Geology topics

Karyn D. Rode

Publications and source records attributed to Karyn D. Rode.

At least 19 recordsLinked to original sources

USGS2025

Hair growth rate estimation in North American ursids

The feeding ecology of wildlife populations has important implications for individual health, population productivity and distribution patterns. For ursids (bears), food resources and feeding behaviour primarily affect population dynamics via effects on cub production and survival. Much of what is known about the feeding ecology of bears is based on analyses of tissues collected from capture-based research efforts, harvested animals or non-invasive approaches. However, inference about diet from hair has been limited by a lack of quantitative data on the timing of the moult and hair growth rates. We conducted a study to develop and test two methods of quantifying hair growth rates of three species in the family Ursidae ( n = 1 polar bear, Ursus maritimus ; n = 3 black bears, Ursus americanus ; n = 3 grizzly bears, Ursus arctos horribilis ). We implemented visual and biochemical approaches, proven safe for humans and other mammals, in a zoo setting. These methods relied on voluntary bear behaviours trained using positive reinforcement. The two methods were: (i) applying a small patch of hair dye (or bleach) on the rump or foreleg, and (ii) feeding an isotopically labelled amino acid (glycine) capsule that ‘marks’ time at a particular location as it is incorporated within the hair. We collected hair at regular intervals (every 1–2 weeks) for five months from body locations on the bear consistent with commonly sampled collection points in wild-caught bears. We found that both methods effectively identified periods of hair growth and detected individual and seasonal variation in hair growth rates. Average guard hair growth rates ranged between 0.10 and 1.05 mm day −1 across the three species. This study provides the first step for developing a foundation for incorporating seasonality in wild-collected bear hair samples by assessing growth over an annual cycle.

Conservation Physiology↗

USGS2025

The effects of carnivory and herbivory on the energy balance of Arctic grizzly bears

Omnivores often face tradeoffs between selecting for spatially dispersed energy-dense vertebrate prey versus densely distributed herbivorous resources that have limited energetic value per unit intake. Arctic grizzly bears ( Ursus arctos ) are large omnivores within a resource-limited ecosystem that are known to exhibit smaller body masses and occur at lower densities than grizzly bears in other regions of North America. We evaluated the energy balance of Arctic grizzly bears during a portion of the fall hyperphagic period in two ecologically differing regions on Alaska’s northern Arctic coast by monitoring mass change, food intake, activity, and energy expenditure of 12 individuals over 17–22 days. Bears in coastal areas were more carnivorous than bears in the foothills that were predominantly herbivorous and frugivorous. Carnivory was associated with greater movement, body fat, and energy expenditure and two of four carnivorous bears lost mass. Overall, the mean body fat of the bears in this study was 34% lower than other grizzly bear populations in North America in the fall. Furthermore, the bears in this study exhibited relatively small changes in body mass (x̄ = 3%, range =−2 to 11%) that were 60% lower than other grizzly bear populations which typically gain substantial mass in the fall in preparation for denning. Our results, while representing a snapshot from a small number of bears during the fall hyperphagic period, are consistent with previous studies and indicate limited availability of energy-dense food resources during this time for grizzly bears in this region of the Arctic.

Alaska↗

USGS2025

Identifying presence or absence of grizzly and polar bear cubs from the movements of adult females with machine learning

