Speaker 1: Welcome to Stuff to Blow Your Mind production of iHeartRadio.
Speaker 2: Hey you welcome to Stuff to Blow your Mind.
Speaker 3: My name is Robert Lamb and I am Joe McCormick,
Speaker 3: and we're back with part two in our series on
Speaker 3: manta rays and their close mobulate relatives. In the last
Speaker 3: episode of this series, we kicked things off by talking
Speaker 3: about an experience that you had rob recently where you
Speaker 3: and your family got to see reef manta rays in
Speaker 3: person while snorkeling in Indonesia, which sounds pretty amazing to
Speaker 3: get the details on that right.
Speaker 2: Correct, Yes, it was. It was amazing. Words can't quite
Speaker 2: describe it.
Speaker 3: Observing them, but not swimming quote with them, You weren't
Speaker 3: You weren't riding the rays.
Speaker 2: Correct, they were. They were doing their own thing. We
Speaker 2: were trying to keep our distance and observe from a distance,
Speaker 2: which which is the correct way of going about things.
Speaker 3: So that was what inspired us to talk about man
Speaker 3: in a series of episodes here on the show. In
Speaker 3: the last episode, we talked about the historical evolution of
Speaker 3: human attitudes toward manta rays with these old stories among
Speaker 3: some divers and sailors that cast manta rays as diabolical
Speaker 3: vampires of the sea. You know, there's one idea that
Speaker 3: they will like fold over a diver like a blanket
Speaker 3: of death. This, of course is not true, and since
Speaker 3: it seems like since roughly the nineteen seventies there has
Speaker 3: been more widespread recognition that mantas are gentle and not
Speaker 3: threatening to humans, though of course that has not stopped
Speaker 3: humans from threatening them, and we talked about all kinds
Speaker 3: of ways that human activity can hurt these animals. These
Speaker 3: impacts range from accidental harms, like when mantas are killed
Speaker 3: as bycatch in commercial fishing. It's not what people are
Speaker 3: fishing for, but they just get caught in nets and
Speaker 3: other lines and other things, all the way to intentional targeting,
Speaker 3: where they are killed for their gill plates, which some
Speaker 3: people falsely allege to have medical powers. And in the
Speaker 3: vein of talking about tall tales of mantas as vicious monsters,
Speaker 3: we also discussed a couple of movies made in the
Speaker 3: nineteen thirties that have a killer Manta Ray or devil
Speaker 3: Ray as the monster.
Speaker 2: I didn't mention this in that episode, but it's worth
Speaker 2: noting that, you, of course have one of Aquaman's arch
Speaker 2: Enemies is Black Manta. Oh, so you know, it's the
Speaker 2: perfect mantle for a villain that was conceived. I believe
Speaker 2: in this era you also have Man Ray, which is
Speaker 2: a villain based on Black Manta that pops up on
Speaker 2: SpongeBob SquarePants, not to be confused with the artist Man Ray.
Speaker 3: I think Black Manta is actually in the Aquaman movie
Speaker 3: with cal Drogo in it, isn't it.
Speaker 2: Oh yeah, yeah, who plays Black Manta? I don't I
Speaker 2: haven't seen any of those films.
Speaker 3: I don't remember any of the cast of that movie
Speaker 3: except in Nicole Kidman in a really funny looking costume.
Speaker 3: So I you know, folks out there, No, I'm not
Speaker 3: the biggest superhero movie fan. I haven't kept up with
Speaker 3: all of the Marvel and DC superhero films, but I
Speaker 3: think I watched Aquaman on a plane for some reason.
Speaker 3: I remember thinking it was really funny, like highly amusing.
Speaker 3: Oh no, wait, I remember another cast member had Patrick
Speaker 3: Wilson like riding on a shark and saying, you will
Speaker 3: call me ocean Master.
Speaker 2: I need to watch those on an airplane sometime.
Speaker 3: Yes, Jason Momoa, I'm sorry I called him Caldroco.
Speaker 4: That's not nice. His name is Jason Momoa.
Speaker 2: Suffice to say, however, the Western American European conceptions of
Speaker 2: the manta ray and related species have evolved since basically
Speaker 2: the nineteen seventies. The nineteen seventies onward. Everyone has come
Speaker 2: to realize that manta rays are peaceful giants of the
Speaker 2: ocean and they are not out to eat us.
Speaker 3: Right, And so we also talked about modern conservation efforts
Speaker 3: aimed at protecting manta's You know, we got into like
Speaker 3: the cost benefit analysis that has to be done if
Speaker 3: you're considering building something like an ecological tourism trade around them.
Speaker 3: You know, there are risks but also potentially rewards. And
Speaker 3: we also talked about the basic biology of manta rays
Speaker 3: and their near relatives, their near relatives being the devil rays.
Speaker 3: Mantas and devil rays together make up the genus Mobula.
Speaker 3: And we got into subjects including their body design, common
Speaker 3: feeding strategies, and leaping or breaching behavior where they jump
Speaker 3: out of the water and slap back down. We talked
Speaker 3: about some reasons they might do that. And we're back
Speaker 3: today to talk about more.
Speaker 2: Yeah, and we're gonna we're gonna pick up in an
Speaker 2: interesting area, you're gonna you're gonna get into some some
Speaker 2: more myths or potential myths about their behavior and what
Speaker 2: we may or may not know about those behaviors.
