Particularly as signal crayfish are one of the most problematic of all invasive non-native species in the UK, and Dalbeattie reservoir and the surrounding Urr Water catchment are popular with the public, including for angling.
Brought to the UK from North America, the species reproduces and spreads rapidly and out-competes native species for food, with potentially devastating impacts on local biodiversity.
The risk of the crayfish spreading from the reservoir into the surrounding rivers and streams was considered very high. This raised the potential of a catastrophic impact on the aquatic ecology downstream of the reservoir and in particular on an important salmon fishery nearby.
Both UK and European legislation mean that water companies and others have a requirement and responsibility to avoid the spread of invasive non-native species and, where possible, to control existing populations.
Scottish Water therefore wanted to act quickly to address the problem and asked APEM to carry out a feasibility study looking into the potential to eradicate the crayfish from the reservoir.
This was completed in March 2016 and the program was subsequently licensed and consented by Scottish regulators and the HSE for application later that year.
APEM then worked closely with Scottish Water, Scottish Environment Protection Agency, Marine Scotland Science, Scottish Natural Heritage, the Galloway Fisheries Trust and the Dalbeattie Angling Association to determine the best way to carry out the eradication program.
Further advice was sought from a global specialist in the field of crayfish colonisation and invasive species control.
In August 2016 the reservoir was drawn down and isolated and then treated with a natural biocide. Dosing of the reservoir used a range of bankside and floating equipment.
Extensive measures were taken to protect all animals in the surrounding catchment, while public access to the site was also controlled to ensure no hazard to the general public.
Over the following eight weeks the reservoir water was tested using bioassays in order to establish the concentrations of biocide remaining in the reservoir. In addition, crayfish surveys were undertaken in and around the reservoir to ascertain the efficacy of the treatment.
By November 2016 the signal crayfish population had been eradicated and the risk to the Urr Water catchment eliminated.
Steven Greenhill, environment team leader at Scottish Water, said: “This has been a fantastic result on a very unusual and extremely complex project and one which is far from the normal Scottish Water day-to-day business.
“The potential damage to the downstream habitat, salmonid population and other species was severe, as was the risk of damage to the economy of the region.
“We are delighted that the eradication program has been a success at Dalbeattie Reservoir and the team have worked together fantastically. The whole project is testament to the awareness and responsibility of the Scottish Water environment team.”
With the threat from signal crayfish eliminated the aquatic ecology of the site is once again thriving and the public have been allowed to return to Dalbeattie reservoir.
If you have any queries, please contact Peter Dennis, principal freshwater scientist.
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