Chukchi Sea polar bears OK for now, Beaufort bears not so well
Western Alaska polar bears are facing challenges from sea ice loss, industrial development and interactions with humans.
Since 2008, the U.S. Fish and Wildlife Service and their partners, including the U.S. Geological Survey, have been studying polar bears in the Chukchi and south Beaufort seas north of the Bering Strait.
Ryan R. Wilson, a wildlife biologist with the U.S. Fish and Wildlife Service shared findings at a Strait Science session June 6 at UAF’s Northwest Campus in Nome. He told about conservation efforts, ongoing research and management strategies. The Chukchi bears are coping for now, according to Wilson. The polar bears farther north in the Beaufort Sea area are not doing as well.
After 10 years of study, this phase of the program has come to a stopping point when the scientists will assess and share information on diet, distribution and response to climate change and other factors while they look at future directions for study.
Globally, the unofficial estimate of the polar bear population is about 25,000, distributed among 19 subpopulations. Alaska has two subpopulations: the Chukchi Sea polar bears and the south Beaufort Sea polar bears. Scientists have estimated the population of Beaufort bears to run about 900 animals. Biologists have been working on estimates of the number in the Chukchi population. Right now the census stands at about 3,000.
“So, not that polar bears wander around here that often [Nome area], but if they did, they would be Chukchi polar bears,” Wilson told his audience.
Some of the study has stemmed from mandates from the Fish and Wildlife Service, helped along by the listing of polar bears as a threatened species under the Endangered Species Act in 2008, at which time scientists realized there was a dearth of information on Chukchi bears, according to Wilson, whereas the Beaufort bears have been studied for around 30 years. There had been a study of the Chukchi subpopulation in the late 1980s, early 1990s, but not a lot of information is available about how the Chukchi polar bears have been impacted by sea ice loss.
By 2016, scientists had a final conservation plan that set priorities including making sure polar bears would be around for subsistence hunting for Alaska and other communities. Among international agreements, the United States and Russia have a bilateral agreement signed in 2000 establishing a shared quota, with representatives meeting annually to discuss new science, sustainable harvests, status of the population and the impact of sea ice loss.
Lately, most of the study has been north of the Seward Peninsula in the Kotzebue area and based at Red Dog Mine where biologists set up studies in March and April each year.
“The folks at Red Dog have been very gracious to us with their assistance,” Wilson said.
What do polar bears eat, anyway? Both adult males and females eat ringed seal, according to Wilson. As it takes a larger bear to capture bearded seals, mostly male polar bears take those. Near Kaktovik and Wrangell Island, bears will eat what they find on beaches. Polar bears will occasionally eat walrus, some beluga whales, but their main diet is ringed seal.
In the spring, when ringed seals are calving, polar bears have a chance to fatten up.
Why study polar bears?
“We want to make sure they are still around by the time we can mitigate or, I hope, mitigate sea ice” Wilson explained.
There have be three main areas of research, according to Wilson: learning about the body condition of the bears, first, and then the issue of the global polar bear population being listed as a threatened species. Add to that some general information on diets, and an understanding on where bears are going, what are their areas of preference, what time of year they are in different areas and generally their distribution and movement patterns.
“We wanted to know the effects of an oil spill in certain parts of the year. We want to protect them from oil and gas drilling, really important to polar bear hunting and other uses of the marine resource,” Wilson said. “All that information was lacking.”
What have they learned so far?
Going into the study, scientists thought the bears would not be doing well because of substantial sea ice loss. Wilson’s collaborator and colleague Karyn Rode, research wildlife biologist with the U.S. Geological Survey – Alaska Science Center led an important study that indicated otherwise.
“What Karyn found out was that actually in the Chukchi Sea, polar bear body condition was pretty good and had stayed the same or improved from a period in the late 1980s to mid-1990s,” Wilson said. “However, the Beaufort Sea polar bears were not doing as well, that the Chukchi Sea bears seemed to be doing a lot better in body condition, sizes, and cub survival,” he said. “Here we had adjacent populations experiencing significant changes in sea ice conditions yet one is presumably responding well, or not showing negative impacts of sea ice loss, compared to the other population showing negative signs.” There was a 75 percent reduction of sea ice, polar bears’ preferred summer habitat, between the 1980s and now.
