Several rheophilic fish species of the prealpine grayling and trout zones are experiencing dramatic population declines and rapid population extinction at a stage before quantitative assessment of genetic, functional and taxonomic diversity. Trying to provide such data, we have been studying four taxa. The first was the enigmatic Nase or Nose carp (Chondrostoma nasus), perhaps the most rapidly declining fish of Swiss rivers. We documented a deep genetic break between populations in the Lake Constance drainage and those in the rest of the Rhine catchment. We also demonstrated phenotypic variation, possibly associated with river size, and evidence of a genetic bottleneck in one population. Based on these findings we made recommendations for management.
Further, we are studying grayling populations in some parts of Switzerland in a similar framework, another species that declines for reasons that are not entirely clear. We are studying native trout of Mediterranean lineages, and the conditions of coexistence with or displacement by introduced Atlantic trout. Finally, we study bullhead (sculpins, Cottus gobio), a little benthic species that is of no commercial interest and supposedly has not been much affected by human translocation.
