1. Freshwater Centre; Finnish Environment Institute; PO Box 413 90014 Oulu Finland
2. Department of Ecology and Genetics; University of Oulu; PO Box 8000 90014 Oulu Finland
3. Natural Resources Institute Finland (Luke); Paavo Havaksen tie 3 90014 Oulu Finland
4. Natural Resources Institute Finland (Luke); Manamansalontie 90 88300 Paltamo Finland
5. Natural Environment Centre; Finnish Environment Institute; PO Box 413 90014 Oulu Finland