Challenging Alaska polar bear research sound bites and bewildering ESA status

Beaufort Sea male polar bear USGS_2005 Amstrup photo

It’s easy to take polar bear research papers at face value but it’s not very scientific. The snappy sound bites provided for the benefit of the media – whether they’re embedded in press releases or in published abstracts – don’t cut it with trained scientists. Trained scientists read the whole report, critically examine the evidence it contains and assess that evidence within the context of previous knowledge. That’s what they are trained to do.

I challenge the superficial summary on the status of Alaskan polar bear populations provided by FactCheck.org journalist Vanessa Schipani.  Schipani disputed a comment made by Alaska Senator Lisa Murkowski that, according to the latest research Alaskan polar bear population numbers are strong and healthy. I’m not especially interested in the political context of the statement, only Schipani’s bald claim that Murkowski’s declaration is false.

I’ve read all the relevant papers in full and I contend that the evidence supports Murkowski’s statement. Schipani is confusing the issue by regurgitating ‘facts’ that don’t tell the truth of the matter. By the sum of accounts, Alaskan polar bear populations are indeed healthy and strong – whether or not this status will continue is an entirely different question.

Amstrup et al 2005_Fig 1 map of CS_SB_NB boundaries

Polar bears have become the favorite icon of a highly politicized issue and there is a price to pay for that. There are complexities to modern polar bear science that isn’t adequately covered by the rhetoric contained in press releases but a few prominent polar bear biologists and their bosses have become masters of media manipulation. I’ve covered these topics before, so look to the links provided below to find references, maps, and quotes from relevant papers.

Conservation status

Polar bears were the first species to be assigned a conservation status of ‘threatened’ based on possible future declines in population number rather than their current counts
(‘threatened’ under the US Endangered Species Act in 2008 and the equivalent ‘vulnerable’ on the IUCN Red List, 2006 and 2015). I’ve pointed out before how confusing this is for the general public, journalists, and even scientists in other fields. Most people simply don’t understand that a totally new set of criteria has been applied to an old classification system and that the ‘threatened’ and ‘vulnerable’ status of polar bears does not refer to their present condition.

That means it is totally correct to say that current populations are strong and healthy even if computer-modelled projections for the future suggest polar bears may be doomed.

[The premises upon which these models are based have so far failed, that’s another story]

These are two different things: present conditions vs. possible future conditions. If polar bear conservation status were based on present conditions only, they would not qualify as ‘threatened’ – possible dire future conditions based on computer models of sea ice are the only way polar bears qualify for the status of ‘threatened’ or ‘vulnerable’.

However, the IUCN Red List folks recently tightened their criteria for using this strategy to list species as ‘vulnerable’ based on future prophesies. The 2015 IUCN Red List assessment for polar bears indeed upheld the status of ‘vulnerable’ – based on concerns of possible future population declines, not current numbers – but it included critical caveats.

Although it is not perfect in my opinion, this Red List assessment is the most statistically robust, in-depth study of the conservation status of polar bears ever produced. Yet those critical caveats it contains – the probability estimates – have been largely ignored by journalist, including Schipani.

Summary below, see it here: 2015 Red List assessment (Wiig et al. 2015):

The previous status of ‘Vulnerable’ was upheld but no projections were made beyond 2050. It said there is only a 70% chance that polar bear numbers could decline by 30% over the next 35 years, which is only slightly higher than a 50:50 chance. It also means there is a 30% chance that the numbers WILL NOT decline by 30% over the next 35 years. The document stated explicitly that the risk of a population decline of 80% or greater by 2050 is virtually zero (pg. 16). There have been no declines in range, no extreme fluctuations in subpopulations, no fragmentation of the population, no continuing declines within subpopulations; the current population size used for the projections was 20,000-31,000 with estimates within several subpopulations still highly uncertain.

In other words, the status of ‘Vulnerable’ is based only on a possible decline in population numbers and there is no imminent risk of extinction. The current population trend is stated as UNKNOWN.

Southern Beaufort Sea polar bears

Southern Beaufort Sea polar bears are a unique population in one respect – they have a long history of population declines every ten years or so that go back to at least the 1970s (and probably to the 1960s and beyond) that are known to be caused by thick sea ice conditions in the spring.This is a natural hazard: the 1974-1976 episode was apparently as severe as the 2004-2006 event but in both cases, the population recovered within a few years.

The last two SBS population assessments included a period (2004-2006) when bear numbers dropped dramatically due to these natural conditions. The last assessment ended before numbers could rebound but subsequent evidence indicates they did eventually recover.

To state, as Schipani did, that SBS numbers declined from 1526 in 2006 to 900 in 2010 is a gross misrepresentation of the evidence.The two studies (Regehr et al. 2006; Bromaghin et al. 2015) used entirely different methods of analysis that are not comparable.

The estimate of the population at 2006 calculated by Bromaghin and colleagues (2015: Fig. 5) was about 1250 bears (900-1526), not 1526 – and the error bars of the 2010 population estimate (900 bears, range 600-1200) overlapped the 2006 estimate by a wide margin.

In addition, the Bromaghin study ending in 2010 did not survey the entire Southern Beaufort range the way the previous study did – it depended on model assumptions to “guess” how many bears were in the territory they didn’t bother to sample. Oddly, data was collected after 2010 (until at least 2013) but it wasn’t incorporated into the estimate.

