Resource managers are currently using reductions in the Upper Mississippi River’s (UMR) water levels during summer to mimic historical water levels and rehabilitate habitats for vegetation and desirable fauna. However, drawdowns may have adverse effects on native mussel populations. Over the past few years, systematic, pool-wide surveys of mussels in Pools 5, 6, and 18 have been conducted. The objective of this study was to characterize the effects of water level drawdown on the mortality, movement, and behavior of a common Lampsilini species, Lampsilis cardium, and a common Amblemini species, Amblema plicata, in Pool 6 of the UMR during 2009 and 2010.
About 460 mussels were tagged and followed about weekly during June to November 2009 and during June to September 2010. Estimated mortality was slightly higher in the drawdown year (2010), with higher mortality inL. cardium than in A. plicata. The percent of mussels completely buried in river sediments were similar in the drawdown and non-drawdown years. However, more L. cardium were buried in the non-drawdown year, compared to more A. plicata being buried in the drawdown year. Overall, net movement was slightly higher at the sites affected by the drawdown, with net movement at treatment sites being greater for L. cardium. Results from this study are being used by resource managers to better evaluate the effects of water level management on native mussel populations.