脆弱天堂 09

Sharks have been top dog in the Pacific for millions of years.

They control the numbers of other fish

And so play a vital role in keeping the underwater ecosystem healthy and diverse.

In French Polynesia, grey reef sharks gather.

While scalloped hammerheads patrol the Galapagos Islands

These are rare hot spots where sharks converge in large numbers.

But divers claim this is just a fraction of the number of sharks they used to see.

Many sharks are ocean migrants

Travelling hundreds of miles in search of prey

Like the oceanic whitetip.

Amazingly, this may once have been the most abundant large animal on the planet.

But it's fallen prey to fishermen's hooks and nets.

Surveys suggest oceanic whitetips may have declined by a staggering 99%.

It's like the disappearance of bison from America's Great Plains

Yet it's only happened in the past 50 years

And almost no one has noticed.

Incredibly, the world's oceans may have lost more than 90%

of their large predatory fish since industrialised fishing began.