Annual catches grew each year until the 1980s, when a high point of more than 3 million metric tons (3.3 million S/T) was reached. Since then, the numbers have fallen back to around 2.3 million tons (2.5 million S/T) annually with considerable differences between years. Besides the fish caught, it is estimated that 150,000 metric tons (165,000 S/T) of unmarketable by-catch are caught and around 85,000 metric tons (94,000 S/T) of dead and injured invertebrates.
Other factors like the introduction of non-indigenous species, industrial and agricultural pollution, trawling and dredging, human-induced eutrophication, construction on coastal breeding and feeding grounds, sand and gravel extraction, offshore construction, and heavy shipping traffic have also contributed to the decline.
The OSPAR commission manages the OSPAR convention to counteract the harmful effects of human activity on wildlife in the North Sea, preserve endangered species, and provide environmental protection.  All North Sea border states are signatories of the MARPOL 73/78 Accords which preserves the marine environment by preventing pollution from ships. Germany, Denmark, and the Netherlands also have a trilateral agreement for the protection of the Wadden Sea, or mudflats, which run along the coasts of the three countries on the southern edge of the North Sea.
At the end of the 19th century large quantities of herring were produced in Scotland. Today mainly mackerel, Atlantic cod, whiting, coalfish, European plaice, and sole are caught. In addition, common shrimp, lobster, and crab, along with a variety of shellfish are harvested.
In recent decades, overfishing has left many fisheries unproductive, disturbing the marine food chain dynamics and costing jobs in the fishing industry. Herring, cod and plaice fisheries may soon face the same plight as mackerel fishing which ceased in the 1970s due to overfishing. Since the 1960s, various regulations have attempted to protect the stocks of fish such as limited fishing times and limited numbers of fishing boats, among other regulations. However, these rules were never systematically enforced and did not bring much relief. Since then, the United Kingdom and Denmark, two important fishing nations, became members of the EU, and have attempted, with the help of the Common Fisheries Policy, to bring the problem under control.
In addition to threats due to food-chain disturbances, non-target species often wind up as victims of intense fishing. Sea turtles, dolphins, harbour porpoises, rays, and dozens of fish species are killed or injured by trawlers nets and beams. Denmark's trawler fishing alone accounts for the deaths of 5,000 porpoises a year. Trawling can also have a destructive effect on seabed habitats as the trawler beams drag along the floor can uproot plants and destroy reefs.
|Fish caught in the North Sea in metric tons|
|Soviet Union / Russia||89,269||352,857||429,182||7,181||1||0||0|
- Ilyina, P Ilyina (2007) The fate of persistent organic pollutants in the North Sea. Springer. ISBN 9783540681625)
- Karlsdóttir, Hrefna M (2005) Fishing on common grounds : the consequences of unregulated fisheries of North Sea herring in the postwar period. ISBN 9185196622)
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