July 8, 2025 • 38 mins
In this series of episodes from Stuff to Blow Your Mind, Robert and Joe discuss the majestic manta ray. In this episode, learn all about manta ray reproduction and accounts of their pulling boats around by their anchors.
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Speaker 1 (00:03):
Welcome to Stuff to Blow Your Mind production of iHeartRadio.
Speaker 2 (00:12):
Hey you welcome to Stuff to Blow your Mind.
Speaker 3 (00:14):
My name is Robert Lamb and I am Joe McCormick,
and we're back with part two in our series on
manta rays and their close mobulate relatives. In the last
episode of this series, we kicked things off by talking
about an experience that you had rob recently where you
and your family got to see reef manta rays in
person while snorkeling in Indonesia, which sounds pretty amazing to
(00:37):
get the details on that right.
Speaker 2 (00:39):
Correct, Yes, it was. It was amazing. Words can't quite
describe it.
Speaker 3 (00:43):
Observing them, but not swimming quote with them, You weren't
You weren't riding the rays.
Speaker 2 (00:48):
Correct, they were. They were doing their own thing. We
were trying to keep our distance and observe from a distance,
which which is the correct way of going about things.
Speaker 3 (00:57):
So that was what inspired us to talk about man
in a series of episodes here on the show. In
the last episode, we talked about the historical evolution of
human attitudes toward manta rays with these old stories among
some divers and sailors that cast manta rays as diabolical
vampires of the sea. You know, there's one idea that
(01:18):
they will like fold over a diver like a blanket
of death. This, of course is not true, and since
it seems like since roughly the nineteen seventies there has
been more widespread recognition that mantas are gentle and not
threatening to humans, though of course that has not stopped
humans from threatening them, and we talked about all kinds
of ways that human activity can hurt these animals. These
(01:41):
impacts range from accidental harms, like when mantas are killed
as bycatch in commercial fishing. It's not what people are
fishing for, but they just get caught in nets and
other lines and other things, all the way to intentional targeting,
where they are killed for their gill plates, which some
people falsely allege to have medical powers. And in the
(02:02):
vein of talking about tall tales of mantas as vicious monsters,
we also discussed a couple of movies made in the
nineteen thirties that have a killer Manta Ray or devil
Ray as the monster.
Speaker 2 (02:14):
I didn't mention this in that episode, but it's worth
noting that, you, of course have one of Aquaman's arch
Enemies is Black Manta. Oh, so you know, it's the
perfect mantle for a villain that was conceived. I believe
in this era you also have Man Ray, which is
a villain based on Black Manta that pops up on
SpongeBob SquarePants, not to be confused with the artist Man Ray.
Speaker 3 (02:38):
I think Black Manta is actually in the Aquaman movie
with cal Drogo in it, isn't it.
Speaker 2 (02:45):
Oh yeah, yeah, who plays Black Manta? I don't I
haven't seen any of those films.
Speaker 3 (02:49):
I don't remember any of the cast of that movie
except in Nicole Kidman in a really funny looking costume.
So I you know, folks out there, No, I'm not
the biggest superhero movie fan. I haven't kept up with
all of the Marvel and DC superhero films, but I
think I watched Aquaman on a plane for some reason.
I remember thinking it was really funny, like highly amusing.
(03:12):
Oh no, wait, I remember another cast member had Patrick
Wilson like riding on a shark and saying, you will
call me ocean Master.
Speaker 2 (03:22):
I need to watch those on an airplane sometime.
Speaker 3 (03:24):
Yes, Jason Momoa, I'm sorry I called him Caldroco.
Speaker 4 (03:27):
That's not nice. His name is Jason Momoa.
Speaker 2 (03:30):
Suffice to say, however, the Western American European conceptions of
the manta ray and related species have evolved since basically
the nineteen seventies. The nineteen seventies onward. Everyone has come
to realize that manta rays are peaceful giants of the
ocean and they are not out to eat us.
Speaker 3 (03:52):
Right, And so we also talked about modern conservation efforts
aimed at protecting manta's You know, we got into like
the cost benefit analysis that has to be done if
you're considering building something like an ecological tourism trade around them.
You know, there are risks but also potentially rewards. And
we also talked about the basic biology of manta rays
and their near relatives, their near relatives being the devil rays.
(04:15):
Mantas and devil rays together make up the genus Mobula.
And we got into subjects including their body design, common
feeding strategies, and leaping or breaching behavior where they jump
out of the water and slap back down. We talked
about some reasons they might do that. And we're back
today to talk about more.
Speaker 2 (04:33):
Yeah, and we're gonna we're gonna pick up in an
interesting area, you're gonna you're gonna get into some some
more myths or potential myths about their behavior and what
we may or may not know about those behaviors.
Speaker 3 (04:45):
Now right, well, I think this might be slightly different
because it would be truths about their behavior with mythical interpretations,
if that makes any sense. So in the last episode,
we were talking about these incorrect folk beliefs about the
man you know that they would attack boats or attack
divers in the form of this underwater death blanket. And
(05:07):
as a source there I referenced an old article called
the Story of the Devilfish from the ear Way back
in the year nineteen ten by the American biologist Theodore
gil There was another thread in this article that I
found interesting and I wanted to come back to it today.
So if you'll recall from last time, in this article Gil,
he's very dismissive of the belief that the manta tries
(05:29):
to smother divers with its body or devour them with
its gaping mouth. He points out that the manta is
a filter feeder which eats tiny planktonic organisms. It does
not eat large prey. There's no evidence of manta's targeting
humans for violence, and they don't even have the right
biological equipment to eat us if they were going to
try to do that, which they're not going to try.
(05:51):
But there is another part of the manta's more frightening
reputation in pre modern times, which is the belief that
mantas will attack boats, not divers, but boats, particularly the
claim that a manta will drag a boat out to
sea by the anchor line. So here I'm going to
read a passage from Gill's article quote in one of
(06:14):
the earliest Notices of the Devilfish by John Lawson in
the History of Carolina seventeen fourteen. This peculiarity is described
the devilfish, he says, has been known to weigh a
ship's anchor and run with the vessel a league or
two and bring her back against tide to almost the
same place. But then the quote ends, and Gill goes
(06:36):
on to say later notices do not give the animal
credit for the same accommodating treatment, And he later alludes
to these other accounts that tell of the devilfish pulling
sailing boats around by the anchor, to the wonder and
fear of the sailors, and he also cites a more
recent source to him at the time of his writing.
(06:56):
This was a French naturalist named Leon de Guett describing
the activity of pearl fishers in the Gulf of California
in a text from eighteen ninety eight, and according to Deget,
when fishers are caught out at sea overnight in the
Gulf of California away from their usual mooring places, he says,
(07:17):
they will always drop two anchors because they fear that
if they only drop one, the anchor line will be
seized by the devilfish in the dark, and thus the
boat will be carried away into the open sea. And
to get back to this up with his own observation,
telling a story of how he was sent out to
harpoon a specimen of a devil ray for the Natural
(07:39):
History Museum of Paris, and he says, quote, after one
had been harpooned, it turned back on the boat, seized
the bow with its head fins, and held it in
its clasp till it was lanced the second time. So
that's Deget's account. But Gil says even this direct observation
(08:00):
does not really lend credence to the idea that Mantas
or devil rays deliberately attack detain or hijack boats because,
based on his own study, Gil writes that this kind
of grasping with the headfins is automatic. He says, it's
an involuntary muscular reaction when something is in front of
(08:20):
the ray's mouth, so in this case, it might happen
to be the bow of the harpooner's boat. And so
even when it's being attacked by somebody on the boat,
when it's being harpooned, Gill argues that the ray was
probably not actually trying to harm the boat, but rather
was just being pulled toward the boat by the tension
of the rope on the harpoon it had just been
(08:41):
lanced with. And even to get himself the person originally
telling the story of it seizing the bow of the boat,
he says the devilfishes are generally timid, non aggressive animals.
Though then after saying this confusingly to get does seem open,
he sort of opens up more claims of devilfish savagery
and alleges that in the Gulf of California, quote numerous
(09:04):
cases have occurred of death resulting to divers as well
as bathers from encounters with the devilfish or manta as
the men call it. On the other hand, the carcasses
of many that are killed are used for bait for
other fishes. The strange detail to include.
Speaker 2 (09:21):
Yeah, yeah, I mean all of this is a pardon
the terminology here, fishy because.
Speaker 3 (09:27):
Dobous third hand Yeah.
