Category
🐳
AnimalsTranscript
00:00 (dramatic music)
00:02 Sharks are often portrayed as ruthless killers.
00:06 But mounting evidence reveals
00:12 they're more intelligent than we believed.
00:14 They're actually more like us.
00:20 They choose friends.
00:23 They learn.
00:24 They may even be able to teach each other
00:28 just how smart are sharks.
00:30 (dramatic music)
00:36 - This is the one we want.
00:41 - One's clear.
00:45 (dramatic music)
00:47 (dramatic music)
00:50 (gentle music)
01:01 At the Bimini Shark Lab,
01:05 a scientific outpost on a remote strand of the Bahamas,
01:09 groundbreaking research into shark intelligence
01:12 is underway.
01:15 The results may reveal just how smart sharks really are
01:19 and help change public perception
01:21 of the ocean's most feared and misunderstood predator.
01:26 One sign of intelligence is the ability to learn.
01:32 Can sharks modify their behavior
01:35 as a result of experience?
01:37 Shark Lab scientists put juvenile lemon sharks to the test.
01:43 In a large outdoor pen,
01:45 researchers train sharks to enter a start zone
01:49 and make contact with a target to receive a food reward.
01:53 Naive sharks, those without any training,
01:57 are then able to observe both trained and untrained sharks.
02:02 Not only will this study determine if sharks can learn,
02:05 it will also unlock a mystery
02:07 that has stumped marine scientists.
02:10 Is it possible that sharks can teach other sharks?
02:14 To answer this question requires a broader understanding
02:19 of sharks and shark behavior.
02:21 In many traditional cultures,
02:29 sharks signify bravery and strength
02:31 and are celebrated as powerful gods,
02:36 guardians of the ocean.
02:39 (dramatic music)
02:41 Yet, due to their elusive nature
02:44 and the difficulties associated with studying
02:46 a large and dangerous predator in the wild,
02:49 sharks have remained a mystery
02:52 until now.
02:57 Marine scientists using state-of-the-art technology
03:03 are on the verge of discovering clues to shark intelligence.
03:07 (dramatic music)
03:10 But there are obstacles.
03:11 Measuring intellect can be problematic.
03:15 - Measuring intelligence in animals is tough
03:21 because it's kind of hard to pinpoint
03:23 exactly what intelligence is.
03:27 We really don't have a good grasp
03:28 on how to even do that in humans.
03:30 So you can imagine it would be hard to translate that
03:33 back to organisms that we can't even contemplate
03:36 really what they think or what they do.
03:39 - Despite the challenges posed in determining intelligence,
03:44 scientists have several reasons
03:46 for concluding sharks are smarter than we thought.
03:50 For one, sharks have exhibited a desire to learn.
03:54 They seem to be curious.
04:04 So-called shark attacks, as rare as they are,
04:07 have more to do with shark curiosity than aggression.
04:11 New Yorkers bite more people than sharks do,
04:14 yet humans remain terrified of being attacked by a shark.
04:18 Each year, millions of people enter shark habitats.
04:25 Still, shark bites are rare.
04:28 People are twice as likely to be killed
04:31 by a falling coconut as a shark.
04:34 Americans are 3,000 times more likely
04:38 to be injured by their own toilet than by sharks.
04:41 When a shark does bite a human,
04:48 the incident bears little resemblance to an attack on prey.
04:51 The shark takes one bite, realizes the target is not food,
04:58 releases its grip, and swims away.
05:01 (dramatic music)
05:03 More than 85% of humans survive shark bites.
05:07 Deaths do occur from blood loss,
05:10 but there are very few cases
05:12 in which a shark has actually consumed a human.
05:16 People aren't on the menu.
05:20 - Sharks are definitely curious.
05:22 When you're in the water with them, they wanna come in.
05:25 A lot of times people will get scared
05:26 thinking that a shark's coming in to attack them,
05:29 but most likely what it's doing
05:30 is just looking at a new item in its environment
05:33 the same way that if you're driving down the highway
05:35 and you see a weird object
05:37 on somewhere that you've always been,
05:38 you might stop and take a second look at that.
05:40 - Taking a nibble is a shark's way
05:44 of exploring a new object.
05:46 Investigative bites are a type of tactile exploration,
05:51 in much the same way as human babies
05:54 put objects in their mouths.
05:56 (dramatic music)
05:58 A shark's teeth and gums are remarkably dexterous,
06:03 much more sensitive than its skin,
06:06 which is why they explore with their mouths.
06:08 Just as humans have taste buds on their tongues,
06:13 sharks have taste buds in their mouths.
