Abstract
Determining the small-scale movement patterns of marine vertebrates usually requires invasive active acoustic tagging or in-water monitoring, with the inherent behavioural impacts of those techniques. In addition, these techniques rarely allow direct continuous behavioural assessments or the recording of environmental interactions, especially for highly mobile species. Here, we trial a novel method of assessing small-scale movement patterns of marine vertebrates using an unmanned aerial vehicle that could complement longer-term tracking approaches. This approach is unlikely to have behavioural impacts and provides high accuracy and high frequency location data (10 Hz), while subsequently allowing quantitative trajectory analysis. Unmanned aerial vehicle tracking is also relatively low cost compared to single-use acoustic and GPS tags. We tracked 14 sharks for up to 10 min in a shallow lagoon of Heron Island, Australia. Trajectory analysis revealed that Epaulette sharks (Hemiscyllium ocellatum) displayed sinusoidal movement patterns, while Blacktip Reef Sharks (Carcharhinus melanopterus) had more linear trajectories that were similar to those of a Lemon shark (Negaprion acutidens). Individual shark trajectory patterns and movement speeds were highly variable. Results indicate that Epaulette sharks may be more mobile during diurnal low tides than previously thought. The approach presented here allows the movements and behaviours of marine vertebrates to be analysed at resolutions not previously possible without complex and expensive acoustic arrays. This method would be useful to assess the habitat use and behaviours of sharks and rays in shallow water environments, where they are most likely to interact with humans.
Highlights
Understanding animal movement requires information on foraging decisions, spatial use, and the distributions of populations [1]
Flight caching was enabled, and the drone was manually piloted over the scientific research zone at an altitude of 15 m when searching for Epaulette sharks, and 40 m when searching for larger sharks
Our study demonstrates that Unmanned aerial vehicles (UAVs) technology is a cost-effective tool for obtaining high-resolution information on the movement and behaviour of marine vertebrates, providing utilisation data of habitats such as the reef flat
Summary
Understanding animal movement requires information on foraging decisions, spatial use, and the distributions of populations [1]. While large-scale movements may be influenced by reproductive requirements or temperature [2], smaller-scale movement patterns of animals may be driven by food patches, habitat, or inter and intraspecific interactions between predator and prey, or commensal relationships [3,4]. Insight into how and why animals move within and across environments can be obtained by understanding the relationship between the environment and movement trajectories [5,6]. Gaining an understanding of the spatial dynamics of larger vertebrates in these coastal zones will facilitate better management of common anthropogenic threats and abatements.
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