Members of the European parliament and green campaigners are to stage a demonstration outside the European commission in Brussels calling for an end to overfishing and sustainable limits on catches.

The demonstration on Wednesday morning is timed to take place before Maria Damanaki, the EU fisheries chief, is expected to unveil the most radical proposals on fisheries reform in four decades.

Chris Davies, the UK Liberal Democrat MEP who is leading the demonstration, said he supported Damanaki's efforts to end overfishing. "Out of sight, beneath the surface of our seas, we have done huge damage to a natural resource that was once abundant and left Europe dependent upon imports for nearly 70% of the fish we eat," said Davies.

He pointed to recent academic studies suggesting Europe's fish stocks had been reduced to less than 10% of their post-war levels.

Damanaki has made clear her intention to phase out the wasteful practice of discarding healthy fish, which fishermen are forced to do under the current rules, for instance if they exceed their quota or because they catch fish for which they do not hold a quota.

But she has come under pressure from fishing groups and some member states who are concerned that ending discards and forcing fishermen to land all they catch could result in lower profits for fishing crews. They could end up having to sell lower value fish or species for which there is less demand, meaning their catches may be worth less than if they could discard at will.

Damanaki has acknowledged the problem, telling a meeting of the European parliament's cross-party Fish for the Future group that some reduction in employment in fisheries was inevitable, but that without change to protect fish stocks the loss of jobs would be even greater, because Europe's seas are so depleted.

She is expected to call on member states for help to compensate fishermen for some of their lost income, and has supported pilot schemes in which fishermen would turn their boats to other uses, such as tourism or collecting plastic litter for recycling.

Her proposals will also replace the current annual shouting match among countries over the size of the quota they should get. At present, ministers vie for the biggest quota with a decision taken each December. But under the new plans, these annual contests would be replaced with long-term management plans, giving greater certainty for the future and less of the wrangling that can result in fisheries losing out. Day-to-day decision making would also be devolved from Brussels to the regions.

Member states would also be encouraged to let the owners of large vessels exchange fishing rights, because there are too many boats hunting too few fish.

Damanaki also wants to reform the fishing agreements that some member states have with developing countries, allowing EU vessels to fish there. These agreements have attracted controversy because, in extreme cases, they can stifle the growth of indigenous fisheries in poorer countries.

Davies said: "Commissioner Damanaki might have been expected to back down in the face of opposition from those who resist change, but she seems fearless and determined to push ahead with reforms that may be the saving of our seas, of the fishing industry, and of coastal communities. Our waters are capable of supporting many times more fish than now exist. It is not too late for the situation to be reversed, but we have now reached a crisis point. Overfishing must cease or there will be no more fish on the plate."