Data from: 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
eight lethally caught North Pacific right whales (E. japonica), for which
body mass was measured. This conversion factor was consequently used to
predict the body mass of the free-living whales. 3. The cross-sectional
body shape (height-width ratio) of the whales was slightly flattened
dorso-ventrally at the anterior end of the body, almost circular in the
mid region, and significantly flattened in the lateral plane across the
posterior half of the body. Compared to a circular cross-sectional model,
our body mass model incorporating body length, width and height improved
mass estimates by up to 23.6% (mean=6.1%, SD=5.27). Our model had a mean
error of only 1.6% (SD=0.012), compared to 9.5% (SD=7.68) for a simpler
body length-to-mass model. The volume-to-mass conversion factor was
estimated at 754.63kg m-3 (SD=50.03). Predicted body mass estimates were
within a close range of existing body mass measurements. 4. We provide a
non-invasive method to accurately estimate body mass of free-living whales
while accounting for both their structural size (body length) and relative
body condition (body width). Our approach can be directly applied to other
marine mammals by adjusting the model parameters (body mass model script
provided).