Eradication of introduced signal crayfish Pasifastacus leniusculus using the pharmaceutical BETAMAX VET.®

Signal crayfish Pasifastacus leniusculus were first discovered in Norway in the Dammane area of Telemark County in October 2006. This introduced population was found to be infected with the oomycete Aphanomyces astaci, the causative agent of crayfish plague. The Dammane watershed consists of 5 small ponds, the largest with a surface area of approximately 2000 m(2). The Norwegian National Veterinary Institute conducted a feasibility study for the eradication of the Dammane signal crayfish population at the request of the Norwegian Food Safety Authority and Directorate for Nature Management. This study recommended the use of the pharmaceutical BETAMAX VET.(R), followed by pond drainage as a feasible course of action. BETAMAX VET.(R) is a cypermethrin-based pharmaceutical developed for treatment of salmon louse (Lepeophtherius salmonis) infestations of farmed Atlantic salmon (Salmo salar). Cypermethrin is a synthetic pyrethroid and a common agent in many insecticides licensed throughout Europe. Following a comprehensive mapping of the Dammane watershed, the ponds were treated with BETAMAX VET.(R) on the 14 and 28 May, 2008. Subsequently, the ponds were drained by pumping out the water in two separate stages on 2-4 June, 2008 and 22-24 December 2008. During the first treatment with BETAMAX VET.(R), signal crayfish were captured in the two upper ponds. During and following the second treatment and draining of the ponds, no signal crayfish were found. The ponds were gradually re-filled with water during the spring of 2009. It is too early to conclude whether the treatment has led to the complete eradication of the signal crayfish, but the results so far are promising. We believe that BETAMAX VET.(R) can be a useful tool in managing alien crayfish populations.