Tag Archives: ecoregrions

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.

Svalbard polar bear_NP015991-isbjorn-JA

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.
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Barents Sea polar bear status and sea ice declines

So far, I’ve not discussed the Barents Sea subpopulation in very much detail, except in comparison to other groups. For example, the Barents is considered to be the same type of sea ice “ecoregion” as the Chukchi Sea and the Southern Beaufort (discussed here). Previous studies on the Barents Sea polar bear population (Derocher 2005) indicate it may have recovered from extreme levels of overhunting (discussed here) and had stabilized, or was increasing very slowly, as early as 2002 (discussed here) — similar to what has happened in Davis Strait (discussed here).

Figure 1. Polar bear subpopulations, with the Barents Sea region highlighted; map courtesy the IUCN Polar Bear Specialist Group (PBSG), extra labels added.

Figure 1. Polar bear subpopulations, with the Barents Sea region highlighted; map courtesy the IUCN Polar Bear Specialist Group (PBSG), extra labels added.

The most recent Barents Sea population estimate was done in 2004 (2,650; range ~1900-3600), based on an aerial survey (Aars et al. 2009). Aerial surveys are the only practical method of establishing population counts in regions like this where many bears never set foot on land. The previous estimate for the Barents (1982) was “2,000-5,000” but its accuracy was considered “poor” (discussed here).

The IUCN Polar Bear Specialist Group (PBSG), in their most recent report, lists the Barents Sea population as “data deficient” for status, current trend and estimated risk of decline within 10 years (Obbard et al. 2010:62, Table 1) and the “notes” for this entry say:

Population estimate is based on a new aerial survey. There was likely an increase in the subpopulation size after 1973 until recently. Current growth trend is unknown.

This 2004 estimate is now almost a decade old and potentially no longer an accurate representation of what’s happening in the Barents Sea. The most up-to-date information has not yet been published but it is available online. It’s eye-opening to say the least, if only that it appears to be yet another example of a polar bear population that is so far not showing signs of being harmed by sea ice declines, as I’ve discussed before (here).

[Update October 15, 2013: I’ve simplified the text discussion and figure regarding the Aars and Andersen denning study from the original posted]

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