NZ fur seal population assessment, Bounty Islands

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POP2019-05: NZ fur seal population assessment Bounty Islands (PDF, 1,421K)

Summary

New Zealand fur seals, Arctocephalus forsteri, are captured in the trawl fishery for southern blue whiting around the Bounty Islands at one of the highest rates of any New Zealand trawl fishery (Abraham and Thompson 2015). Because many of the islands are inaccessible to boat-based landings, aerial photographs appear to be the best way to estimate population numbers across the whole Bounty Island group and assess trends over time. Aerial photographs taken from aeroplane or boat-based helicopter have been used to count fur seals (Taylor 1982, 1996) and, more recently, Salvin’s albatross Thalassarche salvini (e.g. Baker et al. 2012, 2014; Baker and Jensz 2019). However, surveys involving aeroplane charter or helicopters are logistically demanding and expensive, so other methods for aerial surveys are being explored.

Drones hold promise as an alternative way to obtain aerial photographs suitable for estimating fur seal numbers at reduced effort and cost. Also known as unmanned aerial vehicles or remotely piloted aircraft (UAV, RPA), drones are increasingly used for seal population assessment and monitoring worldwide (Adame et al. 2017; McIntosh et al. 2018; Arona et al. 2018; Gooday et al. 2018; Sorrell et al. 2019). 

This study aimed to assess whether a drone can be used for aerial surveys to quantify NZ fur seal population size at the Bounty Islands without impacting on seals, penguins and albatrosses there. The trial had three parts:

• Disturbance trials: Flight characteristics (flight speed, height, time of day) trials to find the combination that causes least disturbance.
• Image capture trials: Using the flight characteristics that cause least disturbance, programmed grids flown.
• Image processing: Images of suitable quality for fur seal detection were stitched and counted.

Publication details

Rexer-Huber K., Parker G.C. 2020. Bounty Islands drone trials: feasibility for population assessment of NZ fur seal. POP2019-05 final report for the Conservation Services Programme, Department of Conservation. Parker Conservation, Dunedin. 18 p.