Marine Protected Areas (MPAs) are widely used tools for conservation and management. Their correct delimitation is challenging, especially when the target species are small, elusive, and inconspicuous, as little data is generally available to adequately assess their distribution at sea. Therefore, currently designated MPAs may not effectively cover key areas for small seabirds, particularly during migration and wintering seasons.

We used Ensemble Species Distribution Models (ESDMs) on a 15-year time-series dataset of at-sea census along the Atlantic Iberian arc to predict the potential distribution of the smallest European seabird, the European storm-petrel (Hydrobates pelagicus), and compare it with official marine Special Protection Areas (SPAs).

Occurrence of European storm-petrel was related to shifts in sea surface temperature, and to small distances from the coast over the continental shelf.

Most relevant area for the species in the Atlantic Iberian arc was west-central Portugal to north-western coast of the Iberian Peninsula, with an additional key area in the Gulf of Cádiz. Both zones host significant SPAs, but they inadequately cover key areas for European storm-petrels. Our findings support extending marine SPAs in the Atlantic Iberian arc to ensure their effective protection.

The distribution of the species expands over the years, varying both in size and location. These changes might be attributed to dynamic oceanographic variables, such as sea surface temperature and biomass of micronekton, which seem to play a significant role in their foraging behaviour.

Synthesis and applications: Our study highlights the importance of analysing long time series and ESDMs to design adequate protected areas which ensure the conservation of small and highly mobile species such as storm petrels. Our results should be considered by decision makers to prioritise and update marine protected areas, while incorporating the dynamic nature of the ocean within an ecosystem-based approach.