1. Norwegian Polar Institute, N-9296 Tromsø, Norway, Norwegian Veterinary Institute, P.O. Box 8156 Dep., N-0033 Oslo, Norway, Norwegian School of Veterinary Science, P.O. Box 8146 Dep., N-0033 Oslo, Norway, Chemistry Department, Carleton University, Ottawa, ON, Canada K1S 5B6, and Warnell School of Forest Resources, University of Georgia, Athens, Georgia, 30602-2152