Airlines have received police warnings that they are unwittingly aiding gangsters by carrying illegal shellfish out of Scotland.

At least one major international carrier has been asked by detectives to stop shipping razor clams to China, The Herald can reveal.

Officers are convinced that the shellfish - better known as "spoots" in Scots - are being caught using banned electro-fishing.

Industry insiders confirm that the sheer volume of clams leaving Scotland could only have been harvested by organised crime groups flouting the ban.

The Herald: Two large freshly dug razor clams in the wrinkled hands of the clam digger

Detective Chief Inspector Garry Mitchell said: "Illegal razor clam fishing is an emerging and developing crime type.

"It affects multinational companies who are unwittingly facilitating organised crime.

"There is no market for razor clams in Scotland. The market is in the far east and they have to get there quickly so they don't spoil."

Police insiders believe there would be no illegal clam-fishing if there was no airline willing to carry the product to markets in China, especially through Hong Kong.

Read More: Rob Edwards in The Sunday Herald on Scotland's Razor Clam Wars.

The Herald understands scores of crates of the clams - still alive in their shells - are every day being flown to China where they sell for £10 a kilo.

The clams are carried in the holds of commercial passenger airliners along with other lucrative Scottish seafood, such as crabs, being rushed to Far East markets.

However, industry insiders do not believe that traditional and legal methods of harvesting clams would generate such volumes of product.

The Herald: Electro-fishingElectro-fishing

Electro-fishing, which sees electrodes trailing from boats shock razor clams in the seabed causing them to rise up where they are easily collected by divers, has been banned across Europe since 1998.

Environmentalists argue the method causes long-standing environmental damage.

Two divers have died while electro-fishing - and there are particular concerns that criminal fishing gangs may take safety shortcuts.

Legitimate seafood firms have stopped using the technique, although some are lobbying for the ban to be lifted.

Police sources suggest criminals have moved in to the gap in the market to shock clams on an industrial scale.

Electro-fishing is not the only way to collect spoots. Some commercial companies have dried dredging for them, but this technique is messy and produces an inferior clam. Salting the clams will cause them to go to the surface but this too won't generate the volumes needed to supply Far Eastern markets.

Mr Mitchell urged fish merchants and other firms to be cautious when buying razor clams. He said: "This is an unusual commodity for criminality, even if you're taking it from a business point of view in Scotland.

"If you are procuring razor clams, please understand who you are buying them from."

Police Scotland in 2014 warned that crime gangs, some described as Eastern European, were earning £65,000 a day selling electro-fished spoots on the black market.

At that time the police said the believed a single electro-fishing boat could harvest 500-600 kilos a day. A boat using legal methods might take 1 kilo. Some officers have claimed the crime is more lucrative than drug dealing.