Andrew E. Derocher

Polar Bears in a Warming Climate

Abstract Polar bears (Ursus maritimus) live throughout the ice-covered waters of the circumpolar Arctic, particularly in near shore annual ice over the continental shelf where biological productivity is highest. However, to a large degree under scenarios predicted by climate change models, these preferred sea ice habitats will be substantially altered. Spatial and temporal sea ice changes will lead to shifts in trophic interactions involving polar bears through reduced availability and abundance of their main prey: seals. In the short term, climatic warming may improve bear and seal habitats in higher latitudes over continental shelves if currently thick multiyear ice is replaced by annual ice with more leads, making it more suitable for seals. A cascade of impacts beginning with reduced sea ice will be manifested in reduced adipose stores leading to lowered reproductive rates because females will have less fat to invest in cubs during the winter fast. Non-pregnant bears may have to fast on land or offshore on the remaining multiyear ice through progressively longer periods of open water while they await freeze-up and a return to hunting seals. As sea ice thins, and becomes more fractured and labile, it is likely to move more in response to winds and currents so that polar bears will need to walk or swim more and thus use greater amounts of energy to maintain contact with the remaining preferred habitats. The effects of climate change are likely to show large geographic, temporal and even individual differences and be highly variable, making it difficult to develop adequate monitoring and research programs. All ursids show behavioural plasticity but given the rapid pace of ecological change in the Arctic, the long generation time, and the highly specialised nature of polar bears, it is unlikely that polar bears will survive as a species if the sea ice disappears completely as has been predicted by some.

Predicting 21st‐century polar bear habitat distribution from global climate models

Projections of polar bear (Ursus maritimus) sea ice habitat distribution in the polar basin during the 21st century were developed to understand the consequences of anticipated sea ice reductions on polar bear populations. We used location data from satellite- collared polar bears and environmental data (e.g., bathymetry, distance to coastlines, and sea ice) collected from 1985 to 1995 to build resource selection functions (RSFs). RSFs described habitats that polar bears preferred in summer, autumn, winter, and spring. When applied to independent data from 1996 to 2006, the RSFs consistently identified habitats most frequently used by polar bears. We applied the RSFs to monthly maps of 21st-century sea ice concentration projected by 10 general circulation models (GCMs) used in the Intergovern- mental Panel of Climate Change Fourth Assessment Report, under the A1B greenhouse gas forcing scenario. Despite variation in their projections, all GCMs indicated habitat losses in the polar basin during the 21st century. Losses in the highest-valued RSF habitat (optimal habitat) were greatest in the southern seas of the polar basin, especially the Chukchi and Barents seas, and least along the Arctic Ocean shores of Banks Island to northern Greenland. Mean loss of optimal polar bear habitat was greatest during summer; from an observed 1.0 million km 2 in 1985-1995 (baseline) to a projected multi-model mean of 0.32 million km 2 in 2090-2099 (� 68% change). Projected winter losses of polar bear habitat were less: from 1.7 million km 2 in 1985-1995 to 1.4 million km 2 in 2090-2099 (� 17% change). Habitat losses based on GCM multi-model means may be conservative; simulated rates of habitat loss during 1985-2006 from many GCMs were less than the actual observed rates of loss. Although a reduction in the total amount of optimal habitat will likely reduce polar bear populations, exact relationships between habitat losses and population demographics remain unknown. Density and energetic effects may become important as polar bears make long-distance annual migrations from traditional winter ranges to remnant high-latitude summer sea ice. These impacts will likely affect specific sex and age groups differently and may ultimately preclude bears from seasonally returning to their traditional ranges.

Genetic structure of the world’s polar bear populations

We studied genetic structure in polar bear (Ursus maritimus) populations by typing a sample of 473 individuals spanning the species distribution at 16 highly variable microsatellite loci. No genetic discontinuities were found that would be consistent with evolutionarily significant periods of isolation between groups. Direct comparison of movement data and genetic data from the Canadian Arctic revealed a highly significant correlation. Genetic data generally supported existing population (management unit) designations, although there were two cases where genetic data failed to differentiate between pairs of populations previously resolved by movement data. A sharp contrast was found between the minimal genetic structure observed among populations surrounding the polar basin and the presence of several marked genetic discontinuities in the Canadian Arctic. The discontinuities in the Canadian Arctic caused the appearance of four genetic clusters of polar bear populations. These clusters vary in total estimated population size from 100 to over 10 000, and the smallest may merit a relatively conservative management strategy in consideration of its apparent isolation. We suggest that the observed pattern of genetic discontinuities has developed in response to differences in the seasonal distribution and pattern of sea ice habitat and the effects of these differences on the distribution and abundance of seals.

