Effects of climate warming on polar bears: a review of the evidence

Unlock the Endangered Species Act to address GHG emissions

For the first time, ESA evaluations can include impacts on polar bears from greenhouse gas emissions.

A body composition model with multiple storage compartments for polar bears (Ursus maritimus)

Climate warming is rapidly altering Arctic ecosystems. Polar bears (Ursus maritimus) need sea ice as a platform from which to hunt seals, but increased sea-ice loss is lengthening periods when bears are without access to primary hunting habitat. During periods of food scarcity, survival depends on the energy that a bear has stored in body reserves, termed storage energy, making this a key metric in predictive models assessing climate change impacts on polar bears. Here, we developed a body composition model for polar bears that estimates storage energy while accounting for changes in storage tissue composition. We used data of dissected polar bears (n = 31) to link routinely collected field measures of total body mass and straight-line body length to the body composition of individual bears, described in terms of structural mass and two storage compartments, adipose and muscle. We then estimated the masses of metabolizable proteins and lipids within these storage compartments, giving total storage energy. We tested this multi-storage model by using it to predict changes in the lipid stores from an independent dataset of wild polar bears (n = 36) that were recaptured 8-200 days later. Using length and mass measurements, our model successfully predicted direct measurements of lipid changes via isotopic dilutions (root mean squared error of 14.5 kg). Separating storage into two compartments, and allowing the molecular composition of storage to vary, provides new avenues for quantifying energy stores of individuals across their life cycle. The multi-storage body composition model thus provides a basis for further exploring energetic costs of physiological processes that contribute to individual survival and reproductive success. Given bioenergetic models are increasingly used as a tool to predict individual fitness and population dynamics, our approach for estimating individual energy stores could be applicable to a wide range of species.

Interactive effects of changes in UV radiation and climate on terrestrial ecosystems, biogeochemical cycles, and feedbacks to the climate system

Terrestrial organisms and ecosystems are being exposed to new and rapidly changing combinations of solar UV radiation and other environmental factors because of ongoing changes in stratospheric ozone and climate. In this Quadrennial Assessment, we examine the interactive effects of changes in stratospheric ozone, UV radiation and climate on terrestrial ecosystems and biogeochemical cycles in the context of the Montreal Protocol. We specifically assess effects on terrestrial organisms, agriculture and food supply, biodiversity, ecosystem services and feedbacks to the climate system. Emphasis is placed on the role of extreme climate events in altering the exposure to UV radiation of organisms and ecosystems and the potential effects on biodiversity. We also address the responses of plants to increased temporal variability in solar UV radiation, the interactive effects of UV radiation and other climate change factors (e.g. drought, temperature) on crops, and the role of UV radiation in driving the breakdown of organic matter from dead plant material (i.e. litter) and biocides (pesticides and herbicides). Our assessment indicates that UV radiation and climate interact in various ways to affect the structure and function of terrestrial ecosystems, and that by protecting the ozone layer, the Montreal Protocol continues to play a vital role in maintaining healthy, diverse ecosystems on land that sustain life on Earth. Furthermore, the Montreal Protocol and its Kigali Amendment are mitigating some of the negative environmental consequences of climate change by limiting the emissions of greenhouse gases and protecting the carbon sequestration potential of vegetation and the terrestrial carbon pool.

A predictive timeline of wildlife population collapse

Contemporary rates of biodiversity decline emphasize the need for reliable ecological forecasting, but current methods vary in their ability to predict the declines of real-world populations. Acknowledging that stressor effects start at the individual level, and that it is the sum of these individual-level effects that drives populations to collapse, shifts the focus of predictive ecology away from using predominantly abundance data. Doing so opens new opportunities to develop predictive frameworks that utilize increasingly available multi-dimensional data, which have previously been overlooked for ecological forecasting. Here, we propose that stressed populations will exhibit a predictable sequence of observable changes through time: changes in individuals' behaviour will occur as the first sign of increasing stress, followed by changes in fitness-related morphological traits, shifts in the dynamics (for example, birth rates) of populations and finally abundance declines. We discuss how monitoring the sequential appearance of these signals may allow us to discern whether a population is increasingly at risk of collapse, or is adapting in the face of environmental change, providing a conceptual framework to develop new forecasting methods that combine multi-dimensional (for example, behaviour, morphology, life history and abundance) data.

Reproductive senescence in polar bears in a variable environment

Reproductive senescence is ubiquitous in mammals. However, patterns of senescence vary across reproductive traits, even within populations, perhaps because of differences in selection pressures, physiological constraints, and responses to environmental conditions. We investigated reproductive senescence in wild female polar bears (Ursus maritimus), using 31 years of capture-recapture data from the Svalbard area. We studied the influence of environmental conditions on age-specific litter production and litter size using generalized linear mixed models. Further, using a capture-recapture model that handles the dependency between vital rates of individuals belonging to the same family unit, we assessed maternal-age-related changes in first year cub and litter survival. We provide clear evidence for reproductive senescence in female polar bears. Litter production and litter size peaked in middle-aged females and declined sharply afterward. By contrast cub and litter survival did not decline after prime age. We found no evidence of terminal investment. The reproductive output of all females was affected by sea-ice conditions during the previous year and the Arctic Oscillation, with some effects differing greatly between age groups. Old females were affected the most by environmental conditions. Our results suggest that the decline in reproductive output is a combination of fertility and body-condition senescence, with a weak contribution of maternal-effect senescence, possibly due to benefits of experience. Further, as predicted by evolutionary theory, senescence appears to be a consequence of failures in early stages of the reproductive cycle rather than in late stages, and environmental variation affected old females more than prime-aged females. Our study emphasizes the need to study several reproductive traits and account for environmental variation when investigating reproductive senescence. Differences in senescence patterns across reproductive traits should be interpreted in light of evolutionary theory and while considering underlying physiological drivers.

Key questions in marine mammal bioenergetics

Bioenergetic approaches are increasingly used to understand how marine mammal populations could be affected by a changing and disturbed aquatic environment. There remain considerable gaps in our knowledge of marine mammal bioenergetics, which hinder the application of bioenergetic studies to inform policy decisions. We conducted a priority-setting exercise to identify high-priority unanswered questions in marine mammal bioenergetics, with an emphasis on questions relevant to conservation and management. Electronic communication and a virtual workshop were used to solicit and collate potential research questions from the marine mammal bioenergetic community. From a final list of 39 questions, 11 were identified as 'key' questions because they received votes from at least 50% of survey participants. Key questions included those related to energy intake (prey landscapes, exposure to human activities) and expenditure (field metabolic rate, exposure to human activities, lactation, time-activity budgets), energy allocation priorities, metrics of body condition and relationships with survival and reproductive success and extrapolation of data from one species to another. Existing tools to address key questions include labelled water, animal-borne sensors, mark-resight data from long-term research programs, environmental DNA and unmanned vehicles. Further validation of existing approaches and development of new methodologies are needed to comprehensively address some key questions, particularly for cetaceans. The identification of these key questions can provide a guiding framework to set research priorities, which ultimately may yield more accurate information to inform policies and better conserve marine mammal populations.

