FunNature & AnimalWhy don't whales drown when they swallow krill?

Why don't whales drown when they swallow krill?

They just need to open their huge mouth and rush forward at 10 km per hour. The person reading this can imagine that the pressure of all that water at that speed is immense. How do baleen whales keep their lungs from filling up with all this massive amounts of water? It is surprising that until now we did not know about a mechanism that has been discovered very recently.

Baleen whales or misticetos (Mysticeti) are a group with fifteen different species. Among them are the right whale ( Eubalaena ), the humpback whale ( Megaptera novaeangliae ) or the monumental blue whale ( Balaenoptera musculus ).

Balenopterids or whales are the most abundant and diverse family of mysticete cetaceans. Dissection of fin whales ( Balaenoptera physalus ) has recently revealed a fatty and muscular sac that prevents the species from drowning . When the whale opens its mouth to feed, this fleshy bulb swings up and obstructs the lower respiratory tract . Like a real stopper.

Such a structure had never before been identified in any other animal, but the study authors suspect it could be present in other animals that feed in the same way, such as humpback and blue whales, both fin whales. Some even venture to speak of sharks or walruses. Although there are researchers that the anti-drowning mechanism is unique in these whales, as it requires a lot of energy and speed to activate, which is only possible in large species.

“There are very few animals with lungs that feed by gobbling up prey and water, so the oral plug is probably a protective structure specific to rorquals, necessary to allow feeding,” explains Kelsey Gil, a zoologist at the University of British Columbia, Canada.

The research team has not been able to see the mechanism in action, but they assume that it works as a switch of pathways . When a whale breathes, the plug pops open, opening the lower respiratory tract. But when a whale feeds, the plug completely blocks this path, making it impossible for water to pass into the lungs.

“The separation of the respiratory and digestive tracts in the pharynx of mammals is essential for survival,” says the study. In the case of humans, the epiglottis closes the respiratory tract when we eat food to prevent us from choking. It is a hanging tissue that obstructs the way to the lungs when we eat. But, “cetaceans have the added problem of feeding underwater.” In other words, the way whales eat and breathe is very different, much more complex. When they breathe through their nostrils, the fatty plug attached to the soft palate prevents water from the mouth from flowing into the lungs. But when they’re eating, this fatty plug has to swing up and back, closing off the path to the whale’s upper blowhole, while opening the esophagus for swallowing. On the other hand, the force of the incoming water pushes the whale’s tongue against the epiglottis, also sealing off the lower airways.

“It’s like when a human’s uvula moves backwards to block our nasal passages and our trachea closes when we swallow food,” says Gil.

But the big difference is the great pressure that the whales work under that the human species does not have to bear .

“Massive filter feeding of krill schools is very efficient and is the only way to provide the enormous amount of energy needed to support such a large body size,” explains Robert Shadwick, a zoologist at the University of British Columbia. It’s easy imagine that a 27 meter long whale needs a lot of energy to be able to swim.

“This would not be possible without the special anatomical features we have described.”

The authors of the current study would like to see a baleen whale eat and breathe in real time. But it is an almost impossible task at the moment, since they would need to create a camera that they can swallow and that can monitor the mechanism. There is much to investigate, for example answering questions such as whether whales cough, hiccup or burp. “Humpback whales blow bubbles out of their mouths, but we’re not exactly sure where the air is coming from, it might make more sense for whales to belch out of their blowholes.”

No whales died for this study. The dissections were not carried out on whales captured for scientific purposes, but on specimens acquired from a commercial whaling operation in Iceland in 2015 and 2018. It is really difficult to study the anatomy of whales, because it often involves dissecting specimens that They have died after being stranded on the shore. The time for its study is reduced to the duration of low tide. However, the research team was able to observe the unwanted parts of the whales at a commercial whaling station in Iceland.

“It is impossible to study this in a living whale, so we rely on tissue from deceased whales and add functional morphology to assess the relationship between structure and function,” said marine biologist Kelsey Gil.

The article Anatomical mechanism for protecting the airway in the largest animals on earth was published on January 20, 2022 in Current Biology under the signature of experts from the University of British Columbia (Canada).

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