Affiliation: | a Department of Limnology and Environmental Protection, University of Helsinki PO Box 65, FIN-00014 Helsinki, Finland b Finnish Game and Fisheries Research Institute PO Box 6, FIN-00721 Helsinki, Finland c Fisheries and Oceans Canada, St Andrews Biological Station 531 Brandy Cove Road, St Andrews, New Brunswick, E5B 2L9 Canada |