Ian Stirling

The role of diet on long-term concentration and pattern trends of brominated and chlorinated contaminants in western Hudson Bay polar bears, 1991–2007

Adipose tissue was sampled from the western Hudson Bay (WHB) subpopulation of polar bears at intervals from 1991 to 2007 to examine temporal trends of PCB and OCP levels both on an individual and sum-(∑-)contaminant basis. We also determined levels and temporal trends of emerging polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD), polybrominated biphenyls (PBBs) and other current-use brominated flame retardants. Over the 17-year period, ∑DDT (and p,p-DDE, p,p-DDD, p,p-DDT) decreased (-8.4%/year); α-hexachlorocyclohexane (α-HCH) decreased (-11%/year); β-HCH increased (+8.3%/year); and ∑PCB and ∑chlordane (CHL), both contaminants at highest concentrations in all years (>1ppm), showed no distinct trends even when compared to previous data for this subpopulation dating back to 1968. Some of the less persistent PCB congeners decreased significantly (-1.6%/year to -6.3%/year), whereas CB153 levels tended to increase (+3.3%/year). Parent CHLs (c-nonachlor, t-nonachlor) declined, whereas non-monotonic trends were detected for metabolites (heptachlor epoxide, oxychlordane). ∑chlorobenzene, octachlorostyrene, ∑mirex, ∑MeSO(2)-PCB and dieldrin did not significantly change. Increasing ∑PBDE levels (+13%/year) matched increases in the four consistently detected congeners, BDE47, BDE99, BDE100 and BDE153. Although no trend was observed, total-(α)-HBCD was only detected post-2000. Levels of the highest concentration brominated contaminant, BB153, showed no temporal change. As long-term ecosystem changes affecting contaminant levels may also affect contaminant patterns, we examined the influence of year (i.e., aging or weathering of the contaminant pattern), dietary tracers (carbon stable isotope ratios, fatty acid patterns) and biological (age/sex) group on congener/metabolite profiles. Patterns of PCBs, CHLs and PBDEs were correlated with dietary tracers and biological group, but only PCB and CHL patterns were correlated with year. DDT patterns were not associated with any explanatory variables, possibly related to local DDT sources. Contaminant pattern trends may be useful in distinguishing the possible role of ecological/diet changes on contaminant burdens from expected dynamics due to atmospheric sources and weathering.

Implications of the Circumpolar Genetic Structure of Polar Bears for Their Conservation in a Rapidly Warming Arctic

We provide an expansive analysis of polar bear (Ursus maritimus) circumpolar genetic variation during the last two decades of decline in their sea-ice habitat. We sought to evaluate whether their genetic diversity and structure have changed over this period of habitat decline, how their current genetic patterns compare with past patterns, and how genetic demography changed with ancient fluctuations in climate. Characterizing their circumpolar genetic structure using microsatellite data, we defined four clusters that largely correspond to current ecological and oceanographic factors: Eastern Polar Basin, Western Polar Basin, Canadian Archipelago and Southern Canada. We document evidence for recent (ca. last 1–3 generations) directional gene flow from Southern Canada and the Eastern Polar Basin towards the Canadian Archipelago, an area hypothesized to be a future refugium for polar bears as climate-induced habitat decline continues. Our data provide empirical evidence in support of this hypothesis. The direction of current gene flow differs from earlier patterns of gene flow in the Holocene. From analyses of mitochondrial DNA, the Canadian Archipelago cluster and the Barents Sea subpopulation within the Eastern Polar Basin cluster did not show signals of population expansion, suggesting these areas may have served also as past interglacial refugia. Mismatch analyses of mitochondrial DNA data from polar and the paraphyletic brown bear (U. arctos) uncovered offset signals in timing of population expansion between the two species, that are attributed to differential demographic responses to past climate cycling. Mitogenomic structure of polar bears was shallow and developed recently, in contrast to the multiple clades of brown bears. We found no genetic signatures of recent hybridization between the species in our large, circumpolar sample, suggesting that recently observed hybrids represent localized events. Documenting changes in subpopulation connectivity will allow polar nations to proactively adjust conservation actions to continuing decline in sea-ice habitat.

