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Whales are greedier than expected, and that’s good news

We knew whales were hell eaters, but not at this point. And that’s great news for marine ecosystems.

Whales are fascinating beasts in many ways. In addition to their remarkable size and behavioral peculiarities, they also play an absolutely decisive role in marine ecosystems; a finding further reinforced by a new study identified by Future, who took an interest in their diet. Not only would they eat nearly three times more than expected, but this would be one of the keys to the dynamism of the oceans!

Among the different groups of whales that inhabit our oceans, there is a group called Mystoceti which has an important characteristic. All of its representatives have baleen, the characteristic horny blades that adorn their upper jaw. Humans have long used it to make umbrellas or corsets, which was one more reason to hunt these majestic cetaceans. But for the latter, they have nothing cosmetic. Thanks to the many hairs that line them, they act like a huge comb capable of filtering water.

This allows the whale to swallow huge volumes of liquid without the risk of swallowing a dangerous or large object; it can thus feed on the young organizations which form the basis of its diet. A fascinating way of feeding for an animal of this size. And for biologists, it is interesting on many levels; if we know this mechanism well, its ecosystem-wide impact still remains quite mysterious. Because it has not escaped you, we are still talking about extremely large animals.

Krill is a very small crustacean species, of which a blue whale can consume up to 16 tonnes per day. © Øystein Paulsen – WikiCommons

Whales, incorrigible gluttons

With such behemoths roaming the waters, one can legitimately expect them to play a key role in the dynamics of their habitat; this is what a team of American researchers sought to verify. But very curiously, the scientific literature did not include until then no precise quantitative study about this question. Until this study, we only had very vague estimates, because they were based on our approximate knowledge of their metabolism.

From 2010 to 2019, they installed tracking devices for 321 whales to track them. At the same time, they sought to quantify their daily diet. For this, they used a very ingenious device. The set includes a small sonar close range mounted on a simple suction cup. This produces a different signal depending on the density of microscopic prey present in the water at that location.

Briefly, the more krill there is suspended in the water, the more intense the return signal from the sonar. After a few calibration steps, this allows them to estimate the concentration of food available. Thanks to a GPS, an accelerometer and measurements taken by a drone, they were able to estimate the average volume swallowed at each “bite”. All they had to do was multiply this number by the concentration of krill measured for get their total consumption.

And when the final results were compiled, the team couldn’t believe their eyes. Their results showed that on average, Mystoceti eat about three times more food than suggested by previous estimates. On the scale of a blue whale, which can happily exceed 20 meters in length in the prime of life, this would represent … the equivalent of two and a half elephants each day, i.e. 16 tonnes per day! That’s more than a tenth of their weight, which can easily exceed 120 tons.

By taking their meals in depth before relieving themselves on the surface, whales “turn” the ocean like a plow would in a field. © sarangib – Pixabay

Marine “plows” that fertilize the oceans

But the researchers’ findings do not stop at this quantitative data. This gigantic consumption also has a rather unappealing corollary; if whales eat so much, it also means that they are excreting much more than expected. And this abundance of whale dung is a real blessing to the oceans. When they feed in depth and defecate on the surface, cetaceans therefore play a role of “ocean plows”Which feeds the entire ecosystem.

Because with these stools, many nutrients are also found in suspension in the water. Now these nutrients are the basis of marine ecosystems. They are what allow plankton to develop. By photosynthesis, this plankton then participates in theoxygenation oceans. This is absolutely fundamental for two reasons. This saves the species that live there, as many of them are today threatened with suffocation by the reverse phenomenon. And since this photosynthesis consumes carbon dioxide, plankton also acts as a greenhouse gas pump.

But above all, this plankton constitutes the basis of many food chains in a marine environment. It is the favorite dish of krill, which is itself the staple diet of whales. The circle is therefore complete, and these works illustrate very well the importance of these majestic beasts. The authors conclude by explaining that the safeguard of these species is essential, and could even make it possible to save certain ecological niches which are today threatened. The text of the study is available here.

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