Speaker 2 (09:30):
Yeah, I mean, because everything we know and have been
discussing about rays, when they're threatened, they use a burst
of speed, they get away. That's their major way of
defending themselves. So it doesn't really make sense based on
what we know that they would turn around an attack
of a ship or a boat, even if they are
being acted upon with harpoons.
Speaker 3 (09:51):
Right, And as we discussed last time, of course, they
are large animals, and any large animal could potentially hurt
you just by bumping into you. Wrong, But there is
really no evidence I could find of manta's being aggressive
toward humans except for these like old third hand stories.
Speaker 4 (10:08):
Yeah.
Speaker 2 (10:08):
And I don't know if Gil gets into this or not,
but for one of the things with you get into
oral histories of things like the devilfish the manta, you
end up having to ask questions, well, is the manta
in this story, even if there's a kernel of truth
to it, Is it indeed talking about the species that
we are talking about as the manta ray, or is
(10:30):
it referring to something else real or imagined.
Speaker 3 (10:32):
Yeah, so, even back in nineteen ten, Gil to me
seems skeptical of these claims about it attacking boats. Certainly,
modern researchers are skeptical of these stories of manterray aggression
towards boats. But to the question of dragging boats specifically
by the anchor cable, is this just a tall tale
like the manta ray death blanket story or is there
(10:55):
something more to that? Is there any modern evidence of
things like this happening sort of?
Speaker 4 (11:00):
This is yes.
Speaker 3 (11:01):
For example, I found a Reuter's article from February eleventh,
nineteen ninety nine, called motor boat no match for manta
ray in tug of war.
Speaker 2 (11:10):
Well, I generally, you know, I generally trust Reuters in
their reporting. Though usual usually I'm not reading about the
marine biology. When I'm reading Reuters. Usually it's a nice
you know, doom scroll into the abyss. So I missed
this one when it came out. If I was in
fact reading Routers at the time.
Speaker 3 (11:30):
I'll read from the beginning of the article and then
summarize some other parts of it and we can make
up our minds about it. Okay, what's going on here?
So Dateline New Smurta Beach, Florida. Two Florida boaters met
a real sea monster when their craft was dragged for
hours by a powerful creature that turned out to be
a giant manta ray, the Coastguard said Wednesday. Coastguard Petty
(11:51):
Officer Scott Barnes said the agency received a radio distress
call from a sixteen foot boat that reported it was
being dragged by its anchor line by something unknown. The
Coast Guard sent a rescue boat to investigate and found
the motor boat was being dragged in circles by something
beneath the surface. The crew transferred the anchor line to
the Coastguard vessel, freeing the men in the motor boat,
(12:13):
who had tried to use their ninety horsepower engine to
go in reverse and stop themselves from being dragged out
to sea. After the Coastguard's forty one foot boat pulled
the anchor line for several minutes, a giant manta ray,
measuring an estimated eighteen feet in width, came to the surface,
and then the article goes on to describe how the
coastguard struggled to pull the rope away. Eventually, the manta
(12:36):
was able to disentangle itself from the rope and it
swam away on its own, And by the end of
the ordeal, the manta, they estimated, had pulled the boat
for almost two hours, taking it about a mile and
a half away from shore. But you could easily get
the wrong idea about this, thinking that it supports this
old notion that mantas will attack boats, that they are
(12:59):
doing this on purpose, they're trying to drag the sailors
out to sea, out to their deaths or something. From
what I've read, there is absolutely zero evidence to support
the idea that the mantas are acting aggressively when they
pull a boat by the anchor line. The zero evidence
that they're acting aggressively or even acting intentionally. Rather, this
(13:20):
is almost certainly a case of mantas getting stuck. They
are getting tangled in underwater ropes and chains by accident
and then pulling the boat because they are unable to
free themselves. And when you look at their heads, you
look up a picture of a manta ray or a
devil ray. You can see how this might easily happen.
They almost have biological mooring cleats with their cephalic fins.
Speaker 5 (13:45):
Yeah, yeah, you can imagine them catching the line.
Speaker 3 (13:58):
For one more example of a mod encounter, I found
a video on YouTube that the title begins with Giant
mantray tangled in anchorchain, forty miles off shore. This is
a video of some people out in a fishing boat
in the Gulf of Mexico and a manta does get
caught in their anchor line. Like it looks when you
can see it, it looks like the line is not just
(14:20):
caught between the cephalic fins, but kind of wrapped around them,
like the lobes on its head have the line going
across as well as between, and you can see it
struggling at a couple of points.
Speaker 4 (14:33):
In this video.
Speaker 3 (14:34):
It quite strangely, almost seems to like be coming up
to the surface and holding still while the fishermen are
trying to get it untangled. That weirdly kind of matches.
But then I don't know how to interpret what I'm
seeing there, so maybe it shouldn't be taken this way,
but it kind of reminds me of all these stories
people talk about of manter rays being very like kind
of slow moving and gentle while they come up to
(14:56):
them and almost kind of letting people, you know, interact
with them. Again, not encouraging people to do that unless
you're trying to free one from a problem you've created.
But anyway, in the end here the people in the
boat are able to succeed by they sever the line
in one place and that allows them to get it
unwrapped from around the manta, and they let the manta
(15:16):
swim away. So it seems like the manta gets away
in the end of this, which is heartwarming. In fact,
all these like bro fishermen are like high five in
each other. They're like, yeah, we did it.
Speaker 4 (15:26):
It's it's sweet.
Speaker 3 (15:27):
But once again seems like a quite clear case of
like the manta is not doing this on purpose. It's
not it's not out here today thing say, and I'd
like to drag a boat around it ended up in
this situation against its will.
Speaker 2 (15:40):
Yeah, yeah, like you said, the cephalic fins are kind
of look like natural line catchers, and then they're also
just quite i mean they're they're wing shaped, they're they're
they're quite wide. We've talked about their their wingspans, and yeah,
that's just more real estate to potentially run into a line.
Speaker 4 (15:57):
Yeah.
Speaker 3 (15:57):
And so Gil talks about this in his article and
says that these the cephalic fins or cephalic lobes, the
kind of horns of the devilfish. They they're like an
elephant's trunk. He he quotes another author saying that then
they can kind of grasp objects and pull them in.
He says they tend to rapidly kind of close in
(16:18):
around the mouth when something appears in front of the mouth,
and that the fish will have a kind of obstinacy in,
you know, refusing to release things that go in like that.
Gil says quote that these arms are muscular and powerful
has been demonstrated on many occasions. The natural movement of
(16:39):
the head fins or corropteries is inward, and when any
object strikes between them, it is instinctively held a proceeding
which explains the undoubted fact that these fishes can run
away with quite large vessels. So Gil's chalking this up
to involuntary motion of the strong cephalic fins closing over
(16:59):
things that in the front of the mouth, which occasionally
in some unlucky circumstances just happens to be an anchor line.
I think gil is absolutely correct that these boat dragging
incidents are not aggressive or intentional on the part of
the ray, but is he correct about the mechanism. I
was looking for modern sources and couldn't really find anything
(17:20):
to confirm or deny his ideas there about the specific
motion of the cephalic fins being involved. But I did
find some commentary from more recent marine biology resources, specifically
something from the organization known as the Manta Trust, which
has a page on the subject of manta mooring line entanglements,
(17:43):
and they highlight some different biological facts which make mooring
line entanglements common for manta rays. Manta rays, like their
cousins sharks, and also like tuna, are obligate ram ventilators,
meaning they do not have the biological equipment needed to
(18:04):
pump water over their gills when their bodies are at rest.
So in order to make water flow over their gills
so they can extract oxygen from the water and breathe,
they have to move their bodies. So you've probably heard
before that if a shark is forced to hold still,
it will die. It has to swim to breathe. That
is essentially true, and it's true for mantas as well.
(18:28):
Fish that don't have to keep moving to breathe have
what's known as a buckle pump system, where you use
muscles around your mouth and throat to pump fresh water
over the gills. Mantis don't have that. They've got to swim.
Speaker 2 (18:40):
Now, I do want to point out that Joe said
essentially true of sharks, so we can get into a
deeper discussion maybe in another episode where we talk about
the different behaviors of different types of sharks. You do
have some shark varieties that live in close to the
reef that are going to be that can be still
for extended periods of time.
Speaker 3 (19:00):
Yeah, they might actually have the buckle pumping equipment. But yeah,
like great white charts, for example, don't they're ram ventilators exactly.
Speaker 2 (19:08):
Yes, absolutely true of great whites.
