Tag Archives: Hudson Bay

Longest-swimming polar bear lost less weight than if she had stayed onshore

Recent media hype over swimming polar bears in the Southern Beaufort has been quite spectacular (still going strong today at the Washington Post here) but a close look at relevant data shows the message is bogus. Researchers admit (in their methods section) they couldn’t tell if bears said to have swum “non-stop” actually hauled out for half a day or more to rest on small ice flows invisible to satellites and astonishingly, the bear getting all the media attention – who swam the longest of any bear – lost less weight than a bear would have done simply sitting on shore for the same length of time.

Washington Post_swimming polar bears_snapshot 21 April 2016

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Most Beaufort polar bears swim from ice floe to floe during breakup, study shows

swimming3_USGS

You may have seen the headlines in Canadian news outlets over the last 2 days.
“Polar bears swimming farther as sea ice recedes, study shows”

“Melting sea ice forces polar bears to swim longer, farther: study”  [“Bear biologist Andrew Derocher says the forced swims are particularly hard on mothers with young cubs”]

“Polar bears swimming longer, farther because of melting sea ice, study finds”

Oddly, none of the above news reports said where the paper was published or mentioned the name of the lead author – only University of Alberta co-author Andrew Derocher was interviewed (see the only press release I could find here, issued by the San Diego Zoo where the lead author is now employed).[update: CBC ran another story a day later that corrected these omissions]

But what did the study actually say?

Significantly, no bears died while swimming during the two lowest sea ice extent summers since 1979 and no evidence was presented that swims were “particularly hard on mothers with young cubs.” The quotes from the paper below sum it up for Beaufort Sea (BS) bears (the inclusion of Hudson Bay (HB) bears in this study seems gratuitous and potentially misleading, since only a few swam anyway – only 15 out of 59):

“….91% (91/100) of the swims in the BS occurred before the annual September minimum sea ice extent had been reached.  In the BS, 81% (29/36) of swims started and ended in pack ice…

So, despite what may be implied during media moments, Beaufort Sea polar bears were  not frantically trying to reach the sea ice from land so that they could attempt to keep feeding over the summer – most of their swimming was done during breakup in July and August from one bit of pack ice to another and they showed no evidence of harm from doing so. Map from the study and more quotes below.
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Hudson Strait and Davis Strait polar bear habitat highest since 1993

Sea ice development over Hudson Bay, Hudson Strait, and Davis Strait has been rather unusual this year but what that might mean for polar bears over the coming winter and spring is hard to tell.

Canadian Arctic Dec 11 2015_CIS

Note: The Canadian Ice Service seems to be in the process of updating its sea ice page and graphing features that used to be available weekly on Thursday have not been available until the following week. This means the most recent graphs available are for the week of 11 December (see below).
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Polar bear habit update – day 333 Arctic sea ice hits 11.1 mkm2

It’s just past the height of fall in the Arctic (Oct-Dec) and polar bear habitat is expanding day by day: according to NSIDC Masie ice charts, the ice has now surpassed 11 mkm2 in extent. Fall is the second most important feeding period for polar bears after spring.

masie_all_zoom_4km 2015 day 333_Nov 29

Only the Barents and Kara Seas (north of Norway and western Russia) are short of ice right now, similar to conditions seen in the fall of 2013. Last fall (2014), conditions were much better and as a consequence, researchers saw a lot of females with healthy cubs in the spring of 2015.

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Polar bear habitat update – Arctic sea ice today covers same area as it did on June 30

Arctic refreeze is well underway. Less than half way through the Arctic autumn (Oct-Dec), polar bear habitat on 11 November 2015 covered the same total area as it did on the last day of Arctic spring (April-June); it’s just distributed differently.

polar_bear_usfws_no date_sm

Yesterday, courtesy NSIDC Masie

masie_all_zoom_4km_2015 Nov 11

Here is what 30 June 2015 ice extent looked like, with the same amount of ice coverage:

masie_all_zoom_v01_2015181_4km

For the week of 12 November, Hudson Bay sea ice development is well underway, with more ice in the north than there has been in many years; Davis Strait ice is the highest this week since 1999 and Baffin Bay ice coverage is above average. Foxe Basin and the Beaufort Sea are both approaching maximum coverage, which means bears there will be back out on the ice hunting. Chukchi Sea ice has finally surrounded Wrangel Island but the Svalbard Archipelago in the Barents Sea is still ice-free. More ice maps and charts below.
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Hudson Bay freeze-up moving faster than recent years, WHB polar bear habitat imminent

There may not be ice for Western Hudson Bay polar bears to walk on yet but there is still more ice forming along the northwest shore of the bay than last year at this time or even the year before. The Canadian Ice Service (CIS) map for 5 November shows this early formation.

Canadian Arctic Nov 5 2015_CIS

What’s present is mostly grey ice defined by CIS as:

“Young ice 10-15 cm thick, less elastic than nilas [a kind of new ice] and breaks on swell. It usually rafts under pressure.”

Polar bears generally need ice about 30 cm thick to support their weight, which could take a day or two – or a week or two, depending on the weather in northwestern Hudson Bay. For Churchill, along the central coast of western Hudson Bay, ice thick enough for walking will not likely be far behind, given the long-range forecast of freezing weather. In recent years, most Churchill polar bears have left the ice by around 20 November. More maps and graphs for this week below.
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2015 may be the earliest in many years that W. Hudson Bay polar bears head for the sea ice

Great news for Western Hudson Bay polar bears! Following up from sea ice conditions last week, CIS maps show ice forming all along western Hudson Bay – not a huge amount, but the beginning of the end of the ice-free season, which recently has not occurred until mid-November (Cherry et al. 2013).

Canadian Arctic Oct 29 2015_CIS

There is above-average sea ice coverage in Foxe Basin and Davis Strait, and only slightly below average coverage in the Beaufort Sea (see graphs below). Polar bear habitat is shaping up very nicely indeed across Canada and the US this year.
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