Action: Procambarus crayfish control: Add chemicals to the water
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- One replicated, controlled study in Italy found that red swamp crayfish could be killed using the natural pyrethrum Pyblast at a concentration of 0.05 mg/l, but that application to drained crayfish burrows was not effective.
Adding chemical toxicants to the water offers the potential for localised control of invasive crayfishes. Chemical ‘dips’ for fishing and sampling gear can also be an effective biosecurity method for preventing the transport of crayfish plague. Most chemicals will have an impact on non-target organisms, and so their use must be carefully considered before being dosed. In many instances, the use of chemicals may be subject to local or national approval by regulatory authorities. Two before and after studies from Norway (Sandodden & Johnsen 2010) and Scotland (Peay et al. 2006) demonstrated that the biocides cypermethin and pyblast, respectively, were both effective at eradicating a different species of invasive crayfish, signal crayfish. A further study using chlorinated lime was ineffective at controlling signal crayfish in the Czech Republic (Zozak & Policar 2002).
Sandodden, R., & Johnsen, S. I. (2010) Eradication of introduced signal crayfish Pasifastacus leniusculus using the pharmaceutical BETAMAX VET®. Aquatic Invasions, 5, 75-81.
Peay S., Hiley P.D., Collen P & Martin I. (2006) Biocide treatment of ponds in Scotland to eradicate signal crayfish. Bulletin Français de la Pêche et de la Pisciculture, 380–381, 1363–1379.
Zozak P. & Policar T. (2002) Practical elimination of signal crayfish, Pacifastacus leniusculus (Dana), from a pond. Pages 200-208 in: D.M. Holdich & P.J. Sibley (Eds.) Management and Conservation of Crayfish Proceedings of a conference held on 7th November 2002 at the Nottingham Forest Football Club, Nottingham, UK.
Supporting evidence from individual studies
One replicated, controlled study in 2009 in Italy (Cecchinelli et al. 2012) found that natural pyrethrum (Pyblast) concentrations of 0.05mg/l and higher resulted in 100% mortality of red swamp crayfish Procambarus clarkii under laboratory conditions, 95% mortality when 0.05mg/l Pyblast was applied to a drainage channel, but no mortality following application of 0.05 mg/l Pyblast into active crayfish burrows. For the drainage channel study, two 50m-long upstream control transects were compared with two downstream transects treated with 0.05 mg/l Pyblast, and mortality of crayfish in each transect was monitored recorded every 24 h for 96 h. For the burrow study, a 0.3 l solution of 0.05 mg/l Pyblast was injected up to 2 m inside active crayfish burrows after the channel had been drained. Crayfish population changes were assessed by comparing capture rates in four replicated, baited traps before and after the treatment.