How Melting Sea Ice Is Driving Polar Bears To Alaska
Climate scientists say polar bears have been showing up more frequently in villages along Alaska’s North Slope, looking for food as warming temperatures cause ice to melt in the Beaufort Sea.
On what makes polar bears come ashore
“What happens is, September is when sea ice reaches its annual minimum extent. And September also coincides with the whaling season, the Bowhead whale whaling season. And what we’ve seen over the least 15 or so years is an increasing amount of bears from the southern Beaufort Sea population — which is the population that we’re talking about — an increasing amount of bears form that population are coming to shore. And they’re coming to shore, they’re coming ashore because there’s no sea ice available anymore, in summer, over the continental shelf, which is a narrow stretch of shallow water off of the Alaska coast. And when that ice is gone, the bears come ashore. And they hone in on that smell of the Bowhead whale, and they aggregate around the village of Kaktovik, beginning as early as the beginning of August, and they generally stay until the beginning of October.”
On how habitat changes are impacting polar bears
“We’ve been tracking changes in the availability of sea ice habitat for over 30 years in the southern Beaufort, and the changes have been — as you’d expect — really dramatic. Just in the last 15 years, we’ve seen the distance of the pack ice from the coast double. It’s now well over 300 miles away from the coast during summer, and that’s well beyond the continental shelf. That equates to basically a loss of habitat for the bears, a loss of prime habitat, and that’s why they’re coming ashore in greater numbers.”
On how far polar bears can swim
“We have recorded some pretty long-distance swims by bears. Every year we go out and sample, or study, the bears in the southern Beaufort — we do about a six-week field season. And one of the things we do is tag 20 or so bears with satellite transmitters. And from that we’ve been able to record long-distance swims of bears leaving the coast, and swimming to the pack ice and vice-versa, leaving the pack ice and swimming to the coast. In some cases, we recorded swims of over 400, 500 miles. That’s a situation where a bear’s getting in the water, thinking it’s going to swim maybe to shore to begin denning, and obviously it doesn’t realize it has a 400- or 500-mile swim ahead of itself.”
On what the trend of bears coming ashore means for the future
“In the early-2000s, we estimated that about 4 percent of the population was coming ashore, and they were spending, you know, maybe 20 or so days on average on shore, so it was a pretty trivial set of circumstances — they were coming to shore in small amounts, and they weren’t really spending much time on shore. In 2014, we estimated that close to 40 percent of the population came ashore, and they spent basically over two months on land. So if you’re spending two months on land and you’re a polar bear, that’s two months less time you have to be on the sea ice hunting seals, depositing body fat, and there’s a benefit of coming to shore in that you get to feed at the bone pile, But you’re fasting until that time when the bone pile is stocked with the Bowhead whale remains. So I think that, for now, when you’ve got 20, 30 percent of the population or so coming ashore, those bears are probably making the right decision. They have to fast for about six weeks, but they get this payoff of this really kind of energy dense food, the blubber from the Bowhead whale.
“The question is, if this trend continues, this trend of increasing bears coming ashore, what’s the payoff going to be for these bears that feed? Because the amount of food in the bone pile doesn’t really change much from year to year. So the more bears that come ashore, the less food for each bear to feed on. The other issue is the bone pile in Kaktovik is about a kilometer, a kilometer and a half from the village. And if you’ve got 200 bears hanging out in the village, or on the outskirts of the village, and they run on the food of the bone pile, that’s a lot of hungry bears to contend with coming into the village, and I worry that that’s going to present a risk to people, and also a risk to the bears.”
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