in Figure 3. Chillicothe Island Chute is an area of prime largemouth 

 bass habitat in Peoria Pool. Midsummer oxygen levels were at 35 percent 

 saturation or below four years out of the eight-year period from 1963- 

 1970. Since the May-August water levels at Peoria did not fluctuate 

 greatly from 1963 through 1970, the decline in the largemouth bass popu- 

 lation is probably attributable to low oxygen levels, perhaps acting in 

 combination with other stresses, such as the presence of toxicants. 

 Spatial distribution 



Tables 33 and 34 show the numbers and pounds of fish of selected 

 species taken in the various pools of the river during the period 1959- 

 1974. 



The following species were more numerous in the two middle pools 

 of the river, LaGrange and Peoria Pools, which have the most connecting 

 lake acreage, than in the other pools: gizzard shad, carp, river carp- 

 sucker, smallmouth buffalo, bigmouth buffalo, black buffalo, yellow bull- 

 head, green sunfish, bluegill, largemouth bass, white crappie, black 

 crappie, and freshwater drum. The bottomland lakes and backwaters 

 provide fish habitat and an invertebrate fauna which supplies food for 

 many fish species. Fish produced in areas lateral to the river are 

 recruited to the river, where they show up in the electrof ishing col- 

 lections. 



The following species showed a trend of increasing abundance in 

 the downstream direction, away from Chicago, with the largest number 

 occurring in Alton Pool: shortnose gar, bowfin, goldeye, mooneye, 

 channel catfish, flathead catfish, white bass (Table 33). Bowfin ap- 

 parently have always been more abundant in the southern part of Illinois 

 than in the northern part (Forbes and Richardson, 1908) . Goldeye and 

 mooneye both appear to be more common in the Mississippi than in the 

 Illinois, and both species probably enter the Illinois from the 

 Mississippi. In 1974, goldeye were taken only from Marseilles Pool and 

 mooneye only from Peoria Pool, so these fish may have run up the 

 Illinois during the high flows of 1971-1973. Other factors which may 

 influence the distribution of fishes whose populations increase in the 



38 



