Effectiveness of EU protected area networks in safeguarding key conservation areas for an aerial marine predator across its breeding range

Protected areas (PAs), the cornerstone of global biodiversity conservation, encompass millions of square kilometers worldwide, with the European Union (EU) hosting the world's largest system, the Natura 2000 network (N2K). However, the effectiveness of EU’s PAs (N2K and other protection network) in safeguarding wide-ranging marine species such as seabirds remains underexplored. We tested the effectiveness of PAs in safeguarding key conservation areas of Scopoli's shearwater (Calonectris diomedea), a colonial seabird breeding on small islands and foraging widely across vast swathes of sea, focusing on the EU population, which includes >95% of the species' colony sites. All known EU breeding sites were located within PAs and N2K. Yet, 66% of the EU breeding population is exposed to high-severity threats, with rats representing the most impactful threat. Overall, only 54% of the most-used marine areas, identified using tracking data from 797 individuals across 27 breeding sites throughout the Mediterranean, overlapped with PAs. Surprisingly, fishing effort, an important threat for shearwaters that reduces prey availability and causes direct mortality through bycatch, was higher in the most-used areas located inside than outside marine PAs. Oil spill risk was lower inside marine N2K, due to lower tanker presence compared to areas outside PAs. Most-used marine areas of a single colony often spanned multiple Exclusive Economic Zones. Together, these findings indicate that PAs and N2K provide limited mitigation of threats across the species’ breeding range and emphasize the need for implementing specific conservation measures for seabirds within PAs and for developing effective cross-border conservation strategies.