12. In 1963, the condition factor of carp, a commercial species, 

 was substantially better in the study reach than in upstream pools, 

 probably because more food items, such as fingernail clams, were avail- 

 able on the bottom in the study reach. Fingernail clams and snails had 

 been eliminated from upstream reaches in the 1950' s, apparently due to 

 some upstream source of toxicity. Between 1963 and 1975, the condition 

 factor of carp declined in the Illinois River as a whole, and the declines 

 were relatively greater in the study reach, so that differences in carp 

 condition in the study area and upstream areas are not as great as 

 formerly. Boat traffic and dredging may affect commercial species of 

 fish and the organisms on which they feed. 



13. The mussel fishery in the study area of the Illinois River 

 declined due to pollution and overharvesting prior to completion of the 

 9-foot navigation system. The increasing sediment input from tribu- 

 tary streams, the dams associated with the 9-foot channel, and the 

 decrease in Lake Michigan Diversion may have affected the mussel fauna 

 by reducing the current velocity and increasing sedimentation in some 

 areas. Dredging operations to maintain the navigation channel can 

 destroy mussel beds. The increase in boat traffic which resulted from 

 construction of the 9-foot channel has probably affected mussels. 

 Barges resuspend bottom sediments and temporarily draw water away from 

 shallow areas as they pass. Large pleasure boats and barges produce 

 wave wash along the shores. All these disturbances can adversely 

 affect mussels in the Illinois River. 



14. We were not able to find any information documenting historical 

 changes in mussel populations in the study area of the Mississippi. 

 Navigation dams in other reaches of the upper Mississippi River have 

 slowed the current and facilitated deposition of sediment, with 

 adverse effects on mussels such as yellow sand-shells ( Lampsilis ano- 

 dontoides ) . Movements of fish which serve as mussel hosts may have 



been impeded by dams. Dredging, deposition of spoil, and boat traffic 

 may have detrimental effects as described above for Illinois fishes. 



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