At least 23 seabird species breed on the coasts of the Celtic Seas. These colonies are particularly important in a global context of abundance for Manx shearwater (Puffinus puffinus), European storm-petrel (Hydrobates pelagicus), and northern gannet (Morus bassanus). The numbers of many breeding species have been declining in the past decade. Widespread seabird breeding failures are frequent in the Celtic Seas and have been documented at 25% or greater since 2010. The variation in habitats (from coastal to shelf break and deep sea) means that the ecoregion is also used during the non-breeding season by many further species and by seabirds that breed elsewhere. Declines may be related to prey availability and contaminant loads. For information on bycatch, see the 'Selective extraction of species' section.