Beaufort Sea polar bear subpopulation boundary has been changed

Environment Canada recently posted a set of maps on its website that show it has moved the boundary between the polar bear subpopulation it shares with the USA — without a word to the media or a note anywhere.

EC S_N Beaufort boundary change Sept 8 2014_cropped PolarBearScience


While a change to the Canada/US Beaufort Sea boundary has been discussed by polar bear researchers for some time (e.g. here), there are no links on the EC website or references listed to explain to readers why this change was made.

In fact, the boundary move between the Southern and Northern Beaufort subpopulations is noted on only one of the five maps posted and even then, the “notification” is present only as a footnote in blurred print. So if you didn’t happen to look closely at that particular map, you might not even realize that the boundary on all the other maps was new.

[The map with the boundary change footnote also highlights another set of changes, which I’ll discuss in my next post]

What is interesting also is that as of today, there was no mention of this boundary change on the Polar Bear Specialist Group website.

Below is the Beaufort Sea boundary change in full context:

Figure 1. Boundary change between Southern Beaufort (SB) and Northern Beaufort (NB) polar bear subpopulations on a map apparently published at the Environment Canada website 8 September 2014.

Figure 1. In full context, the boundary change between Southern Beaufort (SB) and Northern Beaufort (NB) polar bear subpopulations on a map apparently posted on the Environment Canada website on 8 September 2014. Modified from the original here, dated  July 2014.

The exact coordinates of the new boundary line are not stated and it’s hard to tell for sure from the maps provided. However, it looks to be at or near Tuktoyaktuk (i.e., ~1330W) – quite a distance from its former position at ~1220W.

The new eastern boundary for the Southern Beaufort seems to correspond closest to a compromise between the two lines on the right side of Fig. 2 below, from a paper by Steve Amstrup et al. (2005:Fig. 7), which I discussed earlier this year. The line at 135 degrees marks the point where 67% of bears captured can be assumed with high confidence to be truly “Southern Beaufort” bears.

Figure 2. From the paper by Amstrup and colleagues (2005: Fig. 7) showing the restricted region in the central Southern Beaufort (135 to 153 degrees W) where any bear captured can be assumed with confidence to be a Southern Beaufort bear.

Figure 2. From the paper by Amstrup and colleagues (2005: Fig. 7) showing the restricted region in the central Southern Beaufort (135 to 153 degrees W) where any bear captured can be assumed with high confidence to be a Southern Beaufort bear.

Amstrup and colleagues had this to say about the community of Tuk:

“The village of Tuktoyaktuk, Northwest Territories, also sits right on the 50% contour line.

Which means (from the Amstrup et al 2005 abstract), that:

“At Tuktoyaktuk, Northwest Territories, Canada, 50% are from the SBS and 50% from the NBS population.

I guess given the complex nature of polar bear management issues between subpopulations, relocating the boundary to the point where the split of harvest allocations can be 50:50 makes a certain amount of sense.

But how this boundary change will allow anyone to track polar bear population changes over time with any confidence in this highly variable sea ice region remains to be seen.

Related posts:
Why is it that every decade, Eastern Beaufort sea ice gets really thick? June 28, 2013

Did polar bear numbers in E Beaufort fluctuate each decade due to thick ice years? July 2, 2013

Southern Beaufort polar bear ‘decline’ & reduced cub survival touted in 2008 was invalid, PBSG now admits March 24, 2014

Footnote 1: The author or authors of this Environment Canada web page is not identified but I assume that a major part was played by biologist Nick Lunn (Canadian Wildlife Service), who appears to be the most senior member of Environment Canada’s polar bear research team and a member of the Polar Bear Technical Committee (and also, an “advisor” to activist conservation organization Polar Bears International and a member of Polar Bear Specialist Group, see his PBSG profile below (click to enlarge). [The latest date stamp on the web page is 8 September 2014 and as there are five maps with different dates, perhaps not all the maps were posted at that time]

Nick Lunn_PBSG profile_PolarBearScience_Oct 27 2014

References
Amstrup, S.C., Durner, G. M., Stirling, I. and McDonald, T. L. 2005. Allocating harvests among polar bear stocks in the Beaufort Sea. Arctic 58:247-259. http://arctic.journalhosting.ucalgary.ca/arctic/index.php/arctic/article/view/426
Pdf here.

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