I’ve always understood this to be the case…until I saw this video, which purports to show a dolphin that has choked to death on an octopus. The claim in the video is that the octopus tentacles remain active/motile for some time after it’s “dead,” and that dolphins which do not properly bludgeon an octopus before consumption can find that the tentacles may autonomously slither into their respiratory tract, preventing them from breathing.
There is of course no cite on the Wikipedia page for the particular fact in question here, so I put it to the Dope:
Do cetaceans (or even any specific species of them) have completely separate respiratory and digestive tracts, or is there a nexus 'twixt the two, as there is for humans, that puts them at risk for choking to death?
There are two ways to choke somebody to death–blocking the respiratory track from the inside or squeezing it shut from the outside. maybe the octopus pressed against the roof of the dolphin’s mouth enough to compress the airway enough that the dolphin couldn’t breathe.
I used to work at a Dolphin and Whale Hospital in Florida. Everything you ask is answered in a recent study into an increase in dolphin deaths due to choking:
Stolen M, St. Leger J, Durden WN, Mazza T, Nilson E (2013) Fatal Asphyxiation in Bottlenose Dolphins (Tursiops truncatus) from the Indian River Lagoon. PLOS ONE 8(6): e66828. Fatal Asphyxiation in Bottlenose Dolphins (Tursiops truncatus) from the Indian River Lagoon
"[L]aryngeal dislocation into the esophagus can be accomplished with moderate pressure [12] and is necessary to ingest larger prey items. When the larynx is dislocated, the respiratory and digestive tracts comingle. The elongate larynx is vulnerable to compression and obstruction when within the esophageal lumen and asphyxiation and choking can occur. Thus, the unique morphology of the upper respiratory tract in odontocetes may instead make them particularly more vulnerable to esophageal obstruction leading to asphyxiation [11] especially when large or spiny fish are ingested. "
Compression is one cause, but not all of the choking deaths are caused by that. From the same study mentioned above:
“Over the study period, 350 dolphin carcasses were examined in the IRL and examined for cause of death. Fatal asphyxia was diagnosed as the cause of death when laryngeal displacement, compression, or obstruction was indentified and no significant histologic changes were identified as the cause of death. Case review demonstrated 14 cases (4%, Table 1). In at least five cases, dolphins were found with the tail of the prey fish extending from the mouth. On gross examination, all of the dolphins demonstrated fish lodged in the esophagus displacing or compressing the larynx (Fig. 2 and and3).3). In seven cases, fish were firmly lodged and held into the area of the larynx by dorsal spines that were embedded in the esophageal wall.”
Page five here: http://onlinelibrary.wiley.com/doi/10.1002/ar.20745/pdf shows an MRI of a porpoise. The dotted line shows the path from mouth to stomach. It appears to go right through the elongated larynx, but that is because it actually goes around both sides of it. To swallow larger fish, the larynx can be pushed out of the way, in which case the palatopharyegeal sphincter keeps everything closed up and maintains the separation of the two tracts. But if some stuck fish or octopus has pushed this larynx to the side and is preventing it from lining back up and bridging the respiratory tract from lungs to blow hole, in which case, the animal asphyxiates.
Thanks for the link. We’re getting closer, but I’m still not clear on the definition of some terms. When they say “comingle,” do they mean the respiratory and digestive tracts can communicate with each other?
This suggests that they are not permanently isolated from each other, and that it is only muscular action that prevents transferring fluids/solids from one system to the other. Am I understanding this correctly?
The paper appeared to study only bottlenose dolphins, but generalized their conclusions to all the toothed whales. Am I correct in thinking that dolphins don’t typically bite their food into pieces before swallowing (i.e. they swallow prey whole)? What about sperm whales? Don’t they tend to bite giant squid to pieces? How about orcas? They aren’t able to swallow seals whole, are they?
