The European Union, the world's third fishing power, came under sharp pressure from green groups and the EU executive to save the oceans from overfishing at key talks Tuesday to overhaul the sector.

Angry Greenpeace activists waving giant fish bones and banners reading "Stop Overfishing" delayed the start of a much-awaited ministerial meeting originally intended to reform fisheries policy but which may instead net a watered-down compromise.

As fish stocks decline, EU boats are sailing further and further afield to cast nets. "Europe needs clear goals to reduce its fishing fleet," said Maurice Losch of Greenpeace. "It fishes two to three times over sustainable levels."

Though scientists say 80 percent of Mediterranean stocks are overfished -- meaning fish cannot reproduce quickly enough -- fisheries ministers were mulling a so-called "general approach" deal scaling down ambitious reforms previously lobbied by the EU's executive in Brussels.

Among Brussels proposals was a ban on throwing fish caught by accident back into the sea -- a practice known as discards -- that environmentalists say wastes 1.3 million tonnes of fish a year.

"For me this is the heart of the problem," Fisheries Commissioner Maria Damanki told the ministers. "There will be no reform without a discard ban."

Britain, Germany, the Netherlands and Scandinavian nations favour forcing fishermen to bring all catches to port and deduct discards from their quotas. The discards can become fish flour, encouraging fishermen to adopt better practices while providing cheap food for the poor.

But one diplomat said Belgium, France, Spain and Portugal were likely to oppose the idea, highly unpopular with boats that go out to sea for days at a time, potentially stock-piling large quantities of unwanted fish.

"Negotiations will be tough, it will be a difficult day," said Spain's Agriculture Minister Miguel Arias Canete on arrival.

Also on the table is a bid to set so-called Maximum Sustainable Yields (MSY) -- the maximum amount of fish that can be caught without compromising its ability to reproduce -- by 2015.

But just days ahead of the Rio+20 environmental summit, some nations want fishing pressure reduced only progressively with the deadline pushed back to 2020 or beyond.

"It is important to set a firm date for introducing catch levels in line with what the fish stocks allow," Swedish minister Eskil Erlandsson said this week.

Damanaki said as ministers began the talks that the draft compromise text on the table "is rather reluctant to take rapid action" on discards.

"You seem to be choosing to go for a slower growth path," she said. "2020 is too far in the future, we have to act more swiftly on this."

According to a European Commission report last week, the situation is improving in Atlantic waters where overfished stocks have dropped from 94 percent in 2005 to 47 percent this year.

Environmentalists say the compromise stitched together by EU nations will be a missed opportunity to save the oceans.

"No fish means no fishing industry," said Xavier Pastor of the Oceana conservation group. "There can be no social and economic benefits if the environment, which provides the resource, is not prioritised."

Should the 27 ministers agree to this, they will "settle for a European fisheries policy of the lowest common denominator, without any ambition to achieve sustainable fisheries or save fishing jobs," said six NGOs -- BirdLife Europe, Greenpeace, Oceana, Ocean2012, Seas At Risk and WWF.

"The proposed deal would not stop the depletion of fish stocks for another decade," they said.