Environmental Engineering Reference
In-Depth Information
only sterile triploid black carp had been approved for this purpose (Naylor
et al
.
2001). Inevitably, diploid black carp have been released and now appear to have
established in the Mississippi and Atchafalaya Rivers (Jenkins and Thomas 2007).
Escapes and unintentional releases of farmed sea-ranched salmon have been linked
to negative ecological and genetic impacts on wild salmon stocks (Gross 1998). Up
to 40% of wild salmon caught in the North Atlantic and 90% of salmon caught in
the Baltic are of farmed origin (Hansen
et al
. 1997). The use of triploid farmed fi sh
has been proposed as one way to minimize such effects (Cotter
et al
2000). Salmon
farming has also been implicated in the decline of wild salmon stocks by acting as
sources for infestation by parasites. One single salmon farm increased infection
pressure on wild migrating salmon by four orders of magnitude (Krkosek
et al
.
2005). Although salmon farmers routinely treat parasite infestations to reduce
impacts on their stock, farms still provide signifi cant and detrimental infection
pressure on wild salmon, and the ecological effects of sea lice seem to far outweigh
the ecological effects of pesticide treatments on farms (Woodward 2005).
Immediate and early response to a suspected new introduction is critical to the
success of any potential eradication. Suitable control tools need to be available,
such as approvals for chemical eradication and private property access. An excellent
example is the eradication of Australian marron crayfi sh (
Cherax tenuimanus
) and
European gudgeon (
Gobio gobio
) from two locations in the Auckland region of New
Zealand in 2005. The gudgeon were probably smuggled into the country by coarse
fi shing enthusiasts for use as live bait. A coordinated operation involving local and
central government agencies resulted in rapid eradication of both species (MAF
2005) and no subsequent populations have been found to date. Early response to a
possible introduction is clearly crucial in attempting to prevent further spread. One
wonders what the outcome may have been had attempts been made to treat the
initial observation of 1m
2
of
Caulerpa taxifolia
off the Monaco Aquarium in 1984.
Within 8 years the infestation was estimated at 3000 ha (Jousson
et al
. 1998).
13.8.2.1 Preventing spread: physical barriers, electrical barriers,
interstate/interisland biosecurity barriers
Freshwater fi sh generally disperse poorly. Little opportunity exists for fi sh to dis-
perse from discrete water bodies such as isolated ponds and lakes, although eggs
may be carried on aquatic vegetation transported by birds and vehicles. Adhesive
eggs may also be spawned and transported on boat hulls. In contiguous water-
sheds, natural barriers like waterfalls, velocity barriers such as chutes and riffl es,
and of course the saline waters of estuaries and coasts may prevent spread.
