Tag Archives: body condition

Churchill problem polar bear report for week 3, July 23-29 2018

Polar bears that have come off the sea ice of Hudson Bay near Churchill, Manitoba in Western Hudson Bay are apparently in a wide variety of conditions, from very fat to skinny.  So, not all skinny despite the relatively early breakup of ice in the northwest.

Churchill PB reports_week 3_ July 23-29_July 2018

Most of the ice was gone from the NW of Hudson Bay for the week of 23 July 2018 and the graph below shows that this is a new pattern that began in 1997, with only 2009 being an outlier:

Hudson Bay NW same week_ ice coverage 23 July 1971-2018 with trend

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Hansen’s 1988 climate change testimony was the answer to Stirling’s polar bear problem

Last week’s media coverage made me realize that James Hansen’s testimony to a US Senate committee in 1988 provided well-timed answer to a vexatious problem facing polar bear biologist Ian Stirling. Thirty years ago, Stirling was struggling to understand why polar bear productivity in Western Hudson Bay had dropped.  He was ripe for the suggestion from Hansen (and his follow-up paper) that human-caused global warming could be the explanation. An interview with Stirling and colleague Andrew Derocher published in 2016 helps connect the dots.DA-IS-measuring_Ian Stirling

Many bears were in poor condition in the fall of 1983 (Calvert et al. 1986:19, 24; Ramsay and Stirling 1988). In general, the 1980s saw weights of bears decline and cub mortality increase, with a marked increase in the loss of whole litters over what had been documented in the 1960s and 1970s (Derocher and Stirling 1992, 1995).

Until Hansen and climate change came along,  density-dependent effects (such as the number of bears out-pacing food supply) were seen as the most likely explanation. But sea ice decline blamed on human-caused global warming was suddenly a new possibility that Stirling soon embraced (Stirling and Derocher 1993). By the late 1990s, sea ice coverage on Hudson Bay had indeed declined but the correlation with polar bear productivity produced a weak trend that was not statistically significant (Stirling et al. 1999).

The 1999 Stirling paper did not provide scientific evidence to explain the 1980s decline in productivity as much as it presented a novel scapegoat to blame when a more plausible explanation could not be made.

Bottom line: Global warming could not have been the proximate cause of the productivity changes in WH polar bears documented during the 1980s but Stirling spent the next two and a half decades vigorously pushing climate change as the cause of all polar bear ills. Continue reading

Svalbard polar bear data 2016 through 2018 shows no impact of low ice years

Last week, the Norwegian Polar Institute updated their online data collected for the Svalbard area to include 2017 and 2018 — fall sea ice data and spring polar bear data. Older data for comparison go back to 1993 for polar bears and 1979 for sea ice, showing little to no impact of the reduced ice present since 2016 in late spring through fall.

Svalbard polar bear_NP015991-isbjorn-JA

Here’s what the introduction says, in part [my bold]:

“…The polar bear habitat is changing rapidly, and the Polar Basin could be ice-free in summer within a few years. Gaining access to preferred denning areas and their favourite prey, ringed seals, depends on good sea ice conditions at the right time and place. The population probably increased considerably during the years after hunting was banned in 1973, and new knowledge indicates that the population hasn’t been reduced the last 10-15 years, in spite of a large reduction in available sea ice in the same period.”

See Aars et al. 2017 for details on the 2015 Svalbard polar bear population count, keeping in mind that the subpopulation region is called “Barents Sea” for a reason: only a few hundred individuals currently stick close to Svalbard year round while most Barents Sea bears inhabit the pack ice around Franz Josef Land to the east (Aars et al. 2009; Crockford 2017, 2018).
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Critical evidence on W Hudson Bay polar bears still not published after 25 years

Polar bear researchers have been doing capture/recapture studies in Western Hudson Bay for decades yet most of the data claimed to be critical for assessing effects of human-caused global warming on this species have not been published. I raised this point in one of my early blog posts (27 Sept 2012) but the situation has not changed in 6 years. Here’s an update.

Derocher in the field in WH_CBC story 2016

From CBC story 14 Sept 2016.

Years ago now, in an oft-cited paper, Stirling and Derocher (2012) claimed to summarize the evidence that climate warming was negatively impacting polar bear health and survival. Several life history parameters were considered crucial, particularly body condition.

Despite almost a dozen papers (and perhaps more) on various aspects of WH polar bear health and life history studies based on capture/recapture data published since 2004  (e.g. Castro de la Guardia 2017; Lunn et al. 2016; Pilfold et al. 2017), none have reported the body condition data that supposedly support the claim that sea ice loss is having a severe impact — and the same is true for litter size, proportion of independent yearlings, and cub survival.1

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Problem polar bears of Churchill: first report of the season similar to 2016

The first activity report of the Churchill Polar Bear Alert Program has been released for 2017. It comes on the same week as last year’s (so about the same dates for first bears ashore both years), and reports pretty much the same activity.

Churchill PB reports_week 1_ July 10-16_July 2017

Odd that this year’s report contains no mention whatsoever of the condition of the bears as did last year’s (see below), which may have brought criticism for spoiling the media ‘message’ that WHB bears are suffering because of reduced sea ice. Better no comment at all than good news, eh?

Sea ice for the week of 10 July off Western Hudson Bay this year consisted of a broad strip of thick first year ice (>1.2m thick) just off shore.

Hudson Bay weekly ice stage of development 2017 July 10

The ice charted above looked like this on a standard ice map:

Sea ice Canada 2017 July 11

There are no other reports that I could find of polar bears ashore along the coast of Western Hudson Bay, so these bears must be the first wave.

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Much more sea ice in NW Hudson Bay this year than 2016 or 2015 at 27 May

In recent years, sea ice loss over Hudson Bay has begun with open water in the NW corner (which is just as likely due to prevailing offshore winds as ice melt) rather than along the east coast but this year that patch of ice is smaller than its been for the last two years. In addition, despite two patches of open water at either end of the Beaufort Sea, most of the coast of Alaska is still covered in thick ice — much more than existed last year, yet masses of polar bears did not die as far as I know (actually, WHB bears came ashore in excellent condition last year).

Sea ice Canada 2017 May 27

Compare to previous years:

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Polar bear mating season winds down with lots of sea ice habitat available

Habitat for polar bears is abundant worldwide as the prime feeding season passes its peak and mating season for sexually mature bears winds down.

JR1_1266.tif

Battle among polar bear males for the right to mate, from this 2011 DailyMail story here.

There is much more ice than usual around Svalbard in the Barents Sea and off Newfoundland and southern Labrador, home to ‘Davis Strait’ bears. There have been no media reports of polar bears onshore anywhere (since the third week of April in Newfoundland and late January in Svalbard).

Sea ice map below for 12 May 2017:

Svalbard ice extent 2017 May 12_NIS

Compare the extent and concentration of ice around Svalbard above (at 12 May 2017) to conditions that prevailed on the same date in 2015 (below), considered a “good ice” year for local polar bears (and the year of the last population size count which registered an increase over the 2004 count):

Svalbard ice extent 2015 May 12_NIS

There hasn’t been this much ice in the area at this point in the season for many years, especially to the north of Svalbard, and levels since late April have been above even the long-term average (disregard the huge downward blip, which is clearly a sensor malfunction of some kind):

Svalbard ice extent 2017 May 12 graph_NIS

In fact, ice is pretty solid throughout the Barents Sea and East Greenland at this time:

Barents Sea ice extent 2017 May 12_NIS

Across the Atlantic, the situation is similar, with unseasonably heavy sea ice off eastern North America and the Southern Beaufort Sea.

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