El cormorán moñudo y el visón americano en el Parque Nacional Marítimo-Terrestre de las Islas Atlánticas de Galicia

Abstract

In this study, we analysed the viability of seabird population, specifically the European shags (Phalacrocorax aristotelis) at the National Park of the Atlantic Islands of Galicia, after the invasion of the Americanmink (Neovison vison). In the last decade the shags at Cíes islands, the southernmost archipelago of thePark, experienced a population collapse in parallel with a similar reduction in its level of heterozygosity Data from marked individuals suggests that the loss of genetic diversity leaded to a decline in survivaland reproduction. In Cíes, an important episode of mink predation on adult shags occurred in the yearwhen mink arrived in breeding colonies, though the number of shags killed dropped abruptly in subsequent years. We found that, after the arrival of mink, shags nested preferably on sites where the risk ofpredation by mink was low, probably to avoid predators. Nevertheless, mink presence had negative effects on shag reproduction and population growth. Our results indicated that the effects of mink shouldbe integrated in a population dynamics framework together with other threats operating, such as thelong-lasting effects of the Prestige oil spill. We have also analysed the presence of mink in the NationalPark (islands of Cies and Sálvora). In total, 87 minks were captured during 2005-2013, and currently,mink are virtually eradicated from the Park. The genetic analysis of mink populations in both the Parkand the nearby coast suggested that mink invaded these islands in a few or even a single colonizationevents that probably originated from fur-farm escapes rather than from migrants from feral mainlandpopulations. Overall, our results suggest that the phenotypic plasticity of shags and the success of minkeradication campaigns mitigated the effects of mink presence on European shags at Cíes. Nonetheless,this population shows worrying symptoms of concern, which may affect its future persistence.