Tag Archives: pack ice

Svalbard polar bears thrive in part due to ringed seal pups in the spring pack ice

Few people know that Arctic ringed seals (Phoca hispida, aka Pusa hispida) give birth and breed in the offshore pack ice in the spring, as it is seldom mentioned by either seal or polar bear specialists.

While it is true that some ringed seals give birth in stable shorefast ice close to shore, many others give birth well offshore in thick pack ice – where polar bears also live and hunt in the spring but where few Arctic scientists ever venture – and the existence of pack ice breeding ringed seals is one of the reasons that polar bears are such a resilient species.

ringed-seal-in-snow-cave_b-kelly-wikipedia

Ringed seal pup in a snow cave, B. Kelly photo (Wikipedia).

As a consequence, despite fears expressed by Ian Stirling, low shorefast ice and associated snow around Svalbard this winter (and any time in the past) is not necessarily a hindrance to polar bear survival because there are ringed seal pups available out in the surrounding pack ice – where bearded seals also give birth.

Of course, ringed seals pups are also available to Svalbard polar bears in the shorefast ice in the Franz Josef Land archipelago to the east (see map below) but it is the pups born in the offshore pack ice that are of interest here. The existence of pack ice breeding ringed seals may be why Norwegian biologists do not currently monitor ringed seals in the Barents Sea, despite many years of poor ice conditions around Svalbard in spring – this simply is not a species of concern.

barents-sea-ice-2017-feb-6_nis

The fact that distinct ringed seal ecotypes (or habitat-specific morphotypes) exist in the Arctic – one that gives birth and breeds in shorefast ice and another that gives birth and breeds in offshore pack ice, perhaps driven by competition for limited shorefast ice habitat – is a phenomenon a colleague and I discussed in a peer-reviewed book chapter published several years ago. Have a look at the excerpt below and see what you think.

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Polar bear habitat: Spring 2014 in Eastern Canada was much better than 1969

It was a good year for polar bear habitat in the southern portions of Eastern Canada this spring – surprisingly, much better than it was in 1968 through 1970. And since spring conditions are what really matter to polar bears, this is good news indeed.

Environment Canada’s Canadian Ice Service recently published a nice little summary that has some rather eye-opening graphs. These describe the conditions for polar bears in the southern Davis Strait subpopulation – the one whose population size increased so dramatically between 1974 and 2007 despite lower-than-average ice extent in some years, even while their body condition declined (see here and here).

Environment Canada - Ice maps regions at July 26 2014

[Fitting post for the second anniversary of this blog, I think – more below1]

Note that I’ve added a “Blog Archive” page that lists all of my posts, easier to browse now that there are more than 200 of them.
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Is there insufficient ice for polar bears to den offshore?

In an earlier post (July 26), I had some critical things to say about an article in the Edmonton Journal (July 17, 2012) by veteran Arctic science writer and photographer Ed Struzik called “Bleak future for polar bears, U of A scientists say“, which was picked up by news outlets across Canada.

The Struzik article publicized a summary academic paper written by polar bear biologists Ian Stirling and Andrew Derocher (a former Ph.D. student of Stirling) that appeared “in press” behind the paywall at the journal Global Change Biology on July 9.

The academic paper is a summary of Stirling and Derocher’s dire predictions on the future fate of polar bears as a result of melting of Arctic sea ice over the next few decades, one of the prophesied catastrophes of anthropogenic global warming. These views mirror to a large degree the chapter on “climate warming” in Ian Stirling’s book on polar bears released in 2011, which I reviewed recently here.

Let’s look at one of the statements made in the Struzik article:

In Alaska, many bears are denning on land because there is insufficient ice for them to give birth offshore.

Update added Aug. 28, 3:35 PM  below the post
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