Tusks on the cusp of climate change in Arctic

By Dr. David Wartinbee, for the Redoubt Reporter

Walruses (Odobenus rosmarus divergens) are unique within the animal world because of their characteristic tusks. Their scientific name indicates a “tooth-walking sea cow” and may refer to the “head-high” position large males must maintain as they move about because of the long tusks projecting downward. The tusks are actually elongated canines from the upper jaw and can be nearly 4 feet long on some 2,500-pound males.

The tusks are used as a mating display or a weapon when dominance is being challenged. As well, these same tusks are used to carve out breathing holes in the ice packs where they are usually found. Contrary to long held thoughts, these large tusks are not believed to be used when feeding in bottom sediments.

The most important food sources for Pacific walruses are various bivalves (clams) from the ocean sediments. Apparently, walruses are able to sense clams with their stiff whiskers, called facial vibrissae. These vibrissae are actually about as thick as coat-hanger wire. They swim along the bottom sediments with their muzzle in the sediments and occasionally they will sweep water across the sediments with their front flipper.

In addition, it is believed that walruses may squirt water at the bottom sediments to uncover clams and marine worms. When a whole clam is taken into the mouth, walruses are able to use a powerful suction-squirt action within the mouth to separate clams from their shells. Supposedly, walruses can take in and shuck about six clams a minute. While their molar teeth show some wear, it is not believed to come from crushing shells during feeding, but rather from inadvertent sand taken in while feeding. Walruses are known to occasionally feed on seals and even some birds, but it is not known how important these other food sources are in their overall dietary scheme.

While walruses are circumpolar and there are a couple closely related species, 90 percent of the walruses of the world are found near Alaska. Most of them spend much of their life on pack ice, just like ice seals. Arctic pack ice provides a drifting haul-out site over the Arctic shelf where the water is usually 150 to 200 feet deep. This is the ideal depth for walrus feeding forays, as well as an ideal depth for growth of their favorite clams.

During some periods of the summer, male walruses may congregate on certain shore areas, while most females remain on pack ice farther north. There are some islands northwest of Bristol Bay where many walruses haul out and rest on the beaches between feeding forays. When using the shore as a home base, walruses are forced to commute to and from feeding areas. These forays are usually only a few days long and they then return to rest again.

As winter approaches, males start to move north in search of receptive females on the pack ice. Large, dominant males will establish a breeding harem and protect it from other challenging males. Here is where large tusks and a thick hide become important. Mating usually occurs close to February on the ice. After mating, there is delayed implantation and then a very long growth period. Total gestation may take 15 to 16 months.

Thus, females only breed every other year, or maybe every third year. Most pups are born on the pack ice and are actively protected by their mothers. Rich walrus milk contains more than 30 percent fat, and the calf is able to gain 1 to 2 pounds each day. The calf continues to nurse for most of two years, and even longer if the female does not breed again.

With the recent decline in pack ice in the Arctic, walruses are being forced to change some of their behaviors. During the past couple years, the only remaining summer pack ice has been much farther north than normal and it is over much deeper waters. The deeper waters do not contain as many of the needed bivalves and it takes more effort for walruses to reach those depths. Recently, during summer months along the western coast of Alaska, large numbers of walrus have hauled out on open beaches. These haul-outs contain both males and females, along with their calves. They then make 20- to 40-mile foraging trips from shore, instead of simply diving below the floating ice packs.

There have been indications that juveniles are having higher mortality rates due to the long foraging trips they now have to make. There is also some concern that, when startled, the entire herd may bolt toward the water and crush some of the younger, more vulnerable walruses. Because of this stampede possibility, wildlife officials have limited human visitations and flyovers of these haul-out spots.

Walruses have been an important food item for many subsistence communities of Northwest Alaska. The dark-colored meat is a sought-out food source. Since walrus blubber can be 10 inches thick on a larger male, Native populations have used it for food as well as a source of oil. Additionally, the particularly thick and rugged walrus hide is used for covering traditional umiak boats. Because the hide can be an inch thick, Native umiak builders sometimes split the skin and double the coverage area of a single hide. In the past, indigenous populations used walrus intestines for waterproof coats and pants. Walrus tusks have been a source of tools, like harpoon points, for thousands of years. Today, walrus ivory is a medium for highly prized artwork.

With more dramatic warming in Arctic regions than anywhere else, the changes are going to be felt by native animals, especially those that are adapted to cold and ice. Walruses are already being impacted by reductions in pack ice and there are questions about how the overall population will fare. Another coming change to the Arctic, because of the warming, is increased commercial shipping, about which Native subsistence villages are rightfully concerned. No one yet really knows how shipping traffic will impact the local flora and fauna.

David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus.


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Filed under ecology, science of the seasons

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