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 km² 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.

Southeast Greenland (SEG) is characterized by complex morphology and environmental processes that create dynamic habitats for top marine predators. Active glaciers producing solid-ice discharge, freshwater flux, offshore sea ice transport, and seasonal landfast-ice formation all contribute to a variable, transient environment within SEG fjord systems. Here, we investigate a selection of physical processes in SEG to provide a regional characterization that reveals physical system processes and supports biological research. SEG fjords exhibit high fjord-to-fjord variability regarding bathymetry, size, shape, and glacial setting, influencing some processes more than others. For example, during fall, the timing of offshore sea ice formation near SEG fjords progresses temporally when moving southward across latitudes, while the timing of offshore sea ice disappearance is less dependent on latitude. The rates of annual freshwater flux into fjords, however, are highly variable across SEG, with annual average input values ranging from ~1 x 10⁸ to ~1.25 x 10¹⁰ m³ (~0.1–12.5 Gt) for individual fjords. Similarly, the rates of solid-ice discharge in SEG fjords vary widely — partly due to the irregular distribution of active glaciers across the study area (60–70°N). Landfast sea ice, assessed for eight focus fjords, is seasonal and has a spatial distribution highly dependent on individual fjord topography. Conversely, glacial ice is deposited into fjord systems year-round, with the spatial distribution of glacier-derived ice depending on the location of glacier termini. As climate change continues to affect SEG, the evolution of these metrics will vary individually in their response, and next steps should include moving from characterization to system projection. Due to the projected regional ice sheet persistence that will continue to feed glacial ice into fjords, it is possible that SEG could remain a long-term refugium for polar bears and other ice-dependent species on a centennial to millennial scale, demonstrating a need for continued research into the SEG physical environment.

Climate change is rapidly transforming the coastal margins of Greenland. At the same time, there is increasing recognition that marine-terminating glaciers provide unique and critical habitats to ice-associated top predators. We investigated the connection between a top predator occupying glacial fjord systems in Northwest Greenland and the properties of Atlantic-origin water and marine-terminating glaciers through a multiyear interdisciplinary project. Using passive acoustic monitoring, we quantified the summer presence and autumn departure of narwhals (Monodon monoceros) at glacier fronts in Melville Bay and modeled what glacier fjord physical attributes are associated with narwhal occurrence. We found that narwhals are present at glacier fronts after Greenland Ice Sheet peak summer runoff and they remain there during the period when the water column is becoming colder and fresher. Narwhals occupied glacier fronts when ocean temperatures ranged from –0.6 to 0.8°C and salinities between 33.2 and 34.0 psu at around 200 m depth and they departed on their southbound migration between October and November. Narwhals' departure was approximately 4 weeks later in 2019 than in 2018, after an extreme 2019 summer heatwave event that also delayed sea ice formation by 2 months. Our study provides further support for the niche conservative narwhal's preference for cold ocean temperatures. These results may inform projections about how future changes will impact narwhal subpopulations, especially those occupying Greenland glacial fjords.