1. Department of Environmental Biology, University of Guelph, Guelph, Ontario, N1G 2W1, Canada, National Water Research Institute, Environment Canada, 867 Lakeshore Road, Burlington, L7R 4A6, Ontario, Canada, Department of Public Health Sciences, University of Alberta, Edmonton, Alberta, T6G 2G3, Canada, and Canadian Wildlife Service, National Wildlife Research Center, Environment Canada, Ottawa, Ontario, K1A 0H3, Canada