Abstract
Signal crayfish, as an invasive alien species in Europe, have caused impacts on aquatic communities and losses of native crayfish. Eradication of recently established populations may be possible in small ponds (<2.5 ha) and short lengths of small watercourses using a nonselective biocide. Between 2004 and 2012, a total of 13 sites in the U.K. were assessed for suitability. Six were treated with natural pyrethrum and crayfish were successfully eradicated from three. In Norway, five sites were assessed and two sites were treated with a synthetic pyrethroid, cypermethrin, both successfully. In Sweden, three sites were treated with another synthetic pyrethroid, deltamethrin, all successfully. Defining the likely extent of population was critical in determining the feasibility of treatment, as well as the ability to treat the whole population effectively. Important constraints on projects included site size, habitat complexity, environmental risks, cooperation of landowners and funding availability. Successful projects were manageably small, had good project leadership, had cooperation from stakeholders, had access to resources and were carried out within one to three years. Factors influencing success included treating beyond the likely maximum geographical extent of the population and taking care to dose the treated area thoroughly (open water, plus the banks, margins, inflows and outflows). Recommendations are given on assessing the feasibility of biocide treatments and project-planning.
Highlights
This study presents a series of eradication projects using biocide treatment on crayfish in Europe
At eight of the eleven sites, annual monitoring for five years or more did not record any signal crayfish, indicating that eradication was successful at those sites
At the three sites in Sweden, there were no signal crayfish recorded and the re-establishment of populations of noble crayfish was a further indication of absence of crayfish plague and the signal crayfish that carry it
Summary
The number of biological invasions that have economic and or environmental impacts is increasing annually and there is a growing need to manage them [1,2] This is especially so in aquatic ecosystems, because of the impacts that invasive alien species can have on communities and ecosystem processes [3]. Habitat loss and pollution have contributed to fragmentation of populations of native crayfish, but there have been both localised and widespread losses due to the transmission of crayfish plague Aphanomyces astaci (Sikora, 1906) This disease is frequently carried by North American species of crayfish, usually asymptomatically [6]. Eradication of a population of an invasive alien crayfish potentially provides environmental, economic and/or social benefits by preventing any further impacts and wider spread of the population. The study presents case studies (projects) and uses the methods and outcomes of biocide treatments, by the authors and others, to identify factors that affected the success of projects of this type
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