Brienzersee, Thunersee, and Bielersee: Effects of Exploitation and Eutrophication on the Salmonid Communities

• Published in: Journal of the Fisheries Research Board of Canada
• Main Authors: Roth, H., Geiger, W.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1972
• Subjects: General Medicine; Arctic
• Online Access: http://dx.doi.org/10.1139/f72-120; http://www.nrcresearchpress.com/doi/pdf/10.1139/f72-120

These three lakes of the Aare Valley in Switzerland have been subjected to increasingly intense fisheries exploitation in recent decades. Fishing intensities have been roughly comparable in the three lakes in any particular year. Attempts at introducing non-native species have been made in all lakes but none of the attempts have had appreciable effect. Nutrient loading, due to domestic wastes predominantly, has been much greater with the downstream Bielersee than the upper two lakes, and somewhat greater in the Thunersee than the highest lake, Brienzersee. But even the latter is now showing symptoms of nutrient stress, in that populations of indicator phytoplankters have recently erupted.Ecological effects ascribed to the fishery include a marked reduction in stocks of Arctic char due to angling and pelagic coregonines due to commercial gillnetting. The latter taxa have recently shown pronounced fluctuations in year-class abundance. An energetic hatchery program has mitigated exploitation effects to some extent.Total stocks of fishes have increased due to eutrophication with initial increases in all fish taxa, except perhaps Arctic char. The cyprinids, percids, and esocids have increased in the Bielersee to a far greater extent than the salmonids with a result that the latter are now contributing smaller proportions of the catches. The cyprinids have little economic value and their burgeoning stocks are creating ecological and economic problems in the Bielersee as well as many other Swiss lakes. The cyprinids apparently cannot be effectively controlled by piscivores such as esocids, even where the latter are assisted by a hatchery program.