Diet of Phalacrocorax carbo sinensis (Aves, Phalacrocoracidae) and impact on fish stocks: a study case in Cabras and Mistras lagoons (Sardinia, Italy).

Abstract

1 - The work aims to study the feeding habits of Phalacrocorax carbo sinensis wintering in the Cabras and Mistras lagoons and to assess the impact of the cormorants colony on fish stocks.
2 - 438 bird flocks of Great Cormorant (Phalacrocorax carbo sinensis) wintering in the Cabras and Mistras lagoons (central-western Sardinia) (SPA ITB034008 and ITB034006 respectively) were analysed.
3 - Through the morphological analysis of undigested hard body parts, such as otoliths, it was possible to trace to the preyed species and their biomass and, then, to the average daily consumption of cormorants.
4 - The trophic spectrum was dominated almost exclusively by euryhaline, gregarious fish species. Mugilidae, and particularly Liza ramada with a percentage index of relative importance (%IRI) of 75.28 and L. saliens (%IRI = 17.78) were the most important preys, while Dicentrarchus labrax (%IRI = 3.53) was of secondary importance. Other species, as Diplodus vulgaris (%IRI = 0.06), Sparus aurata (%IRI = 0.01), Solea solea (%IRI = 0.04) and Anguilla anguilla (%IRI = 0.01), completed the diet.
5 - The Daily Food Intake (DFI) was estimated in 478.4 ± 18 g/day. The overall amount of biomass preyed by the cormorants during the entire wintering season was calculated in about 422 tons. Considering the Cabras lagoon area, it was possible to estimate an amount of fish taken equal to 189.4 Kg/ha during the same period.