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Biss, III, J., F. H. Laruelle and D. P. Molloy, 1996. Use of Sieves for Size-selection of Dreissena polymorpha, New York State Museum Abstract from The Sixth International Zebra Mussel and Other Aquatic Nuisance Species Conference, Dearborn, Michigan, March 1996 Use of Sieves for Size-selection of Dreissena polymorphaTaking the time to measure the shell length of Dreissena polymorpha (zebra mussels) and sort them into size categories is a frequent and often tedious component of laboratory and field studies. We describe a method employing commercially-available sieves of uniform pore size that is an efficient technique for collecting large numbers of mussels of a selected size class or size sorting entire populations. Although we developed this technique to facilitate our research on the microbial control of zebra mussels (we needed large numbers of mussels of a selected size range for toxicity tests), we believe that this method may be a valuable tool in a wide range of other zebra mussel research projects. The method rapidly and accurately (6% error) yielded hundreds of mussels in selected size ranges in a comparatively short time compared to the more traditional method of hand picking. In laboratory trials (sieving performed within a bucket of water), this technique yielded over three times as many mussels per unit time versus hand picking: 27 versus 8 mussels/min. When the method was performed in the field (sieving directly within the waters of the Mohawk River, NY), it proved even easier to perform and, consequently resulted in a higher yield: 34 mussels/min. Besides the increased efficiency of collection, performing this technique in the field also eliminated the need to transport heavy, mussel-laden substrates back to the laboratory and reduced the time required to properly dispose of mussel-contaminated materials at the laboratory; all of the wash water and substrates (e.g. rocks) were left in the river, with only the mussels of the desired size range transported back to a laboratory. The technique consists of the sieves being used in pairs, with the group of mussels to be sorted placed on the top sieve. The sieves are repeatedly moved vertically in and out of a column of water. The top sieve (the one with the larger pore size) determines the upper size limit of mussels collected between the two sieves, while the lower sieve determines the lower size limit of the selected mussels. Commercially-available sieves pairs with pores of 6.30 and 5.60 mm, 5.60 and 4.75 mm, and 4.75 and 4.00 mm, for example, yielded mussels, respectively, in size classes of ca. 14 to 10 mm, 13 to 8 mm, and 11 to 7 mm. A limitation of this sieving method is that size classes collected are predetermined by the sieve sizes that are commercially available. If a study required mussels in a another size range, custom sieves would have to be made.
Keywords: Zebra_mussel, Filters |