Exotic Zebra Mussels Threaten Fish Life

BOB SPRAGUE'S leathery hand paws through a box of fishing lures as he sits next to the window of his house. A bitter northern Ohio wind blows off Lake Erie. He picks up a new yellow lure, examines it, then tosses it back in with the rest. As he stares out the window his face reddens with anger.

``The zebra mussel,'' he says with an empassioned rage tinged with sadness. ``It's going to be the end of sport fishing in the greatest fishing hole in the world.''

A sport-fishing boat operator for the past 11 years, Mr. Sprague and his wife, Joan, captain two 28-foot fishing boats in Lake Erie's western basin. Now they see their livelihood and the region's fishing industry - which helps pump $1 billion each year into the local economy - threatened by an infestation of the mussels which, until 1985, were unheard of in the United States.

Zebra mussels (Dreissena polymorpha) originated in East Europe, and most of Western and Central Europe have lived with them for about 200 years.

Ohio Sea Grant is part of a national program designed to develop, manage, and utilize the nation's ocean, Great Lakes, and coastal resources. Its scientists estimate that zebra mussels were first introduced into the Great Lakes in 1985, when one or more transoceanic ships discharged ballast water into Lake St. Clair to the northwest of Lake Erie.

The temperate, fresh-water species found plankton-rich Lake Erie to its liking. Although the zebra mussels were nearly unheard of by Lake Erie shoreline residents until 1989, the species had colonized the surfaces of nearly every firm object in the lake by autumn of that year. Scientists expect that Lakes Ontario, Michigan, and Huron will experience extensive colonization this year.

Female zebra mussels have life spans of about a half-dozen years and produce more than 30,000 eggs each year from May through October. Each adult mussel grows to between one and two inches long, and can filter about one liter of water per day. Thus, a great deal of plankton is removed from the water, severely affecting the food chain of Lake Erie's sport and commercial fisheries. And when the mussel's excretions decompose, the water becomes acidic, thus driving out white bass, smallmouth bass, and walleyes.

Not only do zebra mussels attach themselves to hard objects on the lake's bottom, but they also attach themselves to the undersides of boats. Increasingly, there are reports of boat engines overheating due to cooling water inlets being clogged by colonies of mussels. And the water purification plant in the town of Monroe, Mich., was closed down in December when its water-intake pipe became clogged with mussels. Already, beaches are being strewn with sharp-edged shells, and there are concerns that the mussels' parasites may attack swimmers.

While diving birds and certain species of fish are known to prey on mussels, few experts expect such predators will have any real impact on the zebra mussel population. As a result, the mussels are expected to infest two-thirds of the nation's bodies of fresh water by the end of this century.

Speaking to a local community college audience earlier this year, Dave Kelch, an Ohio Sea Grant district specialist, reminded the audience that their lake had already weathered foreign infestations of carp, smelt, sea lampreys, white perch, and Asiatic clams.

``Are we seeing the beginning of the end of Lake Erie?'' he asked the audience. He quickly answered his own question, ``Of course not.''

But pose the question to Captain Sprague, and one gets a different answer.

``Beyond this year I can't even visualize it,'' he says. ``It's disastrous if your livelihood depends on it.''