A federal bill would ban Florida shark dive operators from feeding sharks. Its sponsors say the ban is about safety. People who know the water, including fishers, doubt it would change much.By Kate WaxmanFifteen, 20, 30 feet down, a crate of dead fish hung in the water five miles off of Jupiter, Florida’s coastline, and the sharks rode up and down with it. Every so often, Tanner Mansell would reach into the crate, pull out a fish head and wave it through the water, and the sharks would follow.