I'm Marine biologist Amani Webber-Schultz. I study sharks.

Today, I'll be answering your questions from Twitter.

This is Shark Support.

[upbeat drum music]

@StopFinningDE asks,

What causes sharks to attack humans?

This is a really complicated question.

One of the biggest reasons is we are putting ourself

into their environment.

Now, when it comes to people,

we can put our hands all over the place

to observe our environment.

Sharks don't have that.

And a lot of times what ends up happening

is they might hit their nose on something

to try and figure out what it is.

They also take what we call exploratory bites.

What it appears is that they're actually just trying

to figure out what we are.

@CantoAzul_mc asks, What are shark bones made of?

Sharks don't actually have any bones.

They are made entirely of cartilage.

@Solarglide asks, How many species of sharks are there?

This is a really fun question

because we actually just recently passed

the 500 species mark, which is insane.

So there's many ways to separate a shark

from your standard bony fish.

One of them is their gill slits.

Most sharks have five gill slits,

but they can actually have up to seven gill slits.

Your standard fish usually only has one.

Another thing that separates them

is they have a very fatty liver,

which would be this orange bit here

in this anatomical model,

and the liver is huge.

And the reason for that is sharks lack a swim bladder.

So a bony fish has a swim bladder,

and that's what helps them maintain their buoyancy.

Sharks don't have this.

They have a liver, and it's super oily.

And that's what allows them to maintain their buoyancy

in the water.

@great_thunberg asks,

Is climate change to blame

for a string of shark attacks across America?

When you think about climate change,

one of the things that we really think about

is warming oceans.

One of the things that we're finding

is sharks and fish, in general,

are actually moving northward,

where the water stays cooler for longer months.

But it's not so great for all the people who are going

in the water in New Jersey, in New York, in the beaches.

You're getting into their natural habitat.

And there's a couple of different interactions

that are going on.

Their prey items seem to be moving more in shore

or into shallower waters.

We're also in the shallower waters.

Then there might be an increased chance

of experiencing a shark bite.

But in reality, your chances being bitten

by a shark is about one in 3.7 million.

You are more likely to die

from a vending machine falling on you,

from a coconut falling on your head,

or even just a dog in the street.

@WincentWYedlin asks.

Hammerhead sharks have always fascinated me.

Why do they look like this?

What is the purpose of having a shovel head

and eye position like that?

And do they function better than a normal shark?

Hammerheads are very fascinating.

We all know that they look completely different.

And one of the distinctive features of them

is this hammer part, which is actually called a cephalofoil.

Hammerhead sharks are the most recently diverged species

of shark, meaning that they're the most recently evolved.

And we actually don't really know why

they evolved this hammer,

but we can kind of pick apart maybe some reasons why.

On the bottom, by their mouth,

this whole thing is lined with ampullae of Lorenzini,

which allows them to detect electrical currents.

So as they're swimming along and they eat rays,

and these rays have a tendency

to be kind of buried into the dirt,

this is constantly feeling for electrical pulses.

So any sort of muscle movement, for example.

And they can really pinpoint where that ray might be

without actually having to see them

because of this ability to see through this electricity.

And their eyes are all the way on the outside.

Some of our guesses

is hammerheads have a much wider range of vision.

They can see almost 360 degrees around their body,

which really separates them from other species of shark.

@iamJanKruse asks,

What's the most dangerous type of shark?

There are three that we consider

to be dangerous or more aggressive.

And those are the great white shark,

the tiger shark, and the bull shark.

Now, the bull shark is very famous

because it can actually travel up rivers

into fresher water and is the only species

of shark can go in between seawater and saltwater.

So if we're hanging out

in a river and there's that shark,

one, it's murky, they can't really see anything.

So they have a tendency to be a lot more curious,

and therefore, that appears to be a lot more aggressive.

@Bylan_Durton asks, How do sharks of so many teeth?

They don't even drink milk. WTF.

So if you think of people,

we only have two sets of teeth that come in.

We have our baby teeth, we lose them,

and then we have our adult teeth.

If you look at the inside of a shark jaw,

they actually have teeth that line the upper and lower jaw.

