Why don't whales drown when they fill their mouths with water?

Mouth stoppers prevent species like blue whales from drowning from swallowing large amounts of water. (Photo: mic1805/Depositphotos).

Whales usually feed by swallowing huge amounts of water to catch small krill. Dive foraging is a tactic used by some species of baleen whales such as humpbacks and blue whales. They often swim at high speed into large schools of fish, filling their mouths as much as they can. Of course, this way of feeding entails a huge amount of water overflowing into the mouth. Whales will spit out by filtering through the horns, keeping only the krill food. How do they do this without allowing water to enter their lungs or intestines?

In the new study, published January 20 in the journal Current Biology, scientists discovered a mass of flesh that acts as a stopper at the back of a fin whale's mouth. When the animal breathes, a stopper located at the end of the tongue allows air to pass from the nasal cavity into the lower respiratory tract, while blocking whatever is in the mouth from overflowing.

When the whale wants to swallow food, this button moves up and down, blocking the nasal cavity and opening the passage from the mouth to the esophagus. At the same time, a cartilage structure blocks the entrance to the larynx and lower respiratory tract, preventing food or water from reaching the lungs.

"We have not seen this defense mechanism in any other animal," said lead researcher Dr Kelsey Gil. "Much of our understanding of whales and dolphins comes from toothed whales with completely separate respiratory tracts, so we still assume that diving whales do as well."

The team says this special structure is the key to making whales become the largest animals that have ever lived on Earth. Foraging by filtering water to hunt swarms of krill is the only way to provide the enormous energy to support such a large body size.

The researchers plan to continue studying the whales' physical characteristics to better understand them and the influence of human activity on their feeding habits.