A new paper on Baffin Bay polar bears reports data on body condition and litter sizes collected as part of a major study of the region completed in 2013 compared to sea ice declines since the 1990s; based on a computer model, the authors predict that in 37 years time (if sea ice declines continuously), the incidence of twin litters could “largely disappear.” However, no decline in population numbers was predicted and a critical caveat acknowledges that factors other than changes in sea ice could have affected the body condition and litter size data the authors analyzed, which means the conclusions are scientifically inconclusive.
The last (2013) polar bear population survey of Baffin Bay (SWG 2016) generated an estimate of almost 3,000 (2,826; range 2,059-3,593), which means that regardless of some slight changes in body condition and litter size over the last two decades (which may or may not have been caused by loss of sea ice), there are currently a lot of bears in Baffin Bay.
Posted in Conservation Status, Life History, Sea ice habitat
Tagged baffin bay, body condition, causation, correlation, extinction, fatness, Greenland, litter size, NASA, polar bear, sea ice, weight
Over the weekend in Canada, the CBC ran a polar bear news feature that is now available online (“Polar bears in peril: the bleak future of Churchill bears,” The National, CBC, 3 December 2018). It gave polar bear biologist Nick Lunn of Environment Canada free rein to spread unsubstantiated claims and outright falsehoods about the status of Western Hudson Bay polar bears and sea ice. Apparently, he and the CBC learned nothing from National Geographic‘s fiasco over their ‘starving’ polar bear video last year: they still think the public will be swayed to “act” on human-caused global warming if a persuasive expert tells them that polar bears are on their way to extinction. I expect many were convinced otherwise, since the facts are available for all to see.
No triplet litters born since 1996? Nonsense, as the photo below (from 2017) shows.
The CBC video is described this way:
“They are a majestic icon of Canada’s North, but polar bears have also come to symbolize climate change. And scientists say the future for one particular population of polar bears in northern Manitoba is dire.“
Posted in Advocacy, Conservation Status, Population, Sea ice habitat
Tagged breakup, CBC, Churchill, declining population, fat, freeze-up, Hudson Bay, Nick Lunn, polar bear, sea ice, triplets, weight
Polar bear researchers have been doing capture/recapture studies in Western Hudson Bay for decades yet most of the data claimed to be critical for assessing effects of human-caused global warming on this species have not been published. I raised this point in one of my early blog posts (27 Sept 2012) but the situation has not changed in 6 years. Here’s an update.
Years ago now, in an oft-cited paper, Stirling and Derocher (2012) claimed to summarize the evidence that climate warming was negatively impacting polar bear health and survival. Several life history parameters were considered crucial, particularly body condition.
Despite almost a dozen papers (and perhaps more) on various aspects of WH polar bear health and life history studies based on capture/recapture data published since 2004 (e.g. Castro de la Guardia 2017; Lunn et al. 2016; Pilfold et al. 2017), none have reported the body condition data that supposedly support the claim that sea ice loss is having a severe impact — and the same is true for litter size, proportion of independent yearlings, and cub survival.1
Posted in Conservation Status, Life History, Population, Sea ice habitat
Tagged body condition, capture, Derocher, fat, field work, Lunn, mark-recapture, mass, polar bear, protocol, Sciullo, sea ice, Stirling, unpublished data, weight, western hudson bay
Reposted from 23 March 2016: Despite the fact that the polar bears of Southern Hudson Bay (SHB) live further south year round than any others, a recent study found their average body weight has declined relatively little since the 1980s. There has been no decline in the size of the population over that time either.
Remarkably – despite what we are told about how critical breakup dates are to polar bear health and survival in Hudson Bay – this study found that for SHB bears, the small decline in body condition index correlated only with freeze-up dates, not breakup dates or length of the ice-free season. They also found that regional breakup and freeze-up dates relevant to polar bears in this area was the day when ice cover reached 5% (not 50%).
In other words, SHB polar bears left the ice (or returned to it) when the average ice cover near the coast was about 5%. This finding is yet more evidence that the meteorological definition of “breakup” (date of 50% ice cover) used by many researchers (see discussion here) is not appropriate for describing the seasonal movements of polar bears on and off shore.
The news (two weeks after this post originally went up, see also here), however, is about the bit of weight decline, hyped to the maximum.
The oft-repeated claim that polar bears are starving in Western Hudson Bay (e.g., here, here, here, and here) comes primarily from a 10 year old study that documented a declining trend in polar bear body condition (a biology euphemism for relative fatness) between 1980 and 2004, which appeared to correlate with earlier and earlier breakup dates for Hudson Bay.
Figure 1. Polar bear female with cub, 2009, Churchill, Western Hudson Bay. Wikipedia.
The authors of that study (polar bear specialist Ian Stirling and NASA sea ice researcher Claire Parkinson) reported the body weights of lone female bears captured in Western Hudson Bay between 1980 and 2004. The trend over time in those bear weights was then correlated with the overall change in dates of sea ice breakup on Hudson Bay for that period.
However, it turns out that while the trend of body condition and the trend in breakup dates indeed correlated over time, the actual year to year data did not. The question is, what does that mean for the claim that polar bears in WHB are starving?
Posted in Life History, Sea ice habitat
Tagged body condition, breakup, Cherry, climate change, Parkinson, pregnancy, sea ice, starving polar bears, Stirling, too thin, trends, weight, western hudson bay