Tag Archives: Rode

Terrestrial food fight amongst polar bear researchers reflects political differences

With a few big guns on one side and some fringe folk on the other, a dichotomy of opinion has developed amongst polar bear researchers regarding whether or not consumption of land-based foods is making a difference to polar bear survival (or is likely to in the future).

Polar bears eating terrest foods WHB_Rockwell press release

It’s been going on for a while now. Last year, two US Geological Survey members of the IUCN Polar Bear Specialist Group (PBSG) apparently got fed up with the scatter-shot of papers promoting terrestrial foods as a possible salvation for polar bears (e.g. Iles et al. 2013;  Iverson et al. 2014; Rockwell and Gormezano 2013a, 2013b). In April, they published a canon volley of a paper meant to blow all that ‘polar-bears-might-survive’ talk out of the water once and for all (Rode et al. 2015).

Note that although the PBSG didn’t bother to update their website with the IUCN Red List assessment when it came out last November, they had a link up to the USGS terrestrial feeding paper within 16 days (with an editorial summary in the “NEWS” section as well as a listing of the paper in the “RECOMMENDED READING” section). As I suggest below, this difference in treatment may not be a coincidence.

However, another group of non-PBSG researchers  haven’t given up just yet, as shown by the title chosen for the most recent news report (Alaska Dispatch News, 16 June 2016) on the just-finished International Bear Conference:

Want to know how a changing climate is affecting polar bears? Look at what they’re eating.

Apparently, Jeff Welker, a University of Alaska Anchorage researcher who is co-author on two recent papers on the subject of polar bear consumption of terrestrial foods (Tartu et al. 2016 and Rogers et al. 2015), gave a presentation at the conference that raised this topic yet again. His talk came on the heels of an earlier presentation by Todd Atwood, who suggested Southern Beaufort polar bears might benefit from staying onshore to eat left-over whale scraps instead of staying on the sea ice during the summer (even though he had no data to support that opinion – as I discussed in this post).

Here’s the question: is this dispute really about what polar bears eat or don’t eat when they’re on land – or is it symptomatic of the underlying politics of polar bears? [CBC documentary video by that name here]
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Melt season update – Bering Sea ice abundant & Davis Strait ice 2nd highest since 1971

Polar bear habitat in the eastern Bering Sea has expanded since the official spring “maximum extent” was called for late February, and Davis Strait sea ice is tied for 2nd highest since 1971 for this week. Both regions have healthy polar bear populations and spring conditions suggest this will continue into this year.

Rode and Regehr 2010_Chukchi_report2010_Fig1_triplets_labelled

Although the melt season is underway, as of yesterday (22 April, Julian day 112) overall Arctic sea ice extent (Fig. 1) was higher than it was on the same date in 2014, 2007, and 2004 (see also Fig. 2). Despite the record low extent in February (Fig. 3), that pessimists at Polar Bears International suggested was relevant to polar bear heath and survival, I showed that was misleading.

Figure 1. Sea ice extent at 22 April (Julian day 112) for 2015, at 13.976 mkm2, was well within 2 standard deviations and higher than 2007 (shown) as well as 2004 and 2014 (not shown – see it for yourself here).

Figure 1. Sea ice extent at 22 April (Julian day 112) for 2015, at 13.976 mkm2, was well within 2 standard deviations and higher than 2007 (shown), as well as higher than 2004 and 2014 (not shown – see it for yourself here). Click to enlarge.

Sea ice maps and charts tell the story of current polar bear habitat throughout the Arctic.
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Polar bear consumption of terrestrial foods – new paper misses the point

A new paper by polar bear biologists (Rode et al. 2015) argues that terrestrial (land-based) foods are not important to polar bears now and will not be in the future – a conclusion I totally agree with – but they miss the point entirely regarding the importance of this issue.

Fat bears on land in the Southern Beaufort, Sue Miller photo, well-prepared for a brief summer fast.

Whatever food polar bears consume in the summer – whether they are on land or on the ice – doesn’t really matter. What matters is how many fat-rich seals they can consume between March and June each year. The fat put on in late winter/spring from gorging on baby seals carries polar bears over the summer, no matter where they spend it.

USGS polar bear biologist Karyn Rode and colleagues (press release here) have tried to frame this issue as one about future survival of polar bears in the face of declining sea ice. However, the fact that polar bears in the Chukchi Sea and Southern Davis Strait are thriving despite dramatic declines in summer sea ice (aka an extended open-water season), proves my point and disproves their premise. Bears in these regions are doing extremely well – contrary to all predictions – because they have had abundant baby seals to eat during the spring (see here and here).

