Reposted from Polar Bear Science
Does the following statement stand up to scrutiny – i.e. a fact check – of the scientific literature on polar bear ecology?
In the 1980s, “the males were huge, females were reproducing regularly and cubs were surviving well,” Amstrup said. “The population looked good.”
[Steven Amstrup, Anchorage Daily News (Borenstein and colleagues), 5 November 2021: ‘How warming affects Arctic sea ice and polar bears’]
In short, it does not.
In 2007, polar bear specialist Steven Amstrup was almost single-handedly responsible for the failed survival model that got polar bears classified as ‘Threatened’ under the Endangered Species Act (ESA) in the US. He has admitted that he retired from the US Geological Survey and sought employment with activist organization Polar Bears International (PBI) in 2012 because he wanted a bigger bullhorn for his predictions of polar bear catastrophe than was permitted under his role as a government scientist (Crockford 2019). Unfortunately, he hasn’t been able to refute my analysis showing how and why he was wrong in his prediction – and resolutely refuses to concede his mistake (Crockford 2017, Crockford 2019; Crockford and Geist 2018).
He and his organization use naive and compliant media to present their propaganda as ‘news’. My impression about the role of PBI in promoting a particular agenda is corroborated not only by their mandate but in a revealing 2013 story in The Atlantic about PBI’s influence over media visiting Churchill, an excerpt of which is copied below [my bold]:
Because Polar Bears International operates in close partnership with a tour company in Churchill that owns the majority of the permits and vehicles needed to access the animals on the tundra, the group has been able to intercept most of the major media that come through town. They install biologists and climatologists on the reporters’ buggies like scientific press agents, trying to make sure an accurate narrative comes across, and they provide B-roll footage of bears plunging into melting slush to help newscasters illustrate the problem.
In past years, though, PBI had gone out of its way to help television crews only to feel betrayed by the finished product: the reporters ignore climate change altogether, or regurgitate the junk theories of climate change deniers. Most television crews are now asked to sign memorandums of understanding, outlining certain guidelines, before working with PBI. (As a rule, one PBI staffer told me, Robert [Buchanan, founder of PBI] regards all journalists as “pirates and thieves.”)“
John Mooallem, The Atlantic, 26 May 2013: Martha Stewart and the Cannibal Polar Bears: A True Story
The first week of November is designated ‘Polar Bear Week’ by PBI and so I have come to expect that there will be more than the usual number of media offerings on the dire plight of the bears. This year is no exception. However, in this instance Amstrup has gone over the top in making claims that purport to support his dire predictions with no fact checking or challenge by the media.
Amstrup stated categorically last week that polar bears “in the 1980s” were doing extremely well: in other words, throughout the Arctic, for the entire decade – suggesting the 80s were the good old days for this species. However, I contend the scientific literature produced by his polar bear specialist colleagues does not support that claim.
Where polar bears were not doing well in the 1980s
- Western Hudson Bay, the subpopulation that continues to be used to predict the future of polar bears worldwide
- Chukchi Sea
There were only four subpopulations that are considered reasonably well-studied in the 1980s: only Western Hudson Bay and the Southern Beaufort had had population surveys done by that time, while some work on body condition and cub survival had also been done in the Barents and Chukchi Seas (Derocher 2005; Larsen 1985; Rode et al. 2014; Wiig et al. 1998). Limited data on litter size and reproductive success were available for some years in the 1980s for a few other areas (Derocher 1999; Obbard et al. 2007; Ramsay and Stirling 1988).
Western Hudson Bay
As I discuss in The Polar Bear Catastrophe That Never Happened, poor body condition, lowered reproductive rates and much reduced cub survival was a hallmark of Western Hudson Bay polar bears in the 1980s and early 1990s. That was before declining sea ice was any kind of issue. However, it was also when polar bear numbers were higher than they’d been in perhaps a century or more and too many bears relative to the food supply was seen as the most likely explanation (Derocher 1991; Derocher and Stirling 1992, 1995; Ramsay and Stirling 1988; Stirling and Lunn 1997). Ian Stirling solved the problem of not really being able to explain this situation to his own satisfaction by embracing the concept of catastrophic man-made climate change and its assumed role in summer sea ice loss.
In the worst year, polar bear researchers Ian Stirling and Malcolm Ramsay emphasized that the mean weight of pregnant females they encountered in 1983 was 37kgs lighter than in other years (Ramsay and Stirling 1988:615). These authors stated:
“...bears of all age and sex classes in the summer and autumn of 1983 appeared to us, at the time of capture, to be, on average, in poorer condition than at equivalent seasons in the years previous and subsequent. Some qualitative behavioural observations corroborated this view. During autumn, 1983, the town of Churchill recorded a larger number of bears feeding at its dump (Lunn & Stirling, 1985) than in the previous three years and a higher number of human-bear incidents than in any year of the previous decade. Three cubs-of-the-year were found abandoned by their mothers in autumn and near starvation, something seen in no other year.” [my bold]
In one extreme example, a female they encountered with three cubs-of-the year in November 1983 weighed only 99 kg (218 lb) but survived; by the following July she was pregnant again and weighed a remarkable 410 kg (904 lb), see photo below.
