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View Preprint Testing the hypothesis that routine sea ice coverage of 3-5 mkm2 results in a greater than 30% decline in population size of polar bear (Ursus maritimus). Version 3 Susan J. Crockford University of Victoria 3800 Finnerty Rd Victoria, British Columbia, Canada V8P 5C5 Corresponding author: Susan J. Crockford, [email protected] 1 PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.2737v3 | CC BY 4.0 Open Access | rec: 2 Mar 2017, publ: 2 Mar 2017 1 Abstract 2 The polar bear (Ursus maritimus) was the first species to be classified as threatened with 3 extinction based on predictions of future conditions rather than current status. These predictions 4 were made using expert-opinion forecasts of population declines linked to modeled habitat loss – 5 first by the International Union for the Conservation of Nature (IUCN)’s Red List in 2006, and 6 then by the United States Fish and Wildlife Service (USFWS) in 2008 under the Endangered 7 Species Act (ESA), based on data collected to 2005 and 2006, respectively. Both assessments 8 predicted significant population declines of polar bears would result by mid-century as a 9 consequence of summer sea ice extent rapidly reaching 3-5 mkm2 on a regular basis: the IUCN 10 predicted a >30% decline in total population, while the USFWS predicted the global population 11 would decline by 67% (including total extirpation of ten subpopulations within two vulnerable 12 ecoregions). Biologists involved in these conservation assessments had to make several critical 13 assumptions about how polar bears might be affected by future habitat loss, since sea ice 14 conditions predicted to occur by 2050 had not occurred prior to 2006. However, summer sea ice 15 declines have been much faster than expected: low ice levels not expected until mid-century 16 (about 3-5 mkm2) have occurred regularly since 2007. Realization of predicted sea ice levels 17 allows the ‘rapid sea ice decline = population decline’ assumption for polar bears to be treated as 18 a testable hypothesis. Data collected between 2007 and 2015 reveal that polar bear numbers have 19 not declined as predicted and no subpopulation has been extirpated. Several subpopulations 20 expected to be at high risk of decline remained stable and five showed increases in population 21 size. Another at-risk subpopulation was not counted but showed marked improvement in 22 reproductive parameters and body condition with less summer ice. As a consequence, the 23 hypothesis that repeated summer sea ice levels of below 5 mkm2 will cause significant 24 population declines in polar bears is rejected, a result that indicates the ESA and IUCN 25 judgments to list polar bears as threatened based on future risks of habitat loss were scientifically 26 unfounded and that similar predictions for Arctic seals and walrus may be likewise flawed. The 27 lack of a demonstrable ‘rapid sea ice decline = population decline’ relationship for polar bears 28 also potentially invalidates updated survival model outputs that predict catastrophic population 29 declines should the Arctic become ice-free in summer. 30 31 32 33 34 2 PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.2737v3 | CC BY 4.0 Open Access | rec: 2 Mar 2017, publ: 2 Mar 2017 35 Introduction 36 The polar bear (Ursus maritimus) is the top predator of the Arctic ecosystem and is found 37 in five nations with appropriate sea ice habitat (Fig.1). This icon of the Arctic was the first 38 species to be listed as threatened with extinction based on population declines anticipated to 39 occur as a result of forecasted habitat loss, rather than on current circumstances (Adler 2008). 40 The International Union for the Conservation of Nature (IUCN), via its Red List of Threatened 41 Species, made this unique conservation decision in 2006 (Schliebe et al. 2006a): it assigned polar 42 bears the status of ‘Vulnerable’ after the IUCN Polar Bear Specialist Group (PBSG) in 2005 43 reported that the global population was likely to decline by “more than 30% within the next 35- 44 50 years” (Aars, Lunn & Derocher 2006:61)(note the IUCN Red List status term ‘Vulnerable’ is 45 equivalent to the ESA term ‘Threatened’ (indicating a species likely to become endangered) 46 while both use the term ‘Endangered’ to indicate a higher-risk status). This Red List decision 47 reversed the ‘Lower Risk/Conservation Dependent’ status (now called ‘Least Concern’) that 48 polar bears were assigned in 1996 to reflect their recovery from previous decades of over- 49 hunting (Wiig et al. 2015). 50 3 PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.2737v3 | CC BY 4.0 Open Access | rec: 2 Mar 2017, publ: 2 Mar 2017 51 52 Figure 1. Global polar bear subpopulations, as defined by the IUCN Polar Bear Specialist Group, 53 managed by five nations (Canada, Russia, Norway, United States of America, and Denmark (for 54 Greenland). Image credit: Environment Canada. 