Speaker 3 (19:11):
But anyway, certainly true of manta rays. They have to
swim in order to breathe. They are also ram ventilators.
And so this means that getting entangled in a line
can be deadly to a manta if it is stuck
and it can't swim, around, it can't really breathe, and
this might also explain why a manta would keep swimming
even when it has a boat dragging behind it. It
(19:33):
kind of has to swim. Pair this with a couple
of other biological facts. Mantas can't swim backwards. You know,
they are highly maneuverable fish in a way. They can
turn around and you see them in the water doing
these beautiful summersalts and everything, but it's always with forward motion,
which usually means that the line just gets even more
(19:55):
tangled up on them as they twist and somer salt
around and they would need to really be able to
back up to release the line, but they can't back up.
Speaker 2 (20:04):
Great point.
Speaker 3 (20:05):
The other thing is that the manta trust says is
they are often not able to see the thin line
of a rope or a chain when it's directly in
front of them. And so you put all this together
and it easily explains how mantas can get tangled in
mooring lines and can end up pulling whatever these lines
are attached to. This is usually not threatening to humans,
(20:27):
but it is very threatening to the ray. Rays often
asphyxiate and die when they get caught in moorings, and
so the Manta Trust has this document where they make
recommendations for making mooring lines safer for mantas. You can
actually look this document up on their website for the
full recommendations, but they suggest a few measures, like one
just reducing the presence of especially loose line in the water.
(20:52):
Loose or slack lines are more dangerous to raise than
tight lines. You can probably kind of imagine where they are,
like a looser line is easier to get fully just
tangled up in or as a taut line, you know,
you might more likely bump into and then something can
get Yeah. But then also they recommend this interesting system
that I don't know if I would have thought of this,
(21:13):
but this is cool. They recommend attaching cable ties that
protrude off of mooring lines at a ninety degree angle,
so you imagine, you know, something kind of like zip
ties or something like that, evenly spaced every foot or
so down a mooring line, and they recommend having them
(21:34):
go out around so there's like a little bar sticking
off of the side of the rope going in a
spiral around the rope all the way down, and the
idea here is that it will make the rope more
visible to wildlife, especially they say as you use it,
more algae will attach to the ends of these cable ties,
(21:54):
and it will make them even more visible. And of course,
if the rays can see the mooring lines, they will
avoid them. They're not going to run into them on purpose.
Speaker 2 (22:01):
Okay, So if I'm understanding the illustration you attacked here,
it's like a spiral staircase of zip ties going up
and down this particular line, and then, like you said,
you'll end up with the stuff growing on those ties
as well.
Speaker 3 (22:14):
Yeah, so it makes the rope easy to see in
the water instead of just like a thin kind of
line that is invisible.
Speaker 2 (22:20):
Sometimes that makes sense.
Speaker 3 (22:22):
However, at the very end here, I do want to
come back with some sympathy for the sailors because obviously
I think we have the correct perspective now, like we know,
rays are certainly not attacking boats. They're not trying to
kidnap sailors on purpose or drag the boats. You know,
they're not doing this on purpose. But you can very
well you can understand how it would be frightening to
(22:43):
have something under especially if you couldn't see it. I
don't know whether it be scarier actually if you could
see it or if you couldn't. If you could see
it might be like a twenty foot wide manta ray.
Speaker 2 (22:51):
Yeah, because it's a gigantic and if you don't know
all the details, like we said last time, you know,
it's reasonable for a human to be trepidacious about this
enormous creature in the world water near them or with them.
Speaker 3 (23:02):
Yeah, And if you can't see it, just there's something
invisible under the water that's now pulling your boat around. Yeah,
and you don't know where it's taken you. So I
can understand being scared.
Speaker 4 (23:10):
I mean like that.
Speaker 3 (23:11):
I've got sympathy for that. But yeah, they're not out
there trying to do this. It's just unfortunate.
Speaker 4 (23:16):
It happens sometimes, all right.
Speaker 2 (23:28):
Now, at this point in the episode, I want to
come back and talk in a little more detail about
manta ray reproduction because in the last episode we talked
about how they're particularly vulnerable to various threats, you know,
threats posed by fishing, other human harms, in large part
because of their slow reproductive cycle. So I wanted to
get a little more into this. One of my main sources.
(23:51):
Here again is Guide to the Manta and Devil Rays
of the World by Stevens Fernando Dando in Dyscaria. Very
good book, lots of illustrations. It's technically like a field guide.
I mean, it's not laminated, you can't take it into
the water with you, but it's a great field guide.
And the authors here point out that there are a
(24:13):
lot of gaps in our knowledge about manta ray and
devil rape reproduction, with most of what we know coming
from observations of reef mantas and limited scientific data in
addition to that. So bear that in mind, and I'll
tuck back in on that fact as well. But manta
rays are not like most fish that much we've already established,
(24:36):
and it applies to their reproduction as well. Like all
elasmo broncs that's sharks and other batomorphs like rays, they
practice internal fertilization rather than external fertilization, which is practiced
by most fish species. So they have come so they
have to come into direct contact with each other in
(24:56):
order to.
Speaker 3 (24:56):
Mate, right, So it's not like a releasing unfertil eggs
into the water which then encounter sperm in the water
and become fertilized externally like many fish do.
Speaker 2 (25:06):
Yeah, there's no just like swimming close to each other
or both visiting the same spot at one point or
another that they do have to engage and what is
ultimately rather complex and kind of beautiful and maybe at
times humorous mating ritual. The other amazing thing about manta
reproduction is that, as with a minority of other fish species,
they are live bearers, meaning they give live birth via
(25:30):
an egg that hatches inside the female's uterus. This is
known as a placental viviparity. Now, as many people have
observed and some of your listeners might be thinking, this
practice would seem to be yet another way that the
manta rays resemble certain whale species. Yeah, you know what,
large oceanic filter feeders that give live birth.
Speaker 3 (25:50):
Yeah, they could easily be mistaken for a mammal.
Speaker 2 (25:53):
Yeah, but this is not the same as live mammalian birth.
And while whales lie on their mothers for the first
phase of their lives, mantas are on their own from
the moment they're born. They're just small versions of their
parents that have to just hit the ground running, you know,
not much smaller of course they're still they're still quite big.
(26:14):
A newborn is typically like one point five to one
point eight meters across, or like five to six feet.
Whoa yeah, and sometimes it's twins. That's a big baby.
All right, So let's walk through the courtship. I said
that it was beautiful and weird and sometimes funny again, Stevens,
that all point out that there's much we don't know.
This is a general description. A lot of it's based
(26:35):
on reef mantas, and they're going to be species specific variations,
and I believe it's possible there may be environmental differences
as well, depending on where the mantas are. But in general,
this is how it goes down. So a male will
approach a female and he'll shadow her from above, and
then he may attempt to rub the top of her
(26:56):
head with his cephalic fence the devil horns, right, and
usually what's going to take place at this point is
she's going to shake him. She's going to like, you know,
make a quick turn and say get away from me.
She's just going to reject his advances.
Speaker 3 (27:08):
Okay, so devil horn back, rub and then bolt.
Speaker 2 (27:11):
Yeah, generally she's gonna bolt generally she's going to say
I'm not in the mood and she's going to go in.
But if she is interested, what she's going to do
instead is speed forward, and then he is going to
give chase. And as this chase continues, this is going
to draw in other males who will also give chase,
and we get another situation where we have a line
(27:33):
of manta rays. This time, you know, a train of
manta rays speeding through the water, you know, maybe around reefs,
and these can also kind of quickly get to our
eyes out at hand, like a thirty strong zooming train
of mantas that occasionally leaps out of the water as well.
Speaker 3 (27:52):
This is kind of like the feeding structure you talked
about in the last episode. What was the name of it.
It wasn't cyclone feeding, was it. That was when they
formed ring and they go around and round. But last
time when you talked about how there might be a
big cloud of zooplankton and they're eating them, and so
they line up in this row and they go through
and for some reason they get more food that way.
Speaker 2 (28:15):
Yeah, yeah, chain feeding. So yeah, this is reminiscent of
chain feeding.
Speaker 3 (28:18):
Except not feeding here. This is the it's the first
one is trying to mate with the female.
Speaker 2 (28:23):
Well, yes, well he's trying to to keep up with her.
And in general, she's going to try and shake loose
the less fit pursuers because now she doesn't just have
one manta. She may have up to thirty mantas behind her.
And this is crazy too. She may loop back around
and start chasing the last male in line, So now
we get another like just ring another sort of like
(28:46):
mating cyclone here, okay, or courtship cyclone, I guess, okay.
