Ecosystem overviews

Greater North Sea ecoregion

Pressure: Selective extraction of species, including incidental non-target catch

​​​​​​​​​​​​​​​​​The main contributing activity to selective extraction of species in the Greater North Sea is fisheries. Sustainable fisheries management aims to minimize long-term negative effects on ecosystems while seeking long-term economic and social viability of the fisheries. Overall fishing effort in the Greater North Sea has fallen by approximately 50% (2004–2012). This decline in effort has resulted in a decline in the fishing mortality rate of commercial fish stocks. There have been shifts in fishing techniques. Beam trawling has been increasingly replaced by pulse beam trawling, sum-wing, twin-rigging, and flyshooting, gear types that all require less fuel. The impact of the EU landing obligation is difficult to predict, but fishing behaviour, data gathering, and stock assessments will be affected.

Impacts on commercial stocks

The majority of North Sea fish stocks are now fished at rates at or below FMSY. Overall fishing mortality (F) for shellfish, demersal, and pelagic fish stocks has reduced since the late 1990s (Image B on the right) . The fishing mortality on 24 stocks has been evaluated inimage B against MSY reference points. The relative spawning-stock biomass has also increased since 2000 and is now above or close to the biomass reference points used in stock assessments of most stocks in the Greater North Sea. A number of stocks still have a relatively high fishing pressure, namely mackerel Scomber scombrus, blue whiting Micromesistius poutassou, sole Solea solea in the English Channel, and some Nephrops stocks.
There are also fisheries on forage fish in the North Sea such as sandeel Ammodytidae, sprat Sprattus sprattus, Norway pout Trisopterus esmarkii, and herring, primarily for fish meal and oil (except for herring, where the majority of the catch is for human consumption). Currently, multispecies assessment models (which include trophic interactions) are used to evaluate the impact of fisheries and main predators (gadoids, birds, and sea mammals) on the forage fish stocks. An area in the northwestern North Sea is closed for sandeel fishing to protect food stocks for predators. The proportional impact of recreational fishing is increasing as commercial operations are restrained.​​

Impacts on foodwebs

Fishing changes both community structure and foodwebs. The depletion of larger predatory species has likely perturbed the structure and functioning of the ecosystem. Multispecies assessment methods can account for some of the interactions and indicators like the large fish indicator (LFI) index (describing the proportion -by weight of the demersal fish community catch on surveys that is larger than regional length thresholds) can be used to monitor changes in the fish populations. In the Greater North Sea, the LFI index declined in the mid-1980s and has been relatively stable with annual changes since 2004.

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). These include spurdog Squallus acanthias, the common skate complex Dipturus spp., angel shark Squatina squatina, porbeagle Lamna nasus, and some deep-water sharks. Despite zero TACs or prohibited listings for these species, several elasmobranchs are caught as bycatch in some fisheries.

Impacts on seabirds and marine mammals

Bycatch in bottom-set gillnets is probably the greatest anthropogenic activity affecting population abundance of harbour porpoises Phocoena phocoena in the North Sea. Bycatch of seabirds in the North Sea occurs, but is not believed to be a large pressure on the seabird populations.​​

Other main pressures on the Greater North Sea ecosystem​

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A. Effort trends for regulated gear types in a) Skagerrak/Kattegat, b) North Sea proper, and c) eastern English Channel. TR = demersal otter trawl and demersal seine, BT = beam trawl, GN = gillnet, GT = trammelnet, LL = longline. (STECF, 2013)​ Click image to enlarge.
B. Time-series of average relative fishing mortality (F to FMSY ratio) and biomass (SSB to BMSY trigger ratio) by fish guild. Mean F and mean SSB is by total number of stocks with reference points. Click image to enlarge.​
C. Time-series of the large fish indicator (LFI) for the Greater North Sea. (ICES, 2014)  Click image to enlarge.  
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Greater North Sea ecoregion

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