<p>Predator eradication has been proposed as an effective conservation strategy for endangered species, especially seabirds. Most studies have focused on invasive mammal predators, but to a lesser extent on (expanding) native apex predators and/or cohabitant mesopredators. Moreover, they typically cover a single or a handful of location(s), whereas the effects over larger spatial scales are widely unknown. Here, we assess the effectiveness of several treatment actions carried out in the Baltic Sea-region (Sweden) to control invasive American mink, cohabitant herring gulls (mesopredator), and expanding white-tailed eagle (apex predator) on the Caspian tern from 1990 to 2021 (20 control and 11 treatment colonies). Using a BACI design, we evaluate the differences in (1) fluctuations in Caspian tern colony sizes; (2) the occurrence and abundance of breeding pairs; and (3) the colony reproductive output. Moreover, using nationwide monitoring data of breeding white-tailed eagles and Caspian tern colonies from Finland (<i>N</i> = 55 colonies) we assess whether fluctuations in colony size are linked to the expansion of this predator. Colony fluctuations decreased in treatment colonies after predator control, while it remained unchanged in control ones. Abundance of breeding pairs increased in treatment colonies but decreased in control colonies. Lastly, the colony reproductive output decreased equally in both control and treatment colonies following predator control. These results suggest that predator control has benefited the Caspian tern population in the Baltic Sea and deepen our knowledge on the effectiveness of these actions at the scale of whole populations, an essential step to provide evidence-based guidance.</p>