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The U.S. Army Corps of Engineers <br />has studied the transport of zebra <br />mussels in the inland waterways and <br />determined that barges are very likely <br />responsible for the rapid spread of the <br />mussels throughout the inland system. <br />Of note is the case of a single barge <br />that travelled 14,000 miles through <br />the inland waterway system between <br />May 1991 to May 1992. On May 11, <br />1992, zebra mussels were observed on <br />the barge, occurring: "... in clusters <br />every 2 to 3 feet along the bottom edge <br />of the rub rail ... 10 to 50 zebra <br />mussels were found in each cluster." <br />(U.S. Army Corps of Engineers 1993). <br />The size of the mussels suggested that <br />they attached to the barge in 1991. <br />These mussels probably spread during <br />reproductive periods and perhaps <br />anytime when the barge scraped along <br />locks and other facilities, dislodging <br />the adult mussels. <br />The downstream spread of zebra <br />mussels in the Mississippi system and <br /> <br />~. Natural <br />YES - <br />NO .. <br />YES - <br />NO <br />a. currents ^ ^ <br />b. birds ^ ^ <br />c, other animals ^ ^ <br />2. Huffman YES NO YES NO <br />d. canals(may include pumps) ^ ^ <br />e. ballast water ^ ^ <br />f. vessels ^ ^ <br />g. buoys ^ ^ <br />h. marina/fishing equipment ^ ^ <br />i. fish stocking, bait buckets ^ ^ <br />j. trucking water ^ ^ <br />k. intentional movements ^ ^ <br />I. aquaria releases ^ ^ <br />m. amphibious airplanes ^ ^ <br />n. recreational equipment ^ ^ <br />o. litter, garbage ^ ^ <br />p. scientific research ^ ^ <br />TABLE 2. DISPERSAL MECHANISMS FOR ZEBRA MUSSELS AFTER CARLTON, 1993). <br />NOTE: SOME CATEGOR/ES HAVE BEEN COMB/NED~. <br />its lateral transportation due to <br />commercial water traffic will not be a <br />factor in the further western dispersion <br />of zebra mussels in the United States. <br />(Note: There are some streams that <br />enter the United States from contami- <br />Hated areas in Canada, and this <br />problem will be discussed later). Thus, <br />downstream colonization by zebra <br />mussel veligers, a major problem in the <br />Eastern United States, is not viewed as <br />great a problem for direct western <br />