Die heutigen sympatrischen Felchenpopulationen (Coregonus spp.) des Thuner-und Bielersees und ihre Morphologie

During the past 25 years the effects of eutrophication in the oligo-to mesotrophic Lake Thun and the eutrophic Lake Biel have changed the morphology and biology of theCoregonus spp., as well as the composition of the stock. Statistical procedures and immunodiffusion revealed the existence of threeCoregonus populations in Lake Thun: 5% Kropfer, 28% ‘Albock’ and 67% Brienzlig (local names). Their gillrakers range between 20 and 32, 25 and 40, and 29 and 46, respectively (mean: 22, 31, 40). In Lake Biel two populations were distinguished: 16% Palée and 84% Bondelle with 22–35 and 30–40 gillrakers (mean: 30, 34). Changes of the spawning grounds and periods most probably have led to a bastardization of two species (Schwebalbock and Bodenalbock) to the present ‘Albock’ in Lake Thun. Overlapping values of all 20 morphological characters of the populations studies render the identification of forms difficult. Only gillrakers and a few more characters show significant statistical differences between populations. The determination ofCoregonus spp. of Lake Thun and Lake Biel thus often needs additional data on growth, feed, maturation, spawning ground and/or period.