Invasive alien species in Switzerland - Schweizer ...

An inventory of alien species and their threat to biodiversity and economy in Switzerland FOEN 2006 56
aquaculture plants, etc.) in which certain alien fish taxa can be released without authorization,
while Appendix 3 names fish taxa which are unwanted in Switzerland. In
this section, species mentioned in these two Appendixes are referred to as Appendix 2
and Appendix 3 species, respectively. A total of 15 species will be discussed below
(Table 2.7), although in some cases natural breeding has not yet been reported from
Switzerland. In such cases, populations are based on frequent releases. However, the
species lists in Appendixes 2 and 3 suggest all 15 species should be dealt with here,
since they are regulated in Switzerland. The common carp (Cyprinus carpio L.) is not
included in the species discussed in this section, because it is assumed to be an archaeozoa,
arriving with the Romans in Central Europe. It was also found in most of
Europe before the glacial era. Organisms which occurred before glacial times in Central
Europe often stimulate discussions about definitions of native and alien species.
The bighead carp (Aristichthys nobilis Richardson) (see Fact Sheet) has not yet been
reported to reproduce in Switzerland. However, it is assumed that the species could
breed, and that is the reason for adding the species to Appendix 3. It is reported to
breed in the Danube (Donau).
The asp (Aspius aspius) is a very recent invader in Switzerland, first recorded in 1994
in the Rhine (Rhein) at Basel (Zaugg et al., 2003). It is probably expanding its range
following its introduction into the Rhine in Germany, downstream of Basel. Its natural
range seems to be Central and eastern Europe from Germany eastwards, including the
Danube system. The Rhine population was either introduced for fishing purposes
(Ladiges and Vogt, 1979) or spread from the Danube after the completion of the Rhine–Danube
Canal. This is the only alien fish species which was not introduced directly
into Switzerland but into a neighbouring country, in this case Germany, and is naturally
spreading up the river Rhine. The asp is a large fish (up to one metre long) and prefers
large rivers. It is one of the few cyprinids that is a piscivore. The adults eat mainly fish,
but also mammals and birds, while the more gregarious living young eat smaller animals
such as invertebrates. It is assumed that the species will colonize more parts of
Switzerland. Since the natural range is close to Switzerland, the species might be
acceptable, as a natural expansion rather than an invasion.
The goldfish (Carassius auratus (L.)) is a favourite species for aquariums and garden
and park ponds. Today, it has acquired an almost pan-global distribution through its
ornamental use. It either escapes or is released into the wild. Its native range is Central
and eastern Asia. The Carassius species (two more are discussed below) are difficult to
identify and some records might be misidentifications (Arnold, 1990). Goldfish feed on
a wide range of food including plants and small animals. In some places they are
regarded as a nuisance due to the production of stunted populations. They produce
large numbers of individuals, which mature at a much reduced size, thereby diminishing
the usefulness of the population for sport or commercial fishing (Lehtonen, 2002).
There are indications that they compete with native fish species and increase turbidity
through their bottom dwelling behaviour, as does the common carp, thereby altering
the aquatic community. Introductions limited to closed systems are possible without
authorization (Appendix 2 species).