Do polar bears improve their physique situation in the event that they keep on the ocean ice over the summer season? Do they proceed to hunt efficiently from damaged ice in July and early August in areas like Hudson Bay the place ice finally melts out utterly? There appears to be an assumption that they do however one polar bear specialists repeatedly claims there may be information exhibiting that is the case.
“Anybody saying sea ice presently of 12 months doesn’t have an effect on polar bears is ignoring analysis exhibiting their physique situation continues to extend by means of summer season in the event that they’re out on the ice.” [Andrew Derocher 28 June 2022]
I’d severely wish to know which paper or papers this information seems in however in fact, he doesn’t present that data. As a substitute, it’s ‘belief me, I’m the skilled’.
[See a similar claim from 2019, in which he claims there is “new research” showing that bears continue to accumulate fat stores in July (“more July sea ice=fatter polar bears”), but he doesn’t say where we can find those research results.]
I contend from my assessment of the literature that express ‘earlier than and after’ measurements of the identical polar bears in spring (at mid-Could) and fall after a summer season on the ice haven’t been reported. I contend polar bear specialists assume that each one polar bears which spend the summer season (i.e. July-September) on sea ice both acquire weight or lose a lot much less weight than in the event that they’d been on land consuming nothing however they don’t truly know that is true. If I’m incorrect, present me the info and I’ll revise my statements on the subject.
The one printed paper of which I’m conscious that appears like it gives this data is a report on a research from 1983-1994 within the Southern Beaufort Sea.
“Bears of comparable size had been persistently heavier in autumn than in spring.” [Durner and Amstrup 1996:483]
Word that the researchers didn’t seize the identical bears in spring and fall: they captured a distinct set of bears in every season. As a consequence, the info doesn’t show that particular person bears gained weight over the summer season, as researchers could assume.
Furthermore, as a result of the aim of the research was to generate a formulation for predicting the mass of bears primarily based on girth and size measurements (as a result of weighing bears within the subject is troublesome), the authors don’t inform us how a lot heavier the bears had been in autumn, solely that the distinction was statistically important for his or her mannequin, not biologically important for the bears. Was it 2-3kg or 20-30kg? They didn’t say.
As a result of we can’t know from this research how way more particular person bears weighed within the autumn vs. the spring, it isn’t attainable to evaluate whether or not the vaguely described ‘further weight’ measured for bears normally must be interpreted as proof of a internet survival profit to particular person bears. Actually, the research authors didn’t declare a profit.
In the same vein, Derocher repeatedly states that Western Hudson Bay bears that keep out longer on damaged sea ice by means of July and early August proceed to hunt seals and thus add to their general survival profit: he stated so once more as we speak.
However the video under reveals why polar bears are not often profitable at searching grownup seals in the course of the summer season on damaged ice, whether or not within the Barents Sea or on Hudson Bay. [Hungry Polar Bear Ambushes Seal | The Hunt | BBC Earth, 30 June 2017]
References
Durner, G. M. and Amstrup, S.C. 1996. Mass and body-dimension relationships of polar bears in northern Alaska. Wildlife Society Bulletin 24(3):480-484. https://pubs.er.usgs.gov/publication/70185398
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