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CS 2: Cod, plaice and herring in the North Sea

Foto and Copyright©: Daniel Stepputtis, Rostock (Germany)


In the North Sea, all stocks of roundfish and flatfish have been exposed to high levels of fishing mortality over the past century. For most of these stocks their lowest observed spawning stock biomass has been seen in recent years (ICES 2004). North Sea cod in particular has been outside of 'safe biological limits' since the late 1980s and North Sea plaice since 1994 (ICES 2005). Over the past 2-3 years a number of different management measures (e.g. area closure, effort reduction, drastic TAC cuts) have been applied in an attempt to rebuild the cod stock, yet it is still only at 20-25 % of the level it was in 1990. Similarly, the establishment of a partially closed area in 1989 ('plaice box') has not prevented the plaice stock from continuing to decline (Pastoors et al. 2000). In contrast, North Sea herring completely collapsed in the early 1970s, but has recovered subsequently due to strict management measures. This stock is now considered to be inside 'safe biological limits' and recent spawning stock biomasses are as high as in the 1960s (ICES 2004). The threat of a second collapse was successfully fended off in the mid 1990s due to drastic cuts in the TACs according to 'fast-track-advice' and mid-year revision.

Currently, the most important question for North Sea fishermen, fishery-scientists, and -managers is, why has herring management become a success story whereas all efforts to rebuild the cod and plaice stocks have thus far failed?

The key to the answer lies in understanding the complex interactions between the species' biology and reproduction success, their biotic and physical environment and social, economic and governance forces, all impacting on population dynamics. Therefore, the objectives of the North Sea Case Study in UNCOVER are to

  • characterize the contrasting states of the ecosystem which allow high cod, herring and plaice production;
  • understand and model the spatio-temporal changes in reproductive potential and multi-species interactions leading to contrasting recruitment success under varying environmental regimes;
  • understand and model the effect of social, economic and mixed- fisheries influences on recruitment dynamics and stock dynamics of cod, plaice and herring under varying environmental regimes;
  • develop and improve management strategies which will lead to a sustained recovery of North Sea cod and plaice stocks and sustained maintenance of North sea herring stocks under varying environmental regimes.

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