Posted onApril 5, 2022|Comments Off on Sea ice average for March is the metric used to compare to previous winters
The average sea ice cover at the end of March is the metric used to compare ‘winter’ ice to previous years or decades, not the single-day date of ‘most’ ice. This year, March ended with 14.6 mkm2 of sea ice, most of which (but not all) is critical polar bear habitat. Ice charts showing this are below.
But note that ice over Hudson Bay, which is an almost-enclosed sea used by thousands of polar bears at this time of year, tends to continue to thicken from March into May: these two charts for 2020 show medium green becoming dark green, indicating ice >1.2 m thick, even as some areas of open water appear.
Posted onMay 23, 2021|Comments Off on Spring polynyas in the Arctic then and now as feeding areas for hungry polar bears
Patches of open water in the Arctic that develop in the spring, including polynyas and widening shore leads, are largely due to the actions of wind and currents on mobile pack ice rather than ice melt. Contrary to concerns expressed about possible negative implications of these early patches of open water, these areas have always been critical congregation areas for Arctic seals and are therefore important feeding areas for polar bears in late spring.
Posted onNovember 11, 2020|Comments Off on Shorefast ice formation and the fall feeding season for polar bears
What may seem like a silly question is actually fundamental to polar bear survival: in the fall, why do Western Hudson Bay bears correctly expect to find seals in the new ice that forms offshore? Why are seals attracted to that new ice – called ‘shorefast ice’ or ‘fast ice’ – when they would clearly be safer out in the open water where there is no ice and no bears?
As the picture below attests, polar bears can and do kill ringed seals in the new ice that forms off the coast of Western Hudson Bay even when it is but a narrow strip of thin ice – and so close to shore their successes can be caught on camera.
Three adult male polar bears share a seal kill on the newly-formed ice off Wapusk National Park, Western Hudson Bay. 5 November 2020. Buggy cam, Explore.org
A different bear was also filmed killing another seal on 31 October. And these are only the kills we know about along a very short stretch of coast – the killing is almost certainly going on up and down the entire coast, into James Bay (see below), where there is just as much ice but no cameras.
As far as I am aware, this seal killing by polar bears goes on in newly-formed shorefast ice everywhere across the Arctic in early fall, not just in Hudson Bay. Although the timing varies, virtually everywhere in the peripheral seas of the Arctic Ocean (Barents, Kara, Laptev, Chukchi, Beaufort, as well as Baffin Bay and Davis Strait), shorefast ice forms before the mobile ice pack expands to meet the ice developing from shore.
This shorefast ice formation in fall provides a predictable but short-lived source of prey for polar bears as they strive to regain some of the weight lost over the summer.
Posted onJune 4, 2020|Comments Off on Spring feeding season almost over for polar bears & sea ice becomes less important
Here are ice conditions at the end of May, which signals the near-end of the critical spring feeding period for polar bears. This is because young-of-the-year seals take to the water to feed themselves, leaving only predator-savvy adults and subadults on the ice from some time in June onward (depending on the region).
Spring is the critical feeding period for polar bears (Crockford 2019, 2020; Lippold et al. 2020; Obbard et al. 2016):
“Unexpectedly, body condition of female polar bears from the Barents Sea has increased after 2005, although sea ice has retreated by ∼50% since the late 1990s in the area, and the length of the ice-free season has increased by over 20 weeks between 1979 and 2013. These changes are also accompanied by winter sea ice retreat that is especially pronounced in the Barents Sea compared to other Arctic areas. Despite the declining sea ice in the Barents Sea, polar bears are likely not lacking food as long as sea ice is present during their peak feeding period. Polar bears feed extensively from April to June when ringed seals have pups and are particularly vulnerable to predation, whereas the predation rate during the rest of the year is likely low.“ [Lippold et al. 2019:988]
Posted onJanuary 8, 2019|Comments Off on Svalbard polar bears doing fine with much less sea ice say Norwegian biologists
“…despite the loss of good denning areas and a shrinking habitat for hunting, Svalbard’s bears seem to be doing fine.…The sea ice season is now several months shorter, and the ice edge typically lies several degrees further north than what was normal 20-40 years ago….Polar bears can survive long periods without food, provided they have accumulated a good fat reserve during the few months in spring and summer when sea ice is present, and seals are abundant.” [Jon Aars, Norwegian Polar Institute, 2018]
Posted onNovember 10, 2018|Comments Off on W Hudson Bay freeze-up earlier than average for 2nd year in a row, polar bear hunt resumes
This is the second year in a row that freeze-up of Western Hudson Bay ice has come earlier than average. Movement of tagged bears and reports by folks on the ground in WH show some polar bears are starting to hunt seals on the sea ice that’s developing along the shore. It’s unlikely that a strong wind will again blow the newly-formed ice offshore (as happened earlier this year) because the ice is more extensive. It seems polar bear viewing season in Churchill will be ending early this year, just like it did last year.
