0:03

Okay, I'm sure you've heard this

0:05

story that Sharks the great hunters

0:07

of the deep, can smell the

0:09

blood of humans from a mile

0:11

away. Sharks. Actually have the

0:13

same smelling ability as any

0:15

other fish. It's Wednesday, February

0:17

twenty eighth and most years this would be

0:20

the last day of the month. It's also

0:22

signs ride a. I'm

0:27

John de Gar Ski so I think

0:29

we all know there are a lot

0:31

of myths surrounding sharks and they're amazing

0:34

sense of smell. Guest host Kathleen Davis

0:36

went looking for some answers to the

0:38

question what are shark noses actually capable

0:40

of Here she is. Joining

0:43

me now to talk all things

0:45

Sharks Now is my guest doctor

0:47

Laura and I'm in Eight Us

0:49

National Science Foundation Postdoctoral Fellow in

0:51

Biology at the University of Washington

0:54

and Florida Atlantic University based in

0:56

Boca Raton, Florida. Her research is

0:58

featured in a recent episode of

1:00

the Pbs digital series Sharks Unknown.

1:02

Dr. Simon Eight Us Welcome to

1:04

Science Friday. Think. You guys so much

1:06

for having me! I'm so excited to talk about

1:09

checks new set you guys today. So.

1:11

Am I? So let's start with

1:13

some basics. Hear how good is

1:16

the sense of smell of a

1:18

shark compared to other fish? So

1:20

sharks and all fish smell really,

1:22

really well. So they can smell

1:25

ten to the negative nine miles

1:27

per liter. So basically what that

1:29

means is for one molecule of

1:32

a cent. In. A

1:34

billion molecules of water. That is

1:36

how low of a concentration I

1:39

can smell. but this kind of

1:41

bursts a lot of people's bubbles.

1:43

But sharks actually have the same

1:46

smelling ability as any other fish.

1:48

Cause sharks. Or fish. And they

1:50

smell just like a fish. Wow.

1:53

Okay, so does like the size of the fish

1:55

matter here Are it? Were just talking about any

1:57

fish. any fish So

2:00

all of our recorded sensitivities, so

2:02

we can do these really awesome

2:04

physiological tests where we put electrodes

2:06

into a nose of a fish,

2:08

we put different chemicals on their

2:10

nose and we see how low

2:12

of a concentration we still get

2:14

that brain activity that says, hey,

2:16

I'm smelling something. And

2:18

no matter what fish we test on,

2:21

whether it's a tiny little freshwater fish

2:23

or a saltwater fish or a giant

2:25

shark, we have the same olfactory sensitivity.

2:28

Wow. This is suddenly making me feel really bad

2:30

for all the beta fish I've had who have

2:33

been subject to some cooking experiments. So

2:38

I want to bust a big shark myth

2:40

right here, right now. Can sharks

2:42

actually smell human blood from a mile away?

2:46

So that is a very complicated

2:48

question because when we think about

2:50

smells in the water, the smell

2:53

has to travel to the nose. So

2:56

that depends on so many things in the

2:58

water. It depends on currents. It

3:00

depends on how turbid the water is,

3:02

so how much movement is there and

3:05

where the shark is facing. So is

3:07

it facing into the stream of the

3:09

smell or the blood, which we call

3:11

an odor plume? There's a lot

3:13

of factors that go into this. The

3:16

other important thing to think about

3:18

when we think about how sharks are

3:20

smelling human blood is that our

3:22

blood is really different in

3:24

our chemical composition than that of a

3:26

fish blood or squid blood or something

3:29

like that, which sharks are actually keyed

3:31

in on. So even though they may

3:33

be smelling our blood, they're not necessarily

3:35

attracted to it the same way they

3:38

would be to the chemicals in fish

3:40

blood. So how exactly do

3:42

sharks smell things? What do their

3:44

noses or their snoots, as you

3:46

said, look like? Yeah,

3:49

so one important thing is

3:51

that sharks are passive smellers.

3:54

And what I mean by that is they

3:56

can't sniff. They don't have musculature to sniff

3:59

in like. we do. Instead, they

4:01

swim through the water and

4:03

water passively moves into their

4:06

nose. Their nose is also

4:08

not connected to their respiratory system, so the

4:10

way that they breathe, like we have ours

4:12

super well connected. We don't see that until

4:15

a lot later in evolutionary history. So

4:18

as sharks are swimming through the water,

4:20

water passively moves into one

4:23

of their nostrils. And the reason

4:25

I say that is because on either side of the

4:27

shark head, they have two nostrils. One

4:30

that allows water in, we call that

4:32

the incurrent nostril, and then

4:34

one that allows water out, and that

4:36

is the excurrent nostril. So it's kind

4:38

of like this tunnel where water goes

4:41

in one side, goes into their nose,

4:43

their olfactory organs, and comes

4:45

back out the other side. Okay, so very

4:47

different from our noses and the way that we

4:49

smell. Yes. Okay.

