Saturday, December 18, 2010

Warming means ringed seals face an uncertain future

When a female ringed seal gives birth in a cave scratched out of snow that has drifted over a breathing hole on sea ice, the clock starts ticking for her pup's survival.

The pup has three to seven weeks to grow a blubber layer that will let it survive icy Arctic waters and freezing outside temperatures. Until then, the pup must stay relatively dry and warm in the snow lair.
This ringed seal pup is seriously underweight because its snow den melted before it was old enough to be weaned. Photo © Brendan P. Ford

Climate change threatens that window for ringed seals, according to federal biologists. Projections of a warmer Arctic means sea ice will form later in winter and melt sooner in spring, retaining less snow. Less snow means insufficient shelter, making pups vulnerable to polar bears, Arctic fox, ravens and gulls, or to simply freezing to death if a cold snap follows a thaw.

"You get some sort of unusual warming event, causing the lairs to collapse, and then it gets cold again," said research biologist Brendan Kelly. "Now they're exposed without the protection of the lair."

The National Oceanic and Atmospheric Administration last week proposed listing ringed seals as a threatened species because of the projected loss of snow cover and sea ice from climate warming. The agency also proposed listing bearded seals, which need pack ice over shallow water for reproducing and molting.

Kelly, a research biologist for NOAA's National Marine Mammal Laboratory, has studied ringed seals since 1981 and has trained Labrador retrievers to sniff them out in lairs. He was lead author of the
ringed seal status report.

The Arctic and its ice gives pinnipeds, (at right) the families of marine mammals that include seals, sea lions and walruses, a tremendous defense against human and animal predators such as killer whales that seals in warmer climates don't enjoy.

Ringed seals get their name from their coats' black spots ringed by
light marks. Typically about 155 pounds as adults, they're the smallest and most numerous seals and the main prey of polar bears.

They're the only seals that can survive ice-covered waters. When freeze-up begins, they excavate breathing holes and maintain them throughout the winter by repeatedly scratching with stout claws, an adaptation of their front flippers.

By the end of winter, breathing holes might be nearly 7 feet deep, shaped like a cone that gets narrow near the surface.

Drifting snow covers breathing holes, Within the drift, ringed seal females dig out lairs to give birth to 10-pound pups and nurse, starting in April and continuing through May. Sea water from the breathing hole and reflected body heat warm the tiny cave.

Young ringed seal pups cannot survive in water. They are susceptible to temperature stresses until
they grow a blubber layer and shed their lanugo, the white, woolly coat they're born with.

Early breakup of sea ice threatens lairs during critical rearing periods when pups are too young to survive in water. Warming can expose lairs and make pups vulnerable to polar bears and Arctic foxes.

Ringed seals have a large population, but the entire population is dependent on sea ice, a habitat that is disappearing.

Climate models indicate that precipitation is expected to increase during future winters, according to
NOAA. However, toward the end of the century, a later freeze-up and early snow melts will deprive ringed seals of sufficient snow cover for lairs, especially during spring when the pups are born and nursed.

"Ringed seal pups born on ice will be subject to high rates of mortality through hypothermia and predation," the report concluded.

Birth lairs require snow depths of 20 to 25 inches. According to NOAA's assessment, those depths typically are found only where 8 to 13 inches or more of snow has fallen on flat ice and then drifted up along pressure ridges.

Pups are born with a white, wooly coat called lanugo that provides insulation as long as it stays dry. If a pup has to dive down a breathing hole to escape a predator, it cannot stay in the water indefinitely.

"Once they get wet, it's sort of like you and me wearing a down jacket," Kelly said. "As long as it's dry, it's a great insulator. As soon as it's wet, it's a terrible insulator. They're definitely cold-stressed when they're in the water, but as long as they can get back into a snow cave, into a lair, in a reasonable amount of time, they can regain their normal body temperature and survive that immersion."

The earliest they might be weaned is by the end of May, but late-born pups are still nursing in June.

A polar bear might eat as many as 43 ringed seals per year, collapsing
snow caves like a kid stomping bubble wrap and pouncing on a pup or an adult before it disappears down a breathing hole. Inadequate snow or lairs that melt make pups vulnerable to ravens and gulls.

Ringed seals are notoriously difficult to study or even count because they're spread out over hundreds of miles of remote ice. In summer,
seals are in dark water and in winter they're under snow or ice.

"We just don't have any good, solid estimates of population size," Kelly said.

The state of Alaska sued to overturn the listing of polar bears in part because their numbers have not crashed and because the U.S. Fish and Wildlife Service projected sea ice loss 45 years into the future, the equivalent of three generations of bears. The same objection remains for ringed seals, said Alaska endangered species coordinator Doug Vincent-Lang.

The Endangered Species Act was meant to protect declining species that have an expectation of being threatened with extinction within 20 to 30 years, not a century, Vincent-Lang said.

"There's just too much uncertainty to be able to forecast with any certainty what may occur that far into the future," he said

Kelly said the ringed seal assessment team was comfortable projecting habitat loss to the end of the century. "Most of the change that's going to happen in the next 50 years is already loaded into the atmosphere, if you will," he said.

After that, the models vary but all show the same trend, he said.

"None of the models predict that it will get cooler or that it will even level off," Kelly said. "They all predict continuing warming. That to us says, we can forecast snow and ice out to 100 years and forecast the impact of those changes on marine mammal populations that depend on those habitats."

NOAA will collect public testimony on listing ringed and bearded seals for 60 days. The deadline for a final listing decision is in a year.

Anchorage Daily News, "Warming means ringed seals face an uncertain future", accessed December 14, 2010
The Encyclopaedia of Earth, "Future change in processes and impacts on Arctic biota", accessed December 14, 2010

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