Background Information on reproductive success is crucial to understanding population dynamics but can be difficult to obtain, particularly for species that birth while denning. For grizzly ( Ursus arctos ) and polar bears ( U. maritimus ), den visits are impractical because of safety and logistical considerations. Reproduction is typically documented through direct observation, which can be difficult, costly, and often occurs long after den departure. Reproduction could be documented remotely, however, from post-denning movement data if discernable differences exist between females with and without cubs. Methods We trained support vector machines (SVMs) with eight variables derived from telemetry data of female grizzly (2000–2022) and polar bears (1985–2016) with or without cubs during seven periods with lengths ranging from 5 to 60 days starting at den departure. We assessed SVM classification accuracy by withholding two samples (one cub-present, one cub-absent), training SVMs with the remaining data, predicting classification of the withheld samples, and repeating this process for each sample combination. Additionally, we evaluated how classification accuracy for grizzly bears was influenced by sample size, length of the post-departure period, and frequency of standardized location estimates. Results Accuracy of predicting cub presence or absence was 87% for grizzly bears with only 5 days of post-departure data and increased to a maximum of 92% with 20 days of data. For polar bears, accuracy was 86% at 5 days post-departure and increased to a maximum of 93% at 50 days. Classification accuracy for grizzly bears increased from 76 to 90% when sample size increased from 10 to 30 bears while holding period length constant (30 days) but did not increase at larger sample sizes. When sample size was held constant, increasing the length of the post-departure period did not affect classification accuracy markedly. Conclusion Presence or absence of grizzly and polar bear cubs can be identified with high accuracy even when SVM models are trained with limited data. Detecting cub presence or absence remotely could improve estimates of reproductive success and litter survival, enhancing our understanding of factors affecting cub recruitment.

Alaska, Idaho, Montana, Wyoming↗

USGS2025

Hemoglobin A1c is a retrospective indicator of denning in polar bears (Ursus maritimus)

The nutritional health of polar bears ( Ursus maritimus) is tied to reproductive success, and fasting status can be used to infer recent reproductive history. However, the methods currently used to determine denning and fasting status have their limitations. We examined hemoglobin A1c (HbA1c), an integrative metric of average blood glucose levels over recent months, in free-ranging Southern Beaufort Sea polar bears to assess its usefulness in determining reproductive status and fasting. We compared HbA1c between bears recently in maternity dens that included spring-captured females that were accompanied by cubs-of-the-year ( n = 38), and non-denned bears that included spring-captured females that were accompanied by 1- or 2-yr-old cubs ( n = 39). We predicted that HbA1c would be higher in denned females compared to non-denned females, due to the combined effects of increased circulating glucose associated with insulin resistance from fasting and gestation, as well as the energy mobilization required during early lactation. HbA1c was measured in Polar Bear whole blood samples using an enzymatic assay for quantifying HbA1c and expressed as the percentage of glycated hemoglobin over total hemoglobin. Denned females had higher mean HbA1c ( x̅ 4.70%, 95% CI = 4.54%, 4.86%) than non-denned ( ⁠ x̅ 4.38%, 95% CI = 4.23%, 4.53%, P = 0.005). We trained a binary logistic regression model to classify the probability of recent prior denning based on HbA1c and glucose, and the model classified denning with 75% accuracy. HbA1c can be used as an effective tool for determining denning history and could have implications for monitoring reproductive success.

Alsaka, Northwest Territories, Yukon↗

USGS2025

The importance of method selection when estimating diet composition with quantitative fatty acid signature analysis

Quantitative fatty acid signature analysis (QFASA) is a common method of estimating the composition of prey species in the diets of consumers from polar and temperate ecosystems in which lipids are an important source of energy. A key characteristic of QFASA is that the large number of fatty acids that typically comprise lipids permits the dietary contributions of a correspondingly large number of prey types to be estimated. Several modifications to the original QFASA methods have been suggested in the literature and a significant extension of the original model published in 2017 allows simultaneous estimation of both diet proportions and calibration coefficients, which are metabolic constants in the model whose values must otherwise be estimated in independent feeding experiments. However, comparisons of diet estimates obtained using different estimation options have been limited. QFASA has been used to estimate the diet composition of several polar bear ( Ursus maritimus ) subpopulations, including the Southern Beaufort Sea (SBS) subpopulation. Prior QFASA estimates of SBS polar bear diet composition have most often been obtained using variations of the original QFASA model. We investigated the influence of variations in QFASA analytical methods on diet estimates by re-estimating the diet composition of polar bears from the Alaska portion of the SBS using three different methods and found that differences among the three sets of estimates were substantial. Our results illustrate how important the careful and deliberate selection of QFASA methods can be and we provide some guidance on techniques one might use to evaluate options.