What are the toxicological effects of mercury in Arctic biota

This review critically evaluates the available mercury (Hg) data in Arctic marine biota and the Inuit population against toxicity threshold values. In particular marine top predators exhibit concentrations of mercury in their tissues and organs that are believed to exceed thresholds for biological effects. Species whose concentrations exceed threshold values include the polar bears (Ursus maritimus), beluga whale (Delphinapterus leucas), pilot whale (Globicephala melas), hooded seal (Cystophora cristata), a few seabird species, and landlocked Arctic char (Salvelinus alpinus). Toothed whales appear to be one of the most vulnerable groups, with high concentrations of mercury recorded in brain tissue with associated signs of neurochemical effects. Evidence of increasing concentrations in mercury in some biota in Arctic Canada and Greenland is therefore a concern with respect to ecosystem health.

Relationships between plasma levels of organochlorines, retinol and thyroid hormones from polar bears (Ursus maritimus) at Svalbard.

Associations were determined between retinol and the thyroid hormones thyroxine (T4) and triiodothyronine (T3), respectively, and the organochlorine contaminants (OCs) polychlorinated biphenyls (PCBs), 1,1-dichloro-2,2-bis-(4-chlorophenyl)ethylene (DDE), hexachlorobenzene (HCB), and hexachlorocyclohexanes (HCHs) in blood plasma from polar bears ( Ursus maritimus ) caught at Svalbard. The blood samples were collected from free-ranging polar bears of different age and sex in 1991-1994. The retinol concentration and the ratio of total T4 (TT4) to free T4(FT4) (TT4/FT4 ratio) decreased linearly with increasing concentrations of PCBs and HCB. Retinol was also negatively associated with HCHs, while the TT4/FT4 ratio was positively associated with DDE. The concentrations of retinol and thyroid hormones were significantly higher in females than in males. However, the TT4/FT4 and TT3/FT3 ratios were significantly higher in males than in females. The concentrations of thyroid hormones were negatively correlated with age in male bears, while in females, thyroid hormones did not change with age. The OCs were found to explain 12, 30, and 7% of the variation of retinol concentrations and the TT4/FT4 and TT3/FT3 ratios, respectively, after correcting for age and sex. The potential consequence of these associations for the individual and the population is unknown.

Diet composition of polar bears in Svalbard and the western Barents Sea

Abstract. We estimated both the numerical and biomass composition of the prey of polar bears (Ursus maritimus) from 135 opportunistic observations of kills in Svalbard and the western Barents Sea collected from March to October 1984–2001. By number, the prey composition was dominated by ringed seals (Phoca hispida) (63%), followed by bearded seals (Erignathus barbatus) (13%), harp seals (P. groenlandica) (8%) and unknown species (16%). However, when known prey were converted to biomass, the composition was dominated by bearded seals (55%), followed by ringed seals (30%) and harp seals (15%). Results indicated that bearded seals are an important dietary item for polar bears in the western Barents Sea. We believe that different patterns of space use by different bears may result in geographic variation of diet within the same population.

Organochlorines Affect the Major Androgenic Hormone, Testosterone, in Male Polar Bears (Ursus Maritimus) at Svalbard

Normal sexual development and subsequent reproductive function are dependent on appropriate testosterone production and action. The regulation of steroid hormones, including androgens, can be influenced by both biological and environmental factors, including environmental chemicals. Concentrations of organochlorines are considerably greater in Svalbard polar bears than in polar bears from other regions. Between 1995 and 1998, samples were collected from 121 male polar bears (Ursus maritimus) from the Svalbard area. In this study, testosterone concentration variations were described for male polar bears during different seasons and for all age groups. To study possible relationships between plasma testosterone concentrations and biological factors, such as age, axial girth, and extractable plasma fat, and organochlorine contaminants including hexachlorocyclohexanes, hexachlorobenzene, chlordanes, p,p′–DDE, and 16 individual polychlorinated biphenyl (PCB) congeners, identical statistical analyses were performed on the total population and a subsample of reproductively active adults. Of the biological factors, axial girth showed a significant positive relationship and percentage extractable fat and a significant negative relationship with the testosterone concentrations. Both the Σpesticides and ΣPCBs made significant negative contributions to the variation of the plasma testosterone concentration. The continuous presence of high concentrations of organochlorines in male polar bears throughout their life could possibly aggravate any reproductive toxicity that may have occurred during fetal and early postnatal development.

