Using unmanned aerial vehicle (UAV) surveys and image analysis in the study of large surface‐associated marine species: a case study on reef sharksCarcharhinus melanopterusshoaling behaviour

Abstract

A novel image analysis-based technique applied to unmanned aerial vehicle (UAV) survey data is described to detect and locate individual free-ranging sharks within aggregations. The method allows rapid collection of data and quantification of fine-scale swimming and collective patterns of sharks. We demonstrate the usefulness of this technique in a small-scale case study exploring the shoaling tendencies of blacktip reef sharks Carcharhinus melanopterus in a large lagoon within Moorea, French Polynesia. Using our approach, we found that C. melanopterus displayed increased alignment with shoal companions when distributed over a sandflat where they are regularly fed for ecotourism purposes as compared with when they shoaled in a deeper adjacent channel. Our case study highlights the potential of a relatively low-cost method that combines UAV survey data and image analysis to detect differences in shoaling patterns of free-ranging sharks in shallow habitats. This approach offers an alternative to current techniques commonly used in controlled settings that require time-consuming post-processing effort.

Use of Drones in Fishery Science

“…; Rieucau et al. ), improved tracking of planktonic food and harmful algal blooms (Kislik et al. ), and fluid lensing to see through water and catalog subsurface habitat (Chirayath and Earle ) are examples of novel postprocessing techniques that can provide greater insight into critical questions in fisheries research.…”

“…Rieucau et al. () conducted UAS flights using a DJI Phantom II quadcopter and a GoPro Hero 3+ with a polarizing filter to study shoaling pattern behavior of Blacktip Reef Sharks Carcharhinus melanopterus in a shallow lagoon environment. Four‐hundred‐meter transects were flown at an altitude of 12 m perpendicular to a fringing reef, a deeper channel, and a back reef sandflat to obtain images of Blacktip Reef Shark aggregations.…”

“…For example, Rieucau et al. () presented a novel image analysis technique applied to UAS survey data to detect and locate free‐ranging epipelagic individuals (Blacktip Reef Sharks) within aggregations in a shallow lagoon off the north coast of Moorea, French Polynesia. Their technique relied on the development of a semi‐automated tracking algorithm (see Rieucau et al.…”

“…Their technique relied on the development of a semi‐automated tracking algorithm (see Rieucau et al. : their Figure ) for detecting and precisely positioning each individual shark swimming in shoals close to the surface. Their approach was also employed to provide (1) relative body size estimates (measured in pixels) and (2) intrinsic characteristics of shark shoals (i.e., distance and alignment among shoalmates) across different environmental conditions.…”

“…Chief advantages are maneuverability, the ability to vertically take-off and land without a flat surface (by hand), and the capacity to hover; the weaknesses of the multi-rotor unit are its short flight time and range (González-Jorge et al 2017). Rieucau et al (2018) conducted UAS flights using a DJI Phantom II quadcopter and a GoPro Hero 3+ with a polarizing filter to study shoaling pattern behavior of Blacktip Reef Sharks Carcharhinus melanopterus in a shallow lagoon environment. Four-hundred-meter transects were flown at an altitude of 12 m perpendicular to a fringing reef, a deeper channel, and a back reef sandflat to obtain images of Blacktip Reef Shark aggregations.…”