La Dieta del corb marí emplomallat del Mediterrani (Phalacrocorax aristotelis desmarestii)

Abstract

The European Shag (Phalacrocorax aristotelis) is a seabird species used as an indicator of changes in marine ecosystems. Two subspecies exist in the Iberian Peninsula: P. a. aristotelis, distributed along the Cantabric-Atlantic coast, and P. a. desmarestii, distributed throughout several Mediterranean littoral areas, where is endemic from, being the former one, the object of this study. This subspecies has a low reproductive population in the rocky cliffs of the Mediterranean coast and is listed as Vulnerable in the Red Book of the Birds of Spain. Up to now, multiple studies have focused on studying the diet of the nominal subspecies, however, there is not as much information available regarding the diet of the Mediterranean subspecies. Therefore, the purpose of this study is to analyze the diet of th is subspecies in order to improve the knowledge about its ecology to apply the most appropriate measures for its conservation. Specifically, the main objective of this project is to study the diet of a colony of P. a. desmarestii located in the Maresme during the non-breeding season. In this way, it is expect to determine if the subspecies of the Mediterranean has an opportunistic diet, like other studies had been postulated for the Cantabrian-Atlantic subspecies, or it is specialist. In order to observe the composition of the diet, a total of 91 pellets have been analyzed, identifying 9,222 sagittae otoliths of the fish. The results have been compared between three periods: July, September and November. Also, the preys length of the most abundant taxa has been compared between the same three periods. These taxa were: the species Ariosoma balearicum , which belongs to the Congridae family, which represents the 77.8% of the diet, the Sparidae family the 97%, the Gymnammodytes genus, which belongs to the Ammodytidaefamily, the 5% and the Trachinidae family the 4.5%. Finally, it has been concluded that the Mediterranean shag, as the Cantabrian -Atlantic subspecies, has an opportunistic diet based on the availability of prey species. Additionally, the composition and sizes of these prey species varying according to seasonality, maybe as a result of natural fluctuations in fish populations