Electrofishing survey 30 May 1991 Page 4 



Job 3. 1990 Electrofishing 



Water levels in the Illinois River were high much of the summer (Figure 1). By 7 

 September, water levels in the upper river were close to the mean low river stage, so we 

 began electrofishing that part of the river first. AH 26 stations on the Illinois River and 

 the one station on the Mississippi at Brickhouse Slough were sampled by 28 September 

 (Figure 2 and Table 1). 



Small fish which could not be positively identified in the field were preserved in 

 formalin and brought back to the Laboratory. They were tranferred to alcohol and 

 identified during the winter. 



Several interesting observations were made during the course of the field work. 

 Yellow perch were extremely rare in collections made years ago, but this year 2 were 

 captured at Ballard Island Chute. Most of the goldfish had the "wild type" bronze 

 coloration, rather than the white, black, or bright orange characteristic of the "dime 

 store" varieties. The bright colors are probably rapidly selected out of the population 

 now by predators, whereas the predators were virtually absent from the upper river 15 

 years ago. We saw some "knothead" carp, but the incidence is much lower than formerly. 

 Erosion of fins and barbels on the ventral side of bottom-dwelling fishes is still a 

 problem, indicating some sort of stressor associated with the sediment. An anomalous 

 collection was made at Hennepin Island Chute, where only 2 fish were taken in 0.33 

 hours of electrofishing. The equipment seemed to be working properly, and the 

 abundance of fish in collections made at the stations above and below Hennepin were 

 about as expected. The generator labored when the electrodes were switched on (as it is 

 supposed to under demand) and the voltages to each electrode were in the normal range. 

 It is possible that fish had abandoned the chute because of some noxious material. No 

 dead fish were observed on the shoreline. 



