Hudson Bay and east to eastern Greenland and account for about 54% of the global population. The usual range includes the territory of five nations: Denmark (Greenland), Norway (Svalbard), Russia, the United States (Alaska) and Canada. These five nations are the signatories of the International Agreement on the Conservation of Polar Bears, which mandates cooperation on research and conservation efforts throughout the polar bear's range. Bears sometimes swim to Iceland from Greenland—about 600 sightings since the country's settlement in the 9th century, and five in the 21st century —and are always killed because of their danger, as well as the cost and difficulty of repatriation. Modern methods of tracking polar bear populations have been implemented only since the mid-1980s, and are expensive to perform consistently over a large area. The most accurate counts require flying a helicopter in the Arctic climate to find polar bears, shooting a tranquilizer dart at the bear to sedate it, and then tagging the bear. In Nunavut, some Inuit have reported increases in bear sightings around human settlements in recent years, leading to a belief that populations are increasing. Scientists have responded by noting that hungry bears may be congregating around human settlements, leading to the illusion that populations are higher than they actually are. The Polar Bear Specialist Group of the IUCN Species Survival Commission takes the position that "estimates of subpopulation size or sustainable harvest levels should not be made solely on the basis of traditional ecological knowledge without supporting scientific studies." Of the 19 polar bear subpopulations recognized in 2017, one was in decline, two were increasing, seven were stable, and nine had insufficient data. Habitat The polar bear is a marine mammal because it spends many months of the year at sea. However, it is the only living marine mammal with powerful, large limbs and feet that allow them to cover kilometres on foot and run on land. Its preferred habitat is the annual sea ice covering the waters over the continental shelf and the Arctic inter-island archipelagos. These areas, known as the "Arctic ring of life", have high biological productivity in comparison to the deep waters of the high Arctic. The polar bear tends to frequent areas where sea ice meets water, such as polynyas and leads (temporary stretches of open water in Arctic ice), to hunt the seals that make up most of its diet. Freshwater is limited in