The 9 November map Andrew Derocher (University of Albera) published on twitter showing tagged and collared polar bear movements on Hudson Bay makes it look like almost no ice is present:
Hudson Bay #polarbears are still pretty much on land but a few are edging out on the newly formed ice along shore. A few will kill seals along the new ice & the earlier the ice comes, the better it is for the bears (not as good for the seals). pic.twitter.com/ZWzQNeQje8
Posted onMay 3, 2018|Comments Off on Polynya refresher: open water in spring is due to winds & currents, not ice melt
Arctic sea ice begins to open up in spring at predictable locations due to currents and prevailing winds and this was as true in the 1970s as it is today. Polynyas and widening shore leads that most often get mistaken for early sea ice melt are those in the Beaufort and Chukchi Seas and in Hudson Bay.
But contrary to concerns expressed about possible negative implications of these early patches of open water, these areas have always been critical congregation areas for Arctic seals and are therefore important feeding areas for polar bears.
Seals hauled out beside a lightly frozen over lead in Beaufort Sea ice, 2008. USFWS.
Posted onApril 30, 2018|Comments Off on Low Bering Sea ice mostly due to south winds, no data on an impact for polar bears
Sea ice in the Bering Sea this winter was said to be the lowest since the 1850s, largely driven by persistent winds from the south rather than the usual north winds although warm Pacific water was a factor early in the season (AIRC 2018). But what, if any, impact is this surprisingly low winter and spring ice cover likely to have on Chukchi Sea polar bear health and survival?
In fact, research on Chukchi Sea polar bears has included so few examples of individuals utilizing the Bering Sea in winter (Jan-March) and early spring (April-May) that any conclusions regarding an impact from this year’s sea ice conditions are likely to be invalid. In short, we don’t know what will happen since it has not happened before within living memory; the opinions of polar bear specialists must be taken with a grain of salt because so many of their previous assumptions have turned out to be wrong (Crockford 2017a,b, 2018), see here,here, and here. Seals, walrus and polar bears are much more flexible and resilent to changes in habitat conditions than most modern biologists give them credit for and consequently, it will be fascinating to see how the ice will change over the coming months and how the animals will respond.
Posted onApril 27, 2018|Comments Off on Polar bear habitat update early spring 2018
Spring in the Arctic is April-June (Pilfold et al. 2015). As late April is the peak of this critical spring feeding periodfor most polar bear populations, this is when sea ice conditions are also critical. This year, as has been true since 1979, that sea ice coverage is abundant across the Arctic for seals that are giving birth and mating at this time as well as for polar bears busy feeding on young seals and mating.
Below is a chart of sea ice at 25 April 2018, showing sea ice in all PBSG polar bear subpopulation regions:
Posted onMarch 6, 2018|Comments Off on Winter polar bear sea ice habitat by early March 2018 varied little from 2006 or 2017
Here’s a polar bear habitat update for early March: some folks are wringing their handsover the relatively extent of ice this season but ice maps show that as far as polar bear habitat is concerned, conditions are not materially different this year from what they were in 2006 or 2017. There is still plenty of late winter sea ice for polar bears needing a platform from which to hunt Arctic seals, which in some areaswill have already begun giving birth to their fat furry pups (harp seals first, other species later).
The MASIE map for 5 March 2018 (Day 64) shows ice extent at 14.5 mkm2: