When Will Churchill's Polar Bears Come Ashore?

6/13/2011 9:11:19 PM

When Will Churchill's Polar Bears Come Ashore?

The polar bears of Hudson Bay must sense that their winter world is coming to an end. As the temperatures creep up, the bears are moving for shore. With daytime highs above the long-term average and hitting over 60° F (16° C), the ice is melting quickly.

As of June 6th, the Canadian Ice Service is showing large ice anomalies along both the eastern and western shores of Hudson Bay: that is, these regions have less ice compared with historic levels. The Hudson Bay area is missing a lot of ice and, as of June 4th, had about 52% ice cover compared to the 1979-2000 average of about 65%. But averages don't mean much to a polar bear: the bears will stay on the ice until the cover dips to about 30%. Then, we can expect them ashore within two weeks.

All this leaves us asking the question: when will the Hudson Bay polar bears come ashore this year? Given the missing ice, the rate of ice loss, and the recent temperatures, I'd estimate that some bears should arrive on shore in late June to early July. This would be about the same as the very early arrival time in 2010—or roughly a month earlier than the 1980s.

We won't know what the early break-up means for the bears until they come ashore. As always, some will be fat and some will be skinny. The important part is how many fall into each group. Once ashore, the bears will play the waiting game. An early freeze-up allows the bears to get back on the ice to snag a few seals. A late freeze-up means the bears continue to deplete their fat stores and the skinny ones won't have much in reserve come mid-November or December. The graphic below shows the location of satellite-collared bears on Western Hudson Bay as of June 9, 2011.



Photo ©Daniel J. Cox/Natural Exposures. Graphic courtesy of Dr. Andrew Derocher, professor of biological sciences at the University of Alberta and a scientific advisor to PBI.