Page 



Commercial Mussel Fishery — Mississippi River 45 



Historical Perspective 45 



Pre- and Post-Dam Mussel Harvests 45 



Species Composition Changes 49 



Economic Factors 52 



Recent Trends 53 

 Effects of the Navigation System on the 



Mussel Fauna 54 



Commercial Fishery — Illinois River 56 



Historical Perspective 56 

 Effects of the Navigation System on the 



Commercial Fishery 64 



Commercial Fishery — Mississippi River 67 



Historical Perspective 67 

 Pre- and Post-Construction Statistics on 



Harvests and Number of Fishermen, 1894-1970 68 



Changes in Species Composition, 1894-1970 73 

 Recent Trends in the Commercial Fishery 

 Economic Factors Affecting the Commercial 

 Fishery 



39 



Sport Fishery — Illinois River • 94 



Sport Fishery — Mississippi River 104 



Scientific Surveys of Fish Species Present in 

 1876-1903 and 1944-1971 in the Upper Mis- 

 sissippi River 

 Summary of Effects of the Nine-Foot Navigation 



System on Fish in the Upper Mississippi River 

 Effects of Increased Water Area and 



Reduced Discharge 117 



Effects of Dams on Fish Migration 119 



Effects of Winter Drawdowns 119 



Effects of Other Operation and Maintenance 



Activities - 121 



Wetland Vegetation 122 



Effects of Fluctuating Water Levels 122 



The Effects of Sedimentation and Turbidity 126 



Water Quality 129 



Upper Mississippi River 129 



Dissolved Oxygen 130 



Turbidity, Suspended Sediment, and Water 



Clarity 133 



111 



116 



