Estimating body mass of free-living whales using aerial photogrammetry and 3D volumetrics

1. Body mass is a key life history trait in animals. Despite being the largest animals on the planet, no method currently exists to estimate body mass of free-living whales. 2. We combined aerial photographs and historical catch records to estimate the body mass of free-living right whales (Eubalaena sp.). First, aerial photogrammetry from unmanned aerial vehicles was used to measure the body length, width (lateral distance) and height (dorso-ventral distance) of free-living southern right whales (E. australis; 48 calves, 7 juveniles and 31 lactating females). From these data, body volume was estimated by modelling the whales as a series of infinitely small ellipses. The body girth of the whales was next calculated at three measurement sites (across the pectoral fin, the umbilicus and the anus) and a linear model was developed to predict body volume from the body girth and length data. To obtain a volume-to-mass conversion factor, this model was then used to estimate the body volume of ...