New polar bear subpopulation update: more background facts and details from the paper

Here are the facts you need to put into context the claim that the estimated 234 polar bears recently discovered in SE Greenland have been living ‘without sea ice‘.

The unique genetic isolation of this new subpopulation makes it one of the most interesting discoveries about polar bears we’ve seen in decades, yet the media were primed by a press release loaded with dooms-day climate rhetoric to focus exclusively on the model-predicted precarious future of the species, like this gem from the lead author:

“In a sense, these bears provide a glimpse into how Greenland’s bears may fare under future climate scenarios,” Laidre said. “The sea ice conditions in Southeast Greenland today resemble what’s predicted for Northeast Greenland by late this century.”

As a consequence, the media have been trying to out-do each other with the most over-the-top climate catastrophe headlines, see here and here. The authors of paper itself and a companion piece do the same: instead of focusing on the exciting scientific implications of the genetically isolated population they discovered, they promote the preferred narrative that polar bears have a bleak future and lecture the public (yet again) about the need for limiting CO2 emissions (Laidre et al. 2022; Peacock 2022).

PERTINENT FACTS

Is this region far south? SE Greenland is not an extremely southern habitat for polar bears: the area of SE Greenland where this new subpopulation of polar bears live spans 64-60 degrees N. Being below the Arctic Circle, it has sunlight all winter long, which is similar to the area occupied by polar bears in Davis Strait and in northern Hudson Bay and Foxe Basin (from south of Arviat in western Hudson Bay to Southampton Island (see map below). Western and Southern Hudson Bay polar bears have been thriving south of this latitude for centuries.

Has there been a lack of critical sea ice? No. According to the paper, the land-bound fast ice that most ringed seals use to give birth and nurse their pups in spring (April-May) is still routinely available in SE Greenland. Polar bears need this spring ice because that’s when they feed most heavily on newborn seals: 2/3 of their yearly intake is consumed in these months, making spring ice the most critical ice habitat for polar bear survival. In contrast, lead author Kristin Laidre told The Guardian [my bold]:

“What we know about polar bears is that having sea ice for about 100 days a year is just way too few for bears to survive,” she said.”

However, this statement about knowing polar bears need far more than 100 days of sea ice is not true: it is a model output based on assumptions, not a fact (Molnár et al. 2010, 2020).

With a few exceptions between 2015 and 2019, the fjords used by the bears (see map below) had substantial spring fast ice. In addition, the authors admit that some bears moved over-land between fjords, sometimes over long distances (Laidre et al. 2022:1333 and Fig. S4), suggesting to me that if ringed seal pups were not available some years in one of the three southern-most ‘home fjords’, the bears simply moved to an adjacent one with better feeding opportunities for a few months.

Does summer hunting sustain these bears? The authors assumed that summer hunting of seals from bits of glacier ice has allowed these SE Greenland bears to survive but in reality they saw the bears in March and April only. Any comments they have made to the media or implied in their paper about extensive hunting behaviour during the rest of the year is conjecture. It may be that bears attempt to hunt during the summer and fall from glacier ice but that does not mean they are routinely successful or that prey taken at these times is critical to their survival.

Included in the Laidre paper are two photos said to have been taken in September 2016: one of a bear on a fresh seal kill and the other one shown below. The photo of the seal kill appears to be the only concrete evidence the authors have of successful hunting on the glacier ice in summer. Although most SE Greenland bears probably take a few seals in the glacial ice it may be that they are more like Svalbard bears, who don’t spend much time hunting in fjords in summer and fall even though both ringed seals and bearded seals are present (Hamilton et al. 2017:1060 and 1063).

At issue is whether or not any seals the bears consume over the summer and fall represent a substantial portion of their diet. The authors presume they are but actually provide no data to support their assumption.

Photo of a fat bear taken by Thomas W. Johansen, NASA, in September 2016 at 61 degrees N on bits of glacier ice floating in a fjord in SE Greenland.

Are these bears thriving? It appears they are. The photos provided by the authors indicate that SE Greenland polar bears they encountered were in excellent condition, since I expect that if lean or starving bears had been seen we would have been shown pictures of them. For example, the photo below provided in the press release, taken in March, shows a very fat bear on a bit of glacier ice imbedded in fast ice: it is as fat as the bear in the photo taken in September copied above.