06:16 It just so happens that those mouths
06:20 are packed with razor-like teeth.
06:23 Our shark's curious plays a lot into
06:26 why sharks bite people.
06:28 We think that most of the time that folks are attacked,
06:32 and I sort of use that term broadly,
06:35 usually has nothing to do with
06:37 the sharks being malicious at all.
06:38 Has more to do with the fact that they don't have hands,
06:42 might be hard to see what's in the water with them.
06:45 And their way of sort of sampling the environment,
06:49 especially when it's hard to see,
06:50 would be through touch.
06:53 And coincidentally, that just happens to be around
06:55 the sharp end of the shark, and that's the mouth.
06:58 So we think that generally a lot of shark attacks
07:02 is basically the shark just being curious
07:04 as to what this weird thing is
07:06 that seems to be splashing around a lot.
07:08 That splashing, that idea of struggle,
07:11 so the vibrations that that puts through out the water,
07:15 is a thing that a shark is typically gonna think of as food.
07:18 And it pays to be curious as a predator
07:20 because it could mean prey,
07:22 it could mean a mate,
07:24 it could mean that another shark
07:27 is invading the territory that you protect.
07:30 So sharks are curious because it pays to be curious.
07:33 - Sharks exhibit curiosity in other ways as well.
07:40 Before outright attacking,
07:43 oceanic white tips may bump an unfamiliar object
07:47 to size up potential prey.
07:49 (suspenseful music)
07:52 Sharks swim over reefs,
07:54 finding things that may pique their curiosity
07:58 and approach underwater photographers
07:59 and camera equipment to take a closer look.
08:02 But how many of these investigative behaviors
08:06 are triggered by pure instinct?
08:09 And how much has to do with a shark's ability to remember
08:14 or even learn?
08:16 (suspenseful music)
08:19 Memory can indicate intelligence.
08:26 The ability to remember allows a shark
08:31 to learn from past experiences
08:33 and improve its hunting skills over time.
08:36 For sharks, hunting is not an inborn skill.
08:42 Like all living things,
08:45 they have a survival instinct that includes the need to eat.
08:48 Nature has equipped them to be top predators,
08:53 but they must learn how to use their natural abilities.
08:56 At Guadalupe Island,
09:04 seals and sea lions are the speedy prey of white sharks.
09:08 Researchers say it's not uncommon for young great whites
09:14 to miss out on fast-moving targets
09:16 and that older sharks are more successful hunters
09:20 than younger sharks.
09:22 They learn through trial and error.
09:28 Like humans, practice makes perfect.
09:30 So sharks can learn from their own experience,
09:35 but can they learn from other sharks as well?
09:41 The Bimini Shark Lab in the Bahamas
09:43 endeavored to answer this very question.
09:46 - We did an experiment here to see if sharks
09:49 could pick up information from each other.
09:52 And what we did was we created a novel feeding task.
09:56 We basically trained a number of juvenile lemon sharks
09:59 in an operant conditioning task.
10:01 - Researchers train sharks to swim from one zone to another,
10:07 then bump a target to receive a food reward.
10:11 They then introduce new untrained sharks to the pen.
10:15 These naive sharks observe the behavior
10:18 of both trained and untrained sharks.
10:21 The study revealed that naive sharks
10:24 that had been paired with teacher sharks
10:26 were more successful at completing the task
10:29 than those paired with other naive sharks.
10:31 - Which was a very nice indication
10:34 that they could learn from each other.
10:36 And then what we did was we then separated
10:38 those two individuals and then trained
10:41 the naive one separately.
10:42 And we found that that individual learned quicker
10:45 than the original set of sharks
10:47 that were first taught the task.
10:49 - The unprecedented results of this study are astounding
10:54 and the implications far reaching.
10:56 Not only does it prove sharks can learn,
11:01 but they can teach what they've learned to other sharks.
11:07 The capacity for social learning
11:08 is a key indicator of intelligence.
11:11 Thanks to this study at Bimini,
11:14 researchers now have categorical evidence
11:17 of knowledge sharing among sharks.
11:20 - Do sharks retain memory
11:23 is a really fascinating area of research.
11:25 And the answer seems to be yes.
11:28 Again, when sharks are trained to do tasks,
11:32 they can retain that for up to six months to a year,
11:34 which is as best as we know, probably beyond that.
11:39 - To put this in perspective,
11:40 six months is longer than a school semester,
11:43 meaning sharks could pass an exam
11:45 at the end of a term on material they learned
11:48 at the beginning of a term.
11:50 The capacity to overcome instinct
11:55 is another measure of intelligence.
