Monthly Archives: October 2014

Polar bear habitat update: regional differences, melting vs. freezing

The freeze is on: from an annual low of ~5.1 m sq km at 15 September 2014, the sea ice that provides a hunting platform for polar bears is rapidly reforming.

Note that polar bear habitat world-wide is pretty well defined by the extent of sea ice in spring, with three notable exceptions. There are no polar bears (or fossil evidence of polar bears), in the Sea of Okhotsk, the Gulf of St. Lawrence, or the Baltic Sea.

Bears in some areas spend time on land in late summer/early fall but the amount of time varies widely.

Polar bear distribution and ice extent_PolarBearScience
Have a look at the maps below: the difference in regional coverage between the sea ice at 4 August and 16 October (73 days apart, both covering 7.3 mkm2) might surprise you.
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Churchill problem bears and early breakup dates in WHB: The 1983 & 2004 anomalies

In this part of my critique of Stirling and Parkinson (2006), regarding breakup dates in Western Hudson Bay (see Part I here), I will show that these authors also left out critical data.

Figure 1. A bear is transported to Churchill’s polar bear holding facility, from a 2011 Huffington Post article “Polar Bear Prison.”

Figure 1. A bear is transported to Churchill’s polar bear holding facility, from a 2011 Huffington Post article “Polar Bear Prison.”

Their correlation between number of problem bears in Churchill and breakup dates for WHB worked because some very inconvenient data were simply left out: problem bear data for 1983 and 2004.

Inclusion of that information would have shown 1983 and 2004 were two of the worst years for polar bear problems in recent history despite being late breakup years (1983 also had the last human fatality from a polar bear attack). They could have explained why they did not use the data but they did not — they simply left it out.

Amazingly, this work is being touted as “evidence” that global warming is harming Western Hudson Bay polar bears.
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Where have all the walrus gone?

Yes, I wondered too. After all the kerfuffle at the beginning of the month there’s been rather dead silence [see my last post here]. So I Googled and found some tidbits.

Chukchi Sea walrus, June 2014. US Fish and Wildlife Service.

Chukchi Sea walrus, June 2014. US Fish and Wildlife Service.

An article a few days ago at one media outlet (October 8, 2014) asked someone from the WWF what happened to the ~35,000 females and calves onshore near Point Lay, Alaska — because really, who else would you ask? Or, perhaps more to the point, would anyone at USGS be expected to answer?

And one online media outlet found walrus specialists in Alaska unwilling to lay all the blame for the recent massive haulout at Point Lay at the feet of low Arctic ice levels due to global warming. See what you think.

UPDATE added below October 13, 2014
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Declining polar bear weights and early breakup dates in WHB, Part I: What’s a starving bear?

The oft-repeated claim that polar bears are starving in Western Hudson Bay (e.g., here, here, here, and here) comes primarily from a 10 year old study that documented a declining trend in polar bear body condition (a biology euphemism for relative fatness) between 1980 and 2004, which appeared to correlate with earlier and earlier breakup dates for Hudson Bay.

Figure 1. Polar bear female with cub, 2009, Churchill, Western Hudson Bay. Wikipedia.

Figure 1. Polar bear female with cub, 2009, Churchill, Western Hudson Bay. Wikipedia.

The authors of that study (polar bear specialist Ian Stirling and NASA sea ice researcher Claire Parkinson) reported the body weights of lone female bears captured in Western Hudson Bay between 1980 and 2004. The trend over time in those bear weights was then correlated with the overall change in dates of sea ice breakup on Hudson Bay for that period.

However, it turns out that while the trend of body condition and the trend in breakup dates indeed correlated over time, the actual year to year data did not. The question is, what does that mean for the claim that polar bears in WHB are starving?
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Mass haulouts of female Pacific walrus as a sign of population health

Mass haulouts of female Pacific walrus and their calves in fall don’t happen all the time but they do occur. I recently pointed out (here and here) two instances of such incidents from the 1970s.

I said this provided evidence that the September 2014 incident reported in the media was not “a new phenomenon” for this region, as WWF spokepersons and Alaskan biologists have claimed (reiterated in this PBS interview).

Figure 1. Walrus females and calves hauled out on a beach in Svalbard, photo accompanying an October 6, 2014 news report in “Eye on the Arctic” of the rapidly increasing Atlantic walrus population there. (Photo: Thomas Nilsen/Barents Observer).

Figure 1. Walrus females and calves hauled out on a beach in Svalbard, photo accompanying an October 6, 2014 news report in “Eye on the Arctic” of the rapidly increasing Atlantic walrus population there. (Photo: Thomas Nilsen, Barents Observer).

One aspect of the recent occurrence of a large herd on an Alaskan beach that apparently needs reiterating is that the population of walruses declined rather markedly after a 1970s peak and has rebounded since. This suggests that huge herds of females and calves hauling out on beaches in the fall to feed might only be seen when the population is very large.
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Tracking polar bears in the Beaufort Sea – September 2014 map

Here is the September 2014 follow-up to my post on the July 2013 track map for female polar bears being followed by satellite in the Beaufort Sea by the US Geological Survey (USGS) – “Ten out of ten polar bears being tracked this summer in the Beaufort Sea are on the ice.”

See that post for methods and other background on this topic, and some track maps from 2012 (also available at the USGS website here).

The USGS track map for September 2014 is copied below (Fig. 1).

At the end of September, with sea ice starting to rebuild, it appears there were 8 bears on the ice and three on land.

The situation for September was not very much different from August, except that two of the 11 bears (up from one) were on the ice in the Chukchi Sea in September, a phenomenon that was recently acknowledged to have affected the last population estimate for the Southern Beaufort subpopulation.

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High walrus numbers may explain why females and calves are hauling out in droves

Are the recent mass gatherings of females and calves on the beaches of western Alaska and the Russian Far East a sign that population are again close to the limit the habitat can support, as they were in the 1970s?

At the risk of belabouring the point that lack of sea ice does not seem to be a reasonable explanation for this phenomenon (see my last two posts, here and here, and Andrew Montford’s excellent additions here), I think this is a possibility that needs to be considered.

Walruses at Point Lay Sept 27 2014 NOAA CMDA0007_sm

2014 Point Lay, NOAA photo

Walrus are well protected in the US and Russia, and population numbers have risen again since the 1990s, after significant declines in the early 1900s and again in the 1980s.

A paper from the late 1980s suggests that a return to high population numbers may be a more plausible cause for mass gatherings of females and calves that lead to stampede deaths than does reduced sea ice due to global warming.

Have a look and see what you think. It may not be the only reason but it may be a major contributing factor.

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