Environmental Engineering Reference
In-Depth Information
Some vertebrates are diffi cult to eradicate at the scales needed because we do not
have effective control tools. For example, species such as musk shrews (
Suncus
murinus
) or brown tree snakes (
Boiga iregularis
) that eat only live prey have proved
very diffi cult to eradicate. Success has been achieved only on very small islands
(2 ha Ile de la Passe in the Seychelles for the shrew (Seymour
et al
. 2005) and some
areas of less than 1ha on Guam for the snake (Rodda
et al
. 2002).
Some species learn more quickly than others to avoid control. Eradication of
common mynas (
Acridotheres tristis
) succeeded on 63 ha Aride Island, Seychelles
(Lucking and Ayerton 1994), but most other attempts have failed because the
eff ort or tactics required to get the last, smart individuals have not been applied or
are unavailable (Parkes 2006b).
Some species also appear to retain higher levels of neophobia in the initial
uncontrolled populations than others. For example, one explanation of the failure
to achieve eradication of rabbits with aerial poison baiting is that all rabbit popula-
tions contain some neophobic individuals (Parkes 2006c).
As already mentioned, aquatic pests are also di cult to eradicate. Fish, crust-
aceans, and reptiles have been eradicated by rotenone poisoning (Ling 2003), or
physical draining in small enclosed ponds (e.g. O'Keefe 2005), but to date we lack
the tools to attempt eradication in larger bodies of water or rivers. New develop-
ments in concentrating fi sh to small parts of their habitat where they might be
vulnerable to extirpation (e.g. using pheromone lures for sea lampreys (
Petromyzon
marinus
) (Li
et al
. 2003)) or in genetic manipulation to alter sex ratios (e.g. the
daughterless carp project (Gilligan and Faulks 2005)) hold some hope for control
of these pests. Whether the latter approach could be extended to achieve eradica-
tion without extra conventional control is highly debateable given the fundamen-
tal constraints of natural selection for those that do produce daughters.
Annual weeds are also very di cult eradication targets. Some can reproduce
before they are detectable (e.g. the composite bitterweed
Helenium amarum
)
(Tomley and Panetta 2002) while others, such as root parasites, are only detectable
in some seasons (Panetta and Lawes, 2007). Sustained control may be the only
feasible option to manage such species.
Eradication can be expensive in the short term, and tends to lead some funding
agencies, particularly government ones, to seek to spread the costs across years.
This of course increases the risk that eradication will fail, and several authors (e.g.
Myers
et al
. 2000) have noted the requirement for institutional commitment to the
concept, conditions, and possibility as a prerequisite for success.
Commitment to eradication on islands (where the obligate conditions are most
easily met) is increasing for vertebrate pests at least. Since 2001 we are aware of
reviews of the problem and priorities for action conducted by Britain and France for
their overseas territories (Lorvelec and Pascal 2005; Varnham 2006), by Ecuador
