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The signal crayfish (Pacifastacus leniusculus) has had a significant impact on UK ecosystems since its introduction. It is a fast growing, highly fecund, aggressive, voracious species which has few natural predators.
In conjunction with the School of Marine Sciences and Technology, Newcastle University, and with the support of the River Tweed Commission, the Foundation is investigating the control of signal crayfish on the River Tweed
Crayfish predate and out-compete a number of native species, including several environmentally and economically important native fish species as well as amphibians, and other invertebrate species. Signal crayfish can burrow, causing extensive damage to riparian verges and subsequently to the whole ecosystem. Potential impacts on salmonid rivers could be extensive as the signal crayfish predate eggs and juveniles and they have been shown to compete with over-wintering smolts for shelter. Burrowing could also impact significantly on silting up redds and decreasing invertebrate numbers. The need to control signal crayfish in salmonid rivers is, therefore, paramount.
Currently, there are no management tools that have been fully tested available for eradication or control of invasive crayfish. Previous attempts to control populations focus on the physical removal of animals from watercourses, either through hand removal or trapping and both methods are labour intensive and need to be sustained. Increasing predatory fish numbers has been suggested in a number of cases, but may result in an imbalance of the ecosystem with non-target species becoming severely impacted. This method is also not suitable for a number of water systems where their introduction may not be suitable. Pesticides have been suggested as an effective method of control, but are general biocides that kill all other exposed invertebrates. There is also a possibility of bioaccumulation and biomagnification as crayfish form part of the diet of a number of key predators, including a human risk. Male sterilisation is a method that has been used in the control of a number of other pest species, but has not been investigated for non-native crayfish. In its purest form it involves mass rearing of sterile males that when released compete with normal males, but produce no young, thus the populations breeding capacity is impaired and the population size reduces. This could potentially be achieved, once an appropriate sterilisation technique has been developed, through the capture and release of animals from a population.
Many of the problems with the development of control methods are the lack of understanding of crayfish population dynamics. This is paramount to be able to determine the effect of any control applied to the population as well as determining, age, extent and best method of control.
Objectives of the study
1.To undertake a trapping regime to determine population characteristics in the affected location.
2.To determine the relative effectiveness of different trapping methods.
3.To perform laboratory trials on the efficacy of sterilisation and potential for utilisation of control chemicals (e.g. S-LICE).
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