Impatto del cormorano Phalacrocorax Carbo Sinensis sulle produzioni ittiche delle lagune sarde

The work aims to study the feeding habits of the Great Cormorant (Phalacrocorax carbo sinensis, (Blumenbach, 1798), a species wintering in the transitional environments of Sardinia, and to assess the impact of the cormorants colony on fish stocks, considering the different ecological and economic aspects. During the 2012-2015 period, several monitoring and censuses were carried out, in order to assess and identify the roost or feeding areas with the largest number of cormorants in the different lagoons examined. Numerically, during the three years was observed a significant increase in the number of individuals (rk, p <0.05), which was more than 40% between the first monitoring conducted in 2012 and those 2014. Indeed, in December 2011 was recorded a peak of 9637 animals while in December 2014, there were 13536 individuals. A total of 1402 bird flocks of Great Cormorant wintering in the Cabras and Mistras lagoons (central-western Sardinia), in the S'Ena Arrubia lagoon (southeast of Oristano), in the Sant'Antioco lagoon (south-west Sardinia), in the Santa Gilla lagoon (near to Cagliari), in the Colostrai lagoon (southeastern coast of Sardinia), in the Sa Praia pond (south-east coast of Sardinia) were analysed. Through the morphological analysis of undigested hard structures, such as otoliths, it was possible to describe the preyed species, their size and biomass and, thus, the average daily consumption of cormorants. The trophic spectrum was dominated almost exclusively by euryhaline, gregarious fish species. Mugilidae, and particularly Liza ramada, were the most important prey with a very high percentage index of relative importance (%IRI). The average Daily Food Intake (D.F.I.) for the different lagoons examined was estimated to be equal to 386.8. ± 31 g / day. Specifically, the highest daily requirement was found in the Cabras lagoon with a value of 478.4. ± 18 g / day (Buttu et al., 2013a). The overall amount of biomass preyed by the cormorants during the entire wintering season was estimated over 500 tons. The results obtained by the model applied to a predation economically and ecologically acceptable, specifically, indicate that predation in the Cabras lagoon is outside of economically sustainable levels. This kind of study represent a fundamental step for the development of integrated management plans and protection measures, taking into account both the production requirements, and the environmental factors related to these important ecosystems.