Using Unmanned Aerial Vehicles (UAVs) to investigate visual detection probability of coastal dolphins during aerial surveys

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Project context and overview

Aerial surveys, using human observers in small aircraft, are used around the world to conduct surveys for estimating the abundance of marine mammals, the results of which are used to inform conservation and management strategies. However, in order to obtain reliable estimates of abundance, this technique requires an understanding of the proportion of time animals are visible to the aerial observers – known as ‘availability bias’. Existing methods of estimating this bias (e.g. dive-tag data; observations from helicopters, vessels or land) have many limitations and don’t necessarily reflect true availability in relation to aerial surveys.

The recent advancement and greater accessibility of unmanned aerial vehicles (UAVs, or ‘drones’) provides one potential solution to estimating availability bias. Their use as a non-invasive tool for marine mammal research is increasing globally, and includes successful applications to dugong, humpback and other baleen whales from MUCRU researchers and colleagues to date.

In this project, we are developing methods for using small, vessel-launched UAVs to directly record aerial video of coastal dolphins and estimate their availability. We are focussing on Australian humpback dolphins (Sousa sahulensis) off the Pilbara,  in north-western Australia. Our results will feed directly in to the Western Australian (WA) government’s three-year programme of aerial surveys to estimate the distribution and abundance of humpback dolphins in this region, lead by DBCA’s Dr. Holly Raudino. Furthermore, the methods we develop will be broadly applicable to other species.

Four Australian humpback dolphins close to shore off the Dampier coast, with the salt works providing a backdrop.

Research Team

This project is funded by the WA Department of Biodiversity, Conservation and Attractions and the Sea World Research and Rescue Foundation Inc., with in-kind support provided by Pilbara Ports Authority, Hampton Harbour Boat & Sailing Club, and GUS-UAV.

Objectives and approach

Our specific objectives are to:

  1. Develop and field-test a methodology for recording focal video observations of coastal dolphins from a small vessel-launched, multi-rotor UAV.
  2. Use UAVs to collect aerial video of dive/surface cycles of humpback dolphins across a variety of group sizes and compositions, behavioural states, and environmental conditions.
  3. Analyse UAV video to estimate the proportion of time dolphins are available to be detected from the air, and how this varies according to the variables outlined above.

A UAV being manoeuvred into position over a small group of Australian humpback dolphins, with the research vessel in frame; the image was taken from a second UAV at a higher altitude.

Our approach is to use a small research boat to search coastal waters for dolphins. Once sighted, a multi-rotor UAV is launched and flown into a position above the dolphin group to record video footage of the dolphin group across multiple dive/surface cycles, from which availability data can be directly estimated. By operating a ‘tag-team’ of two UAVs with overlap in video footage, we have the ability to collect continuous footage of the dolphin group for up to two hours. Supplementary behavioural and group composition data are collected simultaneously by observers on the vessel, which is positioned as far away from the dolphins as practical to minimise any influence on the animals’ behaviour.

Retrieving the UAV in calm, overcast conditions in the Dampier Archipelago.

Project schedule

February-March 2017: Having received expert advice on the capabilities of different UAV systems from GUS-UAV’s Robert Lednor and Nick Sargeant, we selected DJI’s Phantom 4 Pro as a suitable and cost-effective UAV for our purposes. The project then commenced with land-based training and field trials in coastal waters off Perth, where the research team became familiar with the UAV system and its safe operation from a small vessel. A local aggregation of Indo-Pacific bottlenose dolphins (Tursiops aduncus) provided an accessible species on which to develop our methodology for collecting aerial video.

A large group of bottlenose dolphins in Cockburn Sound videoed during the pilot study off Perth, with the team practising retrieving the UAV (inset).

April-May 2017: For the main data collection, the research team headed north to spend five weeks collecting aerial video of humpback dolphins off the north-west coast of WA, focussing on the Dampier Archipelago.  Investigators Alex Brown and Simon Allen were lucky enough to have experienced hands Delphine Chabanne and Julian Tyne to assist with the fieldwork. We were also joined by Nick Sargeant from GUS-UAV for the first week, to help iron-out any technical or safety issues with operating the UAVs. A poor weather forecast for the final week in Dampier saw the team relocate to Exmouth to steal a few more days on the water.

Four humpback dolphins close to shore in the Dampier Archipelago, as viewed from the UAV at ~80m altitude, with the research vessel visible in the top right.

Despite experiencing rather more windy days than were anticipated, we had reasonable success in locating animals and accrued 45 sightings of humpback dolphins in total.  The method proved effective, with each successful UAV flight collecting around 20 minutes of video, covering multiple dive/surfacing intervals of dolphins from a typical altitude of 80 metres. Over 30 hours of video was captured, representing a variety of dolphin group compositions, behaviour and environmental conditions (such as water depth, turbidity and wind strength).

A group of four humpback dolphins in more turbid waters close to shore in the Dampier Archipelago.

A large mixed group of humpback and bottlenose dolphins in clear waters off the North West Cape.

June-December 2017: With the video in hand, the next stage is to review the footage from each follow and extract information on time/number of dolphins visible, and combine this with environmental and behavioural data. Ryan Douglas and Corrine Douglas from DBCA are leading the review of footage and we will then conduct the analyses. Ultimately, an availability correction factor will be estimated to correct estimates of humpback dolphin abundance derived from DBCA’s aerial surveys.

Media

Drones shed new light on Australian humpback dolphin in WA, ABC News, May 2017.

Relevant lab publications

  • Hodgson, A., D. Peel, and N. Kelly. 2017. Unmanned aerial vehicles for surveying marine fauna: assessing detection probability. Ecological Applications 27: 1253-1267. doi: 10.1002/eap.1519
  • Hunt, T., Bejder, L., Allen, S.J., Rankin, R.W., Hanf, D. and Parra, G. J.  2017. Demographic characteristics of Australian humpback dolphins reveal important habitat toward the south-western limit of their range. Endangered Species Research 32: 71-88. doi: 10.3354/esr00784
  • Christiansen, F., Rojano-Donate, Madsen, P.T. and Bejder, L. 2016. Noise levels of multi-rotor unmanned aerial vehicles with implications for potential underwater impacts on marine mammals. Frontiers in Marine Science 3: 277. doi: 10.3389/fmars.2016.00277
  • Hanf, D. M., Hunt, T. and Parra, G. J. 2016. Humpback dolphins of Western Australia: a review of current knowledge and recommendations for future management. Advances in Marine Biology 73: 193-218. doi: 10.1016/bs.amb.2015.07.004

Research ethics: This research project is being conducted under a research permit from the WA DBCA (formerly Parks and Wildlife), with approval from Murdoch University Animal Ethics Committee, notifications to CASA and the Department of Agriculture and Food, and following consultation and cultural awareness training with Murujuga Aboriginal Corporation.

Project sponsors:

We are also grateful for favourable boat hire rates from the Univeristy of Zürich/Shark Bay dolphin Research Alliance.

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