Category Archives: Life History

Strange sea ice pattern over Hudson Bay as winds blow polar bears offshore

Winds blew a huge mass of new shorefast sea ice way out into Western Hudson Bay a few days ago (13 November) and very likely took some polar bears with it. This offshore wind phenomenon is common at this time of year – it happened in 2017 – and is often part of the yearly ‘freeze-up’ process for sea ice. But the extent of ice and the distance blown offshore in Hudson Bay this year is impressive.

In previous years, this has happened very early in the freeze-up sequence, well before the ice was thick enough to support polar bears. This year is different: freeze-up was early (starting in late October) and the ice was thick enough off Western Hudson Bay to support bears hunting successfully for seals by the last day of October. By 7 November, most bears had left for the ice, with only a few stragglers left behind – since they were all in good condition due to a late breakup of the ice this summer, there were remarkably few problem with bears in Churchill and some seemed in no hurry to leave once the shorefast ice started to form.

It’s doubtful that any bears out on that wind-blown ice are in any kind of peril. As long as the ice is thick enough to support their weight, they should be fine – and keeping themselves busy catching seals.

The chart above is from NSIDC Masie for 15 November 2020 (Day 320) – it showed the same large offshore patch of ice the day before. However, only today did the Canadian Ice Service (CIS) chart show even part of the offshore patch (below):

In this case, I’m trusting the Masie chart because it seems the CIS sensors aren’t yet set to pick up ice that’s far offshore, as the detailed stage of development chart for 16 November (below) shows (grey-white ice is 15-30 cm thick, grey ice is 10-15 cm, but see discussion below):

However, after I’d almost given up that we’d hear from Andrew Derocher about his polar bears with still-functioning collars, he posted a tracking map late today (below). Even his chart shows that big patch of offshore ice but he didn’t comment on it at all. It appears that of the 9 collars he deployed on females last year only one is on the ice, well offshore (north of Churchill).

Derocher is still claiming that this is not an early freeze-up year even though it’s clear many bears have already left for the ice and only a few stragglers remain, including most of his collared bears. However, some of his bears are probably pregnant (especially the two furthest inland) and won’t be going anywhere this fall. And we already know that many of Derocher’s collared bears were very late to come onshore in August and having only spent 3 months onshore rather than 4 or 5 months they are used to, may now be in no hurry to leave – especially since they know that seals are to be had out on that ‘very thin’ ice just offshore.

Unfortunately, the Polar Bear Alert Program in Churchill decided not to issue a report for the first week in November (2-8 Nov), so there is no information on the progress of freeze-up and polar bear movements from that authority. There might be one issued tomorrow for the second week (9-15 Nov), if so I’ll post it here.

It’s important to know that even big male bears only need ice that’s about 30 cm thick to hold their weight. And while the newly formed grey ice is technically only 10-15 cm (see the stage of development chart above), the ice offshore this year is very compressed and buckled (see below from 7 November), making it thicker than it might appear on the official ice charts.

 

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.

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Western & Southern Hudson Bay polar bears experience earliest freeze-up in decades

This is shaping up to be one of the shortest ice-free seasons in at least 20 years for both Western and Southern Hudson Bay polar bears.

Hudson Bay sea ice at 2 November 2020. NSIDC Masie chart.

Last week, sea ice started forming along the shore of Hudson Bay, from the north end all the way south into James Bay. So far, the shorefast ice that’s forming is only a narrow strip along the coast but is thickening and becoming broader each day, which means that unless something changes dramatically, the bears should all be on the ice at the end of the week, an exodus from shore that hasn’t happened this early in WH since 1993 (the earliest since 1979).

The last WH tagged polar bear didn’t leave the ice this year until 21 August, which means if it’s on the ice by the end of this week it will have spent only 11 weeks onshore – less than 3 months. Even the first bears that came ashore in mid-July will have only spent about 16 weeks on land – at least a month less than they did a decade ago (Stirling and Derocher 2012). Four months spent ashore was the historical average for Western Hudson Bay bears in the 1970s and 1980s (Stirling et al. 1977, 1999). This year, most polar bears will have spent only about 13-14 weeks on land because they did not come ashore until early August.

UPDATE 8 November 2020: Report from Churchill area polar bear guide Kelsey Eliasson, via Facebook Saturday 7 November: “Most bears have left on the ice – including peanut – but still some stragglers” [Peanut’ is a well-known female who has two cubs this year]. See below for sea ice chart for 8 November shows broadening band of grey ice clearly thick enough to support the weight of adult bears (and the same thing is happening in Southern Hudson Bay):

Hudson Bay North daily stage of development 2020 Nov 8_all grey ice

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My new novel set in the Gulf of St. Lawrence has a surprising twist

My fictional story about sea ice, polar bears and upheaval in 2026 – a followup to EATEN – is coming soon. Prepare for the unexpected.

