Pirate fishing is the biggest threat to commercial fish stocks in the North Sea, Barents Sea and the north east Atlantic, and is undermining responsible fishing management plans.

Speaking at the Norwegian Embassy's responsible fishing seminar last week, the country's fisheries minister, Helga Pedersen, said up to 20% of cod caught in the Barents Sea was illegal, undermining management plans. Quotas for domestic fishermen have now been cut to preserve stocks, she said.

The problem was confirmed by the latest scientific advice released by the International Council for the Exploration of the Seas, which said that cod stocks in parts of the north east Atlantic were still poor, and recommended an end to fishing there.

Young's Seafood will no longer purchase Atlantic cod sourced from the North Sea, the company has said.

Defra minister Ben Bradshaw admitted the region's cod had not been preserved as well as had been hoped. But he also ruled out radical action at December's annual EU fisheries council, which sets quotas. "The way it has been reported, you'd think it's the first time ICES has recommended a zero catch. It is not realistic to have a dramatic change in quotas "in view of the fact Brussels wants an all-singing all-dancing change to the system next year", he said.

However, new rules are to be adopted next month by the North-East Atlantic Fisheries Commission. These will enable port authorities to check catches against the quota available to the country where the fish is being landed and the country where the fishing vessel is registered, and should make it harder to land illegal catches.

At present, illegal catches are not registered against the TAC for a species, even if detected. But Norwegian officials said the only truly effective way of stamping out illegal fishing would be to set up a global system of port controls and quotas. A port-state control system being discussed at the UN could be set up in five years.