Here is a look at what polar bear habitat looks like this year at the end of May compared to previous years. It helps put any predictions of impending doom into perspective.
This is the time year when declining sea ice gets some people all worked up. However, declining ice is normal at this time of year and there is always variation in where the most open water appears first. At this time of year, there isn’t much ice ‘melt’ going on. Rather, what we are seeing is the opening up of shore leads and polynyas by winds.
The administrative reports used in 2007 to support the decision to list polar bears as ‘threatened’ under the US Endangered Species Act (ESA) in 2008 disappeared from the US Geological Survey website several years ago. I have archived them here in pdf format to make them easy to find for anyone wishing to access the accuracy of the models, data, and assumptions made in 2007.
Steven Amstrup in 2005, then lead USGS polar bear biologist, with triplet cubs, Prudhoe Bay, AK.
This is a housekeeping post meant for future reference. I’ve included citations for the relevant sea ice projection papers used in the models presented in the 2007 documents and a few other related reports from the same time period. Continue reading
Posted in Conservation Status, Sea ice habitat
Tagged ACIA, Administrative report, Amstrup, Beaufort Sea, Bergen, DeWeaver, Durner, ESA, Executive Summary, Hassol, Holland, Hunter, listing decision, Obbard, polar bear, projections, Regher, Rode, Schliebe, Science Strategy to Support, sea ice, Solomon, Stirling, US Fish and Wildlife Service, us geological survey, USGS, Zhang
The really significant content of a new paper being heavily-hyped by the media1 is what wasn’t said rather than what the authors discovered about metabolic rates and weight maintenance of a small sample of nine Southern Beaufort Sea bears in 2014 to 2016 (Pagano et al. 2018; Whiteman 2018).
This paper does not document starving or dying bears but merely found some (5/9) that lost weight when they should have been gaining, given that early April is the start of the ringed seal pupping season (Smith 1987) and the intensive spring feeding period for polar bears (Stirling et al. 1981).
The question is, why were Southern Beaufort Sea polar bears off Prudhoe Bay (see map of the study area below), still hunting and capturing only adult and subadult ringed seals from sea ice leads when newborn ringed seal pups and their mothers should have been plentiful and relatively easily available in their birth lairs on the sea ice (see below)?
“Using video collar data, we documented bears’ hunting behavior and foraging success. Bears used sit-and-wait tactics to hunt seals 90% of the time, and stalking comprised the remaining 10% of hunts (movies S1 to S4) (19). Bears that successfully killed and ate adult or subadult ringed seals either gained or maintained body mass, whereas bears that only scavenged or showed no evidence of eating lost mass.”
There was no discussion in the paper of ringed seal birth lairs, or sea ice conditions at the time of the study, but several mentions about what might happen in the future to sea ice and potential consequences for polar bears. The press release did the same.
However, as you’ll see by the sea ice thickness maps below, there may be good reason for the lack of ringed seal lairs, and a general lack of seals except at the nearshore lead that forms because of tidal action: the ice just a bit further offshore ice looks too thick for a good crop of ringed seals in all three years of the study. This is reminiscent of conditions that occurred with devastating results in the mid-1970s and mid-2000s (Burns et al. 1975; Cherry et al. 2009; Harwood et al. 2012, 2015; Pilfold et al. 2012; Stirling 2002, Stirling et al. 1987). Those events affected primarily bears in the eastern half of the Southern Beaufort and were almost certainly responsible for the recorded decline in SB bear numbers in the 2001-2010 survey (Bromaghin et al. 2015; Crockford 2017; Crockford and Geist 2018).
It seems very odd to me that Pagano and colleagues suggested no reasons for the unexpectedly poor showing of polar bear hunting success during their study except a bit of hand-waving about higher-than-we-thought metabolic rates in the bears. For years, I’ve worried that the inevitable next episodes of thick Southern Beaufort spring ice would cause problems for polar bears and seals but we wouldn’t know it because whatever effects were documented would be blamed on reduced summer ice: I suspect that time may have come.
Figure 1 from Pagano et al. 2018 cropped to show only the study area off Alaska.
Posted in Advocacy, Conservation Status, Sea ice habitat
Tagged Beaufort Sea, climate change, global warming, polar bear, sea ice, starving, struggling, survival, threatened, trouble, USGS, wasting, worse than we thought
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).
Compare to previous years:
Arctic sea ice is spreading out quickly from its central basin summer refuge – according to this NSIDC Masie ice chart, it has already grown more than 2 mkm2 beyond the annual minimum reached in early September. Ice is already pushing south into the eastern Beaufort and the archipelago of Franz Josef Land in the Barents Sea.
Over the next couple of weeks, shorefast ice will start forming along the coasts of North America and Eurasia (see the first bits off Alaska in the 21 October CIS map below), which will eventually meet the expanding Arctic Basin pack to fill the Basin and Canadian Arctic Archipelago with ice – as it has done for eons.
The evidence from the last decade or so suggests that by the end of October, most of the Arctic north of the 79th parallel (see map below) will be filled with ice – although the Chukchi Sea (north of the Bering Strait) may not fill until sometime in November:
Polar bears usually resume hunting as soon as sea ice conditions permit in the fall, since it’s their last chance to top up their fat reserves before the dark and cold of winter when hunting may become next to impossible.
I’ve copied ice charts from the Masie archives for some previous years at 31 October below.
Posted in Life History, Sea ice habitat
Tagged 79th parallel, Arctic, Barents Sea, Beaufort Sea, Canadian Arctic Archipelago, Chukchi Sea, fall ice growth, hunting, MASIE, NSIDC, platform, polar bears