Zebra Mussels in Ireland

Abstract

The zebra mussel was reported for the first time in Ireland during 1997. It may have been introduced during or before, 1994. Information, based on eye-witness accounts from 1995 and the age structure of zebra mussels sampled during October and November 1997, suggests they first became established in the region between southern Lough Derg and Limerick Docks. The species expanded its range during 1996 to include most of Lough Derg and by 1997 had settled in the remaining north-eastern region of the lake. The mussels could have reached Ireland in several ways. The most likely vectors are boats carried on trailers directly from Britain, and one recently imported barge carrying live mussels was found. There may have been a number of introductions. It is possible that some arrived in ballast water from shipping in Limerick Docks. Mussels foul a wide range of structures and easily settle on firm surfaces, including water supply pipes. For this reason their presence is of serious concern to amenity and industry. In the Shannon they have formed dense concentrations on the dock gates in Limerick and the sluice gates and pillars of the Parteen and Ardnacrusha dams. Piped water to a hatchery was blocked with a subsequent loss of fish. Densities on the hulls of vessels were up to 53,000 per sq.m. They were most frequently found attached to the hulls of barges and private craft not slipped annually. Few hire cruisers were fouled. Some mooring have sunk under the weight of attached mussels. Fresh-water mussels Anodonta anatina, rocks, stones and some aquatic plants were found with attached zebra mussels. It is likely there will be changes to the ecosystem. The overall effects cannot be predicted and will require careful monitoring. It is inevitable that mussels will spread throughout the navigable waterways of the Shannon and Erne and to the Barrow via the Grand Canal. The spread to other waterbodies can be curtailed if boats are cleaned before being transported. Because mussels can survive up to three weeks under damp and dull conditions special care is necessary to ensure that transfers are avoided. Leaflets have been distributed to boat owners and anglers to advise on precautionary measures.