NARRATOR: If tiger sharks are showing up
in the shallows in greater numbers,
then it's not because of deep blue.
The reason for the attacks remains elusive.
But while scouring the ocean for an explanation,
experts come across something else
that also ensnares large amounts of a tiger shark's prey.
But it's not another sea creature.
In fact, it walks on two legs.
NAIA RAE FOX: I think the reason why we are having more sharks
here actually is because the amount of fishing
that's been going on.
NARRATOR: This is one of the island's most popular
activities, sport fishing.
Every year, recreational anglers haul in more
than 2 million pounds of fish.
That means that on any given day off the big island,
there are hundreds of fish being caught and reeled in.
And for scientists like Dr. Dan Huber,
these hooked sea creatures may be attracting sharks.
DAN HUBLER: A struggling fish, as its body
is twitching a bit, that motion is giving
off low frequency sounds.
And shark hearing happens to be tuned
into low frequency sounds.
This is definitely something that could attract a number
of sharks to the same area.
NARRATOR: So could sport fishing be drawing tiger sharks
into the shallows, thereby increasing
the risk of an accidental run in with people?
According to fisherman Rick Rieger,
it comes down to where the best sport fishing takes place.
To demonstrate, he heads out to an area well
known for the popular pastime.
RICK RIEGER: So this is our bottom here.
We have some of the steepest drop offs
in the whole world right here.
This is where you're going to see your tuna, your mahi-mahi,
your ono, your marlin.
NARRATOR: This location could hold a vital clue
to solving the mystery.
Called the pelagic zone, this open water
abyss extends thousands of miles between
the continental shelves.
It's home to an array of large sea creatures--
whales, manta rays, big game fish, and some of the most
dangerous sharks on earth.