Fishy choices: Investigating the dietary composition of European shag (Gulosus aristotelis) and great cormorant (Phalacrocorax carbo) in the Skagerrak

The European shag appears to be rapidly increasing in Sweden, and this increase has sparked an interest in their feeding habits and how their diet compares to the well-established great cormorant. For this reason, the diets of the European shag (Gulosus aristotelis) and great cormorant (Phalacrocorax carbo) were investigated through the analysis of regurgitated pellets collected in two areas in the Skagerrak, Väderöarna and Soteskär, off the Swedish west coast. While this method has inherent limitations, the findings suggest that shags primarily depend on small gadoids (Gadidae), wrasses (Labridae), and sandeels (Ammodytidae). In contrast, cormorants predominantly consume wrasses (Labridae) and gadoids (Gadidae). The diet of the shag was similar at both Soteskär and Väderöarna, these findings also applied to cormorants. However, differences between their diets at both locations were significant. Despite notable differences in their diets, dietary overlap was observed. Cormorants tended to consume larger and more benthic fish species compared to shags. To better understand the ecological role of these predators and their impact on fish populations, further understanding of their ecology in terms of diet, distribution, and number of individuals, among others, is needed.