LARVAL FISH PRODUCTION IN A MOIST SOIL MANAGEMENT UNIT

Kevin S. Irons, Timothy M. O'Hara, James A. Stoeckel, and K. Douglas
Blodgett
Illinois Natural History Survey, Long Term Resource Monitoring Program
(LTRMP) La Grange Reach Field Station, 704 N. Schrader Ave., Havana, Illinois
62644 USA

Moist soil management units usually are manipulated to provide food for
migratory waterfowl; however, if prudently managed, it appears some of these
same units may be used for production of larval fish. Today, watery sediments in
permanently wetted areas of backwaters and management units provide poor
anchorage for rooted plants and are easily resuspended by wind-generated waves,
thereby increasing turbidity levels.  Such substrates are usually unsuitable
spawning and nesting habitats for many native fishes such as bass and other
sunfish.  Dewatering and drying of these substrates, as once occurred naturally
during late summer low-flow periods and today often are accomplished in
management units, consolidates sediments and facilitates plant production. 
Moist soil and rooted aquatic plants can reduce wind-generated waves and
further stabilize sediments, which in turn reduce sediment resuspension and
improve water quality.  Substrate stabilized by vegetation provides better
spawning and nesting habitat for many fish species and increased cover for larval
fish.  While drawdowns can have beneficial impacts on both plants and animals,
timing is critical for both groups.   During 1996 and 1997 we monitored larval
fish production and escapement from Wasenza Pool of Lake Chautauqua, a
backwater lake of the Illinois River and the site of a Habitat Rehabilitation and
Enhancement Project of the Environmental Management Program for the Upper
Mississippi River.  The unit is part of a National Fish and Wildlife Refuge and is
managed by the U.S. Fish and Wildlife Service primarily for production of moist
soil plants for migrating waterfowl.  During 1996 we used electroshocking and
fyke nets to sample adult fish in the pool and collected 2,542 fish representing 31
taxa which included one hybrid cross. In 1997 we collected 2,036 fish
representing 39 species and three hybrid crosses.  We used light traps and
ichthyoplankton nets to sample larval fish.  In 1996 we collected 37,126 larval
fish representing 16 taxa; Clupeidae (shad/herring) dominated the larval fish
catch (87%).  In 1997 Clupeidae accounted for 91% of a total of 14,587 larval
fish from 11 taxa.  Standing stock estimates for the 970-hectare pool ranged from
24 million to 748 million larval fish in 1996 and from 8 thousand to 18 million in
1997. Water levels in the unit varied significantly between the two years with
higher levels during 1996. In 1996, during managed dewatering which started 28
June, we sampled fish as they escaped from the unit; we collected 39,678 fish of
34 taxa and we estimated 18 million to 27 million fish escaped to the Illinois
River.  It appears that during some years, this moist soil management unit may be
used for production of larval fish with only relatively minor modifications in
operating procedures.  

Keywords:  larval fish, backwater lake, moist soil management, multiple use,
Illinois River


Kevin S. Irons, LTRMP La Grange Station, 704 N. Schrader, Havana, Illinois
62644, phone:309-543-6000, fax:309-543-2105, email kevin_irons@usgs.gov
preference=poster