Terrapin, and the whistle is screaming

I am walking down miles of sand where I reach the tallest dunes in view.  I climb them and it gives me a view of a vast beach where there are giant sea turtles, six feet tall and ten long, their craggy shells covered with 6 to a dozen children who are hollering with joy at the ride.  But as I near I see the fear in the kids faces and realize they are screaming.  Somehow being held captive on the backs of these turtles and being hauled into the ocean.

But one of the turtles shells has suddenly been wiped clean of children and I see my uncle [an avid sportsman who makes his own arrows for bowhunting] leaping on the back of a turtle halfway into the surf.  He then takes a hand-carved arrow-head, larger than his head, and twice stabs it into the back of the turtle's neck.   The children are safe.