A COMPARISON OF FISH COLLECTIONS USING RANDOM AND FIXED 
SITE SAMPLING DESIGNS ON THE ILLINOIS RIVER
 
Michael A. McClelland and Thad R. Cook
Illinois Natural History Survey, Illinois River Biological Station, 704 N. Schrader Ave., 
Havana, IL 62644

The Illinois River fish population has been monitored by the Illinois River Biological 
Station since1957 through a long-term electrofishing program (LTEF).  Patterns in fish 
species composition and abundances along six reaches of the Illinois River are examined 
annually using a fixed site sampling design.  In 2005 a series of random sites were added 
to the LTEF sampling regime to supplement current monitoring efforts.  Current protocol 
for fixed site sampling allows for one hour electrofishing runs at 27 sites within the six 
LTEF reaches, while random sampling was accomplished via 30 minute electrofishing 
runs at 32 sampling sites in all six LTEF reaches.  A total of 12,120 fish were collected 
between both sampling designs with 7490 fish collected by fixed sites and 4630 fish 
collected by random sites.  Mean catch per hour were similar between both designs 
overall (292.0 for fixed sites, 294.6 for random sites) and no significant differences 
(P=0.96) were found between the two designs over all reaches and within reaches 
(P=0.15).  Species diversity for both designs was also similar; a total of 62 species were 
collected with numbers ranging from 56 species and two hybrids collected through fixed 
sampling and 54 species and one hybrid collected by random sampling.  Community 
analysis illustrated further similarity in catches between the sampling techniques and both 
were capable of revealing upstream to downstream differences in species composition.  
Although few differences were discovered in the catches between the two designs, 
collections did reveal nine species unique to the fixed site design with six species unique 
to random sampling.  Random sampling also collected two species new to the LTEF 
program where fixed site sampling only collected one new species.  While results 
between these two techniques proved to be very similar in catch, the scientific benefits of 
supplemental random sampling may prove valuable in the future for the LTEF program.

Key words: Illinois River, electrofishing, sampling design, fish population, fish 
community