Changes in the distribution of the North Sea plaice - Pleuronectes platessa -

The North Sea flatfish fisheries generate considerable numbers of discards, especially of plaice (Pleuronectes platessa). Their survival is very low. To reduce discard mortality, a partially closed area was established (“plaice box”) in 1989. The beam trawl fishery in this area was prohibited for vessels larger than 300 hp. Because the Plaice Box encompassed the major nursery grounds of North Sea plaice, it was expected that, at the same rate of exploitation, the introduction of the plaice box would enhance recruitment, yield and spaw-ning stock biomass. During an evaluation of the plaice box in 1999, it became clear that since 1989, the yield and spawning stock biomass had declined by about 40%. A possible explanation for this decline is that there has been a shift in the spatial distribution of North Sea plaice. It is possible that the young undersized plaice inhabit places further away from the coast so that the plaice box is not offering as much protection against discarding as originally supposed. The results showed that the spatial distribution of plaice has indeed changed in time.