Whales are famous for feeding by gulping down huge amounts of water to capture tiny krill. But how do they do this without drowning themselves with every mouthful? Researchers have now discovered an “oral plug” in the throats of some species that blocks either their airways or esophagus as needed.
Lunge-feeding is a specific strategy used by some baleen whales, like humpbacks and blue whales, where the animal swims at high speed towards a big shoal of prey, scooping as many as possible into its gigantic mouth. Of course, doing so also captures huge amounts of water, which the whales spit back out by filtering it through their baleen, leaving behind their meal of krill.
But how they manage to pull off this feat without flooding their lungs or gut with water remained a mystery. It sounds like something that science should know by now, but whale anatomy is a fairly murky subject, since dissections are rarely performed.
In the new study, researchers identified a fleshy bulb that acts like an oral plug, at the back of the mouth of fin whales. When the animal is breathing, this oral plug sits at the bottom behind the tongue, allowing air to pass from the nasal passage into the lower airways while preventing anything in the mouth from getting through.
When the whale wants to swallow its dinner, this plug moves up and back, blocking off the nasal passages and opening a path from the mouth to the esophagus. At the same time, a cartilage structure closes off the entrance to the larynx and the lower airways, preventing food or water from reaching the lungs.
“We haven’t seen this protective mechanism in any other animals, or in the literature,” said Dr. Kelsey Gil, lead author of the study. “A lot of our knowledge about whales and dolphins comes from toothed whales, which have completely separated respiratory tracts, so similar assumptions have been made about lunge-feeding whales.”
The team says that this specialized anatomy was likely key to helping whales grow to be the biggest animals that have ever lived on Earth.
“Bulk filter-feeding on krill swarms is highly efficient and the only way to provide the massive amount of energy needed to support such large body size,” said Dr. Robert Shadwick, senior author of the study. “This would not be possible without the special anatomical features we have described.”
The researchers plan to continue investigating these anatomical features, which could help us better understand these animals and what impact human activity may be having on their feeding habits.
The research was published in the journal Current Biology.
Source: University of British Columbia
