On a moonless night as black as bog oak, their journey begins. They say more lies are told about the pike than any other fish, but the eel's incredible migration almost beggars belief.

After decades of decline so steep it was feared it was facing extinction, the mysterious species appears to have undergone a dramatic recovery.

Bumper numbers of elvers have returned to the Fens, sparking hopes that the snake-like fish might not have had its chips after all.

More than 50,000 used a new fish pass at St Germans in just three weeks in April.

'It's brilliant news, it's a really good sign,' said Peter Carter from Outwell, near Wisbech - one of Britain's last eel fishermen, whose family have been trapping them for centuries.

'Now the old Fen people always reckoned the elvers came every 20 - 25 years. In the 1970s we had millions. Now we've got these eel passes, so it's got to be a good sign.'

Passes, like the structure which now stands alongside St Germans Pumping Station, help eels bypass man-made barriers such as sluices, weirs and locks. Our rivers are now an obstacle course for any species which needs to move up and down them to breed.

A pass joining the Cut-Off Channel to the River Wissey at Stoke Ferry, near Downham Market, is used both by eels and the enigmatic sea trout, which is also clinging on amid the sugar beet and the potato fields.

'Hopefully I'll be a rich man in 10 or 15 years' time,' said Mr Carter, who places hand-woven willow traps baited with road kill in spots passed down through the generations where the eels run.

'But the biggest problem is the silver eels going back to sea. I worry whether we're doing enough to help them.

'There's no point helping them get up the river if we don't help them get back down again. They need to put more weed cover along the river edges, to give them somewhere to hide away again.'

When the eels turn silver and set off for the sea, they face yet more obstacles and barriers in their path. Some blame a parasite which attacks their swim bladders for the species' decline, killing many on their way to their spawnging grounds.

But growing numbers of conservationists and fisheries experts say there is much more which could be done to set our house in order closer to home, by making our river systems easier for migratory fish to negotiate.

All this might cost money. But it's hard to think of a species which adds as much value in terms of providing a high protein food source.

Otters - the apex predator of our waterways - have come back with a bang in recent years, with animals regularly seen in the Fens. The wriggly eel is one of its favourite snacks.

Birds including herons and the mega-rare bittern eat them, while beneath the surface the highly-prized pike also snaps up its fill.

Centuries ago, they were a currency as well as a human staple. In the 12th Century, the stone to build Ely Cathedral was bought from Peterborough Abbey, for 8,000 eels a year. In recent years, as eels have become scarcer, their value has rocketed with dealers in Japan and Asia, where the fish is a delicacy, offering thousands of pounds for a kilo of elvers.

While moves are afoot elsewhere to farm the fish, a recovery in wild stocks offers the best hope for a sustainable future for anguilla anguilla.

While Peter Carter looks forward a decade or so, to when the new generation of elvers matures, scientists will be watching the sluices next spring, to see whether thousands again return to the Fens.