Other females may also be swept up in these processions,
which can result in one line splitting or two lines merging.
They also the authors here also mentioned that she may
end up chasing another female manta as well. So this
you start with one train of mansa's zooming through the water,
(29:09):
and it may go in different directions. It may split,
it may merge, it may loop back around on itself,
and yeah, it's quite spectacular, I'm to.
Speaker 3 (29:17):
Understand, fascinating. Courtship is complicated.
Speaker 2 (29:20):
Yeah, in the course of this, old males are going
to fall fall away, they can't keep up. New mantas
are going to join in. They're like well, I'm fresh,
I'm ready to go. I think I might be able
to catch her. But the author's stress that she's not
actually trying to lose anyone. This isn't one of those
cases where it's like she doesn't want to mate and
it's just whichever male can catch her. It's not a
(29:42):
mating pursuit like you see with other species. She's seemingly
doing all of this to merely assess her suitors and
determine which one is displaying the greatest level of fitness.
But at the same time, the end result is going
to be only one man toa ray can still keep
up with her.
Speaker 3 (29:58):
So you could look at this this is a kind
of mass organized mating dance of rich yeah, yeah.
Speaker 2 (30:05):
Yeah, And it's it's very much a situation where it's
the individual with the greatest degree of fitness is going
to be the one that she mates with, and she
absolutely has to be choosy because a lot is writing
on her selection. And this comes again back to the
gestation period for romantis, which takes a little over a year,
(30:27):
and given the ups and downs of environmental factors, mainly
food in the wild, she's generally not going to be
able to reproduce every year anyway, Carrying such large offspring
to term is costly, and even when food is abundant,
she's just not going to be able to do it
every year, So there ends up being seasonal gaps, and
this generally breaks down to a pregnancy occurring every two
to three years, but the authors of this book point
(30:50):
out that the rate can be as low as once
every seven years in particular environments. Wow. And another factor
involved here in her choosiness is that she may reproduce,
she may mate rather multiple times during the breeding season,
but she's going to store sperm from multiple partners. This
is something we see in other organisms as well, and
(31:12):
then she can use the sperm she wants whenever she
finally gets to fertilizer eggs, whenever it's not finally the
right time to fertilizerr eggs.
Speaker 5 (31:20):
Yeah.
Speaker 3 (31:21):
Yeah, sperm storage like this. I think we've talked about
this happening in some species of sharks also, Yeah, which
of course are closely related to rays.
Speaker 2 (31:28):
So yeah, eventually one male is going to be left.
There can be only one. She's going to slow down
and allow him to shadow her again. You know, it
be you know more or less a top of her,
shadowing her. But then he is going to bite down
hard on her left wing tip, hard enough that this
is going to leave scarring. You can identify, you know,
(31:50):
females that have bred before in the wild because they
will have this scarring on there on their left wingtip.
I want to say, it's like in the high ninety
percents that it's the left wing tip testing. And once
he's he's bit down hard on it, and I think
there's a fair amount of wingtip like going into his mouth.
At this point, he's going to flip so that now
he's belly to belly with her, and then he's going
(32:11):
to use one of his claspers. There are two claspers
on the mail. It's going to use that to ejaculate
sperm into her kloeca. And then he's going to beat
his pectoral fins, causing the two of them to spiral
in the water. This is all going to last about
thirty seconds and then they're going to go their separate ways.
Speaker 3 (32:27):
Wow, that's elaborate.
Speaker 4 (32:29):
Yeah.
Speaker 2 (32:30):
Yeah, there's a whole diagram in the book here was
showing how all of this, all this elaborate dance eventually
comes to a closure.
Speaker 3 (32:37):
It's funny you mentioned the biting down element because this
squares was something I think I was reading in preparation
for the first episode that we didn't end up talking about.
Speaker 4 (32:46):
But the fact that that.
Speaker 3 (32:48):
Manta rays don't have teeth that they use for feeding,
but the teeth are basically, you know, they've got these
little plates, you know, sort of mighty plates. Yeah, little
little tiny amounts of kind of nubby, little teeth that
are apparently only used in mating.
Speaker 2 (33:04):
At any rate, they definitely bite pretty hard. Again, there
are some photos and you can look up photos of
mating scars and manta rays.
Speaker 3 (33:11):
But so, okay, now the egg is fertilized and you
would have a gestation period.
Speaker 2 (33:15):
Right, that's right. Yeah, more than a year of gestation follows.
And this is another area where we have to stress
that like we don't have I believe as even to
this day, I don't think we have any wild observations
of manta ray birth. At the time of this book's
publication in twenty eighteen, there had been I think just
a single incidence of a recorded captive birth at the
(33:39):
Okinawa Aquarium as in I think two thousand and seven.
Since that point, I believe the same aquarium and in
some cases the same manta ray with the same manta ray.
We've seen subsequent berths, with the most recent I believe
being twenty twenty four. You can look up videos. When
I was looking around, there's at least one video that
was easy to find. Some I think have been taken down,
(34:01):
but you can watch as this obviously pregnant female manta ray,
and sometimes you see the female manta rays in the wild.
Some of the Snorkel guides that we had in Indonesia
also pointed out that sometimes you'll just see a male
that happens to be really bloated, but generally you can
tell a pregnant female, and yeah, you can. You can
watch the miracle of birth as this this mother pushes
(34:24):
out a you know, a rather large and ready to
run manta.
Speaker 3 (34:29):
I'm watching it right now.
Speaker 4 (34:30):
It is amazing.
Speaker 2 (34:32):
Wow.
Speaker 3 (34:32):
And then oh yeah it uh it comes out kind
of in a clump, and it's not moving for a second,
and suddenly it just kind of twitches and then starts
jetting around.
Speaker 4 (34:41):
Yeah.
Speaker 2 (34:41):
I think I've seen this described as kind of like
a burrito before their their their their fins are curled
up over their backs, and you know, there's kind of
like a you know, cloud of material that comes out
with them, and then you know, they start moving and
then they swim off and they are on their own. Again.
The there is no mother off bring relationship here. They
(35:01):
go their separate ways. But again, the newborn's actual egg
case would have hatched, if to use perhaps an incorrect
term here, sometime before, inside the female's uterus, and it
would have subsequently fed on the mother's uterine milk, which
in this case is known as histotrophe.
Speaker 3 (35:22):
Manta ray uterine milk. I don't think we ever got
into that. We did an episode or a series of
episodes a ways back about non mammalian milk.
Speaker 2 (35:30):
Yeah, I mean it's one of those things where is
it really milk? Yeah, no, no, but it kind of
serves the purpose of milk, yeah.
Speaker 3 (35:39):
Because we talked about like dinosaurs perhaps producing a milk
like substance.
Speaker 2 (35:43):
Yeah.
Speaker 4 (35:44):
Yeah.
Speaker 2 (35:44):
But again this is to go back to what we
were talking about in the first episode. This is all
exactly the reason that manta rays have such a delicate
place in their environments because again, long gestation period generally
a single berth, and it's not happening every year. It's
you know, there are these big gaps between subsequent births,
so if there's any kind of targeted fishing or any
(36:06):
kind of factor that is that is eating into their population,
it's harder for them to bounce back. Yeah, all right,
Well we're going to go and close out this episode.
We will be back with I believe one more episode
on manta rays, and it should be an equally exciting
one because we're going to talk about their brains, we
are going to talk about their parasites, and we will
(36:26):
talk about cleaning stations, which if you don't know much
about manta cleaning stations or cleaning stations in general with
other species, you might think that this sounds like the
least exciting thing we could talk about, but it's actually
really exciting.
Speaker 4 (36:39):
Yes. Yes.
Speaker 2 (36:40):
In the meantime, definitely right into us. We would love
to hear from anyone out there who has experiences encountering
manta rays or other rays in the wild. Do you
have any tales of tangled mantas. Have you also snorkeled
or scuba dived with mantas or seen them from boats?
What are your observations? Share with us your observations of
(37:03):
the Manta. Just a reminder that Stuff to Blow Your
Mind is primarily a science and culture podcast, with core
episodes on Tuesdays and Thursdays. We do a short form
episode on Wednesdays, and on Fridays we set aside most
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(37:24):
That always helps us out. You can follow us on
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Speaker 3 (37:36):
As always to our excellent audio producer JJ Posway. If
you would like to get in touch with us with
feedback on this episode or any other, to suggest a
topic for the future, or just to say hello, you
can email us at contact at stuff to Blow your
Mind dot com.