Anthropogenic food: an emerging threat to polar bears

Supplemental food from anthropogenic sources is a source of conflict with humans for many wildlife species. Food-seeking behaviours by black bears Ursus americanus and brown bears Ursus arctos can lead to property damage, human injury and mortality of the offending bears. Such conflicts are a well-known conservation management issue wherever people live in bear habitats. In contrast, the use of anthropogenic foods by the polar bear Ursus maritimus is less common historically but is a growing conservation and management issue across the Arctic. Here we present six case studies that illustrate how negative food-related interactions between humans and polar bears can become either chronic or ephemeral and unpredictable. Our examination suggests that attractants are an increasing problem, exacerbated by climate change-driven sea-ice losses that cause increased use of terrestrial habitats by bears. Growing human populations and increased human visitation increase the likelihood of human–polar bear conflict. Efforts to reduce food conditioning in polar bears include attractant management, proactive planning and adequate resources for northern communities to reduce conflicts and improve human safety. Permanent removal of unsecured sources of nutrition, to reduce food conditioning, should begin immediately at the local level as this will help to reduce polar bear mortality.

Temporal change and the influence of climate and weather factors on mercury concentrations in Hudson Bay polar bears, caribou, and seabird eggs

Temporal trends of mercury in Arctic wildlife are inconsistent within and between species and are often insignificant, which limits data interpretation. Recent multivariate analyses have shown that weather and climate factors (e.g. temperatures, sea ice conditions) are related to total Hg (THg) concentrations in wildlife tissues, though relatively few studies have explored these relationships. The present study compared time series of THg concentrations in liver of polar bear (Ursus maritimus, 2007/08-2015/16), eggs of thick-billed murres (Uria lomvia, 1993-2015) and kidney of caribou (Rangifer tarandus groenlandicus, 2006-2015) from the Hudson Bay region of Canada and statistically modelled THg over time with available climate and weather data. Significant temporal trends of THg concentrations were not detected in any species. However, in multivariate models that included time-lagged sea ice freeze up dates, THg concentrations increased 4.4% yr^-1 in Qamanirjuaq caribou. Sea ice conditions were also related to THg levels in polar bear liver but not those in eggs of murres, though year was not a signifcant factor. Greater precipitation levels one to two years prior to sampling were associated with greater THg concentrations in polar bears and caribou, likely due to greater deposition, flooding and discharge from nearby wetlands and rivers. Time-lagged Arctic and/or North Atlantic Oscillation (AO/NAO) indices also generated significant, inverse models for all three species, agreeing with relationships in other time series of similar length. The magnitude and direction of many relationships were affected by season, duration of time-lags, and the length of the time series. Our findings support recent observations suggesting that temporal studies monitoring Hg in Arctic wildlife should consider including key climatic or weather factors to help identify consistent variables of influence and to improve temporal analyses of THg time series.

Carbon dioxide emissions, urbanization level, and industrial structure: empirical evidence from North China

This paper aims to examine the nexus among carbon dioxide (CO₂) emissions, urbanization level and industrial structure in North China over the period 2004-2019, according to an expanded Cobb-Douglas production function. The panel econometric techniques are employed to complete the empirical analysis, including cross-sectional correlation test, panel unit root test, panel co-integration test, and panel Granger causality test. The empirical results support the long-term equilibrium relationship among CO₂ emissions, urbanization level and industrial structure in North China, and the urbanization level contributes most to CO₂ emissions, followed by fossil energy consumption. Furthermore, the bidirectional causality between CO₂ emissions and urbanization level and unidirectional causality from industrial structure to CO₂ emissions are found in North China, indicating that urbanization level and industrial structure have significant impacts on CO₂ emissions. Finally, according to the empirical findings, several policy suggestions are proposed for the purpose of reducing CO₂ emissions in North China.

Case Studies in Polar Bear (Ursus maritimus) Sperm Collection and Cryopreservation Techniques

Simple Summary

Polar bears are threatened by habitat loss, decreased food availability, and reduced reproductive success due to climate change. Zoo populations can support species survival through preservation of genetic diversity and maintenance of insurance populations, but in the US, the zoo polar bear population is currently not sustainable. The development of sperm collection and cryopreservation can help to support the population by providing the biomaterial needed for assisted reproductive techniques, such as artificial insemination. However, these procedures are not well described for polar bears. Data from 38 opportunistic sperm collections, that were conducted between 2011 and 2021, were assessed to establish best practices to date for collecting and preserving polar bear sperm. The information gathered demonstrates that urethral catheterization is an efficient method of sperm collection, sperm can be rescued postmortem from the vasa deferentia and epididymides, and polar bear sperm collection appears to be most effective during the breeding season. Furthermore, polar bear sperm can survive cryopreservation. Further studies will optimize these techniques, but this summary provides information that is immediately applicable to enhancing sample collection and cryopreservation success that could support the long-term genetic management of polar bears in zoos.

Abstract

Assisted reproductive technologies can aid conservation efforts via support of ex situ population management and preservation of genetic material. Data from 38 sperm collection attempts from 17 polar bears (1–5 procedures/bear) were evaluated. Sample collections were attempted via electroejaculation (EEJ; n = 6), urethral catheterization (UC; n = 25), or sperm rescue (SR; n = 7) during the breeding season (Jan. 1-May 21; n = 27) and nonbreeding season (May 22-Dec. 31; n = 11). Sperm retrieval was successful in 1 EEJ (16.7%), 18 UC (72.0%) and 4 SR (57.1%) collections. Initial sperm motility and viability were 50.0% and 77.0% for EEJ, 64.3 ± 7.4% and 80.9 ± 3.8% for UC, and 56.7 ± 8.8% and 80.5 ± 0.5% for SR. UC and SR were more likely to be successful during the breeding season (84.2–100%) than the nonbreeding season (25.0–33.3%). Testicular tumors were observed in four males (57%) during SR. In total, 13 samples were cryopreserved (n = 1 EEJ, 9 UC, and 3 SR) with egg-yolk-based equine extender (EQ) or OptiXcell (OP). For both extenders, post-thaw motility and viability were reduced by 20–60% and 30–65%, respectively. Further efforts to optimize procedures are warranted, but this summary provides data useful for enhancing the success of polar bear sperm collection and cryopreservation.

Distinct gut microbiomes in two polar bear subpopulations inhabiting different sea ice ecoregions

Gut microbiomes were analyzed by 16S rRNA gene metabarcoding for polar bears (Ursus maritimus) from the southern Beaufort Sea (SB), where sea ice loss has led to increased use of land-based food resources by bears, and from East Greenland (EG), where persistent sea ice has allowed hunting of ice-associated prey nearly year-round. SB polar bears showed a higher number of total (940 vs. 742) and unique (387 vs. 189) amplicon sequence variants and higher inter-individual variation compared to EG polar bears. Gut microbiome composition differed significantly between the two subpopulations and among sex/age classes, likely driven by diet variation and ontogenetic shifts in the gut microbiome. Dietary tracer analysis using fatty acid signatures for SB polar bears showed that diet explained more intrapopulation variation in gut microbiome composition and diversity than other tested variables, i.e., sex/age class, body condition, and capture year. Substantial differences in the SB gut microbiome relative to EG polar bears, and associations between SB gut microbiome and diet, suggest that the shifting foraging habits of SB polar bears tied to sea ice loss may be altering their gut microbiome, with potential consequences for nutrition and physiology.