11:58 Sharks can override their natural inclinations
12:00 by learning and remembering new behavior.
12:03 (gentle music)
12:05 A shark's eyes instinctively roll back
12:08 when its snout touches an object.
12:10 This is to protect the eye from prey that might fight back.
12:14 However, as sharks grow accustomed
12:18 to a particular object over time,
12:21 such as bait at a diving cage,
12:23 they no longer perceive it as threatening
12:26 and the eye rolling decreases.
12:28 A shark's memory is key
12:31 to one of its most impressive feats,
12:33 traveling tremendous distances.
12:37 A female white shark tagged with a satellite transmitter
12:42 was tracked from South Africa to Australia and back,
12:47 a trans-oceanic migration of 14,000 miles.
12:51 One reason for these epic trips
12:54 is for female sharks to return to their birthplace
12:57 to give birth themselves.
13:00 (gentle music)
13:02 - A lot of sharks make migrations back
13:05 to where they were pupped.
13:07 So the nursery grounds where they were born and raised.
13:10 And sharks seem to remember where those spots are
13:13 for years and years and years.
13:14 - At the Bimini Shark Lab,
13:20 researchers suspected that female lemon sharks
13:23 were returning to pup in the mangrove lagoons
13:25 where they were born.
13:27 (gentle music)
13:29 They created a genetic database
13:31 of more than 2000 lemon sharks over 18 years.
13:35 The genetic sampling confirmed their belief.
13:39 Female lemon sharks born in Bimini in the late 1990s
13:44 returned to their own birthplace to deliver their young,
13:48 the first ever documentation of sharks coming home to pup
13:51 in the spot where they were born.
13:55 The question that remains is why?
13:57 - Sharks might wanna go back to where they were born
14:01 because there's an idea perhaps
14:03 that that's a good place to pup.
14:05 They were successful.
14:06 They were able to get the energy from that area.
14:10 And it just seems to be hardwired into a lot of species
14:14 to head back to where they were born,
14:17 presumably just because it was a good area to live.
14:22 - But how do sharks find their way back to their birthplace?
14:26 - How they do that is based on an incredible way
14:31 of just knowing where they are in space.
14:34 Some sharks can home in on their home territories
14:37 based on smell, and sharks use the sense
14:40 of the Earth's magnetic field to actually go back
14:43 to where they were born or go back to where they need to be
14:46 at that time of the year, sort of like an onboard GPS.
14:52 - A shark's sixth sense of electroreception,
14:55 so essential for hunting, is vital for navigation as well.
14:59 It senses magnetic fields and uses them
15:03 to create a mental map that helps the shark find its way,
15:07 even over massive distances.
15:09 While impressive, the shark's onboard GPS
15:15 does not necessarily indicate intelligence.
15:18 Salmon have similar capabilities,
15:21 but not the brainpower of sharks.
15:24 - And there are other senses too that sharks have,
15:27 and actually humans do too, that we usually don't think of.
15:30 So the ability to be able to sense direction and velocity
15:34 and sort of what's up from down,
15:36 and you can imagine that would be really, really important
15:38 for an animal that has to chase down prey
15:41 in a sort of environment where they don't have any landmarks.
15:45 - Sharks often travel solo,
15:51 like the female that traversed 14,000 miles.
15:54 But are they more social than we think?
15:57 Are they capable of making friends?
16:01 Contrary to common belief, sharks are not antisocial loners,
16:15 at least not all the time.
16:19 Like people, sharks create social circles
16:22 and prefer some individuals over others.
16:25 - We do know that juvenile sharks especially
16:29 tend to hang out in groups, especially when they're young.
16:32 And those groups tend to be familial groups.
16:36 So those are sharks that are related to each other.
16:40 We think that it might have to do with
16:42 the more of you are in a school or a group together,
16:44 the harder it is for a predator to pick out
16:47 one small shark or one prey from the rest of the herd.
16:52 So shark friends tend to be related to them.
16:55 And again, this seems to be a pattern
16:57 we see in the juvenile sharks.
16:59 - Sticking together for survival is one thing,
17:04 but what about when no threat exists?
17:06 Researchers at the Bimini Shark Lab
17:10 conducted an experiment to test the sociability of sharks.
17:17 They put five young lemon sharks into a large outdoor pen,
17:20 then monitored them for a one-hour period,
17:23 recording every 30 seconds
17:25 whether a shark interacts with its peers.
17:28 One week later, they were tested again.
17:34 The research team found that some prefer to be alone,
17:38 some form small groups,
17:40 and others spend time in pairs.
