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Great Lakes Article:

Great Lakes Exotic Species:

Zebra mussels spreading

Boaters, ducks probably introduced invasive species into inland lakes, rivers

BY LU ANN FRANKLIN Times Correspondent
Posted September 3, 2002

Industries along Lake Michigan that use lake water for manufacturing have been plagued by zebra mussels clogging intake valves since the small fingernail-size freshwater mollusks were introduced accidentally into the Great Lakes in 1988 by a transoceanic vessel.

This pesky species steadily has invaded inland waterways in Northwest Indiana's three counties and is now threatening the ecosystem of these lakes and rivers.

Wolf Lake in Hammond became the first inland waterway outside Lake Michigan to be invaded by the aquatic nuisance species. Adult zebra mussels were discovered there in 1991. Since that time the invasion has been progressive, reaching Pine and Stone lakes in LaPorte County in 1997, Cedar Lake and Deep River in Lake County in 1998 and Flint Lake in Porter County in 2000. Throughout the state of Indiana, there are currently 50 lakes and rivers infested with zebra mussels, according to the Indiana Department of Natural Resources Division of Fish and Wildlife.

Recreational boaters have unwittingly helped spread zebra mussels, said Brian Breidert, a biologist with the DNR office in Northwest Indiana.

When a boat travels through Lake Michigan waters or other areas with zebra mussels, the microscopic free-swimming young zebra mussels make their way into the boat's intakes and also attach themselves to the boat trailer. If the owner then launches the craft into another body of water without a thorough cleaning and drying out period, the zebra mussels are released into that waterway.

"It's important for recreational boaters when they pull out of the lake to chlorinate their boat to help reduce the spread of this invasive species," Breidert said.

The bilge of the boat should be emptied, and household bleach in a 10 percent solution should be used to cleanse the hull of the boat and trailer as well as water intakes.

Breidert said he doesn't recommend using bleach in a live well on a boat unless the well is thoroughly rinsed out. Otherwise, fish caught on the next fishing trip and put into the live well will die from bleach exposure.

The boat and trailer also should be dried out regularly. That's what the DNR does with all the watercraft employees use for work.

Ducks are also probably responsible for the migration of zebra mussels from Lake Michigan to inland waterways, said Marc Tuckman with the U.S. Environmental Protection Agency Great Lakes National Program office in Chicago. The young zebra mussels attach themselves to the ducks' webbed feet and are transported to other waters.

The adult zebra mussels need to attach themselves to a solid surface, which is why they clog water intake valves used by such industries as the steel mills and Lever Bros. located along Lake Michigan's shores. Most industries treat the water at their pumping stations and near their intake valves in May and October with a sodium chloride to kill the zebra mussels. Then before the water is returned to the lake after the manufacturing process, it is treated with sodium sulfide to neutralize the chlorine.

This process has cost Lake Michigan industries millions of dollars in the last 16 years.

The threat to the environment of Lake Michigan and other waterways is growing as the zebra mussel population grows.

Zebra mussels also attach to each other and can colonize on docks, boat hulls, commercial fishing nets and native mollusks such as clams. In fact, Tuckman said, the mussels, which attach with a strong glue substance, can cover native clams and kill them.

The freshwater mollusks, called Dreissena polymorpha, are predators and eat protoplankton and the aquatic animal Diporeia, which are both food sources for young fish.

"The zebra mussel takes out the bottom of the food chain," Breidert said.

Zebra mussels are also thought responsible for an outbreak of botulism that's killing birds around Lake Erie and Lake Ontario, Tuckman said.

"They have huge colonies of zebra mussels, some 1 meter across. They grow on top of each other," Tuckman said. "They are having a negative impact there."

To date, no such instances of botulism related to zebra mussels have been reported in Lake Michigan.

In addition to chlorine bleach, zebra mussels can be killed by specific bacteria.

However, they have only a few known predators, including some diving ducks, freshwater drum, carp and sturgeon. And these are not numerous enough to control the population, according to the DNR.

"Zebra mussels are an invasive species," Breidert said. "They compete with other aquatic life for food and they do a good job."

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