Appendix E continued. 



Results from both pools verified the commercial clammers' 

 reports (Table El) : 35-42% of the commercially valuable Amblema 

 plicata (three-ridge) and Megalonaias gigantea (washboards) had 

 died recently. Mortality in other species for which we had 

 adequate sample sizes (30 or more individuals) ranged from a low 

 of 9.8% for Leptodea fragilis (fragile papershell) to a high of 

 37.6% for Quadrula pustulosa (pimpleback) . Ms. Pamela Thiel, 

 Wisconsin Department of Natural Resources, conducted emergency 

 sampling in Pool 10 and found 20-40% of the mussels had died 

 recently (UMRCC 1983). 



We submitted samples of living but moribund individuals to 

 Fritz and to Richard Ruelle, Ecological Services Office, U. S. 

 Fish and Wildlife Service, Rock Island, Illinois. They in turn 

 submitted them to several laboratories for contaminant analyses. 

 According to both men, the lab results indicated no unusually 

 high concentrations of heavy metals or organic contaminants, 

 although background levels for freshwater mussels have not been 

 determined. Another possible cause for the die-off could be 

 biological — an outbreak of parasites or disease. 



Dr. John Nickum, Iowa Cooperative Fisheries Unit, Iowa State 

 University, is compiling information about the 1982-1983 mussel 

 die-off for the Upper Mississippi River Conservation Committee, 

 and a copy of Table El was mailed to him on 8 March 1984. 



In July 1985, another massive die-off of mussels appeared to 

 be in progress. Biologists were reporting meats floating in the 

 Mississippi River, and divers were finding shells with decayed 

 meats inside and live mussels which were gaping and too weak to 



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