17:45 The results proved that sharks have social traits
17:49 similar to humans.
17:50 This preliminary data suggests
17:54 sharks have individual personalities.
17:57 Some are more social, others are more cautious.
18:01 - Just a little bit more and then it should be good.
18:10 - To learn about the social habits of tiger sharks,
18:13 researchers surgically implant acoustic tags
18:15 to track their movement.
18:17 Data demonstrates that tiger sharks
18:22 will interact repeatedly with the same individuals
18:25 or friends and form groups.
18:28 Depending on the time of year,
18:32 they will then break to spend time alone.
18:34 Large white sharks can go almost two weeks without a meal.
18:42 However, they don't often go so long without interacting.
18:46 Exactly why they meet up is not known,
18:50 but they do so frequently at shark hotspots,
18:54 like the location that has come to be called
18:56 the White Shark Cafe.
18:58 - The White Shark Cafe is a place
19:00 between Hawaii and Guadalupe Island.
19:02 It's very deep, it's like a kilometer depth.
19:05 And scientists have found with satellite transmitters
19:09 that these animals go to this place
19:11 and they stay there from 160 days to 173 days
19:15 doing something.
19:16 - Like mammals, birds, and reptiles,
19:21 it appears sharks inhabit a far richer social world
19:24 than we imagined, even forging friendships.
19:27 But in order to make friends,
19:31 they must first be able to communicate.
19:33 (suspenseful music)
19:36 Most shark behaviors are based on social rank.
19:46 When two stranger sharks meet,
19:50 their first task is deciding which is dominant.
19:53 They need to avoid violent combat.
19:56 Competition among sharks for hunting sites,
20:01 prey, and mates is intense.
20:03 And because sharks are such fierce predators,
20:07 fighting each other is dangerous.
20:09 They avoid bloodshed by determining
20:13 which shark takes precedence.
20:15 Place in the hierarchy is based mainly on sheer size.
20:20 Being large indicates a shark eats well
20:24 and is therefore a formidable hunter.
20:26 Size matters, and sharks go to great lengths
20:32 to make themselves appear as large as possible.
20:35 - A lot of times, if a shark is feeling threatened
20:38 or if it feels like there's something in its space,
20:41 it'll try to make itself look a lot bigger.
20:43 Usually when you see a shark
20:45 that's going through some sort of aggressive display,
20:47 it'll sort of angle down the pectoral fins,
20:51 stare right at you, flare the gills,
20:53 and just try to appear bigger than it is.
20:56 - But it's not just size that determines dominance.
21:01 Females rank above males
21:03 and establish sharks above newcomers.
21:06 There are at least 20 documented behaviors
21:11 sharks use to establish rank,
21:13 one of which is parallel swimming.
21:16 - You get to see that there's a hierarchy.
21:19 When they are in front of a boat and you have bait,
21:21 they do not want to have a fight.
21:23 So they do something that is called a display,
21:25 like an exaggerated behavior,
21:27 like something that is called the parallel swimming.
21:30 They measure each other in order to know who's bigger.
21:33 - After swimming side by side,
21:36 the submissive shark drops away.
21:38 Giving way is a behavior that mirrors a game of chicken.
21:44 Sharks swim toward each other
21:47 until the submissive shark turns
21:50 and gives way to the dominant shark,
21:52 which continues on course.
21:54 - You can definitely tell when a bigger shark comes in
21:57 that the other ones know to make way
21:59 and get out of its way.
22:02 - Unlike dogs, which may fight to determine dominance,
22:06 sharks often take a smarter approach
22:08 and stay clearer of trouble.
22:10 Cocos Island off Costa Rica
22:19 attracts the largest schools of hammerhead sharks
22:21 on the planet.
22:22 Where sharks gather in large groups,
22:28 social status is clear.
22:30 These hammerheads have the most developed social behaviors
22:33 of all sharks.
22:35 - They have this hierarchical system.
22:38 So in the center of the school,
22:40 you have the dominant females, the largest females,
22:43 and around the outskirts of the school,
22:45 you have the smaller, less dominant female hammerheads.
22:50 And they have a social system
22:52 that the female turns in certain directions
22:55 and shows her sides of their belly.
22:58 That means move away from me.
23:01 - Unlike many fish,
23:06 sharks don't produce sound to communicate.
23:08 Instead, they relay information physically.
23:13 Battles over supremacy rarely occur.
23:18 Conserving energy to hunt prey is more important.
23:22 (gentle music)
23:25 And from tip to tail, sharks are designed to hunt.
