Invasive alien species in Switzerland - Schweizer ...

2 > Vertebrates – Vertebrata 61
The origin of the 15 species is obviously correlated with the climate, since all species
are from temperate climates in the Northern Hemisphere, with six each from North
America and Asia, and three from other parts of Europe. Mikschi (2002) lists two
cichlid species for thermal waters in Austria, and these tropical species can only survive
in these warm waters. Three other species from the Neotropics (Poeciliidae)
became extinct after their release in the same waters.
The exact pathways for fish introductions are often not known and in many cases
introductions have been carried out with more than one motive. Taking the most likely
pathways for each species, those released for commercial and sport fishing and aquaculture
will amount to 11 of the 15 species. Two species are ornamental releases and
escapes, and one was introduced as a control measure for unwanted vegetation. Interestingly,
only one species arrived accidentally. However, its arrival is also connected
with aquacultural practices, since it was a contaminant in grass carp shipments. In
conclusion, the potential threats to native biodiversity are primarily due to fishing
activities. Fish releases need to be considered carefully, their threats evaluated, and
specimens quarantined to prevent spread of diseases. The number of introductions on a
global scale has dramatically decreased since the 1960s, when they peaked, partially
because growing awareness of possible negative consequences has led to legislation,
but also because of a saturation effect as some species had been introduced to all
suitable recipient areas (Welcomme, 1988).
The demonstrated impacts of the 15 species are detailed in Table 2.7 and in the accounts
for individual species, above. They encompass the entire range of effects measured,
i.e. predatory and grazing pressure, competition with native species, changes in
water quality, community and food-web changes, disease vectoring and hybridization.
All potentially harmful species are regulated by Swiss law and are listed in Appendix 2
or 3. This is a very good basis for management of alien fish species in Switzerland,
although some of the Appendix 2 species which harm native biodiversity can be stocked
in alpine lakes without authorization. This is especially worrisome in the case of
predatory fish released into previously fishless lakes, where they can damage the
amphibian populations.
Therefore it is recommended that the species of Appendix 2 are re-addressed and
stricter regulations are provided for those species.
Another point of concern are species native to Switzerland released outside their native
range, as noted in the sections of this chapter on reptiles and amphibians. The roach
(Rutilus rutilus (L.)), for example, is native to the northern side of the Alps but was
released in the Ticino, where it competes with the native fish fauna.