From staple to delicacy, the fading fortune of the flat oyster

The oysters found in Loch Sween in the Scottish Highlands were once part of the staple diet of the ordinary people and renowned for their taste and texture.

Now, a century after they were commonly served up across the country, they have become a rich man's delicacy under threat from pollution and poaching.

Beneath the cold wind-swept waters of Loch Sween lies one of the last refuges of Ostrea edulis, the native or flat oyster, which once thrived throughout Britain, from the sheltered bays of Cornwall to the salty sea lochs of the Highlands.

"We have become very concerned over the illegal poaching of oysters from nearby West Loch Tarbert and Loch Sween," said David MacArthur, the Scottish Natural Heritage officer responsible for monitoring parts of Argyll where the oysters still survive.

Nestled beneath the green hills of the Taynish Wood National Nature Reserve, where only the lapping waters of the loch disturb the isolated tranquillity, organised criminals are making a fortune out of oysters, away from the public gaze.

Over-fishing, pollution and bad stock management have also taken their toll on oyster populations but the activities of poachers are the biggest cause for concern for the future of a species that has been supplanted in its environment by the Pacific oyster (Crassostrea gigas). Native oysters used to be considered so cheap and plentiful that recipes for soups and stews often demanded as many as 60 oysters, while 18th-century accounts of life in the Western Isles recorded them growing on rocks to such a size that they had to be cut in four pieces before being eaten.

However, the species was rapidly fished out; the relatively long-lived shellfish reproduces so sporadically that recovery can take a long time.

When hundreds of native oyster beds fell victim to pollution and over-fishing, oysters were almost wiped out. Supplies were kept up only by the introduction in recent decades of commercially cultivated gigas oysters.

While the fan-shaped native oyster might be considered more of a delicacy, it is also harder to cultivate because it reacts to even the slightest environmental change. More than 1,100 tonnes of Pacific oysters are farmed in British waters every year, leaving the native species in fewer than 30 isolated pockets, hidden along the shores of lochs and estuaries.

But what should have proved a reprieve for the native oyster is in danger of becoming its death sentence. Demand for them has never been greater with culinary connoisseurs in Japan, Spain, France and Germany willing to pay top prices for their rarity. The trade is lucrative because illegal fishermen can make thousands of pounds in a few hours harvesting a crop that has cost them nothing to produce.

"This is a very big problem for us," said Neil Duncan, a Pacific oyster farmer on West Loch Tarbert and a member of the Scottish Shellfish Marketing Group. "We have spent more than £100,000 making sure our products comply with all the necessary health regulations, which make them fit to be sold to the public.

"These poachers just lift anything from the loch whether it's healthy or not and sell it on to top restaurants, but if people end up getting ill and they trace the source back to West Loch Tarbert, then it is we who will suffer.

"It is outright theft. Oysters traditionally belong to the Crown and a licence is needed to fish them so we need to see tougher penalties introduced."

In an attempt to gauge the level of danger to the native oyster, Scottish National Heritage launched a survey of coastal areas around Scotland this week to measure the population of native oysters.

David Donnan, the organisation's maritime advisory officer, said: "The native oyster once supported a significant fishery in the Firth of Forth, but now nothing but dead shells can be found. We need to find out exactly what is happening to the oyster population in Scotland and what we can do to help it recover. If oysters are sustainably managed, they can be an important economic resource for Scotland as well as a flourishing part of the ecosystem."

One of the greatest battles to be fought if the oyster is to survive will be the fight against poachers. "These people can literally pick up thousands of pounds from the shore of the lochs as they wade about with litter-pickers, harvesting the oysters without any thought of conservation," said Mr MacArthur, as he stood in the shallows of Loch Sween. "We had one case last year where we managed to catch one of these gangs and they had 15 bags filled with 20 kilos of oysters. Unfortunately. they only received a £50 fine.

"Catching these people is the problem. Areas such as Loch Sween are very secluded. It is not difficult for anybody to park up and just help themselves."

The main British stocks are now in rivers and flats bordering the Thames estuary, the Solent, the Fal river, the west coast of Scotland and Lough Foyle. Scottish National Heritage is keen to identify any other isolated populations.