Speaker 1 (37:58):
Stuff to Blow Your Mind is production of Heart Radio.
For more podcasts from My heart Radio, visit the iHeartRadio app,
Apple Podcasts, or wherever you're listening to your favorite shows.
Welcome to Stuff to Blow Your Mind production of iHeartRadio.
Speaker 2 (00:12):
Hey you welcome to Stuff to Blow your Mind.
Speaker 3 (00:14):
My name is Robert Lamb and I am Joe McCormick,
and we're back with part two in our series on
manta rays and their close mobulate relatives. In the last
episode of this series, we kicked things off by talking
about an experience that you had rob recently where you
and your family got to see reef manta rays in
person while snorkeling in Indonesia, which sounds pretty amazing to
(00:37):
get the details on that right.
Speaker 2 (00:39):
Correct, Yes, it was. It was amazing. Words can't quite
describe it.
Speaker 3 (00:43):
Observing them, but not swimming quote with them, You weren't
You weren't riding the rays.
Speaker 2 (00:48):
Correct, they were. They were doing their own thing. We
were trying to keep our distance and observe from a distance,
which which is the correct way of going about things.
Speaker 3 (00:57):
So that was what inspired us to talk about man
in a series of episodes here on the show. In
the last episode, we talked about the historical evolution of
human attitudes toward manta rays with these old stories among
some divers and sailors that cast manta rays as diabolical
vampires of the sea. You know, there's one idea that
(01:18):
they will like fold over a diver like a blanket
of death. This, of course is not true, and since
it seems like since roughly the nineteen seventies there has
been more widespread recognition that mantas are gentle and not
threatening to humans, though of course that has not stopped
humans from threatening them, and we talked about all kinds
of ways that human activity can hurt these animals. These
(01:41):
impacts range from accidental harms, like when mantas are killed
as bycatch in commercial fishing. It's not what people are
fishing for, but they just get caught in nets and
other lines and other things, all the way to intentional targeting,
where they are killed for their gill plates, which some
people falsely allege to have medical powers. And in the
(02:02):
vein of talking about tall tales of mantas as vicious monsters,
we also discussed a couple of movies made in the
nineteen thirties that have a killer Manta Ray or devil
Ray as the monster.
Speaker 2 (02:14):
I didn't mention this in that episode, but it's worth
noting that, you, of course have one of Aquaman's arch
Enemies is Black Manta. Oh, so you know, it's the
perfect mantle for a villain that was conceived. I believe
in this era you also have Man Ray, which is
a villain based on Black Manta that pops up on
SpongeBob SquarePants, not to be confused with the artist Man Ray.
Speaker 3 (02:38):
I think Black Manta is actually in the Aquaman movie
with cal Drogo in it, isn't it.
Speaker 2 (02:45):
Oh yeah, yeah, who plays Black Manta? I don't I
haven't seen any of those films.
Speaker 3 (02:49):
I don't remember any of the cast of that movie
except in Nicole Kidman in a really funny looking costume.
So I you know, folks out there, No, I'm not
the biggest superhero movie fan. I haven't kept up with
all of the Marvel and DC superhero films, but I
think I watched Aquaman on a plane for some reason.
I remember thinking it was really funny, like highly amusing.
(03:12):
Oh no, wait, I remember another cast member had Patrick
Wilson like riding on a shark and saying, you will
call me ocean Master.
Speaker 2 (03:22):
I need to watch those on an airplane sometime.
Speaker 3 (03:24):
Yes, Jason Momoa, I'm sorry I called him Caldroco.
Speaker 4 (03:27):
That's not nice. His name is Jason Momoa.
Speaker 2 (03:30):
Suffice to say, however, the Western American European conceptions of
the manta ray and related species have evolved since basically
the nineteen seventies. The nineteen seventies onward. Everyone has come
to realize that manta rays are peaceful giants of the
ocean and they are not out to eat us.
Speaker 3 (03:52):
Right, And so we also talked about modern conservation efforts
aimed at protecting manta's You know, we got into like
the cost benefit analysis that has to be done if
you're considering building something like an ecological tourism trade around them.
You know, there are risks but also potentially rewards. And
we also talked about the basic biology of manta rays
and their near relatives, their near relatives being the devil rays.
(04:15):
Mantas and devil rays together make up the genus Mobula.
And we got into subjects including their body design, common
feeding strategies, and leaping or breaching behavior where they jump
out of the water and slap back down. We talked
about some reasons they might do that. And we're back
today to talk about more.
Speaker 2 (04:33):
Yeah, and we're gonna we're gonna pick up in an
interesting area, you're gonna you're gonna get into some some
more myths or potential myths about their behavior and what
we may or may not know about those behaviors.
Speaker 3 (04:45):
Now right, well, I think this might be slightly different
because it would be truths about their behavior with mythical interpretations,
if that makes any sense. So in the last episode,
we were talking about these incorrect folk beliefs about the
man you know that they would attack boats or attack
divers in the form of this underwater death blanket. And
(05:07):
as a source there I referenced an old article called
the Story of the Devilfish from the ear Way back
in the year nineteen ten by the American biologist Theodore
gil There was another thread in this article that I
found interesting and I wanted to come back to it today.
So if you'll recall from last time, in this article Gil,
he's very dismissive of the belief that the manta tries
(05:29):
to smother divers with its body or devour them with
its gaping mouth. He points out that the manta is
a filter feeder which eats tiny planktonic organisms. It does
not eat large prey. There's no evidence of manta's targeting
humans for violence, and they don't even have the right
biological equipment to eat us if they were going to
try to do that, which they're not going to try.
(05:51):
But there is another part of the manta's more frightening
reputation in pre modern times, which is the belief that
mantas will attack boats, not divers, but boats, particularly the
claim that a manta will drag a boat out to
sea by the anchor line. So here I'm going to
read a passage from Gill's article quote in one of
(06:14):
the earliest Notices of the Devilfish by John Lawson in
the History of Carolina seventeen fourteen. This peculiarity is described
the devilfish, he says, has been known to weigh a
ship's anchor and run with the vessel a league or
two and bring her back against tide to almost the
same place. But then the quote ends, and Gill goes
(06:36):
on to say later notices do not give the animal
credit for the same accommodating treatment, And he later alludes
to these other accounts that tell of the devilfish pulling
sailing boats around by the anchor, to the wonder and
fear of the sailors, and he also cites a more
recent source to him at the time of his writing.
(06:56):
This was a French naturalist named Leon de Guett describing
the activity of pearl fishers in the Gulf of California
in a text from eighteen ninety eight, and according to Deget,
when fishers are caught out at sea overnight in the
Gulf of California away from their usual mooring places, he says,
(07:17):
they will always drop two anchors because they fear that
if they only drop one, the anchor line will be
seized by the devilfish in the dark, and thus the
boat will be carried away into the open sea. And
to get back to this up with his own observation,
telling a story of how he was sent out to
harpoon a specimen of a devil ray for the Natural
(07:39):
History Museum of Paris, and he says, quote, after one
had been harpooned, it turned back on the boat, seized
the bow with its head fins, and held it in
its clasp till it was lanced the second time. So
that's Deget's account. But Gil says even this direct observation
(08:00):
does not really lend credence to the idea that Mantas
or devil rays deliberately attack detain or hijack boats because,
based on his own study, Gil writes that this kind
of grasping with the headfins is automatic. He says, it's
an involuntary muscular reaction when something is in front of
(08:20):
the ray's mouth, so in this case, it might happen
to be the bow of the harpooner's boat. And so
even when it's being attacked by somebody on the boat,
when it's being harpooned, Gill argues that the ray was
probably not actually trying to harm the boat, but rather
was just being pulled toward the boat by the tension
of the rope on the harpoon it had just been
(08:41):
lanced with. And even to get himself the person originally
telling the story of it seizing the bow of the boat,
he says the devilfishes are generally timid, non aggressive animals.
Though then after saying this confusingly to get does seem open,
he sort of opens up more claims of devilfish savagery
and alleges that in the Gulf of California, quote numerous
(09:04):
cases have occurred of death resulting to divers as well
as bathers from encounters with the devilfish or manta as
the men call it. On the other hand, the carcasses
of many that are killed are used for bait for
other fishes. The strange detail to include.
Speaker 2 (09:21):
Yeah, yeah, I mean all of this is a pardon
the terminology here, fishy because.
Speaker 3 (09:27):
Dobous third hand Yeah.
