SEASONAL AND LOCATION EFFECTS ON THE GROWTH OF BLUEGILL, LEPOMIS
MACROCHIRUS, IN THE UPPER MISSISSIPPI RIVER.  

Joshua Fye and Michael Delong.   Large River Studies Center and
Biology Department, Winona State University, Winona, MN 55987.  

Two primary models have described trophic dynamics of large
rivers.  The flood pulse concept relies on the predictable,
annual inundation of the floodplain for much of the secondary
production in large rivers.  Predictable floods are typically a
spring event in temperate large rivers.  The riverine
productivity model emphasizes the role of instream primary
production in the generation of new biomass, thus making it more
a summer-fall process.  The objective of this study was to
determine if bluegill growth differed as a function of: (1)
whether fish were found in side channel or backwater habitats;
and (2) time of the year.  Fish were collected in early spring,
summer, and late fall with a boat electroshocker.  Length and
weight was measured for each fish and scales were removed. 
Scales from fish collected in the spring were used to establish
age classes.  Measurements were taken from the last annuli to the
outer edge of the scale on fish collected in the summer and fall. 
Measurements were made using an ocular micrometer.  Preliminary
analysis indicates greater growth in the last half of the year. 
Growth rates were similar for bluegills found in side channel and
backwater habitats, indicating growth occurs at about the same
rate in both habitats.  Data for largemouth bass and smallmouth
bass will be included with this presentation if time permits
completion of analysis.  

Keywords:  growth, fish, habitat, season, Mississippi River,
bluegill, Lepomis macrochirus