1. Centre for Conservation Biology, Department of Biology, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
2. Norwegian Polar Institute, Fram Centre, NO-9296 Tromsø, Norway.
3. Norwegian Institute for Nature Research, Fram Centre, NO-9296 Tromsø, Norway.
4. Department of Arctic and Marine Biology, University of Tromsø, NO-9037 Tromsø, Norway.