Spatial overlap between the European Shag and commercial fisheries in a special protected area: implications for conservation

Abstract

Fisheries pose a significant threat to seabirds through overfishing and bycatch. The European Shag Gulosus aristotelis is a threatened species in Portugal, whose main breeding site in the country is located in the Berlengas archipelago, a Special Protected Area (SPA). This region is also heavily dependent on fisheries and the fishing industry, with a fishing fleet composed mainly of small polyvalent vessels. In this study we quantified and mapped the spatial and temporal overlap between Shags and commercial fisheries operating purse seines, gillnets, longlines, and trawls, during Shag breeding and non-breeding season, to contribute to a better understanding of the effects of these activities on Shags. Spatial overlap between Shags and large vessels was low, but high overlap values were obtained with small vessels (< 15 m), mainly operating longlines. The estimated overlap values were also higher during the non-breeding season, indicating a greater likelihood that fisheries increase the mortality of Shags through resource competition and bycatch in fishing gear. The conservation of Shags in the Berlengas archipelago would benefit from the implementation of measures that contribute to the reduction of spatial overlap with small vessels operating longlines and gillnets, thereby reducing the impacts of fishing activity.