Analysis of pellets of European Shags Phalacrocorax aristotelis desmarestii collected at a non-breeding roost site in southern Mallorca identified 36 species of fish prey, belonging to 27 genera and to 16 families. This diversity is higher than in the diet of P. a. aristotelis in the Atlantic, and higher than in the previous literature for P. a. desmarestii in the Mediterranean. European Shags in southern Mallorca foraged mainly on fishes with a mean estimated length of 11.6 cm (84.1% ranging from 6.1-15.0 cm in estimated length), most being pelagic species (59.6%). The most important fish in numerical frequency (43.9%) and estimated biomass (37.2%) was the Bogue Boops boops (Sparidae). This species has not been reported in European Shag diet in the Atlantic, and its importance was low in other Ph. a. desmarestii populations studied. The second most frequent prey was sand smelt Atherina (15%), but its contribution to biomass was low (1.4% of estimated biomass) because of its small size, as has been reported from other Mediterranean locations. The occurence of Scorpaenidae (10.7% by frequency, 17.4% of estimated biomass) was higher than in previous studies of Ph. a. desmarestii. Scorpaenids have not been found in the diet of Ph. a. aristotelis. Sandeels (Ammodytidae), a key prey for Ph. a. aristotelis in the Atlantic, were very scarce in this study, as in other recent Mediterranean studies. The relative abundance of species anatomically well protected against predation, such as scorpaenids and trachinids, and the diversity of prey probably reflects the scarcity or absence of other preferred prey. This study reflects the opportunistic behaviour of European Shags in the Mediterranean Sea, foraging on fish with very different ecological requirements, in an environment that is poor but diverse.