DULUTH -- Zebra mussels have been moved into yet another popular lake, this time Lake Winnibigoshish in north-central Minnesota, the Minnesota Department of Natural Resources confirmed Thursday.
Zebra mussels and their larger cousins, quagga mussels, feed by filtering tiny organisms out of the water, and they can filter huge amounts of stuff that previously was consumed by small native species. They almost always displace native mollusks, such as clams, and have caused massive changes in the food chain in places such as Lake Erie and Lake Michigan. They have cost millions of dollars over recent decades as industries, shore residents and boaters are forced to clean them off underwater surfaces such as water intake pipes. But the long-term implications on fish populations remain unclear.
The DNR said two larvae of the thumbnail-size mussels were discovered in Lake Winnibigoshish water samples that were collected in July and examined this winter. The microscopic larvae, called veligers, showed up in only one of 15 samples, and so far no adult mussels have been found. But the discovery is enough for the DNR to consider the lake officially invaded.
"Even though we didn't find any adult zebra mussels it's really proactive now to list Winnibigoshish as infested... to prevent the spread to other areas," said Ann Pierce, DNR invasive species unit supervisor for the DNR.
The veligers float around for several weeks before growing large enough to attach to hard objects such as rocks, clams and docks. DNR officials say it's likely there are adult zebra mussels in the lake that haven't been noticed. Biologists say they believe they caught the zebra mussels at a very early stage of their infestation.
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The discovery has implications far beyond one lake, however. Because the big lake is part of the Upper Mississippi River system, DNR officials said it's likely zebra mussels will move downstream to other, connected lakes downstream.
"It's reasonable to believe that any body of water downstream of Winnibigoshish would eventually have their own population of zebra mussels,"said Gary Montz, aquatic invertebrate biologist for the DNR. "There's really no way of preventing this downstream movement at all."
Zebra mussels are native to eastern Europe, including Russia, and moved into the Great Lakes in the ballast of oceangoing ships in the 1980s. They first were found in Minnesota in the Duluth harbor in 1989 and now have been confirmed in more than 80 lakes and rivers across the state.
It's not clear how the mussels got into Winnibigoshish, except that it's clear people were involved. Zebra mussels can't swim -- they only move in current or by hitchhiking from one body of water to another through human action -- boats, trailers, docks, diving equipment, waders, fishing nets or buckets of water moved from one lake or river to another.
"We knew it was coming. We washed our boats. We power-washed our boats. But when this many people use a lake, you can't get to everyone," said Tom Neustrom, a professional fishing guide from Grand Rapids. "There are going to be big implications, for the tourism business and anglers but especially I think for the bait business. Winnie has a huge shiner run, and now there are going to be restrictions on harvesting those shiners, and that's going to be big."
Doug Jensen, invasive species experts for Minnesota SeaGrant in Duluth, said the early detection may help stop the mussels from spreading over land to other waters.
"The education and information efforts are working," Jensen said. "So far, only 12 of the state's infestations have been over land, from a disconnected body of water. ... If people weren't taking action we would be much more inundated with invasive species in a lot more lakes."
