Tag Archives: pack ice

Late fall polar bear habitat 2020 compared to some previous years

It’s time to look at sea ice habitat at 15 December (Julian Day 350), now that virtually all bears except pregnant females throughout the Arctic are either out on the sea ice attempting to hunt for seals or hunkered down against the darkness.

As is usual at this time of year, the Canadian Archipelago, the Beaufort, East Siberian and Laptev Seas are well covered in ice (see regions on map below). As for the rest, despite what one polar bear specialist has implied there is no evidence that a slower-than-usual fall freeze-up in the other peripheral seas of the Arctic negatively affects polar bear health or survival.

In fact, because of the attractiveness of the ice edge for seals in the fall, as I discussed last month, it’s possible that the longer the ice edge persists in fall, the more successful polar bears will be in hunting seals – except those above the Arctic Circle where lack of daylight from early November may cause polar bears to hunker down and rest rather than try to hunt through the darkness. But we’ll never know for sure, because bears have never been studied at this time of year – experts simply make assumptions about what happens (e.g. Stirling and Oritsland 1995).

Sea ice thickness also varies year to year throughout the season but does not matter much to polar bears, who hunt most successfully in first year ice less than 2m in thickness, which comprises all of the regions currently purple in the ice thickness chart below.

Hudson Bay

This year at mid-December, there was more ice than usual in central and southern Hudson Bay (below) and somewhat less than usual in the eastern portion.

However, the ice is forming so fast now that by 18 December there was hardly any open water remaing over Hudson Bay and the ice to the north was solidifying (below). Recall that a similar freeze-up pattern left a pod of a dozen or so killer whales stranded in mid-January 2013 and killed four others in 2016. Such ice-entrapment suggests that despite a ‘warming’ Arctic, freeze-up patterns would have to change very dramatically for Hudson Bay to be an attractive place for killer whales. A recent DFO report concluded:

Killer whale ice entrapments are almost always fatal and can wipe out entire family groups, with long-lasting demographic impacts. Ice entrapments could therefore slow Arctic killer whale range expansions, particularly in areas where killer whales that are unfamiliar with sea-ice patterns fail to exit prior to ice formation in winter.

Compare Hudson Bay weekly stage of development charts (below) for this year back to 2014, from the Canadian Ice Service archives. You’ll see that this year appears to have more extensive 1st year ice (light green, ca. 30-70 cm) than any other year (although last year had almost as much) and that 2016 was notable as being a very late freeze-up year:

Western Hudson Bay polar bears with collars or tags deployed by Andrew Derocher and his University of Alberta crew (below) are spread out over the ice of the bay (two on land are denning females), a number are on the thickest ice in the north but others are on thinner ice to the south and east:

Baffin Bay, foxe basin, and Davis Strait

Ice covereage in the Canadian Eastern Arctic at mid-December is about average this year, according to CIS charts – only a bit of red and pink indicating ‘below normal’ in the east (off of Greenland):

Pack ice has moved down from the north through Baffin Bay into Davis Strait (below) and will soon be off the coast of Labrador, which has somewhat less ice than usual this year at mid-December:

The ice off Labrador at this time is shorefast ice developing and thickening in place (below). As far as we know, few polar bears summer on the northern Labrador coast, so this late ice development is unlikely to affect local bears. However, pack ice will move down during January and February until it engulfs the area north of Newfoundland, bringing some polar bears with it.

Greenland and Barents Sea

Freeze-up in the Greenland Sea is progressing a bit faster than usual for the last five years (below), but not remarkably so:

Ice cover in the Barents Sea (below) has been slow so far but has been progressing faster over the last few weeks. There is now ice off the east coast of Novaya Zemlya, shorefast ice that should allow any bears summering there to hunt for seals just as Western Hudson Bay bears do during early freeze-up stages. Within the next few weeks, the Arctic pack ice will move south into the Kara Sea, allowing bears to move more freely.Ice off Svalbard has been much below normal (below), as it has been for years now, which is why virtually all Barents Sea pregnant females currently make maternity dens in Franz Josef Land or on the sea ice to the north. These alternative areas for safely giving birth is the primary reason that the much reduced sea ice around Svalbard in recent years has not impacted Barents Sea polar bear health or survival.

Kara Sea

Ice cover in the Kara Sea at 15 December (below) is lower compared to the last five years but it’s unclear how much effect this will have on local polar bears.

Animals that have opted to spend the ice-free season on Novaya Zemlya or on the Russian mainland will have had a long wait for ice, but those that spent the summer on the Severnya Zemlya archipelago to the east had access to sea ice before the end of November. There has been no word from Belushaya Guba on whether the polar bear problems they had because of poorly maintained garbage dumps in December 2018 that went on until February 2019 have recurred this year.

Despite what Andrew Derocher claims (below), there is no evidence that slightly less sea ice in the fall is detrimental to polar bear health or survival in the Kara Sea or elsewhere. It is possible that it might but no one has studied it, so to suggest that low sea ice cover is ‘trouble’ for polar bears at this time of year is very misleading.

Chukchi/Bering Sea

Sea ice cover over the Chukchi Sea is a bit lower than it has been over the last few years, about as low as it was in 2017 (below).

Chukchi Sea polar bears at 14 December (below) had abundant sea ice habitat.

In 2016, when Chukchi polar bears were counted for the first time, there was a similar amount of ice at this time of year (below):

References

Stirling, I. and Øritsland, N. A. 1995. Relationships between estimates of ringed seal (Phoca hispida) and polar bear (Ursus maritimus) populations in the Canadian Arctic. Canadian Journal of Fisheries and Aquatic Sciences 52: 2594 – 2612. http://www.nrcresearchpress.com/doi/abs/10.1139/f95-849#.VNep0y5v_gU

Polar bear habitat update for late November

Sea ice formation is ahead of usual in some regions and behind in others but overall, sea ice habitat is abundant enough for this time of year for virtually all polar bears across the Arctic to be back out on the sea ice hunting seals.

Overall, there was more sea ice at 24 November 2020 than there was on the same date in 2016, which was the last year that a number of polar bear subpopulations were surveyed, including Western and Southern Hudson Bay, Southern Beaufort, Chukchi Sea (Crockford 2019, 2020), see graph below from NSIDC Masie:

Northern Hemisphere sea ice at 24 November, 2016-2020.

UPDATE 27 November 2020: Problem bear report published today (for week 13, Nov. 16-22) has been added below.

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Some surprises in polar bear sea ice habitat at mid-October 2020

Arctic sea ice has been growing steadily since the minimum extent was reached a month ago, with shorefast ice now developing along the Russian and Alaskan coastlines as ice cover expands in the Central Canadian Arctic. So while it’s true that the main pack of Arctic ice is far from the Russian shoreline, rapidly developing shorefast ice will allow bears to begin hunting seals long before ice in the central Arctic Basin reaches the Siberian shore, as they do in Western and Southern Hudson Bay every fall.

Cropped sea ice extent at 15 October 2020 (Day 289), NSIDC Masie.

And speaking of Western Hudson Bay, it’s a very slow season around Churchill for problem polar bears (photo below) – the quietest mid-October for the Polar Bear Alert Program in the last five years and perhaps the quietest in decades (which I could say for sure if I had the records but I do not).

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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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