Abstract
Features of Common guillemot (Uria aalge) and Brünnich’s guillemot (U. lomvia) numbers dynamics have been analyzed based on long-term monitoring data obtained from colonies from the southern Barents Sea coast. Since the 2000s, the numbers of guillemots in colonies have been shown to gradually decrease. In 2019–2021, most of the guillemot colonies of the southern Barents Sea coast disappeared. Two factors have been found to affect the guillemot colonies’ dynamics in the last decades: fishing industry and change in oceanographic conditions. These two factors indirectly influence the guillemot populations in the winter-spring area, changing the availability of the birds’ food resources. The former affects only the birds from southwestern Barents Sea colonies, but the second is relevant within the whole winter-spring area from the Barents Sea to the western areas of the North Atlantic. They affect the guillemots’ living conditions in the most critical periods of their life. In future this may cause significant changes in the location of guillemot colonies in the southern Barents Sea.