Speaker 3: Now right, well, I think this might be slightly different
Speaker 3: because it would be truths about their behavior with mythical interpretations,
Speaker 3: if that makes any sense. So in the last episode,
Speaker 3: we were talking about these incorrect folk beliefs about the
Speaker 3: man you know that they would attack boats or attack
Speaker 3: divers in the form of this underwater death blanket. And
Speaker 3: as a source there I referenced an old article called
Speaker 3: the Story of the Devilfish from the ear Way back
Speaker 3: in the year nineteen ten by the American biologist Theodore
Speaker 3: gil There was another thread in this article that I
Speaker 3: found interesting and I wanted to come back to it today.
Speaker 3: So if you'll recall from last time, in this article Gil,
Speaker 3: he's very dismissive of the belief that the manta tries
Speaker 3: to smother divers with its body or devour them with
Speaker 3: its gaping mouth. He points out that the manta is
Speaker 3: a filter feeder which eats tiny planktonic organisms. It does
Speaker 3: not eat large prey. There's no evidence of manta's targeting
Speaker 3: humans for violence, and they don't even have the right
Speaker 3: biological equipment to eat us if they were going to
Speaker 3: try to do that, which they're not going to try.
Speaker 3: But there is another part of the manta's more frightening
Speaker 3: reputation in pre modern times, which is the belief that
Speaker 3: mantas will attack boats, not divers, but boats, particularly the
Speaker 3: claim that a manta will drag a boat out to
Speaker 3: sea by the anchor line. So here I'm going to
Speaker 3: read a passage from Gill's article quote in one of
Speaker 3: the earliest Notices of the Devilfish by John Lawson in
Speaker 3: the History of Carolina seventeen fourteen. This peculiarity is described
Speaker 3: the devilfish, he says, has been known to weigh a
Speaker 3: ship's anchor and run with the vessel a league or
Speaker 3: two and bring her back against tide to almost the
Speaker 3: same place. But then the quote ends, and Gill goes
Speaker 3: on to say later notices do not give the animal
Speaker 3: credit for the same accommodating treatment, And he later alludes
Speaker 3: to these other accounts that tell of the devilfish pulling
Speaker 3: sailing boats around by the anchor, to the wonder and
Speaker 3: fear of the sailors, and he also cites a more
Speaker 3: recent source to him at the time of his writing.
Speaker 3: This was a French naturalist named Leon de Guett describing
Speaker 3: the activity of pearl fishers in the Gulf of California
Speaker 3: in a text from eighteen ninety eight, and according to Deget,
Speaker 3: when fishers are caught out at sea overnight in the
Speaker 3: Gulf of California away from their usual mooring places, he says,
Speaker 3: they will always drop two anchors because they fear that
Speaker 3: if they only drop one, the anchor line will be
Speaker 3: seized by the devilfish in the dark, and thus the
Speaker 3: boat will be carried away into the open sea. And
Speaker 3: to get back to this up with his own observation,
Speaker 3: telling a story of how he was sent out to
Speaker 3: harpoon a specimen of a devil ray for the Natural
Speaker 3: History Museum of Paris, and he says, quote, after one
Speaker 3: had been harpooned, it turned back on the boat, seized
Speaker 3: the bow with its head fins, and held it in
Speaker 3: its clasp till it was lanced the second time. So
Speaker 3: that's Deget's account. But Gil says even this direct observation
Speaker 3: does not really lend credence to the idea that Mantas
Speaker 3: or devil rays deliberately attack detain or hijack boats because,
Speaker 3: based on his own study, Gil writes that this kind
Speaker 3: of grasping with the headfins is automatic. He says, it's
Speaker 3: an involuntary muscular reaction when something is in front of
Speaker 3: the ray's mouth, so in this case, it might happen
Speaker 3: to be the bow of the harpooner's boat. And so
Speaker 3: even when it's being attacked by somebody on the boat,
Speaker 3: when it's being harpooned, Gill argues that the ray was
Speaker 3: probably not actually trying to harm the boat, but rather
Speaker 3: was just being pulled toward the boat by the tension
Speaker 3: of the rope on the harpoon it had just been
Speaker 3: lanced with. And even to get himself the person originally
Speaker 3: telling the story of it seizing the bow of the boat,
Speaker 3: he says the devilfishes are generally timid, non aggressive animals.
Speaker 3: Though then after saying this confusingly to get does seem open,
Speaker 3: he sort of opens up more claims of devilfish savagery
Speaker 3: and alleges that in the Gulf of California, quote numerous
Speaker 3: cases have occurred of death resulting to divers as well
Speaker 3: as bathers from encounters with the devilfish or manta as
Speaker 3: the men call it. On the other hand, the carcasses
Speaker 3: of many that are killed are used for bait for
Speaker 3: other fishes. The strange detail to include.
Speaker 2: Yeah, yeah, I mean all of this is a pardon
Speaker 2: the terminology here, fishy because.
Speaker 3: Dobous third hand Yeah.
Speaker 2: Yeah, I mean, because everything we know and have been
Speaker 2: discussing about rays, when they're threatened, they use a burst
Speaker 2: of speed, they get away. That's their major way of
Speaker 2: defending themselves. So it doesn't really make sense based on
Speaker 2: what we know that they would turn around an attack
Speaker 2: of a ship or a boat, even if they are
Speaker 2: being acted upon with harpoons.
