elucidate, patterns exhibited by particular species, because the total 



abundance can remain constant while some species increase and others 



decline. 



Temporal distribution 



Table 30 shows the average number of fish of all species taken per 

 30 minutes of electrof ishing in the years 1959 through 1974. The 

 greatest number of fish was taken in 1962 from Peoria Pool. This peak 

 in numbers is attributable to a peak in the abundance of one species, 

 gizzard shad, due to unknown causes. More fish were taken from 

 Marseilles Pool in the years 1960-1963, than in subsequent years. Again, 

 this peak is primarily attributable to the abundance of one species, 

 goldfish, although more largemouth bass, bluegills, green sunfish, and 

 white crappie occurred in Marseilles Pool in 1960, than in the years 

 immediately following. 



Table 31 shows the average weight of fish of all species taken per 

 30 minutes of electrof ishing from 1959 through 1974. No consistent pat- 

 terns are evident, except that for five of the six years, 1960-1965, 

 more pounds of fish (primarily carp) were taken from Starved Rock Pool 

 than from the pools immediately above or below it, while just the re- 

 verse relationship has existed since 1965. Within memory of several 

 residents along the Fox River, fishing has gone from excellent to poor. 

 It is likely that the lower end of the Fox River may once have supplied 

 a haven for fishes, some of which found their way into the Illinois 

 and the electrof ishing collections. Now it appears that fish are no 

 longer recruited to Starved Rock Pool from the Fox River. 



When one looks at the distribution of certain species of fish 

 through time (Table 32) a consistent and interpretable pattern is evi- 

 dent. Largemouth bass, black crappie, and white crappie populations 

 declined from 1962 through 1965, a drought period when water levels 

 were low. The maximum numbers of these three species were taken in the 

 fall of 1973, following a period of high-water levels from 1971 through 

 the spring of 1973. In addition, the lowest numbers of bluegill and 



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