Adipose tissue fatty acids suggest spatial and temporal dietary differences in great cormorants of the Baltic Sea area

Abstract Increased numbers of great cormorants ( Phalacrocorax carbo ) in the Baltic Sea may have local impacts on fisheries and salmonid hatcheries. We studied spatial temporal variability cormorant diet, potential consumption hatchery salmonids, by analysing knee subcutaneous adipose tissue fatty acids (FA) specimens (N = 77) collected along Swedish Finnish coasts different seasons during 2013–2017. The FA profiles subspecies sinensis were similar, with large individual variation. proportion C18 polyunsaturated FAs (PUFAs) was largest north, whereas C20–22 monounsaturated (MUFAs) increased towards south, reflecting diminishing freshwater increasing marine food web characteristics south. As an exception, MUFA percentage high June 2017 from northern Sea. source MUFAs probably raised ocean fish feed released 10 days before, near capture site. southern differed each other both early late summer samples, suggesting spatially diets. variation found 22:1n-11, characteristic zooplanktivorous fish, likely originating Atlantic wild or hatchery-reared fish. This study shows that can be used as proxies for seabird diet monitoring indicators predation Obtaining quantitative estimates proportions dietary species requires future feeding experiments, allowing calibration between compositions diet.