Narwhals primarily inhabit the Atlantic sector of the Arctic. The principal distribution is from the central Canadian Arctic (Peel Sound – Prince Regent Inlet and northern Hudson Bay) eastward to Greenland and into the eastern Russian Arctic (around 180°E). They are rarely observed in the far eastern Russian Arctic, Alaska, or the western Canadian Arctic. In summer, narwhals spend approximately two months in high Arctic ice-free shallow bays and fjords; they overwinter in offshore, deep, ice-covered habitats along the continental slope (Heide-Jørgensen and Dietz 1995). The whales migrate annually between these disjunct seasonal areas of concentration, with the migratory periods lasting approximately two months (Koski and Davis 1994; Innes et al. 2002; Heide-Jørgensen et al. 2002; Dietz et al. 2001; Heide-Jørgensen et al. 2003).