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May 6th, 2025
As part of the AMPLIAMAR project’s mission to mitigate anthropogenic threats to vulnerable seabird species, one of our key focal species is the European shag (Gulosus aristotelis).
The European shag is a unique and threatened seabird. This species typically nests on steep, rocky, and inaccessible cliffs along both the Cantabrian-Atlantic and Mediterranean coasts. In recent decades, the European shag has suffered a significant population decline in Spain, mainly due to the overfishing of its prey species, hydrocarbon pollution, disturbance from recreational boating, and entanglement in fishing gear.
The European shag is present along the entire Cantabrian-Atlantic coast—Galicia hosting the largest populations—as well as in parts of the Mediterranean, including the coast of Almería, offshore islets in the Valencian Community, the Balearic Islands, Catalonia, and, more sporadically, the Strait of Gibraltar.
Two subspecies are found in Spanish waters:
Gulosus aristotelis aristotelis, along the Cantabrian-Atlantic coast. (Picture credit: Andreas Trepte)
Gulosus aristotelis desmarestii, across the Mediterranean coast. Picture credit: Adrián Pina.
To better understand the ecology of this species and how it interacts with the marine environment, AMPLIAMAR and its collaborators have undertaken cutting-edge tracking studies in two critical areas of its range in Spain: Isla Grosa, in the Region of Murcia, and the Parque Nacional Marítimo-Terrestre de las Islas Atlánticas de Galicia.
Isla Grosa, located just off the coast of La Manga del Mar Menor, is a small volcanic island that provides essential breeding habitat for several seabird species. Despite its modest size, the island is a biodiversity hotspot, characterized by steep rocky slopes, limited vegetation, and rich surrounding waters that support a high abundance of small coastal fish — a key food source for the European shag. The island is managed as a protected area, but it remains vulnerable to disturbances due to its proximity to a densely populated and touristic coastal area.
In contrast, the Islas Atlánticas — which include the archipelagos of Cíes, Ons, Sálvora, and Cortegada — form one of Spain’s most important marine-terrestrial national parks. Located along the rugged Atlantic coast of Galicia, these islands boast steep cliffs, clear waters, and an abundance of marine life. The European shag maintains significant breeding populations here, and the archipelagos represent some of the most pristine coastal environments in the country. However, the area is not without threats, as increased marine traffic and fishing pressure still pose risks to local wildlife.
The fieldwork was led by Víctor García Matarranz and Andreia Zuzana Ribeiro Días (General Directorate for Biodiversity, Forests and Desertification, Ministry for the Ecological Transition and the Demographic Challenge), along with Ángel Sallent Sánchez from ANSE (Asociación de Naturalistas del Sureste).
To explore how shags use their environment in these two very different regions, our team deployed solar-powered GPS-GSM loggers equipped with depth sensors on 20 adult European shags — 10 individuals in Galicia and 10 in Murcia. These advanced devices allow for high-resolution, real-time tracking of both horizontal movements (via GPS) and vertical movements (via depth sensors), providing a detailed picture of each bird’s behavior at sea.
GSM-GPS deployment on an European shag by Francisco García and Mario González of ANSE in Grosa island.
Real time maps of the shags tagged in Galicia and Murcia respectively. Map credit: Diego Vicente.
What’s Next?
As data collection continues and more individuals are tracked, AMPLIAMAR and its partners will be better equipped to propose evidence-based conservation actions, including the identification of marine areas that may warrant further protection, the evaluation of risks from specific human activities, and the development of region-specific guidelines for reducing seabird bycatch.
These tracking efforts were carried out with the support of the AMPLIAMAR project, funded by the Fundación Biodiversidad of the Ministry for the Ecological Transition and the Demographic Challenge (MITECO). In addition, the work on Isla Grosa was made possible thanks to the collaboration of the Region of Murcia, through the Regional Ministry for the Environment, Universities, Research and the Mar Menor, via the General Directorate for Natural Heritage and Climate Action, and its Sub-directorate for Biodiversity, Protected Areas and Climate Action, which provided the necessary permits and logistical support.
Our goal is to ensure a future in which the European shag — and all seabird species threatened by human activity — can thrive along Spain’s coasts. Thanks to these first insights from Isla Grosa and the Islas Atlánticas, we are one step closer to that goal.
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