PLoS ONE↗

USGS2024

Photogrammetry-based body condition for monitoring an Arctic marine mammal experiencing habitat loss

Monitoring animal body condition can provide insight on population responses to environmental change. Pacific walruses ( Odobenus rosmarus divergens ) are experiencing loss of their sea ice habitat which has decreased the time that females spend foraging during a critical period of pregnancy and lactation. Here we investigate the potential for body condition to track demographic change and be monitored via two-dimensional aerial imagery by (1) examining whether walrus somatic growth and body mass data tracked estimated historic demographic changes, (2) collecting morphometric and body mass data and aerial imagery of walruses in human care to determine if sex, age group, and body size and condition can be determined from imagery, and (3) examining aerial imagery from a large coastal haulout used primarily by females and young to estimate potential sample sizes of measurable walruses. Body mass and growth in body length decreased between the last 1970s and early 1980s concurrent with a period when the population apparently approached carrying capacity and subsequently declined. Measures from aerial imagery (1) accurately distinguished reproductive age females from subadults and adult males and (2) enabled body mass estimates with 6-7% error using either areal footprint or a combination of length and width. We found a mean of 216 ± 77 walruses appropriately positioned for measurement from aerial surveys of the haulout enabling measurements of ≥7000 individuals annually via repeated daily imagery. Our results suggest that body mass of reproductive age females and growth of dependent young may be useful indicators to augment monitoring of the Pacific walrus population and can be achieved via non-invasive aerial imagery collections.

Alaska↗

USGS2024

Increased pathogen exposure of a marine apex predator over three decades

Environmental changes associated with global warming create new opportunities for pathogen and parasite transmission in Arctic wildlife. As an apex predator ranging over large, remote areas, changes in pathogens and parasites in polar bears are a useful indicator of changing transmission dynamics in Arctic ecosystems. We examined prevalence and risk factors associated with exposure to parasites and viral and bacterial pathogens in Chukchi Sea polar bears. Serum antibodies to six pathogens were detected and prevalence increased between 1987–1994 and 2008–2017 for five: Toxoplasma gondii , Neospora caninum , Francisella tularensis , Brucella abortus/suis , and canine distemper virus. Although bears have increased summer land use, this behavior was not associated with increased exposure. Higher prevalence of F. tularensis , C. burnetii , and B. abortus/suis antibodies in females compared to males, however, could be associated with terrestrial denning. Exposure was related to diet for several pathogens indicating increased exposure in the food web. Elevated white blood cell counts suggest a possible immune response to some pathogens. Given that polar bears face multiple stressors in association with climate change and are a subsistence food, further work is warranted to screen for signs of disease.

Alaska↗

USGS2024

The post-emergence period for denning polar bears: Phenology and influence on cub survival

Among polar bears ( Ursus maritimus ), only parturient females den for extended periods, emerging from maternal dens in spring after having substantially depleted their energy reserves during a fast that can exceed 8 months. Although den emergence coincides with a period of increasing prey availability, polar bears typically do not depart immediately to hunt, but instead remain at the den for up to a month. This delay suggests that there are likely adaptive advantages to remaining at the den between emergence and departure, but the influence of the timing and duration of this post-emergence period on cub survival has not been evaluated previously. We used temperature and location data from 70 denning bears collared within the Southern Beaufort Sea and Chukchi Sea subpopulations to estimate the phenology of the post-emergence period. We evaluated the influence of various spatial and temporal features on duration of the post-emergence period and evaluated the potential influence of post-emergence duration on litter survival early in the spring following denning. For dens that likely contained viable cubs at emergence ( n = 56), mean den emergence occurred on 16 March (SE = 1.4 days) and mean departure on 24 March (SE = 1.6 days), with dates typically occurring later in the Chukchi Sea relative to Southern Beaufort Sea and on land relative to sea ice. Mean duration of the post-emergence period was 7.9 days (SE = 1.4) for bears that were observed with cubs later in the spring, which was over 4 times longer than duration of those observed without cubs (1.9 days). Litter survival in the spring following denning ( n = 31 dens) increased from 0.5 to 0.9 when duration of the post-emergence period increased by ~4 days and other variables were held at mean values. Our limited sample size and inability to verify cub presence at emergence suggests that future research is merited to improve our understanding of this relationship. Nonetheless, our results highlight the importance of the post-emergence period in contributing to reproductive success and can assist managers in developing conservation and mitigation strategies in denning areas, which will be increasingly important as human activities expand in the Arctic.

