EFFECT OF BACKWATER LAKE MANAGEMENT ON HABITAT FOR RIVERINE FISH

Thomas R. Timmermann, Chad R. Dolan, and John H. Chick

Great Rivers Field Station, Illinois Natural History Survey, Brighton, IL 61012

      Backwater lakes are critical components of large river ecosystems 
providing nursery, refuge and feeding grounds for many fishes. Due to recent 
alterations in the hydrology of large river systems, many of these backwaters 
have been degraded, filling in with sediment and losing large amounts of aquatic 
vegetation. In Swan Lake, there have been significant alterations made to the 
lake to combat the sedimentation and loss of vegetation. Major alterations 
include construction of a levee, dividing the lake into units, allowing for 
different backwater lake management strategies to be implemented in the 
different units. In the summer and winter of 2005 we examined fish diets to 
determine if a particular management strategy provided for a more suitable 
foraging habitat.  We observed a difference in the total calories consumed 
between units for Crappie (both Pomoxis negromaculatus and P. annularis) for the 
summer and winter.  Examination of the diet of Common Carp (Cyprinus carpio) 
revealed that the fish from one unit had 25% empty stomachs while the other had 
75% empty.  While the overall prey selection did not vary, the total calories 
consumed varied significantly.  This led us to examine the effect of extremely 
flocculent sediments on the vertical distribution of invertebrates.  Core 
samples taken from the Middle Unit revealed that the majority of the prey was 
available within feeding depths, while samples from the Lower Unit showed that 
the majority of the invertebrates were below the feeding depth.

Keywords:  backwater lakes, water level manipulation, diet, Cyprinus carpio, 
macroinvertebrates