Survival of unionids following removal of attached zebra mussels

A mussel mark-recapture study was initiated in the upper Mississippi River, Wisconsin, to measure the survival of Elliptio dilatata colonized by Dreissena polymorpha in Lake Pepin, Mississippi River. In 1996, 240 adult E. dilatata were marked in Lake Pepin. At the time of marking we cleansed zebra mussels from 48 of the 240 E, dilatata to test if a one-time removal of D. polymorpha would be effective in improving survival off. dilatata. In 1997, 1998, and 1999, marked mussels were recovered and identified; survival was determined; and live individuals were returned to the mussel bed. Mean annual survival off. dilatata cleaned of D. polymorpha equaled 94+/-3.0% and was not significantly different from those not cleaned (89+/-1.7%) (chi (2)(df=1) =2.31, p=0.13). The mean number of D. polymorpha colonized upon cleaned and uncleaned E. dilatata at the conclusion of this study in 1999 equaled 105.8+/-12.9 and 94.6+/-8.4 respectively (p>0.05). Since survival rates and the abundance of D. polymorpha on the two groups of E. dilatata were not significantly different following the years after initial cleaning, we suggest that a one time removal of D. polymorpha from native mussels is not a biologically effective management tool.