Most damning is the totally unpublicized fact that an aerial survey conducted by the US Fish and Wildlife Service in the fall of 2012 found more bears than there had been in the previous 10 years.

In short, it doesn’t matter how many times polar bear biologists try to imply that population declines and reduced body condition of bears in the SBS are due to reduced summer sea ice caused by anthropogenic global warming – the facts don’t support their rhetoric. SBS polar bear numbers have declined dramatically – and then rebounded – every ten years since at least 1974 because of thick spring ice conditions that caused ringed seal prey to move offshore or to the west (Burns et al. 1975). As far as we know, this is what’s “natural” for this population.

These facts are well documented in the scientific literature. Polar bear specialists have been trying to change the story of SBS bears for years but the facts contained in their previous work prevent all but the most gullible from taking them seriously: the cause of the poor body condition, starvation, and decline in population numbers for SBS bears in some years is not declining summer sea ice but thick ice conditions in the spring. Summer is not the critical season for polar bear health and survival, spring is – and proof of that is in the record of Alaskan polar bear populations.

Polar bear feeding by season simple_Nov 29 2015

Chukchi Sea polar bears

Chukchi Sea polar bears have not been properly surveyed for population size but they have been studied previously. Chukchi bears were found to be in much better condition in 2011 than they were in the 1980s when the open water season was much shorter (Rode and Regehr 2010; Rode et al. 2013, 2014).

Chukchi bears may spend more time on land than they did in the 1980s but that is to be expected with a longer open water season – the bears were still in excellent condition (only Foxe Basin bears were fatter) and reproducing well. Good body condition and lots of cubs in good condition are indicators of a population that is either stable or increasing.

The ringed seals these bears depend on for food are also in better condition now than in the 1980s and their populations are also healthy; this accounts for the health of the polar bears, who clearly have lots of newborn seals to eat in their critical spring feeding period (March/April to June).

In other words – contrary to predictions by polar bear biologists – we have all the evidence we need to conclude that the Chukchi Sea polar bear population is strong and healthy without a population survey.

Conclusion

Insisting that because the ESA and the IUCN Red List consider polar bears threatened with extinction means polar bear populations currently must be population deficient is false and misleading – the statuses of ‘threatened’ and ‘vulnerable’ for polar bears are based on concerns of possible future declines only.

It is factually correct to say that present populations of polar bears in Alaska are healthy. Scientific studies on polar bears – when all of the data is taken into account and considered in the context of all research on these bears – indicates this statement is true.

All of the evidence suggests Southern Beaufort Sea polar bears have recovered from a known and predictable decline in numbers in the mid-2000s due to natural causes – designating “critical habitat” along the Alaska coast will not protect the bears from repeats of this natural hazard in the future – and Chukchi Sea bears have all the indicators of a stable or increasing population. Those are the scientific facts.

References
Bromaghin, J.F., McDonald, T.L., Stirling, I., Derocher, A.E., Richardson, E.S., Rehehr, E.V., Douglas, D.C., Durner, G.M., Atwood, T. and Amstrup, S.C. 2015. Polar bear population dynamics in the southern Beaufort Sea during a period of sea ice decline. Ecological Applications http://onlinelibrary.wiley.com/doi/10.1890/14-1129.1/abstract [paywalled]

Burns, J. J., Fay, F. H., and Shapiro, L.H. 1975. The relationships of marine mammal distributions, densities, and activities to sea ice conditions (Quarterly report for quarter ending September 30, 1975, projects #248 and 249), pp. 77-78 in Environmental Assessment of the Alaskan Continental Shelf, Principal Investiagors’ Reports. July-September 1975, Volume 1. NOAA, Environmental Research Laboratories, Boulder Colorado. [available online] pdf here.

Polar Bear News 2013-14. 2013. Polar bear newsletter of the US Fish & Wildlife Service, Anchorage, Alaska. Pdf here.

Regehr, E.V., Amstrup, S.C., and Stirling, I. 2006. Polar bear population status in the Southern Beaufort Sea. US Geological Survey Open-File Report 2006-1337. Pdf here.

Wiig, Ø., Amstrup, S., Atwood, T., Laidre, K., Lunn, N., Obbard, M., Regehr, E. & Thiemann, G. 2015. Ursus maritimus. The IUCN Red List of Threatened Species 2015: e.T22823A14871490. Published online here; PDF copy of that report page: 2015 IUCN Red List Ursus maritimus (Polar Bear) – www_iucnredlist_org_Nov 18 2015

Rode, K.D., Douglas, D., Durner, G., Derocher, A.E., Thiemann, G.W., and Budge, S. 2013. Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations. Oral presentation by Karyn Rode, 28th Lowell Wakefield Fisheries Symposium, March 26-29. Anchorage, AK. Abstract below, pdf here.

Rode, K.D., Regehr, E.V., Douglas, D., Durner, G., Derocher, A.E., Thiemann, G.W., and Budge, S. 2014. Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations. Global Change Biology 20(1):76-88. http://onlinelibrary.wiley.com/doi/10.1111/gcb.12339/abstract 

Rode, K. and Regehr, E.V. 2010. Polar bear research in the Chukchi and Bering Seas: A synopsis of 2010 field work. Unpublished report to the US Fish and Wildlife Service, Department of the Interior, Anchorage. pdf here.

Comments are closed.