Overall, survival of cubs, litter sizes and body condition of pregnant polar bears in Western Hudson Bay declined during the 1980s over rates seen in the 60s and 70s, and then declined even more in the 1990s (which was blamed on global warming). Amstup and his colleagues are happy to tell people about the decline between the 1980s and 1990s while keeping silent on the previous decline. However, the evidence in their scientific papers cannot be denied: in Western Hudson Bay, the 1970s (not the 1980s) were the best years for polar bears.
Recent studies have shown that Chukchi Sea polar bears are thriving by all measures used to assess individual and population heath: body condition has been better than it was in the late 1980s (when there was a shorter ice-free period) and females are reproducing well, with a number of triplet litters reported which before this time were rare anywhere outside Western Hudson Bay in the 1970s (see photo below of a litter of triplets about one year old in 2010: rarely do all three members of a triplet litter survive to this age) (Rode and Regehr 2010; Rode et al. 2014, 2018).
In addition, Chukchi Sea ringed and bearded seals – the primary prey of polar bears – were also found to be doing much better in the 2000s (up to 2013) than they were in the 1980s (Crawford et al. 2015), and preliminary data from on-going studies suggest this continues to be the case (Adam et al. 2019).
The documented observation that Chukchi Sea polar bears were doing better during the 2000s than they had been in the late 1980s indicates that they could not have been doing particularly well in the 1980s – certainly not as well as Amstrup’s statement suggests.
Here is the problem: there is no doubt that summer sea ice coverage (extent) was high during the 1980s (relative to now, see graph below) and that polar bear population numbers by the late 1980s showed signs of recovery after decades of over-hunting. Restrictions on hunting imposed in the late 1960s and early 1970s meant more young males were allowed to grow into very large adults and the practice of killing females with cubs largely stopped. As a consequence, population sizes grew quickly.
The fact that the population size had increased up to and including the 1980s does not mean the extent of summer sea ice was a causative factor.
As I have pointed out previously, the thickness of sea ice and depth of snow over the ice during the spring is known to have a more pronounced influence on polar bear health and survival because it impacts their ability to catch as many seals as they require (Crockford 2017; 2019). What we don’t know is how much spring ice thickness and snow cover has varied over Hudson Bay and the Chukchi Sea – decade to decade – since the 1970s. However, it is possible that along with extensive summer ice in the 1980s, there was also thick spring ice and/or heavy snow over ice in both regions, which would account for the lower weights of bears and poorer reproductive success.
It is pertinent to know that early in his career, a young and impressionable Amstrup happened to be involved in capturing a bear from the Southern Beaufort in 1982 that weighed 1400 lb, shown below with its head in Amstrup’s lap. There is no doubt this was a very large bear that left a big impression and is perhaps the real origin of his claim that “males were huge”.
It is also true that the maximum weight of adult males captured in Foxe Basin in the 1970s and 1980s were similar to Amstrup’s big bear: about 1367 lb, with the average weight of males about 1200 lb (Derocher and Stirling 1998; Rode et al. 2014: Fig 5).
However, 1400 lb is far from the record, which belongs to a male weighing 2,209 lb (1,002 kg) shot in the southern portion of the Chukchi Sea subpopulation range in 1960.
In addition, Amstrup’s single 1400 lb bear was not much heavier than three adult males bears captured during the early years of the 2008-2013 survey of the Chukchi Sea (2008-2010), each of which weighed “over 1200 lbs” (Rode and Regehr 2010) and thus similar to those in the 70s and 80s from Foxe Basin.
Also, there have been some photos published recently of some truly big fat bears, including the one below from the Southern Beaufort (Kaktovik) the summer of 2019 whose weight we do not know (compare to the photo from WH in 1984 above):
There is strong evidence from at least two out of four well-studied populations that polar bears were not doing particularly well in the 1980s: certainly not as well as they had been doing before (Western Hudson Bay) or after (Chukchi Sea). It’s likely that other populations were also not doing especially well during the 1980s, especially Davis Strait bears which were still recovering from targeted over hunting and a lack of prey due to over-hunting of harp seals (Peacock et al. 2013). We don’t know for sure because the Davis Strait population was not assessed for the first time until the 1990s (Taylor and Lee; Taylor et al. 2006).
In other words, polar bear specialists didn’t know for sure exactly what body size and cub survival conditions were like for polar bears in many of the unstudied or poorly-studied regions of the Arctic in the 1980s – and for two out of the four for which they did have data the bears were not doing especially well. Therefore Amstrup’s statement last week that the 1980s were golden years for polar bears throughout their range was a falsehood he felt was necessary to promote his failed prediction that polar bears will be threatened with extinction by human-caused global warming at some time in the future.
Adam, R., Bryan, A., Quakenbush, L., Crawford, J., and Biderman, L.2019. Bearded seal productivity in Alaska using harvest-based monitoring, 1975-2016. Poster presentation, Alaska Marine Science Symposium, 28 January-1 February.
