RELATIONSHIP OF  HYDROLOGICAL  REGIME  TO  LARVAL  FISH/ZOOPLANKTON
PRODUCTION IN A MOIST SOIL MANAGEMENT UNIT

James A. Stoeckel 1, Kevin S. Irons 1, Ted E. Snider 2, and Kristy C. Boggs 1.
1 Illinois Natural History Survey, Long Term Rresource Monitoring Program, Havana 
Field Station, 704 North Schrader Avenue, Havana, IL 62644; and 2 Illinois State 
Water Survey, P.O. Box 697, Peoria, IL 61652.

Moist-soil units are typically managed to provide food for migrating waterfowl but 
may also provide valuable habitat for larval fish production.  From 1996-1998, we 
monitored larval fish and zooplankton production in Wasenza Pool of Lake 
Chautauqua (a floodplain lake of the Illinois River).  We hypothesized that flood height 
and duration would have a strong effect on larval fish/zooplankton dynamics.  At one 
extreme, extended flooding may allow for high initial fish production while at the 
same time suppressing zooplankton production via continual flushing by zooplankton-
poor, sediment-rich river water.  At the other extreme, if levees are not overtopped, 
limited access to the lake by adult fish may result in low spawning success, but 
zooplankton production may be high.  In 1996 and 1998, the Wasenza Pool levees 
were overtopped almost continuously from May through July.  In 1997 water levels 
never rose above flood stage during this same time period.  Preliminary analysis 
indicated increased production of larval fish in the high-water years of 1996 and 
1998.  Varied hydrological regimes may result in trade-offs, with fewer fish but better 
food resources being produced in low-water years, and higher (initial) fish production 
but reduced food resources during high water years.
 
Keywords:  larval fish, zooplankton, floodplain, hydrology, Illinois River
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