Environmental Engineering Reference
In-Depth Information
h ere is no universal defi nition of what defi nes an invasive species. While it
is generally acknowledged that an alien species that establishes widespread feral
populations may be considered invasive, not all such species appear to cause eco-
logical damage or pose signifi cant threats to indigenous biodiversity. For instance,
although the goldfi sh (
Carassius auratus
) is one of the most widespread feral species
worldwide, it is generally regarded as benign. By contrast, mosquitofi sh (
Gambusia
spp.) are typically regarded as destructive and nuisance species virtually every-
where they have been introduced, although sometimes the evidence of signifi cant
ecological damage is limited (Ling 2004).
Much effort recently has focused on the development of risk assessment models
for invasive fi shes; the assessment protocol developed by Copp
et al
. (2005b) is
an excellent example. Risk assessment procedures must operate at pre-border and
post-border levels—fi rstly to establish the risk posed by fi shes not already present
in a country and secondly to address the risk posed by further transfer and release
of already naturalized species. National laws restricting the importation of certain
fi shes are typically directed at the aquarium and ornamental fi sh trade. Given that
the worldwide fauna stands at more than 20,000 species, such legislation usually
lists excluded rather than allowed species, and such diversity means that quaran-
tine inspectors may need expert knowledge to identify high-risk species in a mul-
tispecies importation. Taxonomic identifi cation of some fi shes may be diffi cult
even for experts and taxonomic revisions may render older legislation quickly out
of date (McDowall 2004). The situation is exacerbated if only common names
are specifi ed, because names like carp, cod, barb, and shark are applied to species
across widely divergent taxonomic groups. Moreover, many aquarium species
are imported as juveniles that may be diffi cult to identify and easily confused
with allowed species. For instance, in New Zealand, the importation of goldfi sh
is banned because juveniles are diffi cult to distinguish from the prohibited
common carp.
Legislative control over the introduction, spread, and control of fi sh species
(exotic or indigenous) is typically spread across numerous national or state agen-
cies involved with biosecurity, aquaculture, sports fi sheries, and conservation. h e
regulatory framework to control potentially invasive species is often diff use and
uncoordinated (Naylor
et al
. 2001). However, these authors hailed the New Zealand
Hazardous Substances and New Organisms Act (1996) as a simple yet comprehen-
sive measure to control introductions of new organisms whereby all exotic species
are regarded as potentially invasive unless proven otherwise. Simberloff (2005) has
further argued that the regulation of exotic species introduction and spread should
be based on presumption of risk rather than assessment of risk because most cur-
rent risk assessment procedures are 'narrowly focused, subjective, often arbitrary
and unquantifi ed, and subject to political interference'.