Speaker 3: Right, And as we discussed last time, of course, they
Speaker 3: are large animals, and any large animal could potentially hurt
Speaker 3: you just by bumping into you. Wrong, But there is
Speaker 3: really no evidence I could find of manta's being aggressive
Speaker 3: toward humans except for these like old third hand stories.
Speaker 4: Yeah.
Speaker 2: And I don't know if Gil gets into this or not,
Speaker 2: but for one of the things with you get into
Speaker 2: oral histories of things like the devilfish the manta, you
Speaker 2: end up having to ask questions, well, is the manta
Speaker 2: in this story, even if there's a kernel of truth
Speaker 2: to it, Is it indeed talking about the species that
Speaker 2: we are talking about as the manta ray, or is
Speaker 2: it referring to something else real or imagined.
Speaker 3: Yeah, so, even back in nineteen ten, Gil to me
Speaker 3: seems skeptical of these claims about it attacking boats. Certainly,
Speaker 3: modern researchers are skeptical of these stories of manterray aggression
Speaker 3: towards boats. But to the question of dragging boats specifically
Speaker 3: by the anchor cable, is this just a tall tale
Speaker 3: like the manta ray death blanket story or is there
Speaker 3: something more to that? Is there any modern evidence of
Speaker 3: things like this happening sort of?
Speaker 4: This is yes.
Speaker 3: For example, I found a Reuter's article from February eleventh,
Speaker 3: nineteen ninety nine, called motor boat no match for manta
Speaker 3: ray in tug of war.
Speaker 2: Well, I generally, you know, I generally trust Reuters in
Speaker 2: their reporting. Though usual usually I'm not reading about the
Speaker 2: marine biology. When I'm reading Reuters. Usually it's a nice
Speaker 2: you know, doom scroll into the abyss. So I missed
Speaker 2: this one when it came out. If I was in
Speaker 2: fact reading Routers at the time.
Speaker 3: I'll read from the beginning of the article and then
Speaker 3: summarize some other parts of it and we can make
Speaker 3: up our minds about it. Okay, what's going on here?
Speaker 3: So Dateline New Smurta Beach, Florida. Two Florida boaters met
Speaker 3: a real sea monster when their craft was dragged for
Speaker 3: hours by a powerful creature that turned out to be
Speaker 3: a giant manta ray, the Coastguard said Wednesday. Coastguard Petty
Speaker 3: Officer Scott Barnes said the agency received a radio distress
Speaker 3: call from a sixteen foot boat that reported it was
Speaker 3: being dragged by its anchor line by something unknown. The
Speaker 3: Coast Guard sent a rescue boat to investigate and found
Speaker 3: the motor boat was being dragged in circles by something
Speaker 3: beneath the surface. The crew transferred the anchor line to
Speaker 3: the Coastguard vessel, freeing the men in the motor boat,
Speaker 3: who had tried to use their ninety horsepower engine to
Speaker 3: go in reverse and stop themselves from being dragged out
Speaker 3: to sea. After the Coastguard's forty one foot boat pulled
Speaker 3: the anchor line for several minutes, a giant manta ray,
Speaker 3: measuring an estimated eighteen feet in width, came to the surface,
Speaker 3: and then the article goes on to describe how the
Speaker 3: coastguard struggled to pull the rope away. Eventually, the manta
Speaker 3: was able to disentangle itself from the rope and it
Speaker 3: swam away on its own, And by the end of
Speaker 3: the ordeal, the manta, they estimated, had pulled the boat
Speaker 3: for almost two hours, taking it about a mile and
Speaker 3: a half away from shore. But you could easily get
Speaker 3: the wrong idea about this, thinking that it supports this
Speaker 3: old notion that mantas will attack boats, that they are
Speaker 3: doing this on purpose, they're trying to drag the sailors
Speaker 3: out to sea, out to their deaths or something. From
Speaker 3: what I've read, there is absolutely zero evidence to support
Speaker 3: the idea that the mantas are acting aggressively when they
Speaker 3: pull a boat by the anchor line. The zero evidence
Speaker 3: that they're acting aggressively or even acting intentionally. Rather, this
Speaker 3: is almost certainly a case of mantas getting stuck. They
Speaker 3: are getting tangled in underwater ropes and chains by accident
Speaker 3: and then pulling the boat because they are unable to
Speaker 3: free themselves. And when you look at their heads, you
Speaker 3: look up a picture of a manta ray or a
Speaker 3: devil ray. You can see how this might easily happen.
Speaker 3: They almost have biological mooring cleats with their cephalic fins.
Speaker 5: Yeah, yeah, you can imagine them catching the line.
Speaker 3: For one more example of a mod encounter, I found
Speaker 3: a video on YouTube that the title begins with Giant
Speaker 3: mantray tangled in anchorchain, forty miles off shore. This is
Speaker 3: a video of some people out in a fishing boat
Speaker 3: in the Gulf of Mexico and a manta does get
Speaker 3: caught in their anchor line. Like it looks when you
Speaker 3: can see it, it looks like the line is not just
Speaker 3: caught between the cephalic fins, but kind of wrapped around them,
Speaker 3: like the lobes on its head have the line going
Speaker 3: across as well as between, and you can see it
Speaker 3: struggling at a couple of points.
