Determining Stingray Movement Patterns in a Wave-Swept Coastal Zone Using a Blimp for Continuous Aerial Video Surveillance

Abstract

Stingrays play a key role in the regulation of nearshore ecosystems. However, their movement ecology in high-energy surf areas remains largely unknown due to the notorious difficulties in conducting research in these environments. Using a blimp as an aerial platform for video surveillance, we overcame some of the limitations of other tracking methods, such as the use of tags and drones. This novel technology offered near-continuous coverage to characterise the fine-scale movements of stingrays in a surf area in Kiama, Australia, without any invasive procedures. A total of 98 stingray tracks were recorded, providing 6 h 27 min of movement paths. The tracking data suggest that stingrays may use a depth gradient located in the sandflat area of the bay for orientating their movements and transiting between locations within their home range. Our research also indicates that stingray behaviour was influenced by diel periods and tidal states. We observed a higher stingray occurrence during the afternoon, potentially related to foraging and anti-predatory strategies. We also saw a reduced route fidelity during low tide, when the bathymetric reference was less accessible due to stranding risk. Considering the increasing threat of anthropogenic development to nearshore coastal environments, the identification of these patterns can better inform the management and mitigation of threats.

Going Batty: The Challenges and Opportunities of Using Drones to Monitor the Behaviour and Habitat Use of Rays

“…Continuing to publish protocols for studying rays can also provide effective solutions and problem-solving skills to ray researchers using drones as some species may be more sensitive to drone impacts. Blimps have also been successfully to observe ray movement within coastal ecosystems and represent a viable alternative, particularly for species showing sensitivity to drone impacts [69].…”

Drone-Based Tracking of the Fine-Scale Movement of a Coastal Stingray (Bathytoshia brevicaudata)

“…Despite criticism of the limitations presented by the battery life o drones (approximately 30 min for most quad-rotor drones such as those used in thi study), tracks of rays were conducted for extended periods of time, with an average track time of 13 min and 6 s and a maximum of almost 27 min. This is an average track tim approximately four times longer than those collected by Ruiz-Garcia et al (2020) [64] us ing a blimp. The easy maneuverability of drones enabled tracks to occur beyond the op erator's immediate field of view, allowing for track lengths of over 800 m in this study.…”

“…Rays were consistently found in the dredged channel within the estuary and showed little reaction to moored boats, but would often flurry away from nearby moving boats, particularly at shallower depths (Oleksyn, unpublished data). Shorttail stingrays alter their swimming behavior in shallow environments in close proximity to swimmers [64]. While it is possible that similar animal-human interactions would occur at Currambene Creek, none were observed during this study.…”

“…This study is the first to effectively utilize drones to investigate the fine-scale behavior of rays. While other approaches such as acoustic telemetry [85] and aerial surveillance from a blimp [64] have recently been used to observe the movement ecology of rays, drones present a low-cost, non-invasive opportunity to collect data for marine animals at a very high resolution. Despite criticism of the limitations presented by the battery life of drones (approximately 30 min for most quad-rotor drones such as those used in this study), tracks of rays were conducted for extended periods of time, with an average track time of 13 min and 6 s and a maximum of almost 27 min.…”

“…Furthermore, acoustic telemetry requires the rays to be tagged, an expensive and invasive process that can have adverse short-term impacts on fish behavior [61][62][63]. Ruiz-Garcia et al (2020) [64] used a blimp to track stingrays, including short-tail stingrays (Bathytoshia brevicaudata), in a wave-swept coastal zone, finding that stingray movement was impacted by both diel periods and tidal states. This approach recorded tracks of numerous stingrays but could not follow the movement of the stingray once it left the field of view, resulting in a mean track time of approximately 3 to 4 min.…”