Agencies battle to prevent Crayfish Plague from spreading further upstream

Major containment operation in River Suir


Crayfish taken from the river Suir

A major containment operation is underway to stop the further spread of the plague that has killed hundreds of thousands of crayfish along the River Suir between Carrick-on-Suir and Clonmel.

The crayfish population along the river between the Coolnamuck Weir near Carrick-on-Suir town and Sir Thomas' Bridge near Clonmel has been wiped out by Crayfish Plague, a serious disease that only affects the native White Clawed Crayfish.

DNA test results confirmed that the plague was the cause of the mass deaths of the river's crayfish population between both towns last Tuesday, May 16.

According to environmental agencies, this outbreak of Crayfish plague is on a much greater scale than the last Irish outbreak on the Bruskey River in Co. Cavan two years ago. The cause of this outbreak is not known.

Ruth Hennessy, Executive Scientist at Tipperary Co. Council, said so far surveys have found no dead crayfish in Clonmel or upstream of the town. Crayfish are not found downstream of Carrick-on-Suir because the river water is not suitable for them as it's tidal.

"If the disease moves up into Clonmel and further upstream then the impact will be significantly worse. European experiences of similar outbreaks suggest that this may happen," Ms Hennessy warned.

The Co. Council along with Inland Fisheries Ireland, the National Parks and Wildlife Service, Local Authority Waters and Communities Office, other agencies, stakeholders and volunteers have been working together to identify river users and to distribute information to them about the "biosecurity precautions" they must take to stop the spread of the plague further upstream.

The precautions include observing the ‘Check, Clean and Dry’ protocol once they leave the river and before using it again. This means that all wet gear,namely boats, clothing and equipment should be checked for any silt or mud, plant material or animals before being cleaned and finally dried.

Disinfectant or hot water (over 40 degrees Celsius) should be used to clean all equipment and this should be followed by a 24 hour drying period.

The drying period is especially important in ensuring that all equipment is clear of infectious organism, including the removal of any water inside the boat.

The Crayfish Plague organism can be carried on wet equipment to new sites and containment of the outbreak is essential to prevent spread to other unaffected populations in Ireland.

More than 100 signs have been erected along the River Suir and its main tributaries advising river users of these biosecurity measures.

Ms Hennessy said the national agencies are meeting in Clonmel this week to further plan the response to the Crayfish Plague outbreak and develop a longer term strategy in partnership with the relevant bodies.

Dr. Fran Igoe of the Local Authority Waters and Communities Office, appealed to river users to avoid moving from the River Suir below Clonmel to upstream of Clonmel.

"It is possible if the infection is limited to the lower river that it may disappear over the coming weeks once it reaches barriers such as weirs which sick crayfish have difficulty getting over."

He said the River Suir has a significant Crayfish population, which is internationally important on account of the large size of the catchment (3,500km2) and its relatively clean water.

"For this reason Crayfish were listed as a species of conservation importance when the river was designated as a Special Area of Conservation under the EU Habitats Directive. When we surveyed otters last September in Ardfinnan, we found that they were feeding exclusively on Crayfish.

"We know that they are also an important food source and also provide important ecosystem services to the river by cleaning up detritus. Contrary to a popular belief Crayfish are not a threat to fish and both salmon and trout feed on them, especially the juveniles," Dr Igoe added.

Reports of dead and dying crayfish on the River Suir upstream of Carrick-on-Suir were first brought to the attention of Inland Fisheries Ireland by anglers on Friday, May 5 and an investigation was begun.

Pollution was quickly ruled out as the cause of their deaths as water samples taken by Tipperary Co Council found that other invertebrates in the river were not affected.