12/10/2013 5:15:48 PM
Season of Plenty
Hudson Bay began to freeze a couple of weeks earlier than in recent years, lengthening the seal-hunting season for the Western Hudson Bay polar bears—one of the most endangered populations in the world.
Sea ice stretched out about six miles from shore by the third week of November, and the migration of the bears from land to the ice was well underway by that point. Some fortunate visitors in Tundra Buggies® actually witnessed polar bears feasting on seal kills just offshore.
"Sea ice is a notoriously dynamic environment and getting increasingly more so as the climate warms," said Dr. Andrew Derocher, a scientific advisor to PBI. "This was a slightly better year for the Western Hudson Bay population than those of the recent past, with a somewhat later break-up and earlier freeze-up."
One interesting change in the population is an apparent increase in the variation between the health and condition of individual bears and when they return to the ice.
"On December 2nd, despite some rather solid sea ice having formed, only eight of the 15 bears we're following by satellite telemetry were on the sea ice," Derocher said. "Some females were 60 miles (95 km) offshore while some were still 20 miles (32 km) inland but moving towards the coast." But just three days later, on December 5th, all of the bears were back on their seal-hunting grounds. (See map below.)
The cause of the variation is rarely clear, Derocher said. Some bears may be in good enough condition that they're not pressed to return to the ice. On the other end of the spectrum are bears in such poor condition that they're moving slowly; this category may include a mother with cubs running out of stored fat.
Scientist Alysa McCall said the variation this year included several females that left Wapusk National Park in October and headed up close to Arviat, where they were able to return to the ice a bit earlier than the bears that stayed near Churchill. Also unusual were a few collared females with cubs that stayed around Cape Churchill this year and several that decided to hang out farther south in Wapusk and therefore had to wait a bit longer for the bay to freeze in that area.
"It's this sort of individual variation in the population that will drive future changes and we're interested to see what happens," McCall said. "This is why collaring and tracking these polar bears is so important and informative—we still have so many questions to ask."
She adds that they'll continue to monitor these bears on the sea ice and when they return to land next summer and hope to get a visual on their health and the health of the cubs.
Derocher said that, longer term, the bears will have good years and bad years. "We remain particularly concerned that we'll see a very bad year. All indications are that the Western Hudson Bay population is continuing to decline, underscoring the need to take action on climate change."
You can follow the bears on the ice on our Bear Tracker Map.