Far and away, the greatest threat to the ocean, and thus to ourselves, is ignorance. But we can do something about that.

Ten percent of the big fish still remain. There are still some blue whales. There are still some krill in Antarctica. There are a few oysters in Chesapeake Bay. Half the coral reefs are still in pretty good shape, a jeweled belt around the middle of the planet. There's still time, but not a lot, to turn things around.

The Arctic is a place that historically, during all preceding human history, has largely been an icy realm with an impact on ocean currents. That, in turn, influences the temperature of the planet. The Arctic is now vulnerable because of the excess carbon dioxide in the atmosphere, with a rate of melting that is stunning.

Even our rules and regulations, our laws, our policies, favor the destructive nature of taking too much from the ocean and using techniques that are horribly destructive. We know they don't work. We know it's not sustainable.

We have been far too aggressive about extracting ocean wildlife, not appreciating that there are limits and even points of no return.

With knowing comes caring.

Sharks are beautiful animals, and if you're lucky enough to see lots of them, that means that you're in a healthy ocean. You should be afraid if you are in the ocean and don't see sharks.