Journal of Mammalogy↗

USGS2024

Ursids evolved dietary diversity without major alterations in metabolic rates

The diets of the eight species of ursids range from carnivory (e.g., polar bears, Ursus maritimus ) to insectivory (e.g., sloth bears, Melursus ursinus ), omnivory (e.g., brown bears, U. arctos ), and herbivory (e.g., giant pandas, Ailuropoda melanoleuca ). Dietary energy availability ranges from the high-fat, highly digestible, calorically dense diet of polar bears (~ 6.4 kcal digestible energy/g fresh weight) to the high-fiber, poorly digestible, calorically restricted diet (~ 0.7) of giant pandas. Thus, ursids provide the opportunity to examine the extent to which dietary energy drives evolution of energy metabolism in a closely related group of animals. We measured the daily energy expenditure (DEE) of captive brown bears in a relatively large, zoo-type enclosure and compared those values to previously published results on captive brown bears, captive and free-ranging polar bears, and captive and free-ranging giant pandas. We found that all three species have similar mass-specific DEE when travel distances and energy intake are normalized even though their diets differ dramatically and phylogenetic lineages are separated by millions of years. For giant pandas, the ability to engage in low-cost stationary foraging relative to more wide-ranging bears likely provided the necessary energy savings to become bamboo specialists without greatly altering their metabolic rate.

Scientific Reports↗

USGS2024

Polar bear energetic and behavioral strategies on land with implications for surviving the ice-free period

Declining Arctic sea ice is increasing polar bear land use. Polar bears on land are thought to minimize activity to conserve energy. Here, we measure the daily energy expenditure (DEE), diet, behavior, movement, and body composition changes of 20 different polar bears on land over 19–23 days from August to September (2019–2022) in Manitoba, Canada. Polar bears on land exhibited a 5.2-fold range in DEE and 19-fold range in activity, from hibernation-like DEEs to levels approaching active bears on the sea ice, including three individuals that made energetically demanding swims totaling 54–175 km. Bears consumed berries, vegetation, birds, bones, antlers, seal, and beluga. Beyond compensating for elevated DEE, there was little benefit from terrestrial foraging toward prolonging the predicted time to starvation, as 19 of 20 bears lost mass (0.4–1.7 kg•day −1 ). Although polar bears on land exhibit remarkable behavioral plasticity, our findings reinforce the risk of starvation, particularly in subadults, with forecasted increases in the onshore period.

Manitoba↗

USGS2024

Identifying indicators of polar bear population status

Monitoring trends in large mammal populations is a fundamental component of wildlife management and conservation. However, direct estimates of population size and vital rates of large mammals can be logistically challenging and expensive. Indicators that reflect trends in abundance, therefore, can be valuable tools for supporting population monitoring. Polar bears have a relatively simple life history such that a few key variables may be effective indicators for tracking changes in body condition and recruitment that affect abundance. Direct estimates of polar bear abundance are difficult to obtain due to their large home ranges in remote Arctic habitats. Changes in abundance associated with environmental conditions appear to affect polar bears largely via effects on female body condition which influence reproduction and cub survival (i.e., recruitment). Loss of sea ice habitat is further limiting researcher access for population monitoring creating a need for alternative approaches. Here we used relationships established from eight years (2008–2017) of data collected on 439 polar bears in the Chukchi Sea, to transform previously published individual-based relationships with annually available sea ice, atmospheric circulation, and prey body condition variables to predict annual mean body condition and recruitment during 2018–2022. Although annual sample sizes were limited for verifying predicted body condition and recruitment via techniques such as cross-validation, in most cases predicted annual means were closely correlated with observed means for 2008–2017. Summer sea ice and prey body condition remained within or increased relative to levels observed during 2008–2017 and predicted polar bear body condition and recruitment during 2018–2022 were largely within or above observed annual means during 2008–2017. A lack of trend in environmental and ecological variables or polar bear body condition and recruitment metrics during 2008–2022 is suggestive that the Chukchi Sea polar bear population was likely stable during this time. Our results provide support for developing models that predict important population parameters of large mammals based on environmental and ecological indicators. Given that trend information is lacking for 10 of the 19 recognized polar bear populations and is outdated for others, the use of environmental and ecological indicators may be particularly useful for augmenting direct estimates of polar bear vital rates in between periods of data collection. Although demographic assessments for polar bears have primarily focused on correlations with sea ice availability, our study and others highlight that prey health is also an important indicator of polar bear population status.

