UNIONID MUSSELS OF DREDGE CUTS AND PLACEMENT SITES, POOLS 11-22

Jim Eckblad.
Department of Biology, Luther College, Decorah, IA  52101.

Field sampling was conducted in 1998 from 36 former dredge cuts and placement 
sites to evaluate unionid mussel colonization of areas impacted by channel 
maintenance dredging.  The 36 sites included 12 with active dredge cuts or 
placement within the past 5 years, 12 within 5 to 10 years, and 12 with greater than 
15 years.  Maps of each site with GIS coordinates were provided by the Rock Island 
District, Corps of Engineers.  A total of 693 live mussels were taken during 142 10-
minute diver searches at these sites.  An additional 91 live mussels were taken during 
ten 10-minute diver searches of two potential re-handling sites in Pool 18.  The 784 
live mussels included 23 different unionid species; an additional 8 individuals, from 6 
different sites and 5 different species, were recorded as recent dead mussels.  Data 
from this study, in general, supported the hypothesis that colonization of dredge sites 
by mussels may occur within the first five years, failed to detect significant 
differences between different aged sites, and failed to support the contention that 
colonization is correlated with years since the site was last active.  When 
presence/absence frequencies were included in the analysis, mussel colonization was 
associated with substrate composition, water depth, and current velocity.

Keywords:  unionid mussels, Mississippi River, dredge cuts, colonization, Pools 11 to 
22
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