The diet of shag Phalacrocorax aristotelis desmarestii was studied in a NW Mediterranean archipelago (Marseilles, France) through the analysis of 109 regurgitation pellets during the non-breeding period (April to September) from 2004 to 2007. A total of 2 462 pairs of fish otoliths was found in pellets. These fishes belong to 12 families and 25 species. Six fish families (Atherinidae, Pomacentridae, Labridae, Centracanthidae, Sparidae and Serranidae) composed 92% of the shag diet. The diet remained stable during the four year study, but monthly variations were detected. These variations could result from diet changes at the end of the chick rearing period or from seasonal changes of fish community composition. The depth at which shags caught their prey was also determined. Shags mainly fish above or in Posidonia oceanica seagrass meadows, and mainly targeted small fishes (~10 cm TL). The mean fish biomass eaten daily by shag (280 g) was lower than that consumed by this species in the northern areas of its distribution range. The fish biomass eaten by the shag colony was estimated at only 7.4% of the total biomass caught by fishermen in the area. Thus, shags size captures did not strongly overlap with local fishing activities.