Uso de veículos aéreos não tripulados (VANT’s) para monitoramento de condição corporal de pequenos cetáceos sul americanos

Abstract

Body condition in mammals can be interpreted as their energy reserve, where the best body condition is associated with greater reproductive success and better efficiency in thermoregulation processes. The popularization of unmanned aerial vehicles (UAVs or drones), made it possible to monitor the body condition of free-living cetaceans, using aerial photogrammetry techniques. In this work, an aerial photogrammetry protocol using a drone was applied to estimate morphometric and body condition measurements in franciscanas (Pontoporia blainvillei, n = 122) and guiana-dolphins (Sotalia guianensis, n = 41), during the winter (July / 2019) and summer (March / 2020) in Babitonga Bay-SC. A 115 cm object was used as a scale for measurements in corresponding pixels at different altitudes (15-50 m). The scale calibration model considering the altitude and environmental variables (sea state and cloud cover), presented the best fit. Five measurements of the animals were extracted, body length, widths in the anterior portion of the pectoral fin, width in the axilla region, anterior to the dorsal fin and posterior to the dorsal fin (CC, AP, AX, AD, PD respectively). The widths referring to the anterior portions (AP, AX and AD) of the animals were higher in winter. The body condition index AD_CC, reported to be efficient in monitoring seasonal variations in the body condition of the species studied, showing 1.1% higher values in winter. The three categories proposed for the AD_CC index ("Abaixo", "Média" and "Acima"), provide efficient monitoring of the body condition of species between the size classes. The “Média” body condition was the most frequent for both species studied and was observed in all size classes, while the “Abaixo” body condition presented greater frequency in the summer, occurring only in the upper size classes. The presented protocol was able to obtain accurate morphometric and body condition measurements in both species, highlighting the potential of using aerial photogrammetry techniques to monitor morphometric patterns and body condition in the small species of cetaceans studied.