**ABSTRACT NOT FOR CITATION WITHOUT AUTHOR PERMISSION. The title, authors, and abstract for this completion report are provided below. For a copy of the full completion report, please contact the author via e-mail at erin.dunlop@ontario.ca or via telephone at 705-755-2296. Questions? Contact the GLFC via email at frp@glfc.org or via telephone at 734-662-3209.**

Evaluation of changes in lake whitefish feeding habits

Erin S. Dunlop^1,2 and Michael D. Rennie^3,4

¹Aquatic Research and Development Section, Ontario Ministry of Natural Resources, 2140 East Bank Drive, Peterborough ON, K9J 7B8

²Environmental and Life Sciences Graduate Program, Trent University, Peterborough ON, K9J 7B8

³Fisheries and Oceans Canada, Freshwater Institute, 501 University Crescent, Winnipeg MN, R3T 2N6

4Department of Biological Sciences, University of Manitoba, Winnipeg MN, R3T 2N6

May 2013

ABSTRACT:

We found evidence of wide-scale shifts in lake whitefish growth, depth-of-capture, and feeding habits in response to establishment of dreissenid mussels. Since dreissenid mussel establishment, lake whitefish growth rates have declined markedly, depth-of-capture as evidenced by agency netting data has become shallower at several locations, and lake whitefish are making use of more nearshore diets as is indicated by stable isotope trends. The shifts we observed in locations where dreissenids occur are in sharp contrast to those observed in Lake Superior where established populations of dreissenids do not exist. An analysis of benthic invertebrate samples collected along a depth gradient from several locations suggests that underlying trends in the depth dependence of isotope signatures appear universal within the Great Lakes. Down core trends in isotope signatures of sediments reveal a general enrichment in delta C13 and depletion of delta N15 over the past couple of decades, the same time period over which we found a similar direction of trends in scale samples. However, the magnitude of change is smaller than what was observed in our scale samples, providing evidence that the shifts we found in the isotopic signatures of scale samples reveal changes in the depth dependence of whitefish as a result of dreissenid establishment.