SE Greenland fat polar bear on a bit of glacier ice trapped in spring fast ice, Kristen Laidre photo taken in March 2016.

Fellow polar bear specialist Andrew Derocher, interviewed by Vox, implied that SE Greenland bears were ‘not in very good condition‘ and not reproducing well. However, the data reported in the paper do not support this view. The authors actually say [my bold]:

We found no differences in litter sizes between Southeast Greenland and Northeast Greenland subpopulations, which suggests similar cub survival. Adult female body mass, an important determinant of cub production and survival, was lower in Southeast Greenland than in several other subpopulations but was similar to that of Northeast Greenland bears and the Barents Sea subpopulation (fig. S26 and table S11), both of which use glacial fjords. It is possible that low birth rates are influenced by highly fractured fjord and mountain habitats that reduce bear movements and impede breeding pair formation.

Laidre et al. 2022:1334

Are glacier-front habitats rare? The abstract of the paper states, “…marine-terminating glaciers, although of limited availability, may serve as previously unrecognized climate refugia“. Many media outlets interpreted this to mean that marine-terminating glaciers with highly-productive waters in fjords are rare, see here and here. However, an estimated 537 marine-terminating glaciers are scattered along the coast of Greenland alone (Kochtitzky and Copland 2022; Meire et al. 2017) and polar bears are known to hunt in these fjords in NE Greenland as they do in SE Greenland (Laidre et al. 2022).

Furthermore, one group of researchers estimated there are a total of 1,704 marine-terminating glaciers in the Northern Hemisphere (Kochtitzky and Copland 2022, see their Fig. 1 below) and only 43 of those are not in the Arctic. Many marine-terminating glaciers also exist in the Canadian Arctic on Ellesmere, Devon, and Baffin Islands, the Franz Josef Land archipelago, Novaya Zemlya, and Severnaya Zemlya (as well as along the entire Greenland coast and in the Svalbard archipelago). This means that substantial glacial ice in coastal fjords, as potential sea ice ‘refugia’ habitat for seals and polar bears in a warmer world, are rather widespread and abundant, even if many of the glaciers are currently retreating a bit (Choi et al. 2021; Cook et al. 2019; Sommer et al. 2022).

Kochtitzky and Copland 2022.

How did they get there? I am truly disappointed with the authors’ refusal to address why the bears got trapped in SE Greenland in the first place. To me, this is the most interesting scientific question revealed by their research.

In my last post, I offered the hypothesis that very cold conditions and extensive sea ice in the early 1800s may have created conditions conducive to trapping a small number of bears below 64 degrees N and keeping them there for decades (presuming that the authors’ estimate of the timing of this population spit is accurate). It seems to me Laidre and colleagues did not want to mention the possibility that extensive sea ice only a few hundred years ago could have been the cause because it would be an admission that sea ice conditions can change naturally and dramatically over short time periods.

The only information the authors provide with regard to historical climate conditions is found in their Supplemental Data (pg. 7), where they mention that weather records on the SE Greenland coast at 65 degrees N (Tasiilaq, station 4360, 1895-present) indicate the late 1800s had the coldest winters, with warmer winters in the 1920s-1930s followed by cooling, and warming again beginning in the 1980s (citing Cappelen 2014).

Seemingly, no research effort was expended to investigate why bears got trapped in SE Greenland two centuries ago and remained isolated ever since: the paper contains no discussion of the issue and even to the media, they said essentially, “we have no idea“.

Conclusion

It is clear that these SE Greenland polar bear are not surviving without sea ice: they are surviving without sea ice in the summer and fall, just as bears do many areas of the Arctic, including Western and Southern Hudson Bay. These bears still have access to seal pups on the fast ice of the fjords in spring, which is when they really need abundant prey. In fact, I contend this paper provides good additional evidence that sea ice in early spring, not summer and fall, is critical to polar bear survival.

There is no evidence to support the suggestion by Ed Yong at The Atlantic that these SE Greenland bears could be “the last polar bears on Earth” (likened to mammoths surviving the Last Glacial Maximum on Wrangel Island). Aside from the fact that glacier-front habitat like that used by ringed seals and polar bears in SE Greenland today is abundant throughout the Arctic at much higher latitudes (and thus certain to survive a bit more warming), the Laidre paper provides no evidence that these polar bears consume more seals in summer and fall than bears do in open sea ice habitats.

