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CONFERENCE SCHEDULE UPDATES & CHANGES: As a result of the prolonged government shutdown, we experienced a number of cancellations and changes to the schedule. Cancellations and changes are listed here (as of January 26, 2019). 
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Monday, January 28 • 3:40pm - 4:00pm
(SYMPOSIA-04) Diet and Niche Overlap of Lake Michigan Piscivorous Fishes as Revealed by Stable Isotopes

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AUTHORS: Ben Turschak, Michigan Department of Natural Resources; Harvey Bootma, UW-Milwaukee; Chuck Bronte, U.S. Fish and Wildlife Service; Sergiusz Czesny, University of Illinois; Tomas Hook, Purdue; Matt Kornis, U.S. Fish and Wildlife Service; Ben Leonhardt, Purdue; Jacques Rinchard, SUNY-Brockport

ABSTRACT: In the past several decades, the Lake Michigan ecosystem has experienced significant changes at all levels of the food web including major declines in pelagic forage fish biomass. To some degree, loss of pelagic forage has been offset by the invasion of the benthic Round Goby. Several piscivorous species including Lake Trout, Brown Trout, and Burbot have taken advantage of this novel prey source while others such as Chinook and Coho Salmon continue to rely on Alewives and other pelagic forage.  We explored the trophic structure, diet, and potential for niche overlap of Lake Michigan piscivores from 2014-2016 using stable C and N isotopes. To estimate diet proportions among species, Bayesian mixing models were used. Region and year were used as fixed effects with total length as a continuous covariate. Isotopic niche overlap was assessed by fitting Bayesian ellipses to the data and measuring overlap among species. Regional and interannual variability in trophic structure and diet with corresponding changes in niche overlap were observed. Greatest niche overlap corresponded with dependence on Alewife whereas predators that took advantage of other prey sources including Round Goby, and terrestrial invertebrates exhibited lower probability of niche overlap. Degree of overlap also appeared to decrease corresponding to availability of alternative prey sources or reduced alewife abundance.

Monday January 28, 2019 3:40pm - 4:00pm EST