Explaining exactly how much a whale weighs is quite a difficult question to answer because there are currently between 80 and 90 different species of cetaceans and each species has a different size and weight. Cetacean species are divided into two groups known as suborders of toothed whales and baleen whales. And there are a lot of differences that separate them.
All species of dolphins and porpoises also belong to the suborder of toothed whales. Of all the whales, the blue whale is the largest animal ever known on the planet.
How do you weigh the biggest animals on the planet?
As explained in an article by Nobbot, until now it was only possible to weigh whales once they were found dead on the beaches. Now, scientists have solved this problem, thanks to a method called photogrammetry that could contribute to the conservation of the species.
Gram Photogrammetry?
That’s how it is. With the help of aerial photographs taken by drones, an international team led by Danish marine biologist and Aarhus University professor Frederik Christiansen used images taken by drones to create a mathematical model that allowed them to calculate the dimensions and mass of a total of 86 wild southern right whales ( Eubalaena australis ). In fact, this technique is already used to assess calf survival and has many potential uses in species conservation.
Body mass is a key factor in the success of whales as a group, as it determines their energy use, food requirement, and growth rate. However, most of what we knew about whale body size came from ancient literature on whaling or animals that end up stranded on the beach or caught in fishing gear.
“It is very difficult to measure a whale to scale, I mean you have to kill it to do it and that is exactly what we are avoiding here,” said Fredrik Christiansen of the Aarhus Institute for Advanced Study.
The researchers flew a drone over the whales swimming in clear water, capturing photographs as adults and hatchlings surfaced to breathe, including backs and sides as the whales turned around. From all these photographs, they were able to obtain length, width, and height measurements for 86 individuals.
The experts, who detail their study in the specialized journal Methods in Ecology and Evolution, discovered that they could obtain a good representation of the body shape of whales. Then they converted the shape of the body, or volume, into mass.
“The ability to predict the body mass of wild whales opens up an opportunity for us to look at the animals over time and see how they change, how they grow, ” said Professor Christiansen.
Drone studies could aid conservation by monitoring the health of different whale populations in the oceans.
The approach could also be used to estimate the size of other marine mammals by fitting the model parameters.
The research was carried out in collaboration with the Southern Right Whale Health Monitoring Program in Argentina and the Woods Hole Oceanographic Institution in the United States.
Referencia: ‘Estimating body mass of free‐living whales using aerial photogrammetry and 3D volumetrics’ Fredrik Christiansen, Mariano Sironi, Michael J. Moore, Matías Di Martino, Marcos Ricciardi, Hunter A. Warick, Duncan J. Irschick, Robert Gutierrez y Marcela M. Uhart. Methods in Ecology and Evolution 2019. https://doi.org/10.1111/2041-210X.13298
