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Wednesday, January 27 • 11:40am - 12:00pm
Time Warp: Examination of Age-0 Walleye Diets Reveals Foodweb Changes In Western Lake Erie Between 1990s and 2014

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AUTHORS: Dana Castle*, U.S. Geological Survey, Great Lakes Science Center; Carson Prichard, U.S. Geological Survey, Great Lakes Science Center; Ed Roseman, U.S. Geological Survey, Great Lakes Science Center; Robert Hunter, U.S. Geological Survey, Great Lakes Science Center; Chris Vandergoot, Ohio Department of Natural Resources; Mark Rogers, U.S. Geological Survey, Great Lakes Science Center, Lake Erie Biological Station; Kristen Hebebrand, Univeristy of Toledo Lake Erie Center; Kevin Keeler, Cooperative Ecosystem Studies Unit, Michigan State University and University of Toledo; Brian Schmidt, University of Toledo Lake Erie Center; Christine Mayer, University of Toledo Lake Erie Center; William Taylor, Center for Systems Integration and Sustainability, Department of Fisheries and Wildlife, Michigan State University

ABSTRACT: Walleye Sander vitreus play an important role as top predator in Lake Erie and provide valued ecological and economic benefits. Mid-lake rocky reefs and tributaries to western Lake Erie are primary walleye spawning sites and the western basin provides critical nursery habitat for age-0 fish. We supplemented a historic (1994-95) age-0 walleye diet dataset with collections during 2014 to determine how diets may have shifted in response to the recent proliferation of invasive species (e.g. Gobiidae, Bythotrephes). In 1994 and 1995, fish were collected using an ichthyoplankton net from early May until late June. Demersal juveniles were collected using a bottom trawl from June through October. In 2014, pelagic larvae were collected from May to June and demersal juveniles were collected in subsequent months using similar gear types as in the 1990s. In both time periods, preserved stomachs were analyzed to identify diet items. Zooplankton (copepods, large native cladocerans), dominated diets during the pelagic larval period in all years. Fish were important diet items in the 1990s in mid-June when age-0 walleye exceeded 20 mm TL, metamorphosed, and became demersal. Demersal fish collected in 2014 had diets composed of mostly fish, including shiners Cyprinidae, yellow perch Perca flavescens and the invasive Gobiidae, which proliferated the western basin of Lake Erie in the late 1990s. The invasive zooplankton, Bythotrephes, was also found in 2014 diets. Prevalence of fish in age-0 walleye diets increased with size in the 1990s, but not in 2014. Fish also appeared in diets in later months in 2014. Year-class strength in Lake Erie walleye is likely dependent on their first fall, therefore understanding how foraging and food web structure influence recruitment is critical to ensuring the sustainability of the walleye population in Lake Erie.

Wednesday January 27, 2016 11:40am - 12:00pm EST