Diet and niche overlap of Lake Michigan piscivorous fishes as revealed by stable isotopes

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

Benjamin Turschak, Michigan Department of Natural Resources, TurschakB1@michigan.gov
Harvey Bootsma, University of Wisconsin-Milwaukee, hbootsma@uwm.edu
Matthew Kornis, U.S. Fish and Wildlife Service, matthew_kornis@fws.gov
Charles R. Bronte, US Fish and Wildlife Service, charles_bronte@fws.gov
Sergiusz Czesny, University of Illinois, Illinois Natural History Survey, czesny@Illinois.edu
Brandon Gerig, Northern Michigan University, bsgerig@gmail.com
Tomas Hook, Purdue University, Dept. Forestry and Natural Resources, thook@purdue.edu
Benjamin Leonhardt, Purdue University, bleonha@purdue.edu

Abstract

The Lake Michigan ecosystem has experienced changes at all levels of the food web including major declines in pelagic forage fish biomass. Loss of pelagic forage, especially Alewife, has been somewhat offset by alternative prey such as Round Goby or terrestrial invertebrates. We explored the trophic structure, diet, and potential for niche overlap of Lake Michigan salmonines from 2014-2016 using stable C and N isotopes. Bayesian mixing models were used to estimate diet proportions among species while considering region, year, and total length as covariates.  Bayesian ellipses described isotopic niche area and overlap among species. Regional and interannual variability in trophic structure and diet were observed for some species with corresponding changes in niche overlap. Greatest niche overlap corresponded with dependence on Alewife, but some salmonines (e.g., Lake Trout, Brown Trout, Steelhead) also took advantage of other prey including Round Goby and terrestrial invertebrates and thus exhibited larger niche area with lower overlap. Inter-annual variation in isotopic niche area and overlap also corresponded with availability of preferred Alewife size classes (large for Lake Trout and small for others). These results will help fisheries managers distinguish the species most vulnerable to declines in pelagic forage from those that may be resilient.