Speaker 4: In this video.
Speaker 3: It quite strangely, almost seems to like be coming up
Speaker 3: to the surface and holding still while the fishermen are
Speaker 3: trying to get it untangled. That weirdly kind of matches.
Speaker 3: But then I don't know how to interpret what I'm
Speaker 3: seeing there, so maybe it shouldn't be taken this way,
Speaker 3: but it kind of reminds me of all these stories
Speaker 3: people talk about of manter rays being very like kind
Speaker 3: of slow moving and gentle while they come up to
Speaker 3: them and almost kind of letting people, you know, interact
Speaker 3: with them. Again, not encouraging people to do that unless
Speaker 3: you're trying to free one from a problem you've created.
Speaker 3: But anyway, in the end here the people in the
Speaker 3: boat are able to succeed by they sever the line
Speaker 3: in one place and that allows them to get it
Speaker 3: unwrapped from around the manta, and they let the manta
Speaker 3: swim away. So it seems like the manta gets away
Speaker 3: in the end of this, which is heartwarming. In fact,
Speaker 3: all these like bro fishermen are like high five in
Speaker 3: each other. They're like, yeah, we did it.
Speaker 4: It's it's sweet.
Speaker 3: But once again seems like a quite clear case of
Speaker 3: like the manta is not doing this on purpose. It's
Speaker 3: not it's not out here today thing say, and I'd
Speaker 3: like to drag a boat around it ended up in
Speaker 3: this situation against its will.
Speaker 2: Yeah, yeah, like you said, the cephalic fins are kind
Speaker 2: of look like natural line catchers, and then they're also
Speaker 2: just quite i mean they're they're wing shaped, they're they're
Speaker 2: they're quite wide. We've talked about their their wingspans, and yeah,
Speaker 2: that's just more real estate to potentially run into a line.
Speaker 4: Yeah.
Speaker 3: And so Gil talks about this in his article and
Speaker 3: says that these the cephalic fins or cephalic lobes, the
Speaker 3: kind of horns of the devilfish. They they're like an
Speaker 3: elephant's trunk. He he quotes another author saying that then
Speaker 3: they can kind of grasp objects and pull them in.
Speaker 3: He says they tend to rapidly kind of close in
Speaker 3: around the mouth when something appears in front of the mouth,
Speaker 3: and that the fish will have a kind of obstinacy in,
Speaker 3: you know, refusing to release things that go in like that.
Speaker 3: Gil says quote that these arms are muscular and powerful
Speaker 3: has been demonstrated on many occasions. The natural movement of
Speaker 3: the head fins or corropteries is inward, and when any
Speaker 3: object strikes between them, it is instinctively held a proceeding
Speaker 3: which explains the undoubted fact that these fishes can run
Speaker 3: away with quite large vessels. So Gil's chalking this up
Speaker 3: to involuntary motion of the strong cephalic fins closing over
Speaker 3: things that in the front of the mouth, which occasionally
Speaker 3: in some unlucky circumstances just happens to be an anchor line.
Speaker 3: I think gil is absolutely correct that these boat dragging
Speaker 3: incidents are not aggressive or intentional on the part of
Speaker 3: the ray, but is he correct about the mechanism. I
Speaker 3: was looking for modern sources and couldn't really find anything
Speaker 3: to confirm or deny his ideas there about the specific
Speaker 3: motion of the cephalic fins being involved. But I did
Speaker 3: find some commentary from more recent marine biology resources, specifically
Speaker 3: something from the organization known as the Manta Trust, which
Speaker 3: has a page on the subject of manta mooring line entanglements,
Speaker 3: and they highlight some different biological facts which make mooring
Speaker 3: line entanglements common for manta rays. Manta rays, like their
Speaker 3: cousins sharks, and also like tuna, are obligate ram ventilators,
Speaker 3: meaning they do not have the biological equipment needed to
Speaker 3: pump water over their gills when their bodies are at rest.
Speaker 3: So in order to make water flow over their gills
Speaker 3: so they can extract oxygen from the water and breathe,
Speaker 3: they have to move their bodies. So you've probably heard
Speaker 3: before that if a shark is forced to hold still,
Speaker 3: it will die. It has to swim to breathe. That
Speaker 3: is essentially true, and it's true for mantas as well.
Speaker 3: Fish that don't have to keep moving to breathe have
Speaker 3: what's known as a buckle pump system, where you use
Speaker 3: muscles around your mouth and throat to pump fresh water
Speaker 3: over the gills. Mantis don't have that. They've got to swim.
Speaker 2: Now, I do want to point out that Joe said
Speaker 2: essentially true of sharks, so we can get into a
Speaker 2: deeper discussion maybe in another episode where we talk about
Speaker 2: the different behaviors of different types of sharks. You do
Speaker 2: have some shark varieties that live in close to the
Speaker 2: reef that are going to be that can be still
Speaker 2: for extended periods of time.
Speaker 3: Yeah, they might actually have the buckle pumping equipment. But yeah,
Speaker 3: like great white charts, for example, don't they're ram ventilators exactly.