As these teeth fall out, new teeth will replace

and become active teeth and form to help them eat.

And while that's happening, when space is created,

a new tooth will start being formed.

So they essentially end up with these layers

and layers of layers or conveyor belt, as many people say,

of teeth that are perfectly formed and ready to move in.

@ingnog1115 asks, #sharkafterdark.

What's the most unique thing about tiger sharks?

What separates them from other sharks,

aside from their markings?

Tiger sharks also are known to eat almost anything.

People have found license plates, tires,

and even lawn chairs in their stomach.

And one of the things that is super odd about them

is that they consistently throw their stomach up.

Their stomach fully comes out of their mouth

to just eject whatever is in their stomach

that they can't eat.

And this stems from the fact

that their normal prey item is turtles,

and they can't really eat that turtle shell.

@therealansweri1 asks,

What does the skin of a shark feel like?

Shark skin feels two different ways.

So if you move your hand from the head all the way down

to the tail, they feel smooth.

But if you move your hand from the tail to the head,

it's quite rough, and there's a lot of resistance.

And this is because of their scales.

So shark scales are called dermal denticles.

If this very blown up large version

of a scale was placed on this shark,

it would sit like this,

and it would layer and layer and layer.

And this lower part here is the base of it.

This would actually be embedded

below the surface of the shark.

So as they're swimming,

water is almost perfectly moving over their body,

giving them less resistance than what we would experience

and actually helping them be as quiet as they are.

@RuaridhHanna asks,

How sharks can detect blood

at one part per 25 million parts of water?

One of the really big myths about sharks

is that they can smell a drop of blood from a mile away.

A particle of blood actually has to travel

through all of that water and end up in their nose.

They can't just say,

Oh, this is the entire stream it passed.

They have to keep having a stream

of particles that brings them to you.

They can swim around you and have no idea

that your blood is in the water.

@_haleyjacoby asks,

So if sharks have to move to be able to breathe,

how do they sleep?

I wanna address the first part of this question,

which is that sharks don't actually have

to always move to breathe.

There's kind of two separate breathing mechanisms

that sharks employ.

The first is called obligate ram ventilating,

and that is where shark absolutely has to move.

They just hang with their mouth open, essentially,

and the water will just flow out over their gills passively.

Think great white sharks, hammerheads, bull sharks.

They're constantly swimming because they have to be.

But then we have a category known as buccal pumpers.

Think nurse sharks sitting on the sea floor

or any kind of shark that's just hanging out

around the bottom.

They actually have special cheek muscles

that allow them to suck water in

and flush it out over their gills.

So they do not have to be moving to breathe.

When it comes to sleep,

the sharks that we know the most about their resting time

is buccal pumpers.

Some sharks will be observed in this resting period

with their eyes open, which is really fascinating.

So this whole sleep in sharks

is something that we're still researching very heavily.

@misskaylajoi asks, How do you track a shark?

You actually have to catch them first.

Once we've caught the shark,

we can then do a workup on it and add a tag into it.

And there's a couple of different ways we'll tag sharks.

The first one is just a satellite tag.

This is probably what most people would expect of a tag.

It's a decently sized package

that goes right onto the back of that top dorsal fin.

And it actually pings up to satellites.

The next is an acoustic tag.

Now, this is typically implanted into the body of the shark.

Another one is a great way for normal people

and non-scientists to really get into shark research.

And that is just a standard ID tag.

This essentially goes into the dorsal fin of the shark.

You have a little device that lets you do this.

You stick it into the dorsal fin.

So on this tag,

there's a couple of different pieces of information.

The first is just a standard ID number.

We would read this number off,

and then we could go into our Excel sheet and say,

Oh, we caught this shark two weeks ago,

and it was in this place.

There's a lot of different reasons that we tag sharks,

but the overarching question is,

what are they doing and where are they going?

Mostly because we just wanna know

in what areas of the world they're living in.

What are they eating? Where are their nurseries?

So there's all these overarching layers

of why tracking is important.

@RogueSharks asks, What are baby sharks called?

They're called pups, and it's amazing.

@lousyscouty asks, Siri, do sharks lay eggs?

