River Earn Flood Alleviation

Practecology was commissioned to undertake American signal crayfish surveys to determine whether this species was present along parts of the water courses that may be subject to engineering works.

The American signal crayfish

The American signal crayfish is a non-native invasive species previously introduced into the UK 1970’s as a food export commodity. However, it has had a significant detrimental impact on native white clawed crayfish, through competition for food and resources and the transmission of the crayfish plague. Other freshwater species are also out-competed for food and susceptible to predation such that fresh water biodiversity is diminished where American crayfish persist. This species also takes shelter in burrows which it excavates in river banks causing erosion and ultimately bank collapse. 

The American signal crayfish is listed on Schedule 9 of the Wildlife and Countryside Act 1981 (as amended) making it an offence to cause it to spread in the wild. If its presence is suspected then it is prudent to undertake surveys so that appropriate biosecurity controls can be put in place during works. 

  • Searching suitable habitat

    Searching suitable habitat

  • Marginal areas of the River Earn

    Marginal areas of the River Earn

Surveys

Practecology carried out American crayfish surveys of the River Earn close to the confluence with the Water of Ruchill, as well as the River Lednock. All surveys were carried out by qualified ecologists undertaking visual surveys of the river bed and banks in suitable crayfish habitat. Where possible and in agreeable currents kick sampling was also undertaken. 

  • A suitable refuge for crayfish

    A suitable refuge for crayfish

  • Large rocks possibly providing shelter

    Large rocks possibly providing shelter