23:33 Sharks are so powerful,
23:44 their physical qualities overshadow
23:46 their cognitive abilities.
23:50 They're apex predators,
23:52 ruling over 70% of the Earth's surface.
23:55 Over more than 400 million years,
24:02 they've evolved into near perfect hunters.
24:05 But to be a successful hunter requires brains and strategy.
24:11 To execute that strategy,
24:13 the shark must coordinate its many physical gifts.
24:20 On average, sharks have 15 rows of teeth in each jaw.
24:24 Teeth often break off and lodge in prey,
24:29 but grow back within days.
24:31 A shark can produce 50,000 teeth in a lifetime,
24:37 more teeth than the residents in a town of 1,500 people.
24:41 A white shark can bite through a two-ton elephant seal
24:46 like it was butter.
24:48 (gentle music)
24:50 Its ancestor, the prehistoric megalodon or megatooth,
24:55 had a bite force strong enough to crush a car.
24:58 Some sharks can launch their jaws out of their mouths
25:03 like a jack-in-the-box,
25:05 and they sink their teeth into more than prey.
25:09 Courtship rituals involve biting too.
25:14 Male sharks hold onto females with their teeth,
25:18 leaving behind scars long after mating has ended.
25:23 Sharks are protected by thousands of tiny tooth-like scales
25:32 called dermal denticles, which also reduce drag,
25:36 making sharks faster and quieter.
25:38 Beneath this suit of armor,
25:43 their skeletons are made of cartilage,
25:45 much like human ears and noses.
25:47 - You might be thinking,
25:50 "Well, cartilage doesn't seem like such a great deal,"
25:52 but it's so much less dense than bone
25:55 that allows sharks to be pretty much close
25:57 to neutrally buoyant in some respects,
26:00 which makes them really efficient swimmers.
26:03 - The shark uses its pointed fins to maneuver quickly.
26:11 (water splashing)
26:14 Its dorsal fin, which stirs primal fear in so many,
26:18 actually serves a mundane, almost comical purpose.
26:22 It prevents the shark from log rolling in the water.
26:26 They stiffen their tails mid-swing
26:32 to create twice as many jets of water
26:35 as the tails of other fish,
26:37 making sharks almost impossible to out-swim.
26:40 When hunting fast prey,
26:46 a 2,000-pound white shark can swim 40 miles an hour
26:50 and launch itself 10 feet into the air.
26:54 But there is a shark faster than the great white.
26:59 The shortfin mako shark can accelerate quicker
27:05 than a sports car and reach speeds of 60 miles an hour
27:08 when closing in on prey.
27:10 By comparison, the walking sharks of Indonesia
27:22 live life in the slow lane,
27:24 using their pelvic fins as feet
27:26 to amble across the sea floor.
27:34 This spectrum of speed epitomizes
27:36 how the bodies of sharks are tailored
27:38 to suit their prey and their environments.
27:41 Power and strength are unifying traits,
27:49 but beyond brute force,
27:52 sharks are armed with an arsenal of super senses.
27:55 Each requires perceptive abilities to be processed
28:00 and can be tied to intelligence.
28:03 (wind blowing)
28:06 When hunting, sharks rely on a hierarchy
28:10 of sophisticated faculties.
28:12 From a distance, they count on smell.
28:16 Then as they hone in for the kill,
28:20 sharks hear, see, and feel their prey.
28:23 Smell is a shark's primary asset.
28:29 It can detect the scent of prey
28:31 more than half a mile away
28:33 and sniff out a single drop of blood
28:37 in 25 million drops of seawater,
28:40 equivalent to a teaspoon of blood
28:43 in an Olympic-sized swimming pool.
28:45 Not only can sharks detect a faraway scent,
28:49 they can process that information
28:51 to zero in on where it's coming from.
28:53 They know which nostril receives an enticing odor first,
28:58 then follow their noses when something smells fishy.
29:01 As sharks dial in on their prey,
29:08 an acute sense of hearing is next
29:10 in the sensory chain of command.
29:12 They can hear prey from distances of more than 800 feet.
29:19 That's more than the length of two football fields.
29:22 Sharks lack external ears,
29:28 a system of hairline tubes under the skin
29:30 makes their bodies sensitive to vibrations
29:33 caused by sound or movement in the water.
29:36 They can actually feel when an animal is in distress.
29:42 As they draw nearer to their target,
29:50 sharks rely on keen eyesight.
29:56 They can't see as well as they smell or hear,
29:59 but vision is still an integral part
30:01 of the hunting toolkit.
30:02 A layer behind the retina allows extra light
30:07 into their eyes and enables sharks
30:10 to see in dark, murky water.
