ENTRAINMENT MORTALITY OF ADULT FISH CAUSED BY COMMERCIAL TOWBOATS
IN THE UPPER MISSISSIPPI RIVER SYSTEM.  

Steve Gutreuter 1, John M. Dettmers 2, and David H. Wahl 3.   1 U.S.
Geological Survey, Upper Midwest Envrionmental Sciences Center,
La Crosse, WI 54603;  2 Illinois Natural History Survey, Lake
Michigan Biological Station, Zion, IL 60099; 3 Illinois Natural
History Survey, Kaskaskia Biological Sciences, Sullivan, IL
61951.  

Many large rivers are used as transportation corridors for barges
and other large commercial vessels.  The propellers of towboats
that push barges may have diameters exceeding 2.5 m and can
entrain and kill adult fish.  We developed a method to estimate
entrainment mortality of large riverine fishes and applied it to
the Mississippi and Illinois rivers.  Our estimation method
combined quantitative trawl sampling and a hydrodynamic model of
the diffusion of entrained water in river channels.  Gizzard shad
Dorosoma cepedianum was the only killed species detected in
specialized entrainment sampling, and our estimate of entrainment
mortality is 9.5 fish per km of towboat travel with an 80%
confidence interval of 3.8-22.8 fish/km.  We also conducted
ambient bottom trawling to estimate abundance of live fish, and
observed additional recently killed gizzard shad, shovelnose
sturgeon Scaphyrhynchus platorhynchus and smallmouth buffalo
Ictiobus bubalus.  We developed ancillary estimates of
entrainment mortality rates of shovelnose sturgeon and smallmouth
buffalo based on the estimate for gizzard shad and on the
distribution of numbers of killed fish of each species in the
combined ambient and entrainment samples.  For shovelnose
sturgeon and smallmouth buffalo, we estimate that 2.4 fish of
each species are killed per km of towboat travel with 80%
confidence intervals of 0-6 fish/km.  Because total annual tow
distances are large, entrainment cannot be eliminated as an
important source of mortality for gizzard shad, shovelnose
sturgeon and smallmouth buffalo.    

Keywords:  mortality, commercial navigation, entrainment,
estimation, modeling, fish, estimation, barges, towboats,
Illinois River, Mississippi River