Assessing variation in assemblages of large marine fauna off ocean beaches using drones

Abstract

The turbulent waters off ocean beaches provide habitat for large marine fauna, including dolphins, sharks, rays, turtles and game fish. Although, historically, these assemblages have proven difficult to quantify, we used a new drone-based approach to assess spatial and temporal variation in assemblages of large marine fauna off four exposed beaches in New South Wales, Australia. In total, 4388 individual large marine animals were identified from 216 drone flights. The most common taxa, bottlenose dolphins (Tursiops spp.) and Australian cownose rays (Rhinoptera neglecta), occurred in 25.5 and 19.9% of flights respectively. White (Carcharodon carcharias), bull (Carcharhinus leucas) and other whaler (Carcharhinus spp.) sharks were observed in <1% of flights. There was significant variation in the structure of assemblages of large fauna among beaches, with those adjacent to riverine estuaries having greater richness and abundance of wildlife. Overall, drone surveys were successful in documenting the spatio-temporal dynamics of an impressive suite of large marine fauna. We contend that emerging drone technology can make a valuable contribution to the ecological information required to ensure the long-term sustainability of sandy-beach ecosystems and associated marine wildlife.

Variation in cownose ray Rhinoptera neglecta abundance and group size on the central east coast of Australia

“…Although most of the environmental variables we tested did not explain significant variation in the abundance of R. neglecta , wind had a significant negative effect on the number of individuals per transect. Wind can influence the detectability of marine wildlife during aerial surveys (Butcher et al ., ; Lubow & Ransom, ) and limiting surveys to days with favourable weather conditions has been recommended to avoid this issue (Kelaher et al ., ). The negative association between wind and cownose rays may also have been caused by R. neglecta moving offshore into deeper water during periods of strong winds.…”

“…Using DJI Phantom 4 quadcopters (http://www.dji.com) equipped with circular polarising filters, surveys were completed between 09:00–11:00 h each day of sampling. For each flight, starting directly behind the surf break, a drone would traverse a 2 km transect at 60 m altitude with the camera pointed straight down, which provided an c .110 m field of view (Kelaher et al ., ).…”

“…With recent technology advances, unmanned aerial vehicles (hereafter called drones; Chapman, ) are being increasingly used for marine wildlife research (Chabot, ; Colefax et al ., ; Kelaher et al ., ; Rieucau et al ., ). Drone surveys are an effective method for quantifying marine megafauna and are being increasingly used to sample large fishes, including sharks, rays, turtles and gamefish (Colefax et al ., ; Kelaher et al ., ). Compared with catch‐based research methods, drones have limited effect on elasmobranchs and can provide similar results to visual census (Raoult & Gaston, ).…”

“…Relative to aerial surveys using manned planes and helicopters, drone surveys are generally cheaper and come with improved safety (Colefax et al ., ; Jones et al ., ; Watts et al ., ), as well as decreased auditory interfereence for wildlife and people (Erbe et al ., ). Such considerations are driving the increased use of drones for fisheries conservation biology (Kelaher et al ., ), which will probably expand further as sensor technology improves capacity to detect large fish in the water column ( e.g ., hyperspectral imagery; Colefax et al ., ) and regulatory authorities increase permissions for unmanned drones to fly beyond visual line of sight (Colefax et al ., ).…”

Drones detect illegal and derelict crab traps in a shallow water estuary

“…Drones (also known as RPAS or UAV) have recently become sophisticated and affordable to create large‐scale impacts to various commercial and scientific operations, such as fauna surveys (Ezat, Fritsch & Downs, ; Kelaher et al., ), agriculture (Rey‐Caramés, Diago, Martín, Lobo & Tardaguila, ), anti‐poaching (Mulero‐Pazmany, Stolper, van Essen, Negro & Sassen, ), search and rescue (Karaca et al., ), engineering inspections (Omar & Nehdi, ) and habitat mapping (Ventura, Bruno, Jona Lasinio, Belluscio & Ardizzone, ; Chabot, Dillon, Ahmed & Shemrock, ). Drones are also being incorporated into fisheries management, but their use is still largely experimental, rather than part of routine operating procedures (Kopaska, ; Brooke et al., ; Toonen & Bush, ).…”