North American signal crayfish - update

The following are brief summaries of some of the action that we and our partners have done since the Species Action Framework was launched. They're in chronological order, with the most recent updates at the top of the page.

16 December 2009

Working with others

Since the launch of the Species Action Programme in 2007, much has changed with regard to the way in which Scottish Natural Heritage, the Scottish Environment Protection Agency, Government agencies and others involved in the management of freshwater habitats and species, interact when confronted with a new 'crayfish problem'.

During the first two years of the SAF programme it was important to obtain a appreciation of the scale of the signal crayfish problem in Scotland and recent SAF-funded research, undertaken in locations across Scotland from the River Nairn in the north to the Kirkcudbrightshire Dee and Tweed in the south, that at least 58km of river length is currently inhabited by crayfish. The study also confirmed that signal crayfish populations can now be found close to catchment limits and hydraulic boundaries. In locations, such as the interface between the rivers Clyde and Annan, and also the upper Clyde and the Tweed, the relatively small distances separating these systems means that there is the potential for the cross-catchment movement of signal crayfish from one river to another.

Raising Awareness and understanding

The development of a National Signal Crayfish Stakeholders Group has provided a forum for discussion and this has been augmented by the delivery of two Signal Crayfish Awareness courses. These courses were designed to increase capacity within Scotland within Scottish Natural Heritage, SEPA, the Fisheries Trusts and the Constabulary to deal with signal crayfish issues when they arise. Topics covered during the course included legislation, policy, crayfish taxonomy, distribution and ecology, sampling methods, as well as control and eradication techniques.

Awareness amongst the public is one of the key deliverables of the SAF programme, and the Scottish Natural Heritage information leaflet was re-vamped in 2008 - in advance of the delivery new materials which are currently under development.

Developing techniques

Both Scottish Natural Heritage and Environment Agency-funded studies have concluded that the potential to remove signal crayfish is limited once they become established. Intensive trapping, for example, is unlikely to be useful on its own as an eradication tool. It has also been argued that its use for simple control may also be limited, and may, in fact, exacerbate the problem. Eradication trials, using a biocide treatment (a natural pyrethrum) are still novel, but have been shown to be moderately successful in ponds within both the North Esk and River Ardle catchments.

Clearly this technique has to be developed further and in some Scottish localities, there are plans to extend this treatment option to at least one more site during the lifetime of the SAF programme.

Understanding the ecology

If we are to deal effectively with signal crayfish and, if possible, mitigate for their potential impact, it is important to understand the ecology of this organism in a Scottish context. A partnership project, which includes contributions from Scottish Natural Heritage, the Scottish Centre for Ecology and the Natural Environment  (Glasgow University), the Clyde River Foundation  and the Scottish Environment Protection Agency   has funded a PhD programme which aims to:  

1. Consolidate existing fine-scale crayfish distribution data and to identify a consistent and rigorous standard survey protocol;

2. Apply the new standard technique to actively assess the extent of signal crayfish establishment in Scotland;

3. Assess the impact of crayfish on local ecology to allow assessments of the risk to susceptible native fauna and the vulnerability of currently unoccupied systems to further invasion;

4. Model habitat suitability for signal crayfish to determine which areas are most likely to provide refuge (and also to aid modelling of the susceptibility of catchments to invasion) and therefore where potential eradication efforts could be concentrated;

5. Assess the likely degree of interaction between signal crayfish and species of high conservation value to indicate the magnitude of damage potentially visited upon such species when crayfish are introduced to naïve ecosystems; and 

6. Model the potential for eradication of signal crayfish in Scottish rivers to help target effort where success is most likely.

This work is well underway and the broad scope of the work has led to useful collaborations between the project funders and Marine Scotland  , the Rivers and Fisheries Trusts of Scotland   (and in particular the Galloway Fisheries Trust  ) and local fisheries stakeholders (e.g. the United Clyde Anglers Protective Association  ).