Ecosystem overviews

Celtic Seas Ecosystem Overview

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 since its peak in the late 1990s, as can be observed from two of its main pressures, i.e. a 35% reduction in physical seabed disturbance from 2003 to 2014 and species extraction. A further reduction in fishing pressure is likely to improve the status of the majority of ecosystem components.
  • 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.
  • Fishing-induced physical disturbance is estimated to have resulted in an overall decrease of invertebrate benthic biomass of between 59% in offshore mud and 5% in sandy habitats compared to an unfished state. This impact is patchy and may be over 80% in the most heavily fished areas.
  • 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.

Climate change

  • Climate change is causing changes in water masses. Freshening of western subpolar north Atlantic waters is observed in deeper areas of the ecoregion. In addition, the warming of surface water temperature in shallow shelf regions has become increasingly seasonally stratified and nutrient-limited in some areas. This has already changed the spatial distribution of several plankton and fish species within the ecoregion and is likely to continue to do so.
  • Climate change induced cascading effects are likely to occur throughout the ecosystem with consequences for the spatial distribution of fisheries. This should be considered in the marine spatial planning of infrastructure such as wind farms and the implementation of marine protected areas (MPAs).

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 toward 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.

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Celtic Seas Ecosystem Overview

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