First abundance estimate for the East Greenland polar bear subpopulation

Evaluating the demographic status of large mammals in dynamic habitats is challenging. The East Greenland (EG) polar bear subpopulation ranges over approximately 1.5 million km2 of sea ice and 18 degrees of latitude along a mostly uninhabited coastline, making it the most expansive of the world’s 20 polar bear subpopulations. We report on a distance-sampling aerial survey that provided the first estimate of abundance for EG polar bears. We used a density surface model (DSM) that corrected for incomplete detection on the transect line using mark-recapture methods, accounted for overall detectability via distance-sampling methods, and modeled bear density as a function of environmental covariates with a Generalized Additive Model. Our study design was informed by Indigenous Knowledge surveys and three decades of polar bear movement data obtained from satellite telemetry. During March–May 2023, we flew 106.5 hours on-effort over 26 survey days and sighted 84 groups of bears (108 individuals). Mean observed litter size was 1.6 (95% CI = 1.2–2.0) for cubs-of-the-year and 1.6 (95% CI = 1.3–1.8) for yearlings. Polar bear density was higher closer to land and along the continental shelf break offshore, where bathymetry deepens from 300 to 1,000 m. Polar bear density was approximately five times lower within 50 km of subsistence hunting communities (0.06 per 100 km2) compared to the rest to the study area (0.31 bears per 100 km2). The best estimate of abundance for the EG subpopulation, adjusted for animals located outside the sampling area, was 2,275 bears (CV = 0.27, 95% CI = 1,360–3,807). This estimate can be used to identify a sustainable level of subsistence harvest, manage human-bear conflicts, and monitor the effects of climate warming on EG polar bears. Our methods also provide a template for designing and conducting aerial surveys for wildlife populations inhabiting vast and remote regions.