In what looks like a follow-up to last week’s CBC documentary, The Politics of Polar Bears, the London (UK) based DailyMail published interviews with polar bear biologists Mitch Taylor and Andrew Derocher (September 9, 2014).
The CBC film did have a “one scientist vs. another” flavor about it and this article definitely echoes that approach. My comments below on Derocher’s insinuations and questions about starving bears and global warming.
From the article:
“Dr Taylor said that since he made his views known, he has been ostracised by the polar bear scientific community.
Indeed, Dr Derocher is outspoken in his views on scientists who don’t believe that polar bears are threatened by climate change.
‘Some of the scientists that are claiming resilience in polar bears are being paid by right-wing climate change denier groups,’ he said. ‘These individuals are paid to obfuscate the scientific data.
‘If polar bears could garner the resources they need on land, why do they lose about 0.8-0.9 kg of body mass per day?
‘Why do some polar bears starve while on land waiting for the sea ice to reform?’” [my bold]
[Read the rest here]
Mitch Taylor never suggested that polar bears would be OK in the future because they could garner enough resources on land to survive an extended period on land caused by global warming (either in this interview or in the CBC film), but I’ll answer Derocher’s questions anyway
[Steve Amstrup from Polar Bears International also used this tactic of presenting strawman arguments back in January, see my response here].
Derocher asked: “‘If polar bears could garner the resources they need on land, why do they lose about 0.8-0.9 kg of body mass per day?”
Polar bears in many regions of the Arctic (but not all) move to land in early to late summer and go through a period of fasting of varying lengths of time.
This is entirely normal for polar bears, not something new due to global warming (see previous post here about the polar bears of St. Matthew Island, who appear to have spent about 5 months on land during the ice-free period – in 1874).
Polar bears lose “0.8-0.9 kg” (about 2 pounds) a day because they are living off the excess fat they put on in the spring and early summer – well-fed bears do not need to eat while on land, although they will eat what they can find, even if they are fat already.
This is not a new phenomenon – they appear to always have done this: they seem to always be looking for food.
For example, see this post: “Polar bears in winter: insights from Behouden Huys, 1596-1597,” which describes Barents Sea polar bears getting into food stores of William Barents and his crew over the winter of 1596-1597.
Putting on hundreds of pounds of fat in the spring to last through periods of food scarcity later in the year (whether it comes at the end of summer or over the winter, which can also be a time of low seal availability) is the evolutionary adaptation that has allowed polar bears to live successfully in the Arctic through all kinds of changes in sea ice (see previous post here).
Note that it was Robert Rockwell and Linda Gormezano (and very few others) who have repeatedly suggested polar bears could survive on land by eating terrestrial foods, which I think is nonsense. This is what I said in a previous post, in which I countered that claim and agreed with Derocher on this point:
However, it has not been demonstrated that consumption of any of these terrestrial foods assists in polar bear survival. I have to agree with this part of what Andrew Derocher had to say to NBC News reporter John Roach (“As Arctic ice melts, polar bears switch diets to survive, studies say“ January 24, 2014):
“Polar bears will eat anything,” he told NBC News. “The question is: Does is it do them any good? And everything we can see from what bears eat when they are on land is it has a very, very minimal energetic return relative to the cost.” [my bold]
Derocher asked: “’Why do some polar bears starve while on land waiting for the sea ice to reform?‘”
Derocher has spent 30 years studying polar bears but is pretending he doesn’t know that starvation is relatively common in polar bears (especially for young and very old bears). He seems to be suggesting that no polar bear ever starved while on land during the ice-free season before global warming!
But perhaps Derocher hasn’t bother examining the literature of his colleagues on polar bears, as I have?
Did he not ever read about all the bears that starved in the spring of 1974 in the Eastern Beaufort because the ice was too thick? From my previous post, with maps and references:
Here is what Stirling and Lunn (1997:177) had to say about the mortality event of 1974 in the Northern Beaufort that they witnessed (which I cited recently in Featured Quote #29)
“…in the spring of 1974, when ringed seal pups first became scarce, we capture two very thin lone adult female polar bears that had nursed recently, from which we deduced they had already lost their litters. A third emaciated female was accompanied by two cubs which were so thin that one could barely walk. We have not seen females with cubs in this condition in the Beaufort Sea, or elsewhere in the Arctic, before or since.”
And this is what Stirling had to say at the 1979 Polar Bear Specialist Group meeting (Anonymous 1979:52) about his research activities in the eastern Beaufort Sea in the mid-70s:
“…it was apparent from the studies of both polar bears and seals that their populations had undergone marked declines in numbers, productivity, and survival of young in 1974 and 1975. The decline apparently occurred because of natural causes that are not completely understood.”
Polar bears starved in significant numbers in 1974 and again in 1975 – no numbers of deaths for bears have ever been estimated (that I could find), but the decline in ringed seals that caused polar bear numbers to plummet was estimated at 80% or more. With virtually no seals to eat in the spring, a large number of bears – especially females and cubs – must have died of starvation, either that spring or later that year. No cries of “feed the starving polar bears” then – or in the 1980s or the 1990s, when it happened again.
And did Derocher not read Amstrup’s 2003 “Polar bear” entry in “Wild Mammals of North America” where he pointed out that starvation is probably the leading cause of death for young and old bears alike? From a previous post, with maps and references:
“Starvation of independent young as well as very old animals must account for much of the natural mortality among polar bears… Also, age structure data show that subadults aged 2-5years survive at lower rates than adults (Amstrup 1995), probably because they are still learning hunting and survival skills.”
…
“I once observed a 3-year-old subadult that weighed only 70 kg in November. This was near the end of the autumn period in which Beaufort Sea bears reach their peak weights (Durner and Amstrup 1996), and his cohorts at that time weighed in excess of 200 kg. This young animal apparently had not learned the skills needed to survive and was starving to death.” [my bold]
So I have a question for Andrew Derocher: where are all the starving bears he’s talking about? Could we see some pictures and actual data on the bears that you and your colleagues keep insisting are starving due to global warming?
Derocher and his colleagues repeatedly mention the starving bears of Western Hudson Bay but so far, none of the scientific data supporting this claim has been published.
As Reg Sherren’s CBC documentary pointed out, virtually all of the “problem” bears of Churchill who have ended up in polar bear ‘jail’ over the last 5 years or more have been in good condition (which means fat, not starving).
[See the short excerpt of the CBC documentary here. Links to the full length film here and in my previous posts here and here]
References
Amstrup, S.C. 2003. Polar bear (Ursus maritimus). In Wild Mammals of North America, G.A. Feldhamer, B.C. Thompson and J.A. Chapman (eds), pg. 587-610. Johns Hopkins University Press, Baltimore.
