Some Results of Long-Term Counts of Waterbirds Wintering in the Western Part of the Gulf of Gdańsk (Poland), with Special Emphasis on the Increase in the Number of Cormorants (Phalacrocorax Carbo)

Abstract

Regular counts of waterbirds have been conducted in the western part of the Gulf of Gdansk since 1984. About 130 km of coastline were being surveyed within two days every month (September to April). The most common waterbird species (excluding gulls Laridae) are Tufted Duck (Aythya fuligula), Mallard (Anas platyrhynchos), Goldeneye (Bucephala clangula), Mute Swan (Cygnus olor), Coot (Fulica atra), Goosander (Mergus merganser) and Cormorant (Phalacrocorax carbo). The number of wintering birds of each species showed distinct fluctuations. Only Cormorant's number has been rising continually, especially in winter (before 1990 less than 100 individuals, after 2000 more than 3,000). The highest number was recorded in autumn (10,953 in September 2003). In 1998 and 1999 non-breeders and post-breeders Cormorants consumed 300–900 t of fish per year. 73% to 80% of all taken fish were damaging for fishery and biodiversity: round goby (Neogobius melanostomus) and nine-spined stickleback (Gasterosteus aculeatus).