30:12 Like cats, sharks have a mirror-like layer
30:17 of crystals in the back of the eye
30:19 that boosts the intensity of light,
30:21 helping this species, called a prickly shark,
30:24 to see in deep, dark water.
30:27 With eyes set on opposite sides of the head,
30:33 hammerhead sharks have panoramic binocular vision.
30:36 They can see nearly 360 degrees,
30:41 but not what's directly in front of their snout.
30:44 To counterbalance this blind spot,
30:47 hammerheads rely on an extraordinary sixth sense
30:50 called electroreception,
30:53 crucial at the last second
30:55 when prey is literally under their nose.
30:58 - They have pores along their snout
31:01 and also a little bit around the jaws,
31:03 jelly-filled pores that are called
31:05 the ampullae of Lorenzini.
31:07 The jelly that's in the pores conducts electricity
31:11 and those pores are attached to neurons,
31:13 so then sharks can actually find prey
31:15 that are hidden beneath the sand or the mud
31:17 and sort of use that sense to find prey
31:19 that are generally more close.
31:23 - All sharks use electroreception,
31:25 but the great hammerhead in particular is a master.
31:30 Its wide head works like a metal detector,
31:33 sweeping over the bottom to detect stingrays
31:36 buried in the sand.
31:37 Even when an animal is impossible to see,
31:42 the shark is aware of its presence.
31:45 It's a predator from which you cannot hide.
31:51 Sharks are planted at the top of the ocean food chain
31:55 due to their powerful bodies and sharp senses.
31:58 Just as essential is the shark's brain,
32:03 the command center that processes data
32:06 delivered by its suite of super senses.
32:09 The shark's brain may be small in relation to its size,
32:14 but it's surprisingly efficient and complex.
32:18 - They have a quite developed cerebellum
32:20 and cerebellum is used for orientation,
32:22 for movement and all that.
32:24 Hammerheads are the masters of orientation and movement
32:26 'cause they have a big head that works as an antenna.
32:29 And sharks in general are very sensible to electric fields.
32:34 And hammerheads are the most sensible of all sharks.
32:38 They're quite complex and it's been studied
32:41 that hammerheads are the PhD of the sharks
32:45 'cause they have one of the most developed brains
32:47 of all sharks.
32:48 (wind whooshing)
32:51 - How sharks hunt and the prey they pursue
32:56 have a tangible effect on their brain anatomy.
33:00 Sharks that track seals and sea lions,
33:02 like these white sharks at Guadalupe Island, Mexico,
33:06 require greater motor control and have larger cerebellum.
33:10 Over time, seal hunting has caused the cerebellum to enlarge
33:17 so the behavior of sharks informs how their brains evolve.
33:21 That's why plankton feeders, like whale sharks,
33:28 have smaller brains.
33:30 They need less brain power than active hunters
33:33 like the great whites.
33:34 Filtering a meal out of the ocean requires less thought
33:38 than planning and executing an attack.
33:41 - One of the ways that we try to gauge
33:43 how much sort of processing power an animal has
33:47 is by comparing the size of its brain
33:49 to the size of the body.
33:51 And one of the things we know about sharks
33:52 is that their brain size to body size ratio is very high.
33:56 Now we think a lot of that is tied up
33:58 in the ability of sharks to be able to interpret
34:03 and integrate all the sensory stimuli that they get
34:06 from having so many senses.
34:08 But we also know that a good deal of that
34:12 brain processing power is involved
34:14 in filtering out that stimuli,
34:17 identifying threats and prey and mates.
34:19 And a big component could be sharks' abilities
34:22 to remember where they are
34:24 and how they need to get around to find prey and mates,
34:27 all the good things in life.
34:28 - It takes considerable computing power
34:32 to receive and analyze the data
34:34 that continuously streams through a shark's sensory organs.
34:38 Not only does the brain process
34:43 a huge amount of information,
34:45 it's able to quickly sift through the data
34:47 to decide if something is a threat,
34:49 a prey,
34:52 or neither.
34:54 The ability to interpret data demonstrates
35:00 that sharks pack a lot of brain power into a compact space,
35:04 more proof of their sharp and efficient design.
35:07 Sharks have a similar brain structure to their cousins,
35:15 the manta rays,
35:16 essentially a flattened shark
35:19 with internal anatomy similar to its more streamlined kin.
35:23 Sharks and rays are among the oldest fish species on earth.
35:30 They share a common ancestor that existed
35:34 long before the first dinosaur.
