**ABSTRACT NOT FOR CITATION WITHOUT AUTHOR PERMISSION.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 corresponding author via e-mail at afisk@uwindsor.ca or via telephone at 519-253-3000 ext. 4740. Questions? Contact the GLFC via email at frp@glfc.org or via telephone at 734-662-3209.**

Quality or quantity – A temporal analysis using tracers to relate diet to

health of Lake Trout in the Great Lakes

Gord Paterson¹, Aaron Fisk¹, Tim Johnson², Ken Drouillard¹, Michael Arts³, Craig Hebert⁴, Scott Rush¹, Doug Haffner¹, Daryl McGoldrick³ and Sean Backus³

¹Great Lakes Institute for Environmental Research, University of Windsor,

401 Sunset Avenue, Windsor, Ontario N9B 3P4

²Ontario Ministry of Natural Resources, Glenora Fisheries Station,

41 Hatchery Lane, Picton, Ontario, K0K 2T0

³Environment Canada, National Water Research Institute, 867 Lakeshore Road,

P.O. Box 5050, Burlington, Ontario, L7R 4A6

⁴ Environment Canada, National Wildlife Research Centre, Carleton University, Ottawa, Ontario, K1A 0H3

ABSTRACT:

Efforts to rehabilitate the native lake trout (Salvelinus namaycush) in Lakes Ontario and Huron have struggled following decades of overfishing, sea lamprey predation and other stressors. Recent changes to the quantity and quality of the prey base in the Great Lakes, related in large part to the introduction and proliferation of non-indigenous species, have been implicated as factors in poor lake trout recruitment and reproduction. To address the importance of prey quality and lake trout diet, we carried out an intensive temporal (1989-2011) assessment of feeding ecology and health of lake trout in Lakes Huron and Ontario using a combination of stable isotopes, fatty acids, PCB congeners and biological data on archived and freshly collected tissues of lake trout and key prey species (zooplankton, Mysis diluviana, rainbow smelt (Osmerus mordax), round goby (Neogobius melanostomus), alewife (Alosa pseudoharengus) and slimy sculpin (Cottus cognatus)). Carbon (d¹³C) stable isotopes and fatty acids provide strong evidence in a major shift from offshore to near-shore carbon reliance for Lake Ontario lake trout between 1989 and 2008. Although the shift has been slower and less dramatic, isotope and fatty acid data in Lake Huron (1991-2011) also indicate an increasing importance of near-shore redirected production to lake trout. However, there has been a significant change in the growth and health of Lake Huron lake trout between 1991 and 2011, and PCB temporal trends indicate energetic constraints in this population, which was not evident across all age classes of Lake Ontario lake trout. As well, results provided limited evidence for specific ontogenetic related changes in the feeding ecology, growth and/or health of Lake Ontario and Lake Huron lake trout. The results of this study demonstrate substantial differences in the ecological responses of Lake Ontario and Lake Huron lake trout during the time frames associated with the introduction and establishment of non-indigenous species including dreissenid mussels and the round goby in these ecosystems.