A COMPARISON OF TWO ELECTROFISHING GEARS USED FOR FISH MONITORING ON THE 
ILLINOIS RIVER.

Michael A. McClelland, Mark A. Pegg, Kevin S. Irons, T. Matt O’Hara, and 
Thad R. Cook.  
Illinois Natural History Survey, Illinois River Biological Station, 704 N. 
Schrader Ave, Havana, Illinois 62644.

The fish population of the Illinois River has been monitored since 1957 through 
the Long Term Illinois River Fish Population Monitoring Program (LTEF).  
Throughout the project a standard approach using three-phase AC electrofishing 
gear has been used to collect fish at as many as 28 sites within the system.  In 
2001 we began “shadowing” selected sampling sites with pulsed DC electrofishing 
gear used by the Long Term Resource Monitoring Program (LTRMP) in an effort to 
evaluate differences between the two collection methods.  Electrofishing runs 
were standardized by length and a total of 24 runs provided comparisons of 12 
runs for each gear.  Our objectives were to determine differences between the 
gears in fish catch rates across total catch, species diversity, and size 
classes to potentially identify a correction factor that may be useful in 
comparing the two electrofishing approaches.  Overall, total catch was 
significantly higher (P < 0.005) for DC electrofishing where 4368 total fish 
with a mean of 364.0 fish per site were collected while 1423 total fish and a 
mean of 118.6 fish per site were collected by AC electrofishing.  Species 
richness was significantly higher (P < 0.023) for DC electrofishing with 50 
total species and a mean of 22.3 species per site collected compared to 38 total 
species and a mean 15.5 species per site for the AC electrofishing.  Size 
classes, broken into 100 mm groups, also had significantly higher catches (P < 
0.001) for DC electrofishing within the 100, 200, 400, and 500 mm groups. Our 
analyses show collections from the DC electrofishing gear are significantly 
higher for total catch and species richness, but a clear and consistent pattern 
between the two gears was not evident.  Therefore, caution must be taken when 
attempting to compare fish community composition and structure information 
between these gears.

Keywords:  electrofishing gear, fish collection, species richness, fish 
community composition and composition