Drone Surveys Are More Accurate Than Boat-Based Surveys of Bottlenose Dolphins (Tursiops truncatus)
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Date
2022-04
Open Access Location
Authors
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Journal ISSN
Volume Title
Publisher
MDPI (Basel, Switzerland)
Rights
(c) 2022 The Author/s
CC BY 4.0
CC BY 4.0
Abstract
Generating accurate estimates of group sizes or behaviours of cetaceans from boat-based surveys can be challenging because much of their activity occurs below the water surface and observations are distorted by horizontal perspectives. Automated observation using drones is an emerging research tool for animal behavioural investigations. However, drone-based and boat-based survey methods have not been quantitatively compared for small, highly mobile cetaceans, such as Delphinidae. Here, we conduct paired concurrent boat-based and drone-based surveys, measuring the number of individuals in 21 groups and the behaviour within 13 groups of bottlenose dolphin (Tursiops truncatus). We additionally assessed the ability to detect behaviour events by the drone that would not be detectable from the boat. Drone-derived abundance counts detected 26.4% more individuals per group on average than boat-based counts (p = 0.003). Drone-based behaviour observations detected travelling 55.2% more frequently and association in subgroups 80.4% more frequently than boat-based observations (p < 0.001 for both comparisons). Whereas foraging was recorded 58.3% and resting 15.1% less frequently by the drone than by boat-based surveys, respectively (p = 0.014 and 0.024). A considerable number of underwater behaviours ranging from individual play activities to intra-and inter-species interactions (including those with humans) were observed from the drone that could not be detected from the boat. Our findings demonstrate that drone surveys can improve the accuracy of population counts and behavioural data for small cetaceans and the magnitude of the discrepancies between the two methods highlights the need for cautious interpretation of studies that have relied on boat-derived data.
Description
Keywords
Tursiops truncatus, unmanned aerial systems, drone, behavioural ecology, marine mammals
Citation
Fettermann T, Fiori L, Gillman L, Stockin KA, Bollard B. (2022). Drone Surveys Are More Accurate Than Boat-Based Surveys of Bottlenose Dolphins (Tursiops truncatus). Drones. 6. 4.