The Bay of Biscay and the Iberian Coast provide important breeding habitats for several seabird species. These include the European storm petrel (Hydrobates pelagicus), band-rumped storm petrel (Hydrobates Castro), European shag, yellow‑legged gull (Larus michahellis), lesser black-backed gull (Larus fuscus), great black-backed gull (Larus marinus), black-legged kittiwake, common guillemot, Little tern (Sternula albifrons), Audouin´s gull (Larus audouinii) and Cory´s shearwater.
A number of seabird species have experienced declines across the ecoregion, including European shag (Álvarez, 2015), with Iberian guillemot (a subspecies of common guillemot) considered extinct as a breeder in Iberia and the black-legged kittiwake considered regionally extinct.
The breeding populations of Cory´s shearwater demonstrate variable subregional trends. In Portugal, breeding populations have remained stable over the last ten years, whereas the biggest subcolony in the Berlengas archipelago has decreased over a similar time period. The species has recently colonized some areas in Galicia (northwest Spain).
The ecoregion is also important to numerous migratory seabird species as a flyway and wintering area. The most abundant species are: northern gannet, great skua (Stercorarius skua), Balearic shearwater, Manx shearwater (Puffinus puffinus), sooty shearwater (Puffinus griseus), great shearwater (Puffinus gravis), razorbill (Alca torda), common guillemot, Atlantic puffin (Fratercula arctica), and seven species of gull (Larus spp.). Areas of high seabird diversity are primarily located in Galician waters, decreasing towards the inner Bay of Biscay.
A decreasing trend in abundance of northern gannets and great skuas off the Portuguese coast has been observed over the last ten years and in abundance of razorbills and Balearic shearwaters on the western Iberian coast.
Seabirds in this region have been shown to be sensitive to oil spills, fishing bycatch, marine litter, and plastic ingestion. Many migrating seabirds are also dependent on pelagic fishes that are at early life stages such as the European anchovy.