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'Crayfish plague' may be to blame as large numbers of the crustacean die in Westmeath

Over the past number of years, many Irish crayfish has been impacted by the crayfish plague.

File photo
File photo
Image: parasolia via Shutterstock

AN INVESTIGATION HAS been launched by the National Parks and Wildlife Service (NPWS) into the death of large numbers of white-clawed crayfish in Co Westmeath.

The crayfish found at Lough Owel were reported by several visitors to the lake and the NPWS is now working with the Department of Culture, Heritage and the Gaeltacht, Waterways Ireland and the Marine Institute to establish the cause of death.

Lough Owel supports a large and, until now, healthy population of endangered white-clawed crayfish.

In a statement, the Department of Culture and Heritage and the Gaeltacht, which runs the NPWS, said: “Unexplained mortalities of crayfish have previously been reported on Lough Owel but as crayfish plague is present in Ireland, this would seem the most likely explanation.”

The white-clawed crayfish is a globally threatened species and Ireland holds one of the largest surviving populations in the world. It is the only freshwater crayfish species found in Ireland and is present in lakes, rivers and streams over much of the country.

Over the past number of years, many Irish crayfish has been impacted by the crayfish plague which spread to Europe with the introduction of North American species of the fish.

Until 2015, Ireland was considered free of the disease. However, an outbreak was confirmed in Cavan in 2015 and again on a stretch of the River Suir in May 2017.

Samples of the crayfish have been collected by Waterways Ireland staff and these will be tested by the Fish Health Unit of the Marine Institute. It is expected the results will be available in a few days.

Tests on dead crayfish found near the lake earlier in the year proved negative for the plague.

Outbreaks

Many American crayfish species are resistant to crayfish plague but can act as carriers of the disease which is “rapidly fatal” when passed to the white-clawed crayfish, according to the department.

“The combined impact of the introduced crayfish species – which may out-compete the smaller native crayfish – and crayfish plague have completely eliminated the white-clawed crayfish from much of its European range, leaving Ireland as the last stronghold of crayfish,” the department said in its statement.

The species is protected under Irish Law and the EU Habitats Directive, and it is illegal to introduce any non-native species of crayfish to Ireland.

“If crayfish plague becomes established there is a high probability that the white-clawed crayfish will be eliminated from much of the island,” the department said.

“Furthermore, if non-native crayfish are found to be established in Ireland, this could have a severe impact on habitats and other freshwater species, such as salmon and trout fisheries. However, there is no evidence to date that non-native freshwater crayfish have been introduced to Ireland.”

Warning to water users 

All water users who have been on Lough Owel in recent days are being asked by the Department of Culture and Heritage and the Gaeltacht to observe the check, clean and dry protocol and thoroughly clean their equipment before using it again.

This is especially the case if they are moving to another like or river, the department said.

It added that all wet gear should be checked for any silt or mud, plant material or animals. It should then be cleaned and finally dried.

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

A drying period of at least 24 hours is needed to ensure that the boat is clear of infectious organism.

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