The Great White Shark – They are the largest
predatory fish on the planet and as such stand at the very top of the food chain in the oceans. They are built for killing and are without
a doubt one of the most successful predators of our time. Despite this they are also deeply misunderstood
animals. Movies like Jaws turned sharks in particular
Great Whites into bloodthirsty calculated man-eaters and probably into one of the most
feared animals in the world. But do they really deserve their bad reputation? And what even makes them such dangerously
effective predators? That’s what we will discuss today. But before we get started I want to take 30
seconds to talk about this video’s sponsor, Brilliant. Sponsor message
Nobody can deny, Great Whites are dangerous animals – they are highly-specialized killing
machines and perhaps the ultimate predators of the ocean. But are they also the savage man-eaters many
people think they are? Statistically, yes - Great White Sharks are
the most dangerous predator for humans in the ocean. In the US – where most human-shark encounters
are recorded each year – sharks have bitten around 650 people between 2000 and 2015 –15
of them fatally. Tiger Bull and Great White Sharks are responsible
for the largest number of these shark bites. But as tragic as each of these incidents is,
do these statistics really paint the picture of sharks as fearsome man-eaters? Great Whites are some of the largest predators
on the planet. With an average weight of more than half a
ton and average length of 4-5m, top speeds of almost 60 km/h and perhaps the strongest
bite in the animal kingdom, no animal on their menu is safe. If that would include humans, the number of
deaths caused by shark bites every year would certainly not be single digit but probably
go into the thousands – considering the number of people that visit the beach year-round. In the US alone it’s around 50 million people
per year – even though almost the entire US coast is shark territory. With this much potential prey, the few dozen
shark bites that are recorded each year worldwide don’t really support the picture of the
savage man-eating Killer: Because for a Great White a human in the water is about as helpless
as a fish on land and certainly easy prey. They are after all adapted to hunt prey that
is much bigger and more difficult to take down. One of the most amazing of these adaptions
is the battery of senses they have at their disposal. Their sense of smell is probably the most
famous of them all. Even though this ability is often exaggerated
- most likely to make them even more terrifying – it is still unparalleled in the oceans. They can detect specific chemicals such as
blood proteins in minute concentrations: Possibly as low as 1 part per 10 billion. That’s the equivalent to 5 drops of blood
in an Olympic-sized swimming pool. If the current carries the particles in the
right direction this means they can detect wounded prey from as far away as half a kilometre. One of their senses that is often overlooked
and is perhaps even more accurate is their sense of hearing. It is much more sensitive than that of humans
and is especially adapted for detecting low frequency sound below 40 Hz including infrasound. This allows them to hear the low frequency
pulses caused by tiny water vibrations struggling fish or marine mammals make and over great
distances. Because sound travels faster and farther in
water than in air Great Whites can therefore hear the movement of potential pray from sometimes
over a mile away. Despite the reduced visibility underwater
the Great White’s eyesight is equally good. They can probably see as well underwater as
we can above the surface and even in colour – a rare ability in sharks which are typically
colour-blind. Additionally, they possess the same reflective
layer behind the retina that cats do. This allows light entering the eye to strike
the photo-receptors twice, which gives sharks the ability to make out their prey in almost
perfect darkness. But aside from these 3 senses that almost
every vertebrate has and which are already highly developed in sharks they also possess
two additional complementary senses. The first is the lateral line system – a
sensory organ you can find in almost all fish. It consists of a series of fluid-filled canals
running just under the skin along the flanks of the body and over the entire head. With these canals they are able to feel low
frequency pressure changes in the water. This gives them yet another way detect fine
water movements caused by the swimming motion of nearby prey. And finally there is their ability of electroreception. This is a trait that is almost unique to sharks
and their relatives and it allows them to detect the weak electric fields produced by
the bodies of all living organisms. Through a series of specialized sensory cells
connected to the surrounding water via over a thousand jelly-filled
pores distributed over the sharks’ head, the sharks are able to locate prey from about
a meter a three feed away. This helps a shark keep track of its target
just before it bites it, when it’s hidden in the blind spot in front of its nose or
when it’s otherwise hidden from view. They probably also use it for navigation by
orienting along Earth’s magnetic field. All this makes Great White Sharks without
a doubt one of the most dangerous and successful predators on Earth and a human would certainly
be easy prey for them. And yet the number of fatal shark attacks
by Great Whites in minimal. Almost every animal that you would think could
kill a human kills more people every year than sharks. Lions – check, Tigers – check, Wolfs – check,