Ecological Indicators↗

USGS2023

Effects of feeding and habitat on resting metabolic rates of the Pacific walrus

Arctic marine mammals live in a rapidly changing environment due to the amplified effects of global warming. Pacific walruses ( Odobenus rosmarus divergens ) have responded to declines in Arctic sea-ice extent by increasingly hauling out on land farther from their benthic foraging habitat. Energy models can be useful for better understanding the potential implications of changes in behavior on body condition and reproduction but require behavior-specific metabolic rates. Here we measured the resting metabolic rates (RMR) of three captive, adult female Pacific walruses through breath-by-breath respirometry when fed and fasted resting out of water (sitting and lying down) and while fed resting in water. RMR in and out of water were positively related with pretrial energy intake when not fasted and 25% higher than RMR when walruses were fasted and out of water. Overall, RMR was higher than previously estimated for this species. Fasting RMR out of water was only 25% lower than subsurface swimming metabolic rates suggestive of relatively efficient swimming in adult females. Our results identify the importance of considering feeding status and species-specific differences in affecting metabolic costs. Further research is needed to better understand potential energetic costs of thermoregulation at temperatures experienced by wild walruses.

Valencia↗

USGS2023

Forecasts of polar bear (Ursus maritimus) land use in the southern Beaufort and Chukchi Seas, 2040–65

This report provides analysis to extend the 2040 forecasts of polar bear ( Ursus maritimus ) land use for the southern Beaufort and Chukchi Sea populations presented in a recent publication (Rode and others, 2022) through the year 2065. To inform long-term polar bear management considerations, we provide point-estimate forecasts and 95-percent prediction intervals of the proportion of polar bear populations summering onshore for 21 days or more (≥) and their duration onshore every 5 years from 2040 to 2065. Because sea-ice projections based on earth system models show greater divergence with emission scenarios after 2040, we have provided forecasts for three greenhouse gas emission scenarios, SSP1-2.6, SSP2-4.5 and SSP5-8.5, compared to the two emission scenarios used in Rode and others (2022). Our forecasting methods estimated that 61–97 percent of polar bears in the southern Beaufort Sea and 80–100 percent of polar bears in the Chukchi Sea populations may summer onshore for ≥21 days by 2065. Forecasts of mean duration onshore were 105–158 days for polar bears in the southern Beaufort Sea and 111–178 days in the Chukchi Sea populations by 2065. Sea ice conditions projected to occur by 2065 could alter the current patterns of bear behavior from what has been observed over the past 30 years. As a result, these extended projections are associated with a higher degree of uncertainty than estimates through 2040, especially under the SSP5-8.5 scenario.

Open-File Report↗

USGS2022

Diet energy density estimated from isotopes in predator hair associated with survival, habitat, and population dynamics

