SPORTFISH TRENDS IN THE LA GRANGE REACH OF THE ILLINOIS RIVER, 1994-2006

Nerissa N. Michaels, Greg G. Sass, and Kevin S. Irons

Illinois River Biological Station, Illinois Natural History Survey, 704 North 
Schrader Avenue, Havana, Illinois  62644

      The Illinois Natural History Survey’s, Illinois River Biological Station 
has been monitoring fish communities on the La Grange reach of the Illinois 
River as part of the Long Term Resource Monitoring Program (LTRMP) since 1990.  
To date, we have collected 1,375,867 fish comprising 90 native species, 9 native 
hybrids, 9 exotics, and 3 exotic hybrids.  Anecdotal evidence from our 
collections and recreational angler accounts suggest a decline in largemouth 
bass Micropterus salmoides abundances in the La Grange reach.  We used LTRMP 
data from 1994-2006 to test for abundance changes in six common sportfishes.  In 
addition, we examined several abiotic and biotic variables to explain potential 
change. We limited our data analysis to 1994-2006 because of changes in LTRMP 
protocols and unstable river conditions due to the major flood of 1993.  We used 
linear regression to test for changes in catch-per-unit effort (CPUE) of black 
crappie Pomoxis nigromaculatus, bluegill Lepomis macrochirus, channel catfish 
Ictalurus punctatus, largemouth bass, white bass Morone chrysops, and white 
crappie P. annularis among three selected habitats (contiguous backwater-
shoreline, main channel border-unstructured, and side channel border) across 
years. Our results indicated that all species CPUE from combined strata were 
below their respective means and were recently at their lowest, excluding 
bluegill, during the 13 year period.  We observed significant decreases in black 
crappie (P = <0.001) and largemouth bass (P = 0.04) CPUE for all strata 
combined, while black crappie, bluegill, largemouth bass, and white crappie 
showed significant decreases in side channel border habitats (all P < 0.025).  
Channel catfish and white bass CPUE showed no consistent patterns among habitats 
and over time. Our results suggest that the centrarchid fish species assemblage 
of the La Grange reach of the Illinois River may be decreasing due to changes in 
river conditions; specifically, variability in side channel border habitats.  
These unknown changes in habitat appear to have larger effects on fish species 
with nest-guarding life histories compared to alternative spawning strategists.  
The establishment of Asian carp in the Illinois River may have additional, 
compounding negative effects on centrarchid abundances through competitive 
interactions.

Keywords:  Centrarchidae, Illinois River, La Grange reach, Long Term Resource 
Monitoring Program (LTRMP), sportfish