Why do a Crayfish Survey?
White Clawed Crayfish (Austropotamobius pallipes) are protected under Annex II of the EU Habitats Directive.
Whilst relatively widespread in Ireland, this species is endangered throughout Europe as a result of the introduction of the American Signal Crayfish and spread of the Crayfish plague disease. These factors are not present in Ireland and therefore this country is an important refuge for this species in a European context.
The EU Habitats Directive protects this species and Ireland is seen as one of its strongholds. For this reason, Crayfish surveys are often requested by the National Parks and Wildlife Service (NPWS) or local authorities during the planning process.
Where are Crayfish found?
Crayfish can be found in rivers and lakes with cobbles (or eroded, fissured limestone) and areas of thick aquatic macrophyte growth. Crayfish are usually found in slow flowing neutral to hard water, but they can be found in peaty water on a lime substrate at times also.
What is involved in a Crayfish Survey?
There are several different methodologies used when surveying Crayfish depending on the objectives of the survey.
- Hand Search/Snorkel survey involves systematic searching an area of riverbed, turning over stones to find Crayfish.
- Trapping, capture and release over three consecutive nights.
- Torch survey, shining torch into rivers at night when Crayfish are most active.
- Electro fishing.
Crayfish are protected under Annex II of the EU Habitats Directive, and so all surveys require a licence from the NPWS. Often determining presence or absence of Crayfish in a river or stream is all that is required from a survey but in some circumstances it is necessary to remove and relocate individuals to a safe location. This is often the case where in-stream works are required.
When can Crayfish Surveys be completed?
The optimal survey period lies between June and October however surveys can begin in May and end in November. It is best to avoid May and early June, where the females may be carrying young that they may shed when caught or handled.
How long does a Crayfish Survey take?
When surveying for the presence or absence of this species it is generally regarded that if not found after three consecutive nights of trapping Crayfish are absent.