How Do You Weigh A Living Whale?

Credits to Fredrik-Christiansen (Photo from Oceanographic Magazine)

The obvious answer is that scientists can't really use a scale.

For starters, dead whales can weigh as much as 210 kg to a whopping 160 t. Besides, measurements can be inaccurate given the physical distortion of carcasses caused by bloating and deflation.

But scientists have something new in their arsenal.

Something that can be used above the sea...

But first, let’s learn about how whales are weighed in the past.

The only way to get data on the body mass of whales was to weigh dead or stranded individuals. Studying blue whales, for instance, was limited to dead specimens from whaling operations, fisheries bycatch and beach strandings.

This can be especially limiting with scientists boxed from collecting longitudinal data over a whale's lifespan. This has prevented the inclusion of body mass in many studies in ecology, physiology and bioenergetics.

But now scientists can accurately estimate the weight of free-living whales.

The answer? 

Drones.

Scientists took aerial photos of 86 southern right whales off the coast of Península Valdés, Argentina.

The waters were clear and the sheer number of whales gathering every winter to breed allowed for the measurement of both the dorsal and lateral sides of the whales.

With crisp images, they were able to get data for length, width and height.

These values were then plugged into a model (and voila!) an accurate calculation of whales' body volume and mass.

What's more fascinating is that the parameters of the model can be adjusted to estimate as well the size of other marine mammals, an alternative that can be considered over invasive methods.

This discovery opens a lot of doors for research.

For one, they can now explore the growth of known aged individuals to calculate their body mass increase over time and the energy requirement for growth. They can also peek into the daily energy requirements of whales and derive prey consumption.

Weight data can also provide insights on how chronic stressors influence whale survival and how they can produce offspring.

This innovation also paved the way to recreating a 3D mesh of the whale and a full-color 3D model in the works, which can be used for studying movement and for educational purposes.

SeaLifeBase hosts data on the weight of marine mammals, from blue whale to the dwarf sperm whale, the smallest known whale.

Feel free to explore.

Happy learning!

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[1] Christiansen, F., Sironi, M., Moore, M. J., Di Martino, M., Ricciardi, M., Warick, H. A., Duncan, J. I., Gutierrez, R., Uhart, M. M. (2019). Estimating body mass of free‐livingwhales using aerial photogrammetry and 3D volumetrics. Methods in Ecology andEvolution.

[2] EurekAlert! Researchers use drones to weigh wales. Retrieved from  https://www.eurekalert.org/pub_releases/2019-10/whoi-rud100119.php?fbclid=IwAR2aML0gasxOfu2q2IqSwNoax8znfubn0EH36CHKgnz2nhqXi7muvdVjyWI

[3] Jefferson, T.A., S. Leatherwood and M.A. Webber 1993 FAO species Identification Guide: Marine Mammals of the World. Rome, FAO. 320 p. + 587 figures.