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If summer ice was critical for S. Beaufort polar bears, 2012 would have decimated them

Did we hear a huge hue and cry in 2013 about starving polar bears and low cub survival in the Southern Beaufort Sea? No, we did not. Despite the record-breaking low summer sea ice extent the year before (2012), and despite the fact that USGS biologists were putting collars on polar bear females there the spring of 2013 (Rode et al. 2014), we heard not a peep about a polar bear catastrophe in the Southern Beaufort. Odd, isn’t it?

Sea ice extent 2012 Southern Beaufort_PolarBearScience

Several polar bear biologists and sea ice experts were busy late last fall suggesting to the media that a decline in polar bear numbers in the Southern Beaufort was due to declines in summer sea ice, which they blamed on global warming (see quotes below and earlier discussions here, here and here). However, they made no mention of the fact that the record-breaking September ice extent in 2012 did not seem to have any noticeable effect on polar bear health or survival in 2013.

Sea ice maps from the National Snow and Ice Data Center (NSIDC) tell most of the story about what the media were, and were not, told about summer sea ice in the Southern Beaufort between 2001 and 2013.  Continue reading

Polar bear biologists miss the mark in new study on invasive mark-recapture effects

Apparently, some biologists think that outputs from complex computer models will convince native Arctic residents that invasive mark-recapture work has no long-term effect on the health and well-being of polar bears.

 Photo by Jake Steven Arnatsiaq. Original here.


Photo by Jake Steven Arnatsiaq. Original here.

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Recent S. Beaufort polar bear count was a cherry-picked result – new evidence

New evidence has come to light that mark-recapture field work used to calculate a new population estimate for Southern Beaufort polar bears did not conclude in 2010 as implied in a widely-publicized paper last month but continued until 2013.

Amstrup w triplet_Prudhoe Bay 2005_USGS_sm

Steve Amstrup in S. Beaufort, 2005 (USGS photo), co-author of Rode et al. paper.

As I discussed previously, last month’s widely-hyped paper (Bromaghin et al. 2015 in press) – which reported a decline of ~40% between 2004 and 2010 (based on spring mark-recapture work) – was contradicted by fall survey counts that suggested strongly a population rebound would have been apparent if the mark-recapture work had continued another two years.

A new paper by Karyn Rode and colleagues (which includes Bromaghin and others (e.g. Amstrup) from the previous paper), summarized in a USGS press release issued on Monday and published online Tuesday, utilized comprehensive data collected during mark-recapture work carried out in spring from 1982 to 2013 in the Southern Beaufort Sea.

This new paper used the same kind of comprehensive data as Bromaghin and colleagues – from the same season, in the same region – to assess potentially negative effects of the mark-recapture research method itself, up to 2012 and beyond.

More on the Rode et al. conclusions later1 – for the moment, what is important is that the work described in the paper confirms that spring mark-recapture work on polar bears in the Southern Beaufort continued beyond 2010. Bromaghin and colleagues didn’t end their mark-recapture work prematurely — they actually left data collected in 2011 and 2012 out of their population estimate analysis when they had to have known the population had not finished rebounding from the 2004-2006 decline.
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Graphing polar bear population estimates over time

I’ve already commented on the 2013 update of polar bear population status released by the IUCN Polar Bear Specialist Group (PBSG).

However, I thought it might be interesting to graph the changes in global population estimates over time (from 1981-2013) — not just the actual estimates from PBSG status tables (with their min/max error ranges) but those totals plus the so-called “inaccurate” estimates that the PBSG have dropped from their accounts in recent (2005-2013) assessments: Chukchi Sea, East Greenland, Queen Elizabeth Islands (now known as the “Arctic Basin”), and Laptev Sea.

In 2001, those “inaccurate” estimates contributed 5,000-5,400 bears to the global total, but now they’re gone — no bears from those regions contribute to the official totals listed on recent PBSG status tables.

Adding those dropped estimates back into the global totals makes it possible to generate a graph in which the global estimates are truly comparable over time.

To see how the dropped estimates influenced the perception of population change over time, I’ve also graphed the estimates given by the PBSG in their status tables. I’ve combined the two into one image (Fig. 1, click to enlarge) to make comparison easy.

UPDATE 5 December 2014: Links to more recent posts relevant to this issue added below. The most recent numbers, added 31 May 2015, are here.
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