An on-ice aerial survey of the Kane Basin polar bear (Ursus maritimus) subpopulation

There is an imminent need to collect information on distribution and abundance of polar bears (Ursus maritimus) to understand how they are affected by the ongoing decrease in Arctic sea ice. The Kane Basin (KB) subpopulation is a group of high-latitude polar bears that ranges between High Arctic Canada and NW Greenland around and north of the North Water polynya (NOW). We conducted a line transect distance sampling aerial survey of KB polar bears during 28 April–12 May 2014. A total of 4160 linear kilometers were flown in a helicopter over fast ice in the fjords and over offshore pack ice between 76° 50′ and 80° N′. Using a mark-recapture distance sampling protocol, the estimated abundance was 190 bears (95% lognormal CI: 87–411; CV 39%). This estimate is likely negatively biased to an unknown degree because the offshore sectors of the NOW with much open water were not surveyed because of logistical and safety reasons. Our study demonstrated that aerial surveys may be a feasible method for obtaining abundance estimates for small subpopulations of polar bears.

Yes, they can: polar bears Ursus maritimus successfully hunt Svalbard reindeer Rangifer tarandus platyrhynchus

The polar bear Ursus maritimus is one of the species most endangered by the rapidly declining sea–ice cover in the Arctic, which they use as a platform to hunt fatty, high-energy seals. In recent decades, more polar bears have been forced to remain longer on land, so their access to seals is limited. The importance of terrestrial food to polar bears is disputable, and more data are needed. Terrestrial ungulates could be an attractive substitute prey for them. Svalbard reindeer Rangifer tarandus platyrhynchus are prevalent and their distribution is completely within the range of polar bears. They constitute an attractive potential prey offering a significant energy return. Pre-2000 sources state that polar bears do not attack Svalbard reindeer. This report is the first description and documentation of the complete course of a polar bear hunt for adult reindeer in Hornsund, SW Spitsbergen, and also of the bear’s hunting behaviour and the reindeer’s response. Further, we report several other recent instances of bear–reindeer interactions in Svalbard, suggesting that polar bears now hunt reindeer more frequently than they used to. This increase in hunting is probably linked to the reduced ice cover, with bears spending more time on land, and a growing reindeer population. This study adds to earlier papers on how polar bears in Svalbard have increasingly shifted to a more terrestrial diet, and indicates that they may have an enhanced role as an apex predator in the terrestrial ecosystem.

A novel mark-recapture-recovery survey using genetic sampling for polar bears Ursus maritimus in Baffin Bay

Changes in sea-ice dynamics are affecting polar bears Ursus maritimus across their circumpolar range, which highlights the importance of periodic demographic assessments to inform management and conservation. We used genetic mark-recapture-recovery to derive estimates of abundance and survival for the Baffin Bay (BB) polar bear subpopulation—the first time this method has been used successfully for this species. Genetic data from tissue samples we collected via biopsy darting were combined with historical physical capture and harvest recovery data. The combined data set consisted of 1410 genetic samples (2011-2013), 914 physical captures (1993-1995, 1997), and 234 harvest returns of marked bears (1993-2013). The estimate of mean subpopulation abundance was 2826 (95% CI = 2284-3367) in 2012-2013. Estimates of annual survival (mean ± SE) were 0.90 ± 0.05 and 0.78 ± 0.06 for females and males age ≥2 yr, respectively. The proportion of total mortality of adult females and males that was attributed to legal harvest was 0.16 ± 0.05 and 0.26 ± 0.06, respectively. Remote sensing sea-ice data, telemetry data, and spatial distribution of onshore sampling indicated that polar bears were more likely to use offshore sea-ice habitat during the 1990s sampling period compared to the 2010s. Furthermore, in the 1990s, sampling of deep fjords and inland areas was limited, and no offshore sampling occurred in either time period, which precluded comparisons of abundance between the 1993-1997 and 2011-2013 study periods. Our findings demonstrate that genetic sampling can be a practical method for demographic assessment of polar bears over large spatial and temporal scales.

Long-term increases in pathogen seroprevalence in polar bears (Ursus maritimus) influenced by climate change

The influence of climate change on wildlife disease dynamics is a burgeoning conservation and human health issue, but few long-term studies empirically link climate to pathogen prevalence. Polar bears (Ursus maritimus) are vulnerable to the negative impacts of sea ice loss as a result of accelerated Arctic warming. While studies have associated changes in polar bear body condition, reproductive output, survival, and abundance to reductions in sea ice, no long-term studies have documented the impact of climate change on pathogen exposure. We examined 425 serum samples from 381 adult polar bears, collected in western Hudson Bay (WH), Canada, for antibodies to selected pathogens across three time periods: 1986-1989 (n = 157), 1995-1998 (n = 159) and 2015-2017 (n = 109). We ran serological assays for antibodies to seven pathogens: Toxoplasma gondii, Neospora caninum, Trichinella spp., Francisella tularensis, Bordetella bronchiseptica, canine morbillivirus (CDV) and canine parvovirus (CPV). Seroprevalence of zoonotic parasites (T. gondii, Trichinella spp.) and bacterial pathogens (F. tularensis, B. bronchiseptica) increased significantly between 1986-1989 and 1995-1998, ranging from +6.2% to +20.8%, with T. gondii continuing to increase into 2015-2017 (+25.8% overall). Seroprevalence of viral pathogens (CDV, CPV) and N. caninum did not change with time. Toxoplasma gondii seroprevalence was higher following wetter summers, while seroprevalences of Trichinella spp. and B. bronchiseptica were positively correlated with hotter summers. Seroprevalence of antibodies to F. tularensis increased following years polar bears spent more days on land, and polar bears previously captured in human settlements were more likely to be seropositive for Trichinella spp. As the Arctic has warmed due to climate change, zoonotic pathogen exposure in WH polar bears has increased, driven by numerous altered ecosystem pathways.

Survival and abundance of polar bears in Alaska's Beaufort Sea, 2001-2016

The Arctic Ocean is undergoing rapid transformation toward a seasonally ice-free ecosystem. As ice-adapted apex predators, polar bears (Ursus maritimus) are challenged to cope with ongoing habitat degradation and changes in their prey base driven by food-web response to climate warming. Knowledge of polar bear response to environmental change is necessary to understand ecosystem dynamics and inform conservation decisions. In the southern Beaufort Sea (SBS) of Alaska and western Canada, sea ice extent has declined since satellite observations began in 1979 and available evidence suggests that the carrying capacity of the SBS for polar bears has trended lower for nearly two decades. In this study, we investigated the population dynamics of polar bears in Alaska's SBS from 2001 to 2016 using a multistate Cormack-Jolly-Seber mark-recapture model. States were defined as geographic regions, and we used location data from mark-recapture observations and satellite-telemetered bears to model transitions between states and thereby explain heterogeneity in recapture probabilities. Our results corroborate prior findings that the SBS subpopulation experienced low survival from 2003 to 2006. Survival improved modestly from 2006 to 2008 and afterward rebounded to comparatively high levels for the remainder of the study, except in 2012. Abundance moved in concert with survival throughout the study period, declining substantially from 2003 and 2006 and afterward fluctuating with lower variation around an average of 565 bears (95% Bayesian credible interval [340, 920]) through 2015. Even though abundance was comparatively stable and without sustained trend from 2006 to 2015, polar bears in the Alaska SBS were less abundant over that period than at any time since passage of the U.S. Marine Mammal Protection Act. The potential for recovery is likely limited by the degree of habitat degradation the subpopulation has experienced, and future reductions in carrying capacity are expected given current projections for continued climate warming.

