1. Department of Fisheries and Oceans, Freshwater Institute, Winnipeg, Manitoba, R3T 2N6 Canada, Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, R3T 2N2 Canada, Department of Zoology, University of Manitoba, Winnipeg, Manitoba, R3T 2N2 Canada, and Warnell School of Forest Resources, University of Georgia, Athens, Georgia 30602