[dramatic music]
NARRATOR: Along a roughly 25-mile stretch of shore,
there have been more than 60 shark
attacks since records began and almost half of them fatal.
In fact, this small area accounts for almost 50%
of recorded attacks in the entire continent.
As a result, it's earned a chilling designation as South
America's deadliest coastline.
[water splashes]
ANDRE AFONSO: In Recife, the shark
attack problem is very serious.
It's probably one of the most dangerous cities
in the world for having a swim.
NARRATOR: Residents are at their wits end.
I want to know why it happens here and always here.
NARRATOR: In an attempt to prevent further attacks,
authorities banned surfing in certain areas,
and signs line the beaches warning of the dangers
of entering the ocean.
But the only real way to stop this bloody barrage
is to figure out how it started.
FABIO HAZIN: It's absolutely crucial
to find the cause of the problem because, if we don't, we
can't build a solution.
NARRATOR: So what's driving this terrifying onslaught
along with Recife's shores?
And could other coastal resorts be next?
According to former instructor Fernando Clark,
something makes diving in this area unique.
And it hides deep beneath the waves.
Recife is the shipwrecked capital off Brazil.
NARRATOR: The area around the attack zone
is home to dozens of sunken vessels, some
dating as far back as the 16th century.
But according to Clark, these ill-fated ships are
more than just rusty relics.
FERNANDO CLARK: The shipwrecks become a reef
completely full of marine life.
NARRATOR: Fish, crustaceans, and mollusks
call these down vessels home.
But it's what these marine inhabitants attract that could
be problematic for people.
FERNANDO CLARK: When you go shipwreck diving here,
most of the time we see a lot of sharks.
NARRATOR: The presence of sharks near shipwrecks
is a phenomenon that can be seen elsewhere too.
In the US, sunken vessels along the shores
of Oregon, Florida, and North Carolina
are inhabited by these predators.
The sharks are attracted to the shipwreck
because of the food.
NARRATOR: So could the wrecks of Recife
be responsible for luring dangerous predators
near shore where people are?
Clark says the answer comes down to the species of shark
he sees most often on his dives.
To demonstrate, he plunges into the shark-infested waters.
[water splashes]
[gentle music]
Before long, he spots just what he's looking for--
nurse sharks.
[energetic music]
Nurse sharks are bottom dwellers,
attracted to the crustaceans inhabiting
Recife's sunken ships.
Measuring up to 9 feet, they possess powerful jaws
with serrated teeth.
And, worldwide, they have been implicated
in multiple attacks on humans.
So could nurse sharks be responsible for Recife's spike?
Dr. Fabio Hazin is one of the lead investigators
trying to get to the bottom of what's
happening along this coast.
And when he analyzes the details of each incident,
he comes to an important conclusion.
FABIO HAZIN: Nobody in Recife has ever reported being
attacked by the nurse shark.
So the shipwrecks are not at all to blame for the attacks.
NARRATOR: Instead, Hazin's analysis points
to two other suspects, both of which
have reputations for attacking humans.
The first one is tiger sharks.
NARRATOR: Tiger sharks can grow up to 18 feet in length
and weigh in at 1,400 pounds.
Known for their undiscerning palates,
they're equipped with sharp, serrated teeth
that allow them to rip through seabirds,
turtles, and even people.
[dramatic music]
Perhaps even more imposing is the other culprit
Hazin implicates in the spike.
And that is bull sharks.
[energetic music]
NARRATOR: Bull sharks bite with the most force pound
for pound of any large shark.
They are fast and aggressive.
And they're often found in the same shallow coastal waters
as humans.
So it appears tigers and bulls may
be responsible for the spike.
The question is, why?