This report presents results from the first systematic aerial survey of muskoxen in southwest Greenland. The survey involved the North region (66°-68°N), which was divided into three sub-areas (Angujaartorfiup, Sisimiut, Sisimiut South). The survey occurred early March 2018 and provides the first estimate for muskox abundance in two muskox harvest management areas, Maniitsoq (66°-67°N) and Sisimiut (67°-68°N).The behavior of most muskox groups was unaffected by the helicopter fly-by at 40 m altitude. Regardless of group size, 77% of groups simply stood still. Detecting stationary groups is clearly essential for accurate population estimates. Sisimiut muskoxen were most often observed at elevations of ca. 200 m, which is typical for this species as they prefer to forage in lowland elevations even in winter. In sharp contrast, Maniitsoq muskoxen used 700-800 m elevations, despite their documented year-round preference for lowlands <400 m. Further, at the time of the survey, Maniitsoq muskoxen were clumped into two ‘hotspots’ almost inaccessible by motor vehicle and relatively far from human habitation. Since 84% of all muskox harvest (commercial and recreational), as well as most trophy hunting and qiviut (muskox inner wool) production in Greenland are taken from the Maniitsoq muskoxpopulation, these activities may have a role in the disruption of normal lowland distribution of the Maniitsoq muskoxen in winter.From a subset of the Maniitsoq data, the calf (age <1-year) percentage was ascertained ca. 18% for Maniitsoq muskoxen. Considering the absence of large predators, the current value is considered low. Factors involved may include density-dependent issues associated with the Maniitsoq muskoxen now foraging on high elevation suboptimal habitat in winter. Since this coincides with late gestation for muskoxen, calf production could be negatively affected. Whether current calf percentage is sufficient to support population size stability or growth is debatable.Population size & density estimatesConventional Distance Sampling (DS) design-based methods and analyses, as well as Generalized Additive Models/Density Surface Modelling (GAM/DSM) based analyses were applied to the dataset to obtain estimates of muskox population size and density. Most muskoxen occurred in the Maniitsoq muskox harvest management area(surveyed Angujaartorfiup sub-area). Far fewer muskoxen inhabited the Sisimiut muskox harvest management area (surveyed Sisimiut sub-area), and zero muskoxen were observed in the surveyed Sisimiut South sub-area. Densities from the GAM/DSM model-based analysis supported that in early March, muskoxen strongly preferred9Southwest facing slopes and specifically for Maniitsoq muskoxen the highest densitiescoincided with high elevations. For the entire North region, the DS design-based March 2018 muskox population abundance was estimated at 21,746 muskoxen (95% CI: 11,061–42,751; CV = 28.5%; SE: 6,194), with a density of 1.1 muskoxen/km2 (95% CI: 0.559–2.160; CV = 28.5%; SE = 0.313). Alternately for the entire North region, the GAM/DSM model-based March 2018 muskox population abundance was estimated 23,256 muskoxen (95% CI: 18,102–29,877; CV = 11.36%), with mean density of 3.69 muskoxen/km2(95% CI: 2.87-4.74). DS estimates as per specific sub-area:Maniitsoq muskoxen (Angujaartorfiup sub-area): The DS design-based estimate was ca. 18,906 muskoxen (95% CI: 8,726–40,960; CV = 0.315; SE = 5,948), with a density of ca. 2.6 muskoxen/km2 (95% CI: 1.223–5.742; CV = 0.315; SE = 0.834). Sisimiut muskoxen (Sisimiut sub-area): The DS design-based estimate was ca. 2,840 muskoxen (95% CI: 662–12,178; CV = 0.568; SE = 1,613), with a density of ca. 0.22 muskoxen/km2 (95% CI: 0.052–0.962; CV = 0.568; SE = 0.127).The population size estimates from the two approaches were similar since the 95%CIs overlap. Despite the good survey coverage (10.6%), the high variability within the dataset was responsible for substantial uncertainty in the DS estimates and less so in the GAM/DSM. Regardless, calculating the CV for probability of detection of muskoxen permitted comparison of the two approaches. The DS probability of muskox detection had a CV of 5.98%, which was better than the CV of 11.36% for the GAM/DSM. Thus, for the 2018 survey for muskoxen, we recommend using the DS design-based abundance and density estimates when making management decisions. Alone, the 2018 estimate cannot indicate population trend. That requires at least two additional aerial survey estimate points using similar methods. Meanwhile, past counts, densities, harvests, and calf percentages do not suggest recent population growth but possibly a decline prior to the 2018 survey. Regardless, specifically the 2018 population size estimate for Maniitsoq muskoxen is larger than previous estimates for populations anywhere in Greenland. Also, Maniitsoq muskox density is much higher than elsewhere in the Arctic. This could increase exposure of individuals to infectious pathogens. Given possible density-dependent influences acting at current population size, population growth may not be advisable. Whether the 2018 population size and density for the Maniitsoq muskox harvest management area are within the current herbivore carrying-capacity of the pasture/range remains to be seen.