Speaker 2 (09:30):
Yeah, I mean, because everything we know and have been
discussing about rays, when they're threatened, they use a burst
of speed, they get away. That's their major way of
defending themselves. So it doesn't really make sense based on
what we know that they would turn around an attack
of a ship or a boat, even if they are
being acted upon with harpoons.
Speaker 3 (09:51):
Right, And as we discussed last time, of course, they
are large animals, and any large animal could potentially hurt
you just by bumping into you. Wrong, But there is
really no evidence I could find of manta's being aggressive
toward humans except for these like old third hand stories.
Speaker 4 (10:08):
Yeah.
Speaker 2 (10:08):
And I don't know if Gil gets into this or not,
but for one of the things with you get into
oral histories of things like the devilfish the manta, you
end up having to ask questions, well, is the manta
in this story, even if there's a kernel of truth
to it, Is it indeed talking about the species that
we are talking about as the manta ray, or is
(10:30):
it referring to something else real or imagined.
Speaker 3 (10:32):
Yeah, so, even back in nineteen ten, Gil to me
seems skeptical of these claims about it attacking boats. Certainly,
modern researchers are skeptical of these stories of manterray aggression
towards boats. But to the question of dragging boats specifically
by the anchor cable, is this just a tall tale
like the manta ray death blanket story or is there
(10:55):
something more to that? Is there any modern evidence of
things like this happening sort of?
Speaker 4 (11:00):
This is yes.
Speaker 3 (11:01):
For example, I found a Reuter's article from February eleventh,
nineteen ninety nine, called motor boat no match for manta
ray in tug of war.
Speaker 2 (11:10):
Well, I generally, you know, I generally trust Reuters in
their reporting. Though usual usually I'm not reading about the
marine biology. When I'm reading Reuters. Usually it's a nice
you know, doom scroll into the abyss. So I missed
this one when it came out. If I was in
fact reading Routers at the time.
Speaker 3 (11:30):
I'll read from the beginning of the article and then
summarize some other parts of it and we can make
up our minds about it. Okay, what's going on here?
So Dateline New Smurta Beach, Florida. Two Florida boaters met
a real sea monster when their craft was dragged for
hours by a powerful creature that turned out to be
a giant manta ray, the Coastguard said Wednesday. Coastguard Petty
(11:51):
Officer Scott Barnes said the agency received a radio distress
call from a sixteen foot boat that reported it was
being dragged by its anchor line by something unknown. The
Coast Guard sent a rescue boat to investigate and found
the motor boat was being dragged in circles by something
beneath the surface. The crew transferred the anchor line to
the Coastguard vessel, freeing the men in the motor boat,
(12:13):
who had tried to use their ninety horsepower engine to
go in reverse and stop themselves from being dragged out
to sea. After the Coastguard's forty one foot boat pulled
the anchor line for several minutes, a giant manta ray,
measuring an estimated eighteen feet in width, came to the surface,
and then the article goes on to describe how the
coastguard struggled to pull the rope away. Eventually, the manta
(12:36):
was able to disentangle itself from the rope and it
swam away on its own, And by the end of
the ordeal, the manta, they estimated, had pulled the boat
for almost two hours, taking it about a mile and
a half away from shore. But you could easily get
the wrong idea about this, thinking that it supports this
old notion that mantas will attack boats, that they are
(12:59):
doing this on purpose, they're trying to drag the sailors
out to sea, out to their deaths or something. From
what I've read, there is absolutely zero evidence to support
the idea that the mantas are acting aggressively when they
pull a boat by the anchor line. The zero evidence
that they're acting aggressively or even acting intentionally. Rather, this
(13:20):
is almost certainly a case of mantas getting stuck. They
are getting tangled in underwater ropes and chains by accident
and then pulling the boat because they are unable to
free themselves. And when you look at their heads, you
look up a picture of a manta ray or a
devil ray. You can see how this might easily happen.
They almost have biological mooring cleats with their cephalic fins.
Speaker 5 (13:45):
Yeah, yeah, you can imagine them catching the line.
Speaker 3 (13:58):
For one more example of a mod encounter, I found
a video on YouTube that the title begins with Giant
mantray tangled in anchorchain, forty miles off shore. This is
a video of some people out in a fishing boat
in the Gulf of Mexico and a manta does get
caught in their anchor line. Like it looks when you
can see it, it looks like the line is not just
(14:20):
caught between the cephalic fins, but kind of wrapped around them,
like the lobes on its head have the line going
across as well as between, and you can see it
struggling at a couple of points.
Speaker 4 (14:33):
In this video.
Speaker 3 (14:34):
It quite strangely, almost seems to like be coming up
to the surface and holding still while the fishermen are
trying to get it untangled. That weirdly kind of matches.
But then I don't know how to interpret what I'm
seeing there, so maybe it shouldn't be taken this way,
but it kind of reminds me of all these stories
people talk about of manter rays being very like kind
of slow moving and gentle while they come up to
(14:56):
them and almost kind of letting people, you know, interact
with them. Again, not encouraging people to do that unless
you're trying to free one from a problem you've created.
But anyway, in the end here the people in the
boat are able to succeed by they sever the line
in one place and that allows them to get it
unwrapped from around the manta, and they let the manta
(15:16):
swim away. So it seems like the manta gets away
in the end of this, which is heartwarming. In fact,
all these like bro fishermen are like high five in
each other. They're like, yeah, we did it.
Speaker 4 (15:26):
It's it's sweet.
Speaker 3 (15:27):
But once again seems like a quite clear case of
like the manta is not doing this on purpose. It's
not it's not out here today thing say, and I'd
like to drag a boat around it ended up in
this situation against its will.
Speaker 2 (15:40):
Yeah, yeah, like you said, the cephalic fins are kind
of look like natural line catchers, and then they're also
just quite i mean they're they're wing shaped, they're they're
they're quite wide. We've talked about their their wingspans, and yeah,
that's just more real estate to potentially run into a line.
Speaker 4 (15:57):
Yeah.
Speaker 3 (15:57):
And so Gil talks about this in his article and
says that these the cephalic fins or cephalic lobes, the
kind of horns of the devilfish. They they're like an
elephant's trunk. He he quotes another author saying that then
they can kind of grasp objects and pull them in.
He says they tend to rapidly kind of close in
(16:18):
around the mouth when something appears in front of the mouth,
and that the fish will have a kind of obstinacy in,
you know, refusing to release things that go in like that.
Gil says quote that these arms are muscular and powerful
has been demonstrated on many occasions. The natural movement of
(16:39):
the head fins or corropteries is inward, and when any
object strikes between them, it is instinctively held a proceeding
which explains the undoubted fact that these fishes can run
away with quite large vessels. So Gil's chalking this up
to involuntary motion of the strong cephalic fins closing over
(16:59):
things that in the front of the mouth, which occasionally
in some unlucky circumstances just happens to be an anchor line.
I think gil is absolutely correct that these boat dragging
incidents are not aggressive or intentional on the part of
the ray, but is he correct about the mechanism. I
was looking for modern sources and couldn't really find anything
(17:20):
to confirm or deny his ideas there about the specific
motion of the cephalic fins being involved. But I did
find some commentary from more recent marine biology resources, specifically
something from the organization known as the Manta Trust, which
has a page on the subject of manta mooring line entanglements,
(17:43):
and they highlight some different biological facts which make mooring
line entanglements common for manta rays. Manta rays, like their
cousins sharks, and also like tuna, are obligate ram ventilators,
meaning they do not have the biological equipment needed to
(18:04):
pump water over their gills when their bodies are at rest.
So in order to make water flow over their gills
so they can extract oxygen from the water and breathe,
they have to move their bodies. So you've probably heard
before that if a shark is forced to hold still,
it will die. It has to swim to breathe. That
is essentially true, and it's true for mantas as well.
(18:28):
Fish that don't have to keep moving to breathe have
what's known as a buckle pump system, where you use
muscles around your mouth and throat to pump fresh water
over the gills. Mantis don't have that. They've got to swim.
Speaker 2 (18:40):
Now, I do want to point out that Joe said
essentially true of sharks, so we can get into a
deeper discussion maybe in another episode where we talk about
the different behaviors of different types of sharks. You do
have some shark varieties that live in close to the
reef that are going to be that can be still
for extended periods of time.
Speaker 3 (19:00):
Yeah, they might actually have the buckle pumping equipment. But yeah,
like great white charts, for example, don't they're ram ventilators exactly.
Speaker 2 (19:08):
Yes, absolutely true of great whites.
