Diet Complexity of Lake Michigan Salmonids: Contrasting Trophic Indicators

Session: 57. - Advances in Understanding Nearshore Ecosystems in Great Lakes and Connecting Channels

Benjamin Leonhardt, Purdue University, [email protected]
Benjamin Turschak, Michigan Department of Natural Resources, [email protected]
Austin Happel, Colorado State University, [email protected]
Harvey Bootsma, University of Wisconsin-Milwaukee, [email protected]
Sergiusz Czesny, University of Illinois, Illinois Natural History Survey, [email protected]
Jacques Rinchard, The College at Brockport, State University of New York, [email protected]
Matthew S. Kornis, U.S. Fish and Wildlife Service, [email protected]
Charles R. Bronte, US Fish and Wildlife Service, [email protected]
Tomas Hook, Purdue University, Dept. Forestry and Natural Resources, [email protected]

Abstract

Salmon and trout in Lake Michigan have relied primarily on pelagic Alewife as forage since the 1950’s. However, various ecosystem changes have recently led some salmon and trout species to partially shift to other prey resources and thereby diversify their diets. A variety of methods (e.g., stomach content, fatty acid and stable isotope analyses) are available for indexing diets of salmon and trout and may separately quantify different aspects of prey consumption. Moreover, the level of agreement among different diet methods has not been fully quantified. Stomach content analysis provides a relatively straightforward method to index diets at a high taxonomic resolution; however prey in a fish’s stomach only reflect relatively recent foraging and may not adequately account for differential digestion and assimilation rates. Instead, other trophic indicators, such as stable isotopes and fatty acids, better reflect long-term resource use. To elucidate agreement of three trophic indicators and understand patterns of prey consumption of five Lake Michigan salmonid species, we quantitatively compared stomach contents, fatty acids, and stable isotope ratios simultaneously measured for individual salmonids. We compare and contrast how agreement among trophic indicators varies across the five species of salmonids and discuss implications for future diet analyses.

1. Keyword
isotope studies

2. Keyword
Lake Michigan

3. Keyword
salmon

4. Additional Keyword
fatty acids

5. Additional Keyword
diets