Background
Effective conservation and fisheries management rely on robust biological data collected using methods suited to the target species, habitat, and research objective. In elasmobranch studies, techniques range from catch-based approaches to non-invasive methods like visual surveys and remote video systems. Emerging technologies, such as underwater drones, offer opportunities to combine the strengths of these approaches while extending survey coverage across broader spatial and temporal scales. Remotely operated vehicles (ROVs) are particularly promising for accessing habitats and conditions beyond the reach of traditional techniques.
Aims
This study evaluates the potential of ROVs for surveying elasmobranchs and compares their effectiveness to established techniques. The primary goal was to modify observation-class ROVs for elasmobranch-specific monitoring. We assessed ROV performance across temporal and spatial gradients relative to three widely used survey methods: UVS, BRUVs, and catch data. Rather than identifying the best method, we aimed to contextualise ROV data within existing frameworks.
Methods
A BlueROV2 was customised with four top-mounted GoPros for 360° video coverage and bottom-mounted torches for crepuscular and nocturnal surveys. Four pilot experiments were conducted across varying habitats and conditions. In three, ROVs were compared to other methods; the fourth tested ROV performance at night. Performance was evaluated based on species richness and relative abundance detected.
Results
ROVs produced data comparable to diver-based transects and offered advantages including deeper access, night survey capability, and enhanced safety. ROVs also complemented BRUVs and catch surveys by improving abundance and occurrence estimates. The iterative process revealed practical insights on optimising survey design in strong currents, and the four-camera setup proved especially useful, capturing individuals missed by forward-facing cameras.
Conclusion
Overall, this study provides practical guidance and best practices for ROV-based elasmobranch surveys and highlights the value of integrating ROVs into traditional survey frameworks to address spatial and temporal limitations in elasmobranch research.