Crawford, J.A., Quakenbush, L.T. and Citta, J.J. 2015. A comparison of ringed and bearded seal diet, condition and productivity between historical (1975–1984) and recent (2003–2012) periods in the Alaskan Bering and Chukchi seas. Progress in Oceanography 136:133-150.
Crockford, S.J. 2017. Testing the hypothesis that routine sea ice coverage of 3-5 mkm2 results in a greater than 30% decline in population size of polar bears (Ursus maritimus). PeerJ Preprints 19 January 2017. Doi: 10.7287/peerj.preprints.2737v1 Open access. https://peerj.com/preprints/2737/
Crockford, S.J. and Geist, V. 2018. Conservation Fiasco. Range Magazine, Winter 2017/2018, pg. 26-27. Pdf here.
Derocher, A.E. 1991. Population dynamics and ecology of polar bears in western Hudson Bay. Ph.D. Thesis, Univ. Alberta, Edmonton.
Derocher, A.E. 1999. Latitudinal variation in litter size of polar bears: ecology or methodology? Polar Biology 22:350-356.
Derocher, A.E. 2005. Population ecology of polar bears at Svalbard, Norway. Population Ecology 47:267-275. http://www.springerlink.com.ezproxy.library.uvic.ca/content/765147518rp35613/fulltext.pdf
Derocher, A.E. and Stirling, I. 1992. The population dynamics of polar bears in western Hudson Bay. pg. 1150-1159 in D. R. McCullough and R. H. Barrett, eds. Wildlife 2001: Populations. Elsevier Sci. Publ., London, U.K.
Abstract. Reproductive output of polar bears in western Hudson Bay declined through the 1980’s from higher levels in the 1960’s and 1970’s. Age of first reproduction increased slightly and the rate of litter production declined from 0.45 to 0.35 litters/female/year over the study, indicating that the reproductive interval had increased. Recruitment of cubs to autumn decreased from 0.71 to 0.53 cubs/female/year. Cub mortality increased from the early to late 1980’s. Litter size did not show any significant trend or significant annual variation due to an increase in loss of the whole litter. Mean body weights of females with cubs in the spring and autumn declined significantly. Weights of cubs in the spring did not decline, although weights of both female and male cubs declined over the study. The population is approximately 60% female, possibly due to the sex-biased harvest. Although estimates of population size are not available from the whole period over which we have weight and reproductive data, the changes in reproduction, weight, and cub mortality are consistent with the predictions of a densitydependent response to increasing population size. [my bold]
Derocher, A.E. and Stirling, I. 1995. Temporal variation in reproduction and body mass of polar bears in western Hudson Bay. Canadian Journal of Zoology 73:1657-1665. http://www.nrcresearchpress.com/doi/abs/10.1139/z95-197
Derocher, A.E. and Stirling, I. 1998. Geographic variation in growth of polar bears (Ursus maritimus). Journal of Zoology London 245: 65–72. https://www.cambridge.org/core/journals/journal-of-zoology/article/abs/geographic-variation-in-growth-of-polar-bears-ursus-maritimus/038F98EECC07331D0EE9F75926B12025
Larsen, T. 1985. Polar bear denning and cub production in Svalbard, Norway. Journal of Wildlife Management 49:320-326. http://www.jstor.org/discover/10.2307/3801524?uid=3739400&uid=2&uid=3737720&uid=4&sid=21101182267021
Obbard, M.E., McDonald, T.L., Howe, E.J., Regehr, E.V. and Richardson, E.S. 2007. Polar bear population status in southern Hudson Bay, Canada. Administrative Report, U.S. Department of the Interior- U.S. Geological Survey, Reston, VA.
Peacock, E., Taylor, M.K., Laake, J., and Stirling, I. 2013. Population ecology of polar bears in Davis Strait, Canada and Greenland. Journal of Wildlife Management 77:463–476. http://onlinelibrary.wiley.com/doi/10.1002/jwmg.489/abstract?deniedAccessCustomisedMessage=&userIsAuthenticated=false
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Rode, K.D., Regehr, E.V., Douglas, D., Durner, G., Derocher, A.E., Thiemann, G.W., and Budge, S. 2014. Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations. Global Change Biology 20(1):76-88. http://onlinelibrary.wiley.com/doi/10.1111/gcb.12339/abstract
Rode, K. D., R. R. Wilson, D. C. Douglas, V. Muhlenbruch, T.C. Atwood, E. V. Regehr, E.S. Richardson, N.W. Pilfold, A.E. Derocher, G.M Durner, I. Stirling, S.C. Amstrup, M. S. Martin, A.M. Pagano, and K. Simac. 2018. Spring fasting behavior in a marine apex predator provides an index of ecosystem productivity. Global Change Biology http://onlinelibrary.wiley.com/doi/10.1111/gcb.13933/full
Stirling, I. and Lunn, N.J. 1997. Environmental fluctuations in arctic marine ecosystems as reflected by variability in reproduction of polar bears and ringed seals. In Ecology of Arctic Environments, Woodin, S.J. and Marquiss, M. (eds), pg. 167-181. Blackwell Science, UK.
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Wiig, O. 1998. Survival and reproductive rates for polar bears at Svalbard. Ursus 10:25±32
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November 10, 2021 at 04:18AM