Environmental Engineering Reference
In-Depth Information
(181/754) of waypoints, equating to ~25 km
2
of island forest. h ird, burrow dens-
ities at waypoints indicated that YCA had killed c.15 million red crabs (c.25% of
the total island population).
Simultaneously with development of the IWS, two other key elements for the
response were initiated. First, PANCI commenced eff orts to source and evaluate
an eff ective ant bait. Initial trials with commercially available bait formulations
were unsuccessful. Eventually, Presto®01, a fi shmeal bait with an active constituent
of fi pronil, was identifi ed as eff ective (Fig. 11.2c). At the time this bait was unregis-
tered in Australia, but use was permitted on Christmas Island under an emergency
permit issued by the National Registration Authority. Ground crews treated a total
of 371ha of YCA supercolonies between 2000-2001, achieving a knockdown of
>
95% of ant workers within days.
Second, a small steering committee comprising volunteer scientists, managers,
and policymakers was formed, independent from the management authority. h e
key functions of the committee were to provide advice and support for the oper-
ational programme, strategic direction, and, on occasion, advice to the Director
of National Parks. Committee members met regularly by teleconference, and rou-
tinely produced discussion papers to present, evaluate, and recommend options for
the programme, establish timelines for actions, and review and monitor progress.
The genesis of the aerial control campaign lay in the compelling fi ndings of the
IWS (Orchard
et al
. 2002); two-thirds of supercolonies were in areas too rug-
ged for fi eld crews to operate safely and effectively, and in any case, ground con-
trol was impractical given the sheer pace and scope of the invasion relative to the
number of personnel available. In late 2001, the steering committee canvassed
the idea of an aerial approach to YCA control, based largely on the aerial cam-
paigns in New Zealand to control invasive rats (e.g. Towns and Broome 2003) and
the newly initiated campaign to eradicate the red imported fi re ant in Brisbane
(Vanderwoude
et al
. 2003).
Given the novelty of an aerial approach, the Steering Committee recommended
in February 2002 that a trial be conducted to determine if YCA supercolonies could
be eff ectively controlled from the air. Two timelines were considered: (1) where
both the trial and island-wide control programme were conducted during a single
3-week period in September 2002, whereas (2) involved a staged approach with
a trial in 2002 followed by control in 2003. h e fi rst plan was considered feasible
within the 3-week window because the ant bait is fast acting so the e
cacy of aerial
broadcasting of bait would be evident within days. h ree factors weighed in the
recommendation:
The urgency of controlling all supercolonies as soon as possible.
1)
2)
The high cost involved in transporting a helicopter to the island twice.
3)
The high purchase and transport costs of stockpiling tonnes of ant bait if the
fi rst plan was adopted but the trial failed.
