The fish stock in the North Sea

Averaged over the year, an estimated 11 to 15 million tons of fish swim in the whole North Sea. More than 220 different species of fish can be found here. These species, and the amounts in which they are found, are not evenly spread throughout the North Sea. In the Dutch section of the North Sea, one can recognize around 145 different species of fish, including sharks and rays.

The fisheries in the North Sea concentrate on approximately 25 species, of which the cod species (cod, coal fish, haddock, whiting), flatfish (plaice, sole, dab, turbot and brill), herring, sprat, Norway pout, lesser sandeel and mackerel are the principle sorts.

Compared to other seas, the North Sea is very productive and heavily fished. Around 3 to 3.5 million tons of fish are caught yearly. When converted to the total surface of the North Sea, one comes up with a figure of 50 to 60 kilograms fish per hectare.

In comparison: in all of the world seas together, 90 to 100 million tons of fish (including shellfish) are caught. These fisheries concentrate on the continental plates (roughly the coastal seas) and in areas where nutrient-rich water wells up near the ocean surface (upwelling areas). All together, these fish-rich areas make up around 8 % of the whole sea surface. The rest consists of the large, relatively nutrient-poor, 'blue deserts' in the sea. The North Sea only makes up a small part of the total surface of the seas and oceans on the planet Earth.

Fish communities

The same species of fish are not found in the same amounts throughout the North Sea. Three different characteristic fish communities can be distinguished: a continental edge community, a Central North Sea community and a Southern North Sea community. The water depth, water temperature, properties of the sea bottom and the food supply determine where which community is found. In the Southern North Sea, the fish community consists mainly of fish that look for their food on the sea floor. When looking at the amount as weight, then dab, whiting and grey gurnard make up half of the total weight in fish in the Southern North Sea. The small gobies, solenette and dragonet are also very numerous, but because they do not weigh much, they do not account for much. In addition, their presence is more difficult to estimate because they easily escape through the meshes of the net.

In the Central North Sea, haddock, whiting, cod, coal fish and Norway pout are found in the greatest amounts. In addition, flatfish such as dab are also found.

In the Northern North Sea, coal fish, haddock, Norway pout, whiting, scad, blue whiting, mackerel, cod, hake and ling account for the largest amount weight-wise.

Overfishing

The amount of fish in the past century has declined drastically due to overfishing. The Atlantic coastal seas contained around ten tons of larger fish per square kilometer around 1900, five times more than in 2007. Larger species have practically disappeared while smaller pelagic species and flatfish are very common.

Source: de Vleet, Ecomare