Thursday, June 23, 2022

They're Always in the Last Place You look (Polar Bears, that is)

From Dr. Susan Crockford at WUWT, Newly-discovered SE Greenland Polar Bear Subpopulation: Another Assumption Proven False

Researchers have discovered that the 300 or so polar bears living in SE Greenland (below 64 degrees N) are so genetically distinct and geographically isolated that they qualify as a unique subpopulation, adding one more to the 19 subpopulations currently described by the IUCN Polar Bear Specialist Group.

Previously, polar bear researchers simply assumed all of the bears in East Greenland were part of the same subpopulation but no field work had been conducted in the extreme southern area until 2015-2017. When they included this region, they got they got a big surprise: now they are spinning it as significant for polar bear conservation (Laidre et al. 2022).

From a new paper by Kristin Laidre and colleagues today in the journal Science, the map below shows this newly-defined population in red in SE Greenland (south of 64 degrees N), which is known as the King Frederick VI Coast:
This newly-discovered population of SE Greenland bears apparently uses marine-terminating glacier fronts (including calved pieces of freshwater glaciers) that exist in deep coastal fjords as platforms to hunt ringed seals when the land-locked fast ice disappears. As they also do in Svalbard, some ringed seals use glacier-front habitat year round, likely because the presence of ice generates upwelling of nutrients and thus, fish to eat (Hamilton et al. 2016, 2017). In other words, ringed seals and polar bears throughout the Arctic are almost certainly capable of utilizing glacier-front habitats where ever they occur, as they have been doing in SE Greenland.


According to the authors:
Southeast Greenland bears appear to have adapted their movements to the region’s specific physical geography. The high-velocity East Greenland Coastal Current (12) seasonally brings a narrow band of low-concentration pack ice south of 64°N and around the southern tip of Greenland (figs. S8 to S10) (13). All tracked Southeast Greenland bears that moved out of the fjords (n = 11) became caught in this
current’s drift ice and were transported southward toward Cape Farewell, drifting an average of 189 km in <2 weeks (fig. S4). Notably, all swam ashore and walked via land to their home fjord within 1 to 2 months, demonstrating high site fidelity. Bears in Southeast Greenland must remain inside fjords or risk export to human inhabited areas of South Greenland or into the North Atlantic.Lairdre et al. 2022:1333.
The map above from the Laidre paper shows the genetic distinctiveness of this subpopulation (‘SEG’). Evidence of some immigration from the north indicates the group is not totally isolated and the authors mention that new immigrants soon learn to live in this glacier-front environment (Laidre et al. 2022:1337).

However, the genetic data also indicate the subpopulation has been separate for only about 200 years (189-264). This suggests to me the possibility that the thick ice at around 65 degrees N that stopped the northward travel of Graah in 1829 mentioned above may have been a decades-long phenomenon that also trapped polar bears on the SE coast and kept them entirely separate from NE Greenland bears until very recently. The authors did not mention this as a possibility: in fact, they didn’t provide any explanation at all for why the populations became separated about 200 years ago or comment why such distinctive genetic signatures would be evident after such a short period of evolutionary time.

Of course, the authors suggest this new subpopulation–although unnoticed by them for decades while easily surviving an ice-free period similar to conditions predicted for the High Arctic in the late 2100s–must be conserved to protect the genetic diversity of the species (Peacock 2022). In other words, they see it primarily as welcome additional pressure to protect polar bears from global warming.

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