Ecosystem overviews

Celtic Seas ecosystem overview

Our Ecosystem Overviews use risk-based methods to identify the main human pressures and explain how these affect key ecosystem components in each ICES ecoregion

​​​​​​​​​​​​​​​​​​​​The Celtic Seas ecoregion covers the northwestern European continental shelf and seas, from western Brittany in the south to north of Shetland.​ It is characterized by a diversity of habitats, such as an extensive slope, canyons, ridges, and seamounts that support vulnerable marine ecosystems (VMEs).

The oceanography and climate of the region is strongly influenced by conditions in the adjacent Atlantic Ocean. Ocean currents support strong linkages between the Celtic Seas ecoregion and its neighbouring ecoregions.

 Key signals

Human activities and their pressures​

  • Fishing continues to be the main threat to ecosystem health. This is despite a decrease in fishing pressure from its peak in the late 1990s, as can be observed from a 35% reduction in two of its main pressures: physical seabed disturbance and species extraction. A further reduction in fishing pressure is likely to improve the status of the majority of ecosystem components.
  • Across the ecoregion, the depth zone 0-200m is the most impacted by bottom fishing pressure. On average (including areas not trawled), the seabed in this depth zone was trawled 1.3 times in 2022. When evaluated at the c-square scale (0.05x0.05 degrees), 66% of grid cells in the 0-200 m zone are at least partly trawled, compared to 59% in the 200-800 m depth zone. 39% of the ecoregion is deeper than 800 m and this zone is not currently trawled.
  • Land-based industry and wastewater continue to be important causes of pressures like marine litter, nutrient enrichment, and the introduction of contaminants from riverine run-off.
  • Tourism and recreation were also found to contribute to marine litter.​

State of the ecosystem

  • Changes to the composition and distribution of plankton species in inshore areas have been observed. This may have implications for the frequency and intensity of harmful algal bloom events (HABs), which have caused widespread closures of shellfish farming areas and occasional mortalities of benthic organisms as well as farmed and wild fish.
  • Offshore mud is mainly affected by Norway lobster (Nephrops norvegicus) fisheries and has experienced the highest fishing pressure and impact compared to other habitats.
  • The stock sizes of most groups of commercial species are now overall above levels that can provide the maximum sustainable yield (MSY); however, some individual species within these groups may still be below MSY levels.
  • The numbers of many seabird species breeding in the ecoregion 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. Declines may be related to prey availability and contaminant loads.
  • The abundance of grey seals in the ecoregion is stable; there is little information on the overall trends of harbour seals and cetaceans.

State of the ecosystem

  • Changes to the composition and distribution of plankton species in inshore areas have been observed. This may have implications for the frequency and intensity of harmful algal bloom events (HABs), which have caused widespread closures of shellfish farming areas and occasional mortalities of benthic organisms as well as farmed and wild fish.
  • Offshore mud is mainly affected by Norway lobster (Nephrops norvegicus) fisheries and has experienced the highest fishing pressure and impact compared to other habitats.
  • The stock sizes of most groups of commercial species are now overall above levels that can provide the maximum sustainable yield (MSY); however, some individual species within these groups may still be below MSY levels.
  • The numbers of many seabird species breeding in the ecoregion 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. Declines may be related to prey availability and contaminant loads. 
  • The abundance of grey seals in the ecoregion is stable; there is little information on the overall trends of harbour seals and cetaceans.​​

Environmental and socio-economic context

  • The current trend of increased fuel prices and resulting decrease of fishing with bottom‑towed gears is likely to result in a further reduction of the extraction of demersal fish and disturbance of seabed habitats. If this also results in a shift towards less fuel‑intensive fisheries, such as gillnets, it is likely to result in increased bycatch risk of seabirds and marine mammals, including the longer-term effects from lost and abandoned fishing gear. Considering the ongoing downward trend in seabird numbers, such increased pressures on seabird populations should be avoided.
  • Small-scale coastal fisheries contribute less than 10% of total fish landings but attract 22% of full-time equivalent (FTE) employment in the sector and 14% of total fisheries revenue. Coastal fisheries can therefore have a higher local social and economic importance than that expected by landings volume alone.​

​Download the Ecosystem Overview.

View the interactive diagram.​​



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Celtic Seas ecosystem overview

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