Sea ice loss is fundamentally altering the Arctic marine environment. Yet there is a paucity of data on the adaptability of food webs to ecosystem change, including predator-prey interactions. Polar bears ( Ursus maritimus ) are an important subsistence resource for Indigenous people and an apex predator that relies entirely on the under-ice food web to meet their energy needs. Here, we assessed whether polar bears maintained dietary energy density by prey switching in response to spatial-temporal variation in prey availability. We compared the macronutrient composition of diets inferred from stable carbon and nitrogen isotopes in polar bear guard hair (primarily representing summer/fall diet) during periods when bears had low and high survival 2004-2016, between bears that summered on land versus pack ice, and between bears occupying different regions of the Alaskan and Canadian Beaufort Sea. Polar bears consumed diets with lower energy density during periods of low survival suggesting that concurrent increased dietary proportions of beluga whales ( Delphinapterus leucas ) did not offset reduced proportions of ringed seals ( Pusa hispida ). Diets with the lowest energy density and proportions from ringed seal blubber were consumed by bears in the western Beaufort Sea (Alaska) during a period when polar bear abundance declined. Intake required to meet energy requirements of an average free-ranging adult female polar bear was 2.1 kg/day on diets consumed during years with high survival but rose to 3.0 kg/day when survival was low. Although bears that summered onshore in the Alaskan Beaufort Sea had higher fat diets than bears that summered on the pack ice, access to the remains of subsistence-harvested bowhead whales ( Balaena mysticetus ) contributed little to improving diet energy density. Because most bears in this region remain with the sea ice year-round, prey-switching and consumption of whale carcasses onshore appear insufficient to augment diets when availability of their primary prey, ringed seals, is reduced. Our results show that a strong predator-prey relationship between polar bears and ringed seals continues in the Beaufort Sea. The method of estimating dietary blubber using predator hair, demonstrated here, provides a new metric to monitor predator-prey relationships that affect individual health and population demographics.

Ecological Applications↗

USGS2022

Intrapopulation differences in polar bear movement and step selection patterns

Background The spatial ecology of individuals often varies within a population or species. Identifying how individuals in different classes interact with their environment can lead to a better understanding of population responses to human activities and environmental change and improve population estimates. Most inferences about polar bear ( Ursus maritimus ) spatial ecology are based on data from adult females due to morphological constraints on applying satellite radio collars to other classes of bears. Recent studies, however, have provided limited movement data for adult males and sub-adults of both sexes using ear-mounted and glue-on tags. We evaluated class-specific movements and step selection patterns for polar bears in the Chukchi Sea subpopulation during spring. Methods We developed hierarchical Bayesian models to evaluate polar bear movement (i.e., step length and directional persistence) and step selection at the scale of 4-day step lengths. We assessed differences in movement and step selection parameters among the three classes of polar bears (i.e., adult males, sub-adults, and adult females without cubs-of-the-year). Results Adult males had larger step lengths and less directed movements than adult females. Sub-adult movement parameters did not differ from the other classes but point estimates were most similar to adult females. We did not detect differences among polar bear classes in step selection parameters and parameter estimates were consistent with previous studies. Conclusions Our findings support the use of estimated step selection patterns from adult females as a proxy for other classes of polar bears during spring. Conversely, movement analyses indicated that using data from adult females as a proxy for the movements of adult males is likely inappropriate. We recommend that researchers consider whether it is valid to extend inference derived from adult female movements to other classes, based on the questions being asked and the spatial and temporal scope of the data. Because our data were specific to spring, these findings highlight the need to evaluate differences in movement and step selection during other periods of the year, for which data from ear-mounted and glue-on tags are currently lacking.

Movement Ecology↗

USGS2022

The role of satellite telemetry data in 21st century conservation of polar bears (Ursus maritimus)

Satellite telemetry (ST) has played a critical role in the management and conservation of polar bears ( Ursus maritimus ) over the last 50 years. ST data provide biological information relevant to subpopulation delineation, movements, habitat use, maternal denning, health, human-bear interactions, and accurate estimates of vital rates and abundance. Given that polar bears are distributed at low densities over vast and remote habitats, much of the information provided by ST data cannot be collected by other means. Obtaining ST data for polar bears requires chemical immobilization and application of a tracking device. Although immobilization has not been found to have negative effects beyond a several-day reduction in activity, over the last few decades opposition to immobilization and deployment of satellite-linked radio collars has resulted in a lack of current ST data in many of the 19 recognized polar bear subpopulations. Here, we review the uses of ST data for polar bears and evaluate its role in addressing 21 st century conservation and management challenges, which include estimation of sustainable harvest rates, understanding the impacts of climate warming, delineating critical habitat, and assessing potential anthropogenic impacts from tourism, resource development and extraction. We found that in subpopulations where ST data have been consistently collected, information was available to estimate vital rates and subpopulation density, document the effects of sea-ice loss, and inform management related to subsistence harvest and regulatory requirements. In contrast, a lack of ST data in some subpopulations resulted in increased bias and uncertainty in ecological and demographic parameters, which has a range of negative consequences. As sea-ice loss due to climate warming continues, there is a greater need to monitor polar bear distribution, habitat use, abundance, and subpopulation connectivity. We conclude that continued collection of ST data will be critically important for polar bear management and conservation in the 21 st century and that the benefits of immobilizing small numbers of individual polar bears in order to deploy ST devices significantly outweigh the risks.

