Sentinels of coastal ecosystems: the spatial ecology of European shags breeding in Normandy

Abstract

To use seabirds as ecological sentinels of marine ecosystems under the incidence of global changes, it is essential to understand linkages between their spatial ecology and environmental conditions. Such information is still lacking for some key areas, including in Europe. We studied the spatial ecology of European shags (Phalacrocorax aristotelis) in Normandy, France, where > 1% of the species’ world population, and ca. 20% of its French population breeds. Working on 29 breeding individuals at two colonies (Chausey and Saint-Marcouf), we performed the first GPS-tracking study for the species in this region. On the basis of GPS positions and dive information across 244 foraging trips, we present a general methodological framework to map existing, and model potential seabird habitats. Shags performed dives between 9 and 17 h, and fed at average distances of 5.3 km (Chausey) and 3.3 km (Saint-Marcouf) from their nests. They used 186 km2 (Chausey) and 143 km2 (Saint-Marcouf) areas with a depth < 15 m over rocky and sandy habitats. Shags selected areas with an SST around 18 °C (Chausey) and 12–13 °C (Saint-Marcouf). There is strong evidence that they are year-round residents in these coastal areas and we identified four major environmental changes to which they may react as spatial ecological indicators: climate change, which may impact them directly, or indirectly via shifting prey distributions; fisheries, which may target small pelagic fish such as sandeels, upon which they depend; sediment extraction which may remove benthic habitats critically important to sandeels; and marine windfarms which may result in feeding habitat loss.