​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​The main contributing activity to selective extraction of species in the Celtic Seas ecoregion is fisheries, with demersal and pelagic fisheries occurring in most parts of the ecoregion. There has been an overall reduction in fishing effort by the most used gears. 

Impacts on commercial stocks

Overall fishing mortality (F) for shellfish, demersal, and pelagic fish stocks has reduced since the late 1990s although the pelagic stock are now above the reference point. Mean F is now closer to the level that produces maximum sustainable yield (MSY). The fishing mortality on 45 stocks has been evaluated in the figure on the right a5 against MSY reference points; of these, 30 stocks are now fished at or below MSY. The relative spawning-stock biomass has also increased since the late 1990s and is now above the biomass reference points used to assess 78% of the stocks in the Celtic Sea. A number of stocks still have very low stock biomasses, namely cod Gadus morhua, haddock Melanogrammus aeglefinus, and whiting Merlangius merlangus to the west of Scotland, cod and sole Solea solea in the Irish Sea, and herring Clupea harengus in ICES Divisions 6a, 7b, and 7c.​

​Impacts on threatened and declining fish species

Several fish species have been depleted by fishing in the past and are now on the OSPAR list of threatened and declining species (see full list below), including spurdog Squallus acanthias, the common skate complex Dipturus spp., angel shark Squatina squatina, porbeagle Lamna nasus, and some deep-water sharks. Although there are zero TACs or prohibited listings for these species, several of them remain vulnerable to existing fisheries. Spurdog and the common skate complex are caught as bycatch in mixed demersal trawl fisheries and gillnet fisheries, and deep-water sharks are caught in the mixed deep-water trawl fishery. 

Impacts on seabirds and marine mammals

Longline fisheries pose the greatest threat to seabirds offshore, while inshore net fisheries may catch diving species. Largescale bycatch of great shearwaters Puffinus gravis has been reported from the hake longline fishery on the Grand Sole fishing bank, and based on information from elsewhere, longline fisheries in waters west of Scotland would likely catch northern fulmars Fulmarus glacialis. Fisheries with high risk of cetacean bycatch in the Celtic Sea are bottom setnets (bycatch of harbour porpoises Phocoena phocoena) and pelagic trawls, particularly those for bass (bycatch of common dolphin Delphis delphinus). Modelling indicates that it is likely that the bycatch of harbour porpoises in gillnets on the Celtic shelf has affected population abundance at least in some past periods. Bycatch in both fisheries may have reduced in recent years due to less fishing activity and the use of acoustic alarms attached to fishing gear as a mitigation technique.