Aquatic Environment – Zebra Mussels & the Environment

ALERT ZEBRA MUSSELS IN IRELAND

A recently introduced pest and what you need to know to limit its spread

Zebra Mussels are small shellfish shaped like marine mussels. They are striped with varying patterns of dark and pale bands., hence the zebra name. They attach themselves to hard surfaces using special anchoring threads such as wood, plastic, stones e.t.c. They live in fresh water and the upper reaches of tidal estuaries, but cannot live in seawater. They usually grow to 15 – 25mm but can attain 50mm ( 2 inches ).

Zebra Mussels life history

Zebra Mussels feed by filtering the surrounding water and removing plankton from it. Each individual sieves as much as one litre a day. They can reproduce within a year when temperatures exceed 12 degrees Celsius, releasing many thousands of the tiny swimming stage which are moved easily by currents. They settle after about three weeks and soon grow into the shape of a miniature adult. Mussels can live 3 to 5 years, and rapidly increase their numbers.

Why are Zebra Mussels a problem to industry ?

Due to the ability to attach to hard surfaces zebra mussels clog pipes, drains and screens as many as 100,000 per square metre. This causes reduced water delivery to boat engines, power plants, industries, fish hatcheries and municipal waterworks resulting in engine overheating, fish moralities, increased maintenance costs and sometimes short term closures in production. In addition mussels occur in such numbers that they can change the ecology of some aquatic systems.

Where did they come from ?

Zebra Mussels expanded their range from rivers entering the Black Sea and Caspian Sea to much of Europe, attached to ships and boats, following the building of canals. The zebra mussel was established in Britain by 1830. In 1986 they were introduced to North America in ships’ballast water and now cause serious fouling problems there.

How did they get here ?

Zebra Mussels have recently appeared in very large numbers in the River Shannon in Limerick, Lough Derg and on boats as far north as Carrick on Shannon and to Laytown on the Grand trailers.

What can you do about Zebra Mussels ?

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.

Users of the Shannon

If you have been on Lough Derg you may carry some zebra mussels on your hull. They can only be spread upstream and to other areas by boats and fishing gear. All boats including, angling boats, houseboats, yachts, cruisers and barges can spread 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.

Recent studies suggest that barges, and private boats which do not regularly slip for hull cleaning, are most likely to spread zebra mussel within waterways. Before you move from the Shannon get a hull inspection. Should it be fouled, arrange to have it cleaned. Fouling reduces the performance of craft so it pays to remove the shells. It may be possible to prevent its eventual spread to other rivers and lakes by ensuring that they are not transported by trailers, boats and fishing gear.

What to do:

Before you remove your boat;

Give the boat a high speed run to help detach fouling mussels. ( Hull waxes or silicone applications can significantly reduce fouling )

When you remove your boat:

• Hose and brush down the boat
• Drain all bilge water, live wells, bait buckets and waste.
• Destroy and dispose of all live bait.
• Remove all weed from boat and trailer
• Clean down your engine
• Allow the boat to dry out and leave in the sunshine for a week – longer if the weather is dull and wet.
• Ensure that zebra mussels are not returned alive to the water.
• Dry keep nets or dip them in hot water.

Please report zebra mussels from new areas to:

Dr Dan Minchin, Marine Institute.

Fisheries Research Centre,

Abbotstown, Dublin 15

Tel: + 353 1 8210111

Fax: + 353 1 8205078

email: dminchin@frc.ie

or

Dr T.K. Mc Carthy, Zoology Department

University of Galway

Tel: + 353 91 512008 or + 353 91 750379

Fax: + 353 91 750526

email to tk.mccarthy@ucg.ie or visit their webpage at http://www.nuigalway.ie/freshwater/zebra/

Source: Marine Institute ‘Foras na Mara’