NARRATOR: It's been building for years.
But now the invasion begins.
Despite the increasing numbers of sharks in the water,
a select few fishermen will go one
step further to bag a once-in-a-lifetime trophy fish.
While fishing from a boat is safer,
it does not guarantee a successful catch.
But fishing in the water gets your eyes on the prize.
And the bigger the risk, the bigger the reward.
When spear fishermen get wind of Ascension's giant fish,
it doesn't take long before flights fill up
and the fishing tourism expands into spear fishing.
Everyone wants a piece of Ascension's bounty.
And believe it or not, some are crazy enough to compete
with sharks to get it.
If the fishermen had begun to ring Pavlov's bell,
the spear fisherman turned it into a sounding gong.
Spearfishing is a very attractive activity for sharks.
First of all, you have the sound associated with a spear gun
hitting the fish.
And then you have highly irregular activity probably
from the speared animal.
On top of that, it's going to be bleeding.
And so all of those things go to the brain of a shark--
the sound, the smell, the sight--
is a perfect storm for a shark to get
multiple signals coming into the brain
that says there's a meal here.
NARRATOR: Spear fishermen also don't use bait or lures.
The only way they can attract big game fish
is to chum on a large scale.
Blocks of chum are deployed at dive sites.
This mega chumming has a profound effect
on the big tuna and wahoo.
But with them come the sharks.
They brought all those sardines
here and attracted the fish.
And of course, it attracted the sharks too.
And that's what started the whole thing.
The sardines, when they were imported here,
was just brought as an attractant.
And because they have a lot of oil content
and it's very strong, that is what attracted
the shark, in my opinion.
That was why all the sharks came here.
NARRATOR: An experienced spear fisherman
knows how clever a shark is.
With enough sardines to eat, the sharks leave the divers be.
They're only here for a meal of sardines,
and they need surprisingly few of them.
Most people think that sharks need to eat great chunks
of flesh to survive.
But just two pounds of oily fish packed with protein and omega 3
will fill these hungry requiem sharks for a week.
And they don't have to waste any energy chasing this meal down.
Suddenly, the sharks of Ascension
have a novel and high energy food source on tap.
When you get a free meal, that's where you'll go.
Everybody does that.
Sharks have always come here, but they never stay quite
as much as the last two years.
They came and they stayed.
And I think that interference by man
caused that interruption to nature.