Globally sharks have been killed for their fins, for their cartilage, for their livers, for their meat. But mostly what has driven some species of sharks to near extinction - including the hammerhead shark - is the new luxury taste for shark fin soup.

We are taking way more out of the ocean than the ocean can replenish.

There is this sweet spot in time when we have an opportunity to stop killing sharks and tunas and swordfish and other wildlife in the sea before it's too late.

Some experts look at global warming, increased world temperature, as the critical tipping point that is causing a crash in coral reef health around the world. And there's no question that it is a factor, but it's preceded by the loss of resilience and degradation.

I personally have stopped eating seafood.

What we put into the atmosphere in terms of burning fuel is unprecedented.

Since I began exploring the ocean in the 1950s, 90 percent of the big fish have been stripped away. Tuna, sharks, swordfish, cod, halibut, you name it, the numbers have just collapsed. Also, about half of the coral reefs are gone, globally, from where they were just a few decades ago.