Environmental Engineering Reference
In-Depth Information
assessment techniques have been developed to analyse and manage the various
elements of the ballast water cycle in order to aid pre-border interception of AIS
through the identifi cation of high/low risk vessels (Hayes and Hewitt 1998, 2000)
and high/low risk transport routes (e.g. GloBallast risk assessments, see Clarke
et al
. 2004). Such techniques can be highly fl exible, operating at several levels of
complexity, depending upon the availability of data (Hayes and Hewitt 1998,
2000).
At a more applied level, International Maritime Organization (IMO) guidelines
currently require vessels to conduct mid-ocean ballast water exchange (BWE), and
to not discharge any unexchanged water unless exempted on the grounds of safety
(IMO 1997). h e premise of this approach is that BWE will substantially reduce
the risk of new introductions by displacing pest species during exchanges, or
uploading oceanic species that are unlikely to survive in the recipient coastal zone.
In general, however, the eff ectiveness of BWE has been shown to be highly variable
and organisms from the port of origin invariably remain in the ballast tanks (Taylor
et al
. 2007). Adopted by the IMO in 2004, the International Convention for the
Control and Management of Ships' Ballast Water and Sediments, introduces new
standards for the management of ships' ballast water, and progress is now being
made on the development of various ballast water treatment technologies (Herwig
et al
. 2006; Tang
et al
. 2006; Gregg and Hallegraeff 2007).
Although pre-border prevention of species transfer via hull fouling is technically
feasible, widespread implementation and enforcement of viable management tools
(e.g. hull cleaning) is largely impractical. As a result, hull fouling management
usually focuses on the use of risk analysis for identifying specifi c high-risk vectors
or routes (e.g. specifi c countries or regions) and target pest species. Such analyses
involve developing a target list of potentially invasive species, based upon pre-
defi ned selection criteria (e.g. Hewitt and Hayes 2002; Hayes and Sliwa 2003).
Such criteria may be as simple as selecting species based upon their invasiveness
or impacts elsewhere, but may also involve examining species' attributes in an
attempt to characterize their invasibility and potential distribution ranges (Forrest
et al
. 2006). It is also useful to characterize the attributes of receiving environments
to determine habitats at greatest risk from invasion, which can help determine
values at risk, and hence priorities for management.
Given the complexity of marine ecosystems, the lack of effective or affordable pre-
vention tools, and the large number of managed and unmanaged vectors able to
facilitate species transport, it is unrealistic to expect a 100% effective pre-border
management strategy (Wotton and Hewitt 2004). This raises the question as to
whether post-border management, which has a track record of various successes in
freshwater and terrestrial systems (e.g. Genovesi 2005; Allen and Lee 2006), might
also be feasible in the marine environment.
