The results of monitoring of three major colonies of large gulls in the Kizhi Skerries of Lake Onega in 1974-2014 are summarized. It is shown that the numbers of the Herring Gull L. a. argentatus Pontopp. have been growing, and the numbers of the Lesser Black- backed Gull L. f. fuscus L. have remained at a low level since its sharp decline in the skerries late in the 1980s. Local factors (weather conditions, human pressure) were found to cause relatively synchronous changes in the abundances of the two species on each of the islands and in the distribution of the birds across the archipelago, but the Lesser Black-backed Gull was more severely affected. For several decades the eastern subspecies of the Lesser Black-backed Gull, which breeds in Russia, has been declining throughout the range under the impact of global factors, first of all in wintering areas and along flyways. This subspecies is red-listed in neighbour countries, the Republic of Karelia and the Leningrad Region. Given the narrow distribution range and instability of the Russian part of the population, this subspecies of the Lesser Black-backed Gull should be included in the Red Book of the Russian Federation under category 3 (IUCN category VU, vulnerable).