Can sharks really smell blood from a mile away?

Is it safe to get in the water when you have a scrape?

I'm meeting with shark sensory expert Dr. Lauren Simonitis here in the Florida Keys to learn about how she studies sharks’ sense of smell and the science that goes into creating the ultimate shark repellent.

Welcome to KML, to Keys Marine Lab.

This is where I do a lot of my field research, and it's really a perfect place for it because we have the ocean right here.

Do you want to go see my sharks in a tank?

Absolutely.

And I'm sure as a fellow bonnethead aficionado, you'll enjoy these guys.

Aw, look at them.

They're so cute.

Yeah they’re pretty tiny.

They're cute little guys.

So these are for your nose shark experiments?

Yeah, exactly.

So we like to really focus on both the form and the function in these guys.

So form is, I study in the lab, I look at what their noses look like.

But here in the field, I can test how well their noses work and what they do.

Bonnethead sharks are a smaller species of the hammerhead.

And they're called bonnetheads because you can also look like they're wearing a little bonnet.

And these guys are really great for me, because in that cephalofoil or the hammerhead part, they have really, really giant olfactory organs or the parts of their noses that process smells.

So it's really nice for me to be able to see those organs and to look at them because they're nice and big.

But it's also really nice because we can keep them in this tank and really test their noses and how they work and how they respond to different chemicals in the water.

So can I see your experiment?

Yeah.

Let's test some shark noses.

We’re gunna have a couple of things we can put in the water to see how they’re going to react.

We have an attractant which is this fish smoothie of blood and guts and yumminess for sharks.

And the way we test this is we use this acrylic plate.

It has a little target on it.

And the odor is going to come out of this center part and we'll use this plunger here to send us now out of that tube.

I would love to plunge some fish guts.

All right.

Smells nice and fishy.

All right.

And plunge away.

Oh I see the bubbles.

Okay, we have one coming in here.

Okay.

I'm going to plunge.

I see the red coming out.

There it goes, there's a red here.

Here he comes.

He looks like he’s targeting in.

They're both coming.

Coming to take a little smell test.

Come on.

Oh yeah.

Oh yeah.

Yeah.

That was - That was a little drive by sniff.

They're definitely interested.

I love Plunge and fish guts.

Who doesn't?

So I know as someone who studies shark noses, you probably get this question all the time.

This myth that everyone keeps perpetuating, which is that sharks can smell a drop of blood from a mile away.

Yes.

So that has been debunked a long time ago.

But we’re still talking about it.

So there are a lot of things that go into how a shark smells.

So a lot of times sharks are not in stagnant water and sharks use currents to navigate through odor plumes.

So that's like odor being carried in the water.

They're not super into human blood.

Our blood smells pretty differently.

But even when we think about the blood of the animals that they do eat, they're not mindless creatures.

So it's not like they smell a little drop of blood and they go into this feeding frenzy.

These guys can make decisions based on what their body feels like, what they're thinking.

They're pretty smart animals.

So the answer to the question, can sharks smell a drop of blood from a mile away is?

No.

If sharks were to smell human blood, would they be attracted to it?

No.

Should you be worried about getting attacked by a shark while going to the beach?

Now No.

You heard it here folks, it's safe to go into the water.

There's no need to fear the sharks.

They are unconcerned about you and they do not smell you from a mile away.

But beyond that, we are trying to figure out what the perfect shark deterrent is to keep humans happy and shark safe.

So now we're going to put the opposite, something they absolutely don't want.

Do not like.

To see how they react to it.

Yes.

So here we have cuttlefish ink.

So it's this really dark black, nasty stuff.

So cuttlefish, little small, cephalopods related to squids who are famous for inking, also ink.

Yes.

Cuttlefish are cool because not only do they ink, right, this is like a last resort because they also have this amazing ability to camouflage themselves.

Right.

So they actually will employ that color changing with the inking behavior.

So a lot of times they will change to this dark black color ink and then either hide in the ink or jet away.

