An assessment of survey techniques using unmanned aerial vehicles to monitor Nile crocodiles (Crocodylus niloticus)

Abstract

Monitored populations of the Nile crocodile Crocodylus niloticus at the southern end of its distribution, in the KwaZulu-Natal province of South Africa, are largely in decline. Trophy hunting of wild Nile crocodiles is only permitted at Pongolapoort Dam in the province, and monitoring of this population is required to enable the setting of annual hunting quotas. The aims of this study were to determine the feasibility of using drones to count and measure Nile crocodiles in the inlet to the dam and evaluate the utility of photomosaics, individual photographs, and videos for this purpose. A total of 16.5 km of shoreline was surveyed and 183 sub-adult and adult crocodiles observed, averaging 10.74 crocodiles per kilometer. The use of drones was cost-effective compared to traditional survey methods even though a higher number of person hours were required for data collection and processing. We recommend that drones be used to acquire video footage, supplemented by photomosaics in areas where large aggregations of crocodiles occur, to regularly monitor this crocodile population.