Lastly, the failure of the authors to address the most interesting scientific question of all is a big let-down, especially since they chose to publish this research ahead of a population size estimate for East Greenland, which is decades overdue. They spent plenty of effort tying this phenomenon of an isolated subpopulation living amongst melting glaciers to future global warming but seemingly none attempting to discover why the bears got trapped in SE Greenland in the first place. Have they no scientific curiosity? Or did they push it aside in deference to the global warming narrative because it must always take precedence? Either option is a real loss for science.

Footnote: The specific population size estimate cited in the opening line of this post (234, for 2016-2017) is provided only in the Supplemental Data (pg. 26): in the paper and press release, the authors say “a few hundred”.

References

Cappelen, J. (Editor) 2014. Greenland – DMI Historical Climate Data Collection 1784–2013. Technical Report 14-04, Danish Meteorological Institute. https://www.dmi.dk/fileadmin/user_upload/Rapporter/TR/2014/tr14-04.pdf.

Choi, Y., Morlighem, M., Rignot, E. et al. 2021. Ice dynamics will remain a primary driver of Greenland ice sheet mass loss over the next century. Nature Communications Earth & Environment 2: 26. Open access https://doi.org/10.1038/s43247-021-00092-z

Cook, A.J., Copland, L., Noel, B.P., et al. 2019. Atmospheric forcing of rapid marine-terminating glacier retreat in the Canadian Arctic Archipelago. Science Advances 5(3):eaau8507. DOI:10.1126/sciadv.aau8507

Hamilton, C.D., Kovacs, K.M., Ims, R.A., Aars, J. and Lydersen, C. 2017. An Arctic predator–prey system in flux: climate change impacts on coastal space use by polar bears and ringed seals. Journal of Animal Ecology 86:1054–1064.

Kochtitzky, W. and Copland, L. 2022. Retreat of Northern Hemisphere Marine-Terminating Glaciers, 2000–2020. Geophysical Research Letters 49(3):e2021GL096501. https://doi.org/10.1029/2021GL096501

Laidre, K.L., Supple, M.A., Born, E.W., et al. 2022. Glacial ice supports a distinct and undocumented polar bear subpopulation persisting in late 21st century sea-ice conditions. Science 376 (6599): 1333-1338. https://www.science.org/doi/10.1126/science.abq5267

Peacock, E. 2022. A new polar bear population: Can the international conservation agreement protect these bears? Science 376(6599):1267-1268. https://www.science.org/doi/10.1126/science.abq5267

Mauritzen, M., Derocher, A.E. and Wiig, Ø. 2001. Space-use strategies of female polar bears in a dynamic sea ice habitat. Canadian Journal of Zoology 79:1704-1713. http://www.nrcresearchpress.com/doi/abs/10.1139/z01-126#.U0spVlda9lo

Mauritzen, M., Derocher, A.E., Wiig, Ø., Belikov, S.E., Boltunov, A.N., Hansen, E. and Garner, G.W. 2002. Using satellite telemetry to define spatial population structure in polar bears in the Norwegian and western Russian Arctic. Journal of Applied Ecology 39:79-90. http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2664.2002.00690.x/abstract

Meire, L., Mortensen, J., Meire, P., et al. 2017. Marine-terminating glaciers sustain high productivity in Greenland fjords. Global Change Biology 23:5344-5357. Open access https://doi.org/10.1111/gcb.13801

Molnár, P.K., Bitz, C.M., Holland, M.M., Kay, J.E., Penk, S.R. and Amstrup, S.C. 2020. Fasting season length sets temporal limits for global polar bear persistence. Nature Climate Change 10:732-738.  https://doi.org/10.1038/s41558-020-0818-9

Molnár, P.K., Derocher, A.E., Theimann, G., and Lewis, M.A. 2010. Predicting survival, reproduction and abundance of polar bears under climate change. Biological Conservation 143:1612-1622. http://www.math.ualberta.ca/~mlewis/Publications%202010/Molnar-Derocher-Thiemann-Lewis.pdf

Sommer, C., Seehaus, T., Glazovsky, A. and Braun, M.H. 2022. Increased glacier mass loss in the Russian High Arctic (2010–2017). The Cryosphere 16:35-42. https://doi.org/10.5194/tc-16-35-2022

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