Temporal changes in the diet of great cormorant (Phalacrocorax carbo sinensis) on the southern coast of Finland — comparison with available fish data

The population increase of the piscivorous cormorant in the archipelago areas of the Baltic Sea, Finland, has raised discussion about the potential harm to the commercial fisheries. We investigated the diet of the cormorant in the western Gulf of Finland and compared the results with commercial and test fishing catches from nearby waters. The most numerous species in the diet were eelpout, roach, perch and three-spined stickleback, respectively. The annual proportion of perch and roach decreased, while the proportion of sticklebacks in the diet increased significantly during 2002–2010. At the same time, the size of prey eelpout decreased significantly. No decreasing trends were found in gillnet monitoring catches of perch or roach, or in the commercial perch catches in nearby waters during 2005–2010. Thus, based on the available fish data, no impacts of cormorant predation on the local perch and roach populations were detected.