Drone images afford more detections of marine wildlife than real-time observers during simultaneous large-scale surveys

Amanda J Hodgson; Nat Kelly; David Peel

doi:10.7717/peerj.16186

Drone images afford more detections of marine wildlife than real-time observers during simultaneous large-scale surveys

PeerJ. 2023 Nov 3:11:e16186. doi: 10.7717/peerj.16186. eCollection 2023.

Authors

Amanda J Hodgson^{1

2}, Nat Kelly³, David Peel⁴

Affiliations

¹ School of Science, Edith Cowan University, Joondalup, Western Australia, Australia.
² Harry Butler Institute, Murdoch University, Murdoch, Western Australia, Australia.
³ Australian Antarctic Division, Kingston, Tasmania, Australia.
⁴ Data 61, CSIRO, Hobart, Tasmania, Australia.

Abstract

There are many advantages to transitioning from conducting marine wildlife surveys via human observers onboard light-aircraft, to capturing aerial imagery using drones. However, it is important to maintain the validity of long-term data series whilst transitioning from observer to imagery surveys. We need to understand how the detection rates of target species in images compare to those collected from observers in piloted aircraft, and the factors influencing detection rates from each platform. We conducted trial ScanEagle drone surveys of dugongs in Shark Bay, Western Australia, covering the full extent of the drone's range (∼100 km), concurrently with observer surveys, with the drone flying above or just behind the piloted aircraft. We aimed to test the assumption that drone imagery could provide comparable detection rates of dugongs to human observers when influenced by same environmental conditions. Overall, the dugong sighting rate (i.e., count of individual dugongs) was 1.3 (95% CI [0.98-1.84]) times higher from the drone images than from the observers. The group sighting rate was similar for the two platforms, however the group sizes detected within the drone images were significantly larger than those recorded by the observers, which explained the overall difference in sighting rates. Cloud cover appeared to be the only covariate affecting the two platforms differently; the incidence of cloud cover resulted in smaller group sizes being detected by both platforms, but the observer group sizes dropped much more dramatically (by 71% (95% CI [31-88]) compared to no cloud) than the group sizes detected in the drone images (14% (95% CI [-28-57])). Water visibility and the Beaufort sea state also affected dugong counts and group sizes, but in the same way for both platforms. This is the first direct simultaneous comparison between sightings from observers in piloted aircraft and a drone and demonstrates the potential for drone surveys over a large spatial-scale.

Keywords: Abundance; Aerial photography; Aerial survey; Detection probability; Drone; Dugong; Environmental covariates; Imagery; UAV; Unoccupied aerial system.

MeSH terms

Aircraft
Animals
Animals, Wild*
Dugong*
Humans
Surveys and Questionnaires
Unmanned Aerial Devices

Grants and funding

This project was funded by the Australian Marine Mammal Centre (AMMC) under the Bill Dawbin Postdoctoral Research Award granted to Amanda Hodgson. Additional funding was received from AMMC to conduct the manual image review. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.