The thick-billed murre and common murre have ranges 1,000,000 km2 and number in the millions or tens of millions of breeding pairs. However global populations are declining, although increases have occurred in some regions. These seabirds, together with other species of alcids, face a number of direct and indirect marine and terrestrial threats, which influence their survival and reproductive success. These include transboundary pollutants, by-catch mortality from fisheries, competition with fisheries for fish stocks, disturbance of breeding sites/habitat, and unsustainable harvesting. Marine pollution, especially oil, is a significant threat. Alcids are particularly sensitive to even small oil spills because of their concentrated aggregations. There is also concern over the impacts of cruise ship tourism on Arctic seabird colonies, given its rapid growth. Greater ship traffic increases the risk of groundings and other accidents, which may result in oil spills and other consequences.