Speaker 3 (19:11):
But anyway, certainly true of manta rays. They have to
swim in order to breathe. They are also ram ventilators.
And so this means that getting entangled in a line
can be deadly to a manta if it is stuck
and it can't swim, around, it can't really breathe, and
this might also explain why a manta would keep swimming
even when it has a boat dragging behind it. It
(19:33):
kind of has to swim. Pair this with a couple
of other biological facts. Mantas can't swim backwards. You know,
they are highly maneuverable fish in a way. They can
turn around and you see them in the water doing
these beautiful summersalts and everything, but it's always with forward motion,
which usually means that the line just gets even more
(19:55):
tangled up on them as they twist and somer salt
around and they would need to really be able to
back up to release the line, but they can't back up.
Speaker 2 (20:04):
Great point.
Speaker 3 (20:05):
The other thing is that the manta trust says is
they are often not able to see the thin line
of a rope or a chain when it's directly in
front of them. And so you put all this together
and it easily explains how mantas can get tangled in
mooring lines and can end up pulling whatever these lines
are attached to. This is usually not threatening to humans,
(20:27):
but it is very threatening to the ray. Rays often
asphyxiate and die when they get caught in moorings, and
so the Manta Trust has this document where they make
recommendations for making mooring lines safer for mantas. You can
actually look this document up on their website for the
full recommendations, but they suggest a few measures, like one
just reducing the presence of especially loose line in the water.
(20:52):
Loose or slack lines are more dangerous to raise than
tight lines. You can probably kind of imagine where they are,
like a looser line is easier to get fully just
tangled up in or as a taut line, you know,
you might more likely bump into and then something can
get Yeah. But then also they recommend this interesting system
that I don't know if I would have thought of this,
(21:13):
but this is cool. They recommend attaching cable ties that
protrude off of mooring lines at a ninety degree angle,
so you imagine, you know, something kind of like zip
ties or something like that, evenly spaced every foot or
so down a mooring line, and they recommend having them
(21:34):
go out around so there's like a little bar sticking
off of the side of the rope going in a
spiral around the rope all the way down, and the
idea here is that it will make the rope more
visible to wildlife, especially they say as you use it,
more algae will attach to the ends of these cable ties,
(21:54):
and it will make them even more visible. And of course,
if the rays can see the mooring lines, they will
avoid them. They're not going to run into them on purpose.
Speaker 2 (22:01):
Okay, So if I'm understanding the illustration you attacked here,
it's like a spiral staircase of zip ties going up
and down this particular line, and then, like you said,
you'll end up with the stuff growing on those ties
as well.
Speaker 3 (22:14):
Yeah, so it makes the rope easy to see in
the water instead of just like a thin kind of
line that is invisible.
Speaker 2 (22:20):
Sometimes that makes sense.
Speaker 3 (22:22):
However, at the very end here, I do want to
come back with some sympathy for the sailors because obviously
I think we have the correct perspective now, like we know,
rays are certainly not attacking boats. They're not trying to
kidnap sailors on purpose or drag the boats. You know,
they're not doing this on purpose. But you can very
well you can understand how it would be frightening to
(22:43):
have something under especially if you couldn't see it. I
don't know whether it be scarier actually if you could
see it or if you couldn't. If you could see
it might be like a twenty foot wide manta ray.
Speaker 2 (22:51):
Yeah, because it's a gigantic and if you don't know
all the details, like we said last time, you know,
it's reasonable for a human to be trepidacious about this
enormous creature in the world water near them or with them.
Speaker 3 (23:02):
Yeah, And if you can't see it, just there's something
invisible under the water that's now pulling your boat around. Yeah,
and you don't know where it's taken you. So I
can understand being scared.
Speaker 4 (23:10):
I mean like that.
Speaker 3 (23:11):
I've got sympathy for that. But yeah, they're not out
there trying to do this. It's just unfortunate.
Speaker 4 (23:16):
It happens sometimes, all right.
Speaker 2 (23:28):
Now, at this point in the episode, I want to
come back and talk in a little more detail about
manta ray reproduction because in the last episode we talked
about how they're particularly vulnerable to various threats, you know,
threats posed by fishing, other human harms, in large part
because of their slow reproductive cycle. So I wanted to
get a little more into this. One of my main sources.
(23:51):
Here again is Guide to the Manta and Devil Rays
of the World by Stevens Fernando Dando in Dyscaria. Very
good book, lots of illustrations. It's technically like a field guide.
I mean, it's not laminated, you can't take it into
the water with you, but it's a great field guide.
And the authors here point out that there are a
(24:13):
lot of gaps in our knowledge about manta ray and
devil rape reproduction, with most of what we know coming
from observations of reef mantas and limited scientific data in
addition to that. So bear that in mind, and I'll
tuck back in on that fact as well. But manta
rays are not like most fish that much we've already established,
(24:36):
and it applies to their reproduction as well. Like all
elasmo broncs that's sharks and other batomorphs like rays, they
practice internal fertilization rather than external fertilization, which is practiced
by most fish species. So they have come so they
have to come into direct contact with each other in
(24:56):
order to.
Speaker 3 (24:56):
Mate, right, So it's not like a releasing unfertil eggs
into the water which then encounter sperm in the water
and become fertilized externally like many fish do.
Speaker 2 (25:06):
Yeah, there's no just like swimming close to each other
or both visiting the same spot at one point or
another that they do have to engage and what is
ultimately rather complex and kind of beautiful and maybe at
times humorous mating ritual. The other amazing thing about manta
reproduction is that, as with a minority of other fish species,
they are live bearers, meaning they give live birth via
(25:30):
an egg that hatches inside the female's uterus. This is
known as a placental viviparity. Now, as many people have
observed and some of your listeners might be thinking, this
practice would seem to be yet another way that the
manta rays resemble certain whale species. Yeah, you know what,
large oceanic filter feeders that give live birth.
Speaker 3 (25:50):
Yeah, they could easily be mistaken for a mammal.
Speaker 2 (25:53):
Yeah, but this is not the same as live mammalian birth.
And while whales lie on their mothers for the first
phase of their lives, mantas are on their own from
the moment they're born. They're just small versions of their
parents that have to just hit the ground running, you know,
not much smaller of course they're still they're still quite big.
(26:14):
A newborn is typically like one point five to one
point eight meters across, or like five to six feet.
Whoa yeah, and sometimes it's twins. That's a big baby.
All right, So let's walk through the courtship. I said
that it was beautiful and weird and sometimes funny again, Stevens,
that all point out that there's much we don't know.
This is a general description. A lot of it's based
(26:35):
on reef mantas, and they're going to be species specific variations,
and I believe it's possible there may be environmental differences
as well, depending on where the mantas are. But in general,
this is how it goes down. So a male will
approach a female and he'll shadow her from above, and
then he may attempt to rub the top of her
(26:56):
head with his cephalic fence the devil horns, right, and
usually what's going to take place at this point is
she's going to shake him. She's going to like, you know,
make a quick turn and say get away from me.
She's just going to reject his advances.
Speaker 3 (27:08):
Okay, so devil horn back, rub and then bolt.
Speaker 2 (27:11):
Yeah, generally she's gonna bolt generally she's going to say
I'm not in the mood and she's going to go in.
But if she is interested, what she's going to do
instead is speed forward, and then he is going to
give chase. And as this chase continues, this is going
to draw in other males who will also give chase,
and we get another situation where we have a line
(27:33):
of manta rays. This time, you know, a train of
manta rays speeding through the water, you know, maybe around reefs,
and these can also kind of quickly get to our
eyes out at hand, like a thirty strong zooming train
of mantas that occasionally leaps out of the water as well.
Speaker 3 (27:52):
This is kind of like the feeding structure you talked
about in the last episode. What was the name of it.
It wasn't cyclone feeding, was it. That was when they
formed ring and they go around and round. But last
time when you talked about how there might be a
big cloud of zooplankton and they're eating them, and so
they line up in this row and they go through
and for some reason they get more food that way.
Speaker 2 (28:15):
Yeah, yeah, chain feeding. So yeah, this is reminiscent of
chain feeding.
Speaker 3 (28:18):
Except not feeding here. This is the it's the first
one is trying to mate with the female.
Speaker 2 (28:23):
Well, yes, well he's trying to to keep up with her.
And in general, she's going to try and shake loose
the less fit pursuers because now she doesn't just have
one manta. She may have up to thirty mantas behind her.
And this is crazy too. She may loop back around
and start chasing the last male in line, So now
we get another like just ring another sort of like
(28:46):
mating cyclone here, okay, or courtship cyclone, I guess, okay.