Speaker 2: Yes, absolutely true of great whites.
Speaker 3: But anyway, certainly true of manta rays. They have to
Speaker 3: swim in order to breathe. They are also ram ventilators.
Speaker 3: And so this means that getting entangled in a line
Speaker 3: can be deadly to a manta if it is stuck
Speaker 3: and it can't swim, around, it can't really breathe, and
Speaker 3: this might also explain why a manta would keep swimming
Speaker 3: even when it has a boat dragging behind it. It
Speaker 3: kind of has to swim. Pair this with a couple
Speaker 3: of other biological facts. Mantas can't swim backwards. You know,
Speaker 3: they are highly maneuverable fish in a way. They can
Speaker 3: turn around and you see them in the water doing
Speaker 3: these beautiful summersalts and everything, but it's always with forward motion,
Speaker 3: which usually means that the line just gets even more
Speaker 3: tangled up on them as they twist and somer salt
Speaker 3: around and they would need to really be able to
Speaker 3: back up to release the line, but they can't back up.
Speaker 2: Great point.
Speaker 3: The other thing is that the manta trust says is
Speaker 3: they are often not able to see the thin line
Speaker 3: of a rope or a chain when it's directly in
Speaker 3: front of them. And so you put all this together
Speaker 3: and it easily explains how mantas can get tangled in
Speaker 3: mooring lines and can end up pulling whatever these lines
Speaker 3: are attached to. This is usually not threatening to humans,
Speaker 3: but it is very threatening to the ray. Rays often
Speaker 3: asphyxiate and die when they get caught in moorings, and
Speaker 3: so the Manta Trust has this document where they make
Speaker 3: recommendations for making mooring lines safer for mantas. You can
Speaker 3: actually look this document up on their website for the
Speaker 3: full recommendations, but they suggest a few measures, like one
Speaker 3: just reducing the presence of especially loose line in the water.
Speaker 3: Loose or slack lines are more dangerous to raise than
Speaker 3: tight lines. You can probably kind of imagine where they are,
Speaker 3: like a looser line is easier to get fully just
Speaker 3: tangled up in or as a taut line, you know,
Speaker 3: you might more likely bump into and then something can
Speaker 3: get Yeah. But then also they recommend this interesting system
Speaker 3: that I don't know if I would have thought of this,
Speaker 3: but this is cool. They recommend attaching cable ties that
Speaker 3: protrude off of mooring lines at a ninety degree angle,
Speaker 3: so you imagine, you know, something kind of like zip
Speaker 3: ties or something like that, evenly spaced every foot or
Speaker 3: so down a mooring line, and they recommend having them
Speaker 3: go out around so there's like a little bar sticking
Speaker 3: off of the side of the rope going in a
Speaker 3: spiral around the rope all the way down, and the
Speaker 3: idea here is that it will make the rope more
Speaker 3: visible to wildlife, especially they say as you use it,
Speaker 3: more algae will attach to the ends of these cable ties,
Speaker 3: and it will make them even more visible. And of course,
Speaker 3: if the rays can see the mooring lines, they will
Speaker 3: avoid them. They're not going to run into them on purpose.
Speaker 2: Okay, So if I'm understanding the illustration you attacked here,
Speaker 2: it's like a spiral staircase of zip ties going up
Speaker 2: and down this particular line, and then, like you said,
Speaker 2: you'll end up with the stuff growing on those ties
Speaker 2: as well.
Speaker 3: Yeah, so it makes the rope easy to see in
Speaker 3: the water instead of just like a thin kind of
Speaker 3: line that is invisible.
Speaker 2: Sometimes that makes sense.
Speaker 3: However, at the very end here, I do want to
Speaker 3: come back with some sympathy for the sailors because obviously
Speaker 3: I think we have the correct perspective now, like we know,
Speaker 3: rays are certainly not attacking boats. They're not trying to
Speaker 3: kidnap sailors on purpose or drag the boats. You know,
Speaker 3: they're not doing this on purpose. But you can very
Speaker 3: well you can understand how it would be frightening to
Speaker 3: have something under especially if you couldn't see it. I
Speaker 3: don't know whether it be scarier actually if you could
Speaker 3: see it or if you couldn't. If you could see
Speaker 3: it might be like a twenty foot wide manta ray.
Speaker 2: Yeah, because it's a gigantic and if you don't know
Speaker 2: all the details, like we said last time, you know,
Speaker 2: it's reasonable for a human to be trepidacious about this
Speaker 2: enormous creature in the world water near them or with them.
Speaker 3: Yeah, And if you can't see it, just there's something
Speaker 3: invisible under the water that's now pulling your boat around. Yeah,
Speaker 3: and you don't know where it's taken you. So I
Speaker 3: can understand being scared.
Speaker 4: I mean like that.
Speaker 3: I've got sympathy for that. But yeah, they're not out
Speaker 3: there trying to do this. It's just unfortunate.
Speaker 4: It happens sometimes, all right.
Speaker 2: Now, at this point in the episode, I want to
Speaker 2: come back and talk in a little more detail about
Speaker 2: manta ray reproduction because in the last episode we talked
Speaker 2: about how they're particularly vulnerable to various threats, you know,
Speaker 2: threats posed by fishing, other human harms, in large part
Speaker 2: because of their slow reproductive cycle. So I wanted to
Speaker 2: get a little more into this. One of my main sources.