Wilson and colleagues found that Chukchi Sea adult male bears were larger than Beaufort Sea bears, on average 50 kilograms heaver. The Chukchi Sea adult females were also larger than Beaufort Sea females by an average of 30 kilograms. The Chukchi Sea polar bears had better body conditions.
How could that be? According to Wilson’s information, some factors deal with interruption of feeding— fewer days’ access to ice, less access to shallow productive waters for feeding, and use of land in the summer where they would be fasting
Again, Karyn Rode, a zoologist with USGS did a study on fasting, differences in accessibility to food via sea ice and water depth. She studied ratios of components in blood samples that indicate fasting—long-term and short-term. The biologists used the urea and creatinine ratios to determine that polar bears from south Beaufort Sea to Chukchi Sea had not eaten for seven to 10 days. The sampling was done in spring when there is an abundance of seals and other food.
They charted bears that had below an 80 percent chance they had been fasting and bears that had more than an 80 percent probability they were fasting. In the Chukchi Sea, most of the bears had fed in the last week, but in the Beaufort Sea, a lot more bears had not been catching prey in the last seven to 10 days when there should be an abundance of prey in an ideal hunting period.
Rode, as part of her study, also looked at a reduced number of ice days —the days that sea ice has a concentration of at least more than 15 percent occurring over the continental shelf and water shallower than 300 meters, conditions conducive to polar bears being able to hunt.
During the past 30 years there has been some number of days when ice has been off the continental shelf or the Beaufort Sea, but only recently we begin to see it for the Chukchi Sea.
“Even then it is a lot higher. There is a lot more time the ice is off the continental shelf in the south Beaufort Sea than the Chukchi Sea, so south Beaufort Sea polar bears are having a lot less time to hunt over productive waters, having only a small strip of continental shelf with ice over it.
“This is borne out by looking at collared bears in the summer time on land and on the continental shelf and off the continental shelf. Chukchi Sea polar bears are spending a lot less time over deep waters and more time over the more productive waters of the continental shelf for feeding,” Wilson said.
Additionally, Rode found out, according to Wilson, that Chukchi Sea and south Beaufort Sea female bears were spending more time on land, where they would be fasting. Chukchi Sea polar bears were using land twice as long as in the 1980s and 1990s. Up to 40 percent of females are summering a month longer on land now. “Denning females, we’re seeing that increasingly summering on land as well, Wilson said that they are seeing increasingly denning females summering on land, which is not good, because they are fasting unless a whale washes up on shore.
“So eventually that might catch up with them if it’s two months or three months that they’re going without prey leading up to that winter when they’re giving birth and having to support these dependent young before they emerge. The following spring they are coming on shore earlier,” Wilson said.
The biologists fly 110 miles out from land toward the International Dateline for helicopter-based capture of polar bears for study. A fixed wing aircraft goes along to refuel the helicopter while it is on the Chukchi Sea.
“We are looking for mostly white animals on mostly white background—quite challenging,” Wilson said. “Most of the time we are just looking for tracks on the sea ice. If they look fresh, we follow them.”
If the team is lucky, they spot a polar bear and start the capture process—cautiously.
“Bears when they are frightened or feel threatened, their chosen place to go is open water, the last place the team wants them to go because with drugs in them, they are susceptible to drowning,” he said. Before staging a capture, the scientists survey the area for open water and other hazards.
The aircraft hovers over the bear at about 15 feet while they prepare a dart and then aim at the animal’s neck and shoulder area. They have a protocol usually of not sending more than three darts, so as not to overly stress the animal.
After a dart goes in, it takes about five minutes for the bear to go down so that the helicopter can land nearby and measurements and samples can be taken.
“We take hair samples, blood samples and fat samples,” Wilson explains. “We take measurements of the length and width of the skull, body length, we get its weight [using a tripod]. We’ll take a small vestigial tooth for aging.”
So while some further studies of polar bears will be in abeyance for a year, how will continued ice recession impact the polar bears in the Chukchi Sea and south Beaufort Sea?
Rick Thoman, climate expert with Alaska Center for Climate Assessment and Policy said a month ago that the sea ice in the Bering Sea had all disappeared following an early spring of numerous storms and southwest winds ripping up new thin ice. “I’m speechless right now because we have record low sea ice extent in the Chukchi Sea, the largest departures from normal are in the north, and in Kotzebue Sound,” Thoman told a biotoxins workshop audience earlier this month. “The departures [from normal] were this high earlier this summer, late spring and summer in the Bering sea and still are in some areas.”