Conceptualizing and quantifying body condition using structural equation modelling: A user guide

Body condition is an important concept in behaviour, evolution and conservation, commonly used as a proxy of an individual's performance, for example in the assessment of environmental impacts. Although body condition potentially encompasses a wide range of health state dimensions (nutritional, immune or hormonal status), in practice most studies operationalize body condition using a single (univariate) measure, such as fat storage. One reason for excluding additional axes of variation may be that multivariate descriptors of body condition impose statistical and analytical challenges. Structural equation modelling (SEM) is used in many fields to study questions relating multidimensional concepts, and we here explain how SEM is a useful analytical tool to describe the multivariate nature of body condition. In this 'Research Methods Guide' paper, we show how SEM can be used to resolve different challenges in analysing the multivariate nature of body condition, such as (a) variable reduction and conceptualization, (b) specifying the relationship of condition to performance metrics, (c) comparing competing causal hypothesis and (d) including many pathways in a single model to avoid stepwise modelling approaches. We illustrated the use of SEM on a real-world case study and provided R-code of worked examples as a learning tool. We compared the predictive power of SEM with conventional statistical approaches that integrate multiple variables into one condition variable: multiple regression and principal component analyses. We show that model performance on our dataset is higher when using SEM and led to more accurate and precise estimates compared to conventional approaches. We encourage researchers to consider SEM as a flexible framework to describe the multivariate nature of body condition and thus understand how it affects biological processes, thereby improving the value of body condition proxies for predicting organismal performance. Finally, we highlight that it can be useful for other multidimensional ecological concepts as well, such as immunocompetence, oxidative stress and environmental conditions.

Are tissue samples obtained via remote biopsy useful for fatty acid-based diet analyses in a free-ranging carnivore?

Fundamental knowledge on free-ranging animals has been obtained through capture-based studies; however, these may be logistically intensive, financially expensive, and potentially inconsistent with local cultural values. Genetic mark–recapture using remote tissue sampling has emerged as a less invasive alternative to capture-based population surveys but provides fewer opportunities to collect samples and measurements for broader ecological studies. We compared lipid content, fatty acid (FA) composition, and diet estimates from adipose tissue of polar bears (Ursus maritimus) obtained from two collection methods: remote biopsies (n = 138) sampled from helicopters and hunter-collected tissue (n = 499) from bears harvested in Davis Strait and Gulf of Boothia, Nunavut, 2010 – 2018. Lipid content of adipose tissue was lower in remote biopsies than harvest samples likely because remote biopsies removed only the outermost layer of subcutaneous tissue, rather than the more metabolically dynamic innermost tissue obtained from harvest samples. In contrast, FA composition was similar between the two collection methods with relatively small proportional differences in individual FAs. For diet estimates in Davis Strait, collection method was not a predictor of prey contribution to diet. In Gulf of Boothia, collection method was a predictor for some prey types, but the differences were relatively minor; the rank order of prey types was similar (e.g., ringed seal; Pusa hispida was consistently the primary prey in diets) and prey proportions differed by < 6% between the collection methods. Results from both methods showed that diets varied by geographic area, season, year, age class, and sex. Our study demonstrates that adipose tissue from remote biopsy provides reliable estimates of polar bear diet based on FA analysis and can be used to monitor underlying ecological changes in Arctic marine food webs.

Migratory movements of Atlantic puffins Fratercula arctica naumanni from high Arctic Greenland

Although the Atlantic puffin Fratercula arctica is well studied throughout its temperate and low Arctic breeding range, few have studied the species in its far northern distribution. This study is the first to present data on the migratory movements of the "large-billed" subspecies, F. a. naumanni, that breeds in the high Arctic and which has significantly larger body size than those farther south. During 2013-2015, migration tracks were collected from nine adult puffins (6 males and 3 females) tagged with geolocators in northwest Greenland. Overall, female puffins traveled farther than males on their annual migration, with one female puffin traveling over 13,600 km, which was nearly a third farther than any tagged male in our study. Differential migration was observed in migratory phenology and route, with males using a form of chain migration with acute synchrony between individuals while females appeared to largely use leap-frog migration and showed little synchrony between individuals. Extreme sexual segregation in wintering areas was evidenced by two females that migrated to the southern limit of the species' range while the six males remained at the northern limit, and wintered along the sea ice edge during portions of the non-breeding season. Male puffins thus wintered in regions with sea surface temperatures up to 10° C cooler than female puffins, and in areas with generally colder sea surface temperatures when compared to previously known wintering areas of temperate and low Arctic puffin breeding populations. The degree to which body size enables male F. a. naumanni to remain in colder waters likely reflects differing life history constraints between sexes and populations (i.e., subspecies). Further study is warranted to investigate how recent changes in climate have further exacerbated the observed differences between sexes in high Arctic puffins and possibly other marine avian species.

Modeling the demography of species providing extended parental care: A capture-recapture multievent model with a case study on polar bears (Ursus maritimus)

In species providing extended parental care, one or both parents care for altricial young over a period including more than one breeding season. We expect large parental investment and long-term dependency within family units to cause high variability in life trajectories among individuals with complex consequences at the population level. So far, models for estimating demographic parameters in free-ranging animal populations mostly ignore extended parental care, thereby limiting our understanding of its consequences on parents and offspring life histories.We designed a capture-recapture multievent model for studying the demography of species providing extended parental care. It handles statistical multiple-year dependency among individual demographic parameters grouped within family units, variable litter size, and uncertainty on the timing at offspring independence. It allows for the evaluation of trade-offs among demographic parameters, the influence of past reproductive history on the caring parent's survival status, breeding probability, and litter size probability, while accounting for imperfect detection of family units. We assess the model performance using simulated data and illustrate its use with a long-term dataset collected on the Svalbard polar bears (Ursus maritimus).Our model performed well in terms of bias and mean square error and in estimating demographic parameters in all simulated scenarios, both when offspring departure probability from the family unit occurred at a constant rate or varied during the field season depending on the date of capture. For the polar bear case study, we provide estimates of adult and dependent offspring survival rates, breeding probability, and litter size probability. Results showed that the outcome of the previous reproduction influenced breeding probability.Overall, our results show the importance of accounting for i) the multiple-year statistical dependency within family units, ii) uncertainty on the timing at offspring independence, and iii) past reproductive history of the caring parent. If ignored, estimates obtained for breeding probability, litter size, and survival can be biased. This is of interest in terms of conservation because species providing extended parental care are often long-living mammals vulnerable or threatened with extinction.

