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

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18 NSW DPI Observers were requested to identify the deployed analogues to body-type (white shark, tiger shark or hammerhead shark) for all sightings during the last four days of the trials. However, identifications were made for only 34% and 55% of sightings for the fixed-wing and helicopter observers, respectively. Although the accuracy of identified analogues was relatively high (77% and 98%), the low rate of attempts meant that overall only 26% and 55% of deployments were correctly identified to ‘species’ for the fixed-wing and helicopter observers, respectively. Importantly, none of the 38 white shark or tiger shark deployments were successfully identified, with only hammerhead shark analogues correctly identified as such. Estimates of distance to the high-visibility surface shark analogues showed no correlation with the actual deployment distance for fixed-wing observers (regression analysis: n = 23, slope = 0.05, F = 0.45, p = 0.51). A significant relationship was found between the helicopter observer distance estimates and actual deployment distances (regression analysis: n = 26, slope = 0.48, F = 41.67, p < 0.001), however estimates were 52% lower than the real distances. Both aircraft maintained altitudes of 500 ft (~150 m) throughout the experiments, eliminating vertical variations as a confounding effect. Instead, it appears that reliable distance estimates are extremely difficult to obtain while travelling aerially at speed. The accuracy of the observers’ angle estimates was relatively high for both aircraft. There was only a 5% decrease in the number of validated analogue sightings if the leeway was reduced to 22.5º, and 14% less sightings if only 15º leeway was given (Fig. 7). Neither angle change significantly altered the sighting rates of either the fixed-wing (k-s tests; z = 0.426, p = 0.993; z = 0.426, p = 0.993, respectively) or helicopter observers (k-s tests; z = 0.213, p = 1.000; z = 0.426, p = 0.993, respectively). Robbins et al. Assessment of shark sighting rates by aerial beach patrols
NSW DPI 19 Number of analogues sighted Number of analogues sighted 80 Fixed-wing 60 40 20 0 100 80 60 40 20 0 0 m 0 m 50 m Helicopter 50 m 100 m 100 m 150 m 150 m 200 m 200 m 250 m 250 m 300 m 300 m Distance to analogue (m) 350 m 350 m 400 m 400 m 450 m 450 m 500+ m 15 deg leeway 22.5 deg leeway 30 deg leeway Figure 7. Number of validated shark analogue sightings with three levels of sighting angle leeway across all trials for each aircraft (closed bars). The total number of analogues deployed at each distance from the flight paths is indicated by open bars. Assessment of shark sighting rates by aerial beach patrols Robbins et al. 500+ m
Page 1 and 2: Assessment of shark sighting rates
Page 3 and 4: Contents i TABLE OF CONTENTS TABLE
Page 5 and 6: Acknowledgements iii ACKNOWLEDGEMEN
Page 7 and 8: NSW DPI 5 1. BACKGROUND 1.1. Aerial
Page 9 and 10: NSW DPI 7 2. METHODS 2.1. Study loc
Page 11 and 12: NSW DPI 9 The six flight transects
Page 13 and 14: NSW DPI 11 A B Figure 3. (A) Google
Page 15 and 16: NSW DPI 13 3. RESULTS 3.1. Depth ex
Page 17 and 18: NSW DPI 15 3.2. Distance experiment
Page 19: NSW DPI 17 Percentage of analogues
Page 23 and 24: NSW DPI 21 Table 3. Regression anal
Page 25 and 26: NSW DPI 23 3.4. Coastal aerial patr
Page 27 and 28: NSW DPI 25 Number of sightings per
Page 29 and 30: NSW DPI 27 too deep, or are in wate
Page 31 and 32: NSW DPI 29 4.3. Conclusion Severe l
Page 33 and 34: NSW DPI 31 Clark CW, Brown MW, Cork
Page 35 and 36: NSW DPI 33 Rowat D, Gore M, Meekan
Page 37 and 38: NSW DPI 35 No. 27 Rowling, K.R. and
Page 39 and 40: NSW DPI 37 No. 82 Silberschnieder,

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