mussels fishermen sought. The pearl-culture fishery required thick- 

 shelled mussels of the genera Amblema , Ouadrula , Pleurobema , and Mega - 

 lonaias (Cahn, 1949: 49, in Starrett, 1971: 267). The interest in 

 these mussel species is fortunate as some of those valued as pearl- 

 button stock, such as the ebony shell and yellow sand-shell, probably 

 were not available in quantities to sustain the increased harvests 

 brought by the pearl-culture industry. The Illinois catch from the 

 Mississippi River during 1965-1967 was comprised mostly of washboards 

 ( Megalonaias g.) (75-80%) and three-ridges (Amblema p.) (15-20%) (Lopinot, 

 1968: 8). 



The pearl-culture-related harvest did not last and during 1967 

 shell production dropped drastically (Table 7 ) . This reduction was the 

 result of the Japanese requiring larger shells and possible overharvesting 

 in 1966 (Lopinot, 1968: 19). During this period the market price paid 

 for shells was $40-60 per ton ($78-117 in 1977 dollars) (Nord, 1967: 

 187; Lopinot, 1967: 12). 



Effects of the Navigation System on the Mussel Fauna. The possible 

 effects that the navigation system has had on the mussel fauna of the 

 study reach are probably very similar to those outlined for the Illinois 

 River (see Illinois section) . The potentially adverse effects that the 

 navigation system could have on the mussel fauna of the Mississippi 

 River were recognized early when the Fisheries Service stated in their 

 March, 1930 bulletin that the proposed nine-foot channel would be detri- 

 mental to clams (Carlander, 1954: 48). 



Several biologists have stated that the Mississippi River dams 

 have slowed the current and facilitated deposition of sediment: 



The navigation dams have slowed down the current and 

 silt deposits have smothered many formerly productive beds 

 (of mussels). (Nord, 1967: 194) 



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