Speaker 2: Here again is Guide to the Manta and Devil Rays
Speaker 2: of the World by Stevens Fernando Dando in Dyscaria. Very
Speaker 2: good book, lots of illustrations. It's technically like a field guide.
Speaker 2: I mean, it's not laminated, you can't take it into
Speaker 2: the water with you, but it's a great field guide.
Speaker 2: And the authors here point out that there are a
Speaker 2: lot of gaps in our knowledge about manta ray and
Speaker 2: devil rape reproduction, with most of what we know coming
Speaker 2: from observations of reef mantas and limited scientific data in
Speaker 2: addition to that. So bear that in mind, and I'll
Speaker 2: tuck back in on that fact as well. But manta
Speaker 2: rays are not like most fish that much we've already established,
Speaker 2: and it applies to their reproduction as well. Like all
Speaker 2: elasmo broncs that's sharks and other batomorphs like rays, they
Speaker 2: practice internal fertilization rather than external fertilization, which is practiced
Speaker 2: by most fish species. So they have come so they
Speaker 2: have to come into direct contact with each other in
Speaker 2: order to.
Speaker 3: Mate, right, So it's not like a releasing unfertil eggs
Speaker 3: into the water which then encounter sperm in the water
Speaker 3: and become fertilized externally like many fish do.
Speaker 2: Yeah, there's no just like swimming close to each other
Speaker 2: or both visiting the same spot at one point or
Speaker 2: another that they do have to engage and what is
Speaker 2: ultimately rather complex and kind of beautiful and maybe at
Speaker 2: times humorous mating ritual. The other amazing thing about manta
Speaker 2: reproduction is that, as with a minority of other fish species,
Speaker 2: they are live bearers, meaning they give live birth via
Speaker 2: an egg that hatches inside the female's uterus. This is
Speaker 2: known as a placental viviparity. Now, as many people have
Speaker 2: observed and some of your listeners might be thinking, this
Speaker 2: practice would seem to be yet another way that the
Speaker 2: manta rays resemble certain whale species. Yeah, you know what,
Speaker 2: large oceanic filter feeders that give live birth.
Speaker 3: Yeah, they could easily be mistaken for a mammal.
Speaker 2: Yeah, but this is not the same as live mammalian birth.
Speaker 2: And while whales lie on their mothers for the first
Speaker 2: phase of their lives, mantas are on their own from
Speaker 2: the moment they're born. They're just small versions of their
Speaker 2: parents that have to just hit the ground running, you know,
Speaker 2: not much smaller of course they're still they're still quite big.
Speaker 2: A newborn is typically like one point five to one
Speaker 2: point eight meters across, or like five to six feet.
Speaker 2: Whoa yeah, and sometimes it's twins. That's a big baby.
Speaker 2: All right, So let's walk through the courtship. I said
Speaker 2: that it was beautiful and weird and sometimes funny again, Stevens,
Speaker 2: that all point out that there's much we don't know.
Speaker 2: This is a general description. A lot of it's based
Speaker 2: on reef mantas, and they're going to be species specific variations,
Speaker 2: and I believe it's possible there may be environmental differences
Speaker 2: as well, depending on where the mantas are. But in general,
Speaker 2: this is how it goes down. So a male will
Speaker 2: approach a female and he'll shadow her from above, and
Speaker 2: then he may attempt to rub the top of her
Speaker 2: head with his cephalic fence the devil horns, right, and
Speaker 2: usually what's going to take place at this point is
Speaker 2: she's going to shake him. She's going to like, you know,
Speaker 2: make a quick turn and say get away from me.
Speaker 2: She's just going to reject his advances.
Speaker 3: Okay, so devil horn back, rub and then bolt.
Speaker 2: Yeah, generally she's gonna bolt generally she's going to say
Speaker 2: I'm not in the mood and she's going to go in.
Speaker 2: But if she is interested, what she's going to do
Speaker 2: instead is speed forward, and then he is going to
Speaker 2: give chase. And as this chase continues, this is going
Speaker 2: to draw in other males who will also give chase,
Speaker 2: and we get another situation where we have a line
Speaker 2: of manta rays. This time, you know, a train of
Speaker 2: manta rays speeding through the water, you know, maybe around reefs,
Speaker 2: and these can also kind of quickly get to our
Speaker 2: eyes out at hand, like a thirty strong zooming train
Speaker 2: of mantas that occasionally leaps out of the water as well.
Speaker 3: This is kind of like the feeding structure you talked
Speaker 3: about in the last episode. What was the name of it.
Speaker 3: It wasn't cyclone feeding, was it. That was when they
Speaker 3: formed ring and they go around and round. But last
Speaker 3: time when you talked about how there might be a
Speaker 3: big cloud of zooplankton and they're eating them, and so
Speaker 3: they line up in this row and they go through
Speaker 3: and for some reason they get more food that way.
Speaker 2: Yeah, yeah, chain feeding. So yeah, this is reminiscent of
Speaker 2: chain feeding.
Speaker 3: Except not feeding here. This is the it's the first
Speaker 3: one is trying to mate with the female.
Speaker 2: Well, yes, well he's trying to to keep up with her.
