According to a study published in “Nature”, whales eat three times more than what was estimated. The return of these “seas engineers” could paradoxically boost the productivity of the oceans.
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“impressive”, “exceptional”, “major”: the adjectives rain in the world of marine biology to qualify the study on the diet of whales published Wednesday 3 November in the journal Nature. At the end of eleven years of research, developing, measures and calculations, an international team has just reviewed the extent of prey consumption by these cetaceans, the largest animals on our planet. Based on various recent technologies, the team led by Jeremy Goldbogen, from the University of Stanford, California, concludes that the seven major baler whales absorb three times more zooplankton that we thought until then. A spectacular result that could have major consequences in terms of the diversity and productivity of the oceans if the return of cetaceans, started for forty years, had to increase.
As often in science, everything started with an annex question. “I wanted to know how much pollutants, microplastics or fibers, a whale could ingest, says Matthew Savoca, researcher in Stanford and the main author of the article. I had to know how much she was eating. And to my surprise, I realized that no measure of the consumption of prey by whales existed. “
These cetaceans have three major defects for the naturalist. Their size and lifestyle prohibit to observe them in captivity. In nature, the deep water night makes it impossible to directly follow their eating habits. In addition, if counting the number of antilopes crushed by a lion does not have difficulty, determining the amount of microscopic prey filtered by the whalenakes raises the challenge. So far, researchers had fallen on two alternative methods. Some had tried to assess the metabolic needs of the animal “often extrapolating those of smaller animals such as dolphins, ignoring the multiple biological differences between species,” says Matthew Savoca. Others had analyzed the stomach content of the corpses. “But it only gives you a photo at a given moment and it often leaves aside a part of the intestinal system,” continues the researcher.
Camera, Micro, Accelerometer, GPS and Drones
This time, the team took advantage of several technological advances. It has equipped 321 individuals, from seven different species, from rorqual common blue whale, of state-of-the-art equipment: camera, micro, GPS and accelerometer. In three oceans (Pacific, Atlantic, Austral), scientists were able to follow in detail the behaviors of cetaceans, very different depending on the species, and determine in particular the number and duration of their meals. The researchers then used drones to fix images of 105 of these specimens, determine their length, mass, and thus evaluate the volume of filtered water. Finally they have equipped small boats of sonars to measure the density of Krills, copepods or other zooplanktons present on the hunting ground of these gargantua seas.
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