35:36 Like sharks, rays detect electrical impulses
35:41 through jelly-filled pores in their heads.
35:44 (wind blowing)
35:47 Unlike sharks, rays have the largest
35:52 brain-to-body mass ratio of any fish species.
35:56 Their forebrain, responsible for learning and memory,
35:59 is supersized.
36:00 Manta rays are highly social and curious about humans.
36:09 - I think the first thing that surprised me,
36:13 how self-aware they are,
36:14 which very few animals are, like dolphins or monkeys,
36:18 they actually love camera domes
36:20 and they come to see themselves
36:21 'cause they see themselves in the dome of the camera.
36:24 When you look at them, you start realizing
36:26 they can recognize certain dive guides.
36:28 They will go over a dive group
36:29 and go straight for the dive guide.
36:31 They will play with divers when it's not too crowded.
36:34 You can see it's an intelligent animal,
36:36 like a dog or a cat, and they can learn.
36:38 (wind blowing)
36:41 - Mantas entangled in fishing nets,
36:45 or pierced with hooks, will approach boats,
36:48 then wait patiently as divers free them
36:51 or remove fishing gear lodged into their flesh.
36:54 Even more amazing, rescued mantas
36:59 have been known to swim next to divers,
37:01 then follow them back to their boats,
37:03 continuing the interplay with their rescuers.
37:07 (wind blowing)
37:10 Sharks may not be as cognitively complex
37:12 as their manta ray cousins,
37:14 but they too continue to surprise.
37:17 They're among the oldest living species on earth,
37:21 yet their hunting techniques are hardly primitive.
37:24 (upbeat music)
37:28 Sharks don't merely sense prey nearby and attack randomly.
37:36 (upbeat music)
37:37 They require a lot of food to sustain themselves
37:41 and must be energy efficient hunters.
37:43 A great white eats more than a ton of food each year.
37:50 Studies have found that great whites
37:55 have individual prey-specific hunting strategies.
37:59 They've learned to attack elephant seals from behind
38:05 to avoid knife-like claws
38:07 that can leave deep and painful wounds.
38:09 The sharks take a bite,
38:14 then retreat to let the seal bleed out and avoid a struggle.
38:18 When hunting seals and sea lions,
38:22 great whites rely on stealth and ambush strategies.
38:25 They stalk prey from hidden depths,
38:29 then rocket up from below.
38:34 The timing and location of seal attacks is also strategic.
38:38 Sharks usually hunt them around sunrise when light is low.
38:43 At that time, the silhouette of the seal
38:47 is easier for sharks to see above,
38:49 and the dark water makes it harder for seals
38:52 to see sharks below.
38:53 In South Africa, sharks patrol for long periods
39:00 before sneak attacking seals sunbathing on the rocks.
39:04 (dramatic music)
39:07 Great whites target prey selectively.
39:09 At Guadalupe Island,
39:13 they ignore the large tuna and jacks
39:15 that swim in their path.
39:16 They're focused on seals and sea lions,
39:20 marine mammals that yield more caloric bang for the buck.
39:24 When hunting schooling fish,
39:29 they pick off the weakest, sickest, and slowest prey.
39:34 Not only is this easier for the shark,
39:36 it also helps prevent the spread of disease
39:38 and strengthens the gene pool of the fish,
39:41 making sharks evolution's invisible hand.
39:44 They learn from past failed strategies
39:48 and adjust their techniques accordingly.
39:50 This adaptive behavior
39:54 is more evidence of their intelligence.
39:56 (water splashing)
40:03 - I think that they are very smart.
40:05 When you come here and when you throw the bait,
40:07 they never get the bait at the first moment.
40:11 They always look around.
40:13 They are very inquisitive.
40:14 They come closer until they are very sure
40:16 that it's a possible food item.
40:19 It's when they get closer, they get it.
40:21 But also, they are all different.
40:22 They have different personalities.
40:24 Most of them are very cautious.
40:26 They do not come very close easy,
40:28 but some of them do that.
40:30 In one day, we had a female
40:32 and she took eight baits from one boat.
40:35 And then she came to my boat
40:36 and she took the bait from my boat.
40:37 So she took nine baits in one day
40:39 because she learned that it was easier
40:41 if she could come from behind and from underneath fast.
40:45 And they can get like 40 kilometers per hour.
40:47 So that female in particular was very smart
40:49 and she took a lot of baits.
40:51 But most of them are very inquisitive
40:54 and they take their time.
40:55 - Just like humans,
40:59 some sharks are smarter and quicker witted than others.
41:02 They use different hunting strategies
41:07 based on circumstance
41:08 and what they've learned works best.
