Late winter surge in sea ice habitat and the resilience of Svalbard polar bears

The Barents Sea – and Svalbard in particular – has had very little sea ice this winter but recent evidence suggests pregnant females adapted by moving east to Franz Josef Land to have their cubs. The surge in ice that’s come over the last few weeks will, however, be welcome habitat for the critical hunt of fat newborn seals that takes place primarily in April and May.

It was only last fall that Norwegian biologist Jon Aars (photo above taken by him in August 2015) was touting the fat condition of Svalbard-area polar bears he and his team saw in August and admitted the population had increased by a whopping 42% since 2004 – despite dire predictions of a drastic decline. In fact, 2014/2015 was a great year for the area’s polar bears.

However, in the fall of 2015 sea ice was so late forming around Svalbard that it seemed impossible that any females would get to traditional denning grounds on the east coast in time to give birth. There was no sea ice to speak of until late December, so it seemed virtually certain that all females had gone to Franz Josef Land further east (in Russia) – as they are known to do – to utilized its alternative denning sites.

It’s called resilience – the ability to shift behaviour in response to changing conditions. In this case, all indications are that shifting den locations to Franz Josef Land is a long-standing response of Svalbard area polar bears to low ice conditions. This shift does not even require a movement outside their subpopulation boundaries, let alone a movement outside the ill-defined “sea ice ecoregions” originally defined by Steven Amstrup and colleagues (2008) to support their prediction that polar bears will likely be extinct by 2100, taken up later by others since.

Some polar bear specialists appear to believe that if Barents Sea conditions are not precisely what they were in the 1980s (examples here and here), polar bears cannot possibly survive. But the bears are showing them otherwise – and demonstrating how they likely survived previous warm periods like the Holocene Optimum ~9,000 years ago and the Eemian Interglacial ~115,000-130,000 years ago (CERQA 2014:66) without population numbers getting anywhere near extinction levels.

The US sea ice agency NSIDC pointed out in their press release announcing the yearly maximum on Monday:

As noted by Ingrid Onarheim at the Bjerknes Centre for Climate Research in Bergen, Norway: “A decrease in Barents Sea ice extent for this winter was predicted from the influence of warm Atlantic waters from the Norwegian Sea.”

Even if it was expected, the results were dramatic – but far from unprecedented. Sea ice was also very late arriving in the fall of 2012 (after the lowest summer extent since 1979 the previous September, which was caused by a massive, late-season storm) and the polar bears survived quite well. In fact, the sea ice distribution in 2012 was remarkably similar at the end of December to conditions on the same date in 2015 – lots of ice around Franz Josef Land to the east but little around Svalbard (see maps below).

The cluster of islands known as Franz Josef Land (see map above) lies in Russia, well east of the Norwegian islands of Svalbard, but all are part of the Barents Sea polar bear subpopulation as defined by the IUCN Polar Bear Specialist Group.

Svalbard polar bear females must have gone to Franz Josef Land to have their cubs in 2012 because otherwise, the population could not have increased as it did by the summer of 2015. In the fall of 2014, when ice conditions were high, females that traditionally made their maternity dens on Svalbard appear to have returned there to have their cubs and lingered in the region into the summer where they were available to be counted.

So, when someone says that Svalbard area polar bears must be in serious trouble this year because of low ice levels over the winter, point them to the Norwegian Ice Service archive and tell them to look at the ice conditions in late 2012/early 2013.

And then send them to the press release issued by the Norwegian Polar Institute (pdf here, picked up by the Arctic Journal) as well as the interview he gave to High North News just after the survey was completed (Google Translate required) and this one from early December 2015.

Movement to Franz Josef Land keeps Svalbard area bears within their sea ice ecoregion (called “Divergent Ice”), as shown below (Amstrup et al. 2008), as does the movement of Southern Beaufort Sea bears into the Chukchi Sea. Too bad that polar bears don’t care this means they are crossing international boundaries.

[Norwegian Polar Institute polar bear data (here) is updated routinely; see previous posts discussing some of that data here and here. Note that although the sea ice was late to Svalbard in the fall of 2013 as well, it was not quite as late as in 2012 and 2015. As might have been expected, many fewer cubs were born on Svalbard that spring, almost certainly because some bears went to Franz Joseph Land instead to make their maternity dens]

Below map of polar bear denning areas, from Anderson et al. 2012. Note how few denning areas are on the west and north coasts of Spitzbergen (the main island). There has been no sea ice in these regions throughout the winter since at least 2006 but as records of den use documented by Anderson and colleagues go back to 1972, it suggests that Spitzbergen has seldom been a preferred denning area.

References
Amstrup, S.C., Marcot, B.G., Douglas, D.C. 2008. A Bayesian network modeling approach to forecasting the 21^st century worldwide status of polar bears. Pgs. 213-268 in Arctic Sea Ice Decline: Observations, Projections, Mechanisms, and Implications, E.T. DeWeaver, C.M. Bitz, and L.B. Tremblay (eds.). Geophysical Monograph 180. American Geophysical Union, Washington, D.C. http://onlinelibrary.wiley.com/doi/10.1029/180GM14/summary and http://alaska.usgs.gov/science/biology/polar_bears/pubs.html

Anderson, M., Derocher, A.E., Wiig, Ø. and Aars, J. 2012. Polar bear maternity den distribution in Svalbard, Norway. Polar Biology 35:499-508.

Committee on Emerging Research Questions in the Arctic (CERQA). 2014. The Arctic in the Anthropocene: Emerging Research Questions. National Academies Press, Washington D.C. [download free ebook version here]