In the summer of 2020 and 2021, a study of diel migrations of Baikal-origin amphipods Gmelinoides fasciatus was conducted in the littoral zone of Lake Ladoga skerries. These organisms are an important food object for fish, and, accordingly, play a role in aquatic ecosystems, maintaining their stability and providing a high level of biological stocks. This species is noted for performing active movements, or migrations. Studying the migrations of amphipods and identifying the sites where they concentrate helps us detect
the potential food-rich areas for fish. The phenomenon of active migrations is known for many groups and species of aquatic organisms and is associated with more efficient use of space and resources, protection from predators, and energy redistribution. Spatial movement, in both the vertical and the horizontal directions, is observed, in particular in amphipods, on a daily scale. As a rule, during daytime, they seek to avoid predators by burrowing into the ground or hiding under dense substrates, and as illumination decreases they re-enter the water column. As our research has shown, important factors affecting the movement of Gmelinoides in the shallow littoral area of Lake Ladoga are the following: the type of habitat, changes in water and air temperature, moon phase, cloud cover, wind speed and direction, illumination, precipitationintensity, and total rainfall. The study has revealed patterns in how these factors influence the population density of the
crustaceans. A number of patterns were identified in the daily activity of the species. Both vertical and horizontal migrations were observed. The highest concentration of Gmelinoides was found between sunset and midnight and was formed by juveniles. Adults reach their maximum numbers in the water column at midnight. During the daytime, amphipods leave the water column of the shallow zone, burrowing into soft sediment or finding shelter under rocky debris.