TEMPORAL TRENDS OF THE DIETS OF FISH IN THE OHIO RIVER USING STABLE ISOTOPES

James M. Hofmann1, Michael D. Delong1, and James H. Thorp2
1Large Rivers Studies Center, Biology Department, Winona State University, 
Winona, MN 55987. 
2Kansas Biological Survey and Department of Ecology and Evolutionary Biology, 
University of Kansas, Lawrence, KS 66047

      Most large rivers throughout the world have been heavily impacted by human 
activity for a century or more. These long-term disturbances make it difficult 
to determine the extent of change from one activity. This study examines the 
changes in nitrogen (Delta15N) and carbon (Delta13C) stable isotopes of fish 
from the Ohio River over the past century. During this time, the Ohio River was 
subjected to organic pollution, introduction of non-native species, and the 
construction of navigation dams. Museum specimens, which will allow us to look 
at the isotope levels before and after the disturbances, were obtained from 
different museums around the country. Muscle tissue samples were dried at 60°C 
for 48 hr, ground into a fine homogenous powder, and 1.5 to 2.0 mg of the ground 
sample was placed in tin capsules, and shipped to Kansas State University for 
stable isotope measurements. Preliminary results show that Delta15N remains 
relatively the same over the past century. Delta13C decreases in planktivores 
and piscivores. Omnivorous fish have an increased level of Delta13C. This 
increase of Delta13C may be caused by the construction of the multiple 
navigation dams on the river. Navigation dams increase near shore productivity 
and a shift toward benthic food sources. Consumers will also shift toward 
benthic sources from increased competition caused by the introduction of zebra 
mussels to the Ohio River in the early 1990’s. 

Keywords: Ohio River, nitrogen isotope, fish diets, carbon, carbon isotopes, 
disturbance