European ministers are meeting for the annual process of setting fisheries quotas for the year ahead.
The European Commission is proposing cuts in quotas for cod, a small increase for herring and major curbs on deep-sea fishing.
Scientific advice issued in October recommended the suspension of all cod fishing in some areas.
But lobbying by the industry means it is likely to continue, despite the parlous state of some populations.
Under Britain's EU presidency, the discussions in Brussels will be chaired by UK Environment Secretary Margaret Beckett and Marine Affairs Minister Ben Bradshaw.
Ministers will debate recommendations made by the European Commission on the basis of scientific advice from the International Council for the Exploration of the Sea (Ices).
Down to zero
The latest Ices advice, released in October, was that "cod stocks in the North Sea, Irish Sea and west of Scotland remain well below minimum recommended levels and the advice for these stocks... is zero catch".
Ices made a similar recommendation for hake fleets off the coast of Spain and Portugal.
However, the commission has chosen to depart from the scientific advice, and recommend a 15% reduction in cod catch and in the number of days which boats can spend at sea.
Accidental and unregistered catches are major issues
More than half of the cod killed are caught accidentally in nets designed for other fish, so the commission is also recommending a 15% reduction in trawling for whiting and flatfish, and in gillnet fishing.
This has not been received well by fisheries leaders and politicians with fleets to protect, with Scottish Fisheries Minister Ross Finnie saying he is "resolutely opposed" to any reduction in days at sea.
However, there have been some constructive proposals from the industry, including a two-month closure of the Celtic Sea fishery to allow cod a reasonable period in which to reproduce.
Of even greater concern to Ices scientists is the condition of deep-sea species, including some sharks.
Many deep-sea fish grow very slowly and take years, even decades, to reach reproductive age.
The commission is asking for a 20% reduction in take from these deep ecosystems, though many conservation bodies believe nothing less than a global moratorium is needed.
There will also be stringent curbs on fishing for sand eel, anchovy and pout.
Better short-term news for fishermen is that numbers of herring and northern hake are recovering, and an increase in quotas is likely.
A separate ambition of the negotiations is to develop longer-term agreements in order to diminish the role of the annual ructions between conservation and industry.
There will also be discussion of monitoring and enforcement, given extra urgency by recent indications that regulations are routinely flouted.
In July, the European Court of Justice fined France 20m euros (£14m) for failing to enforce EU rules on mesh sizes and catching undersized fish.
Earlier this month, almost the entire fleet in the Yorkshire port of Whitby was fined for failing to declare all of its catch, while Ices said that a quarter of Irish Sea catches went unrecorded.