Estimated Ages of Southern Beaufort Sea Polar Bears Based on DNA Methylation, 1987-2016

This dataset contains known and estimated ages of polar bears sampled from the southern Beaufort Sea of Alaska. Whole blood was collected from polar bears of known chronological age between 1987 and 2016. Chronological age was known because all the bears in this data set were initially captured as a dependent cub-of-the-year, yearling, or 2-year-old, and that allowed us to know chronological age at subsequent recapture. DNA methylation (DNAm) was used to estimate age as predicted by an epigenetic clock and compared to known chronological age to assess accuracy. DNA methylation is the addition of methyl groups (CH3) to cytosine-guanine sites in DNA (Horvath and Raj 2018). The methylation patterns found at these sites result in epigenetic changes to the genome which can be used to develop an 'epigenetic clock' (i.e., a biochemical measure of age) (Newediuk et al., 2025). Because DNA methylation levels are highly correlated with chronological age, a clock trained with samples from known-aged individuals can be used to predict age of individuals of unknown age (Bors et al., 2021). This dataset was used as the training data in development of the polar bear epigenetic clock.