Estimating the weight of free-living whales using drones

James Marshall
October 4, 2019

But trying to determine the weight of a living whale based on a carcass is hard.

Video was taken under research permit.

But now a new method, presented in the British Ecological Journal Methods in Ecology and Evolution, will mean scientists can accurately issue doses of sedatives to animals caught in fishing nets.

From these they were able to obtain length, width and height measurements and develop a model that accurately calculated the body volume and mass of the whales.

Due to their large size and penchant for staying in ocean waters, the only way to get an idea of the body mass of whales is to weigh them once they died or are stranded.

"Knowing the body mass of free-living whales opens up new avenues of research", says Christiansen. "We will now be able to look at the growth of known aged individuals to calculate their body mass increase over time and the energy requirements for growth". They added that that the use of drones to estimate whale weight and condition, and also to individually track their young ones, was a real breakthrough in their investigation.

As study co-author Michael J. Moore, a biologist and director of the Marine Mammal Center at the Woods Hole Oceanographic Institution, tells Jessica Leigh Hester of Atlas Obscura, body mass "tells you about the health of the animal, and in the context of its environment, it gives you a sense of how it's doing nutritionally".

As part of the study, the researchers took aerial photos of 86 free-living southern right whales off the coast of Peninsula Valdes in Argentina.

The team worked with the Digital Life Project at the University of MA at Amherst, a nonprofit initiative that creates digital 3D models of living organisms, to create a full-color 3D model of a right whale you can view and download on Sketchfab. What's more, lethal sampling-or killing a whale for the purposes of scientific study-is widely considered to be unethical.

The model can also be used to estimate the size of other marine mammals.

That way of determining body mass has limitations. However, data on their size has historically been limited to dead specimens, with most samples coming from whaling operations, accidental fisheries bycatch or beach strandings. For one thing, scientists aren't able to collect longitudinal data over the lifespan of the whale.

"This conversion factor was consequently used to predict the body mass of the free‐living whales", the study authors explain.

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