IMPACT OF Phalacrocorax carbo sinensis (AVES, PHALACROCORACIDE) ON TRANSITIONAL ENVIRONMENTS IN CENTRAL-WESTERN SARDINIA 1BUTTU S., 1MULAS A., 1PALMAS F. 1Dipartimento di Scienze della Vita e dell’Ambiente – Università degli Studi di Cagliari, Via T.Fiorelli, 1 – 09126, Cagliari simone.buttu@hotmail.it Sardinia, for its peculiar environmental characteristics, the relative abundance and the quality of its lagoons and ponds, hosts the biggest wintering population of the Cormorant (Phalacrocorax carbo sinensis) on the Italian territory. Since the early ‘80s this species has began to rise considerably, probably due to conservation programs held in North Europe colonies. This fast population growth is cause of major concern among fishermen, afraid for the loss of the fish stocks. In this work we analyse, through the mucous mixtures method (flock or bolus), the diet composition of the cormorants from the colony located in Cabras lagoon dormitory (ZPS ITB034008), to evaluate which species were more preyed and their impact on fisheries. The study of the diet was conducted during the wintering season 2010/2011, between October and March. A total of 438 pellets were collected. Through morphological analysis of hard body parts, such as otoliths found in the flock, it was possible to evaluate biomass and prey species composition as well as the average daily consumption. The trophic spectrum was dominated almost exclusively by euryhaline fish species. The most important preys, by frequency of occurrence, belonged to Mugilidae (86%), Moronidae (7%), Atherinidae (4%) and Sparidae (3%) families. Regarding the qualitative composition of the diet, Mugilidae (mainly Liza spp. and Mugil spp. ) showed the highest index of relative importance (%IRI = 97,656). Moronidae (%IRI = 2,185) represented the second most important prey taxon, while Sparidae were the less (%IRI = 0,001). The values of percentage prey biomass of the entire wintering season amounted to 87% for Mugilidae and 10% for Moronidae, while the remaining 3% is represented by other prey taxa. Based on the data collected, it was estimated an average daily consumption (Daily Food Intake) of 478.4 g / day for example. The Cabras lagoon represents the main Cormorants feeding area in Sardinia, with the highest concentration of specimens of the entire island. This fragile system seems to have reached, for some years, the carrying capacity in terms of presence of ichthyophagous birds, and it appears to have established a situation of balance between the various components of the ecosystem, which still requires constant monitoring.