By measuring the body width, length and height of free-living southern right whales photographed by drones, researchers have been able to create a model that accurately calculated the body volume and mass of the whales. Up until this point, scientists have had to rely on stranded or dead whales to measure an accurate weight.
To calculate the body volume and mass of southern right whales the researchers took aerial photos of 86 individuals off the coast of Península Valdés, Argentina. This area boasts clear waters and hosts vast numbers of right whales each winter for breeding, making it the perfect spot to capture imagery. The researchers were focussed on gathering quality data of the dorsal and lateral sides of the whales in order to determine width length and height measurements.
“Knowing the body mass of free-living whales opens up new avenues of research,” said Assistant Professor Fredrik Christiansen from the Aarhus Institute of Advanced Studies, who was the lead author of the study. “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. We will also be able to look at the daily energy requirements of whales and calculate how much prey they need to consume.”
Baleen whales are the largest known animals on the planet, and their huge body mass has been central to their success. Unfortunately, historical data regarding their size has been limited to dead specimens, with many samples coming from whaling operations, beach strandings or accidental fisheries by-catch.
“Weight measurements of live whales at sea inform how chronic stressors affect their survival and fecundity, as well as enabling accurate sedative dosing of animals entangled in fishing gear that are aversive to disentanglement attempts,” said Dr. Michael Moore, co-author and senior scientist at the Woods Hole Oceanographic Institution.
The model also allowed the researchers to collaborate with the Digital Life Project at the University of Massachusetts, USA to first recreate a 3D mesh of the whale, and then to work with artist Robert Gutierrez to recreate the full-colour 3D model of the right whale. These models can be used for both scientific and educational purposes.
“We used this model to estimate the body volume of whales caught in scientific whaling operations, for which body girth and mass was known,” added Christiansen. “From these estimates of body volume, we could then calculate the density of the whales, which we in turn could use to estimate the mass of free-living whales photographed by our drones.”
This innovative approach can be used to learn more about the physiology and ecology of whales, and by tweaking the parameters of the model, this method could be used to estimate the size of other marine mammals where alternative or more invasive methods aren’t desirable or possible.
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Photographs courtesy of Prof. Fredrik Christiansen.
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