Frosty's Ramblings: The mystery of the disappearing eel

Eel, pie and mash, served with thick green sauce - always known as liquor - was a delicious and sustainable staple cockney food for centuries.

Eel and mash shops were a feature of every working-class area's high street or market. Today those shops are a dying breed.

So too it seems are the eels. Over the last five years, river scientists have recorded a disastrous 98 per cent drop in the number of European eels (Anguilla anguilla) living in the Thames.

It isn't just in London's rivers. There is massive decline right across other British rivers and all across Europe.

Today the eel is classified as critically endangered by the International Union for Conservation of Nature.

No one knows why eels are disappearing. With food tastes changing, eels have become less popular so it's unlikely to be overfishing.

So what do we know about the mystery of the disappearing eel? Actually we don't really know much about the eel at all.

Take their amazing lifestyle. Most fish biologists believe that European eels originate from the seaweed forests of the Sargasso Sea far across the Atlantic Ocean.

After a long life in European waters, the 20-year-old adults swim across the Atlantic to spawn and then to die. The tiny worm-like glass eels hatch and then spend up to three years drifting back across the ocean to arrive back at the very same waters their parents once inhabited.

On that epic journey they turn into small, worm-like elvers. The elvers arrive in the estuaries of our rivers in spring only to be confronted by fishermen tempted by the amazing price paid by eel farms and the exotic seafood market for these tiny fish.

Young eels that avoid the nets make their homes in these rivers and even wriggle across wet grass to find more comfortable ponds, lakes and reservoirs.

For around 20 years they live in these waters, growing longer and fatter and changing colour from gold to silver.

Traditionally during this time they provide sport for the angler and the occasional harvest for stewed eels with mash, the cockney's other delight of jellied eels or the sophisticated delicacy smoked eel.

The Dutch and Germans eat eels in huge quantities. Belgians stew them in green herbs, French chefs cook them with prunes and the Japanese import them for the vast sushi market.

Back in our rivers the adult eels that have avoided the fishermen are ready to set off on their epic 3,000-mile voyage back to the Sargasso Sea to spawn and die.

That's the theory, but amazingly, in this age where wildlife cameras and film teams seem to have captured all the secrets of nature on screen nobody - no, not even David Attenborough - has ever seen, never mind filmed, the mating and spawning of the eel.

Their amazing life cycle might be a mystery but there seems to be no doubt about the rapidity of their disastrous decline.

Conservationists are looking for an explanation. Changes in oceanic currents due to climate change, dams, flood barriers structures and the presence of certain diseases and parasites are all suspects in the search for an answer.

Our eels have been under threat before.

Fifty years ago, when London's proud river was just a sewer, the first signs that the long-awaited clean-up of the 1960s was working was the return of the long-absent eel.

Those of us concerned about all kinds of wildlife and the health of our natural environment need to see the decline of the eel as yet another serious warning on what we are doing to our planet.

Oh yes, and we really miss our eel, pie and mash.