Barriers go up in bid to keep salmon river free of killer crayfish

BRITAIN'S first barriers specifically aimed at blocking the relentless spread of an alien crayfish have been installed between two Scottish river systems to prevent the threat the deadly invader poses to one of the country's premier salmon rivers.

The voracious North American signal crayfish, which feasts on salmon eggs and freshly hatched salmon, has already been found in the catchment of the River Clyde, where they are threatening to devastate stocks of the King of Fish.

In a landmark attempt to prevent the invaders' spread in the south of Scotland, dams have been erected to control the movement of the crayfish from the Clyde catchment into the head waters of the River Annan, only 200 metres away.

The invasive crustaceans were first seen in Scotland in 1995, in the catchment of the River Dee in Kirkcudbrightshire, and in the Clyde a year later.

Although the crayfish can move up river systems on their own, criminal gangs are stocking rivers with them before harvesting them for clandestine sales to restaurants. Once established in rivers, they are virtually impossible to eradicate.

In a pioneering bid to prevent their spread in the south of Scotland, Scottish Natural Heritage has joined forces with Annan District Salmon Fisheries Board, the Clyde River Foundation and South Lanarkshire Council to install two dams 20 metres apart at a site close to where the headwaters of the rivers Clyde and Annan meet.

Dr Colin Bean, an adviser at SNH, explained that survey work on the Clyde has shown that signal crayfish had spread into many of its head-waters and there were fears that they might move into the Annan, one of the best salmon and sea trout rivers in the south of Scotland.

He said: "There are no techniques that will allow us to get rid of signal crayfish from rivers and streams, so taking the radical step of developing and installing a physical barrier may offer us the best hope of stopping the species from moving into new catchments."

"The headwaters of the Clyde and Annan rivers are separated by a small field that occasionally floods. As signal crayfish are able to travel short distances across land, the partnership decided to put two barriers into the burn to stop them crossing from one catchment to the other. It is the first time this approach has been tried anywhere in the UK or beyond."

Dr Bean added: "If the barrier proves to be successful, then we may use it in other parts of the country to help prevent crayfish moving into new areas. We can't prevent them from becoming a problem in rivers where they currently exist, but at least this would give us some hope that we can control their spread."

Nick Chisholm, the director of the River Annan Trust and Fisheries Board, said the presence of crayfish on the Clyde was a major concern.

He warned: "The head waters of the Annan are very important for salmon and trout spawning and also important for the rural economy.

"At the moment we are confident there are no crayfish in the Annan. If they get in there would be quite dramatic consequences."