Environmental Engineering Reference
In-Depth Information
purposes (Carlton and Mann 1996; Minchin 2007). Short distance translocations
are also commonplace. For example, industries such as mollusc aquaculture collect
spat in diff erent areas to where adults are ultimately grown and harvested (Minchin
2007). With the continued development of faster and more reliable transport, the
distribution of cultivated species is becoming more globally widespread (Minchin
2007). Non-target species associated with cultured organisms may also be unin-
tentionally introduced via aquaculture, e.g. epibiota on mollusc shells (Critchley
and Dijkema 1984) or fouling taxa attached to gear and equipment (Forrest and
Blakemore 2006). Additionally, a multitude of transport modes (e.g. air, water,
road, rail) with ever decreasing journey times allows the rapid deliberate and unin-
tentional dissemination of live aquatic products (and their associated pest para-
sites and diseases). Hence pinpointing transfer pathways can be extremely di cult
owing to the complex array of transport networks (Minchin 2007).
h e aquarium and ornamental marine species trade is emerging as an important
source for AIS introductions globally (Padilla and Williams 2004). h ousands of
species and millions of individuals of aquarium fi sh alone are transported world-
wide annually (McDowall 2004). h e popularity of e-commerce and Internet-
based trading of aquarium species (e.g. the invasive marine alga Caulerpa taxifolia ,
see Walters et al . 2006) will undoubtedly see this trend continuing. Intentional
and inadvertent releases of aquarium species have long been recognized as a leading
source of AIS in freshwater systems (Courtenay and Robins 1973; Courtenay and
Stauff er 1990) and, more recently, as a vector for the introduction of marine algae
and fi sh species into natural systems (Whitfi eld et al . 2002; Semmens et al . 2004;
Walters et al . 2006). h e introduction of invasive species via the aquarium trade
is di cult to manage, however, as the aquarium industry remains largely unregu-
lated, and has traditionally received little attention from ecologists, conservation-
ists, and policy makers (Padilla and Williams 2004).
14.2.2 Management of human-mediated pathways
Given the technical and fi nancial constraints associated with controlling marine
pests after they have established in a new location, it is clearly preferable to prevent
the initial introduction as a fi rst line of defence (e.g. Bax et al . 2001; Meyerson and
Reaser 2002; Simberloff 2003b; Branch and Steffani 2004; Hewitt et al . 2004). The
key method for the prevention of marine AIS introductions involves the analysis,
identifi cation, and management of known transport vectors (Fig. 14.1c). There
has been considerable effort globally to identify risks associated with international
vessel traffi c (Carlton 1985; Coutts et al . 2003; Coutts and Taylor 2004; Verling et
al . 2005), and to develop target lists of high-risk species (or 'next pests'), their likely
distribution ranges, and potential high risk entry locations. These approaches may
all be used as a means of prioritizing and focusing pre-border management efforts
(Gollasch and Leppäkoski 1999; Hayes and Sliwa 2003).
Currently, pre-border management of maritime pathways mainly focuses on
exotic species transported via ships' ballast water. Qualitative and quantitative risk
 
 
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