Ecosystem overviews

Celtic Seas key signals

Ecosystem and environmental trends
  • ​​​​​​​​​​​​​​​​​​Long-term datasets from the Malin shelf (from 1959 on) and the upper 800 m of the Rockall Trough (from 1975 on) indicate an overall rise in sea surface temperature. Mean annual temperature of the Rockall Trough increased from ~9.3°C in 2001 to a peak 10.1°C in 2006. A steady cooling trend has been noted since then. In the last decade, the same trends are apparent on the Malin shelf. Salinity in the upper 800 m of the Rockall Trough has shown an increase from the early nineties until 2010, with a decrease in the following four years. 
  • Temperature affects the migration, distribution, and onset of spawning of blue whiting (Micromesistius poutassou), Northeast Atlantic mackerel (Scomber scombrus), western horse mackerel (Trachurus trachu​rus), and boarfish (Capros aper). 
  • Sea temperature affects the recruitment of some gadoids in the Irish Sea, Celtic Sea, and west of Scotland. The Celtic Seas ecoregion is at the edge of the geographical range of several species, potentially making these species more susceptible to environmental variation. 
  • Species richness (number of species) is higher in the Celtic Sea than in the rest of the ecoregion due to the number of warm-favouring Lusitanian species present here. 
  • Phytoplankton abundance and the abundance of diatom and dinoflagellate species in shelf and oceanic waters west of the European shelf show long-term declines since 1958, while diatom and dinoflagellate species abundances increased in coastal waters of the Malin shelf and southwest of Ireland between 1990 and 2010. 
  • There has been a decline in overall copepod abundance since 1958. The cold-water species Calanus finmarchicus and Pseudocalanus spp. have decreased in abundance; however, the warm-water copepod C. helgolandicus has increased in abundance and has spread northwards, presumably in response to ocean warming. 
  • The abundance of breeding seabirds has shown a broad downward trend since the early 2000s. Populations of grey seals have been increasing over at least the past thirty years, though the populations are becoming more stable now. Overall trends in the abundances of cetaceans and harbour seals are not known.  
  • Overall fishing pressure on the commercial fish and shellfish stocks in the Celtic Seas ecoregion has decreased since its peak in 1998 and the average F to FMSY ratios for the combined demersal, flatfish, and pelagic stocks is now close to FMSY. 
  • Overall biomass of commercial fish and shellfish stocks in the Celtic Sea has increased and the average SSB to Btrigger ratio for the combined demersal, shellfish, and pelagic stocks in the Celtic Seas ecosystem is now above Btrigger. 
  • The fishing effort of bottom mobile gears in the Celtic Seas ecoregion decreased by 35% from 2003 to 2014. This has reduced the spatial fishing footprint and the average number of times the seabed is trawled per year.
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Celtic Seas key signals

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