4:52

So shark noses all look pretty

4:54

different from the outside, like the

4:56

hammerhead, spider face looks

4:58

different than the face of a great

5:00

white shark. Is the nose anatomy similar?

5:04

So there is kind of

5:06

a generalized nose plan, and

5:09

how that works is we have two

5:11

paired structures. They're called lamella,

5:14

and these lamella, they are sitting on either

5:16

side and they're connected by this center tube.

5:18

So there's a bunch of them stacked along

5:20

this tube. You can kind of think of

5:23

it as like dishes stacked in dishwasher. So

5:25

there are all these plates back to back

5:27

to back. And as water

5:29

flows through these tubes and

5:32

between these lamella, these dishes in

5:34

the dishwasher, there are olfactory receptor

5:36

neurons that sit there. And

5:38

when a chemical in the water binds to these

5:40

neurons, the neuron sends a chemical signal

5:42

to the brain that says, hey, I'm selling

5:45

something. I have this chemical

5:47

in my little neuron grasp. So here

5:49

is an electrical signal that tells you

5:51

that I'm selling this. So that general

5:54

plan is pretty conserved throughout

5:56

all shark species. However, how that

5:58

looks is different. So hammerheads,

6:01

like you mentioned, are really long

6:03

elongated tubes that have this

6:05

really nice corridor to allow for water

6:07

to pass by pretty easily. But then

6:09

if we think of more of their

6:11

pointy headed cousins, they have more of

6:13

a spherical shape, so less of a

6:15

tube, more of a ball. So

6:18

does that difference affect anything about if

6:20

one shark can smell better than another?

6:23

So as far as we know, they're equals.

6:25

All of our physiological testing has told

6:28

us that sharks, regardless of what their

6:30

nose looks like, they all have the

6:32

same smelling ability. And this

6:34

is something that has really plagued sensory

6:36

biologists or people that study the shark

6:38

sensory systems for years. Why do they

6:41

have such different noses if

6:43

it doesn't mean that they smell better or

6:45

worse? Like it would make sense that a

6:47

bigger nose has more area for smelling, so they

6:49

should be better smellers. But that's not

6:51

the case. So what we think it

6:53

might be is having to do with water

6:56

flow. So sharks swim at really different speeds.

6:58

They live in really different areas. So if

7:00

you think about an open ocean shark that

7:02

is kind of swimming really passively in this

7:05

big open ocean environment versus a shark that's

7:07

swimming in a coral reef that has all

7:09

of these different water flows, they're living in

7:11

different flow regimes, which means that the water

7:14

is flowing differently around them in their normal

7:16

life. So we think that the

7:18

way that their nostrils are shaped, the way that

7:20

their internal rosettes these

7:22

beautiful rose-like structures of all these

7:25

lamella attached to this tube, that

7:27

has to do more with what

7:29

water flow is doing rather than

7:31

sensitivity. So presumably

7:33

a shark can't tell you what they're

7:35

smelling, but as somebody

7:37

who researches this, how do you actually

7:40

test the sense of smell of sharks? So

7:43

we use those physiological tests that I

7:45

told you before, but really what that

7:47

does is tell us if a shark

7:49

can or can't smell something. So we

7:51

just get a yes or no answer.

7:54

We don't get an idea of how

7:56

they feel about that smell. What

7:58

we do is we tie physiological tests. So

8:00

how that shark is smelling with behavior,

8:03

how they're reacting to these smells. So

8:06

I have this experimental tank where I have

8:08

these sharks swimming freely, and

8:10

then I have these randomized points

8:13

where I introduce a smell into the

8:15

water. And I videotape

8:17

them with this camera that sits overhead, and

8:20

I use something called kinematics,

8:22

which is basically how we

8:24

understand how an animal moves through space.

8:28

So if you've ever seen a behind

8:31

the scenes of CGI, your video games

8:33

being filmed, where people wear those little

8:35

ping pong ball suits. So

8:37

I give my sharks ping pong ball suits.

8:40

I paint them with little white dots. And

8:43

I can digitize these dots in my software.