Think of the teeth–modern* toothed whales have peg-like teeth with no cutting edges. That design is good for grabbing food and preventing it from escaping, but you need serrated teeth for cutting and flattened teeth for chewing. So whales either grab food that they can swallow whole or rip out parts of bigger animals by biting down and jerking their head to the side.
*There are extinct species of whale with much morecutty (and much more cool) teeth.
I worked with dolphins and other toothed whales for a number of years and never heard of a case where a animal suffocated because of something it ingested. We used to have to force feed sick animals using ground up fish in a blender and a rubber hose inserted down their throat and into their stomach. This never caused a respiratory issue that I can remember. I think the airway and digestive tracks are functionally separate in normal cetaceans.
Hmmm. I’ve never thought about this point in detail before, but it makes sense. The esophagus is dorsal to the trachea in vertebrates, but the mouth is ventral relative to the nostrils. So the paths must cross* in some fashion. Its obvious in retrospect.
“Excuse me, Egon, you said crossing the streams was bad.”
They’re describing how the whole larynx can be dislodged from the roof where it normally sticks up into the the airway leading to the blow hole. When this happens, there is a break in the airway at the esophagus. The top airway is sealed by a sphincter, and the larynx portion gets sealed off by (I believe) an epiglottis-like structure.
Page 1265 (document page 4) of that porpoise link showing the hyolaryngeal complex has a decent diagram of it. Look at the box labeled “b”. See how the laynx is just kind of jammed up into the roof where it sticks into the rest of the airway? That’s it’s normal condition. That sphincter there keeps everything water and air tight. This whole assembly is inside of–not along side–the esophagus. Similar to humans. So picture a huge pipe (the espophagus) and inside of that pipe is a smaller pipe that protrudes from the bottom and goes to a hole in the top. Most food can easily pass around this smaller pipe as it goes from the mouth to the stomach. Yes, by the way, dolphins swallow their food whole. If the food is too large to pass on either side of the trachea, the entire larynx is dislodged from the hole at the top. It is pushed to the side by the food as the food passes by it. After the food is clear, the larynx muscles push it back into place, lodged into the airway leading to the blow hole where it belongs. Food cannot lodge inside of the trachea, because it gets sealed off on both ends when the larynx is dislodged. However, if large food gets stuck in the esophagus, then the larynx cannot re-position itself back into it’s airway hole. Without the two sections of the airway lined up, the dolphin can’t breath.
Kind of. It’s not purely muscular action though. The larynx usually protrudes into the top portion of the airway. It this normal position, the two passages (esophagus and trachea) are physically separate. Imagine a human in the hospital with swollen vocal cords that have sealed off the trachea. The person has a breathing tube through his nose. He could still probably eat small things as it would pass around the tube on its way to the stomach. The tube stays isolated from the esophagus and from the food. Now imagine a large meal going down the throat that dislodges the tube. If the tube cannot be positioned back into the trachea, the person cannot breathe. It’s kind of like that, except in a dolphin the tube goes from the trachea to the nose (so the scenario is backwards but it should give you an idea.
Dolphins swallow hole. It’s true they have no gag reflex. I’d only be guessing about other whales though.
I’ve forced plenty of tubes down the throats of dolphins, both to feed them and to take stomach samples. The tubes would never cause respiratory issue because it easily passes along either side of the larynx. I suppose, if you tried hard enough, you could dislodge the larynx, but there is a lot of muscles holding it in place. It would simply reposition itself and push the hose out of the way. It can’t push a lodged animal out of the way, though. So if its a spiny fish or large octopus blocking the way, the larynx cannot reposition itself.
In case my explanation wasn’t horrible and confusing enough, I sketched a quick picture of the whole thing. 20170714 114640 hosted at ImgBB — ImgBB
The far left is a front view of the esophagus (the circle). It’s showing how the larynx passes up from the bottom and protrudes into the sphinctered hole at the top. I labeled the portion of the airway that leads from the roof to the blow hole the “trachea” though I’m sure it has a different name. Food easily passes to either side of the larynx in this normal position.
