The big appetite of whales, an asset for the oceans

“Impressive”, “exceptional”, “major”: adjectives rain in the world of marine biology to qualify the study on the feeding of whales published Wednesday, November 3 in the journal Nature. After eleven years of research, development, measurements and calculations, an international team has just radically reviewed the extent of the consumption of prey by these cetaceans, the largest animals on our planet. Based on various recent technologies, the team led by Jeremy Goldbogen of Stanford University in California concludes that the seven main baleen whales absorb three times more zooplankton than previously thought. A spectacular result which could have major consequences in terms of the diversity and productivity of the oceans if the return of cetaceans, which began forty years ago, were to increase.

As often in science, it all started with a related question. “I wanted to know how many pollutants, microplastics or fibers a whale could ingest, says Matthew Savoca, researcher at Stanford and lead author of the article. So I needed to know how much she was eating. And to my surprise, I found that no measure of whale prey consumption existed. “

These cetaceans indeed present three major faults for the naturalist. Their size and lifestyle make it impossible to observe them in captivity. In nature, the deep night water makes it impossible to directly follow their eating habits. In addition, if counting the number of antelopes a lion bites is hardly difficult, determining the amount of microscopic prey filtered by whalebone is a challenge. So far, researchers have relied on two alternative methods. Some had tried to assess the metabolic needs of the animal “Often by extrapolating those from smaller animals like dolphins, ignoring the multiple biological differences between species”, explains Matthew Savoca. Others had analyzed the stomach contents of the corpses. “But that only gives you one photo at a given time and it often leaves out a whole part of the intestinal system”, continues the researcher.

Camera, microphone, accelerometer, GPS and drones

This time, the team took advantage of several technological advances. It has equipped 321 individuals, from seven different species, from fin whales to blue whales, state-of-the-art equipment: camera, microphone, GPS and accelerometer. In three oceans (Pacific, Atlantic, Southern), scientists have been able to follow in detail the behavior of cetaceans, which are very different depending on the species, and in particular determine the number and duration of their meals. The researchers then used drones to fix images of 105 of these specimens, determine their length and mass, and thus assess the volume of water filtered. Finally, they equipped small boats with sonar in order to measure the density of krills, copepods or other zooplankton present on the hunting grounds of these Gargantua of the seas.

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The big appetite of whales, an asset for the oceans