Degraded rivers are one of the major causes of brown trout decline in Switzerland.

Fish catch declines have been reported in many European countries. Poor health and an alarming decline of brown trout catch in Swiss rivers prompted the Federal Office for the Environment (FOEN/SAEFL) and the Federal Institute of Aquatic Science and Technology (EAWAG) to launch the national project ‘Fischnetz’ in 1998. The participation and close cooperation with the Fisheries Association, the Society of Chemical Industries, the 26 cantons, Liechtenstein, several universities and repeated public information contributed to the success of the five-year project.

Results showed that the causes for the catch decline vary across regions and are mainly due to combined effects. Nevertheless, three main causes could be identified. Firstly, habitat degradation including blocked connectivity, changed flow regime, lack of shelter, poor local water quality, and substantial stream warming
reduced the availability of good trout habitats. Secondly, the proliferative kidney disease especially affecting young trout at increased water temperatures above 15°C can result in high mortalities. Finally, changed fishery management also contributed partly to the reported catch declines.

The implementation of the findings is now supported by the follow-up project ‘Fischnetz+’.

For more information and publications please visit: www.fischnetz.ch

Karin Scheurer
was a member of the Fischnetz project management
and currently lives in Bratislava working at SHMU in EU water projects.