Snakes, Snails, Elephants, Dogs, Jellyfish, Hippos, Bears, Bees Scorpions, Cows crocodiles
even Horses. It is more likely you will drown before ever
getting bitten by a shark. Even getting hit by lightning is more likely. One reason is that we are simply a too bony
meal for a shark. Because Great Whites have a very slow digestion
while having a comparably high metabolism they are actually very picky eaters. They need gourmet food - prey with a high
fat-bone ratio, like marine mammals which have a thick layer of blubber. Humans simply have too little fat and too
much muscle and bone to be a viable food source. If anything we would probably cause them serious
indigestion at which point they would likely just vomit us back into the ocean. Sharks actually do that - it is called gastric
eversion – It’s when a shark turns its stomach inside out, extending it from its
mouths and ejecting unwanted contents like bones or low quality meat of the stomach to
make room for better food. But if they don’t view us as prey then why
do shark bites happen. There is a lot of misinformation about this
too. For a long time we thought that sharks simply
mistake us for their usual prey. This, however, seems unlikely to be the case
given their incredible array of senses. The attack pattern also doesn’t support
this notion. Great Whites usually attack seals with tremendous
force and speed, often catapulting themselves up to 3m or 10 ft out of the water. This is not how attacks on humans usually
take place. In most cases the sharks approach at a relaxed
pace, take a bite or two and then swim off again. New research on shark behaviour suggests that
these bites are in most cases simply the result of their curiosity. Just like most animals, that have almost nothing
to fear in their environment, sharks are very curious animals. When they see something they don’t know,
they like to investigate it. And since they neither have arms nor legs
the only thing left they can use to get a feel for something is their mouth. A bite tells them everything they need to
know about an object. So, if anything, it’s this curiosity what
makes them dangerous to us not their lust for human flesh. The second reason why shark bites happen is
a similarly normal behaviour for wild animals: Competitive behaviour. In the wild the strongest most dominant individuals
tend to get the best food. And while sharks don’t have territories
the sense that terrestrial predators do, they are still very territorial. Especially in areas where a lot of sharks
congregate - for instance around a whale carcass - a dominance hierarchy need to be established
to determine who eats first. Great Whites do this in a number of ways. Despite sharks generally being lone predators
we have already identified at least twenty distinct social behaviours that help them
establish social rank and avoid physical conflict: “parallel swimming”, for instance. Here, two great whites swim side-by-side to
figure out who is bigger. Another way is a literal splash fight. Two or more sharks swim to the surface and
splash each other with their tails. The shark that makes the most or biggest splashes
wins. Great Whites even play “chicken”: They
swim at one another and the first to swerve loses. In rare cases, if all these peaceful methods
have proved futile they attack each other to ultimately figure out who’s stronger. Once the dominance hierarchy is established
feeding is generally orderly and well-behaved as each shark patiently waits for its turn. These complex social behaviours show that
Great Whites aren’t just dumb killing machines, but in fact very intelligent animals. Humans that invade their habitat can sometimes
be similary seen as competitors - especially in the vicinity of large schools of fish or
seal colonies – In rare cases this might provoke a bite to try to chase us off. That sharks almost never bite to kill can
also be seen in the shark bite statistics as the number of fatal bites is very low compared
to the number of non-fatal ones. Even in cases that unfortunately ended in
death, it was usually the consequences of the bite, most commonly the blood loss that
were the cause of death and not the attack itself. Because for the fragile human body even a
single shark bite will of course often result in serious injury or even loss of limbs. Hopefully by now it has become clear that
Great White sharks are not the bloodthirsty savage man-eaters film and media typically
make them out to be. But we also mustn’t forget that sharks are
wild animals – predators – und even though we are not on the menu, there is always a
risk involved when you invade their habitat If you are willing to look beyond their bad
reputation they are actually very fascinating animals. For instance, Great Whites have extreme regenerative
abilities. Their wounds not only heal extremely quickly
they are also able to survive injuries that would kill just about any other animal. But this ability goes beyond the physical. Earlier this year a team of scientists has
completed its task to decode the entire genome of the great white. Their genetic code has revealed a surprisingly
high number of genome stability genes – so genes that are tied to DNA repair and DNA
tolerance. These genes help to repair and prevent copy
mistakes and random mutations inside the DNA that could otherwise lead to abnormal changes
in those cells. These finds seem to confirm a long-standing
suspicion that great whites are extremely resilient against cancer and other age-related
diseases – This however doesn’t mean that eating these Sharks will somehow give you
