Western Hudson Bay polar bear numbers are stable, no trend in ice breakup or freeze-up

This needs saying again: the latest study on Western Hudson Bay polar bears reveal the population has been stable since 2004 and there has been no significant trend in either breakup or freeze-up dates since 2001.

Triplets in Wapusk NP from McCall webpage 2013

Environment Canada and the IUCN Polar Bear Specialist Group concur that the current size of the WHB subpopulation is about 1030 bears. Documents found online indicate a new version of the 2013 WHB mark-recapture report (Lunn et al. 2013) is now available (Lunn et al. 2014) and that a new population survey is planned for 2016. A 2013 story based on false information produced by The Guardian that is still in circulation should be retracted.

A few days ago, reminded by a recent The Guardian article (see below), I went looking for the 2013 government report on the WHB subpopulation (Lunn et al. 2013) at Environment Canada, just to see if it had been posted since the last time I looked. It had not; it is still only available in the form provided to Inuit groups in 2014 as part of community hearings. As a consequence, it was available to the public in 2014 but only if you knew where to look.

However, my Google search last week revealed that a revised version of this report was posted at the US Geological Survey (USGS) website in June 2015, on the web page of report co-author Sarah Converse, with a July 2014 publication date. This American website appears to be the only place this 2014 version of the report is available.

The 2014 version of the 2013 report looks to be the draft of the paper destined for publication and it has changed substantially, mostly in the amount of scientific jargon and ambiguity inserted.1

Lunn et al. 2013, 2014. Map of study area.

This study area map is Figure 1 from Lunn et al. 2013, 2014. The 2011 mark-recapture study (Lunn et al. 2013, 2014) did not include bears from Areas A or D, and only a few from Area B. The 2011 aerial survey (Stapleton et al. 2014) covered Areas A-D. This is why the estimate of 1030 from the aerial survey is considered the most accurate assessment.

Figure 1. This is Fig. 8 from Lunn et al. (2013), the most recent report on the estimated size of the Western Hudson Bay polar bear population.

This is Fig. 8 from Lunn et al. (2013, 2014), the most recent report on the estimated size of the Western Hudson Bay polar bear population showing no declining trend since 2004. Click to enlarge.

Lunn et al 2013 breakup freeze up dates marked

Here are some relevant quotes from the 2014 version of the WHB mark/recapture report [pg. 21]:

“Our updated analysis suggested that the growth rate of the WH subpopulation has, overall, been negative since capture‐recapture studies began in the mid‐1980s, and has been relatively stable over the last decade (Figure 8). The major driver of population change for female polar bears was the timing of sea ice break‐up and formation, which was correlated from year‐to‐year with survival of all age and reproductive categories of females, but not with annual reproductive rates (cub production and survival to first autumn). In contrast, the survival of male polar bears was not closely linked to sea ice, but was instead primarily a function of their age class.

The matrix projection model results suggest that the lack of a negative trend in spring sea ice break‐up date from 2001‐2010 resulted in a stable female population, and this was generally supported by the relatively stable abundance estimates, suggesting consistency between these two different (but not independent) methods of inference.

Evidence for the dependence of the WH subpopulation on sea ice conditions, combined with forecasts of decreasing duration and extent of ice cover in southern and western Hudson Bay from regional climate models (Joly et al. 2011), suggests that the long‐term population trend is likely to be negative. However, our results suggest that the WH population is able to respond positively when climatic and sea ice conditions improve; assuming that the abundance and availability of prey populations also respond similarly. [my bold]

Regarding the WHB count from the 2011 aerial survey (Stapleton et al. 2014), they said [pg. 23]:

Comparison of the 2011 point estimate of 806 (95% CI =653‐984) from this study with the estimate of 1030 (95% CI = 754‐1406) from the 2011 aerial survey requires careful interpretation. The aerial survey likely provides an accurate “snapshot” estimate of the total number and distribution of polar bears in the WH management area at the time of the survey. This differs from the point estimate of population size from capture-recapture models, which represents the group of bears with a non‐zero probability of moving through the capture‐recapture sampling area (a much smaller area than that covered by the aerial survey; defined as the “superpopulation”; e.g., Williams et al. 2002). Furthermore, the 2011 population size estimates from the two approaches cannot definitively be said to be different, as evidenced by overlap in their confidence intervals. We suggest that considering results from the capture‐recapture and aerial surveys together, keeping the strengths and limitations of each method in mind, provides a more complete picture of the distribution, status, and trend of the WH population.” [my bold]

In other words, they found that sea ice conditions in Western Hudson Bay have been stable since 2001 and the population has also been stable. Survival of female bears correlated with changes in sea ice conditions but survival of male bears and cubs did not. Sea ice changes were also not correlated with cub production.

The study did not examine litter size or body condition correlations with sea ice. That means any comments made by polar bear biologists or activist organizations regarding current trends in body condition or litter size for Western Hudson Bay polar bears are conjecture or based on out-of-date information.

Finally, note that this mark-recapture study did not produce a definitive new estimate of the size of WHB subpopulation. Their study surveyed only a small portion of the WHB population region (see map above) – it did not include animals from the entire territory as other studies have done. The Canadian government and the IUCN PBSG (see screenshot below) have chosen to use the aerial survey results (i.e., 1030) as the official WHB population size estimate because it was more complete.

IUCN PGSG WHB population status_10 Oct 2015

In other words, all that capture-recapture effort from Lunn and colleagues in 2011 did not produce results comparable to previous studies and as a result, it has limited scientific value.  Which brings me to the next point – that another population estimate study is planned for 2016.

