012animation.html
U.S. Geological Survey : "Tracking Pacific Walrus: Expedition to the Shrinking Chukchi Sea Ice" http://alaska.usgs.gov/science/biology/walrus/index.html
U.S. Geological Survey : "Whales and Walrus: Tillers of the Seafloor" http://marine.usgs.gov/fact-sheets/whales/