Measures to Control Invasive Crayfish Species in Switzerland: A Success Story?

Raphael Krieg,Alex King,Armin Zenker

doi:10.3389/fenvs.2020.609129

Abstract

Invasive crayfish species were first documented in Switzerland in the 1970s. Today, North American crayfish species dominate in most major lakes and streams in Switzerland. In combination with the crayfish plague, they pose a substantial threat to our native crayfish. Over the past 20 years, various techniques have been applied to reduce negative impacts of these invasive crayfish in Switzerland: eradication (temporary drainage or destruction of a water system, biocides), suppression (intensive trapping, electricity introduction of predatory fish) and containment (construction of crayfish barriers). Temporary drainage or filling-in of isolated ponds, in combination with calcium hydroxide application has been successful in eradicating populations of invasive crayfish. However, trapping and introduction of predatory fish led to a reduction in population density but neither method has ever caused the extinction of a population. Invasive crayfish have not yet reached crayfish barriers, therefore, long-term functionality of these barriers still needs to be proven. Nevertheless, functional controls with native crayfish have shown that barriers prevent their upstream movement. Implementation of crayfish barriers is the most promising method to protect native crayfish from displacement by invasive crayfish species. Many measures are expensive, time consuming, and show little or no success in controlling invasive crayfish. Therefore, we recommend to focus on implementing drastic measures, such as filling-in or draining of isolated waters or a combination of various methods to maximise the reduction of population size.

Highlights

Preventing the widespread disappearance of indigenous crayfish species (ICS) in Europe is an on-going challenge
In addition to habitat destruction by river engineering and water pollution, invasive non-indigenous crayfish species (NICS) from North America are becoming increasingly widespread in Europe and pose a major threat to ICS (Kouba et al, 2014)
When catch per unit effort (CPUE) values were recorded over several years or when the functionality of a crayfish barrier was tested in the field with ICS, data was assessed as “valid.” Personal assessments, measures which have started within the last 3 years and catch figures without indication of the sampling effort were rated as “insufficient” to produce valid data and are classified and referred to as “unclear” success in this paper

Summary

Introduction

Preventing the widespread disappearance of indigenous crayfish species (ICS) in Europe is an on-going challenge. Various methods have already been applied and tested across the world to reduce or eradicate the negative impacts of the unwanted intruders as well as to prevent them from spreading further These methods include: intensive trapping (Bills and Marking, 1988; Hein et al, 2007), male sterilisation (Piazza et al, 2015), the use of biocides (Cecchinelli et al, 2012), habitat destruction, the release of predators (Musseau et al, 2015), the construction of barriers (Cowart et al, 2018) or a multi-method approach combining different combinations of these methods (Hein et al, 2006; Freeman et al, 2010; Stebbing et al, 2014). Since invasive crayfish have a negative influence on native plants and animals, the pros and cons of each control method must be considered to determine which will be most beneficial for each site

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Conclusion