Canadian Polar Bear populations

With Arctic sea-ice – on which the polar bears depend for survival – disappearing at a rate of 11% a decade, the habitat that sustains these bears is in jeopardy.  As the Arctic continues to warm due to climate change, this trend poses a serious threat to polar bears, especially at the southern edges of the current range.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
A polar bear in the Churchill Wildlife Management Area (C)Jacquie Labatt/WWF-Canada
New Population Studies
Long-term monitoring studies have been conducted by the Canadian Wildlife Service (now Environment Canada) for the Western Hudson Bay subpopulation for several decades. The last population estimate for this region used data collected between 1984 and 2004, and was published in 2007. WWF is proud to have supported some of this world-class scientific work.
In 2010, two new population estimation projects got underway for this region: one using aerial surveys led by the Government of Nunavut, and one using traditional mark and recapture techniques led by the Environment Canada.  Aerial surveys involve spotting bears from a plane or helicopter while traveling along a line that transects a specific area, which then act as the sample to determine the population size for the whole area.  Mark-recapture work involves handling a sample of bears for tagging and detailed measurements, and then recapturing a portion of them at a later point, thereby calculating ratios and a fairly tight estimate of the total population size.
Recognizing the unique opportunity to compare methods, the likelihood of obtaining somewhat different results, and the political and cultural sensitivities around polar bears, both research teams agreed to work together towards a co-publication of results in 2012 with a full discussion of pros and cons for each method.
The Government of Nunavut recently released the summary of findings from their aerial survey research team and we expect results from Environment Canada this summer. Neither the Government of Nunavut nor the Environment Canada studies have been through peer review or publication yet, so any meaningful comment or action on their results is premature at this point.
The results from the 2011 aerial survey show no significant change* in the estimated total number of polar bears for Western Hudson Bay compared to the last mark and recapture estimate, though it is not yet clear if the methods are directly comparable. One result that is troubling: only 22 yearlings (cubs born in 2010) were seen amongst the 701 actual bears seen – a very low number compared to previous studies in this region and elsewhere.

*Compared to the most recent 2004 mark-recapture estimate of 934 bears (95% Confidence Interval, 794-1076), the 2011 aerial survey  finds no significant change in the number of polar bears for the Western Hudson Bay with a new estimate of 1,013 (95% Confidence Interval, 717-1,430).
We at WWF are eager to see the results of a new ‘mark-recapture’ population analysis (the same method previously used) that was started in 2011.  Once we have all the data, we can then use them to assess the health of the Western Hudson Bay subpopulation of polar bears, and to determine how comparable the different methods actually are, and look at the strengths and weaknesses of each.
By summer this year we should be in the fortunate position of having two new published population reports.  Hopefully we’ll be able to see all the available data used by governments and decision-makers responsible for addressing pressures on polar bears and other ice-dependent species.
Why the Western Hudson Bay Subpopulation is Important
The Western Hudson Bay subpopulation lives right at the southern edge of Canada’s Arctic sea-ice – and (along with Ontario’s Southern Hudson Bay subpopulation) the southernmost wild polar bear subpopulation in the world.  This means they are the most affected by the current impacts of climate change, primarily the melting of Arctic sea-ice.
We know that the unprecedented rapid decline in sea-ice (especially the earlier spring melt) is causing well-documented problems for wildlife species and humans that have depended on predictable sea-ice for thousands of years.   With 30 years of data on this decline, we are able to connect it to declines in polar bear population health measures, like cub survival and body condition.  (If you’d like to learn more, check out these charts measuring the changes.)
These are the affects of rapid climate change, fueled by our greenhouse gas emissions – an important reminder that we all have a global responsibility to address that while we still can, and shift towards a renewable energy-powered society by 2050.