Rare North Sea fish

There are more rare fish off the Dutch coast than in the open North Sea.

Current situation

There are more rare fish off the Dutch coast (to a depth of 20 m) than in the open North Sea (in Dutch: Noordzee). This is shown in the figure by means of a rarity index per 10 x 10 mile quadrant. The index is the sum of the rarity values of all the fish species occurring in that quadrant. The higher the value, the more numerous are the rare species in that quadrant.

The relatively warm and nutrient-rich inshore waters have an important function as a nursery for various species.

Technical note

The map shows the entire North Sea, not just the Dutch Continental Shelf. It is based on an analysis of the 124 fish species that together form the North Sea fish community. Species that are incidental visitors have been excluded.

The map shows what each 10 mile x 10 mile quadrant contributes to the "total rarity" for the North Sea. The calculation method entailed first calculating the rarity. The fewer quadrants in which a species occurs and the fewer the number of individuals caught, the higher the rarity. The value per quadrant per species is the product of the rarity and the number of individuals in that quadrant, divided by the total number of individuals of this species caught in all quadrants. The values for all species in a given quadrant are then totalled. It is this figure that is given in the figure. The map covers the period 1969-1999. The data are from the catches made by research vessels.

References

Daan, N. (2000). De Noordzee-visfauna en criteria voor het vaststellen van doelsoorten voor het natuurbeleid. Nederlands Instituut voor Visserijonderzoek. Rapport C031/00. IJmuiden.

Heessen, H.J.L., H.C. Welleman, N. Daan, A.C. Smaal en G.J. Piet (2001). Bijdrage RIVO aan Natuurcompendium 2001. Nederlands Instituut voor Visserijonderzoek RIVO. Intern rapport C058/01. IJmuiden.