Speaker 2: And in general, she's going to try and shake loose
Speaker 2: the less fit pursuers because now she doesn't just have
Speaker 2: one manta. She may have up to thirty mantas behind her.
Speaker 2: And this is crazy too. She may loop back around
Speaker 2: and start chasing the last male in line, So now
Speaker 2: we get another like just ring another sort of like
Speaker 2: mating cyclone here, okay, or courtship cyclone, I guess, okay.
Speaker 2: Other females may also be swept up in these processions,
Speaker 2: which can result in one line splitting or two lines merging.
Speaker 2: They also the authors here also mentioned that she may
Speaker 2: end up chasing another female manta as well. So this
Speaker 2: you start with one train of mansa's zooming through the water,
Speaker 2: and it may go in different directions. It may split,
Speaker 2: it may merge, it may loop back around on itself,
Speaker 2: and yeah, it's quite spectacular, I'm to.
Speaker 3: Understand, fascinating. Courtship is complicated.
Speaker 2: Yeah, in the course of this, old males are going
Speaker 2: to fall fall away, they can't keep up. New mantas
Speaker 2: are going to join in. They're like well, I'm fresh,
Speaker 2: I'm ready to go. I think I might be able
Speaker 2: to catch her. But the author's stress that she's not
Speaker 2: actually trying to lose anyone. This isn't one of those
Speaker 2: cases where it's like she doesn't want to mate and
Speaker 2: it's just whichever male can catch her. It's not a
Speaker 2: mating pursuit like you see with other species. She's seemingly
Speaker 2: doing all of this to merely assess her suitors and
Speaker 2: determine which one is displaying the greatest level of fitness.
Speaker 2: But at the same time, the end result is going
Speaker 2: to be only one man toa ray can still keep
Speaker 2: up with her.
Speaker 3: So you could look at this this is a kind
Speaker 3: of mass organized mating dance of rich yeah, yeah.
Speaker 2: Yeah, And it's it's very much a situation where it's
Speaker 2: the individual with the greatest degree of fitness is going
Speaker 2: to be the one that she mates with, and she
Speaker 2: absolutely has to be choosy because a lot is writing
Speaker 2: on her selection. And this comes again back to the
Speaker 2: gestation period for romantis, which takes a little over a year,
Speaker 2: and given the ups and downs of environmental factors, mainly
Speaker 2: food in the wild, she's generally not going to be
Speaker 2: able to reproduce every year anyway, Carrying such large offspring
Speaker 2: to term is costly, and even when food is abundant,
Speaker 2: she's just not going to be able to do it
Speaker 2: every year, So there ends up being seasonal gaps, and
Speaker 2: this generally breaks down to a pregnancy occurring every two
Speaker 2: to three years, but the authors of this book point
Speaker 2: out that the rate can be as low as once
Speaker 2: every seven years in particular environments. Wow. And another factor
Speaker 2: involved here in her choosiness is that she may reproduce,
Speaker 2: she may mate rather multiple times during the breeding season,
Speaker 2: but she's going to store sperm from multiple partners. This
Speaker 2: is something we see in other organisms as well, and
Speaker 2: then she can use the sperm she wants whenever she
Speaker 2: finally gets to fertilizer eggs, whenever it's not finally the
Speaker 2: right time to fertilizerr eggs.
Speaker 5: Yeah.
Speaker 3: Yeah, sperm storage like this. I think we've talked about
Speaker 3: this happening in some species of sharks also, Yeah, which
Speaker 3: of course are closely related to rays.
Speaker 2: So yeah, eventually one male is going to be left.
Speaker 2: There can be only one. She's going to slow down
Speaker 2: and allow him to shadow her again. You know, it
Speaker 2: be you know more or less a top of her,
Speaker 2: shadowing her. But then he is going to bite down
Speaker 2: hard on her left wing tip, hard enough that this
Speaker 2: is going to leave scarring. You can identify, you know,
Speaker 2: females that have bred before in the wild because they
Speaker 2: will have this scarring on there on their left wingtip.
Speaker 2: I want to say, it's like in the high ninety
Speaker 2: percents that it's the left wing tip testing. And once
Speaker 2: he's he's bit down hard on it, and I think
Speaker 2: there's a fair amount of wingtip like going into his mouth.
Speaker 2: At this point, he's going to flip so that now
Speaker 2: he's belly to belly with her, and then he's going
Speaker 2: to use one of his claspers. There are two claspers
Speaker 2: on the mail. It's going to use that to ejaculate
Speaker 2: sperm into her kloeca. And then he's going to beat
Speaker 2: his pectoral fins, causing the two of them to spiral
Speaker 2: in the water. This is all going to last about
Speaker 2: thirty seconds and then they're going to go their separate ways.
Speaker 3: Wow, that's elaborate.
Speaker 4: Yeah.
Speaker 2: Yeah, there's a whole diagram in the book here was
Speaker 2: showing how all of this, all this elaborate dance eventually
Speaker 2: comes to a closure.
Speaker 3: It's funny you mentioned the biting down element because this
Speaker 3: squares was something I think I was reading in preparation
Speaker 3: for the first episode that we didn't end up talking about.
Speaker 4: But the fact that that.
