OTOLITH MICROCHEMISTRY AND STABLE ISOTOPIC COMPOSITION AS INDICATORS OF 
ENVIRONMENTAL HISTORY FOR MIDDLE MISSISSIPPI RIVER FISHES

Gregory W. Whitledge and John M. Zeigler

Fisheries and Illinois Aquaculture Center, Southern Illinois University, 
Carbondale, IL 62901-6511

Knowledge of environments used by fish throughout their life history is 
important for management and conservation of riverine fish populations and 
habitats.  Naturally occurring stable isotope and trace elemental markers in 
otoliths have emerged as powerful tools for determining natal origins and 
environmental history of fishes (including early life stages) in a variety of 
marine and freshwater environments.  Otoliths maintain a permanent record of 
chemical "signatures" from environments in which a fish has lived; 
associating otolith biochronology with changes in otolith stable isotopic and 
elemental composition enables retrospective description of environmental 
history for individual fish.  However, no studies have examined the 
applicability of this technique in large floodplain rivers in the U.S.  Our 
study evaluated otolith microchemistry and stable isotopic composition as 
tools for determining environmental history of fishes in the middle 
Mississippi and lower Illinois Rivers, their tributaries, and associated 
floodplain lakes.  Fishes were collected from 21 sites and water samples 
obtained from 26 sites during summer and fall 2006 and spring 2007.  Otolith 
and water samples were analyzed for stable oxygen isotopic composition (d18O) 
and concentrations of suite of trace elements; otoliths were also analyzed 
for d13C.  Results indicated that tributaries, floodplain lakes, and the 
Illinois and Mississippi Rivers have distinct isotopic and elemental 
signatures.  Tributaries on the Missouri and Illinois sides of the middle 
Mississippi River can also be distinguished by their elemental and isotopic 
fingerprints.  Otoliths reflected differences in water chemistry among large 
river, tributary, and floodplain lake habitats.  Results indicate that 
otolith microchemistry and stable isotope analyses can be applied to 
accurately determine natal origins and describe environmental history of 
fishes in the middle Mississippi and lower Illinois Rivers.

Keywords:  otolith chemistry, middle Mississippi River, tributaries, 
floodplain lakes, fish