The whale's flukes are lifted out of the water and, the non-buoyed weight helps to propel the whale down on a deep dive that may last between ten and twenty minutes.     Notice the "fluke-print" below - it's the smooth area of water in front of the flukes. The fluke-print is caused by the whale propelling itself below the surface.  By imagining a line between several fluke-prints, you can predict where the whale will surface.