This is a really interesting question.

Sharks actually have three ways of reproducing.

The first is they'll just lay eggs.

You can swim around the sea floor,

and you'll see things like a mermaid purse,

which is basically just an egg case

that sits on the sea floor and develops the shark.

And when they're ready,

they kind of punch out of that egg and they're ready to go.

They get the term purse

because they actually kind of look like a purse,

depending on the egg that you're looking at.

The second is they have eggs inside the mom,

and in each egg, there's one shark.

And that shark is slowly developing over time

with a yolk sack attached to it.

And once they hatch inside the mom from their egg,

the mom will then give birth to the live pups,

which is really fascinating.

And the last one is just live birth.

So similar to how we do, they just give birth to live pups.

And a really interesting example of this

is sand tiger sharks.

Sand tiger sharks will have a whole bunch

of eggs inside their body.

Some sharks eggs will become fertilized.

And as they begin to grow,

they actually start eating their siblings

while they're in the womb.

So there's kind of this crazy

Hunger Games thing going on inside.

And instead of giving birth

to a whole bunch of different pups all at once

and hoping that they'll be able to live,

they actually give birth to just two pups

that are already very strong

and already know how to behave like a shark.

@DiveMagazine asks, Why do sharks glow in the dark?

Well, some sharks have this really cool ability

to bioluminesce, which is producing light

from organs within their body.

One in the case of the cookie cutter shark

is to actually attract larger prey items

that may want to eat them.

So they can whip around

and take that nice cookie cutter bite out of them.

Another is countershading.

Sharks that can bioluminesce

in specific ways produce some light

to blend in with any light

that a predator below them might see above.

They're able to avoid being eaten

because they have this bioluminescent ability.

@BlakeneyCFA asks,

Shark week trivia. What is the fastest shark?

The fastest shark is the shortfin mako,

and it can swim up to 45 miles per hour,

which is very different from most

of the other species that we know of.

@hurtolympics asks,

What are sharks afraid of? Those [beep] ain't God.

Whether or not sharks actually experience the emotion

of fear or being afraid of something is hard to say.

When you're in the water with sharks,

a lot of them have a tendency to be skittish.

Some of them are really curious.

You can think sharks that people dive with,

nurse sharks, oceanic white tips,

but many sharks actually just avoid people altogether

because we're not a natural item in their habitat.

And they're generally pretty cautious,

so they're not really gonna come up to you

and be curious about you.

They'd rather just steer clear of something

that they're not sure what it is.

@Kelello_ asks, For how long do Greenland sharks live?

Greenland sharks inhabit very cold water,

and they have a very slow metabolism.

Based on our research,

we estimate that they live 250 to 500 years old.

@teamfinfree tweets,

Question. What's your favorite shark?

Go. #FinFree.

My favorite shark is the bonnethead.

This is the smallest species in the hammerhead family.

So it is actually related to the great hammerhead.

And they also have this really insane ability.

Dr. Samantha Lee discovered

that this is actually the only species

of shark that is omnivorous,

meaning that they can actually digest grass,

which is not a thing that we'd expect from sharks.

We generally think of them as being carnivorous only.

@hunter_jordan asks, Does the Megalodon really exist?

It did exist. It's extinct now.

Megalodon was a really big shark,

and they also had these really big teeth.

So this is a replica.

A lot of people have actual Megalodon teeth

that they find when they go diving

and actually lets us figure out what the size

of the animal might have been.

They lived in kind of the warmer ocean regions.

And our oceans have a tendency to be pretty cold now.

When you consider all this together,

there's really not any territory

in the ocean that the Megalodon could thrive in.

There's no nursery grounds that we know of,

and their prey items kind of just disappeared

and changed to make it harder

for them to actually be able to eat.

@DarkerDazai asks,

How to take care of sharks? Google search.

In captivity, usually what aquarists will do

is make sure that that temperature of the water

is the optimal temperature for them to live in.

And they'll make sure that they're feeding them

as often as they need to.

Sharks don't necessarily make good pets,

and they're also not always great in aquarium.

So there's not a whole lot

of great whites in aquariums, for example.

