As specific riverine habitats were reduced following impoundment, 

 one would expect changes in the fish species composition. In a pre- 

 vious section, we noted that the species composition in the upper Mis- 

 sissippi River has remained almost the same for the past 100 years. 

 However, 10 forage species were lost in the period 1903-1944 based on 

 a comparison of pre- and post-construction scientific surveys. These 

 included the mudminnow, Ozark minnow, blackchin shiner, blacknose 

 shiner, redfin shiner, steelcolor shiner, Southern redbelly dace, lake 

 chubsucker, freckled madtom, and crystal darter. An examination of 

 fish habitat requirements (Trautman, 1957) revealed that most of these 

 species preferred a clear-water environment with sand or gravel bottoms 

 and appreciable current. The mudminnow was found to require a soft 

 bottom, but undisturbed clear water (Trautman, 1957: 205). Smith (1971: 

 9) stated that the mudminnow, lake chubsucker, and blackchin shiner 

 ranges in Illinois shrunk most likely as a result of floodplain drain- 

 age of lakes and sloughs marginal to large rivers. 



In addition to the loss of certain forage species, 3 commercial 

 species (pallid sturgeon, river redhorse, and brown bullhead) and a 

 predatory species (alligator gar) virtually disappeared from the 

 upper Mississippi River between 1903 and 1944. The pallid sturgeon was 

 considered rare in the upper Mississippi River in the period 1876— 

 1903 and was thought to prefer a swift-water habitat (Forbes, 1920: 

 29). In a 1944-1946 survey, Barnickol and Starrett (1951: 290) found 

 that this species only occurred in the Mississippi near its confluence 

 with the Missouri. The river redhorse was described as intolerant 

 of turbidity and siltation (Trautman, 1957: 262). The brown bullhead 

 was also considered sensitive to turbid waters (Trautman, 1957: 426). 

 In 1944-1946 collections, the alligator gar was found predominantly in 

 the unpooled section of the Mississippi River between Alton, Illinois 

 and Caruthersville, Missouri (Barnickol and Starrett, 1951: 320). 



As described above, most of the fish species which disappeared from 

 the upper Mississippi River required clear, fast-flowing water environ- 

 ments with sand or gravel bottoms and were intolerant of siltation and 



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