POPULATION ESTIMATES OF NATIVE FRESHWATER MUSSELS IN POOL 5 OF THE UPPER 
MISSISSIPPI RIVER, 2006 

Mike Davis1, John Kern2, Teresa Newton3, and Brian Gray3
1Minnesota Department of Natural Resources, Lake City, MN 55041.  2Kern 
Statistical Services, Inc., Sauk Rapids, MN 56379.  3U.S. Geological Survey, 
Upper Midwest Environmental Sciences Center, La Crosse, WI  54603.

      During summer 2005, water levels in Pool 5 of the Mississippi River were 
held about 0.5 m below historically targeted levels to reestablish plant 
communities.  Native freshwater mussels living in the dewatered areas were 
stranded, resulting in substantial, but inadequately measured, mortality.  To 
better understand the possible adverse effects of this management action on 
freshwater mussels, we conducted a mussel survey during summer of 2006.  Our 
objective was to obtain pool-wide relative density and population estimates for 
mussels, stratified by depth.  We used a systematic grid with multiple random 
starts to provide an unbiased estimation of the total number of mussels within 
each zone of interest.  The shallow water zone was all depths 0-0.5 m, including 
the areas dewatered in 2005, and the deep water zone was all depths >0.5 m.  
Samples were allocated more densely in the shallow zone (1 sample per 5 ha), 
than in the deep zone (1 sample per 13 ha).  Two 0.25m2 total substrate samples 
were obtained at each of 359 sites.  All live mussels were counted, measured for 
shell length, aged (if < 10 yrs), and the number of attached zebra mussels was 
recorded.  A total of 669 live mussels, representing 16 species, were obtained.  
Abundance ranged from 0 to 13 live mussels per sample, with 66% of the samples 
containing no mussels and 6% of the samples containing >= 5 mussels.  Five 
common species (Amblema plicata, Obliquaria reflexa, Fusconaia flava, Quadrula 
pustulosa, and Utterbackia imbecillis) accounted for 90% of the mussels.  Pool-
wide population estimates are forthcoming.  High-density sites identified during 
this survey will be targeted for additional research in the future.

Keywords: mussel survey, systematic sampling, population estimate, pool 5