CONSERVATIONISTS suspect humans have illegally introduced a species of crayfish, which has devastated fish stocks in lochs and rivers, to a quarry pond in the Highlands.

The North American signal crayfish has been discovered at the once world famous Ballachulish slate quarry near Glencoe.

The site is 60 miles, as the crow flies, from the species’ next nearest habitat – the River Kelvin, near Glasgow – and scientists believe specimens may have been taken there by someone hoping to provide a food source for fish or to harvest them for human consumption.

It is not only illegal to transport the species, but the crayfish is a voracious predator that feeds on insects, frogs and young fish and their eggs.

It has wiped out stocks of fish in Loch Ken, near Castle Douglas in Dumfries and Galloway, despite a Scottish Government scheme to trap and kill more than a million crayfish there.

The discovery in Lochaber is the first time a North American signal crayfish has been found as far north on the west coast.

Dr Colin Bean, Freshwater Adviser at Scottish Natural Heritage, said: “These animals can grow to the size of a small lobster and we are very concerned about its spread as it presents a significant threat to native wildlife.

“It is disappointing to now find signal crayfish in relatively remote areas of the west of Scotland. The nearest population to this one is more than 60 miles away at the River Kelvin, so it is clear the Ballachulish population was established by humans.

“As it is against the law to capture, keep, transport or release live signal crayfish into the wild without a licence, the establishment of this population is the result of an illegal act.”

Signal crayfish were introduced to waters in England and Wales from fish farms in the 1980s. In Scotland, they were first recorded in the catchment of the Kirkcudbrightshire Dee in 1995. Since then, specimens have been found in ponds, rivers and lochs. The River Nairn is their most northerly location in Scotland and there are populations in Dee, the South Esk and the Ardle.

As well as wiping out stocks of fish, signal crayfish burrow into the banks of rivers and lochs. This can lead to increased erosion and damage to the spawning grounds of a variety of fish. In some situations it may cause some banks to become unstable. Their presence is a threat to both conservation and angling interests.

Dr Bean said that one “berried” female carries eggs beneath its tail and warned: “By introducing one berried female you could be potentially introducing 300 animals. The upside in Ballachulish is that, because it is a small pond, we may be able to eradicate them.”

But he added it would first have to be established whether there were fish or other aquatic life in the pond.

The site is owned by Highland Council, which is now discussing the appropriate course of action with Scottish Natural Heritage and the Lochaber Fisheries Trust.

Eilidh-Ann Madden, Highland Council’s Senior Countryside Ranger for Lochaber, said: “The crayfish were discovered in the Ballachulish Quarry pond by one of our own rangers earlier this month and we are extremely concerned by this.

“While there is no need to restrict access to Ballachulish Quarry pond for recreational purposes, we will be erecting signs to make the public aware of some sensible precautions in order to minimise the risk of inadvertently spreading the crayfish.

“Members of the public who think they have seen signal crayfish anywhere else in the area should report this to the Lochaber Fisheries Trust.”

Last year the Galloway Fisheries Trust and ScottishPower, which runs a huge hydro-electric scheme with six dams in the area, drew up plans to introduce the European eel into Loch Ken, as eels prey on young crayfish.