Environmental Engineering Reference
In-Depth Information
poisoned. Modern trends in poison use are diverging. Some research aims to fi nd
a toxin, bait, and bait delivery system that can simultaneously control multiple
pests at lowest possible cost, particularly for large-scale control and eradication
campaigns. In New Zealand, for example, a broad-spectrum poison, 1080, is aeri-
ally applied over up to one million hectares annually, with introduced brushtail
possums (
Trichosurus vulpecula
) the primary target (because they damage native
ecosystems and carry bovine tuberculosis; Cowan 2005) (Fig. 12.1). Increasingly
these operations are being designed to simultaneously target other sympatric pests
such as ship rats (
Rattus rattus
), mice (
Mus musculus
) (Nugent
et al
. 2007) and
stoats, some of which are killed by secondary poisoning (Murphy and Fechney
2003). Unanswered questions include:
1)
Whether achieving high kills of the secondary pests (such as mice in the
example above) is worthwhile where they have much faster breeding rates
and smaller home ranges than the main target, and so require fi ner-scale,
more frequent, and therefore more expensive control.
Whether it is better to fi nd a universal bait or to mix different bait types
2)
(Morgan 1993). The main problem with broad-spectrum baits and toxins is
the increased likelihood that some non-target species will also be killed. This
can include native species, so managers need to ensure that kills of these are
not so high as to outweigh the benefi ts of removing the pests (e.g. Powlesland
et al
. 1999). It can also include non-target exotic species such as domestic
animals and deer (Nugent and Fraser 2005), which understandably pro-
vokes opposition from farmers and hunters, which may constrain where poi-
soning can be used. There is also often similar public opposition from those
concerned about environmental contamination and direct threats to human
health (Environmental Risk Management Authority 2007).
To avoid such constraint, other research is directed at fi nding species-specifi c
baits or toxins—the Achilles heel approach (Marks 2001). At its simplest, all
but the target pests can be physically excluded from toxic bait by using specially-
designed bait stations. Likewise, the bait can be altered to make it less attractive to
non-target species; 1080-cereal baits used to kill possums in New Zealand are often
dyed green to reduce the likelihood of native birds feeding on them (e.g. Day
et al
.
2003), and increasingly may be coated with a repellent that deters deer but not
possums, in order to reduce incidental by-kill of deer (Morriss
et al
. 2005).
h e major alternative approach is the search for toxins that pose no incidental
threat to humans or non-target animals. Even many commonly used acute or anti-
coagulant toxins have a wide range of toxicity across taxa (Eason and Wickstrom
2001), so the risks to both target and non-target animals can be manipulated to
some extent by choice of toxin, careful selection of the dosages available in indi-
vidual baits, and the number and distribution of baits available to each animal.
Further, there are toxins that are eff ective against only one trophic level (e.g. para-
aminopropiophenone for control of carnivores; Savarie
et al
. 1983), and even some
that aff ect only one species or genus (e.g. toxins that target just
Rattus
; B. Hopkins,