Speaker 3: Manta rays don't have teeth that they use for feeding,
Speaker 3: but the teeth are basically, you know, they've got these
Speaker 3: little plates, you know, sort of mighty plates. Yeah, little
Speaker 3: little tiny amounts of kind of nubby, little teeth that
Speaker 3: are apparently only used in mating.
Speaker 2: At any rate, they definitely bite pretty hard. Again, there
Speaker 2: are some photos and you can look up photos of
Speaker 2: mating scars and manta rays.
Speaker 3: But so, okay, now the egg is fertilized and you
Speaker 3: would have a gestation period.
Speaker 2: Right, that's right. Yeah, more than a year of gestation follows.
Speaker 2: And this is another area where we have to stress
Speaker 2: that like we don't have I believe as even to
Speaker 2: this day, I don't think we have any wild observations
Speaker 2: of manta ray birth. At the time of this book's
Speaker 2: publication in twenty eighteen, there had been I think just
Speaker 2: a single incidence of a recorded captive birth at the
Speaker 2: Okinawa Aquarium as in I think two thousand and seven.
Speaker 2: Since that point, I believe the same aquarium and in
Speaker 2: some cases the same manta ray with the same manta ray.
Speaker 2: We've seen subsequent berths, with the most recent I believe
Speaker 2: being twenty twenty four. You can look up videos. When
Speaker 2: I was looking around, there's at least one video that
Speaker 2: was easy to find. Some I think have been taken down,
Speaker 2: but you can watch as this obviously pregnant female manta ray,
Speaker 2: and sometimes you see the female manta rays in the wild.
Speaker 2: Some of the Snorkel guides that we had in Indonesia
Speaker 2: also pointed out that sometimes you'll just see a male
Speaker 2: that happens to be really bloated, but generally you can
Speaker 2: tell a pregnant female, and yeah, you can. You can
Speaker 2: watch the miracle of birth as this this mother pushes
Speaker 2: out a you know, a rather large and ready to
Speaker 2: run manta.
Speaker 3: I'm watching it right now.
Speaker 4: It is amazing.
Speaker 2: Wow.
Speaker 3: And then oh yeah it uh it comes out kind
Speaker 3: of in a clump, and it's not moving for a second,
Speaker 3: and suddenly it just kind of twitches and then starts
Speaker 3: jetting around.
Speaker 4: Yeah.
Speaker 2: I think I've seen this described as kind of like
Speaker 2: a burrito before their their their their fins are curled
Speaker 2: up over their backs, and you know, there's kind of
Speaker 2: like a you know, cloud of material that comes out
Speaker 2: with them, and then you know, they start moving and
Speaker 2: then they swim off and they are on their own. Again.
Speaker 2: The there is no mother off bring relationship here. They
Speaker 2: go their separate ways. But again, the newborn's actual egg
Speaker 2: case would have hatched, if to use perhaps an incorrect
Speaker 2: term here, sometime before, inside the female's uterus, and it
Speaker 2: would have subsequently fed on the mother's uterine milk, which
Speaker 2: in this case is known as histotrophe.
Speaker 3: Manta ray uterine milk. I don't think we ever got
Speaker 3: into that. We did an episode or a series of
Speaker 3: episodes a ways back about non mammalian milk.
Speaker 2: Yeah, I mean it's one of those things where is
Speaker 2: it really milk? Yeah, no, no, but it kind of
Speaker 2: serves the purpose of milk, yeah.
Speaker 3: Because we talked about like dinosaurs perhaps producing a milk
Speaker 3: like substance.
Speaker 2: Yeah.
Speaker 4: Yeah.
Speaker 2: But again this is to go back to what we
Speaker 2: were talking about in the first episode. This is all
Speaker 2: exactly the reason that manta rays have such a delicate
Speaker 2: place in their environments because again, long gestation period generally
Speaker 2: a single berth, and it's not happening every year. It's
Speaker 2: you know, there are these big gaps between subsequent births,
Speaker 2: so if there's any kind of targeted fishing or any
Speaker 2: kind of factor that is that is eating into their population,
Speaker 2: it's harder for them to bounce back. Yeah, all right,
Speaker 2: Well we're going to go and close out this episode.
Speaker 2: We will be back with I believe one more episode
Speaker 2: on manta rays, and it should be an equally exciting
Speaker 2: one because we're going to talk about their brains, we
Speaker 2: are going to talk about their parasites, and we will
Speaker 2: talk about cleaning stations, which if you don't know much
Speaker 2: about manta cleaning stations or cleaning stations in general with
Speaker 2: other species, you might think that this sounds like the
Speaker 2: least exciting thing we could talk about, but it's actually
Speaker 2: really exciting.
Speaker 4: Yes. Yes.
Speaker 2: In the meantime, definitely right into us. We would love
Speaker 2: to hear from anyone out there who has experiences encountering
Speaker 2: manta rays or other rays in the wild. Do you
Speaker 2: have any tales of tangled mantas. Have you also snorkeled
Speaker 2: or scuba dived with mantas or seen them from boats?
Speaker 2: What are your observations? Share with us your observations of
Speaker 2: the Manta. Just a reminder that Stuff to Blow Your
Speaker 2: Mind is primarily a science and culture podcast, with core
Speaker 2: episodes on Tuesdays and Thursdays. We do a short form
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Speaker 3: As always to our excellent audio producer JJ Posway. If
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