Since then, EU governments have struggled to agree with the bloc's executive Commission as to how this should be done.

The solution is for countries that fish transparent juveniles called glass eels -- France, Spain, Britain and Portugal -- to reserve a percentage to restock Europe's rivers.

"It's a matter of achieving a balance between what is desirable from a scientific standpoint and what is achievable politically," one EU diplomat said.

"If eel were to be further endangered in the short term, then it would become extinct. But that's if we do nothing."

The restocking percentage was the main obstacle to a deal, since it prevents those countries from exporting much of their juvenile eel catch to Asian markets where prices reach 1,000 euros (US$1,300) per kg.

"We get to 60 percent by end of July 2013, starting from 35 percent in the first year of the plan, which will be in 2009," one EU diplomat said.

"The restocking percentages only apply to proper glass eels that measure 12 centimetres or less. But national funding can be provided for restocking of eels that go up to 20 centimetres."

Another part of the compromise deal was for the Commission to able to intervene if prices for eels used for restocking were to fall sharply compared with eels used for other purposes.

Diplomats said a 20 percent price fall would be enough for the Commission to propose a temporary reduction in restocking percentages, satisfying countries like France and Spain.

Eels are found in virtually every coastal and inland water around Europe and along the Mediterranean coasts, providing income for more than 25,000 fishermen.

No one knows exactly where eels spawn, but the smallest larvae are found in the Sargasso Sea, south of Bermuda. They then drift towards Europe.

When they arrive, the leaf-like larvae transform into glass eels, which wait for river estuaries to warm before swimming into inland waters. It is while they are waiting that they become a target for fishermen.