A Diet Study of Brook And Brown Trout
Inhabiting Three Streams


Renell Simrau
School of Science and Natural Resources
Lake Superior State University

Abstract:	Brook trout (Salvalinus fontinalis) and brown trout (Salmo trutta) were
collected from three streams in northwestern Gladwin county, the Sugar River, Cedar
River, and Stone Creek, during the summer of 1996. 5 brook trout were caught in the
Cedar River and 35 in Stone Creek. 13 brown trout were caught in the Cedar River, 15
in the Sugar River, and I from Stone Creek. These rivers were similar in substrate,
riparian vegetation and temperature. The fish were collected by hook and line, recording
weights, lengths, species, and location. The gut contents were preserved for subsequent
analyses which consisted of sorting into food type categories, bloning dry, and weighing
on a four point balance. Each weight was then recorded in a spreadsheet. The objectives
of this study was to 1) note any similarities or differences in diet between brook and
brown trout; 2) note any similarities or differences in diets between streams; 3) determine
if brook trout are selectively feeding on certain food types using Ivlev's Electivity Index;
and 4) examine potential niche overlap using Schoener's Index. Brown trout collected in
the Sugar River had proportionally more minnows, orthropods, isopods, coleoptera and
gastropods than those in the Cedar River, which had more decapods, megaloptera,
millipedes, trichoptera and ephemeroptera. Brook trout in Stone Creek had more diet
variety than those in the Cedar River, which had diet restricted to ephemeroptera,
plecoptera, amphipods, diptera, and millipedes. The Ivlev Index showed that brook trout
selectively feed on nine different orders. This index is used to express electivity relative
to ambient food type densities. The Schoener's Index gave a value of .53 indicating that
there is a potential niche overlap between brook and brown trout. Due to a small sample
size rigorous tests could not be done, however, noticeable trends are apparent in the diet
of both brook and brown trout.


References

Cummins, K. W. and R. W. Merrit. 1996. Aquatic Insects of North America. 6th ed.
Kendall/Hunt. Dubuque, Iowa.
Wootton, Robert J. 1990. Ecology of Teleost Fishes. Series I. Chapman and Hall, New
York,NewYork. p43.