Category Archives: Life History

Summer sea ice melt and polar bear maternity dens

The yearly sea ice minimum extent is almost upon us, which has recently been the seasonal signal for excitable biologists and their activist groupies to resume their breathless rants about what sea ice loss could mean for polar bears.

Polar bear den_CreditUSFWS_labeled

Never mind that the summer minimum extent reached in September, no matter how low it goes, is pretty much irrelevant to polar bear health and survival. As I’ve discussed before, what’s really important is the presence of not-too-thick ice during the spring, so they can catch lots of young seals and put on lots of fat.

But to a lesser degree, the extent at mid-to-late summer is important because this is when pregnant females that prefer to make their maternity dens on shore are looking for good places to spend the winter.

So the topic for today is this: how much does the extent of ice at the height of summer dictate where polar bear females make their winter dens?
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Bearded seals in Alaska face no serious threat of reduction, let alone extinction, judge rules

Here’s a significant turn of events involving a story I reported on earlier: a US District Court judge ruled on Friday 25 July 2014 that the Bering/Chukchi Sea population of bearded seal (Erignatha barbatus) was improperly given ‘threatened’ species status in 2012. Judge Beistline ordered the National Marine Fisheries Service (NMFS) to correct deficiencies in its study of the population.

Bearded seals are important secondary prey species for polar bears in some regions of the Arctic (Thiemann et al. 2008), after ringed seals (which were also listed as ‘threatened’ in 2012).


Among other points made in his written decision, the judge is quoted as saying (reported here):

“A listing under the ESA based upon speculation, that provides no additional action intended to preserve the continued existence of the listed species, is inherently arbitrary and capricious.” [my emphasis]

Arbitrary and capricious — now that’s a slap-down. He also reportedly called the ESA listing “an abuse of discretion.”

The question is, how often have other ESA listings – not challenged in court – been based on similarly arbitrary and capricious decisions that also involved an abuse of discretion?

More quotes from Judge Beistline’s decision, and reaction to it, below.
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Tracking polar bears in the Beaufort Sea: June 2014 map

Here is the June 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 June 2004 is copied below (Fig. 1).

Compare this to May’s map (Fig. 2) – the 20 bears from last month are down to 14, and all seven of the bears outfitted with glue-on satellite transmitters in April [either males or subadult animals] have either moved out of the area or their tags have fallen off or stopped transmitting. This means that all of the bears shown on the June map below are females with satellite radio collars.
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Barents Sea polar bear cubs – new data for 2014 made to sound ominous

Last week, Damian Carrington (May 28, 2014) at The Guardian offered a scary-sounding polar bear story, based on the work of Jon Aars and colleagues from the Norwegian Polar Institute (Fewer polar bear cubs are being born in the Arctic islands, survey finds). As often is the case however, once you see the scientific data, you will sleep better.

[Dr Aars also gave a radio interview with CBC Canada (May 29): "Is climate change the cause of lower polar bear birth rates in Norway?"; audio available]

[Update June 24, 2014 — see below]

Female polar bear with cubs. (U.S. Fish & Wildlife Service/AP)

Female polar bear with cubs. (U.S. Fish & Wildlife Service)

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Tracking polar bears in the Beaufort Sea – more bears added to the April 2014 map

Polar bears were tagged in 2013 and 2014 on the spring-time sea ice of the southern Beaufort Sea. Seventeen of these bears have satellite collar transmitters and 7 of these bears have glue-on satellite transmitters” say the folks at the USGS Alaska Science Center.

I guess that’s why the April map was late getting posted.

Polar bear ear tag_USFWS_PolarBearNews2010

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Polar bear habitat update – ice coverage at the beginning of this year’s critical feeding period

Polar bears are all out on the sea ice at this time of year, feeding on new-born seal pups. Here’s a look at what the ice conditions are like at this critical time.

Polar_Bear_male on sea ice_Alaska Katovik Regehr photo_April 29, 2005_sm labeled

end April extent NSIDC May 4

The ice extent is still well within two standard deviations from the 1981-2010 average, which indicates no deviation from natural variation, as the graph (below) for May 1, 2014 from the US National Snow and Ice Data Center (NSIDC) shows.

Sea ice extent 2014 May 1_NSIDC_graph

Between the official spring maximum (according to the NSIDC ) on March 21, with a total extent of 14.8 million km2, the ice slowly retreated in some regions and increased in others, while most regions remained pretty much the same. This is an important reminder that the Arctic as a whole is not a homogeneous region but one with marked regional variation.

As has been noted elsewhere (Sunshine Hours), ice in the Greenland Sea (habitat of ‘East Greenland’ bears) and the Barents Sea both increased in extent over this period. Bering Sea ice (habitat of southern ‘Chukchi Sea’ bears) declined markedly but Baffin Bay/Gulf of St. Lawrence ice (habitat of ‘Davis Strait’ bears) declined much less, as NOAA’s MASIE maps copied below show very well.

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Current ice conditions don’t bode well for Beaufort Sea polar bears

Thick spring ice along the shore of the Eastern and Southern Beaufort is bad news for polar bears, especially females emerging from their dens with new cubs. Are those conditions developing now?

Beaufort Sea pressure ridges_Spring 1949 wikipedia sm

Every 10 years or so, since at least the 1960s, nearshore ice gets too thick for ringed seals to maintain their breathing holes and many breeding seals depart the area. This leaves a lot of polar bears without the baby seals they need to consume to get them through the rest of the year (that’s if they don’t (or can’t) leave themselves).

I’ve discussed various aspects of this phenomenon before, with references – see the list at the end of this post.

Sadly, we are on schedule for such conditions to recur – could be this year, could be next. The last time of heavy spring ice was 2004 and previous heavy ice conditions occurred the springs of 1964, 1974 (the worst), 1984, 1992 and 2004. The 2004-2006 event was reportedly almost as bad as the 1974-1976 event.

So, prompted by reports of the heaviest sea ice conditions on the East Coast “in decades” and news that ice on the Great Lakes is, for mid-April, the worst it’s been since records began, I took a close look at ice thickness charts for the Arctic. I’m not suggesting these conditions are necessarily related to Beaufort ice, just that they got me thinking.

Here’s a screencap of the US Navy ice thickness animation chart for yesterday [from WUWT Sea Ice Page]

Figure 1. Arctic Sea Ice Thickness (NRL), for April 18, 2014. Look at thick ice (yellow, 3.5-4.0 meters thick) spreading along the north coast of Alaska. See the 30 day animation here.

Figure 1. Arctic Sea Ice Thickness (NRL), for April 18, 2014. Look at thick ice (yellow, 3.5-4.0 meters thick) spreading along the north coast of Alaska. See the 30 day animation here.

Below is a similar image from about the same time last year, with the Southeast Beaufort Sea marked.

Figure 2. Arctic Sea Ice Thickness (NRL), for April 13, 2013. Southeastern Beaufort marked.

Figure 2. Arctic Sea Ice Thickness (NRL), for April 13, 2013. Southeastern Beaufort marked.

I don’t think this bodes well for Beaufort bears but we’ll have to wait and see if there are any reports of starving bears bit later this spring and summer. Sea ice charts aren’t a guarantee that this heavy spring ice phenomenon is developing in the Beaufort, but they could be a warning.

Below are archived ice thickness charts from the US National Snow and Ice Data Center (NSIDC) for some previous years when Beaufort bears had trouble, especially 2004-2006, with which I compare this year’s conditions. [h/t Steve Goddard for alerting me to this resource]

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