Geology topics

Susannah P. Woodruff

Publications and source records attributed to Susannah P. Woodruff.

4 recordsLinked to original sources

USGS2025

Estimating polar bear (Ursus maritimus) age based on an epigenetic DNA methylation clock

Knowledge of animal age is essential to wildlife managers for obtaining meaningful and accurate insights into demographic parameters. A common approach to aging wildlife, including bears ( Ursus spp.), has been extracting a tooth during physical capture and counting the cementum annuli. Limitations to tooth-based aging include questionable accuracy and differing results based on the observer and laboratory. DNA methylation-based epigenetic aging clocks have been developed for many species but not yet for polar bears ( Ursus maritimus ). We generated DNA methylation data from whole blood samples ( n = 109) obtained during live capture operations from polar bears of known age in the Chukchi Sea and southern Beaufort Sea subpopulations. We used these samples to calibrate a species-specific epigenetic clock to estimate polar bear chronological age from DNA methylation (DNAm) age. The final polar bear clock was highly accurate ( r = 0.97) with a median absolute error of approximately 9 months. We applied the polar bear clock to 74 blood samples from live-captured polar bears with a cementum annuli-estimated age. Predicted age estimates for these bears ranged from 1.43 to 18.63 years compared to the estimated tooth age range of 3.23–25.27. These epigenetic clocks can be used for polar bear research and management where accurate estimates of age are needed for estimating demographic parameters.

Ecology and Evolution↗

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

Potential impacts of an autumn oil spill on polar bears summering on land in northern Alaska

Demand for oil and natural gas continues to increase, leading to the development of remote regions where it is riskier to operate. Many of these regions have had limited development, so understanding potential impacts to wildlife could inform management decisions. In 2017, the United States passed legislation allowing oil and gas development in the coastal plain of the Arctic National Wildlife Refuge in northeastern Alaska. This area has received limited industrial development and is an important region for polar bears that use the coastline as a travel corridor in autumn. We sought to understand how an autumn near-shore oil spill in the Refuge could affect polar bears. We simulated oil spills from shallow sub-sea pipelines at 3 locations along the coastline of the Refuge and allowed spills to discharge 4800 barrels of oil per day for 6 days, and tracked oil for 50 days. We interacted the trajectories with simulated polar bear movements to estimate how many bears might be exposed. Oil spread quickly along the coastline and during some weeks exposed an average of 10 bears (95 % CI: 0–37) to lethal levels of oil, and 60 (95 % CI: 9–120) to sub-lethal levels. Our results suggest a significant number of polar bears could become oiled from a spill in the region and require decontamination. Therefore, future mitigation strategies could include careful siting of future development and additional capacity to capture and decontaminate bears in the event of an oil spill.

Alaska↗

USGS2022

Evaluating the efficacy of aerial infrared surveys to detect artificial polar bear dens

The need to balance economic development with impacts to Arctic wildlife has been a prominent subject since petroleum exploration began on the North Slope of Alaska, USA, in the late 1950s. The North Slope region includes polar bears ( Ursus maritimus ) of the southern Beaufort Sea subpopulation, which has experienced a long-term decline in abundance. Pregnant polar bears dig dens in snow drifts during winter and are vulnerable to disturbance, as den abandonment and mortality of neonates may result. Maternal denning coincides with the peak season of petroleum exploration and construction, raising concerns that human activities may disrupt denning. To minimize disturbance of denning polar bears, aerial infrared (AIR) surveys are routinely used to search for dens within planned industry activity areas and that information is used to implement mitigation. Aerial infrared surveys target the heat signature emanating from dens. Despite use by industry for >15 years, the efficacy of AIR and the factors that impact its ability to detect dens remains uncertain. Here, we evaluate AIR using artificial dens and observers naïve to locations to estimate detection probability and its relationship with covariates including weather variables, den characteristics, infrared sensor and altitude, and survey order to identify potential evidence of in-flight observer learning occurring between surveys. In December 2019 we constructed 14 dens (each with an artificial heat source), and 11 control sites (disturbed sites without dens). Between December 2019 and January 2020, 3 survey crews flew 6 independent AIR surveys within the vicinity of dens and control sites and video-recorded AIR imagery. Observers identified putative dens either in flight or during post-flight review of recordings. We assessed detection probability with a simple Bayesian model using 3 subsets of data: 1) all detection/non-detection data; 2) detection/non-detection data restricted to instances where sample sites were confirmed to have been properly scanned by AIR during post-study verification (i.e., when den locations were known); and 3) all dens visible on the recorded imagery during post-study verification, even if they were not seen during the survey or during post-flight review. Subsets 1 and 2 most closely resembled den surveys flown for oil and gas industry and had detection probabilities of 0.15 (95% CI = 0.08–0.23) and 0.24 (95% CI = 0.13–0.37), respectively. Detection probability was 0.41 (95% CI = 0.25–0.58) for subset 3. Higher wind speeds and larger den volume negatively influenced detection probability. Our low detection rate compared to previous studies could partially be the result of differences in study design, such as survey flight patterns. Our results suggest that AIR, as it is currently used, is unlikely to detect most polar bear dens in surveyed areas. Resource managers who use AIR should consider a suite of additional methods (e.g., habitat mapping, probabilistic den distribution, AIR methodology improvements) for minimizing impacts of industry on denning polar bears.

Alaska↗