Unmanned Aerial Vehicle (UAV) Remote Sensing of Behaviour and Habitat Use of the Nationally Endangered Bottlenose Dolphin (Tursiops Truncatus) off Great Barrier Island
Bottlenose dolphins (Tursiops truncatus) are widely distributed in temperate and tropical waters. In New Zealand, Bottlenose dolphins are classified as “nationally endangered”, as there are fewer than 1,000 adults. Great Barrier Island, New Zealand has been identified as a potential hotspot for the North Island population of bottlenose dolphins, with dolphins observed year-round, exhibiting evidence of site fidelity. However, it is unclear how many dolphins are using these areas and why. How the animal uses its environment is a critical step in conservation management for this species and behaviour patterns have not been described for this region. Oceanographic features (e.g. currents, fronts and upwelling), other abiotic factors (temperature, bathymetry and topography), prey distributions and human influences (boating, fishing and environmental contaminants) are known to influence behaviour patterns, group size, and group composition in cetaceans. Behavioural observations in cetaceans are, however, challenging to study, that is, most of the animal activities take place below the water surface, out of sight of boat based observers. Vertical take-off and landing (VTOL) unmanned aerial vehicles (UAVs) represent a novel and cost-effective research tool to investigate cetacean behaviour, as conventional aircraft are expensive, limited in the altitude they can fly at and potentially disturb sensitive wildlife. UAVs are an economical, easy to use and operate, safe, portable and a versatile alternative that may cause little disturbance. In addition, the aerial observation from the UAVs allows assessment of cetacean behaviour from an advantageous perspective and can collect high spatial and temporal resolution data, providing the opportunity to gather accurate data about group size, age class and subsurface behaviour.
The use of UAVs is rapidly becoming a common practice both for marine mammal researchers and whale-watchers around the world. However, this new research tool has not yet been used to study bottlenose dolphins in New Zealand waters. In the absence of previously undertaken dedicated UAV surveys, the present thesis is dedicated to investigating and determining how effective lightweight low altitude UAVs are in describing behaviour of bottlenose dolphins off Great Barrier Island. In addition, the thesis compares UAVs with traditional boat-based observations in terms of effectiveness, safety and impact on dolphin behaviour. Surveys were conducted between July 2015 and March 2017 at the west coast of Great Barrier Island. Initially, boat-based surveys were conducted to assess the short term behavioural responses of resting bottlenose dolphins to the VTOL UAV flown at 10 m, 25 m and 40 m altitude. The number of reorientation and tail slap events increased significantly between controls and flights when the UAV was flown at 10 m altitude over the animals. In contrast, no significant difference was detected when the aircraft was flown at 25 m and 40 m altitude. A total of 71 UAV operations were performed over 21 independent groups of bottlenose dolphins. Aggregations of between 6 to 66 individuals were observed with a median group size of 41, whereas 23.8% (n = 5) of the groups contained between 51 and 55 individuals. Calves and neonates were present in the majority of the groups (85.7%, n = 18). Dolphins were found to travel more in summer and autumn, and rest more in winter and spring. Results derived from UAVs were compared with boat data and showed that overall, group size from UAV-derived counts was 71.4% (n = 15) higher, and UAV-derived observations detected significantly more travelling and less resting and less foraging than observations by boat.
Results indicate that low altitude UAVs can be used for surveys over a short duration and range and represented a non-invasive tool to study dolphin behaviour when flying at and above 25 m altitude. The UAV surveys can minimise bias and deliver data that are more robust. However, the results conservatively suggest that UAV similar to the Splashdrone should not be flown at 10 m over bottlenose dolphins. Future research should further identify the threshold at which disturbance occurs (i.e. between 10 and 25 m) and also identify how this differs during different behavioural states other than resting. Finally, this research provides baseline information on the optimal use of UAV for bottlenose dolphins surveys and behavioural studies. Additionally, this study contributed to the development of guidelines for future operational use of UAVs around cetaceans in New Zealand waters.