Changes in the Abundance of the Arctic Skuas (Stercorarius Parasiticus (L., 1758)) and the Great Skuas (Stercorarius Skua (Brunnich, 1764)) (Stercoraridae) on the Murman Islands as a Response to the Dynamics of Trophic Conditions in the Southwestern Barents Sea

Based on the results of long-term monitoring on the Murman Islands, southwestern Barents Sea, the population dynamics of the Arctic skuas (Stercorarius parasiticus) and the Great skuas (S. skua) were determined. Both species were found to have reached their highest numbers at the end of the second decade of the 2000s and, starting with 2018, a rapid decline in the numbers of Arctic skuas was observed (by 71% by 2024), as well as the complete disappearance of Great skuas by 2022 on two of the three Murman archipelagos. The nesting biology of both species in the Murman conditions was studied during observations, mainly of individually tagged individuals. 45 Arctic skuas and 5 Great skuas were tagged. The maximum duration of continuous nesting of the Arctic skua on the Seven Islands archipelago was found to be 10 years; for the Great skua it amounted 5 years. The breeding success in 1991–1995 was 1.6 chicks/pair for the former, and two times lower for the latter. A comparative analysis of the trophic relationships of both species showed that Arctic skuas obtained most of their food as fish and crustaceans through kleptoparasitism on seabirds, while Great skuas preyed on eggs, chicks, and adult seabirds in adjacent areas. The population development crisis of both species in recent decades was established to have been caused by immense deterioration of the trophic conditions in the coastal waters of Murman. The root cause is a change in the oceanographic conditions in the North Atlantic and adjacent seas.