the same ability – sorry china. Much of what we have covered this far is of
course not necessarily unique to Great Whites and can be said about many of the roughly
500 different shark species. But one characteristic of them is much more
unique and clearly makes them stand out among other large species such as tiger and bull
sharks – and that’s their ability to elevate their core body temperature above that of
the water. Unlike most other sharks which are – like
basically all fish – cold-blooded, Great Whites and 5 other species - all of the order
of mackerel sharks - are able to achieve a kind of warm-blooded-ness. By holding their body temperature constant
at around 25°C or 77°F they are able to operate in both warm and very cold waters
and hunt where other large sharks can’t. But how does it work? In most sharks the powerful red swimming muscles
are located along the flanks, directly below the skin. The big dorsal aorta, the central running
artery, supplies them with the necessary oxygen through a handful of arterial branches. Afterwards, the carbon-dioxide rich blood
is pumped back towards the heart. Most of the metabolic heat sharks produce
is generated inside these muscles while swimming. But because water conducts heat 10-20 times
better than air this heat is normally immediately lost to the environment resulting in no significant
temperature increase. The Great White however has evolved in such
a way that they can greatly reduce this heat loss and thereby maintain an elevated body
temperature. This is only possible through a series of
modifications to the structure of their swimming muscles and their circulatory system. The first important change is that the red
swimming muscles are buried deep within the sharks body on each side of the backbone - there
is also much more of it. Red muscle compared to the predominantly white
muscle of coldblooded fish is much more powerful and produces more heat as a result. It does, however require a much higher metabolism
and more importantly a greater supply of oxygen. The additional oxygen is provided by enlarged
arteries along the flanks of the fish that redirect blood inward through a dense bundle
of smaller arteries and veins. This fine network is called the rete mirable
- which roughly translates to wonderful net. The central arrangement of the swimming muscles
means that far less of the red muscle mass has direct contact with the surrounding water,
which reduced the immediate heat loss. But much more important is the extensive counter
current heat exchange enabled by the dense array of veins and arteries that supplies
the muscles with oxygen. Through the countless small arteries and veins
that pass very close to one another, carrying blood in opposite directions, the retia act
as heat exchanger. Because of the intimate counter current blood
flow, most of the heat is transferred from the veins to the arteries and cycled back
to the muscles that produced it originally. In contrast to a concurrent flow system where
the continued heat exchange between two liquids will eventually lead to an equilibrium that
is somewhere in the middle of the two original temperatures. In a counter current system the exchanged
heat is constantly is carried away, pushed forth by new cold blood. This means the upper stream will always have
the lower temperature and more heat can be exchanged. Here, an equilibrium is only reached when
nearly all the original temperature difference was exchanged. This makes counter current exchange so effective
as nearly all of the metabolic heat in the venous blood is transferred to the arterial
blood, thus conserving most of muscles temperature. This is how Great Whites maintain a higher
body temperature and because of it they are able to inhabit a much wider range of environments
with varying water temperatures. The additional red muscle mass makes them
powerful swimmers than can travel great distances fast and effortlessly even into colder waters
where their inner heat warms their brain muscles and stomach and therefore allows them to catch
even swift and agile prey like marine mammals that would be inaccessible for any cold-blooded
predators. As you can see Great whites or sharks in general
are truly fascinating animals and more than just terrifying sets of teeth. As apex predators they are also extremely
important for the ecosystem. While they sit on top of the food chain, the
health of the ecosystem actually rests on their shoulders – they keep the balance
and without them the oceans ecosystem as we know it would collapse: That’s why protecting
these animals is very important. Of the approximately 500 species of sharks
over 100 are threatened – some even critically. This includes Great whites, various species
of Hammer heads, Whale Sharks and Basking Sharks to name a few. But this isn’t really surprising given how
many sharks are still killed each year in attempts to make beaches safer as by catch
by commercial fishing vessels, as trophy catches and for shark fin soup, a popular delicacy
in China. Only a few years ago it was estimate that
the number of sharks that are killed each year is likely between 100 and 250 million. That a shocking 11000 that are killed every
single hour – hour after hour, day after day, year after year, and will not stop until
almost every shark in the ocean is dead – unless we do something about it. Thankfully a lot has already been done in
the past years and decades but unfortunately shark conservation depends on public acceptability
and as long as sharks are still viewed by many as savage man-eaters conservationists
will continue to fight an uphill battle to protect these magnificent creatures.
