Abstract
The paper reports on research into the available published literature concerning those smaller cetaceans which penetrate into the Baltic Sea, bearing in mind that the Skagerrak is not included in the Baltic waters. Species documented are: Balaenoptera acutorostrata, Delphinapterus leucas, Monodon monoceros, Hyperoodon ampullatus, Mesoplodon bidens, Ziphius cavirostris, Orcinus orca, Pseudorca crassidens, Globicephala melaena, Grampus griseus, Lagenorhynchus albirostris, L. acutus, Tursiops truncatus, Delphinus delphis and Phocoena phocoena. Three or perhaps four species are considered normal inhabitants of these waters: P. phocoena, L. albirostris, O. orca and T. truncatus. The morphology of the Baltic Sea and its particular ecological conditions should be considered as the principal factors regulating the presence of cetacean species in these waters.