1. National Water Research Institute, Environment Canada, Burlington, Ontario L7R 4A6, Canada, Department of Fisheries and Oceans, Great Lakes Laboratory for Fisheries and Aquatic Sciences, Burlington, Ontario L7R 4A6, Canada, National Wildlife Research Center, Hull, Quebec K1A 0H3, Canada, and Warnell School of Forest Resources, University of Georgia, Athens, Georgia 30602-2152