Galapagos: Realm of Giant Sharks Page #3

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place satellite tracking tags

into their skin.

But if startled, a whale shark is

capable of moving swiftly out of reach.

At full size, a whale shark is powerful

and potentially dangerous.

If the approach is not just right,

or the tag inserted too deeply,

the response can be violent.

In the first of three expeditions to

Darwin Island, Jonathan

Green and his team

managed to tag 14 whale sharks.

To get reliable results, the team needs

at least twice that number.

So they are making the 30-hour

journey again on a small

but trusty expedition boat,

the Queen Mabel.

It's the heart of the cool season, and

the boat is carried along by north-bound

swells generated by a

current that flows from

Antarctica up the coast

of South America.

On his journey to the

Galapagos Islands, Charles

Darwin noted 'the

singularly low temperature

of the surrounding water, brought here

by the great southern Polar current.'

For thousands of humpback

and other whales,

it offers a free ride north from

summer feeding grounds off Antarctica.

The Humboldt current is thought to have

transported many of the unique creatures

that Darwin observed on these islands.

From the mainland, giant tortoises were

probably washed into the sea by storms.

The current carried them

across the thousand kilometers

of ocean to reach the Galapagos.

They gradually dispersed among the

islands, each one a world unto itself.

Down through the generations,

the tortoises adapted

to unique local conditions

and developed differences,

especially in their shells.

Iguanas most likely arrived

on rafts of vegetation.

Once here, they adapted to feeding

within intertidal zones.

It's in the sea that the Humboldt

current has had its greatest impact.

You can see its fertile wake in a

satellite image tracking chlorophyl,

a tracer for plankton blooms.

In combination with

west-bound trade winds,

it causes deep nutrient-rich water

to well up along the

South-American coast,

turning it into one of the world's

most productive fisheries.

Rising up onto the Galapagos plateau,

the Humboldt mixes with the cool

waters of the Cromwell Current,

surging in from the Pacific,

and with warmer currents moving

down from the equator.

That combination sets off an

explosion of sea life.

Manta rays arrive to

sift the upper levels

of the ocean for microscopic plankton.

When conditions are right,

sardines, anchovies,

mackerel and other bait

fish fill the seas.

That can attract

legions of striped marlin

from around the region and beyond.

Watching for a school to

be caught out in the open,

these swift predators

dart up from below.

The school closes ranks,

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