And then from the predator's perspective, it's going to get a mouthful of ink and no cuttlefish.

Oh look at that.

It's like a mixture of tar and molasses.

Ew.

I did not like how it plopped.

Oh wow.

Oh yeah.

That really disperses.

And you can see how dense it is.

Yeah, it's it's very thick.

Very effective at that visual smokescreen.

So let's see how the bonnetheads react.

Yeah.

Let's do it.

All right, we got one coming.

Oh both of them are coming, actually.

Oh man.

They did not like it.

Both of them were like, Nah, I'm out of here.

Yeah, it's really, really effective.

What we wanted to do is we wanted to look at ink from cuttlefish and try to create this perfect shark deterrent in order to keep those human and shark interactions as safe as possible.

That was cool.

And they did it in sync., too.

They were both like, whoop.

Right.

Because it has that visual and that chemical, they can kind of use both of those senses together to be like, no this is not a thing.

When we do these experiments too, we do use just a food coloring that is a similar color to this.

And what we found is the food coloring alone does not cause that kind of reaction.

They are pretty much unbothered by it.

Yeah.

I would not want this in my nose.

No.

I don't want it on my fingers if I’m being honest.

We can take a look at the internal structures and we head back to the lab.

Come in.

Thanks.

Wow.

This is such a nice lab.

Right?

You saw my outdoor lab, and I get to see my indoor lab.

So if you go this way, I'll show you some shark heads.

Okay, let's see it.

So to make a shark repellent, first, we got to look at what a nose looks like.

And I do this by collecting a bunch of different shark heads in jars.

Hey, I think I collected some of these for you.

Yes.

So lots of really great noses here.

So, obviously, sharks don't like sniffs like we do.

So how does shark smell work, actually?

Yeah.

So it's actually a totally passive function.

Basically, their noses and their mouths are not connected at all.

So when they breathe, they're not bringing any water into their noses.

So they have these two paired nostrils on either side of their head.

And water flows passively inside of the olfactory organ.

You can see that there is an in-current, which means the water goes in and then back out an ex-current.

So these little folds are called?

These individual folds are lamellae.

So each of these individual LA melee sets in this nice structure here that's called a rosette.

It's called a rosette because some people think it looks like a pretty flower and they're stacked like dishes in a dishwasher.

I'd love to see your process of how you do the CT scans.

Can we actually scan these right here?

Yeah.

So we will go ahead and pack these up.

We make them into little fish burritos and get them in the CT scanner if you want to pack with me.

Wow!

And you can see these big nasal capsules out here, too, which is where that olfactory rosette that we were holding essentially fits right into this.

Oh yeah, I see where it fits in.

Yeah, right.

It's like a perfect little fit.

And then these individual lamellae that make up this rosette sit in here.

So water is flowing between this structure and then in between all of these little dishes and the dishwasher, and that's how they're smelling.

So in this individual lamellae, there are olfactory receptor neurons, or ORN’s, and these are little guys that are just sitting there waiting with their little arms open for a chemical to combine and bind to that olfactory receptor neuron.

And then it sends a signal that goes through the lamellae to the olfactory bulb, which sits right here.

And the olfactory bulb is where all of that initial information runs to.

And then it goes along a little path called the olfactory track and then into the brain that says, “hey, smelling something, what you want to do about it?” You said that despite the shape, there's not a big difference in smell.

Right.

So for a really long time, scientists have tried to figure out why these noses look so different.

And the first thought was maybe sharks with bigger noses like hammerheads are better at smelling because they have these big noses.

They must be really good at sampling water.

And what they did was when they tested the sensitivity, regardless of what the nose looks like, they all have the same smelling capabilities.

What we find is it's really related to their environment.

So deep sea sharks that really have limited vision and have limited other sensory cues really rely on their noses.

So they have really big noses.

But coastal sharks that are getting a lot of cues, you know, they're living in a brightly lit coral reef, so they get all of these sensory cues together, their noses and the olfactory bulb and all those kind of associated structures are smaller.