Influence of sea ice dynamics on population energetics of Western Hudson Bay polar bears

The Arctic marine ecosystem has experienced extensive changes in sea ice dynamics, with significant effects on ice-dependent species such as polar bears (Ursus maritimus). We used annual estimates of the numbers of bears onshore in the core summering area, age/sex structure and body condition data to estimate population energy density and storage energy in Western Hudson Bay polar bears from 1985 to 2018. We examined intra-population variation in energetic patterns, temporal energetic trends and the relationship between population energetics and sea ice conditions. Energy metrics for most demographic classes declined over time in relation to earlier sea ice breakup, most significantly for solitary adult females and subadult males, suggesting their greater vulnerability to nutritional stress than other age/sex classes. Temporal declines in population energy metrics were related to earlier breakup and longer lagged open-water periods, suggesting multi-year effects of sea ice decline. The length of the open-water period ranged from 102 to 166 days and increased significantly by 9.9 days/decade over the study period. Total population energy density and storage energy were significantly lower when sea ice breakup occurred earlier and the lagged open-water period was longer. At the earliest breakup and a lagged open-water period of 180 days, population energy density was predicted to be 33% lower than our minimum estimated energy density and population storage energy was predicted to be 40% lower than the minimum estimated storage energy. Consequently, over the study, the total population energy density declined by 53% (mean: 3668 ± 386 MJ kg-1/decade) and total population storage energy declined by 56% (mean: 435900 ± 46770 MJ/decade). This study provides insights into ecological mechanisms linking population responses to sea ice decline and highlights the significance of maintaining long-term research programs.

Climate-associated drivers of plasma cytokines and contaminant concentrations in Beaufort Sea polar bears (Ursus maritimus)

Assessing polar bear (Ursus maritimus) immune function in relation to environmental stressors, including habitat change, nutritional stress, pathogen prevalence, and pollution, has been identified as critical for improved understanding of the species' health. The objectives of this study were two-fold: 1) to assess the role of climate-associated factors (habitat use, body condition) in explaining the plasma concentrations of contaminants in southern Beaufort Sea (SB) polar bears, and 2) to investigate how climate-associated factors, contaminant concentrations, and pathogen sero-prevalence influence the plasma concentrations of immune-signaling proteins called cytokines. A commercially available multiplex canine cytokine panel was validated for the quantification of five pro- and anti-inflammatory cytokines in polar bear plasma: tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6), IL-8, IL-10, and interferon gamma-induced protein 10 (IP-10). This panel was then used to measure cytokine concentrations in 49 SB polar bears sampled in the springs of 2013 and 2014. Mean ∑PCBs (plasma), ∑OCs (plasma), and THg (hair) were 13.01 ± 1.52 ng g^-1 w.w. (range: 0.17-52.63), 19.46 ± 1.17 ng g^-1 w.w. (range: 6.63-45.82), and 0.49 μg g^-1 d.w. (range: 0.99-15.18), respectively. Top models explaining variation in concentrations of plasma PCBs, plasma OC pesticides, and hair THg in SB polar bears included body mass index and/or habitat use (onshore versus offshore), with higher contaminant concentrations in leaner and/or offshore bears. Plasma cytokine concentrations were influenced most strongly by plasma PCBs and age, with little to no influence found for plasma OCs or hair THg concentrations, habitat use, or pathogen sero-prevalence. The lack of association between cytokines and these latter variables is likely due to a temporal disconnect between measured endpoints. The change of polar bear habitat use, feeding ecology, and body condition with ongoing climate warming is affecting exposure to contaminants and pathogens, with potential adverse consequences on a well-balanced immune system.

Transient benefits of climate change for a high-Arctic polar bear (Ursus maritimus) subpopulation

Kane Basin (KB) is one of the world's most northerly polar bear (Ursus maritimus) subpopulations, where bears have historically inhabited a mix of thick multiyear and annual sea ice year-round. Currently, KB is transitioning to a seasonally ice-free region because of climate change. This ecological shift has been hypothesized to benefit polar bears in the near-term due to thinner ice with increased biological production, although this has not been demonstrated empirically. We assess sea-ice changes in KB together with changes in polar bear movements, seasonal ranges, body condition, and reproductive metrics obtained from capture-recapture (physical and genetic) and satellite telemetry studies during two study periods (1993-1997 and 2012-2016). The annual cycle of sea-ice habitat in KB shifted from a year-round ice platform (~50% coverage in summer) in the 1990s to nearly complete melt-out in summer (<5% coverage) in the 2010s. The mean duration between sea-ice retreat and advance increased from 109 to 160 days (p = .004). Between the 1990s and 2010s, adult female (AF) seasonal ranges more than doubled in spring and summer and were significantly larger in all months. Body condition scores improved for all ages and both sexes. Mean litter sizes of cubs-of-the-year (C0s) and yearlings (C1s), and the number of C1s per AF, did not change between decades. The date of spring sea-ice retreat in the previous year was positively correlated with C1 litter size, suggesting smaller litters following years with earlier sea-ice breakup. Our study provides evidence for range expansion, improved body condition, and stable reproductive performance in the KB polar bear subpopulation. These changes, together with a likely increasing subpopulation abundance, may reflect the shift from thick, multiyear ice to thinner, seasonal ice with higher biological productivity. The duration of these benefits is unknown because, under unmitigated climate change, continued sea-ice loss is expected to eventually have negative demographic and ecological effects on all polar bears.

Adipose Tissue Transcriptome Is Related to Pollutant Exposure in Polar Bear Mother-Cub Pairs from Svalbard, Norway

Being at the food chain apex, polar bears (Ursus maritimus) are highly contaminated with persistent organic pollutants (POPs). Females transfer POPs to their offspring through gestation and lactation; therefore, young cubs present higher POPs concentrations than their mothers. Recent studies suggest that POPs affect the lipid metabolism in female polar bears; however, the mechanisms and impact on their offspring remain unknown. Here, we hypothesized that exposure to POPs differentially alters genome-wide gene transcription in the adipose tissue from mother polar bears and their cubs, highlighting molecular differences in response between adults and young. Adipose tissue biopsies were collected from 13 adult female polar bears and their twin cubs in Svalbard, Norway, in April 2011, 2012, and 2013. Total RNA extracted from biopsies was subjected to next-generation RNA sequencing. Plasma concentrations of summed polychlorinated biphenyls, organochlorine pesticides, and polybrominated diphenyl ethers in mothers ranged from 897 to 13620 ng/g wet weight and were associated with altered adipose tissue gene expression in both mothers and cubs. In mothers, 2502 and 2586 genes in total were positively and negatively, respectively, correlated to POP exposure, whereas in cubs, 2585 positively and 1690 negatively genes. Between mothers and cubs, 743 positively and negatively genes overlapped between mothers and cubs suggesting partially shared molecular responses to ΣPOPs. ΣPOP-associated genes were involved in numerous metabolic pathways in mothers and cubs, indicating that POP exposure alters the energy metabolism, which, in turn, may be linked to metabolic dysfunction.

