Predation on zebra mussels by freshwater drum and yellow perch in western Lake Erie

Although considerable research has been done regarding zebra mussel (Dreissena polymorpha) expansion in the Great Lakes, information on fish species preying on zebra mussels is lacking. We examined diets of freshwater drum (Aplodinotus grunniens) and yellow perch (Perca flavescens) collected in western Lake Erie, 1992. Stomach contents were quantified in May, July, and October to examine the importance of zebra mussels in the diets and to determine if either-fish species exhibited size-selective feeding. Zebra mussels were consumed by freshwater drum and yellow perch once they reached 250 mm and 150 mm total length, respectively. Consumption by freshwater drum was highest in May and July and lowest in October. Most yellow perch consumption occurred in May. Chesson's alpha indicated that freshwater drum less than 350 mm TL and yellow perch less than 200 mm TL selected small zebra mussels and generally rejected larger individuals. Larger fish exhibited less selectivity, consuming zebra mussels in proportion to their estimated availability in western Lake Erie. Small fish just beginning to prey on zebra mussels may be physically limited to small sizes or clumps by their pharyngeal gape and musculature. Large freshwater drum and yellow perch are restricted more by the sizes of zebra mussels available on the surface of the substrate and possibly the size of clumps which they remove, rather than by their physical abilities to crush any one size. This may explain the strong selection for small zebra mussels by both species even though they are capable of eating larger sizes.