In a first, researchers have developed a model to accurately calculate the weight of southern right whales using measurements made by drones of the colossal mammal's body length, width, and height.
The study, published in the journal Methods in Ecology and Evolution, noted that the only way to get information on the body mass of whales until now was to weigh dead or stranded individuals. The researchers, including those from the British Ecological Society in the UK, developed the new method to learn more about the physiology and ecology of whales.
"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," said Fredrik Christiansen, lead author of the study from Aarhus Institute of Advanced Studies in Denmark.
Christiansen added that the calculated weight could be used to look at the daily energy requirements of whales, and estimate how much prey they needed to consume.
"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 co-author of the study Michael Moore from the Woods Hole Oceanographic Institution in the US.
The researchers mentioned that the model was already being used to assess the health impacts of constant injury caused to the whales by birds called the kelp gulls.
According to a study, published in the journal PLOS One in 2015, photos from the 1970s showed almost no whales with wounds from the gulls. However, the PLOS one study noted that this number increased to more than a third of mother-calf pairs in the 1980s, with the number steeply climbing up to 84 per cent in the 90s.
Nearly 99 per cent of mother-calf pairs had gull wounds in the 2000s, according to the PLOS One study. The researchers behind the current study added 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.
The researchers also collaborated with the Digital Life Project at the University of Massachusetts in the US to recreate a 3D mesh of the whale. They also generated a full-colour 3D model of the right whale. The models can be used for both studying the movement of the southern right whales, and also for educational uses, the researchers said.
This approach, according to the researchers, could be used to estimate the size of other marine mammals where alternative, and more invasive methods aren't feasible or desirable. The study noted that difficulties in reliably measuring the body mass of free-living whales prevented the inclusion of the parameter in many studies in ecology, and physiology.
Now, with the new method, the researchers are hopeful that this crucial variable will be figured into future studies of free-living whales. 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.
They mentioned that the clear waters in the region, and the large number of whales gathering there every winter for breeding, made it an ideal place for collecting high quality images of both the dorsal and lateral sides of the whales. The researchers obtained length, width and height measurements from these photos from which they were able to model the body shape and volume of the whales.
They used the model to estimate the body volume of whales caught in scientific whaling operations, whose girth and mass was already known. "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," Christiansen said.