Martin M, Wilson RR, Durner GM, Regehr EV, Talbot SL, Sage GK, Pagano AM, Simac KS. Identifying reliable indicators of fitness in polar bears

Animal structural body size and condition are often measured to evaluate individual health, identify responses to environmental change and food availability, and relate food availability to effects on reproduction and survival. A variety of condition metrics have been developed but relationships between these metrics and vital rates are rarely validated. Identifying an optimal approach to estimate the body condition of polar bears is needed to improve monitoring of their response to decline in sea ice habitat. Therefore, we examined relationships between several commonly used condition indices (CI), body mass, and size with female reproductive success and cub survival among polar bears (Ursus maritimus) measured in two subpopulations over three decades. To improve measurement and application of morphometrics and CIs, we also examined whether CIs are independent of age and structural size–an important assumption for monitoring temporal trends—and factors affecting measurement precision and accuracy. Maternal CIs and mass measured the fall prior to denning were related to cub production. Similarly, maternal CIs, mass, and length were related to the mass of cubs or yearlings that accompanied her. However, maternal body mass, but not CIs, measured in the spring was related to cub production and only maternal mass and length were related to the probability of cub survival. These results suggest that CIs may not be better indicators of fitness than body mass in part because CIs remove variation associated with body size that is important in affecting fitness. Further, CIs exhibited variable relationships with age for growing bears and were lower for longer bears despite body length being related to cub survival and female reproductive success. These results are consistent with findings from other species indicating that body mass is a useful metric to link environmental conditions and population dynamics.

Isotopic niche of the American pika (Ochotona princeps) through space and time

Anthropogenic climate change is influencing the ecology and distribution of animals. The American pika (Ochotona princeps (Richardson, 1828)) is considered a model species for studying the effects of climate on small alpine mammals and has experienced local extirpation across its range. Using stable isotope analysis of two seasonal molts and bone collagen, we characterize the isotopic carbon and nitrogen niche of pika populations across their range and through time. We find pika isotopic diet to be stable across both time and space compared with other animals and considering the geographic and environmental extent of their range. We find that climatic, not geographic, factors explain part of the isotopic variation across their range. Both δ13C and δ15N from the fall-onset molt decrease with relative humidity of the environment and δ15N values from bone collagen increase with temperature and precipitation. We find a small but significant seasonal difference in δ13C, which could be explained by microbial enrichment of cached haypiles. We establish a baseline of pika isotopic diet and patterns related to climate across their range. We conclude that differences in isotopic signature between pika populations likely reflect the physiology of their forage plants in different environmental conditions.

The stress of Arctic warming on polar bears

Arctic ecosystems are changing rapidly in response to climate warming. While Arctic mammals are highly evolved to these extreme environments, particularly with respect to their stress axis, some species may have limited capacity to adapt to this change. We examined changes in key components of the stress axis (cortisol and its carrier protein-corticosteroid binding globulin [CBG]) in polar bears (Ursus maritimus) from western Hudson Bay (N = 300) over a 33 year period (1983-2015) during which time the ice-free period was increasing. Changing sea ice phenology limits spring hunting opportunities and extends the period of onshore fasting. We assessed the response of polar bears to a standardized stressor (helicopter pursuit, darting, and immobilization) during their onshore fasting period (late summer-autumn) and quantified the serum levels of the maximum corticosteroid binding capacity (MCBC) of CBG, the serum protein that binds cortisol strongly, and free cortisol (FC). We quantified bear condition (age, sex, female with cubs or not, fat condition), sea ice (breakup in spring-summer, 1 year lagged freeze-up in autumn), and duration of fasting until sample collection as well as cumulative impacts of the latter environmental traits from the previous year. Data were separated into "good" years (1983-1990) when conditions were thought to be optimal and "poor" years (1991-2015) when sea ice conditions deteriorated and fasting on land was extended. MCBC explained 39.4% of the variation in the good years, but only 28.1% in the poor ones, using both biological and environmental variables. MCBC levels decreased with age. Changes in FC were complex, but more poorly explained. Counterintuitively, MCBC levels increased with increased time onshore, 1 year lag effects, and in poor ice years. We conclude that MCBC is a biomarker of stress in polar bears and that the changes we document are a consequence of climate warming.

Unravelling the health effects of fasting: a long road from obesity treatment to healthy life span increase and improved cognition

In recent years a revival of interest has emerged in the health benefits of intermittent fasting and long-term fasting, as well as of other related nutritional strategies. In addition to meal size and composition a new focus on time and frequency of meals has gained attention. The present review will investigate the effects of the main forms of fasting, activating the metabolic switch from glucose to fat and ketones (G-to-K), starting 12-16 h after cessation or strong reduction of food intake. During fasting the deactivation of mTOR regulated nutrient signalling pathways and activation of the AMP protein kinase trigger cell repair and inhibit anabolic processes. Clinical and animal studies have clearly indicated that modulating diet and meal frequency, as well as application of fasting patterns, e.g. intermittent fasting, periodic fasting, or long-term fasting are part of a new lifestyle approach leading to increased life and health span, enhanced intrinsic defences against oxidative and metabolic stresses, improved cognition, as well as a decrease in cardiovascular risk in both obese and non-obese subjects. Finally, in order to better understand the mechanisms beyond fasting-related changes, human studies as well as non-human models closer to human physiology may offer useful clues.KEY-MESSAGESBiochemical changes during fasting are characterised by a glucose to ketone switch, leading to a rise of ketones, advantageously used for brain energy, with consequent improved cognition.Ketones reduce appetite and help maintain effective fasting.Application of fasting patterns increases healthy life span and defences against oxidative and metabolic stresses.Today's strategies for the use of therapeutic fasting are based on different protocols, generally relying on intermittent fasting, of different duration and calorie intake.Long-term fasting, with durations between 5 and 21 days can be successfully repeated in the course of a year.

Two Decades of Mercury Concentrations in Barents Sea Polar Bears (Ursus maritimus) in Relation to Dietary Carbon, Sulfur, and Nitrogen

Temporal trends of total mercury (THg) were examined in female polar bear (Ursus maritimus) hair (n = 199) from the Barents Sea in 1995-2016. In addition, hair values of stable isotopes (n = 190-197) of carbon (δ¹³C), sulfur (δ³⁴S), and nitrogen (δ¹⁵N) and information on breeding status, body condition, and age were obtained. Stable isotope values of carbon and sulfur reflect dietary source (e.g., marine vs terrestrial) and the nitrogen trophic level. Values for δ¹³C and δ³⁴S declined by -1.62 and -1.18‰ over the time of the study period, respectively, while values for δ¹⁵N showed no trend. Total Hg concentrations were positively related to both δ¹³C and δ³⁴S. Yearly median THg concentrations ranged from 1.61 to 2.75 μg/g and increased nonlinearly by 0.86 μg/g in total over the study. Correcting THg concentrations for stable isotope values of carbon and sulfur and additionally breeding status and age slightly accelerated the increase in THg concentrations; however, confidence intervals of the raw THg trend and the corrected THg trend had substantial overlap. The rise in THg concentrations in the polar bear food web was possibly related to climate-related re-emissions of previously stored Hg from thawing sea-ice, glaciers, and permafrost.

