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 ( Ursus maritimus ) subpopulation ranges over approximately 1.5 million km 2 of sea ice and 18° 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 3 decades of polar bear movement data obtained from satellite telemetry. During March-May 2023, we flew 106.5 h 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 1000 m. Polar bear density was approximately 5 times lower within 50 km of subsistence hunting communities (0.06 bears 100 km -2 ) compared to the rest to the study area (0.31 bears 100 km -2 ). The best estimate of abundance for the EG subpopulation, adjusted for animals located outside the sampling area, was 2275 bears (CV = 0.27, 95% CI = 1360-3807). 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.