Invasive alien species in Switzerland - Schweizer ...

An inventory of alien species and their threat to biodiversity and economy in Switzerland FOEN 2006 58
very similar not only in appearance but also in their biology. They are listed in Appendix
3, because of their potential negative impacts on native biodiversity.
The brightly coloured pumpkinseed (Lepomis gibbosus (L.)) (see Fact Sheet) is an
example of an ornamental fish introduced into Europe. It has an interesting breeding
behaviour and is very showy. However, in some cases the species flourished and has
reached high densities. In these circumstances, this predatory fish will almost certainly
have an impact on the food web through selective feeding. It is an Appendix 3 species.
One of the most popular sport fish in North America, the largemouth bass (Micropterus
salmoides (Lacépède) (see Fact Sheet), was widely distributed in North America
outside its natural range, and imported to Europe in the 1880s. The adult is a specialized
fish predator and a decline in native fish species was observed in Italy after its
introduction (Welcomme, 1988). It was also one factor, amongst others, in the extinction
of the Atitlán grebe (Podilymbus gigas Griscom) which was endemic to Guatemala
(BirdLife International, 2000). The bird’s population dropped drastically to 80 as
a result of competition and predation by the introduced largemouth bass, but recovered
to a high of 232 in 1975 when the numbers of the bass plummeted (LaBastille, 1984).
Later the grebe became extinct through other factors.
The only established alien Percidae is the pike-perch (Sander lucioperca (L.)), a
species from Central and eastern Europe. It is one of the most popular sport fishing
species and a highly priced commercial fish. Hence it has been widely released and has
built up self-sustaining populations. It prefers large rivers and lakes, where it is a
ferocious solitary pelagic predator. In the UK negative impacts on native fish populations
have been confirmed; populations of Esox lucius L. and Perca fluviatilis L.
declined after the introduction of pike-perch (Welcomme, 1988). In Switzerland,
releases of the pike-perch without authorization are allowed in contained water bodies
and where the pike-perch already occurs without negative effects on the fauna and flora
(Appendix 2 species). However, the latter is difficult to prove or disprove, so that this
predatory species can be released in many open waters. It was found in 137 localities
during the survey for the fish atlas of Switzerland (Zaugg et al., 2003). More rigid
legislation would be desirable for this species.
The rainbow trout (Oncorhynchus mykiss Walbaum) is probably the most widely
distributed freshwater fish species and may be regarded as a species of global distribution
today. It is a highly prized game fish as well as being widely valued for commercial
use. In Switzerland its natural reproduction is suspected but has been proved only
in the ‘Alpine Rhinesystem’. The observed populations are probably based on extensive
stocking of the species. Zaugg et al. (2003) found it in 39 % of the Swiss lakes and
regarded it as a common species. A self-sustaining population is undesirable, because it
would be difficult to control its spread or prevent competition for breeding grounds
with the native brown trout (Salmo trutta ssp. fario L.). Where rainbow trout is extensively
released, it will have a negative impact on native salmonids. Mahan (2002)
showed that the introduction of the rainbow trout into a North American lake caused a
decline of an endemic congeneric species (O. negratis) with local extinctions. Drake
and Naiman (2000) explain the impact on the habitat. The exception of authorization