Influence of Long-Term Fasting on Blood Redox Status in Humans

Fasting is increasingly practiced to improve health and general well-being, as well as for its cytoprotective effects. Changes in blood redox status, linked to the development of a variety of metabolic diseases, have been recently documented during calorie restriction and intermittent fasting, but not with long-term fasting (LF). We investigated some parameters of the blood redox profile in 109 subjects before and after a 10-day fasting period. Fasting resulted in a significant reduction in body weight, improved well-being and had a beneficial modulating effect on blood lipids and glucose regulation. We observed that fasting decreased lipid peroxidation (TBARS) and increased total antioxidant capacity (TAC) in plasma, concomitant with a uric acid elevation, known to be associated with fasting and did not cause gout attacks. Reduced glutathione (GSH), glutathione reductase (GR), glutathione peroxidase (GPx) and catalase in erythrocytes did not show significant changes. In addition, reduction in body weight, waist circumference, and glucose levels were associated to a reduced lipid peroxidation. Similar results were obtained by grouping subjects on the basis of the changes in their GSH levels, showing that a period of 10 days fasting improves blood redox status regardless of GSH status in the blood.

Interrelated ecological impacts of climate change on an apex predator

Climate change has broad ecological implications for species that rely on sensitive habitats. For some top predators, loss of habitat is expected to lead to cascading behavioral, nutritional, and reproductive changes that ultimately accelerate population declines. In the case of the polar bear (Ursus maritimus), declining Arctic sea ice reduces access to prey and lengthens seasonal fasting periods. We used a novel combination of physical capture, biopsy darting, and visual aerial observation data to project reproductive performance for polar bears by linking sea ice loss to changes in habitat use, body condition (i.e., fatness), and cub production. Satellite telemetry data from 43 (1991-1997) and 38 (2009-2015) adult female polar bears in the Baffin Bay subpopulation showed that bears now spend an additional 30 d on land (90 d in total) in the 2000s compared to the 1990s, a change closely correlated with changes in spring sea ice breakup and fall sea ice formation. Body condition declined for all sex, age, and reproductive classes and was positively correlated with sea ice availability in the current and previous year. Furthermore, cub litter size was positively correlated with maternal condition and spring breakup date (i.e., later breakup leading to larger litters), and negatively correlated with the duration of the ice-free period (i.e., longer ice-free periods leading to smaller litters). Based on these relationships, we projected reproductive performance three polar bear generations into the future (approximately 35 yr). Results indicate that two-cub litters, previously the norm, could largely disappear from Baffin Bay as sea ice loss continues. Our findings demonstrate how concurrent analysis of multiple data types collected over long periods from polar bears can provide a mechanistic understanding of the ecological implications of climate change. This information is needed for long-term conservation planning, which includes quantitative harvest risk assessments that incorporate estimated or assumed trends in future environmental carrying capacity.

Faecal glucocorticoid metabolites as a measure of adrenocortical activity in polar bears (Ursus maritimus)

Analysis of faecal glucocorticoid metabolites (FGMs) is frequently applied to assess adrenocortical activity in animal conservation and welfare studies. Faecal sample collection is non-invasive and feasible under field conditions. FGM levels are also less prone to circadian rhythms, episodic fluctuations and short acute stressors than glucocorticoid (GC) levels obtained from other matrices, for example blood or saliva. To investigate the suitability of FGM measurement in polar bears (Ursus maritimus), a species listed as Vulnerable by the IUCN (International Union for Conservation of Nature), a cortisol enzyme immunoassay (EIA) was biologically validated by demonstrating a significant increase in FGMs after five zoo-to-zoo transports. In addition to validating the method, the study also documented an average delay of 7 h until the first occurrence of food colorants in the monitored polar bears, which provides essential information for future studies. After validation, the assay was applied to measure FGM concentrations of five polar bears over a 1-year period. Several pre-defined potentially stressful events were recorded in an event log to measure their effect on FGM concentrations. A mixed model analysis revealed significant increases in FGM concentrations after social tension and environmental changes, whereas season and sex had no significant effect. The study demonstrates that the applied cortisol EIA is suitable for measuring FGM levels in polar bears and that using a carefully validated assay for FGM analysis in combination with a detailed sampling protocol can serve as a valuable tool for evaluating mid- to long-term stress in polar bears. FGM levels can be used to monitor stress in captive polar bears in order to optimize housing conditions but also to elucidate stress responses in wild populations for targeted conservation measures.

Contrasting Temporal Patterns of Mercury, Niche Dynamics, and Body Fat Indices of Polar Bears and Ringed Seals in a Melting Icescape

Polar bears (Ursus maritimus) and ringed seals (Pusa hispida) have a strong predator-prey relationship and are facing climate-associated Arctic habitat loss and harmful dietary exposure to total mercury (THg) and other pollutants. However, little is known about whether both species inhabiting the same area exhibit similar temporal patterns in Hg concentration, niche dynamics, and body fat indices. We used THg, δ¹³C, and δ¹⁵N values of western Hudson Bay polar bear hair (2004-2016) and ringed seal muscle samples (2003-2015) to investigate temporal trends of these variables and multidimensional niche metrics, as well as body fat indices for both species. We found a decline in THg concentration (by 3.8% per year) and δ¹³C (by 1.5‰) in ringed seals suggesting a change in feeding habits and carbon source use over time, whereas no significant changes occurred in polar bears. In contrast, the polar bear 3-dimensional niche size decreased by nearly half with no change in ringed seal niche size. The δ¹³C spacing between both species increased by approximately 1.5× suggesting different responses to annual changes in sympagic-pelagic carbon source production. Ringed seal body fat index was higher in years of earlier sea ice breakup with no change occurring in polar bears. These findings indicate that both species are responding differently to a changing environment suggesting a possible weakening of their predator-prey relationship in western Hudson Bay.

Identifying individual polar bears at safe distances: A test with captive animals

The need to recognise individuals in population and behavioural studies has stimulated the development of various identification methods. A commonly used method is to employ natural markers to distinguish individuals. In particular, the automated processing of photographs of study animals has gained interest due to the speed of processing and the ability to handle a high volume of records. However, automated processing requires high-quality photographs, which means that they need to be taken from a specific angle or at close distances. Polar bears Ursus maritimus, for example, may be identified by automated analysis of whisker spot patterns. However, to obtain photographs of adequate quality, the animals need to be closer than is usually possible without risk to animal or observer. In this study we tested the accuracy of an alternative method to identify polar bears at further distances. This method is based on distinguishing a set of physiognomic characteristics, which can be recognised from photographs taken in the field at distances of up to 400 m. During five trials, sets of photographs of 15 polar bears from six zoos, with each individual bear portrayed on different dates, were presented for identification to ten test observers. Among observers the repeatability of the assessments was 0.68 (SE 0.011). Observers with previous training in photogrammetric techniques performed better than observers without training. Experience with observing polar bears in the wild did not improve skills to identify individuals on photographs. Among the observers with photogrammetric experience, the rate of erroneous assessment was on average 0.13 (SE 0.020). For the inexperienced group this was 0.72 (SE 0.018). Error rates obtained with automated whisker spot analysis were intermediate (0.26–0.58). We suggest that wildlife studies will benefit from applying several identification techniques to collect data under different conditions.