55 56 The Fish and Wildlife Service (USFWS) of the United States of America (US), in 2008, 57 similarly declared polar bears ‘Threatened’ in response to a petition filed in 2005 by the Center 58 for Biological Diversity and two other not-for-profit conservation organizations (Schliebe et al. 4 PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.2737v3 | CC BY 4.0 Open Access | rec: 2 Mar 2017, publ: 2 Mar 2017 59 2006b). Said the US Fish & Wildlife Service as it invoked the Endangered Species Act (ESA) to 60 protect polar bears (USFWS 2008: 28213): 61 “We find, based upon the best available scientific and commercial information, that polar 62 bear habitat—principally sea ice—is declining throughout the species’ range, that this 63 decline is expected to continue for the foreseeable future, and that this loss threatens the 64 species throughout all of its range. Therefore, we find that the polar bear is likely to 65 become an endangered species within the foreseeable future throughout all of its range.” 66 ESA protection for polar bears (referred to henceforth as the “ESA decision”) came on 67 top of existing regulations mandated by the 1972 US Marine Mammal Protection Act (which 68 gave broad-scale safeguards to polar bears and other marine mammals), as well as a specific 69 international treaty signed in 1973 by all Arctic nations to protect polar bear populations against 70 over-hunting and poaching (Larsen & Stirling 2009; Marine Mammal Commission 2007). 71 The 1973 international treaty spawned the formation of the IUCN Polar Bear Specialist 72 Group (PBSG), tasked with coordinating the research necessary for assessing polar bear health 73 and population size worldwide (Anonymous 1968). For management purposes, the PBSG 74 divided polar bears into more than a dozen more or less discrete subpopulations. At present, the 75 19 designated subpopulations are continuously distributed across available sea ice habitat (Fig. 1 76 – note the abbreviations for subpopulations used throughout this analysis). Polar bears have 77 experienced no recent range contractions due to habitat loss, no continuous declines within any 78 subpopulation, and currently have a large population size estimated at more than 22,000-31,000 79 bears (Norwegian Polar Institute 2015; SWG 2016; Wiig et al. 2015)(see “Global population size 80 observations” below). Thus, by all measures used to assess contemporary conservation status 81 (Akçakaya et al. 2006), the global polar bear population is currently healthy and would qualify 82 for the IUCN Red List status of ‘Least Concern’ and would not qualify as a threatened species 83 under the ESA based on these parameters – a fact which was also true in 2006 and 2008. 5 PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.2737v3 | CC BY 4.0 Open Access | rec: 2 Mar 2017, publ: 2 Mar 2017 84 Therefore, the ’Vulnerable’ to extinction and ‘Threatened’ with extinction status granted 85 polar bears in 2006 and 2008, respectively, referred exclusively to what might occur in the 86 future, should sea ice continue to decline in response to rising carbon dioxide levels in the 87 atmosphere generated by human fossil fuel use, variously called anthropogenic global warming, 88 climate warming, or climate change (Derocher, Lunn & Stirling 2004, Derocher et al. 2013; 89 Furevik, Drange & Sorteberg 2002; Stirling & Derocher 2012). The Red List assessment and the 90 ESA decision, based on comparable sets of assumptions and modeled forecasts of habitat loss, 91 predicted potentially catastrophic declines in the global population of polar bears by 2050 as a 92 direct effect of crossing a particular threshold of sea ice loss based on a number of research 93 reports produced by the US Geological Survey (USGS)(e.g., Amstrup, Marcot & Douglas 2007; 94 Durner et al. 2007; Hunter et al. 2007; Regehr, Amstrup & Stirling 2006; Regehr et al. 2007a; 95 Rode, Amstrup & Regehr 2007). Based on similar models and assumptions, the US Fish & 96 Wildlife Service subsequently declared Arctic ringed seals (Phoca hispida, aka Pusa hispida) 97 and Pacific bearded seals (Erignathus barbatus nauticus) to be ‘Threatened’ (USFWS 2012a, 98 2012b) – with the same proposed for Pacific walrus (Odobenus rosmarus divergens) (USFWS 99 2011, 2014) – but the IUCN did not (Kovacs 2016; Lowry 2015; Lowry 2016). 100 As Amstrup, Marcot & Douglas (2007:1) stated: “Our modeling suggests that realization 101 of the sea ice future which is currently projected would mean loss of ≈ 2/3 of the world’s current 102 polar bear population by mid-century.” Although other potential future risks were considered 103 (such as contamination with pollutants, oil spills, and poaching), IUCN and USGS/USFWS 104 biologists determined that future declines in sea ice constituted the overwhelmingly largest threat 105 to future health and survival of polar bears.
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