Galapagos: Realm of Giant Sharks Page #3

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We find huge variations

in currents. Daily

you can have very low

current when you dive

first thing in the morning, 6:30 AM,

virtually no current.

By mid-day, you've got a howling

current going through.

What we've had here is not only

a complete change in direction,

but the strength seems to be

going up and down.

This morning when we jumped in,

we had something

probably around

a five-knot current, and that

simply becomes unworkable at that point.

Not only unworkable, but dangerous

because of the fact

that you've got divers

then that may be swept away from

the area that we're working in

and taken out into the

very rough ocean beyond.

Narrator:
The next day,

Jonathan is eager to know

whether the tags

they set are on securely.

Jonathan Green:
Do you have any data

on that, anything new?

Narrator:
He calls Alex Hearn, who

is monitoring the satellite signals

from the University of

California at Davis.

Jonathan Green:
Conditions that are not

too good. We've got a southerly current.

We put the two tags on, but we just

need to know if they're on the surface,

or if you have any data

that might show what

they're doing, if the

tags are still on, yeah.

Okay, you do. 1-0-7.

Okay, fantastic, fantastic.

Narrator:
One of the tagged sharks

has surfaced 40 kilometers North

and West of Darwin Island.

It's following the same route taken

by Jaws and Kimberley.

Are these sharks following the flow of

food driven by the Humboldt current,

or are they pursuing

some other imperative?

Consider their response to conditions

below Darwin's Arch.

As deep currents hit

the island, they carry

a flood of nutrients to the surface.

As a result, the rocky

reefs beneath the arch

are enveloped by

what one biologist called,

"a Great Wall of Mouths."

Everything from microscopic zoo-plankton

to schools of fish.

Moving through them are predators

such as sharks, and jacks,

along with those giant filter feeders,

the whale sharks.

And yet, even as they encounter

enormous schools

of small fish and dense plankton,

they keep their mouths shut tight.

There must be another reason

they are coming here.

Jonathan Green:
We know that they are

coming here for a specific reason,

but it's got to be something important

enough that we see literally

hundreds of whale sharks

in an area like the

Darwin Arch during the season.

And we don't see

whale sharks anywhere else

in the Galapagos Archipelago,

so they're coming to Darwin's Arch

for a specific reason.

I still think that

the Whale Sharks are

coming here for birthing.

One thing that just

about all the females,

the big female whale

sharks have in common

is that they're pregnant, they

seem to be in an advanced

stage of pregnancy, and so

we think that they are probably

birthing down at depth.

Alex Hearn:
There's a steady trickle

of sharks coming through.

Why aren't they all coming at once,

you know? Are they coming

when they're ready to come perhaps?

I suspect that there's an internal

clock that's telling them it's time

to move up to Darwin, and then,

out to wherever it is that

they're giving birth.

Narrator:
If not in the deep

channels surrounding

Darwin Island, then perhaps these

females are giving birth out in the

Galapagos rift zone to the north.

This region took shape

millions of years ago,

when titanic sections of the Earth's

crust began pulling apart.

The undersea terrain is lined

with ridges and sea-mounts,

and hydrothermal vents that attract

a variety of deep ocean creatures.

The nooks and crannies of the ocean

bottom could offer

could offer myriad safe havens for

infant whale sharks to grow.

Where and when the females give birth

is just one of the mysteries of

whale shark reproduction.

A single pregnant female

captured by fishermen in Taiwan

offered some remarkable clues.

Scientists moved in quickly to

dissect the shark.

They found that she was

carrying 300 offspring.

They represented all

stages of development,

from tiny embryos to

pups ready to be born.

That's not all - Genetic tests

showed that each of

the offspring was fathered

by the same male.

The female had been able

to maximize an encounter with this

male, by storing up his semen,

then using it over time

to fertilize her eggs.

This may be an adaptation to lives spent

traveling alone over long distances.

One of the longest documented

whale shark journeys, was made by

a mature female named Rio Lady.

She was tagged off Mexico's Yucatan

Peninsula in the year 2007

by researchers from Florida's Mote

Marine Lab and Mexico's Domino Project.

They watched as she headed over

to the coast of Cuba,

then turned south into the Caribbean.

Past Jamaica, she turned and swam

straight for the Atlantic Ocean.

Moving out to the middle of the

Atlantic, Rio Lady crossed the equator.

That's where her tag

stopped transmitting,

after a journey of more

than 7,000 kilometers.

But that wasn't the end of Rio Lady.

Four years later, scientists

photographed her back off

the Yucatan, identifying

her by her spots.

She had returned as part of the largest

known gathering of whale sharks,

with hundreds arriving to feed on

eggs spawned by a type of tuna.

If Rio Lady's story is any indication,

whale sharks swim with a purpose,

with clear routes and destinations.

How do they navigate the featureless

and murky depths of the ocean,

to reach places like the

Yucatan or Darwin's arch?

The answer may lie in another shark

species:
The scalloped hammerhead.

For the last decade, Alex Hearn,

from the University of California

at Davis, has been

spearheading an effort

to track the movement of hammerheads and

other sharks throughout the region.

It's part of a much larger effort by

the Galapagos National Park

to understand the role

these islands play in

the survival of migratory

marine species.

This team's goal is to find out where

various shark populations go,

what routes they use, and

how far they travel.

The study centers on a series

of 'listening stations, '

set up all around the

archipelago in conjunction

with the Charles Darwin Foundation.

Placed in shallow water, the stations

record high frequency beeps,

emitted by tags that have been

placed on the sharks.

Attaching a tag to a hammerhead

is a special skill.

The noise from scuba tanks is

known to scare them off,

so team members must free dive

down to get close.

The object:
To jab the tag into the

muscle on the shark's back.

The tags usually fall

off after about a year.

The data shows that while hammerheads

travel throughout the region,

they congregate in large numbers only

where strong south currents sweep the

edges of Darwin and nearby Wolf island.

It's a remarkable sight,

considering that these strange

creatures were practically

fished out of here in the mid 1990's.

Their population surged again

with protections offered by

the Galapagos Marine Reserve,

established in 1998.

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