8:46

And I get a little stick figure shark

8:48

that swims around my tank. And I can

8:50

use that stick figure to tell me how

8:52

fast the shark is going. Is it turning

8:54

towards or away from the smell? How quickly

8:56

does it turn towards or away from the

8:58

smell? And these kind of

9:00

metrics tell me how strong

9:02

is this behavior? Is it an attractant?

9:04

Is it a deterrent? Do they not

9:07

care at all? And how strong is

9:09

that reaction? What smells

9:11

have you found sharks are like especially

9:13

interested in? So

9:16

sharks are especially interested

9:18

in fish blood, squid

9:21

blood, shrimp blood. On

9:23

that note, I will say that sharks are

9:25

smart. They are like us,

9:27

they can modulate their behavior. So just

9:29

like us, if we are walking by

9:31

a restaurant, and it smells really good,

9:34

we may be inclined to go in if we're

9:36

hungry. But if we just ate a

9:38

giant meal, we're not going to go after that. So

9:41

there has been plenty of times where

9:43

I'm literally dumping fish blood into the

9:45

water. And my sharks are not

9:47

interested at all because they just ate. They're

9:49

like maybe give us a couple of hours and we'll

9:52

be a little better. Exactly. They

9:54

get hungry pretty fast. So I get them

9:56

interested eventually. So why is

9:59

it so important to better... better understand shark

10:01

smell and the mechanics around it. Yeah,

10:04

so sharks smelling is really

10:06

important because olfaction, or

10:09

the sense of smell in the underwater

10:11

environment, is one of

10:13

the most important senses that underwater

10:15

creatures have. It travels really

10:17

far underwater, so it's able to be carried

10:19

on these ocean currents. It

10:21

can diffuse at different rates, so the

10:23

intensity of the smell changes how far

10:25

it is. And especially when

10:28

you're thinking about the other senses, like light

10:30

or sense of feeling

10:32

or sense of taste or hearing,

10:34

those are all really limited in

10:36

the water. So olfaction is really,

10:39

really important. It is a chemical

10:41

sense which relies on the chemical

10:43

makeup of the water. So

10:45

when we think about things like

10:47

ocean acidification or pollution, things that

10:49

are changing the water chemistry, that

10:52

is going to impact how animals, like

10:54

sharks, are able to

10:56

respond to chemicals in the water.

10:58

So despite sharks being not necessarily

11:01

super interested in human blood, you

11:04

are working on developing a shark

11:06

repellent. Tell me a little bit

11:08

about this. Why do we need shark repellent? Yeah,

11:11

so while sharks may not be

11:13

seeking out human blood, they

11:16

can be interested in it. And not

11:18

only are they interested in human blood,

11:20

but they're interested in fish blood. And

11:22

if we are fishing, so we're creating

11:24

fish blood in the water, or

11:26

we're swimming near a hurt

11:28

fish or something, sharks may come in

11:31

and investigate. Unfortunately, sharks don't

11:33

have hands, so they can't pick something up

11:36

and feel it and look at it. They

11:38

investigate with their mouths. That's where their electro

11:40

senses are. That's where their taste is. Their

11:43

nose is up there. They're really head-focused

11:45

animals. So they're

11:48

taking these exploratory bites. And

11:51

you can see that a lot of times humans

11:53

will be bit by sharks, but the sharks will

11:55

not stay and chomp and eat them. They'll just

11:57

kind of take a bite and leave.

12:00

Unfortunately, that bite doesn't feel great for

12:02

us. So making sure

12:04

that these shark-human interactions are done in

12:06

a safe way, where sharks can be

12:09

in our area but not necessarily come

12:11

and investigate us, that's why it's important

12:13

to look into these preventative measures, to

12:16

keep sharks away from us, to

12:18

keep sharks away from fishing lines and

12:20

bait that can either hurt them or

12:23

get fishers angry because sharks are now

12:25

eating their fish catch. So there's

12:27

a lot of reasons to make sure

12:29

shark-human interactions are done in a safe

12:32

way. So how did you originally get

12:34

interested in studying shark smell? This seems

12:36

like a very specific area

12:39

of research. It

12:41

is a very specific area of

12:43

research and it's a very small

12:45

world, which I'm super happy to

12:47

be in, but I actually was

12:49

not super interested in sharks. I

12:51

was a sea slug aficionado.

12:53

I'm like much more of a sea slug

12:56

girly than anything. And sea

12:58

slugs have really cool chemical defenses.