Other females may also be swept up in these processions,
which can result in one line splitting or two lines merging.
They also the authors here also mentioned that she may
end up chasing another female manta as well. So this
you start with one train of mansa's zooming through the water,
(29:09):
and it may go in different directions. It may split,
it may merge, it may loop back around on itself,
and yeah, it's quite spectacular, I'm to.
Speaker 3 (29:17):
Understand, fascinating. Courtship is complicated.
Speaker 2 (29:20):
Yeah, in the course of this, old males are going
to fall fall away, they can't keep up. New mantas
are going to join in. They're like well, I'm fresh,
I'm ready to go. I think I might be able
to catch her. But the author's stress that she's not
actually trying to lose anyone. This isn't one of those
cases where it's like she doesn't want to mate and
it's just whichever male can catch her. It's not a
(29:42):
mating pursuit like you see with other species. She's seemingly
doing all of this to merely assess her suitors and
determine which one is displaying the greatest level of fitness.
But at the same time, the end result is going
to be only one man toa ray can still keep
up with her.
Speaker 3 (29:58):
So you could look at this this is a kind
of mass organized mating dance of rich yeah, yeah.
Speaker 2 (30:05):
Yeah, And it's it's very much a situation where it's
the individual with the greatest degree of fitness is going
to be the one that she mates with, and she
absolutely has to be choosy because a lot is writing
on her selection. And this comes again back to the
gestation period for romantis, which takes a little over a year,
(30:27):
and given the ups and downs of environmental factors, mainly
food in the wild, she's generally not going to be
able to reproduce every year anyway, Carrying such large offspring
to term is costly, and even when food is abundant,
she's just not going to be able to do it
every year, So there ends up being seasonal gaps, and
this generally breaks down to a pregnancy occurring every two
to three years, but the authors of this book point
(30:50):
out that the rate can be as low as once
every seven years in particular environments. Wow. And another factor
involved here in her choosiness is that she may reproduce,
she may mate rather multiple times during the breeding season,
but she's going to store sperm from multiple partners. This
is something we see in other organisms as well, and
(31:12):
then she can use the sperm she wants whenever she
finally gets to fertilizer eggs, whenever it's not finally the
right time to fertilizerr eggs.
Speaker 5 (31:20):
Yeah.
Speaker 3 (31:21):
Yeah, sperm storage like this. I think we've talked about
this happening in some species of sharks also, Yeah, which
of course are closely related to rays.
Speaker 2 (31:28):
So yeah, eventually one male is going to be left.
There can be only one. She's going to slow down
and allow him to shadow her again. You know, it
be you know more or less a top of her,
shadowing her. But then he is going to bite down
hard on her left wing tip, hard enough that this
is going to leave scarring. You can identify, you know,
(31:50):
females that have bred before in the wild because they
will have this scarring on there on their left wingtip.
I want to say, it's like in the high ninety
percents that it's the left wing tip testing. And once
he's he's bit down hard on it, and I think
there's a fair amount of wingtip like going into his mouth.
At this point, he's going to flip so that now
he's belly to belly with her, and then he's going
(32:11):
to use one of his claspers. There are two claspers
on the mail. It's going to use that to ejaculate
sperm into her kloeca. And then he's going to beat
his pectoral fins, causing the two of them to spiral
in the water. This is all going to last about
thirty seconds and then they're going to go their separate ways.
Speaker 3 (32:27):
Wow, that's elaborate.
Speaker 4 (32:29):
Yeah.
Speaker 2 (32:30):
Yeah, there's a whole diagram in the book here was
showing how all of this, all this elaborate dance eventually
comes to a closure.
Speaker 3 (32:37):
It's funny you mentioned the biting down element because this
squares was something I think I was reading in preparation
for the first episode that we didn't end up talking about.
Speaker 4 (32:46):
But the fact that that.
Speaker 3 (32:48):
Manta rays don't have teeth that they use for feeding,
but the teeth are basically, you know, they've got these
little plates, you know, sort of mighty plates. Yeah, little
little tiny amounts of kind of nubby, little teeth that
are apparently only used in mating.
Speaker 2 (33:04):
At any rate, they definitely bite pretty hard. Again, there
are some photos and you can look up photos of
mating scars and manta rays.
Speaker 3 (33:11):
But so, okay, now the egg is fertilized and you
would have a gestation period.
Speaker 2 (33:15):
Right, that's right. Yeah, more than a year of gestation follows.
And this is another area where we have to stress
that like we don't have I believe as even to
this day, I don't think we have any wild observations
of manta ray birth. At the time of this book's
publication in twenty eighteen, there had been I think just
a single incidence of a recorded captive birth at the
(33:39):
Okinawa Aquarium as in I think two thousand and seven.
Since that point, I believe the same aquarium and in
some cases the same manta ray with the same manta ray.
We've seen subsequent berths, with the most recent I believe
being twenty twenty four. You can look up videos. When
I was looking around, there's at least one video that
was easy to find. Some I think have been taken down,
(34:01):
but you can watch as this obviously pregnant female manta ray,
and sometimes you see the female manta rays in the wild.
Some of the Snorkel guides that we had in Indonesia
also pointed out that sometimes you'll just see a male
that happens to be really bloated, but generally you can
tell a pregnant female, and yeah, you can. You can
watch the miracle of birth as this this mother pushes
(34:24):
out a you know, a rather large and ready to
run manta.
Speaker 3 (34:29):
I'm watching it right now.
Speaker 4 (34:30):
It is amazing.
Speaker 2 (34:32):
Wow.
Speaker 3 (34:32):
And then oh yeah it uh it comes out kind
of in a clump, and it's not moving for a second,
and suddenly it just kind of twitches and then starts
jetting around.
Speaker 4 (34:41):
Yeah.
Speaker 2 (34:41):
I think I've seen this described as kind of like
a burrito before their their their their fins are curled
up over their backs, and you know, there's kind of
like a you know, cloud of material that comes out
with them, and then you know, they start moving and
then they swim off and they are on their own. Again.
The there is no mother off bring relationship here. They
(35:01):
go their separate ways. But again, the newborn's actual egg
case would have hatched, if to use perhaps an incorrect
term here, sometime before, inside the female's uterus, and it
would have subsequently fed on the mother's uterine milk, which
in this case is known as histotrophe.
Speaker 3 (35:22):
Manta ray uterine milk. I don't think we ever got
into that. We did an episode or a series of
episodes a ways back about non mammalian milk.
Speaker 2 (35:30):
Yeah, I mean it's one of those things where is
it really milk? Yeah, no, no, but it kind of
serves the purpose of milk, yeah.
Speaker 3 (35:39):
Because we talked about like dinosaurs perhaps producing a milk
like substance.
Speaker 2 (35:43):
Yeah.
Speaker 4 (35:44):
Yeah.
Speaker 2 (35:44):
But again this is to go back to what we
were talking about in the first episode. This is all
exactly the reason that manta rays have such a delicate
place in their environments because again, long gestation period generally
a single berth, and it's not happening every year. It's
you know, there are these big gaps between subsequent births,
so if there's any kind of targeted fishing or any
(36:06):
kind of factor that is that is eating into their population,
it's harder for them to bounce back. Yeah, all right,
Well we're going to go and close out this episode.
We will be back with I believe one more episode
on manta rays, and it should be an equally exciting
one because we're going to talk about their brains, we
are going to talk about their parasites, and we will
(36:26):
talk about cleaning stations, which if you don't know much
about manta cleaning stations or cleaning stations in general with
other species, you might think that this sounds like the
least exciting thing we could talk about, but it's actually
really exciting.
Speaker 4 (36:39):
Yes. Yes.
Speaker 2 (36:40):
In the meantime, definitely right into us. We would love
to hear from anyone out there who has experiences encountering
manta rays or other rays in the wild. Do you
have any tales of tangled mantas. Have you also snorkeled
or scuba dived with mantas or seen them from boats?
What are your observations? Share with us your observations of
(37:03):
the Manta. Just a reminder that Stuff to Blow Your
Mind is primarily a science and culture podcast, with core
episodes on Tuesdays and Thursdays. We do a short form
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(37:24):
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Speaker 3 (37:36):
As always to our excellent audio producer JJ Posway. If
you would like to get in touch with us with
feedback on this episode or any other, to suggest a
topic for the future, or just to say hello, you
can email us at contact at stuff to Blow your
Mind dot com.
Speaker 1 (37:58):
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