Global warming may be harming Pacific walrus: scientists

The Pacific walrus may be the new icon of global warming. Like polar bears, walruses are dependent on floating sea ice to rest, forage for food and nurture their young. Like polar bears, walruses are suffering because of a scarcity of summer and fall sea ice in Arctic waters that scientists attribute to climate change.

And like polar bears, which were listed as threatened in 2008, protections under the Endangered Species Act may be granted to walruses, even though it is hard to get an accurate count of their population.

"You don't have to know how many passengers are on the Titanic to know it's in trouble when it hits an iceberg," said Rebecca Noblin, staff attorney for The Center for Biological Diversity, which sued to obtain Endangered Species Act safeguards for the walrus.

For the lumbering, long-tusked marine mammals, problems caused by scarce ice are showing up on beaches in northwestern Alaska and across the Bering Strait in northeastern Siberia.

For the third time in four years, thousands of walruses have hauled out on the Alaska shore, congregating this summer on the shorelines of the Chukchi Sea instead of spreading over chunks of floating ice.

That ice has largely disappeared. This year, summer sea ice levels reached their third-lowest point since satellite measurements started in 1979, according to the National Snow and Ice Data Center in Boulder, Colorado.

As the sea ice retreats away from the shore, there is less and less ice available to the walruses -- mostly females and their young -- over relatively shallow waters where they can feed. Ultimately, if they no longer can find ice over shallow waters, they must swim ashore -- sometimes over great distances. Those that survive the trip "haul out" along the shoreline where conditions tend to much less favorable than they would be on ice over shallow waters.

As many as 15,000 walruses began crowding the shore near Point Lay, Alaska, in August and are just starting to disperse as ice forms in chilly fall weather, federal biologists said. (At right: walruses in 2009 from a similar haul-out).

According to Alaska Dispatch:

"USGS scientists traveled to Point Lay earlier this month to tag some of the walruses in an effort to track and study their movement. They're particularly interested in how much more swimming the hauled out walruses, most of which are females, will have to do to find food and how that extra effort will affect the animals' health. They're also worried about how young walruses -- which rely on a mother's care for two years and which nurse for the first six to seven months of life -- will fare."

CROWDED BEACHES

Such congregations place walruses far from the best sources of clams and other food they pluck from the icy waters and, if they are young and small, at risk of sudden and grisly death especially if there is a stampede.

Under similar conditions in September 2009, large numbers of walruses hauled out along the Alaskan and Russian shores. On 14 September 2009, scientists encountered 131 walrus carcasses near Icy Cape, Alaska. (see left) A USGS report (Enumeration of Pacific Walrus Carcasses on Beaches of the Chukchi Sea in Alaska Following a Mortality Event, September 2009) said:

"All appeared to be young animals .... The events that led to the death of these animals are unknown, but appear to be related to the loss of sea ice over the Chukchi Sea continental shelf. In years prior to this event, other investigators have linked walrus deaths at other Chukchi Sea coastal haulouts to trampling, exhaustion from prolonged exposure to open sea conditions, and separation of calves from their mothers."

The U.S. Fish and Wildlife Service was to announce last month its recommendation for an Endangered Species Act listing. The deadline was extended to January 31 to give the agency time to evaluate two new studies. (Walrus distribution map at left)

Both reports warn of a grim future. One predicts that the Chukchi Sea will be ice-free for three months a year by mid-century and up to five months by the end of the century, and that ice-free periods in the Bering Sea also will expand.

The other study calculates that the ice-dependent walruses have a 40 percent chance of being extinct or in danger of extinction by century's end.

A LONGER 'COMMUTE?'

The latest estimate of the total Pacific walrus population is 129,000, said Joel Garlich-Miller, a Fish and Wildlife Service biologist. That figure is based on incomplete aerial surveys conducted by U.S. and Russian scientists and is probably on the low end, he said. (Map at right: Walrus range)

Another key question is whether walruses stuck on shore are spending significantly more energy searching for food than they would if they could forage from floating ice.

"There's this commute that's new to them, and it costs them," said Anthony Fischbach, a biologist and walrus specialist with the U.S. Geological Survey.

He also suspects there may be fewer calves than there should be.

"It's certainly shocking to see over 100 dead calves that were apparently healthy. But it's hard to put it in context," said Fischbach, one of the biologists who documented the carnage.

"Are these the strong ones that come ashore, whereas the ones that are weaker couldn't make the 150-mile swim to shore?"

To try to find answers, he and his colleagues have embarked on studies to count the adult-calf ratio within herds and use radio tracking to pin down their travels for food.

Advocates of Chukchi Sea oil drilling and other development are expected to oppose any Pacific walrus listing. The state of Alaska, which supports oil drilling in walrus habitat, already has sued to overturn the listing of polar bears and formally opposed new protections considered by the government for ice-dependent Arctic seals. The state also objected to habitat protections proposed for polar bear and endangered Steller sea lions.

Source:
Reuters, "Global warming may be harming Pacific walrus: scientists", accessed October 5, 2010