Invasive alien species in Switzerland - Schweizer ...

2 > Vertebrates – Vertebrata 59
(Appendix 2 species) for stocking in alpine lakes should be re-addressed, because of
the potential impact on amphibians. Amphibian populations in naturally fishless ponds
and lakes will suffer from introductions of alien predatory fish species.
A favourite species for fly-fishing, the brook trout (Salvelinus fontinalis (Mitchill)), is
today a common species in alpine and subalpine lakes of Switzerland (Zaugg et al.,
2003). This species probably competes with the native brown trout. Impacts on lake
communities have not been studied in Switzerland. In a North American study Bechara
et al. (1992) investigated the impact of brook trout on native communities. Overall,
their results suggest that size-selective predation by brook trout can cause profound
changes in the structure of epibenthic communities at primary as well as secondary
trophic levels. Releases of this species are restricted, since it is also an Appendix 2
species.
The lake trout (Salvelinus namaycush (Walbaum)) was chosen to stock many high
altitude lakes based on its cold-tolerant, northern distribution in North America. It is a
large predatory fish, which can probably cause negative impacts on native fish species.
The lake trout is a favourite in recreational fishing. Stocking alpine lakes with this
Appendix 2 species is permitted. This will have an effect on amphibians sharing the
habitat.
The frequent stocking of water bodies with alien fish species, and also native fish
species from abroad, for sport and commercial fishing increases the possibility of
introducing diseases (see for example the nematode Anguillicola crassus in the Nemathelminthes
section in the chapter on ‘other selected invertbrate groups’), in addition
to the issue of the potential establishment of the alien fish species themselves. Environmental
risk studies are recommended before any fish introductions to investigate
potential threats. Once the decision to introduce a species is taken, the material may be
imported as eggs and some type of quarantine measures should be adopted for imported
material prior to its release into natural waters.
The 15 introduced species in Switzerland belong to five families (Fig. 1.1) (as explained
above, not all of the species definitely have established populations, but they
are included here, since they are listed in Appendixes 2 and 3). Two families are
naturally restricted to North America, thus they are new to Switzerland. The Cyprinidae
are the most species-rich family in the world with about 2,000 species, so it is not
surprising that the highest number of native as well as introduced species belong to this
family. It is also interesting to note that eleven families with only one species occur in
Switzerland, although several had more members before some became extinct. Today
50 % of the salmonids in Switzerland are introduced (three species).
The high number of introduced salmonids reflects their popularity as game fish and for
aquaculture. On the other hand, as Table 2.6 shows by comparing the total number of
species per family and the number of species introduced to Switzerland, the number of
species is a stochastic phenomenon – the smaller families produced a higher percentage
of invaders.