Shannon Regional Fisheries Board - Spring Issue'98 Page 4

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A new pest, the Zebra Mussel (Dreissena polymorpha), has been found in the Shannon System during 1997. The zebra mussel was first found in the summer of 1997 by researchers working with the ESB in Lough Derg and populations have been found from upper Lough Derg to Limerick Docks. They have also been found on boats as far north as Carrick on Shannon.

Zebra mussels are small shellfish shaped like marine mussel. The shells are striped with patterns of dark and light bands. They live in freshwater and the upper reaches of tidal estuaries and attach themselves to hard surfaces such as rocks, boats, etc.

Zebra mussels feed by filtering the surrounding water and removing plankton from it with each individual filtering as much as a litre of water a day. The mussels reproduce by releasing many thousands of tiny swimming larvae which drift downstream and eventually settle and grow into the shape of miniature adults.

Due to their ability to attach to hard surfaces zebra mussels clog intake pipes, drains and screens at a density of as many as 100,000 per square metre. This can cause reduced water delivery to boat engines, power plants, industries, fish hatcheries and municipal water works resulting in engine overheating, fish mortalities, increased maintenance costs and sometimes short term closures in production. The ecological effects of the introduction of the zebra mussel to Ireland are not yet known but because of the numbers in which they occur it is likely that they will change the ecology of some aquatic systems.

The Shannon Board is concerned at the introduction of the Zebra mussel and have been instrumental in getting the Marine Institute to set up a National Co-ordination Committee to monitor and take action on the issue. While much information is available on the devastating effects which can be caused to water plants, etc., little is known as to the effects on angling waters. The Board has therefore requested that this area be investigated as a matter of urgency. The Board would urge people to report any new sightings of zebra mussels to the Marine Institute or Dr T K McCarthy, UCG

Zebra mussels can live out of water for several days in moist shaded areas. When kept wet, adults can survive for more than a week. This means that they can be transported easily from one region to another. Should your boat or fishing gear have been in an infested area for even a few days it could carry zebra mussels upstream or, by being moved by road, introduce them to another lake or river.

If you have been on Lough Derg you may carry some zebra mussels on your hull. Zebra mussels can only be spread upstream and to other areas by boats or fishing gear. All boats including angling boats, houseboats,yachts, cruisers and barges can spread zebra mussels to the upper Shannon and to the Erne and the Barrow via the canals. Boats transported between river systems can bring the zebra mussel to new regions.

Before you move from the Shannon get a hull inspection. Should it be fouled arrange to have it cleaned. It may be impossible to prevent its eventual spread but it is worthwhile to attempt to control it. Every effort should be made to prevent the spread of zebra mussels to other rivers and lakes by ensuring that they are not transported by trailers, boats and fishing gear.

Dr Dan Minchin Marine Institute Fisheries Research Centre Abbotstown Dublin 15 Tel: 01 820 5078 or e-mail:

dminchin@frc.ie or: Dr T K McCarthy Zoology Dept. University of Galway Galway Tel: 091 750379 or e-mail:

tk.mcarthy@ucg.ie

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