Correlates of seasonal change in the body condition of an Arctic top predator

Climate-driven sea ice loss has led to changes in the timing of key biological events in the Arctic, however, the consequences and rate of these changes remain largely unknown. Polar bears (Ursus maritimus) undergo seasonal changes in energy stores in relation to foraging opportunities and habitat conditions. Declining sea ice has been linked to reduced body condition in some subpopulations, however, the specific timing and duration of the feeding period when bears acquire most of their energy stores and its relationship to the timing of ice break-up is poorly understood. We used community-based sampling to investigate seasonality in body condition (energy stores) of polar bears in Nunavut, Canada, and examined the influence of sea ice variables. We used adipose tissue lipid content as an index of body condition for 1,206 polar bears harvested from 2010-2017 across five subpopulations with varying seasonal ice conditions: Baffin Bay (October-August), Davis Strait and Foxe Basin (year-round), Gulf of Boothia and Lancaster Sound (August-May). Similar seasonal patterns were found in body condition across subpopulations with bears at their nadir of condition in the spring, followed by fat accumulation past break-up date and subsequent peak body condition in autumn, indicating that bears are actively foraging in late spring and early summer. Late season feeding implies that even minor advances in the timing of break-up may have detrimental effects on foraging opportunities, body condition, and subsequent reproduction and survival. The magnitude of seasonal changes in body condition varied across the study area, presumably driven by local environmental conditions. Our results demonstrate how community-based monitoring of polar bears can reveal population-level responses to climate warming in advance of detectable demographic change. Our data on the seasonal timing of polar bear foraging and energy storage should inform predictive models of the effects of climate-mediated sea ice loss.

Pelagic vs Coastal-Key Drivers of Pollutant Levels in Barents Sea Polar Bears with Contrasted Space-Use Strategies

In the Barents Sea, pelagic and coastal polar bears are facing various ecological challenges that may explain the difference in their pollutant levels. We measured polychlorinated biphenyls, organochlorine pesticides, polybrominated diphenyl ethers in fat, and perfluoroalkyl substances in plasma in pelagic and coastal adult female polar bears with similar body condition. We studied polar bear feeding habits with bulk stable isotope ratios of carbon and nitrogen. Nitrogen isotopes of amino acids were used to investigate their trophic position. We studied energy expenditure by estimating field metabolic rate using telemetry data. Annual home range size was determined, and spatial gradients in pollutants were explored using latitude and longitude centroid positions of polar bears. Pollutant levels were measured in harp seals from the Greenland Sea and White Sea-Barents Sea as a proxy for a West-East gradient of pollutants in polar bear prey. We showed that pelagic bears had higher pollutant loads than coastal bears because (1) they feed on a higher proportion of marine and higher trophic level prey, (2) they have higher energy requirements and higher prey consumption, (3) they forage in the marginal ice zones, and (4) they feed on prey located closer to pollutant emission sources/transport pathways.

Global change biology: A primer

Because of human action, the Earth has entered an era where profound changes in the global environment are creating novel conditions that will be discernable far into the future. One consequence may be a large reduction of the Earth's biodiversity, potentially representing a sixth mass extinction. With effective stewardship, the global change drivers that threaten the Earth's biota could be alleviated, but this requires clear understanding of the drivers, their interactions, and how they impact ecological communities. This review identifies 10 anthropogenic global change drivers and discusses how six of the drivers (atmospheric CO₂ enrichment, climate change, land transformation, species exploitation, exotic species invasions, eutrophication) impact Earth's biodiversity. Driver impacts on a particular species could be positive or negative. In either case, they initiate secondary responses that cascade along ecological lines of connection and in doing so magnify the initial impact. The unique nature of the threat to the Earth's biodiversity is not simply due to the magnitude of each driver, but due to the speed of change, the novelty of the drivers, and their interactions. Emphasizing one driver, notably climate change, is problematic because the other global change drivers also degrade biodiversity and together threaten the stability of the biosphere. As the main academic journal addressing global change effects on living systems, GCB is well positioned to provide leadership in solving the global change challenge. If humanity cannot meet the challenge, then GCB is positioned to serve as a leading chronicle of the sixth mass extinction to occur on planet Earth.

Body condition impacts blood and muscle oxygen storage capacity of free-living beluga whales (Delphinapterus leucas)

Arctic marine ecosystems are currently undergoing rapid environmental changes. Over the past 20 years, individual growth rates of beluga whales (Delphinapterus leucas) have declined, which may be a response to climate change; however, the scarcity of physiological data makes it difficult to gauge the adaptive capacity and resilience of the species. We explored relationships between body condition and physiological parameters pertaining to oxygen (O₂) storage capacity in 77 beluga whales in the eastern Beaufort Sea. Muscle myoglobin concentrations averaged 77.9 mg g^-1, one of the highest values reported among mammals. Importantly, blood haematocrit, haemoglobin and muscle myoglobin concentrations correlated positively to indices of body condition, including maximum half-girth to length ratios. Thus, a whale with the lowest body condition index would have ∼27% lower blood (26.0 versus 35.7 ml kg^-1) and 12% lower muscle (15.6 versus 17.7 ml kg^-1) O₂ stores than a whale of equivalent mass with the highest body condition index; with the conservative assumption that underwater O₂ consumption rates are unaffected by body condition, this equates to a >3 min difference in maximal aerobic dive time between the two extremes (14.3 versus 17.4 min). Consequently, environmental changes that negatively impact body condition may hinder the ability of whales to reach preferred prey sources, evade predators and escape ice entrapments. The relationship between body condition and O₂ storage capacity may represent a vicious cycle, in which environmental changes resulting in decreased body condition impair foraging, leading to further reductions in condition through diminished prey acquisition and/or increased foraging efforts.

Concentrations of legacy and new contaminants are related to metabolite profiles in Hudson Bay polar bears

There are very few metabolomics assessments based on field accumulated, uncontrolled contaminant exposures in wildlife, particularly in the Arctic. In the present study, targeted metabolomics and contaminant data were analyzed together to assess potential influences of contaminant exposure on the hepatic metabolome of male polar bears (n = 29) from the southern and western Hudson Bay (SHB and WHB respectively), Canada. The 29 metabolites identified as important in the differentiation of the two subpopulations after partial least squares discriminant analysis (PLS-DA) included phosphatidylcholines (PCs), acylcarnitines (ACs; involved in β-oxidation of fatty acids), and the fatty acid (FA) arachidonic acid (ARA). Perfluorinated alkyl substances, polybrominated diphenyl ethers, dichlorodiphenyldichloroethylene (p,p'-DDE) and some highly chlorinated ortho-polychlorinated biphenyl congeners were greater in the SHB bears and were consistently inversely correlated with discriminating ACs and PCs between the subpopulations. The concentrations of discriminatory, legacy organochlorine pesticides along with one tetrachlorobiphenyl were greater in the WHB and were directly correlated with the VIP-identified ACs and PCs. ARA, glycerophospholipid and several amino acid metabolic pathways were identified as different between subpopulations and/or were impacted. ARA is an important, conditionally essential, dietary n-6 FA and is also part of the inflammation response, and elevated concentrations in the SHB could be related to differences in chronic contaminant exposure and/or differences in diet and/or season, among a number of possible explanations. Dietary tracers (stable isotopes of carbon and nitrogen) were correlated with some discriminatory metabolites, supporting the hypothesis that dietary variation was also an important factor in the differentiation of the subpopulations. The results suggest linkages between contaminant exposure in Hudson Bay polar bears and elements of the hepatic metabolome, particularly those related to lipid metabolism.