The dams have also restricted the movements of at least one fish, 

 the skipjack herring ( Alosa chrysochloris ) , which serves as host for 

 the formerly important ebony shell mussel. According to Barnickol 

 and Starrett: 



The scarcity of the skipjack in the collections of the 

 1944 survey tends to indicate that this fish may have been 

 affected by the locks and dams constructed below Keokuk 

 . . . (1951: 323) 



The restriction of this fish, which is uncommon in the study reach, has 

 adversely affected the ebony shell population. It is possible that 

 restrictions of the movements of other species of fish which serve as 

 mussel hosts have reduced mussel populations (Coker, 1914: 8; Ellis, 

 1931: 6; Parmalee, 1967: 13). 



Dredging, deposition of spoil, and barge traffic might have detri- 

 mental effects like those already described for the Illinois River. Be- 

 cause the Illinois is narrower, shallower, and has a predominantly 

 mud, rather than sand bottom, the effects of boat traffic may be more 

 pronounced in the Illinois than in the Mississippi. 



55 



