Many species of seabirds breed on the coasts of the Baltic Sea. Different species have shown different trends in breeding numbers: nine species have declined, ten have increased, nine were stable, and the trend was uncertain in one species. The greatest declines in breeding numbers were observed in common eider Somateria molllissima and great black-backed gull Larus marinus. Three species that feed mainly on herring and sprat (common guillemot, razorbill, and Arctic tern) have increased in number over recent decades. White-tailed sea eagle and great cormorant have increased, following the cessation of hunting and the decline in persistent pollutants.
The Baltic Sea is an important wintering area for many species, including the globally threatened long-tailed duck, velvet scoter Melanitta fusca, and Steller's eider Polysticta stelleri. These three species have been declining in number during the last 25 years, as have many other benthic-feeding species.
Figure 18: Development in the breeding populations of common eider (SOMMO), great black-backed gull (LARMA), and Arctic tern Sterna paradisaea (STEPA) in the Baltic Sea in the period 1991–2015.