41:11 There's no rule book.
41:14 - They're very unpredictable animals.
41:17 If you see a school of fish,
41:18 you see them kind of predictably moving certain directions.
41:21 Sharks are not like that.
41:22 They're unpredictable.
41:23 'Cause most of them are top predators.
41:26 So that's their nature, to be unpredictable.
41:28 And that way they're efficient in hunting.
41:30 - These unpredictable techniques keep prey on their toes.
41:37 Hidden hunters like Wobbegon sharks lie low in weight,
41:46 often partially buried and camouflaged on the ocean floor.
41:49 They won't make a move unless a prey comes very close.
41:58 Bottom hunters like nurse sharks lack the speed
42:01 and stamina to chase prey.
42:05 Instead, they cruise above the bottom
42:08 in search of resting crustaceans.
42:10 Filter feeders like whale sharks
42:18 target plankton and small fish.
42:20 Giant gulps at the surface draw water into the mouth,
42:26 suctioning in plankton.
42:28 Pads that cover the entrance of the throat
42:31 filter the plankton.
42:33 A single shark can filter more than 160,000 gallons
42:38 of water per hour.
42:40 In just four hours, it can filter enough water
42:44 to fill an Olympic-sized swimming pool.
42:46 At Costa Rica's Cocos Island,
42:56 white tip reef sharks prefer to hunt in packs and at night,
43:01 poking their heads into crevices on the reef
43:03 to flush out resting fish.
43:05 Efficient hunting strategies have made sharks
43:10 the most successful predators in the ocean,
43:13 but not the most successful on the planet.
43:16 One third of all sharks are threatened by overfishing.
43:23 (waves crashing)
43:26 For every human killed by a shark,
43:32 humans kill two million sharks.
43:35 As a result, about 100 million sharks are killed each year.
43:42 That's 11,000 sharks per hour.
43:46 Most are killed for their fins, used in shark fin soup,
43:52 or as bycatch in nets meant to snare other marine life.
43:57 Great white sharks take between nine and 16 years
44:03 to reach maturity.
44:05 Females give birth to just two to 10 pups
44:08 every two or three years.
44:10 This slow climb to maturity makes white sharks vulnerable
44:16 to even moderate levels of fishing.
44:18 (dramatic music)
44:21 Sharks simply can't replenish themselves
44:24 at the rate they're being fished and killed.
44:26 Habitat loss also poses danger for sharks,
44:33 as nets are cast to protect swimmers and surfers at beaches.
44:37 - We don't fully understand what is gonna happen
44:41 to the oceans when you remove these top predators.
44:43 And I think by the time that it's fully understood,
44:47 it's gonna be because it's reached that tipping point,
44:49 and then it might be a matter of looking back and saying,
44:51 oh, we've overfished them, you know,
44:53 we've killed too many in nets or drum lines
44:56 or from shark finning and things like that.
44:58 - In spite of the destruction caused by some humans,
45:04 others work to discover just how smart these predators are,
45:08 to demonstrate that they're worth saving.
45:11 The evidence they've uncovered reveals
45:16 that sharks are intelligent and operate at a much higher
45:20 and more nuanced level than we believed.
45:22 They're not mindless eating machines,
45:27 ruthlessly pursuing their next meal by instinct alone.
45:30 To outwit their prey, they must operate
45:35 on an intellectual level, higher than ordinary fish.
45:43 They're efficient hunters with an innate curiosity
45:46 that's been mistaken for savagery.
45:49 - A lot of TV shows make sharks out to be
45:52 particularly voracious and malicious.
45:55 And actually, I would argue that they have no maliciousness.
46:00 They're a predator just like anything else,
46:03 like a lion or a bear.
46:06 And I think the thing that really terrifies people
46:08 about sharks is, for the most part,
46:10 a lot of those terrestrial predators we've exterminated.
46:15 So you might be able to see a lion in a game park in Africa,
46:20 and cougars might be around in the mountains.
46:22 But for the most part, we've eliminated the influence
46:27 of these large, scary things with big teeth
46:30 in our day-to-day lives.
46:32 And the thing that we haven't really done that to yet
46:34 is sharks.
46:38 - Sharks engage in elaborate social behaviors,
46:41 have distinct personalities, and create social networks.
46:48 They're pillars of evolution that have existed
46:53 100 times longer than humans.
46:56 Yet their true nature is only just being revealed.
47:05 Ongoing exploration promises even greater discoveries
47:10 as scientists aspire to once and for all
47:13 solve this undersea mystery.
47:16 How smart are sharks?