* Fishing ban unilaterally imposed as eel population slumps
* Eels in sharp decline also in Asia, cause unknown
* Lifecycle still a mystery, captive breeding impossible
By Reed Stevenson and Catherine Hornby
NUMANSDORP, Netherlands, Oct 12 When Aart van der Waal chose 20 years ago to fish for eel rather than join the legal profession, he didn't expect to be told someday to make a choice between making a living and breaking the law.
The burly 40 year-old, a tattoo-bearing Rolling Stones fan, says he has made a comfortable enough living so far. Now he would have extra benefit of the dark moon in October.
Not only is it the time to catch most eels, but also the cover may help as he breaks a Dutch government ban on commercial eel fishing, risking a fine of 3,000 euros ($4,400).
Fishing the muddy, shallow canals near his home for plump, fattened eels that the Dutch consider a delicacy smoked on toast or in bread -- and which are eaten in stews across Europe -- is no longer allowed during October and November.
"I'm just going to keep fishing," he said, hauling up dozens of writhing eels from a 4 metre-long trap net.
"That's what I do."
Bringing his catch back to a wooden shed reeking of dried slime and muddy fish, he will be defying a government ban aimed at stemming a 95 percent slide in the European eel population in the past four decades.
It has prompted the International Union for Conservation of Nature and Natural Resources to classify Anguilla anguilla, or the European eel, as "critically endangered".
Eel catches in Asia have also fallen 82 percent since 1969, researchers say.
The Dutch ban will increase to three months in coming years, and despite planned compensation has aroused anger in the vastly depleted community of fishermen in a country where in the 19th century people rioted for days about eels.
Just over 900 tonnes of eel are caught in Dutch canals, lakes and rivers every year. Europe's total annual eel catch is estimated by the European Union at 18,000 tonnes.
The government will pay a total of 700,000 euros, which fishermen say amounts to about 1,000 euros each per month. Van der Waal says he sells 9,000 euros worth of eels monthly.
The ban, a unilateral step, has been complicated by the fact no one knows what is behind the decline.
"Nobody knows why, that's the bottom line," said Willem Dekker, senior scientist and eel researcher at Dutch marine ecology institute IMARES.
Several theories exist, ranging from the presence of pollutants in ocean waters through over-fishing to a viral infection.
The Dutch arm of environmental group WWF, supporting the ban, blames fishing for 70 percent of eel deaths in the Netherlands, and says eating an eel roll is like consuming a panda sandwich.
"There is a high chance European eel becomes extinct if we don't do anything," said Clarisse Buma, a WWF spokeswoman. "We know it's a problem for fishermen but if we don't do anything, we will never be able to eat eel in the future."
The European Commission has been telling member states for the past five years to restrict eel fishing. Non-member Norway has adopted restrictions this year, but the Dutch are the first EU member state to adopt a ban.
The Dutch are often the first to adopt such measures, tending to be activist on environmental issues, said Koen Van den Bossche of the Institute for European Environmental Policy.
"The Dutch want to tackle this issue," Van den Bossche said.
A long dark-grey snake-like fish with a silver belly, the eel's decline acquires significance in the light of the fact that restoring their numbers through breeding isn't an option, because the eel's life cycle remains a mystery to science.
European eels spend most of their lives in freshwater tributaries and canals along the coast of Europe and the Mediterranean, but return 5,000 km (3,100 miles) to the Sargasso Sea in the North Atlantic to reproduce.
They have never been observed mating or spawning in the wild, captive breeding has been unsuccessful and the only way to farm them has been by capturing and raising wild baby eels.
Many blame the harvesting of these young fish, known as "glass eels" because they are transparent, for the decline. Apart from being caught on the coast of Spain and France, glass eels are also bought by fishermen in Europe and Asia to stock aquaculture farms, where they are raised for consumption.
Van der Waal drives to France every year to buy glass eel from coastal fishermen, and releases them in the canals where he fishes. It's a significant investment: restocking costs him up to 12,000 euros yearly and eels take 15 years to reach maturity.
A cheap fish decades ago, eels now cost upwards of 10 euros per kg. In Europe, grown eels are mostly caught in the Nordics, Netherlands and Italy.
Eels hold a special place in Dutch history: in the 19th century, people died in the "eel uprising" that followed a ban on the sport of "eel pulling", which involved stringing a rope across a canal and hanging an eel for people on boats to try to grab. Many ended up in the water.
But Dutch livelihoods threatened by the ban already represent a shrinking tradition.
Only about 240 eel fisheries remain in the Netherlands, employing 715 people. That is about a tenth of what it used to be, nearly mirroring the decline in the eel population.
Even farmed eel is bad news for 69-year old eel smoker Joost Kant as he gutted fresh fish and strung them for smoking.
"It's a disaster," he said, pungent fumes rising in the room. "Smoking's not the same without wild eel."
Another factor that may be aggravating the decline is the way eels are caught in the Netherlands. Usually fished in coastal freshwaters, the Dutch also catch them when their route to sea is blocked by the pumps and dikes used to manage water.
Fishermen like Van der Waal set traps near the pumps, which eventually lead out to bigger rivers and canals and out to sea.
"I'm trying to turn the polders and dikes into aquaculture areas," he said.
The Dutch Commercial Fishers Association, opposing the fishing ban, argues these obstacles are more to blame. The association has proposed transporting 157 tonnes of the catch to the sea so mature eels can return to their spawning waters.
But Europe's regulators say not enough eels are returning to spawn: the fishing bans aim to allow 4 out of every 10 eels to return to the seas. (Editing by Sara Ledwith)