ON HUDSON BAY (AP) - Searching for polar bears where the Churchill River flows into Canada's vast Hudson Bay, biologist Geoff York scans an area that, because of climate change, has a diet low in fat and ice.
And for polar bears the values are getting lower and lower.
There are now about 600 polar bears in western Hudson Bay, one of the most endangered of the white beasts' 20 populations. That's about half the number from 40 years ago, says York, director of research at Polar Bear International. His latest research, with a team of scientists from several disciplines, shows that if the world doesn't further reduce emissions of heat-trapping gases, "we could lose this population entirely by the end of the century," he says.
More than just polar bears are threatened in this changing gateway to the Arctic, where warmer waters are melting sea ice earlier in the year and the open ocean is hanging on longer. For what grows, lives and, most importantly, eats in this region, it's like shifting the foundations of a house. "The entire marine ecosystem is tied to the seasonality of that sea ice cover," said Julienne Stroeve, a sea ice scientist at the University of Manitoba.
When sea ice melts earlier, the overall water temperature rises and algae growth changes. This in turn changes the plankton that feed on the algae, which in turn leads to changes in the fish. And this includes belugas, seals and polar bears, scientists say.
"What we're seeing is a transformation from an Arctic ecosystem to more of a southern open ocean," York said in August from the bobbing edge of a 12-foot Zodiac boat. "We're seeing a transformation from the high-fat plankton that lead to things like beluga whales and polar bears to the low-fat plankton that ultimately make up the last part of the food chain, which is jellyfish."
Here fat is good.
"To live in the Arctic, you have to be fat, or live on fat, or both," said Kristin Laidre, a marine mammal scientist at the University of Washington who specializes in Arctic species.
The polar bear - a symbol of both climate change and a region warming four times faster than the rest of the world - is the king of fat. When mother polar bears nurse their young - as an Associated Press crew saw on cliffs outside Churchill, Manitoba, the self-proclaimed polar bear capital of the world - the milk is 30 percent fat, York says.
"If you think about the heaviest whipped cream, it's like drinking it," York says. "That's why you can have cubs that are born in January the size of my fist and come out in March weighing 20 to 25 pounds."
Fewer cubs are born and they are less likely to survive the first year because their mothers are not fat or strong enough to become pregnant, York says.
Polar bears feed like crazy in the ice-covered spring, using the sea ice platforms as a base to hunt their favorite prey: high-fat seals, especially baby seals.
In Hudson Bay, unlike other areas where polar bears live, the sea ice naturally disappears in the summer. So the polar bears lose their food supply. That has always happened, but now it happens earlier in the year and the ice-free zone lasts longer, York and Stroeve say.
So most polar bears go hungry. Recent studies have shown that even hunting on land - caribou, birds, human garbage - takes so much energy that bears that do it don't really get any more calories than bears that just sit and starve.
"Here in Hudson's Bay, we know from long-term studies that bears now stay on land up to a month longer than their parents or grandparents. That's 30 days longer without access to food, and that's on average," York says.
Some years, the bears reach the 180-day starvation threshold. Polar bears can fast for less time and do well, largely because they're so good at storing and accumulating fat for these lean periods, York says. During that lean period, researchers who monitored the bears found that 19 out of 20 of them lost 47 pounds in just three weeks, about 7 percent of their body weight.
According to the National Snow and Ice Data Center, Arctic sea ice has been shrinking about 13 percent per decade since 1979, with major steps and plateaus. Although Arctic sea ice reached its fourth lowest extent on record in late August, unusual winds in western Hudson Bay have caused the ice to remain in place longer than normal, but it is a temporary and very localized respite.
A peer-reviewed study by Stroeve and York this year looked at sea ice levels, that 180-day starvation threshold, and climate simulations based on different levels of carbon pollution. The researchers found that once the Earth warms another 1.3 or 1.4 degrees Celsius (2.3 to 2.5 degrees Fahrenheit), polar bears will likely pass that point of no return. Bears will be too hungry, and this population will likely go extinct.
Studies, including those by the United Nations, of current efforts to limit carbon dioxide emissions predict warming of about 1.5 to 1.7 degrees Celsius (2.7 to 3.1 degrees Fahrenheit) by the end of the century.
"The populations will certainly not survive," said Stroeve.
There are about 4,500 polar bears in the three Hudson Bay populations, and 55,000 beluga whales. Together, that's more than 141 million pounds of big, fat mammals. That sounds like a lot, but those white beasts are losing a battle against an even bigger weight: the amount of heat-trapping carbon dioxide the world is spewing into the air. It's 154 million pounds every minute.
It's not just polar bears.
Laidre of the University of Washington said some scientists think the smallest aquatic zooplankton, called copepods, are the most important animals in the Arctic. They are heavy and the basis of bowhead whales.
But copepods feed on the smaller plankton that are changing. The timing of when copepods can flourish changes and new species come in, "and they're not as rich in lipids," Laidre said.
"It's not that there's nothing alive," York says, looking out over the bay. "It's that the things that are alive in the North are changing and becoming much more like the South."
According to Stroeve, what is happening in Hudson Bay is a foretaste of what is to happen further north.
Stroeve, an ice scientist, says polar bears have something very special.
"It just makes you so happy to see them, to see an animal living in such a harsh environment," Stroeve said. "And somehow they survived. And are we going to make it so that they can't survive? That makes me sad."
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