Drones deployed to determine the weight of whales
Image credit: Holger Karius | Dreamstime.com
Researchers have developed a model that can accurately calculate the body volume and mass of free-living southern right whales by measuring the body length, width and height of the mysterious creatures using photographs obtained by drones.
Due to the giant mammals' large size and aquatic life, the only way scientists could previously obtain data on the body mass of whales was to weigh dead or stranded individuals that have been washed up on beaches.
“It is very difficult to measure a whale on a scale – I mean, you have to kill it to do it and that’s exactly what we're avoiding here,” said assistant professor Fredrik Christiansen from the Aarhus Institute of Advanced Studies in Denmark.
However, with the assistance of aerial photographs and videos taken by drones, this new approach has helped them to avoid this situation, allowing researchers to calculate the body volume and mass of wild southern right whales.
As part of the collaborative study, the researchers investigated the movements of this species of whales, which gather in large numbers at their winter breeding grounds off the coast of Península Valdés, Argentina.
The team flew a drone over whales swimming in clear water, capturing photographs when the adults and calves came up to the surface to breathe, including their backs and sides when they rolled over. From these photos, the team were able to obtain length, width and height measurements for 86 individuals.
They found they could get a good representation of the body shape of the whales, which they linked back to old whaling literature recording body length, girth and mass. They were then able to convert body shapes, or volumes, to mass.
“We used this model to estimate the body volume of whales caught in scientific whaling operations, for which body girth and mass was known,” said 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.”
The innovative method can also be used to learn more about the physiology and ecology of whales, with Christiansen adding that knowing the body mass of free-living whales “opens up new avenues of research”.
“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,” he added. “We will also be able to look at the daily energy requirements of whales and calculate how much prey they need to consume.”
Dr Michael Moore, a senior scientist at the Woods Hole Oceanographic Institution and co-author said: “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.”
The model is already being used to assess the impacts of kelp gull harassment on the health and survival of southern right whale calves.
“The use of drones to estimate whale weight and condition, as well as to individually track calves while they grow beside their mothers, has been a real breakthrough in our investigation,” said Dr Mariano Sironi and Dr Marcela Uhart from the Southern Right Whale Health Monitoring Program.
“In the past, we’ve had to rely entirely upon stranded carcasses which added all sorts of uncertainties to our studies.”
Furthermore, the model has allowed the researchers to collaborate with the Digital Life Project at the University of Massachusetts in the US. Here, they recreated a 3D mesh of the whale and worked with CG artist Robert Gutierrez to recreate the full-colour 3D model of the right whale.
Drone studies could help in conservation by monitoring the health of different whale populations in the oceans. Furthermore, by adjusting the parameters of the model, the approach could be used to estimate the size of other marine mammals where alternative, more invasive, methods aren’t feasible or desirable.
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