Estimating Polar Bear ( <i>Ursus maritimus</i> ) Age Based on an Epigenetic <scp>DNA</scp> 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 (<i>Ursus</i> 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 (<i>Ursus maritimus</i>). We generated DNA methylation data from whole blood samples (<i>n</i> = 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 (<i>r</i> = 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.