Abstract
BackgroundBiologging studies have revealed a wealth of information about the spatio-temporal movements of a wide range of vertebrates large enough to carry electronic tracking tags. Advances in autonomous underwater vehicles (AUVs or UAVs) and unmanned aerial vehicles (commonly known as drones), which can carry far larger payloads of sensor technologies, have revealed insights into the environment through which animals travel. Some AUVs have been used to film target animals, but are generally limited to periods as long as a drone operator can actively follow an animal. In the present study, we use an AUV, the REMUS-100 SharkCam, paired with a custom transponder tag attached to the shark, to autonomously follow three basking sharks for a cumulative total of 10.9 h to collect video and environmental data on their sub-surface behaviour. The basking shark is the second largest fish in the world and is endangered globally, but despite being subject to various biologging studies, little is known of this species breeding ecology and their mating grounds remain unknown.ResultsWe detail the first successful autonomous tracking of basking sharks, comprising three missions that filmed basking sharks in mid-water and close to benthic habitats. Sharks spent very little time feeding, and travelled relatively close to sandy, rocky and algae-covered benthos. One basking shark was observed defecating. Conspecifics were not observed in the three missions, nor were courtship or breeding behaviours. AUV offset distances for videography were determined iteratively through tracking. These offsets varied depending on the trade-off of between water clarity and proximity of the AUV for obtaining useful video data and directly influencing shark behaviour.ConclusionsThe present study is the first successful use of an AUV to gain insight into the sub-surface behaviour of basking sharks.
Highlights
Biologging studies have revealed a wealth of information about the spatio-temporal movements of a wide range of vertebrates large enough to carry electronic tracking tags
Between 11th and 16th July 2019, three autonomous underwater vehicles (AUVs) missions were conducted on two female and one male basking shark gathering a range of insights into surface and subsurface behaviour of these animals (Table 1; Fig. 2)
The AUV was fitted with a rearward facing camera for this mission
Summary
Biologging studies have revealed a wealth of information about the spatio-temporal movements of a wide range of vertebrates large enough to carry electronic tracking tags. Developments in autonomous underwater vehicles (AUVs) and remote sensing have opened up the possibility of using robotic camera and sensing technologies to film both the environment [20] and animals themselves [21] These AUVs can carry larger payloads, and collect more sensor data, and because they can carry a larger payload of batteries, can often last longer than animal-borne cameras. In the present study, basking sharks (Cetorhinus maximus) were tagged with a custom acoustic tracking beacon, recording temperature and pressure (‘retag’ from hereon), and filmed using a REMUS-100 SharkCam Autonomous Underwater Vehicle (AUV from hereon) that could locate and autonomously follow the retag, in the waters of the Inner Hebrides, Scotland (Fig. 1a). The overall purpose of the project was to attempt to film courtship and mating by basking sharks in Scottish waters, as well as to gain a greater insight into basking shark behaviour sub-surface (at depths where they can cannot be directly observed)
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