Assessment of shark sighting rates by aerial ... - Fisheries Reports

NSW DPI 9
The six flight transects lay 150 m apart, running in an east-west orientation to minimise sun glare to
the sideways-looking observers. Two transects (E-F and G-H) lay within the deployment grid,
while the other four lay outside (Fig. 2B). For each trial, the aircraft flew all six transects at 500 ft
(~150 m), in the directions that ensured the observer was always facing towards the centre of the
grid. When a shark analogue was sighted, the observer would notify the rest of the aircrew,
signalling the pilot to mark a GPS waypoint, and the recorder to note both the GPS waypoint
number and the observer’s estimate of the angle relative to the aircraft and distance to the analogue.
Unless permitted, the aircraft would not deviate from its flightpath. Pilots would radio the number
of analogues seen at the end of each transect, which was later verified against the datasheets.
Datasheets were faxed by aircrew at the end of each day, with the latitude and longitude of each
GPS waypoint included.
On a number of occasions, analogues were deployed on the far northern or southern edge of the
grid. In these cases, the individual analogues were outside the viewing area of observers on
transects E-F or G-H, respectively (Fig. 2B). These analogues were therefore not included when
calculating sighting rates of those transects.
A
C
E
G
I
K
B
X
A
X
Jervis Bay,
NSW
X
Figure 2. (A) Study location on the NSW coast showing the position of the survey grid in
Jervis Bay. (B) Representation of the deployment grid (grey shading) showing the
six 5 km-long transects flown by each aircraft per trial (not to scale). Letters
represent transect coding given to aircrews. “X”s represent hypothetical analogue
deployments. Observers faced southwards in transects A-B, C-D and E-F, and
northwards in G-H, I-J and K-L. In this example, the circled analogue could not be
seen on transect E-F and would not be included in that transect’s calculations. All
other analogues could potentially be seen during each transect (up to six sightings
per trial).
Assessment of shark sighting rates by aerial beach patrols Robbins et al.
X
5 km
N
X
X
B
D
F
H
J
L