I am dropping down into Belize's Blue Hole letting my body free fall past a rugged wall into cooler clearer waters until a large cavern appears and the dive master who has been drifting below me puts his flat hand to his head - the signal for shark. I look around and fail to see one. We hold up at 145 feet and enter the cavern, swimming around huge column-thick stalactites in what was once a massive underwater cave complex before the roof collapsed. After eight minutes of exploring this saltwater Howe Caverns it's time to return to the surface, which is why they call it a "bounce dive." At this depth you don't have much playtime before the nitrogen builds up in your tissue threatening you with the bends.

Our group halts at 90 feet, gathering on a sandy ledge as the dive master points up. Forty feet above us half a dozen large Caribbean reef and bull sharks are circling. Soon I notice a couple more cruising below me. We begin making our way towards the surface along an underwater dune as a dozen of the curious 6-7 foot sharks slide past within two yards of us. Unlike shallow-water nurse or leopard sharks that are docile enough to approach, no one attempts to approach these big fellas. Bull sharks are the species responsible for more human deaths than any other. Churning bubbles and adrenalin I'm reminded of a saying by naturalist author Ed Abbey, "If there's not something bigger and meaner than you are out there it's not really wilderness.

Still the odds are unfairly stacked. Every year about 5-7 humans are killed worldwide by sharks while we kill over 100 million of these sleek, slow-growing top predators, mostly for their fins that are used in a tasteless but expensive cartilage soup popular in Asia.

Number 39 in my book 50 Ways to Save the Ocean (illustrated by Sherman's own Jim Toomey) is titled, "Don't Exploit Sea Creatures for Vanity's Sake." It notes that along with Shark Fin Soup in China, shark meat and dietary supplements like Shark Liver oil and shark cartilage are popular in the West. But any useful nutrients such as vitamin A, found in a shark's liver can also be had by eating dark green vegetables. And unlike the real-life Shermans of the sea, Spinach and Kale are not threatened with extinction by the vanity, greed and ignorance of "hairless beach apes," as our species is known on the comic pages.

To find out more, buy a copy of 50 Ways to Save the Ocean or go to our Blue Frontier Campaign website, which also has a directory of over 1,500 marine activist groups around the United States working to protect sharks and other marine wildlife and to restore our magnificent public coasts and oceans from sea to shining sea.

David Helvarg