PREDATION OF ZEBRA MUSSELS, DREISSENA POLYMORPHA, BY
RIVERINE FISHES IN THE UPPER MISSISSIPPI RIVER

Renae B. Servaty and Michael D. Delong.
Large River Studies Center and Biology Dept., Winona State University, Winona,
MN 55987.

Previous studies of zebra mussels, Dreissena polymorpha, in the upper
Mississippi River have indicated that fish are actively feeding on this exotic
species.  Furthermore, these studies suggest that fish are selectively removing
zebra mussels larger than 8-mm. The objective of this study was to analyze gut
contents of fish to determine what fish are consuming zebra mussels and to verify
size selectivity of mussels larger than 8-mm.  Samples were taken by boat with an
electroshocker along three 400-m transects from backwater and main channel
shoreline habitats in Pool 6 of the upper Mississippi River.  Fish were identified,
weighed, measured, and the stomachs were examined for the presence of zebra
mussel shells.  Septum width and total length, when possible, were measured.  A
regression model was developed to estimate total length using septum length
when damage to the shell made it impossible to measure the former.  Several
species of fish were found to consume zebra mussels.  Major predators in the
main channel included redhorse (Moxostoma spp.), carp (Cyprinus carpio), and
freshwater drum (Aplodinotis grunniens).  All three species were also found to
consume zebra mussels in addition to bluegill (Lepomis macrochirus).  Bluegill
exhibited a preference for zebra mussels of 4 - 7 mm total length whereas other
predators consumed zebra mussels most frequently of 5 - 20 mm total length. 
Fish predators in the main channel appeared to prefer zebra mussels > 6 mm.  The
results of this study suggest that differences in size preference exist between main
channel and backwater habitats, with the composition of fish assemblages being a
major factor.  As a result, zebra mussel population dynamics may differ in main
channel and backwater areas of the upper Mississippi River.

Keywords: zebra mussels, fish predation, main channel, backwaters, population
dynamics

Renae Servaty
Large River Studies Center, Biology Department, Winona State University,
Winona MN 55987
Office 507-457-2458
FAX 507-457-5681

Poster Only; Presenter is a student