Frontiers in Marine Science↗

USGS2022

Summer/fall diet and macronutrient assimilation in an Arctic predator

Free-ranging predator diet estimation is commonly achieved by applying molecular-based tracers because direct observation is not logistically feasible or robust. However, tracers typically do not represent all dietary macronutrients, which likely obscures resource use as prey proximate composition varies and tissue consumption can be specific. For example, polar bears ( Ursus maritimus ) preferentially consume blubber, yet diets have been estimated using fatty acids based on prey blubber or stable isotopes of lipid-extracted prey muscle, neither of which represent both protein and lipid macronutrient contributions. Further, additional bias can be introduced because dietary fat is known to be flexibly routed beyond short-term energy production and storage. We address this problem by simultaneously accounting for protein and lipid assimilation using carbon and nitrogen isotope compositions of lipid-containing prey muscle and blubber to infer summer/fall diet composition and macronutrient proportions from Chukchi Sea polar bear guard hair ( n = 229) sampled each spring between 2008 and 2017. Inclusion of blubber (85–95% lipid by dry mass) expanded the isotope mixing space and improved separation among prey species. Ice-associated seals, including nutritionally dependent pups, were the primary prey in summer/fall diets with lower contributions by Pacific walruses ( Odobenus rosmarus ) and whales. Percent blubber estimates confirmed preferential selection of this tissue and represented the highest documented lipid assimilation for any animal species. Our results offer an improved understanding of summer/fall prey macronutrient usage by Chukchi Sea polar bears which likely coincides with a nutritional bottleneck as the sea ice minimum is approached.

Alaska↗

USGS2022

Observed and forecasted changes in land use by polar bears in the Beaufort and Chukchi Seas, 1985–2040

Monitoring changes in the distribution of large carnivores is important for managing human safety and supporting conservation. Throughout much of their range, polar bears ( Ursus maritimus ) are increasingly using terrestrial habitats in response to Arctic sea ice decline. Their increased presence in coastal areas has implications for bear-human conflict, inter-species interactions, and polar bear health and survival. We examined observed trends in land use over three decades by polar bears in the southern Beaufort Sea (SB) and Chukchi Sea (CS) where bears have traditionally spent most of the year on the sea ice. Using data from 408 adult females fitted with satellite radio-collars, we examined trends in the annual proportion of bears coming onshore (hereafter referred to as “percent of bears”) during the summer for ≥21 days, arrival and departure dates, duration spent onshore and relationships with sea ice metrics. We then estimated future land use through 2040 by extrapolating trends and by combining observed relationships between land use and sea ice with projections of future sea ice from an ensemble of earth system models. The observed percent of bears summering onshore and their duration onshore was correlated with the percent of open water that occurred within their population’s range between July and October. As sea ice declined, the percent of bears summering onshore increased from ~5 to 30% in the SB and ~10 to 50% in the CS and duration onshore increased by >30 days to 60–70 days in both populations. Using a range of greenhouse gas emission scenarios and adjustments for faster than forecasted sea ice loss we estimated that 50-62% of SB and 79-88% of CS bears will spend 90–108 and 110–126 days onshore during summer in the SB and CS, respectively, by 2040. Sea ice projections varied little between greenhouse gas emission scenarios prior to 2040 but diverged thereafter. Observed and forecasted increases in polar bear land occupancy puts more bears in proximity to human activities and settlements for longer durations while extending the lack of access to their primary prey. Because human conflict is one of the primary factors affecting the conservation of large carnivores worldwide, mitigation of bear-human interactions on land will be an increasingly important component of polar bear conservation.

Alaska↗