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Discovery of larval mussels in Missouri cause for concern

From the Missouri Department of Conservation

-- In spite of its lack of legs, wings or fins, the zebra mussel has pulled off an end run, surprising biologists who are monitoring Missouri waters for the potentially destructive invader.

Microscopic zebra mussel larvae turned up in samples of water taken by workers with Missouri Department of Conservation at Pomme de Terre Lake in June. The discovery came as a surprise to Invasive Species Coordinator Tim Banek.

“If I would have been asked to choose the highest risk reservoirs for zebra mussel infestation in 2009, Pomme would not have made the list,” said Banek.  “One of my first thoughts was whether the veligers (zebra mussel larvae) might have come in sampling nets that had been used at Lake of the Ozarks. However, after speaking with those who did the field work, I am convinced that the samples were not contaminated.”

Banek said two-thirds of water samples taken this summer remain to be checked for zebra mussel veligers. It will take approximately six weeks to analyze the remaining samples and determine whether other Missouri reservoirs are infested. Because Pomme de Terre Lake is upstream from Truman Reservoir, discovery of zebra mussel velligers in the larger reservoir is almost certain.

The zebra mussel is native to Eurasia. It hitched a ride to North America in the 1980s, arriving in the Great Lakes in the ballast tanks of oceangoing ships. Since then, the thumbnail-sized invader has leapfrogged across much of the continent on commercial and pleasure boats, whose owners unwittingly transport the mollusks when trailering boats from one body of water to another.

While a few zebra mussels were found in the lower Meramec River in 1999 and in the Missouri River in 2001, the first known infestation of Missouri’s interior waters was discovered at Lake of the Ozarks in 2006. Today, the lake has dozens of known infestation sites throughout the lake. The pests also have turned up in Lake Taneycomo, Bull Shoals Lake and in the Osage River below Bagnell Dam. More recently, zebra mussel infestations were discovered in the Missouri River around Kansas City and Chamois.

Zebra mussels pose a threat to Missouri’s economy as well as the state’s ecology. They compete with native fish and other animals for food, making them a potential threat to the Show-Me State’s lucrative sportfishing industry. Their habit of attaching themselves to any solid object dooms native mussels, which are smothered by dense encrustations of the invaders.

Heavy zebra mussel infestations can weigh down docks, buoys and other marine equipment. Infestations on boat hulls increase water drag, leading to higher fuel and maintenance costs. They can clog marine engines’ cooling systems, creating a danger of damage due to overheating.

Zebra mussels also drive up utility bills by clogging water intakes of public and private utilities. Keeping those pipes open requires millions of dollars of maintenance annually.

Banek said the Conservation Department will begin immediately spreading the word that marina owners, anglers and pleasure boaters at Pomme de Terre Lake should take all precautions to avoid spreading zebra mussels.

“We still have many, many lakes and streams that are zebra mussel-free as far as we know,” said Banek. “Boaters and anglers have it in their power to keep it that way. At present, we don’t have any way to eradicate this pest once it is established. Even if we eventually find effective ways to control zebra mussels, that job, and the damage to our fisheries, can be dramatically reduced by citizen action now.”

Among measures Banek urges citizens to take are:

--Inspecting hulls, drive units, trim plates, transducers and other submerged portions of boats for adult zebra mussels after each use. Adult zebra mussels are fingernail sized with dark and light stripes. Small zebra mussels give hard surfaces a sandpapery feel.

--Examining crevices and recessed areas around motor housings, trim tabs and behind water intake screens on motors’ lower units.

--Checking trailers, ropes, minnow buckets and anything else that was in the water. Report any suspected zebra mussels to the nearest Conservation Department office.

--Removing all suspected zebra mussels, along with vegetation or other material clinging to boats and trailers and put it in a trash container.

--Rinsing boat bilges, trailers, motor drive units and live wells before launching them in another location helps prevent transferring microscopic zebra mussel larvae. Use water at least 104 degrees if live zebra mussels are found, or if your craft has been in waters known to be infested with zebra mussels. Most commercial car washes meet this standard.

--Allowing boats and other equipment to dry in the sun for at least five days before re-launching in another lake or stream.  

 – By Jim Low

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