Yeah, I'm more with WolfofLon here. Sharks play a huge roll in the ecosystem, as they are pretty much at the top of the food chain in just about every water environment out there.
I remember watching this show on the National Geographic channel. There was one area, I forget where, that had a shark that was legendary for its size. The thing was a great white, like 25 feet long. So some deep sea fishers decided to go catch it. They were successful, but they later realized that one shark single-handedly (or singled-fin'edly) kept the local seal population under control. After the shark was killed, the seal population skyrocketed the next few years.
Just goes to show how delecate the ecosystem can be.