Environmental Engineering Reference
In-Depth Information
allowed a detailed assessment of how well target areas had been treated, in terms of
both accuracy around the perimeter, and coverage across the treatment area.
11.3.2.3 Dispersion of Presto
®
01 ant bait
Ant bait was dispersed from a bucket suspended beneath the helicopter (Fig. 11.2b).
This bucket was an inverted cone into which about 90 kg of bait was loaded
(Fig. 11.2d). A key factor in bait dispersal was its moisture content—the pelletized
bait had to be dry enough to fl ow without blockage through a 25 mm diameter
hole at the bottom of the bucket, onto a petrol-driven, rotating spreader. Despite
prior testing on the mainland to establish the ideal moisture content, the Presto
®
01
shipped to the island was too moist and would not fl ow. So, all 13,000 kg of
Presto
®
01 had to be dried by spreading it thinly with garden rakes on sheets of black
plastic in full sun. This was an incredibly labour-intensive exercise, required 250
person hours to complete, and risked photodegradation of fi pronil. Drying barely
kept pace with the demands of fl ight operations.
11.3.2.4 Mapping supercolonies
The accurate mapping of YCA supercolonies was crucial to the success of the
control programme.
The map was based largely on the results from the 2001 IWS,
followed by boundary delimitation during the four months leading up to aerial
operations in September 2002 (Fig. 11.4b). All boundaries were mapped in the
fi eld with hand-held GPS units, and maps were generated using the CIGIS. Field
crews used several cues to determine the boundaries of supercolonies, including
subjective assessments of crazy ant abundance, both on the ground and as 'trunk
traffi c' on trees, and the presence or absence of dead crabs. In areas where super-
colony boundaries did not correspond with a physical feature of the landscape
(e.g. a cliff, forest edge), three fi eld workers walked abreast 10-20 m apart along
the length of the boundary, with the two outer people keeping the middle person
accurately positioned on the boundary—the outer person continually confi rmed
the absence of ants, while the inner person continually confi rmed their presence.
The middle person held the GPS unit and coordinates were taken every 20-50 m.
Some boundaries were easily identifi able by observers on the ground, but often
there was a wide 'transition zone' between heavily ant-infested forest and intact
forest (Abbott 2006). These boundaries proved too fi nely resolved to be practic-
able for aerial operations. Accordingly, boundaries were rounded on the CIGIS,
but this process never pared off sections of supercolonies. This increased the total
treatment area increased by 167 ha from 2378 ha to 2545 ha.
Sections of several supercolonies were excluded from the aerial control pro-
gramme. h ese included all freshwater streams and soak areas, including the two
Ramsar Wetlands of International Importance. Fipronil is reported to have strong
negative eff ects on freshwater fauna, so exclusion zones of 100 m were imposed
around these areas. Five supercolony research plots were excluded from the aerial
baiting programme but later treated by ground baiting. h e total area excluded
from the baiting programme was 76.2 ha.
