How Do Sharks' Senses Work?

Sharks are such successful hunters in part because their senses are so well-adapted to finding prey in the water. Learn about sharks' senses of smell, hearing, sight, taste, and electroreception in this episode of BrainStuff, based on these articles: https://animals.howstuffworks.com/fish/sharks/shark-senses.htm/printable; https://animals.howstuffworks.com/fish/sharks/shark-yummy-hum.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff
Lauren Vogelbam here sharks are cool that these beautiful, powerful,
toothy creatures have been swimming Earth's oceans for some three
hundred million years. Some species that exist today haven't really
changed much since the age of the dinosaurs. They fascinate

(00:25):
and sometimes frighten us because they're such keen predators thanks
to a number of adaptations that have clearly stood the
test of time. Though to be clear, we are far
more of a danger to them than they are to us.
Toilets injure some forty thousand Americans every year, and sharks
injure right around fifteen. Not fifteen thousand, just fifteen. But

(00:49):
it's easy to see why they make us a little
nervous or perhaps appropriately wary. When we humans swim in
the ocean, our senses are limited, our hearing is muffled.
We can't really see without goggles. We can't smell anything
without breathing in water. But shark senses are perfectly primed
for an underwater environment. Today, let's talk about how those

(01:09):
senses work. A firstep smell. The sharks have been referred
to as swimming noses. A research has shown that some
sharks can sniff out fish extracts in water at a
ratio of one part in ten billion. Other research found
that sharks can respond to as little blood in the
water as one part in a million. That's like being

(01:30):
able to detect one teaspoon of something in an Olympic
sized swimming pool. How does the shark do this? Just
under the snout are two nasal cavities or neries. Each
nars has two openings, one for water to enter and
one for water to exit. The shark sucks or pulls
the water into the naries through what's called a nasal sack.

(01:51):
The nasal sack is filled with a series of skin
folds that contain sensory cells, which send signals to the
shark's brain. The olfactory lobes and the shark's brain analyze
the data looking for anything that matches the scent of
potential prey or potential mates. And sharks have pretty advanced
equipment up there. The olfactory lobes can make up two
thirds of a shark's brain weight. Once a shark identifies

(02:14):
a scent and decides to pursue, it starts swimming the
shark's natural swimming motion moves its head from side to side,
which provides further assistance and determining where the scent is
coming from. Because a shark's sense of smell is directional,
with each movement the snout picks up more water for
the shark to analyze and hone in on whatever it's smelling.

(02:35):
Its sense of smell works so well partially because a
shark's nose doesn't have anything else to do well. Unlike
a human with a nose connected to our lungs, sharks
breed through separate gills. Next up hearing. If you've never
seen a shark's ear, that's because they have no outer
ear structures, just a hole on either side of their head.

(02:57):
But because injured and therefore e prey tend to flop
around and emit low frequency pulsing hums, it pays for
sharks to be tuned into those sounds. That pulse is
sometimes called a yummy hum for that reason, it's like
a dinner belt to a shark. A shark's ear consists
of three D shaped, fluid filled canals that allow the

(03:19):
shark to orient and balance itself like you're inner ears do,
and tiny hair like structures that sense the vibrations of
sound waves in the water. Because sound, and especially that
low frequency sound, travels farther and faster underwater, sharks are
easily able to detect their prey from distances of more
than eight hundred feet that's about two hundred and fifty

(03:40):
meters or more than two football fields. And sharks also
here with another sensory organ called lateral lines. These are
a set of tubes that crisscross just under the shark's skin.
Two main ones run on both sides of the body
from the shark's head all the way to its tail.
Water flows into these main tubes through pores on the
skin in surface. The insides of the tubes are lined

(04:02):
with more hair like sensory structures. A sound waves or
nearby movement will cause vibrations in the water in the
lateral lines, which the shark can interpret to help it
hone in on things around it. But let's talk vision.
Some less active sharks that stay near the water's surface
don't have particularly acute eyesight, while sharks that live in

(04:23):
the deeps have very large eyes that let them see
in near darkness. A Most have eyes positioned one on
each side of their heads, giving them a nearly three
hundred and sixty degree field of vision. They can typically
only see about fifty feet or fifteen meters around them,
and they do have two major blind spots, one right
in front of the snout and one behind their head,

(04:44):
so sense of sight is really only important to a
shark once it's closed in on its prey. Their eyes
work much like ours, but unlike us, sharks that swim
in the deep dark parts of the ocean can still
see well thanks to the tapedum lucidum. This is that's
the structure located behind the retina that's made of mirror
like crystals. When light goes through the retina and hits

(05:06):
those crystals, it's reflected back onto the retina, giving the
shark a second chance of perceiving anything moving through its
field of view. A cat's eyes have the same structure,
and that's why both cat eyes and shark eyes appear
to glow in the dark, though a shark's to pedem
lucidum can be about two times as effective as a cat's.
Humans lack this structure, which is why some sharks can

(05:28):
see about ten times better than a human can in
dim light. Another unique thing about shark eyes is the eyelid.
Sharks use their eyelids primarily as protective measure. When it's
feeding time or when the shark has an encounter with
another shark, it will close its eyelids to protect the
eyes from abrasion. However, a shark's eyelids don't close all

(05:49):
the way. Some sharks have a third lid, known as
a nictitating membrane, which will fully protect the eye. Sharks
that don't have this feature, such as the great white
and the whale shark, will roll their eyes back into
their heads to protect the delicate structures. This is also
why they look wildly wide eyed while they're attacking. Many

(06:10):
shark species also rely heavily on their sense of taste.
Before these sharks eat something, they'll give it a test
bite first. The sensitive taste buds, clustered in the mouth
analyze the potential meal to see if it's a good one.
Sharks will often reject prey outside of their ordinary diet,
such as human beings, after this first bite. And Sharks

(06:31):
also possess electra reception. They can sense electrical fields elect
the faint ones created by a beating heart. The organ
that lets them do this is called the ampullae of Lorenzini.
These are small clusters of electrically sensitive receptor cells positioned
under the skin in the shark's head. They're connected to
pores on the skin's surface via small, jelly filled tubes.

(06:53):
Researchers are still learning about this organ, but they seem
to help sharks sense potential prey even if it's not
flopping about. So yes, all of this makes sharks extremely
good at what they do and should inspire a healthy
respect in anything swimming with them. I certainly prefer my
shark encounters to be from behind some good, thick aquarium glass.

(07:22):
Today's episode is based on the article how do Sharks
ce Smellin' Here? On how stuff Works dot Com written
by Molly Edmonds, with additional material from the article What's
the Shark's Bummy Hum? By Josh Clark and the brain
stuff video how do Shark Senses Work? Written by Ben Bollen.
Brainstuff is production of i Heeart Radio in partnership with
how stuff Works dot Com, and it's produced by Tyler Klang.
Four more podcasts my heart Radio, visit the iHeartRadio app,

(07:44):
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