Tracking polar bears gives scientists insight into the bears' lives: their movement choices across seasons, the ice they travel and hunt on, and when they choose to return to land. Photo copyright Downs Matthews/Polar Bears International.

9/12/2016 1:56:11 PM

The Bears Are Back on Shore

It has been a long and cold winter on Hudson Bay for the polar bears that call this region home, but all good things must come to an end. It's summer, which means that the annual Hudson Bay sea ice that polar bears use as a platform for hunting their main prey, seals, has melted completely and the bears have returned to land to fast until the ice returns.

The Polar Bears International Bear Tracker has followed a sampling of GPS-collared female polar bears from the Western (WHB) and Southern Hudson Bay (SHB) populations for many years now. It's been fascinating to follow their movements this past winter, especially since no two bears are ever alike, and the data provides us with insights that help with polar bear conservation.

This year, none of the collared females from these two populations overlapped each other, somewhat unusual to see on the Tracker. Even though we didn't see intermingling on the Tracker, it undoubtedly happened across Hudson Bay. Research shows gene flow amongst the three populations in Hudson Bay (SHB, WHB, and Foxe Basin) meaning that, when it comes to mating, population boundaries mean very little. What was very normal to see, though, was the wide variety in movement choices and home range sizes amongst the collared polar bears.

While some Southern Hudson Bay bears chose to leave James Bay and travel up the coast of Quebec, other SHB bears preferred to stay in James Bay all year. While these James Bay bears had much smaller home ranges compared to their cousins in the north, it doesn't matter much as long as there were enough seals to eat. The SHB bears on PBI's Bear Tracker have since returned closer to James Bay and Polar Bear Provincial Park in Ontario.

The Western Hudson Bay bears that PBI followed also chose different strategies, though all stayed exclusively in the western part of Hudson Bay this year and have since returned to land near Wapusk National Park in Manitoba. In particular, X33410 (AKA Ursula), moved over 2378 kilometers (1477 miles) across the sea ice from October to August. After heading high up north with her yearling at the beginning of the freeze-up season, Ursula eventually traveled back south and spent the last six months zigzagging toward land. We think she weaned her cub several months ago and found a spring fling or two between April and June, hoping to get pregnant. She came ashore in early August right at Cape Churchill and we expect she will enter a den this fall if she is fat enough (420 pounds seems to be the cut-off; below that a female cannot give birth successfully).

It is impossible to know what's going on in a bear's head or on the ice, but tracking polar bears can give researchers insight into their lives: their movement choices across seasons, the ice they travel/hunt on, and when they choose to return to land. These insights become even more important as sea ice conditions continue to change in the Arctic; understanding the needs of polar bears can help inform effective conservation measures in a rapidly changing ecosystem.

As of September 5, Arctic sea ice extent remains below average everywhere except for a small area off of Russia. While it is unlikely that a new record low will be reached, total sea ice extent is lower than at the same time in 2007 as of August 26, and is currently tracking as the second lowest daily extent on record (NSIDC). We have yet to hear about when the September minimum sea ice extent will be reached-indicating the lowest point for the summer-but it should be any day.

It will be a long wait on land with no seal fat to eat, but these bears have done it before. We can only hope they came ashore healthy and that the sea ice freezes up again at a reasonable time this fall so hunting can recommence. Until then, we'll be keeping an eye on these collared bears and the new bears that will join the tracker this fall. Please also join us while we bring you into the lives of these polar bears during the upcoming polar bear migration in Churchill, Manitoba. Live cams will be streaming every day and we'll be hosting webcasts and live chats dedicated to these bears throughout October and November. Stay tuned for the schedule! 

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