Diet Complexity Of Lake Michigan Salmonines

Session: Exploring Predator-Prey Relationships and Feeding Ecology in the Great Lakes (3)

Benjamin Leonhardt, Purdue University, bleonha@purdue.edu
Harvey Bootsma, University of Wisconsin-Milwaukee, hbootsma@uwm.edu
Sergiusz Czesny, University of Illinois, Illinois Natural History Survey, czesny@Illinois.edu
Austin Happel, John G. Shedd Aquarium, ahappel@sheddaquarium.org
Matthew Kornis, U.S. Fish and Wildlife Service, matthew_kornis@fws.gov
Jacques Rinchard, The College at Brockport, State University of New York, jrinchar@brockport.edu
Benjamin Turschak, Michigan Department of Natural Resources, TurschakB1@michigan.gov
Tomas Hook, Purdue University, Dept. Forestry and Natural Resources, thook@purdue.edu

Abstract

In Lake Michigan, the introduction of invasive species (e.g., zebra and quagga mussel, Dreissena polymorpha, D. bugensis; round goby, Neogobius melanostomus) and reduced nutrient loading has resulted in changes in production pathways and community composition over the past two decades. As a result, abundances of many forage fish have declined, including alewife (Alosa pseudoharengus) which have historically supported the five dominant salmonid species of Lake Michigan (brown trout, Salmo trutta; Chinook salmon, Oncorhynchus tshawytscha; Coho salmon, Oncorhynchus kisutch; lake trout, Salvelinus namaycush; rainbow trout, Oncorhynchus mykiss). With these ecosystem changes, there is uncertainty as to the extent different species of salmonids will transition to alternative prey items (e.g., round goby). We investigated the diet complexity of Lake Michigan salmonids by evaluating stomach content composition, diet diversity, and lengths of alewife consumed. Stomachs collected in 2015 and 2016 in Lake Michigan revealed that Chinook salmon almost exclusively consumed alewife and had a lower diet diversity compared to the other four species, which consumed round goby (brown trout and lake trout), aquatic invertebrates (Coho salmon), and terrestrial invertebrates (rainbow trout) in addition to alewife. Additionally, salmonid species appeared to consume the entire size range of alewife that were available to them despite year to year changes in alewife length availability. Due to their

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