But you do see things like sand tiger sharks,

whale sharks, nurse sharks,

which are sharks that are a lot easier to take care of

and aren't as finicky in the environment

that they need to be in.

@NatGeo asks,

How long have sharks been swimming in the ocean?

Sharks have been around for around 450 million years.

@mattnj81 asks, What is the most endangered shark species?

Now, it's really hard to pinpoint exactly what species

is the most endangered.

If you find a shark that is critically endangered,

that means that we are really unsure

of either if they might exist,

or we've only seen a couple of them.

A really good example of this is the Ganges shark,

which was actually a river shark

that we haven't seen in a really long time

@mjgx_ asks, 'Jaws' wasn't a real shark, was it?

Just based on a real story or something?

So Jaws was not based off of a true story.

The shark you see in the film is a robotic shark,

and his name was Bruce.

But while they're hunting around for Bruce

and Bruce is supposedly eating all these people,

they do pull up a shark that they put up on a crane.

And this is a tiger shark.

You know that this shark is in fact real

because it has its claspers attached.

Claspers are the male sexual organ on sharks

that are just hanging off the back of the shark

in all their glory.

So next time you watch Jaws, be on a lookout for that.

@JeffOllerton asks, Did sharks go

through a mass extinction 19 million years ago?

We think that at some point something changed

that resulted in a mass extinction of all these sharks.

And the way that we know that

is because in our fossil record,

there's a sudden drop in the amount of shark denticles,

or teeth, from before the 19 million years to after.

That lets us know that there was this big extinction.

We're not entirely sure what it was,

but it seems like the population's really dropped.

@stackeddeck3 asks,

Why do sharks migrate to different places?

This is a really good question.

And we're really still trying

to figure out a whole answer to it.

Some sharks have specific places that they go to mate.

There are specific areas called nurseries

where young sharks will live until they're big enough

to kind of venture out into the open ocean.

Another reason is to follow prey.

We, as people, will fly to other places all around the world

just because we're curious about traveling.

Sharks kind of have a tendency to also travel,

and we don't really know why for some reasons,

but we do for others.

@abirupan asks, How do sharks see, smell, and hear?

So sharks have eyes just like us.

So they do actually use their vision

to observe their environment.

They do not have 20/20 vision.

Neither do I, as you can see.

To aid with that, they have all of their other senses,

like hearing, and smell,

and the ability to sense pressure changes,

and the ability to detect electricity,

to create this whole overarching picture

of what their environment looks like in a 360 view.

You'll see all these spots all over the bottom of their head

and sometimes even on the top.

And this is an organ

that essentially can detect different electrical pulses.

So sharks have a lot of different senses

that allow them to sample their environment

at a way higher level than we are able to.

@mcmsharksxx asks,

How are #sharks important?

And why do they matter in regards to our ocean?

We think of sharks as being apex predators.

So they're at the top of that food chain.

And in an ecosystem,

there's constant control going up and down.

If you think of grass growing and a fish coming

and maybe eating that grass,

and then there's a carnivore that eats that fish,

and then there's a bigger carnivore that eats that fish.

Let's say we remove the fish that eats the grass,

and the predator that was eating that fish

might not have any prey to keep eating.

And if that fish is gone,

then sharks don't have anything to eat.

When sharks are removed from an ecosystem,

there's kind of all these crazy environmental changes

that can happen.

And some of that ends up being less control on things

that are below them.

@_zixd asks, Sharks have eyelids? Do sharks blink?

Sharks don't blink in the sense that we do.

They do have something called a nictitating membrane,

which is an eyelid that will fold over some sharks' eyes

when a predator gets close.

And it's just a protection mechanism.

@EOSGreenBay asks, #Tuesday trivia.

What is the largest species

of shark currently living in the ocean?

The largest species of shark, actually, is the whale shark,

which can get up to 18 meters.

People often will say

that it gets up to the length of a school bus,

which is massive.

They actually eat plankton.

So they don't eat meat

in the same way that we expect other sharks to,

which is really fascinating.

So those are all the questions for today.

I really loved answering them,

and I hope that you learned something new.

Thanks for watching Shark Support.