American and Danish researchers have devised a way to weigh live whales through drones. The scientists describe their finding in the journal Methods in Ecology and Evolution.

Previously, scientists used dead whales, such as those washed ashore or caught by hunters, to investigate the body mass of the whale. However, carcasses have their limitations, for example because the body is damaged or swollen.

The researchers went to the Valdés peninsula in Argentina, where southern hijacker whales gather to mate in the winter. By allowing drones to fly above the relatively clear water and making recordings, the biologists were able to measure the dimensions of the animal and calculate the body mass. They also made a 3D model with the collected data.

"It is a nice tool", says Lonneke IJsseldijk, biologist at the Faculty of Veterinary Medicine at Utrecht University where she leads marine mammal stranding research. IJsseldijk is not involved in American-Danish research.

"With this technique, you as a researcher do not have to approach an animal from close by, but you can still gather valuable information, which was previously impossible."

Whale body mass provides health information

The body mass of a whale says a lot about the health of the animal. For whales, the following applies: fat is better. "Measuring body mass tells us something about whether the animals are doing well," says IJsseldijk.

By 'weighing' with drones, researchers can observe a living whale several times and measure physical changes. IJsseldijk mentions as an example whales that live in sea areas that people also use. "With such research we can keep track of how the animals are doing and take measures when necessary."

IJsseldijk does not exclude the possibility that drone technology could be used in the Netherlands, but it would be more difficult.

Currently, the measurement method is aimed at larger, slower whales that are individually recognizable by, for example, color patterns on the fins. The relatively small and fast porpoises live in the North Sea, which camouflage themselves in the dark sea water. These animals are therefore more difficult to photograph.