The polar bears are still doing all right
November 13th 2023
Over the summer, when the sea ice melts, hundreds of polar bears come ashore near Churchill. As they wait for the ice to reform in the fall, they are viewed by tens of thousands of tourists and studied by a few dedicated polar bear scientists. Even though Southern Hudson polar bears (hereafter “southern bears”) live further south than any other in the Arctic and should logically garner the most attention from those seeking signals of human-caused climate change, it is Western Hudson polar bears (we’ll call them “western bears”) that get all the notice.
The earliest rough estimate of southern bear numbers (254 bears) was completed in 1973 and published in a 1976 Canadian Wildlife Service report, while the first western bear count (308 bears) was done in 1975 and published in 1977. These remarkably low estimates, although crude, reflected decades of wanton polar bear slaughter in Hudson Bay that had decimated bear populations. Evidence of similar declines across the Arctic prompted an international treaty to protect polar bears in 1973.
It is now known that both western and southern bears, as well as bears from Foxe Basin to the north, hunt on the ice over the winter, with the potential for interbreeding during the spring mating season. A genetic study published in 2016 suggested moving the long-established boundaries for western bears, since it was apparent that they may come ashore over a much larger range of coastline than previously thought. Southern bears, on the other hand, rarely move out of James Bay, not even to hunt during the winter.
This brings us to the 2021 population surveys that revealed an apparent 27 per cent decline in the western bear population but a 30 per cent increase for southern bears. Unfortunately, the survey for southern bears was not available when news of the western bear decline was made public — and generated considerable alarm — in December 2022.
According to the report released first, which was by Stephen Atkinson and colleagues, the three most recent population estimates for western bears were 949 (range 618-1,280) in 2011, 842 (range 562-1,121) in 2016 and 618 (range 385-852) in 2021. As mentioned, the apparent change from 2016 to 2021 was a 27 per cent decline — although, as the authors noted, that’s not statistically significant.
The overall drop apparently was driven by a decline of more than 200 adult females and subadult bears, especially in the area around Churchill. The authors considered but rejected the possibility that these bears had simply relocated into southern Hudson Bay. Oddly, in light of the 2016 study about changing habitat boundaries, they did not consider the possibility that the “missing” animals had relocated northward into Foxe Basin territory.
Sea ice in Foxe Basin almost always lingers well into August, so it might now be preferred as a summering and denning area by some western bear females and young bears looking for more predictable ice conditions. Foxe Basin bears haven’t been surveyed since 2010 but they were then doing very well, with an estimated population size of 2,580.
As for southern bears, their numbers went from 943 in 2012 (range 6581,350) to 780 in 2016 (range 590-1,029), and then to a whopping 1,119 in 2021 (range 860-1,454) — which gives, as noted, an increase of 30 per cent over five years. The study’s authors don’t actually say if that’s statistically significant but it seems likely it is, since they concluded a natural increase in numbers had indeed occurred and they couldn’t verify immigration of bears from another subpopulation.
Overall, the authors of both reports seemed hardpressed to explain their results. A loss of hundreds of western bears from 20162021 is not consistent with the prevailing hypothesis that lack of sea ice drives long-term declines in polar bear numbers: sea ice conditions in western Hudson Bay were better for the first four of those years than they had been in decades — only 2021 was not as good — and southern bear numbers increased markedly with similar ice conditions in their part of Hudson Bay over the same period.
Were polar bears dying in one region during 2017-2021 — for reasons not having to do with sea ice — but reproducing like crazy just next door? Or were hundreds of western bears moving undetected between subpopulation boundaries? If movement into Foxe Basin does explain the recent survey results for western bears, it means they haven’t been counted properly for decades.
That’s a big problem for polar bear scientists and conservation organizations because it suggests western bears — and therefore all polar bears — may not be threatened with extinction due to loss of sea ice, as previously thought.
Credits to National Post, Susan J. Crockford
nationalpost.com
The earliest rough estimate of southern bear numbers (254 bears) was completed in 1973 and published in a 1976 Canadian Wildlife Service report, while the first western bear count (308 bears) was done in 1975 and published in 1977. These remarkably low estimates, although crude, reflected decades of wanton polar bear slaughter in Hudson Bay that had decimated bear populations. Evidence of similar declines across the Arctic prompted an international treaty to protect polar bears in 1973.
It is now known that both western and southern bears, as well as bears from Foxe Basin to the north, hunt on the ice over the winter, with the potential for interbreeding during the spring mating season. A genetic study published in 2016 suggested moving the long-established boundaries for western bears, since it was apparent that they may come ashore over a much larger range of coastline than previously thought. Southern bears, on the other hand, rarely move out of James Bay, not even to hunt during the winter.
This brings us to the 2021 population surveys that revealed an apparent 27 per cent decline in the western bear population but a 30 per cent increase for southern bears. Unfortunately, the survey for southern bears was not available when news of the western bear decline was made public — and generated considerable alarm — in December 2022.
According to the report released first, which was by Stephen Atkinson and colleagues, the three most recent population estimates for western bears were 949 (range 618-1,280) in 2011, 842 (range 562-1,121) in 2016 and 618 (range 385-852) in 2021. As mentioned, the apparent change from 2016 to 2021 was a 27 per cent decline — although, as the authors noted, that’s not statistically significant.
The overall drop apparently was driven by a decline of more than 200 adult females and subadult bears, especially in the area around Churchill. The authors considered but rejected the possibility that these bears had simply relocated into southern Hudson Bay. Oddly, in light of the 2016 study about changing habitat boundaries, they did not consider the possibility that the “missing” animals had relocated northward into Foxe Basin territory.
Sea ice in Foxe Basin almost always lingers well into August, so it might now be preferred as a summering and denning area by some western bear females and young bears looking for more predictable ice conditions. Foxe Basin bears haven’t been surveyed since 2010 but they were then doing very well, with an estimated population size of 2,580.
As for southern bears, their numbers went from 943 in 2012 (range 6581,350) to 780 in 2016 (range 590-1,029), and then to a whopping 1,119 in 2021 (range 860-1,454) — which gives, as noted, an increase of 30 per cent over five years. The study’s authors don’t actually say if that’s statistically significant but it seems likely it is, since they concluded a natural increase in numbers had indeed occurred and they couldn’t verify immigration of bears from another subpopulation.
Overall, the authors of both reports seemed hardpressed to explain their results. A loss of hundreds of western bears from 20162021 is not consistent with the prevailing hypothesis that lack of sea ice drives long-term declines in polar bear numbers: sea ice conditions in western Hudson Bay were better for the first four of those years than they had been in decades — only 2021 was not as good — and southern bear numbers increased markedly with similar ice conditions in their part of Hudson Bay over the same period.
Were polar bears dying in one region during 2017-2021 — for reasons not having to do with sea ice — but reproducing like crazy just next door? Or were hundreds of western bears moving undetected between subpopulation boundaries? If movement into Foxe Basin does explain the recent survey results for western bears, it means they haven’t been counted properly for decades.
That’s a big problem for polar bear scientists and conservation organizations because it suggests western bears — and therefore all polar bears — may not be threatened with extinction due to loss of sea ice, as previously thought.
Credits to National Post, Susan J. Crockford
nationalpost.com
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