In Finding Nemo’s most harrowing scene, Marlin and Dory get swallowed by a great blue whale. Only later do we learn that the whale hasn’t eaten them at all — blue whales eat krill, not anxious and forgetful fish — but safely carries them to P. Sherman, 42 Wallaby Way, Sydney (repeat 10 times). Perhaps it’s occurred to some viewers: How did the whale swallow all that water (plus our heroes) without inhaling it and drowning? Scientists didn’t know the answer either — until now. Nearly 20 years after we beheld this benevolent chauffeur whale, we know precisely how such a feat is anatomically possible.
What’s new — A paper published Thursday in the journal Current Biology reveals the secret to engulfing colossal amounts of seawater without drowning is an oral plug that protects respiratory passages while the immense amounts of food and seawater flow through. The researchers have found this structure in 10 whales so far, including the blue whale.
“We know a lot about the mechanics of how these whales are actually engulfing their food, but that's pretty much where the knowledge stops,” zoologist and lead author Kelsey Gil tells Inverse. “Nobody's looked at this problem afterward of how they’re swallowing it and how everything in the respiratory tract is staying safe.”
Gil and her team investigated recovered whale tissue from a whaling station in Iceland. Upon opening the mouth, she and her team noticed a big plug and decided to start there.
Here are the 10 whales that have the oral plug that allows them to feed:
These are all baleen whales. In particular, they’re the largest baleens, and they’re also part of a group called rorquals. Rorquals devour krill and crustaceans in a process called lunge-feeding.
“The process of lunging is kind of crazy,” says Gil.
A fin whale, for instance, will dive down a few hundred meters. While deep underwater, it will make four big lunges before resurfacing. In each lunge, the whale accelerates toward a patch of prey at about three meters per second with its mouth open, and “engulfs the volume of prey and water that can be as large as its own body.” Then, it swallows its meal while pushing seawater out through its baleen plates, which are those rows of brush-like fibers where teeth would be.
Digging into the details — The oral plug comes into action once most of the seawater has filtered from the whale’s mouth. It shifts backward and upward, blocking off access to the upper respiratory tract that leads to the blowholes. Gil says the motion is likely triggered by the whale’s swallowing reflexes. At rest, it’s passively sitting there and requires muscle activation to move out of the way. Rorquals also have a muscular sac attached to the bottom of their larynx or voice box, that can collapse upward, filling the larynx with tissue. This process prevents prey and water from coming into the lungs.
Essentially, the oral plug protects the upper respiratory system while the cartilage sac protects the lower respiratory system, allowing food to shoot through the esophagus to the stomach.
But wait — an oral plug that prevents food from getting into the lungs? That sounds a lot like the human uvula. The two are actually analogs of sorts. Our uvula lifts through a muscle contraction that keeps our nasal cavity safe. Our larynx has a flap of cartilage that covers its top and then shifts forward a bit as we swallow.
Gil believes one big reason for this similarity between whales and humans is head and body position. Humans have a distinct head and neck, and the digestive tract begins horizontally and then moves down vertically. “For whales, the whole thing is pretty much horizontal,” she says. But, we both share an area called the pharynx, where the respiratory and digestive tracts cross over. While whales might be all horizontal, we share the same protective mechanism.
Why it matters — Aside from discovering the oral plug, we also know now that it’s instrumental for rorquals to feed. Gil says lunge-feeding is “a remarkable way of feeding and would not be possible without the oral plug.” She believes that she and her team are the first ones to discover and publish the existence and purpose of this plug, which is actually pretty freaking big.
The oral plug, Gil estimates, weighs hundreds of pounds. “We had to use a forklift to move it over,” she says. Adult blue whales can weigh up to 220,000 pounds and grow to 98 feet long. So even the tiny parts of their anatomy end up being quite large.
Other whales, such as right whales and bowhead whales, use a method called skim feeding. Both these species are also baleen whales, but since they don’t engage in lunge-feeding they are not rorquals. To skim feed, the whale simply drifts through a patch of prey with its mouth wide open. Water filters through the mouth, making this way of eating apparently simpler.
What’s next — Gil and her team will continue plumbing the rorqual’s digestive system. Her next question is how they’re able to swallow so much food in a single lunge, which occurs in mere seconds. She wants to understand the mechanics of the pharynx and esophagus.
“Imagine an entire bathtub’s worth of krill just flowing down as fast as possible so they can feed again,” Gil describes.
The next time you watch Finding Nemo, definitely pause the movie and explain how the oral plug functions in lunge-feeding in excruciating detail. Your fellow movie watchers will almost certainly thank you.
Abstract: Separation of respiratory and digestive tracts in the mammalian pharynx is critical for survival. Food must be kept out of the respiratory tract, and air must be directed into the respiratory tract when breathing.1 Cetaceans have the additional problem of feeding while underwater. Lunge-feeding baleen whales (rorquals) open the mouth while swimming at high speeds to engulf a volume of prey-laden water as large as their own body2 and experience tremendous forces as water floods the mouth. How the respiratory tract is protected in the pharynx during engulfment and while swallowing a massive slurry of tiny living prey remains unknown, despite its importance to survival. By dissecting adult and fetal fin whales, we determined that a large musculo-fatty structure passively seals the oropharyngeal channel. This ‘‘oral plug’’ is not observed in other animals, and its position indicates it must be shifted to allow swallowing; it is a part of the soft palate and can only shift posteriorly and dorsally. Elevation of the oral plug allows food transfer to the pharynx and protects the upper airways from food entry. The laryngeal inlet in the floor of the pharynx is sealed by laryngeal cartilages, and the muscular laryngeal sac moves upward into the laryngeal cavity, completely occluding the airway. The pharynx is dedicated to the digestive tract during swallowing, with no connection between upper and lower airways. These adaptations to facilitate swallowing were a critical development in the evolution of large body size in these largest animals on earth.