Researchers discover an ‘oral plug’ that allows minke whales to ingest a volume of water and krill even larger than their own body
Whales have a curious way of feeding, which is well known. To catch their tiny prey, called krill, they dart through the water with their mouths wide open. In one giant gulp, they ingest a volume of water and krill that can be even larger than their own body. It’s an impressive feat, especially considering the size of a humpback or blue whale, the largest animal on Earth. How are they able to do something like that without drowning?
A group of researchers has discovered a structure in humpback whales, which probably exists in all whales, similar to an ‘oral plug’, a fleshy bulge that moves backward and blocks the channel between the mouth and the pharynx.
“It means that when a whale lunges (through the water to eat), the entrance to the pharynx and therefore the airway is protected,” says Kelsey Gil of the University of British Columbia.
Human bell
The plug prevents water from entering the cetacean’s lungs while it feeds. “It’s like when a human’s uvula moves backward to block our nasal passages and our trachea closes when swallowing food,” says Gil.
It turns out that humans have a similar system for swallowing food without anything entering the lungs: the epiglottis and soft palate, a ‘cap’ of cartilage, and a flap of muscle in the throat and mouth, respectively. Humans could probably also eat underwater, the researcher says, but it would be like swimming at high speed towards a hamburger and opening your mouth as you approach; it is difficult not to flood the lungs.
Since it is impossible to study all this in a living whale, the researchers analyzed tissue from deceased specimens in Iceland. They closely examined the anatomy of the whale, both intact and through careful dissection of the pharynx. They manipulated the various structures to see how they could be moved. They also looked at the direction of the muscle fibers to understand how they would move when the muscles contract and shorten.
Cetacean burp
The findings also show that in fin whales the pharynx can only be used by the respiratory or digestive tract at the same time. Interestingly, according to the researchers, no structure like the oral plug has been reported in any other animal. “There are very few animals with lungs that feed by gobbling up prey and water, so it is likely that the oral plug is a protective structure specific to rorquals that is necessary to enable lunge feeding,” says the researcher.
The findings, published in Current Biology, are a reminder that there are still many unknowns about whales. There is much more to discover, even if they 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 from their blowholes.”