CTV news_Cathy Erlene sealer heavy ice off North Sydney_Saturday March 28 2009

A video to help set the mood…

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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Churchill problem polar bear report for week 3 and a triplet litter of cubs spotted

Courtesy the Town of Churchill:

Also, note that a mother with a litter of triplets spotted along the coast of Wapusk National Park (just east and south of Churchill) in good condition, 15 September 2020 (see photo below). Biologist Nick Lunn falsely claimed in 2018 that no triplet litters had been born in Western Hudson Bay since 1996 – a correction made later claimed Lunn meant there hasn’t been any triplet litters seen in the fall, which was also not true in 2017 or in 2020:

Compare weekly stats above for this year to a few previous years at the second week in September:

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First polar bear alert report for Churchill an astonishing seven weeks later than last year

The first report of the Polar Bear Alert Program in Churchill, Manitoba was released today (1 September), a full seven weeks later than last year due to many bears remaining on the Western Hudson Bay ice much later than they have done in the past.

2020 Aug 31 - Polar Bear Stats_week 1 jpeg

As I mentioned previously, as long as I’ve been collecting these published reports (2015), there has not been a first report of the season issued later than the second week in July, so this year is really unusual and I suspect similar to the 1980s.

I thought it possible that this was a Covid-related delay getting conservation officers to Churchill but as you’ll see above, that appears not to be the case: there simply have been not enough serious problems with bears in Churchill to warrant sending officers out before last week. No information on the general condition of bears was included this year, as it has been in other years (see below).  Activity this last week in August 2020 was similar to the first week in July 2018.

Polar bear Cape East 0 Wakusp NP _24 Aug 2020 earlier

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Amid crying over low Arctic ice, W Hudson Bay polar bears leave ice as late as 2009

This year, the last collared Western Hudson Bay polar bear to leave the ice left as late, or later, than the last collared bear did in 2009 (which was an unusually late breakup year) and so far, all bears spotted have been in good physical condition despite inhabiting one of the most southern regions of the Arctic. All the while, sea ice experts have been hand-wringing about low Arctic sea ice –– in general and as polar bear habitat.

Polar bear Cape East 0 Wakusp NP _24 Aug 2020 earlier

A female with two yearling cubs on the shore of Wakusp National Park, Western Hudson Bay on 24 August 2020. Taken via livecam from almost a mile away.

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Few bears on the ice off Western Hudson Bay at 14 August but will be onshore soon

Polar bear biologist Andrew Derocher published a tracking map of his collared polar bear females that shows one bear (out of 11) still on the rapidly diminishing ice north of Churchill in Western Hudson Bay – and where there is a collared female, there is almost certainly other bears doing the exact same thing:

Derocher 2020 WHB tracking map 14 Aug_1 bear still on the ice

Without evidence to support such a claim, Derocher (below) assumes this collared female is probably hunting seals. In fact, last year he admitted that most bears on Hudson Bay from at least July onward are unlikely to be successfully hunting seals:

Derocher 2020 Aug 14_1 bear still on the ice at 14 Aug odd behaviour

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Many W Hudson Bay polar bears still offshore at 7 August despite apparent low ice levels

Contrary to all expert expectations, five female polar bears (45%) out of eleven that had tracking collars attached last year were still out on the sea ice that’s lingering along the western shore of Hudson Bay as of 7 August. And if five collared bears are out there, then there are almost certainly many more without collars doing the same thing. This pattern of bears staying out on the ice long after the so-called ‘critical threshold’ of 50% concentration has passed has been going on since at least 2015 and many bears on tracking maps in July and August appear to be on ice that doesn’t exist.

Chukchi Sea polar bear Arctic_early August 2018_A Khan NSIDC small

There are two explanations for this pattern and both are likely true: 1) much more ice actually exists on Hudson Bay than satellites can detect and 2) polar bear experts are wrong that Western Hudson Bay polar bears head to land soon after sea ice concentration drops below 50%. Models that predict a catastrophic future for Western Hudson Bay polar bears (Castro de la Guardia et al. 2013; Molnar et al. 2020) assume that ice coverage of less than 50% in summer greatly reduces polar bear survival. However, if polar bears do not always head to land when sea ice drops below 50% then the models cannot possibly describe their future accurately. In other words, depending on the discredited ‘worst case’ RCP8.5 climate scenario for the most recent polar bear survival model that extrapolates from Western Hudson Bay bear data to many other subpopulations, as I discussed previously, may not be its only fault.

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