Misconceptions about Sharks - mental_floss on YouTube (Ep. 30)

Hey, I'm Elliot and this is Mental Floss on YouTube

Today I'm going to talk about some misconceptions about sharks. Misconception number one

Sharks have poor eyesight. People use this myth to explain why sharks are known to attack so many different animals, including humans

Actually, sharks have something called a tepidum lucidum in their eyes. These are mirrored crystals behind the retina that allow sharks to see clearly in dark or murky water

In fact, they can see ten times better than humans in clear water. Many believe that great white sharks sometimes attack humans because they confuse people for seals

That would explain why they typically don't eat the people they attack, which I'll get to in a minute

But, shark experts maintain that a great white's behavior when attacking a seal is definitely different from when they attack a person

They tend to attack seals with much more vigor. They just settle for us. Misconception number two, sharks eat people

First of all, it's worth noting that there are over 400 species of sharks that we know of

Only around 12 of those are what experts would consider dangerous to people, including the great white shark, tiger shark, and bull shark

And even still, human isn't an ideal food to them. They prefer things like fish and seal and porpoise

Typically, sharks that attack humans will spit them out because of their bones. Those bones will affect a shark digestive tract for days so they choose their food carefully And that brings me to misconception number three sharks will eat anything This doesn make sense if you think about it If you ever been to an aquarium you probably seen a shark swimming around with other fish

that it seems to have no interest in eating. And like I just mentioned, sharks won't eat things

that negatively affect their digestive tracts. There are some sharks that will eat pretty much

whatever they can find, but there are also species like the basking shark and whale shark that only

eat plankton. Misconception number four, sharks aren't very smart. Actually, many sharks have a

pretty high learning capacity. For instance, a 1975 study determined that lemon sharks were able

to learn a classical conditioning task a full 80 times faster than a cat or rabbit could

Experts also consider the great white shark to be intelligent and curious despite its reputation

as mindless. In a 1996 study conducted in South Australia, a researcher found that 9 to 31 percent

of white sharks were more likely to investigate a floating square rather than a seal-shaped object

And experts continually find that white sharks will approach objects that are new and unique to

their environment. Misconception at number five. If a shark attacks you, you should punch it in the

nose. Okay, before I talk about this, it's worth mentioning that according to the International

Shark Attack File, a database on shark attacks, you have a 1 in 3.8 million chance of being attacked

by a shark. So don't be worried. Anyway, it turns out that this common advice might not be the best

way to handle an attack One major problem is that water affects your perception of where the shark actually is Plus punching underwater is not that effective You ever tried it You have a brother Me too While attempting this on a shark your fist might miss and just go straight into its mouth

So, what should you do? First of all, some experts claim that swimming away fast from a shark pre-attack

will also draw more attention to yourself. But if it's too late for that advice to be relevant

poke the shark's sensitive eyes and gills. Misconception number six. If a shark stops swimming, it dies

This used to be the popular belief, but it isn't anymore. Basically, most sharks breathe by swimming fast

Their gills allow them to absorb the oxygen and water, keeping them alive

But, if they need to stay still, there's also a method of breathing known as buckle pumping

This is when muscles near the shark's mouth pump water, accomplishing the same thing that swimming does

There are some sharks that aren't capable of buckle pumping, but experts have seen them take a break from swimming from time to time

They get exhausted. You got what you want from them. Misconception number seven. Sharks have sharp teeth

Hashtag not all sharks. Like the horned shark has teeth that resemble molars

They use them to crush up their prey, and the basking shark has tiny hooked teeth

Misconception number eight, sharks do not get cancer. This one was popularized in the 1992 book Sharks Don't Get Cancer

Plus, many believe that shark cartilage is a cure for cancer, but there is no evidence that it is

Sharks do get cancer. As of December 2013, scientists know of 23 species of sharks that can get tumors, including the great white shark

That same year researchers discovered a great white with a tumor under its mouth that was one foot long and one foot wide That a big tumor Misconception at number nine bull sharks have more testosterone than any other animal

This myth gained popularity thanks to internet rumors and a character in Grand Theft Auto 4

who says he injects bull shark testosterone. There hasn't been a big study testing testosterone levels in bull sharks

One study did test three bull sharks and found testosterone levels of 0.1 nanograms per milliliter

2.7 nanograms per milliliter, and one with 358 nanograms per milliliter. So, one did have high levels, but the other two weren't exceptional

To compare, a male bonnethead shark has been found with 303 nanograms per milliliter of

testosterone, and male rainbow trout have similar numbers. This one needs to be tested more, but it's safe to say that the bull shark isn't anything

special compared to other animals when it comes to testosterone levels. So if you find one bragging about it, don't listen to it

Misconception number 10, sharks don't have any predators. They do have some. For example, killer whales prey on some sharks, including mako sharks

And let's end this episode on a depressing note, shall we? are actually considered the shark's greatest predator

People kill tens of millions of sharks every year for their fins. Thank you so much for watching Misconceptions

on Mental Floss on YouTube, which is made with the help of all of these nice people. If you have a topic for an upcoming Misconceptions episode

that you would like to see, why don't you just leave it in the comments and we'll check them out. And I'll see you next week. Bye