The assessment of fish vulnerability in Switzerland based on distribution data Original Research Article

A nationwide study on the distribution of the fish fauna served as the basis for a vulnerability assessment of fish and cyclostomes in Switzerland. In all, 1900 river sections and 249 lakes were sampled in several stages using various methods. In 941 of these sampling sites fish were present with 1–37 taxa. The vulnerability of each taxon was assessed using the relationship between the numbers of actual occurrences, extinct populations, present population sizes and population stability. Each of these variables was transformed to respond in the form ‘lower VALUE = higher threat’, and then all were summed to give a ‘vulnerability score’. This gave a standardised preliminary classification into five categories for 43 of the total 54 native taxa. However, further criteria not covered by the quantitative distribution data, such as zoogeography and fishery management, had to be included for several taxa in the final allocation of conservation status. In the resulting Red List, seven taxa are listed as extinct, five as critical, eight as endangered, eight as vulnerable and 14 as susceptible. Twelve native taxa are considered as not threatened, and for 13 introduced taxa no conservation status was assigned.