Polar bears in the southern Beaufort Sea II: Demography and population growth in relation to sea ice conditions

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Rebuttal of “Polar Bear Population Forecasts: A Public-Policy Forecasting Audit”

Observed declines in the Arctic sea ice have resulted in a variety of negative effects on polar bears Ursus maritimus. Projections for additional future declines in sea ice resulted in a proposal to list polar bears as a threatened species under the United States Endangered Species Act. To provide information for the Department of the Interiors listing-decision process, the US Geological Survey USGS produced a series of nine research reports evaluating the present and future status of polar bears throughout their range. In response, Armstrong et al. [Armstrong, J. S., K. C. Green, W. Soon. 2008. Polar bear population forecasts: A public-policy forecasting audit. Interfaces385 382--405], which we will refer to as AGS, performed an audit of two of these nine reports. AGS claimed that the general circulation models upon which the USGS reports relied were not valid forecasting tools, that USGS researchers were not objective or lacked independence from policy decisions, that they did not utilize all available information in constructing their forecasts, and that they violated numerous principles of forecasting espoused by AGS. AGS p. 382 concluded that the two USGS reports were “unscientific and inconsequential to decision makers.” We evaluate the AGS audit and show how AGS are mistaken or misleading on every claim. We provide evidence that general circulation models are useful in forecasting future climate conditions and that corporate and government leaders are relying on these models to do so. We clarify the strict independence of the USGS from the listing decision. We show that the allegations of failure to follow the principles of forecasting espoused by AGS are either incorrect or are based on misconceptions about the Arctic environment, polar bear biology, or statistical and mathematical methods. We conclude by showing that the AGS principles of forecasting are too ambiguous and subjective to be used as a reliable basis for auditing scientific investigations. In summary, we show that the AGS audit offers no valid criticism of the USGS conclusion that global warming poses a serious threat to the future welfare of polar bears and that it only serves to distract from reasoned public-policy debate.

The Nature and Impacts of Thunderstorms in a Northern Climate

Thunderstorms and associated lightning play an important role in the cycling of water and energy during the warm season, over the boreal and subarctic ecosystems of northern Canada, including the Mackenzie Basin. A variety of observational data sets and model-derived products have been used to characterize these storms, to examine their impacts on the forests of the Basin and on polar bear habitat in western Hudson Bay, and to assess predictive applications of lightning information.

E. W. Born, A. Heilmann, L. K. Holm and K. L. Laidre: Polar bears in Northwest Greenland

Between the early 1990s and the mid-2000s, there were reports that the number of polar bears being harvested in Northwest Greenland had increased markedly and that significant changes were being observed in weather conditions, sea ice cover, and glaciers. Satellite data from several studies confirmed significant declines in the extent of ice in Baffin Bay, particularly adjacent to the coast of northwestern Greenland (UNEP 2007), and progressively earlier breakup of the sea ice in spring (Stirling and Parkinson 2006). At the same time, concern was expressed by the IUCN Polar Bear Specialist Group (Aars et al. 2006) because, on the basis of scientific assessments of population size (Taylor et al. 2005, 2008), it appeared that the recorded harvest levels of polar bears in Kane Basin and Baffin Bay have been unsustainable for several years. This created a discrepancy between a significant increase in the annual harvest (possibly because of an increase in the number of bears occurring in the hunting areas and nearer the settlements), while at the same time, population inventories and modeling of the impact of the harvest indicated steadily declining populations in Kane Basin and Baffin Bay. It was recognized that the long-term observations of polar bears by resident professional hunters in Northwest Greenland might offer some insight into whether apparent changes in environmental conditions affected polar bears and, in turn, the harvest. Thus, in February 2006, a total of 72 experienced hunters from two settlements were asked the same 31 questions (in Greenlandic) about their observations and conclusions about polar bear biology: the northernmost settlement, Qaanaaq (25), and Upernavik (47), more than 500 km to the south. The categories of the questions included: details of the harvest of polar bears, hunting and traveling conditions, climate change, changes to the catch and occurrence of polar bears, and aspects of the biology and behavior of polar bears. The questions were carefully worded and presented in a neutral, or nonleading manner. For example, ‘‘Have you observed changes to ice conditions?’’ and not something like ‘‘Have you noticed an increase in the amount of open water in recent years?’’ This structure also reduced the risk of a lack of focus or associative leaps that may result in ordinary conversation and which make seeking consensus difficult on most subjects. Although there were wide variations in the responses of individual hunters from the same settlement, as well as between those from different settlements, to most of the questions, there were some overall trends reported that could be confirmed independently. Beginning at least by the 1990s, a majority of hunters noted marked environmental changes and, most important for hunting, earlier breakup in spring and later freeze-up in fall, resulting in an overall decrease in sea ice cover. In this category, their observations were independently validated by observations from polar-orbiting satellites. Although a majority of hunters (81%) noted an increase in the number of polar bears close to the coast, there were differences between individuals as to whether that resulted from an increase in population size or a decrease in sea ice cover that forced a change in distribution. However, there was agreement that because the increasing amount of open water and earlier breakup made hunting by dog sled more difficult, hunting from boats (faster, easier, and with much greater range) I. Stirling (&) Wildlife Research Division, Environment Canada, Edmonton, AB, Canada e-mail: ian.stirling@ec.gc.ca