Population Viability Analysis of Caspian tern (Hydroprogne caspia) on an island in the northern Gulf of Bothnia

Seabirds demonstrate a global decline due to loss of habitat, climate change, invasive alien species and predation. Population Viability Analyses can be used as a tool for strategies in conservation of threatened species. The Caspian tern (Hydroprogne Caspia) breeds in two European locations - The Black Sea and The Baltic Sea, the former has shown declining population size since the 1970’s. The species is classified as Near Threatened (NT) in Sweden. The aim of this study was to investigate the extinction risk of the Caspian tern colony at Storgrundet, focusing on the effects that altered levels of predation in different age categories and habitat quality had on the extinction risk of the colony. Analyses of inventory data indicated a slight increase of Caspian terns, both nationally and at Storgrundet. A Population Viability Analysis (PVA) showed that the survival of the colony is more dependent on the survival of adults than juveniles, regardless of the level of habitat quality. Juvenile survival appeared more correlated to the quality of the habitat in comparison to what adult survival exhibited. Future studies should mainly be focusing on the prevention of adult mortality. Though continuous efforts in monitoring, predatory prevention, habitat restoration and protection along the migration route should be carried on.