CHEMICAL warfare will be used to kill off an enemy invader lurking in two ponds at Ballachulish in south Lochaber.
Highland Council has announced proposals to poison North American signal crayfish, an invasive species, to eradicate them from the ponds in Ballachulish Quarry.
The crayfish, a small lobster-like species that can have a devastating effect on native wildlife, were first discovered in the quarry waters by one of the council’s own countryside rangers in August 2011.
It is the first time that signal crayfish have been found in Lochaber and it is the most northerly recorded occurrence of this species on the west coast of Scotland.
Signal crayfish can compete with fish for food and shelter and they can be a significant predator of a range of freshwater animals, meaning their presence is of concern to conservationists and anglers alike.
The local authority has worked with Lochaber Fisheries Trust, Scottish Environmental Protection Agency (SEPA) and Scottish Natural Heritage (SNH) to prepare the £76,000 eradication plan.
It will involve the controlled application of a chemical called pyblast to the two ponds in the quarry and this work is due to start on Monday, June 11, subject to suitable weather conditions, and is expected to be completed within a four week period.
Pyblast is toxic to fish, crustacea and insects but has very low toxicity to mammals and birds, and the council said the risk to humans or any otter, mallard, heron and domestic dogs that use the site will be "low".
A council spokeswoman said: "The crayfish in the ponds will be killed within the first three days after treatment, after which the toxicity of the pond will begin to fall.
"Recovery of the pond will then be enhanced by actively pumping the water within the ponds to accelerate breakdown. Pumps will also be used to disturb and suspend the layer of sediment present on the bed of the ponds as this will also speed up the recovery process.
"The toxicity of the ponds will be monitored throughout and the site is expected to have returned to normal within 21 days."
The spokeswoman said the proposal to use pyblast has been authorised through SEPA and approved through the Health and Safety Executive chemicals regulation directorate.
Access to the ponds will be restricted during treatment and until monitoring indicates the chemical has broken down.
Temporary fences will be erected around the ponds, but access to the wider site for recreational purposes, will not be restricted.
Signal crayfish were first 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 in 13 Scottish river catchments. They are now found as far north as the Inverness area.
This species is a voracious predator which feeds on insects, frogs and young fish and their eggs. Signal crayfish also have an impact on the banks of rivers and lochs by burrowing into them. This can lead to increased erosion and damage to the spawning grounds of a variety of fish and, in some situations, it may cause some river banks to become unstable.
Sightings of the crayfish outwith Ballachulish Quarry should be reported to the Lochaber Fisheries Trust, telephone number 01397 703728 or email Lochaberfisheriestrust@gmail.com