Publications

We describe a method that uses sieves of uniform pore size for rapidlysize sorting large populations of Dreissella polymorpha (zebra mussels) or collecting large numbers within a selected size range. This method may be a valuable tool applicable to a wide range of zebra mussel research projects and possibly also useful in size sorting other bivalve species. Sieves are used in pairs and are repeatedly moved vertically in and out of a water column, with mussels passing lengthwise down through the pores. The upper and lower limits of the size range of mussels collected between the sieves are determined by the pore sizes of the upper and lower sieves, respectively. Sieve pairs with pore sizes of 6.30 and 5.60 mm, 5.60 and 4.75 mm, and 4.75 and 4.00 mm, for example, yielded mussels in size classes of 13.8-10.3, 12.6-8.5, and 10.6-7.0 mm in length, respectively. Sieving in the field eliminated the need to transport mussel-laden rocks and other substrates to the laboratory, reduced the effort required to properly dispose of musselcontaminated materials, and proved even simpler to perform than in the laboratory. One of the challenges in using this sieving procedure is determining the exact sieve sizes that will retain mussels only within a particular length range. For example, because large numbers of zebra mussels 6-11 mm in length are used in our laboratory's research program, trials were conducted to compare the effectiveness of sieving and hand picking to obtain mussels solely within this size class. With sieves of 5.6 and 2.8 mm pore sizes, the mean yield of mussels was over three times faster by sieving than hand picking (10.2 versus 3.0 mussels/min), but 7.1% of the mussels collected were outside the desired length range of 6-11 mm. In judging the usefulness of this sieving procedure, an error factor such as this is unavoidable and must be weighed in individual research projects against the significant increase in mussel yield.