Possible immunotoxic effects of organochlorines in polar bears (Ursus maritimus) at Svalbard.

Associations between immunoglobulin G (IgG) levels and the organochlorine contaminants (OCs) polychlorinated biphenyls (PCBs), chlordanes, 1,1-dichloro-2,2-bis(4-chlorophenyl) ethylene (DDE), hexachlorobenzene (HCB), and hexachlorocyclohexanes (HCHs) in blood plasma from polar bears caught at Svalbard were determined. The blood samples were collected from free-living polar bears of different age and sex between 1991 and 1994. The IgC concentration increased with age and was significantly higher in males than in females. IgG was negatively correlated with sigmaPCB level and with three individual PCB congeners, IUPAC numbers 99, 194, and 206. HCB was also negatively correlated with IgG. The significant negative OC correlation with IgG levels may indicate an immunotoxic effect.

Does high organochlorine (OC) exposure impair the resistance to infection in polar bears (Ursus maritimus)? Part I: Effect of OCs on the humoral immunity.

This study was undertaken to assess if high levels of organochlorines (OCs) are associated with decreased ability to produce antibodies in free-ranging polar bears (Ursus maritimus) and thus affect the humoral immunity. In 1998 and 1999, 26 and 30 polar bears from Svalbard, Norway, and Churchill, Canada, respectively, were recaptured 32–40 d following immunization with inactivated influenza virus, reovirus, and herpes virus and tetanus toxoid. Blood was sampled at immunization and at recapture for determination of plasma levels of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs), serum immunoglobulin G (IgG) concentrations, and specific antibodies against influenza virus, reovirus, and herpes virus, tetanus toxoid, and Mannheimia haemolytica. The OCs alone contributed with up to 7% to the variations in the immunological parameters. The combination of ∑PCBs (sum of 12 individual PCB congeners), ∑OCPs (sum of 6 OCPs), and biological factors accounted for 40–60% of the variation in the immunological parameters. Negative associations were found between ∑PCBs and serum immunoglobulin G (IgG) levels and between ∑PCBs and increased antibody titers against influenza virus and reovirus following immunization. In contrast, a positive association was registered between ∑PCBs and increased antibodies against tetanus toxoid. ∑OCPs also contributed significantly to the variations in the immunological responses. OCs did not have the same impact on the antibody production against M. haemolytica. The present study demonstrated that high OC levels may impair the polar bears ability to produce antibodies and thus may produce impaired resistance to infections.

Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations

Polar bears (Ursus maritimus) have experienced substantial changes in the seasonal availability of sea ice habitat in parts of their range, including the Beaufort, Chukchi, and Bering Seas. In this study, we compared the body size, condition, and recruitment of polar bears captured in the Chukchi and Bering Seas (CS) between two periods (1986-1994 and 2008-2011) when declines in sea ice habitat occurred. In addition, we compared metrics for the CS population 2008-2011 with those of the adjacent southern Beaufort Sea (SB) population where loss in sea ice habitat has been associated with declines in body condition, size, recruitment, and survival. We evaluated how variation in body condition and recruitment were related to feeding ecology. Comparing habitat conditions between populations, there were twice as many reduced ice days over continental shelf waters per year during 2008-2011 in the SB than in the CS. CS polar bears were larger and in better condition, and appeared to have higher reproduction than SB bears. Although SB and CS bears had similar diets, twice as many bears were fasting in spring in the SB than in the CS. Between 1986-1994 and 2008-2011, body size, condition, and recruitment indices in the CS were not reduced despite a 44-day increase in the number of reduced ice days. Bears in the CS exhibited large body size, good body condition, and high indices of recruitment compared to most other populations measured to date. Higher biological productivity and prey availability in the CS relative to the SB, and a shorter recent history of reduced sea ice habitat, may explain the maintenance of condition and recruitment of CS bears. Geographic differences in the response of polar bears to climate change are relevant to range-wide forecasts for this and other ice-dependent species.