Observer: Three decades have passed since the movie Jaws sent terrified bathers scrambling out of the ocean. But as any beach lifeguard knows, there’s still nothing like a gory shark attack to stoke public hysteria and paranoia. Two deaths in the waters off California and Mexico last week and a spate of shark-inflicted injuries to surfers off Florida’s Atlantic coast have left beachgoers seeking an explanation for a sudden surge in the number of strikes. In the first four months of this …