13:00

So they have these chemicals that

13:03

they can use to defend their

13:05

soft little sedentary squishy bodies from

13:07

predators. One species

13:09

of sea slugs, they're called the

13:12

aplegia species, they release ink, just

13:14

like we see in squids and

13:16

cuttlefish octopuses and even

13:18

whales. There are inking whales. So

13:21

there's all of these different animals that produce

13:23

ink. And ink is

13:25

not only very visually distracting, but

13:28

it smells bad. So I

13:31

was really interested in studying why

13:33

are all these animals evolving the

13:35

ability to ink? So why

13:38

are we picking this really dramatic,

13:40

really costly defense? And

13:42

it's used between slugs, between

13:45

cephalopods, and even whales. And

13:47

I was really just using sharks kind of

13:50

as this common predator, this little thermometer, to

13:52

test how effective these different inks are.

13:55

That's what I did for my PhD. The

13:57

sea slug to shark pipeline seems...

14:00

like you may be the only one, but

14:02

I'm glad that that happened for you. There's

14:04

still a lot that we don't know about shark smell,

14:06

right? I mean, what's the biggest

14:09

question that remains for you? One of

14:11

the biggest questions for me is still

14:13

understanding that water flow part. So like

14:16

I mentioned, we think that a lot

14:18

of the way that a shark's nose

14:20

is shaped has to do on how

14:22

water is flowing into that system. And

14:26

we really only have

14:28

one really intense study on

14:30

how water moves through a

14:32

shark's nose. And it was done on a

14:34

hammerhead, so a very

14:36

weird nose. So I'm

14:38

really interested in looking at all

14:41

of these different shark noses of

14:43

so many different sizes, shapes, arrangements.

14:45

How does that influence how water is flowing

14:47

through that nose? And how does

14:50

water flow impact their ability

14:52

to smell? Do you have a favorite

14:54

shark fact? So it's not a nose-related

14:56

fact, but whale sharks,

14:58

their eyes are covered by dermal

15:00

denticles, which are the teeth-like scales

15:03

that cover shark bodies. Whoa. It

15:05

doesn't really make a lot of

15:07

sense to have teeth on your

15:09

eyes, but they have them. And it's

15:11

super weird. Yeah, we didn't know that until a couple of

15:13

years ago. That is fascinating. That would be

15:16

my favorite shark fact too, I think. I wanna

15:18

ask really quick before we're done, you're a

15:20

member of a group called Minorities in Shark

15:22

Science. Tell me a little

15:24

bit about this group and how you got

15:26

involved. Yeah, so Minorities in Shark Sciences was

15:28

formed in June of 2020 by

15:31

our four amazing co-founders who are all

15:33

black women who essentially took to Twitter

15:35

and were like, does anybody else who

15:38

is a black woman study shark science

15:40

help? We are alone. And they found

15:42

each other and they realized that there

15:45

is a really big need for those

15:47

of us who are not what

15:49

you normally see on shark media programming,

15:52

which is a cis straight

15:54

white male, to have representation and

15:56

to have community in shark science.

15:59

I will say that. Personally, I.

16:01

First. Entered the shark science

16:03

world as a baby. Graduate

16:06

students and eight was. A

16:08

Super. Other ring and negative

16:10

and toxic space and a lot

16:12

of that was rooted in Massage

16:14

Any and Racism and I immediately

16:17

said I'm not a shark scientist,

16:19

I am a thought scientists. I'm

16:21

a convergent evolution biologists. But I

16:23

do not that he served as

16:25

I didn't want to be lumped

16:27

in with this. Negative.

16:29

Community that I had experience. And.

16:32

It wasn't until the final year

16:34

of my Ph the when myth,

16:36

Minorities and Shark Sciences was founded

16:38

that I felt comfortable calling myself

16:40

a Shark Science as The Guy

16:42

because I found people who were

16:44

like me and our allies to

16:46

support our presence and are inclusion

16:49

in the field. While

16:51

I'm glad that you found your nice

16:53

in the search science community because the

16:55

says a lovely conversation and such a

16:58

pleasure to talk to you Thank you

17:00

so much for joining me! Thank you

17:02

so much for having me. I will

17:05

happily talk about sex nice anytime. Her

17:07

Doctor Lawrence Lemonade Us National Science Foundation

17:09

Postdoctoral Fellow in Biology at the University

17:12

of Washington and Florida Atlantic University base

17:14

in Boca Raton, Florida and if you

17:16

wanna see pictures of doctors I'm in

17:19

a this is Cirque research and. Watch

17:21

her episode of Pbs

17:24

is serves unknown Gotta

17:26

science friday.com/cirque smell. That's

17:29

it for today. Join us for our

17:31

next episode, where will get a primer

17:33

on the burgeoning field of Space law.

17:36

I'm Job and Cosby Thanks so much

17:38

for wasn't.