The next picture to the right shows what happens when large food is eaten. The larynx is dislodged from its normal position. With the larynx no longer bisecting the esophagus, larger food can pass unhindered.
The third picture is simply a side view of the normal position. I used different colors to represent the food in order to show how it goes to either side.
Imagine a person who can dislocate and repositio his/her shoulder at will. That’s kind of like the whole dolphin trachea thing works.
Great diagrams, Bear_nenno. Allowing the trachea to dislocate and then return to position is a clever design. However, running the trachea through the esophagus is a pretty dumb design. Things like this (and humans have some, too) make me wonder about evolution!
Your text explanation in #12 was great, and your drawing was absolutely unambiguous and confirmed my understanding of what you had written. Thanks for laying all that out!
I think I get it from a human anatomy perspective now. I looked at BearNemo’s pictures and the MRI in the diagram, but did not read the article.
Embroligically, the trachea and lungs of vertebrates arise from a ventral diverticulum from the gut (esophagus more specifically). This is ‘locked in’ as far as design modifications go.
In a human, and just about every air breathing vertebrate besides whales I suppose, the nasal airway and the oral airway/“foodway” are separated by the palate. In humans the tip of the palate is the uvula (the thing you see hanging down in the back of people’s throats, for Far Side fans). The paths commingle in the oropharynx, then separate into larynx anteriorly and hypopharynx (which leads to esophagus) posteriorly. The epiglottis helps protect the anterior airway from food and liquid during swallowing.
If you wanted to modify a human to be an obligate nose breather (to separate the streams) using the tools at hand…
You could elongate the larynx (elongate larynx was mentioned in paper) so that it projected upward into the nasopharynx. The uvula could then serve as a sort of reverse epiglottis. Meaning the paths are mostly separated, not completely. And the food now passes to either side of the larynx (which acts as a conduit between nasal passage and trachea). The tube by blowhole in diagrams is not trachea, but nasal passages and nasopharynx.
OK, got a good grasp on dolphin anatomy. Still a little puzzled.
Octopussies are famous for being able to squeeze their bodies through relatively tiny spaces. So what’s going on with the choking of dolphins that are trying to swallow them? I assume the octopus has no problem being propelled past the dolphin’s throat-snorkel. The video I linked to indicates that the tentacles remain motile after the octopus dies, and that this somehow interferes with respiration.
Are those tentacles reaching up from the stomach, dislodging the dolphin’s throat-snorkel and preventing it from re-engaging with the blowhole duct? If so, couldn’t the dolphin just get his blowhole and mouth above the water to continue breathing until the octopus finally gives up and truly dies?
Or is the octopus actually getting his tentacles to physically block the blowhole duct and/or throat-snorkel?
It’s a completely unnatural act for the animal to breath through a dislodged throat-snorkel (love it!) and open mouth. I would have said it is not possible–like sneezing with your eyes open. But the link to that mouth-breathing dolphin shows that it is possible for the animal to adapt in such a way.
Regardless, the compression from octopus bolus would prevent it.
I think I know what you’re saying about the octopus being able to go through small spaces, so it should be compressible enough to swallow easily. I think that only works when it goes through a certain deliberate way. Kind of like how you could pull a sheet through a small tube if you grab the corner and feed (no pun intended) it through that way. But if you tried to wad it up, you’d never get it through. And it could end up stuck in there. Same for that octopus. If the dolphin slurped it up like a spaghetti noodle, it would probably go right through with no problem. But swallowing it whole, all at once, can get it stuck in there. I bet if the dolphin just opened its mouth, the octopus could figure out how to get itself out (provided the octopus was still alive). But because 1) the octopus was probably killed before it was swallowed, and 2) the dolphin doesn’t think to just open its mouth and let the octopus free itself, instead the animal tries to swallow, keeping its mouth closed. Then probably panics (wouldn’t you?). Then dies.
