Developing tools for the management of freshwater crayfish

The introduction of non-indigenous crayfish into Europe is causing the loss of indigenous crayfish, due to transmission of crayfish plague and competition. Other factors are reductions of habitat quality and in some areas harvesting. This study deals with issues facing environmental agencies and other resource managers about how manage crayfish; from prevention of further introductions, to eradication where feasible, or control if it is cost-effective, or where it is not, then applying measures to mitigate the effects of invasion by finding or establishing isolated areas for indigenous crayfish, i.e. ark sites. It provides a range of decision-making tools for management. The study includes a literature-based risk assessment for non-indigenous crayfish in Great Britain. It presents the first evidence of the negative impact of signal crayfish Pacifastacus leniusculus on salmonid fish in a headwater stream. The study shows how the technique of biocide treatment against signal crayfish has developed, the outcomes and the lessons learned from the projects and factors that will contribute to other successful eradication treatments in future. Another new potential method for eradication or control is electric shock treatment, which was field-tested in this study. As an aid to assessing the feasibility of eradication or control, a simple cost-model was developed using the potential impact on salmonid fish and a re-stocking cost as a surrogate for environmental impact of crayfish invading a catchment. This was used to compare the costs of eradication or control and showed the benefit of early eradication and the unsustainably high cost of control by trapping. As signal crayfish are already widespread in England and Wales, risk-based selection criteria were developed to help identify potential ark sites for white-clawed crayfish. In addition, a decision-making tool has been prepared to help conservation managers understand the issue and develop conservation action plans at catchment scale.