Movement Patterns of Native Mussels in the Upper Mississippi River: Response to Water Level Management

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Impact of UMESC Science

This research aims to estimate the fraction of mussels that are able to avoid short-term mortality during a water level drawdown by burrowing or moving horizontally into deeper water. Resource managers can use this critical information about mussel behavior and survival to make informed river management decisions.   

Resource managers are lowering water levels in some areas of the Upper Mississippi River to restore shallow-water habitats for plants. However, this water level management technique, referred to as drawdown, may have unintended effects on native mussel populations. Recent surveys of mussels show that there is a considerable mussel population in Pool 6, but that a small, but significant, fraction resides in shallow water—the area presumed to be most affected by a drawdown. Lacking definitive studies, resource managers have had to assume that all mussels residing in the drawdown zone are killed during a drawdown. However, it is likely that some mussels are able to either move horizontally out of the drawdown zone and reach deeper water or survive by vertically burrowing into river sediments. In 2009 scientists began a study to evaluate how a drawdown may influence movement patterns of native mussels.

How can you track mussel movements?

  • Scientists followed the movement and survival of two common mussel species, the pocketbook mussel (Lampsilis cardium) and the threeridge mussel (Amblema plicata), by attaching small transponder tags and fly fishing line to the mussels' shells. 
  • About 120 mussels of each species were tagged in 2009 (a non-drawdown year) and 2010 (a drawdown year). 
  • Researchers tracked individual mussels weekly within 12 study plots, including control areas unaffected by the drawdown, and areas likely to be dewatered.

     

Image of a pocketbook mussel (Lampsilis cardium) showing the transponder tag and fly fishing line attached to its shell.

Image of a pocketbook mussel (Lampsilis cardium) showing the transponder tag and fly fishing line attached to its shell. The fly fishing line is used to measure how deep the mussel is burrowed into the substrate without disturbing the mussel.(Public domain.)

How successful was the tracking?

  • During 2009, over 93% of mussels were successfully located over a five month period. 
  • Mussels could be typically relocated within about a 30 cm distance and to a depth of at least 20 cm.
  • Background morality during a non-drawdown year (2009) was about 5%.

How far do mussels move?

  • Preliminary findings suggest that mussel movement is highly variable among sites and between species. Some mussels stayed within the 2x3 meter study plots while others moved >10 meters.
  • Mussels generally migrated from shallow water in the summer to deeper water in the fall.
Picture of one of the 12 study plots showing PVC pipes that outline where the mussels were placed before the 2010 drawdown began

Picture of one of the 12 study plots showing PVC pipes that outline where the mussels were placed before the 2010 drawdown began. This image was taken about 4 days after the drawdown began. Note the movement of a mussel from the study plot in the lower right.(Public domain.)

 

How do mussels react to a drawdown?

  • This study is still in progress, but a few general observations have been made.
  • Mussels at sites with low slopes (more difficult for mussels to reach deep water) appear to get stranded in dewatered areas more than mussels at sites with higher slopes (easier for mussels to reach deep water).
  • Threeridge mussels often burrowed into the substrate, whereas pocketbook mussels were more likely to move horizontally.
  • Pocketbook mussels appear to have higher mortality than threeridge mussels.
  • Temperature recording devices (I-buttons) were placed in river sediments alongside study plots to determine sediment temperatures to provide insight on environmental conditions that might influence mussel movements.