So we have the bonnethead here, and when we were outside doing the experiments with the ink, how exactly was the ink making it in and how were the sharks reacting to that?

Yeah, So the ink was basically flowing into this chamber here and then going back around and out through the excreting chamber here.

And then all of these individual lamellae have those olfactory receptor neurons.

And so chemicals in the ink bind to the olfactory receptor neurons.

The olfactory receptor neurons send a signal that's like, I smell something and I do not like how it smells.

And they send that signal to the olfactory bulb, which then translates it up to the olfactory tract and then into the brain.

But it seemed to happen pretty fast when we were out there.

They would swim into the plume and then they would instantly turn.

Yeah, it's a super quick process.

It's very similar to us.

So one of the coolest things about noses is that it is the only sensory system that the receptors touch the external environment just like us.

So if you think about like your touch receptors, those are under your skin.

Everything that sees in your eyes is inside of your eye.

Your nose is in direct contact with whatever you're smelling.

And it's the same way for them.

Their nose comes into direct contact with the water.

So Lauren, I feel like I've seen this before.

Don't you have a tattoo of this exact thing?

I do.

So, yeah, you can see the rosette, the olfactory bulb, the olfactory peduncle, and then the brain right there.

So Bonnetheads - got to have bonnetheads on me.

But I'm getting a little hungry.

Do you want to grab a snack?

Yeah.

Let's grab a snack.

So I brought this pastelito de guayaba to share.

And this is, like, my favorite pastry.

Have you ever had one?

No.

So it is delicious.

Inside is guava paste, and then there's like, this really nice flaky, soft, delicious crust on the outside.

This kind of reminds me of the cuttlefish ink.

Right?

Yeah.

It's sticky, but instead of smelling bad, I think it smells kinda of good.

It tastes good too.

Smells delicious.

Yeah.

So is this like a Cuban pastry?

Yeah.

So I'm from Miami.

Born and raised.

My mom was born in Cuba and came over here when she was young.

So I grew up constantly coming down here to the Keys.

Can go snorkeling and then I got certified.

So we started diving together and I just loved going into the ocean.

And then you fell in love with sharks.

I did.

And you know, like a lot of people, I just assume that we know so much about sharks.

We know so much about their noses.

Like you just hear so much about how sharks are run by their noses and they're so famous for it.

But then when I started looking into the literature for my Ph.D., I realized sharks, they're cued into fish blood.

They're cued into cephalopod or invertebrate blood.

They're really not attracted to human blood.

Sometimes I will drop some fish blood into the water and they're just not interested because it's just like us, so we can smell something that smells really good.

But if we've recently eaten and we're super full, we're not always going to go back and take another bite.

These guys are able to use all of their senses together.

They're able to make decisions.

So why is it important to understand how a shark nose works?

The first is that their noses are how they process chemical communication, so how they test and smell chemicals in their environment.

And when we think about things like ocean acidification or pollution, that changes what the chemical makeup of the ocean is like.

So it's really important for us to understand how these systems work at baseline before we can study how they work in future ocean conditions or under human caused stressors.

So us changing the chemistry of the ocean could actually make shark's ability to smell less effective.

Yeah, it is definitely a possibility.

We really don't know.

It's a huge area of research that is lacking because we don't have this basic understanding of how their noses work.

Another really important thing when we think about studying shark deterrence is we want to make sure that human and shark interactions are safe so we can use them to keep humans and sharks separate at beaches or swimming areas where sharks and humans might have some unfortunate interactions.

But also we can put it on fishing lines or onto fishing techniques so that we can keep sharks away from bait because we know that that's a huge cause of shark mortality.

So that's why it's really important to study and try to figure out what these shark deterrents are, in order to keep those human and shark interactions as safe as possible.

Keep sharks alive, keep humans happy.

Who knew that the nose could be the key to saving sharks.

Right?

Yeah, the nose.

The nose knows.

The nose knows.

Do you want to print your own shark rosette?

Answer yes.

Yes, you do.

Go down to the description, download it, take it to your nearest library or school.