My Google search also found a letter from Canadian Wildlife Service Director General dated 14 November 2014 (PDF HERE) confirms that 1030 is the estimate they are using for the WHB population and reveals that a new survey of both Western and Southern Hudson Bay polar bear populations is planned for 2016.

“As you are aware, the results of the 2011 Western Hudson Bay aerial survey have recently been published and provide a population estimate of 1,030 (95% CI: 715-1,398) bears. The Environment Canada study noted above reports a 2011 population estimate of 806 (95% CI: 653 – 984). While based on different methodologies, the overlapping confidence intervals of these two estimates indicate that they are therefore not significantly different. However, we note that the PBTC status table reflects the Committee consensus to use the 2011 aerial survey estimate of 1,030 bears.

The Government of Nunavut is proposing a survey in 2016, in collaboration with other parties, to update the population estimates for both the Western and Southern Hudson Bay subpopulations. Having up-to-date population information is essential for effective management, and conducting surveys of the entire Hudson Bay coast in one year will put to rest concerns about double-counting of bears or of missing bears during surveys.” [my bold]

Which “other parties” will participate in the 2016 survey are not stated.

False 2013 report by The Guardian needs to be retracted

I noticed on 5 October 2015 that a story about a zoo polar bear in The Guardian included a link to its 2013 graphic report (November 27, 2013; Paddy Allen and Suzanne Goldenberg that falsely claimed Canada’s polar bear population (not just Western Hudson Bay’s, click on graphic below for a clearer image) was “dwindling,” and proclaimed:

“Climate change is thinning sea ice, cutting off the dwindling population of polar bears from their food source. Scientists predict that with ice-free season lengthening every year in west Hudson Bay, its polar bear population will collapse in 17 years.”

Guardian pg interactive 2013_03 graphs

An associated story by Goldenberg (“Polar bear numbers in Hudson Bay of Canada on verge of collapse” 27 November 2013; backup here) also stated that the population size of WHB was 850 bears – a number which did not appear anywhere in the official government report (Lunn et al. 2013). It came from lead author Nick Lunn, who was quoted as saying the population size was now “somewhere in the ballpark of 850.” That’s suspiciously close to the 10% decline said to be “braced for” by polar bear experts (a 10% from 935 would be 842) – in other words, the number Goldenberg used was what these biologists predicted it would be, not what the study found it to be.

Regardless, the official 2013 mark-recapture government report made it clear that the actual population estimate of 806 (because it used a different method than that used in 2004 and did not survey the entire population) was not a statistically significant decline from the 2004 estimate of 935 or from the aerial survey estimate of 1030. The Guardian graphic showing a declining trend is bogus.

The official estimate for the WHB population, used by all scientific stakeholders, including the IUCN PGSG, is 1030.

The official report referred to in Goldenberg’s article (Lunn et al. 2013) had a publication date of 26 November 2013. Goldenberg’s article, which came with the graphics shown above, was published the very next day, 27 November 2013 – further evidence that the basis for the graphics was not the official report but false information provided to her by polar bear biologists Lunn and/or Stirling weeks or even months before the official report was finalized:

“The latest Canadian government estimates, which have yet to be shared with independent scientists or the public, confirm scientists’ fears that the polar bears of the western Hudson Bay have little chance of long-term survival.”

This means The Guardian used numbers that had no relationship to the official report although no one could tell that at the time since the official report had not been made publicly available. However, it is now clear that the 2013 Guardian article and its associated graphics were entirely false – and were known to be false when they were published — they need to be retracted and record corrected.

See also: “Are Polar Bears Really Endangered” and “Global polar bear population estimate about 26,000 (20,000-32,000), despite PBSG waffling”

Footnote 1. Changes I found between version “2013 final” and “2014 final” (there are many). Note in particular: Author order changed, Lunn, Regehr, Converse to Lunn, Servanty, Converse; 

Removed from pg 18 of the 2013 report:

“The appropriate comparison would be between the estimates taken from the recent analysis, thus comparing the 2011 estimate of 806 with the new 2004 estimate of 742 (95% CI = 630-872), which are not significantly different (Figure 8).” [In other words, they calculated a new estimate for 2004 using the same method they used for 2011, which gave 742 (range 630–872) for 2004 and 806 (653–984) for 2011, indicating no decline since the last estimate was calculated in 2004]

Changed to (2014, pg 19):

“A more reliable indicator of recent trend is the mean observed population growth rate, which is 1.01 over the years 2004‐2011.” [In other words, the population rate remained stable – but you’d have to be a scientist to know that]

Lunn, N.J., Regehr, E.V., Servanty, S., Converse, S., Richardson, E. and Stirling, I. 2013. Demography and population assessment of polar bears in Western Hudson Bay, Canada. Environment Canada Research Report. 26 November 2013. PDF HERE

Lunn, N.J., Servanty, S., Regehr, E.V., Converse, S.J., Richardson, E. and Stirling, I. 2014. Demography and population assessment of polar bears in Western Hudson Bay, Canada. Environment Canada Research Report. July 2014. PDF HERE  [This appears to be the version submitted for publication]

Stapleton S., Atkinson, S., Hedman, D., and Garshelis, D. 2014. Revisiting Western Hudson Bay: using aerial surveys to update polar bear abundance in a sentinel population. Biological Conservation 170:38-47. http://www.sciencedirect.com/science/article/pii/S0006320713004618#

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