Forget zebra mussels — there's a new exotic threat to the Great Lakes fisheries. The quagga mussel was almost unknown five years ago, but they're now blanketing much of the bottom of Lake Michigan. "The quagga mussels are extremely good at filtering plankton from the water," says Russell Cuhel, senior scientist at UW-Milwaukee's Great Lakes WATER Institute . He says quaggas are definitely having an impact on the prey species of fish, which in turn are eaten by the larger species sought by anglers and commercial fishermen on the lake. However, Cuhel adds that he's "not certain that it will continue to be this way, because it wasn't this way five years ago, when zebra mussels were the big issue. We don't know that something new won't come in, and change the quagga mussel story."
In a response to the quagga mussel and numerous other foreign plant and animal species which have hitched rides on ocean going ships entering the Great Lakes through the St. Lawrence Seaway, Wisconsin will spend $6 million to invest in experimental ballast water treatment systems for the Milwaukee, Green Bay and Superior harbors. However, Cuhel says it's difficult to clean all the ballast water in a ship: "it only takes a couple gallons to bring in a lot of these invaders."
Cuhel says the mussels are probably not the only thing affecting the food web in Lake Michigan. He suggests an alternate theory, that the elimination of phosphates from household detergents has resulted in clearer water, but also less of the larger species of algae which fish feed on.